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   2563篇
  免费   227篇
  国内免费   5篇
耳鼻咽喉   29篇
儿科学   91篇
妇产科学   40篇
基础医学   468篇
口腔科学   133篇
临床医学   256篇
内科学   627篇
皮肤病学   46篇
神经病学   222篇
特种医学   42篇
外科学   225篇
综合类   37篇
预防医学   220篇
眼科学   83篇
药学   152篇
中国医学   1篇
肿瘤学   123篇
  2022年   16篇
  2021年   41篇
  2020年   29篇
  2019年   46篇
  2018年   43篇
  2017年   45篇
  2016年   56篇
  2015年   52篇
  2014年   69篇
  2013年   100篇
  2012年   115篇
  2011年   140篇
  2010年   65篇
  2009年   67篇
  2008年   156篇
  2007年   133篇
  2006年   129篇
  2005年   149篇
  2004年   135篇
  2003年   137篇
  2002年   125篇
  2001年   39篇
  2000年   56篇
  1999年   34篇
  1998年   42篇
  1997年   32篇
  1996年   18篇
  1995年   19篇
  1994年   25篇
  1993年   16篇
  1992年   30篇
  1991年   26篇
  1990年   29篇
  1989年   19篇
  1988年   27篇
  1987年   31篇
  1986年   39篇
  1985年   38篇
  1984年   25篇
  1983年   26篇
  1982年   25篇
  1981年   26篇
  1980年   22篇
  1978年   19篇
  1977年   21篇
  1976年   24篇
  1975年   16篇
  1974年   20篇
  1973年   17篇
  1971年   13篇
排序方式: 共有2795条查询结果,搜索用时 15 毫秒
21.
General practitioners' access to remote data bases using microcomputers is increasing, making even the most obscure information readily available. Some of the systems available to general practitioners in the UK are described and the methods of access are outlined. General practitioners should be aware of the advances in technology; data bases are increasing in size, the cost of access is falling and their use is becoming easier.  相似文献   
22.
We studied 10 cases of primary pure testicular neuroendocrine carcinoma. Patients were between 16 and 48 years old and had testicular swelling with pain or a painless testicular mass and no history of neuroendocrine carcinoma or other malignant neoplasm. All underwent orchiectomy. The tumors were low (n = 9) and intermediate (n = 1) grades with a variegated histologic appearance characterized by a nesting pattern, cords of neoplastic cells with rosettes, or sheets of neoplastic cells. Mitotic activity was lacking in 9 cases. In 1 case, mitotic figures ranged from 7 to 8 per 10 high-power fields, and cellular atypia and comedo-like necrosis were present. Immunohistochemical studies using a keratin cocktail, chromogranin, synaptophysin, epidermal growth factor, p53, placental-like alkaline phosphatase, and CD117 (c-kit) were performed in all cases. Keratin, chromogranin, and synaptophysin were positive in all tumors. Clinical follow-up information was obtained for 6 patients (range, 12-60 months): 5 with low-grade tumors were alive 24 to 60 months after diagnosis; 1 with an intermediate-grade tumor died of tumor 12 months after initial diagnosis. The behavior of these tumors, while in the testicular region, correlates well with the histologic grade. We propose replacing the term testicular carcinoid with neuroendocrine carcinoma, which better reflects the nature of these neoplasms.  相似文献   
23.
This study examined the effects on food choice of increasing the number of healthy items available (fruit) and decreasing the number of unhealthy items available (candy bars). A similar choice, involving nonfood items, was also examined. Two hundred eighty-nine men and women were randomly assigned to 1 of 4 experimental groups: (a) control group, (b) increased number of fruits, (c) decreased number of candy bars, and (d) combination. Between 30% and 40% of participants chose fruit regardless of the amount of fruit and candy presented: there was no effect of increasing fruit or decreasing candy bars. However, restrained participants and current dieters were more likely to choose fruit. In contrast, both stimulus control techniques were effective in increasing the percentage of participants choosing a nonfood item. These results suggest that stimulus control may not be sufficient to modify food choice: other powerful factors affect eating behavior, and these must be considered.  相似文献   
24.
A set of neurofibromatosis type 1 (NF1) patients was screened for large NF1 gene deletions by comparing patient and parent genotypes at 10 intragenic polymorphic loci. Of 67 patient/parent sets (47 new mutation patients and 20 familial cases), five (7.5%) showed loss of heterozygosity (LOH), indicative of NF1 gene deletion. These five patients did not have severe NF1 manifestations, mental retardation, or dysmorphic features, in contrast to previous reports of large NF1 deletions. All five deletions were de novo and occurred on the maternal chromosome. However, two patients showed partial LOH, consistent with somatic mosaicism for the deletion, suggesting that mosaicism may be more frequent in NF1 than previously recognised (and may have bearing on clinical severity). We suggest that large NF1 deletions (1) are not always associated with unusual clinical features, (2) tend to occur more frequently on maternal alleles, and (3) are an important mechanism for constitutional and somatic mutations in NF1 patients.  相似文献   
25.
Red blood cells (RBC) have unique flow-affecting properties--namely, aggregability, deformability and adherence to endothelial cells (EC)--which play major roles in blood flow. Under normal flow-induced shear stress RBC are dispersed, their adherence to EC is insignificant, and they are sufficiently deformable to enable tissue perfusion. However, in pathological conditions that are associated with low-flow states (e.g., trauma, ischemia), elevated plasma components (mainly fibrinogen), or altered RBC properties (e.g., hemoglobinopathies, oxidative stress, inflammation, diabetes), RBC flow properties are altered and present a circulatory risk.  相似文献   
26.
Although infants have been noted to have greater relative right or left frontal EEG as early as the neonatal period, other ways in which these newborns differ have not been reported. In this study, 48 newborns were divided on the basis of greater relative right versus greater relative left frontal EEG to determine whether these groups differed in other ways at the neonatal period including behavior, physiology, and biochemistry. We also were interested in whether these EEG patterns were related to any prenatal maternal variables including mood states (depression, anxiety, anger) and biochemistry as well as fetal activity. The greater relative right frontal EEG newborns had mothers with lower prenatal and postnatal serotonin and higher postnatal cortisol levels. The mothers of the greater relative right frontal EEG newborns also had greater relative right frontal EEG activation and lower vagal tone. The greater relative right frontal EEG newborns themselves had elevated cortisol levels, showed a greater number of state changes during sleep/wake behavior observations, and performed less optimally on the Brazelton Neonatal Behavior Assessment (T. B. Brazelton, 1973) including the habituation, motor, range of state, excitability, and depressive symptoms scales. These data suggest that greater relative right frontal EEG newborns may be at greater risk for developmental problems than those with greater relative left frontal EEG activation. In addition, a discriminant function analysis correctly classified 67% of the newborns' EEGs by prenatal maternal variables, suggesting that these might be used to target pregnant women for prenatal intervention.  相似文献   
27.
Mixed epithelial and stromal tumors of the kidney. A report of 22 cases   总被引:16,自引:0,他引:16  
Mixed epithelial and stromal tumor of the kidney (MESTK) is a recently described subset of renal neoplasm that tends to occur in middle-aged and older women and is characterized by a distinctive histological appearance. To further characterize this lesion, we report the clinicopathological and immunohistochemical features of 22 additional cases from our institutional files. Grossly, the tumors ranged in size from 1 cm to 14 cm (mean 6.7 cm), were well circumscribed but unencapsulated, and showed a cystic cut surface. The tumors were composed of a spindle cell proliferation that resembled ovarian stroma, as well as an epithelial component lining the cystic structures, which usually consisted of flat to hobnailed cells typical of collecting-duct epithelium. Areas displaying features of Müllerian differentiation were also documented in 6 cases, including epithelium of endometrioid, tubal, clear cell and squamous cell type as well as one case showing an architecture that closely resembled Müllerian adenofibroma and adenosarcoma. Follow-up in 14 patients (average 4.4 years) showed no evidence of recurrence or metastasis. We believe these tumors represent the renal counterpart of similar mixed epithelial and stromal neoplasms occurring in the biliary tract and pancreas, which is also characterized by cystic structures lined by epithelium, admixed with ovarian-type stroma. The differential diagnosis for these tumors includes cystic nephroma and cystic partially differentiated nephroblastoma, which we believe to represent clinically and morphologically distinct entities from MESTK. In particular, the distinction from cystic nephroma in adult male patients is emphasized, and two cases of this entity are included in the study for comparison.  相似文献   
28.
As yeast colonies ceased growth, cells at the edge of these colonies transited from the cell division cycle into meiosis at high efficiency. This transition occurred remarkably synchronously and only at late stages of colony maturation. The transition occurred on medium containing acetate or low concentrations of glucose, but not on medium containing high glucose. The repression by high glucose was overcome when IME1 was overexpressed from a plasmid. Experiments with different growth media imply that meiosis in colonies is triggered by changes in the nutrient environment as colonies mature. HAP2 is required to sporulate in any carbon source, whereas GRR1 is required for glucose repression of sporulation. CLN3 is required to repress meiosis in colonies but not in liquid cultures, indicating that the regulators that mediate the transition to meiosis in colonies are not identical to the regulators that mediate this transition in liquid cultures.  相似文献   
29.
The usefulness of assertive training for elderly psychiatric outpatients was assessed through a quasi-experimental evaluation of a program at a community geriatric facility. Elderly clients are frequently labeled as untreatable and are therefore often denied therapeutic treatment. This study is an example of the potential effectiveness of applying treatment techniques which have been developed with younger populations to a geriatric population. Nineteen clients, aged 50–75, participated in the study, either as participants in the assertion training or as members of a no-treatment control group. The assertion training consisted of 14 semi-weekly sessions, with coaching and feedback provided by the therapists. Assertive behaviors were assessed through self-report, role play and staff ratings of adaptive behaviors of clients. Pre-intervention comparisons between the groups along these dimensions were nonsignificant. However, post-test assessment indicated a significant between group difference in self-reported assertiveness-(t(17)=2.69;p<.05). Dependent t-tests indicated that the experimental group became more assertive (t(9)=2.59;p<.05), but the control group did not. Changes as assessed by role play and staff rating did not reach statistical significance. Results which indicate the potential effectiveness of assertive training with this population are discussed in terms of a specificity conceptualization of assertiveness and implications for assertive training with this population.This paper is based upon their masters' theses.  相似文献   
30.
The effects of hydrostatic pressure on the ciliateSpirostomum ambiguum, when the organism is uncalcified in the early stage of culture and when it is calcified after periods of time are described. Uncalcified cells are sensitive to pressure, becoming quiescent at 250 atm, distorting at 300 atm and disrupting at 550 atm. In contrast, the mature calcified animals show no changes at 550 atm. and small temporary increases in diameter only during 2 hr of treatment at 1000 atm.
Zusammenfassung Es wird der Einfluß von hydrostatischem Druck auf die CiliatenSpirostomum ambiguum beschrieben, einerseits auf nicht verkalkte, im frühen Stadium der Kultur stehende Infusionen, anderseits auf verkalkte, längere Zeit gewachsene Mikroorganismen. Nicht verkalkte Zellen sind druckempfindlich; bei 250 Atm. verlieren sie ihre Mobilität, bei 300 Atm. verändern sie ihre Form und bei 550 Atm. platzen sie. Im Gegensatz dazu weisen die ausgewachsenen verkalkten Tiere bei 550 Atm. keine Veränderungen auf; nach Einwirkung von 1000 Atm. während 2 Std zeigen sie nur eine kleine vorübergehende Zunahme ihres Durchmessers.

Résumé Les effets de la pression hydrostatique ont été étudiés surSpirostomum ambiguum cilié, à un stade précoce du culture, lorsqu'il n'est pas calcifié et plus tardivement lorsqu'il est calcifié. Les cellules non calcifiées sont sensibles à la pression. Elles deviennent inertes à 250 atm.; elles changent de forme à 30 0atm. et elles éclatent à 550 atm. Par contre, les organismes calcifiés adultes ne sont pas altérés à 550 atm. et ne présentent qu'une faible augmentation transitoire de diamètre qu'au bout de 2 heures de traitement à 1000 atm.
  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