首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   21426篇
  免费   1437篇
  国内免费   84篇
耳鼻咽喉   144篇
儿科学   670篇
妇产科学   499篇
基础医学   3390篇
口腔科学   475篇
临床医学   2109篇
内科学   4235篇
皮肤病学   468篇
神经病学   2255篇
特种医学   514篇
外国民族医学   1篇
外科学   1991篇
综合类   119篇
一般理论   27篇
预防医学   2249篇
眼科学   370篇
药学   1245篇
中国医学   38篇
肿瘤学   2148篇
  2023年   187篇
  2022年   345篇
  2021年   643篇
  2020年   425篇
  2019年   610篇
  2018年   687篇
  2017年   532篇
  2016年   610篇
  2015年   694篇
  2014年   844篇
  2013年   1186篇
  2012年   1682篇
  2011年   1676篇
  2010年   950篇
  2009年   848篇
  2008年   1481篇
  2007年   1419篇
  2006年   1290篇
  2005年   1247篇
  2004年   1095篇
  2003年   1119篇
  2002年   976篇
  2001年   134篇
  2000年   87篇
  1999年   122篇
  1998年   183篇
  1997年   154篇
  1996年   123篇
  1995年   124篇
  1994年   104篇
  1993年   101篇
  1992年   56篇
  1991年   74篇
  1990年   55篇
  1989年   48篇
  1987年   56篇
  1986年   58篇
  1985年   64篇
  1984年   59篇
  1983年   55篇
  1982年   80篇
  1981年   61篇
  1980年   47篇
  1979年   41篇
  1978年   42篇
  1977年   28篇
  1976年   31篇
  1975年   33篇
  1974年   36篇
  1973年   31篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
IntroductionNECPAL is a tool for identification of patients with advanced chronic disease in need of palliative care. The main objective of the study is to know the prevalence of patients with palliative needs in an acute respiratory ward in a Spanish tertiary hospital using NECPAL. A second objective of the study is to know the annual mortality rate of these patients.Materials and methodsCross sectional study and prospective monitoring of a cohort identified as palliative patients with the NECPAL tool for 12 months. Patient identification was performed in patients admitted to the respiratory ward of our hospital for longer than 3 days. We have assessed the annual vital status (deceased or not deceased) of patients and have recorded demographics, clinical and functional data, as well as the use of healthcare resources.ResultsWe monitored a cohort of 363 patients. Of them, 87 patients (24.3%) (IC 95% 19–30) were identified as NECPAL positive. 60% of patients (n = 64) died within 12 months of their admission. There was no significant difference in the mortality ratio of oncologic versus non oncologic patients. In a multivariable analysis, mortality was associated with demand by patients or relatives for palliative care and with the presence of specific disease progression markers or indicators.Conclusionsprevalence of patients with palliative needs in acute respiratory wards is high (one out of four patients). 60% of the patients identified as NECPAL positive in our cohort died in the first 12 months. Training of healthcare professionals as well as availability of appropriate resources are indispensable factors to improve care of this population.  相似文献   
102.

Sexual minority emerging adults are more likely to engage in suicidal ideation than their heterosexual counterparts. Experiences of homophobic violence are associated with suicidal ideation. Yet, the specific mechanisms linking homophobic violence to suicidal ideation remain unclear. Entrapment and social belongingness were tested to determine their relevance for understanding the link between homophobic violence and suicidal ideation. A sample of sexual minority Dutch emerging adults (N?=?675; ages 18–29, M?=?21.93 years, SD?=?3.20) were recruited through online platforms and flyers. Homophobic violence was expected to be positively associated with suicidal ideation and entrapment. The association between homophobic violence and suicidal ideation was expected to be indirectly linked through entrapment. We explored whether various sources of social belongingness moderated the path between entrapment and suicidal ideation and whether those sources of social belongingness moderated the indirect effect of homophobic violence on suicidal ideation through entrapment. Results showed that homophobic violence and entrapment were positively associated with suicidal ideation and that family belongingness was negatively associated with suicidal ideation. Homophobic violence and suicidal ideation were not indirectly linked through entrapment. The interaction effect between entrapment and family belongingness was significant, suggesting that, on average, the effect of entrapment on suicidal ideation decreased when family belongingness was high. These results suggest that family belongingness may reduce the association between entrapment and suicidal ideation while adjusting for homophonic violence. Reducing entrapment and improving family belongingness may be useful targets for programs aimed at preventing suicidal ideation among sexual minority emerging adults.

  相似文献   
103.
Zusammenfassung In Hirntumoren und tumorfreien Hirngeweben von Mensch und Kaninchen wurden verschiedene Phospholipoid-Fraktionen bestimmt. Die statistische Auswertung ergab für Tumoren eine signifikante Senkung aller absoluten Parameter. Der Quotient aus den nach alkalischer Hydrolyse erhaltenen cholinhaltigen und cholinfreien Fraktionen ist in den Hirntumoren signifikant erhöht. Unterschiede im Phospholipoidgehalt zwischen malignen und benignen Hirntumoren waren statistisch nicht erfaßbar.
Summary Various phospholipoid fractions were estimated in brain tumours an in normal human and rabbit brain tissue. A statistical evaluation showed a significant diminution of all absolute values in brain tumours. The ratio of choline-containing to choline-free fractions, measured after alkaline hydrolysis, is significantly higher in brain tumours. No statistically significant differences were noted in the phospholipoid contents of malignant and benign brain tumours.

Resumen En tumores cerebrales y en tejido cerebral no tumoral humano y de conejo se analizaron diversas fracciones de fosfolípidos. La valoración estadística dió por resultado, para los tumores, una disminución significante de todos los parámetros absolutos. El cociente de las fracciones conteniendo colina y libres de la misma, tras la hidrólisis alcalina, está significantemente aumentado en el caso de tumores cerebrales. Estadisticamente no se apreciaron diferencias entre el contenido de fosfolípidos en los tumores cerebrales malignos y benignos.

Résumé Les auteurs ont étudié la présence de différentes fractions phospholipidiques dans les tumeurs du cerveau et le tissu cérébral non tumoral de l'homme et du lapin. Les évaluations statistiques mettent en évidence pour les tumeurs une baisse significative de tous les paramètres absolus. La proportion entre les fractions contenant de la choline et les fractions n'en contenant pas, après hydrolyse alcaline, est augmentée de façon significative dans les tumeurs cérébrales. Par contre, une différence de teneur en phospholipides entre tumeurs malignes et tumeurs bénignes, n'a pu être statistiquement mise en évidence.

Riassunto Gli AA. hanno deterrninato le varie frazioni di fosfolipidi in tumori cerebrali ed in tessuti cerebrali esenti da tumori dell'uomo e del coniglio.L'elaborazione statistica dà per i tumori un significativo abbassamento di tutti i parametri assoluti. Il quoziente ricavato dalle frazioni a contenuto colinico e da quelle esenti da colina, in seguito ad idrolisi alcalina, risulta significativamente aumentato nei tumori.Non è stato possibile rilevare delle differenze statisticamente significative del contenuto di fosfolipidi tra tumori cerebrali maligni e benigni.


Herrn Dipl. Math.Günther Caroli möchten wir an dieser Stelle recht herzlich für seine Hilfe bei der statistischen Auswertung unserer Ergebnisse danken.  相似文献   
104.
A hospital-based case-control study of renal cell cancer was conducted in northern Italy betwen 1986 and 1989, with 240 cases of renal cell cancer (150 males and 90 females), and 665 controls (445 males and 220 females) chosen on the basis of age, sex, and area of residence. No associations were found between renal cell cancer and: body mass index (BMI); number of cigarettes smoked; age at starting to smoke; years of smoking; consumption of wine, beer, spirits, coffee, decaffeinated coffee; tea; intake of animal protein, fruits, and vegetables; various resproductive factors; hormonal use; sexual habits; sexually transmitted diseases; or selected occupational exposures. The odds ratio (OR) was above unity in smokers (OR=1.34 for 15 cigarettes/day), but the trends in risk with dose or duration were not statistically significant. Significant positive associations were found between renal cell cancer and sources of fat intake, especially margarine (OR for highest vs lowest intake = 1.71), and oils (OR=1.89) whereas carrot intake showed a negative association (OR=0.62). Also, a history of nephrolithiasis and multiple episodes of cystitis showed weak positive associations (OR=2.00, 95 percent confidence interval (CI) 1.07–3.73; and OR=1.60, 95 percent CI 0.95–2.70, respectively).Address reprint requests to Dr Talamini. The work was conducted with the contribution of the Italian Association for Cancer Research, Milan, Italy and the CNR (Italian National Research Council) Applied Projects Oncology (Contract n. 85.02209.44).Drs Talamini, Barón, Barra, Bidoli, Serraino, and Franceschi are in the Epidemiology Unit, Aviano Cancer Center, Via Pedemontana Occ. 33081 Aviano (PN) Italy. At the time of this work, Dr Barón was a visiting biostatistician from the Department of Preventive Medicine and Biometrics, University of Colorado, Health Science Center, CO, funded by the National Cancer Institute (US) and the Italian National Research Council. Dr Franceschi is also chief of the Hormones and Sexual Factors and Cancer Working Group of the European Organization for Cooperation in Cancer Prevention Studies, Bruxelles, Belgium. Drs La Vecchia and Negri are in the Mario Negri Institute for Pharmacological Research, Milan, Italy. Dr La Vecchia is also in the Institute of Social and preventive Medicine, University of Lausanne, Switzerland.  相似文献   
105.
Purpose. To study intestinal transport and metabolism of three new -selective tetrapeptide enkephalin analogues, LEF537, LEF553 and TAPP These peptides are stabilized against enzymatic hydrolysis by having a D-aminoacid in position 2 and a blocked COOH-terminal. Methods. We used a single-pass perfusion technique to study the transport of the peptides in rat jejunum. To reduce luminal and/or brush-border metabolism during the perfusion we used protease inhibitors (Pefabloc® SC, bestatin and thiorphan). The rate of metabolism was studied by incubations in rat jejunal homogenate, rat jejunal fluid and human gastric and jejunal fluid with and without these inhibitors. Results. The jejunal permeabilities (Peff) of the peptides were 0.43–0.78 10–4 cm/s without inhibitors and 0.09–0.45 10–4 cm/s in presence of the inhibitors. All three peptides were rather rapidly degraded by enzymes in rat jejunal homogenate with half-lives of between 11.9 ± 0.5 and 31.7 ± 1.5 min. The addition of inhibitors to the homogenate prolonged the half-lives substantially for LEF553 (167 ± 35 min) and TAPP (147 ± 2 min), but only slightly for LEF537 (16.4 ± 0.5 min). LEF553 and TAPP were both hydrolyzed in rat and human jejunal fluid, while LEF537 was metabolized less in these fluids. When LEF553 and TAPP were incubated with intestinal fluid in the presence of inhibitors, metabolism was almost completely inhibited. There was no metabolism for any of the peptides in human gastric juice. Conclusions. The replacement of the terminal free carboxylic group with an amide group did not increase the stability of the peptides in jejunal tissue enough to allow successful oral drug delivery.  相似文献   
106.
Background: The highly swelling poly(glycerol monomethacrylate) gel (polyGLYMA) and hydrophilic polymer poly(triethylenglycol monomethacrylate (polyTEGMA) were tested as potential viscoelastics for intraopertive use in anterior segment surgery. Methods: PolyGLYMA was implanted into the anterior chamber in 5 rabbits, and 40% polyTEGMA in 16 rabbits. The eyes were enucleated 1 week to 3 months after the operation. The corneal endothelium was examined with specular microscopy, and then the whole eye histopathologically. Results: In all eyes of the polyGLYMA group, the clinical findings were characterized by a marked ciliary injection and severe secondary glaucoma, and the histologic ones by a marked inflammatory infiltration and thickening of Descemet's membrane in the anterior chamber angle. Specular microscopy revealed a decrease in the endothelial cell density and polymorphism of the endothelial cells. In the polyTEGMA group, the anterior segment and the fundus were physiologic all the time, and specular microscopy and histologic findings showed no degenerative and/or inflammatory changes. Conclusions: PolyGLYMA proved unsuitable for intracameral application in rabbits. The new polymer polyTEGMA is characterized by high biologic tolerance after its implantation into the anterior chamber of rabbits. PolyTEGMA 40% might be considered as a potential viscoelastic material in humans.  相似文献   
107.
To describe the relationship between sociodemographic factors, life-style habits, selected dietary indicators, smoking-related variables, and quitting smoking we analyzed data derived from the comparison group of a case-control study of colorectal and breast cancers based on a network of teaching and general hospitals in Northern Italy. A total of 2621 subjects (1215 women and 1406 men) who were ever cigarette smokers were included for analysis. Age-adjusted rates of stopping smoking (quit rates) and multivariate odds ratios (OR) of quitting smoking were computed. The overall age-adjusted quit rate was 38.6% for males and 24.9% for females, corresponding to an OR of quitting of 0.6 (95% CI: 0.5–0.7) for females vs males. The quitting rate increased with increasing age. After allowing for age, smoking cessation was more frequently reported by more educated or higher social class individuals. No relationship was present between quitting smoking and alcohol consumption, but quitting smoking was inversely related to coffee consumption. The probability of quitting smoking increased directly with number of cigarettes among males but not among females, who showed a J-shaped pattern. Older, heavy smokers were more likely to give up smoking. A general pattern of increasing rates of quitting smoking with higher consumption of vegetables and fruit, and hence -carotene, was present. This study confirms a positive association between quitting smoking and increasing age, higher education, low coffee consumption, heaviness of smoking and high consumption of vegetables and fruit.  相似文献   
108.
The possible presence of -aminobutyric acid (GABA) specificbinding sites on human spermatozoa was investigated. Swim-uppreparations of human spermatozoa were incubated with radiolabelledGABA in the presence of unlabelled GABA, alternatively displacersof GABAA/B receptors and GABA transport proteins. The resultsindicate that GABA specific binding sites are present on thesurface of human spermatozoa, and that these binding sites possiblyindicate the presence of GABA transport proteins. Furthermore,GABA at different concentrations was added to swim-up preparationsof human spermatozoa. Possible effects of GABA on sperm motility,hyperactivation and acrosome reaction were explored. No significantdifferences were observed between treated groups and controlsconcerning motility parameters and hyperactivation. Incubationwith GABA did not cause any increase in spontaneous acrosomereaction. However, spermatozoa treated with the calcium ionophoreA-23187 showed a small but significantly increased ability toundergo the acrosome reaction following preincubation in 10–4M GABA (P < 0.05).  相似文献   
109.
Swedish guidelines for early childhood education emphasize the importance of children's existential questions. The program encourages preschool to offer children different opportunities to work on questions like what it is to be, to live and die, grow old, about religion, beliefs, traditions, etc. at their level of maturity (Social-styrelsen, 1987). Our experience in teacher education and early childhood programs is, however, that this is an area in which many teachers have difficulties. In the present empirical study 13 teachers were interviewed to find outwhat they consider existential questions for their children to be, and whatstrategies or methods they have for dealing with these questions. Teachers' conceptions about the what and how aspects of existential questions are described in terms of their qualitative differences. Each teacher was then asked to keep a diary of the existential questions children raised during the following month. Differences between the teachers' conceptions, which showed hesitation, and the spontaneous approaches and active involvement that emerged in reality, as recorded in their own diaries, are discussed.  相似文献   
110.
The direct-current electroretinogram of seven pigmented and seven albino rabbits was recorded from both eyes for almost 4 h in response to repeated identical light stimuli. Stimulus duration was 10 s, light intensity was 6.8 × 102 lux, and the interval between the beginning of succeeding light stimuli was 3 min. The dark-adaptation period preceding light stimulation was 30 min for one of the eyes (unoccluded eye) and 150 min for the contralateral eye (occluded eye), which was patched during the first part (117 min) of the experiment. In pigmented animals, the b- and c-wave amplitudes of the unoccluded eye slowly increased during the first part of the experiment but not significantly during the second. The a-wave amplitude was not significantly changed. After removal of the cover, the a- and b-wave amplitudes of the occluded eye immediately attained but did not exceed the level of those in the unoccluded eye, irrespective of the light adaptation induced by the stimulus flashes previously presented to the unoccluded eye. (Control experiments on six pigmented rabbits confirmed that stimuli identical to those used in the main part of the study caused a light adaptation, since a decrease in a- and b-wave amplitudes occurred after the first light stimulus following an initial dark-adaptation period of 2 h for both eyes.) In albino rabbits, electroretinogram responses were clearly discernible in the occluded eye also during the first part of the experiment, probably because of transillumination of the head. In other respects, the results were essentially similar to those of pigmented animals. The observation that occluded eyes did not dark adapt better, as judged by the electroretinogram responses, than contralateral eyes given repeated light adaptive stimuli may indicate the presence of a mechanism for transfer of adaptation information between the eyes.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号