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   18595篇
  免费   1440篇
  国内免费   624篇
耳鼻咽喉   78篇
儿科学   330篇
妇产科学   179篇
基础医学   1167篇
口腔科学   643篇
临床医学   1719篇
内科学   3238篇
皮肤病学   432篇
神经病学   689篇
特种医学   721篇
外科学   1634篇
综合类   1768篇
现状与发展   3篇
一般理论   3篇
预防医学   1998篇
眼科学   173篇
药学   4281篇
  4篇
中国医学   260篇
肿瘤学   1339篇
  2024年   23篇
  2023年   243篇
  2022年   438篇
  2021年   699篇
  2020年   641篇
  2019年   639篇
  2018年   642篇
  2017年   635篇
  2016年   688篇
  2015年   755篇
  2014年   1084篇
  2013年   1944篇
  2012年   1064篇
  2011年   1128篇
  2010年   900篇
  2009年   847篇
  2008年   872篇
  2007年   850篇
  2006年   710篇
  2005年   692篇
  2004年   589篇
  2003年   569篇
  2002年   458篇
  2001年   389篇
  2000年   311篇
  1999年   260篇
  1998年   228篇
  1997年   246篇
  1996年   176篇
  1995年   185篇
  1994年   151篇
  1993年   155篇
  1992年   139篇
  1991年   137篇
  1990年   113篇
  1989年   112篇
  1988年   102篇
  1987年   109篇
  1986年   82篇
  1985年   97篇
  1984年   85篇
  1983年   67篇
  1982年   68篇
  1981年   49篇
  1980年   57篇
  1979年   46篇
  1978年   40篇
  1977年   31篇
  1976年   34篇
  1975年   20篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
132.
Previous ultrastructural examination of peripheral blood lymphocytes revealed the presence of intranuclear filamentous structures in multiple sclerosis (MS) and in some optic neuritis (ON) patients. The present investigation was undertaken in the attempt to correlate the presence of such structures with the etiology of ON and MS and possibly to demonstrate the viral origin of the filaments. Suitable virological and serological techniques were used to detect and isolate infectious agents from peripheral blood samples and body excretions of 12 monosymptomatic ON patients at their first acute attack. Nevertheless, any efforts to demonstrate the presence of a virus in these patients have been unsuccessful: no evidence of active viral infection was obtained by serological studies of serum and cerebrospinal fluid samples, nor could viral antigens or inclusions be observed by immunofluorescence and cytochemical analysis. Negative results were also obtained from studies performed in parallel on MS patients and various controls. The significance of the failure to isolate infectious agents from either ON and MS patients is discussed.  相似文献   
133.
As an alternative to genetic theories of handedness, some theorists have offered an environmental mechanism, associated with birth stress, for the appearance of left-handedness. They suggest that brain damage as a result of birth difficulties can lead to a switch in hand preference from the right side to the left side. Consequently, one should find more left-handers in groups where the probability of the occurrence of birth stress is greater. Three studies are presented which explore the laterality of not only hand but also foot, eye, and ear, in a total of 5161 individuals, in an attempt to assess any relationship to birth stress. Maternal age seems to predict deviations from dextrality, dependent on the sex of the offspring, while paternal age and birth order do not. The use of a direct measure of conditions predisposing toward birth stress suggests that these results depend on prenatal or perinatal environmental trauma rather than chromosomal factors.This research was supported by grants from the Medical Research Council of Canada and from the Natural Sciences and Engineering Research Council of Canada, and represents an equal and shared contribution of both authors.  相似文献   
134.
目的 探讨口服长春瑞滨联合卡培他滨治疗葸环类、紫杉类耐药的转移性乳腺癌的疗效及不良反应。方法 80例确诊葸环类、紫杉类耐药的转移性乳腺癌患者随机分为两组。口服长春瑞滨联合希罗达组(试验组):40例患者口服江苏豪森酒石酸长春瑞滨软胶囊45.50mg/(m^2-d),第1、8、15天服用,口服卡培他滨1650mg/(m^2·d),连服1—14d,每3周为1个周期,连用4个周期。注射长春瑞滨联合希罗达组(对照组):40例患者,长春瑞滨(江苏豪森)25mg/(m^2·d)第1、8天静脉滴注,口服卡培他滨1650mg/(m^2·d),连服1-14d,每3周为1个周期,连用4个周期。治疗结束2周后评价疗效。结果 入组患者80例均可评价疗效,试验组有效率为42.5%,1年生存率为45.0%,中位进展时间4.7月,中位生存时间11.0月;对照组有效率为37.5%,1年生存率为42.5%,中位进展时间4.6月,中位生存时间10.6月;两组比较差异无统计学意义(P〉0.05)。在毒副反应方面,Ⅲ/IV便秘、局部静脉炎、HB下降、WBC下降、ANC下降、总Ⅲ/IV反应率两组比较。差异均有统计学意义(P〈0.05)。结论 口服长春瑞滨联合卡培他滨治疗葸环类、紫杉类耐药的转移性乳腺癌与静脉剂型疗效一致,并且在毒副反应上,口服长春瑞滨明显较静脉剂型轻,并且应用方便。  相似文献   
135.
Summary The interrelationships among age, cardiovascular pressor reactivity to intravenously infused norepinephrine (NE) or angiotensin II, and endogenous plasma NE or renin (PRA) levels were evaluated in 31 normal subjects and 37 patients with essential hypertension. In normal subjects both angiotensin II pressor dose and PRA decreased progressively with aging. Angiotensin pressor dose correlated positively with PRA (r=0.41,P<0.025) and inversely with age (r=–0.46,P<0.02). NE pressor dose and basal plasma NE were also positively correlated (r=0.53,P<0.005), but the two factors remained largely unchanged with aging. Findings in essential hypertension differed in certain aspects. Angiotensin II pressor dose did not correlate with either basal PRA or age; and pressor doses of NE and angiotensin II tended to be lower in some patients than in normal subjects. These findings indicate that aging is accompanied by a physiologic increase in cardiovascular reactivity to angiotensin II, probably due to a concomitant decrease in circulating renin. The dissociation between angiotensin pressor dose and PRA in essential hypertension suggests an interference from an other factor.This work was supported by the Swiss National Science Foundation  相似文献   
136.
H. Harving  J. Korsgaard  R. Dahl 《Allergy》1994,49(10):866-870
In temperate climates, energy-conserving measures may increase indoor humidity, enhancing house-dust mite (HDM) growth. Movement of families to "healthy" homes with mechanical ventilation systems reduced HDM exposure. The effect on asthma control of moving to the "healthy" homes was studied in 14 asthmatic patients allergic to HDM. Base-line evaluations of lung function, asthma symptoms, and medication requirements were made before moving and again after 5 and 15 months' residence. A control group of 11 mite-sensitive asthmatic patients who did not move were examined contemporaneously with the study group at base line and at the first follow-up investigation. After 5 months, the residents of the "healthy" homes improved in forced expiratory volume in 1 s (FEV1), medicine score, and serum IgE. These changes were significantly different from control group measurements. After 15 months, statistically significant improvements from base line were found in FEV1, average daily peak expiratory flow values, medicine score, symptom score, and serum IgE. Insignificant trends toward improvement were seen in provocation concentration of histamine and blood eosinophils. A significant relation was found between reduction in medicine score and fall in HDM exposure. The present study shows that a specific HDM-avoidance procedure can result in an overall, clinical improvement in HDM-sensitive asthmatic patients.  相似文献   
137.
Summary Active ion transport in the colon is generating a transmucosal electrical potential difference (PD) of about 40 mV. Cathartic agents inhibit electrolyte and water net-absorption or cause net-secretion which should be reflected in a change of PD.In 83 normal subjects the effect of an isotonic eletrolyte solution (control) and different cathartic agents on rectal PD was tested: Laxatives (bisacodyl, rhein), bile acids (cholic and deoxycholic acid), fatty acids (oleic and ricinoleic acid) and cardiac glycosides (meproscillarin, digitoxin, digoxin). Bisacodyl, deoxycholic acid in high concentration, meproscillarin and digitoxin significantly decreased PD, while the other substances did not.Cathartics act on different transport mechanisms which together with different absorption characteristics of the proximal and distal colon may explain the difference in effecting the PD. Rectal PD measurement provides an easy and convenient tool to document effects of cathartic agents on electrolyte transport, otherwise difficult to obtain, and is applicable for clinical use.To Prof. Dr. H.P. Wolff on the occasion of his 65th birthday  相似文献   
138.
BACKGROUND: Studies of immigrants represent an useful tool to determine the relative relevance of environmental vs genetic factors in causing the reported rapid increase of the prevalence of sensitization and allergic diseases. METHODS: A total of 152 Albanian migrants to Southern Italy responded to a questionnaire based on the European Community Respiratory Health Survey (ECRHS) and 139 of them underwent skin prick test, and 61 serological assays for total IgE and IgG antibodies against Toxoplasma gondii (TG), herpes simplex virus 1 (HSV-1), hepatitis A virus (HAV) and Helicobacter pylori (HP). RESULTS: Reported asthma was rare (2/152; 1.3%) and reported nasal allergies rather frequent (24/152; 15.8%). Sensitization to common inhalant allergens occurred in 27/139 (19.4%) subjects. The frequency of skin sensitization to pollen (P = 0.003) and that of hay fever (P = 0.004) increased with the time spent in Apulia. All the 61 sera had antibodies against HAV, 59/61 (96.7%) against HSV-1, 48/61 (78.7%) against HP and 34/61 (55.7%) against TG. The prevalence of skin sensitization and hay fever symptoms were correlated to the duration of residence in Southern Italy. CONCLUSIONS: Data presented indicate that Albanian migrants to Italy, in spite of the low prevalence of allergic diseases and sensitization in their country of origin, manifest with time an increasing prevalence of sensitization to local allergens and nasal symptoms after immigration to Italy. This would suggest a permanent role of allergen exposure and lifestyle factors in influencing the appearance of sensitization and symptoms of allergic diseases.  相似文献   
139.
 目的 探讨抗癌生物活性肽(ACBP)对人乳腺癌 nm231细胞的作用及其机制。 方法 nm231 细胞经不同浓度(0.05、0.10、0.20、 0.25 µg/ml)ACBP 作用 72 h,以噻唑蓝(MTT)法测定细胞增殖活性。以 0.25 µg/ml 的 ACBP 分别作用于 nm231 细胞 4、6、24、48、72 h,行光镜和透射电镜(作用 48 h 细胞)观察。应用 DNA 凝胶电泳和磷脂结合蛋白 V(Annexin V,AV)/碘化丙啶(PI)双标记染色流式细胞术等方法,观察 0.25 µg/ml 的 ACBP 作用不同时间对nm231 细胞凋亡发生及作用 48 h 对细胞周期的影响。以上各项检测均设以 RPMI 1640 培养液取代 ACBP 的对照组。 结果 浓度为 0.1 µg/ml 的 ACBP 即对 nm231 细胞的增殖有明显抑制作用,抑制率为 10.3%,抑制作用具有浓度依赖性,ACBP 浓度为 0.25 µg/ml 时抑制率达 35.1%。光镜观察显示,经 0.25 µg/ml 的 ACBP 作用 24 h,细胞出现凋亡特征;作用 48 h,光镜及电镜下均可见大量的典型凋亡细胞。DNA 凝胶电泳显示,经 0.25 µg/ml 的ACBP 作用 24 h 的细胞出现 DNA 断裂;作用 48 h 的细胞出现典型的梯形电泳图谱。流式细胞术分析显示,ACBP 作用后AV(+)/ PI(-)细胞和 AV(+)/ PI(+)细胞比例均随培养时间延长而增大;作用 48 h 的 nm231细胞 G0/1 期细胞比例高于对照组(P < 0.01),而细胞增殖指数低于对照组(P < 0.01)。 结论 ACBP 可抑制 nm231 细胞的增殖,其机制与抑制nm231 细胞的 DNA 合成和诱导细胞凋亡相关。  相似文献   
140.
Heritability and molecular genetic studies of endometriosis   总被引:22,自引:0,他引:22  
Endometriosis is a common disease defined as the growth of endometrial tissue outside the uterine cavity that often results in a vast array of gynaecological problems including dyspareunia, dysmenorrhoea, pelvic pain and infertility. Despite the increasing evidence that supports a genetic component to this common gynaecological condition, the basic aetiology and pathogenesis of endometriosis remain unknown. It is likely that endometriosis is a common polygenic/multifactorial disease caused by an interaction between multiple genes as well as the environment. Such conditions do not have a clear Mendelian pattern of inheritance. Recent molecular cytogenetic studies on endometriotic tissue and an established endometriosis-derived cell line provide novel evidence that acquired chromosome-specific alterations may be involved in endometriosis, possibly reflecting clonal expansion of chromosomally abnormal cells. Molecular DNA studies examining the role of loss of heterozygosity in endometriotic lesions has identified candidate tumour suppressor gene loci, including 5q, 6q, 9p, 11q and 22q, that may play a role in the malignant transformation of endometriotic implants to endometrioid ovarian cancers. Evidence of mutations in the tumour suppressor PTEN gene in the endometrioid subtype of epithelial ovarian cancer further suggests that somatic genetic alterations represent early events in the transformation of benign endometriotic cells. Genetic factors are also likely to influence individual susceptibility to endometriosis. There is now evidence that heritable allelic differences in drug-metabolizing enzymes play an important role in the development of endometriosis. Further studies are warranted to identify major susceptibility gene(s) and the mechanism involved in endometriosis to assist in the development of better methods for early detection, diagnosis and prevention.  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