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   9055篇
  免费   721篇
  国内免费   68篇
耳鼻咽喉   195篇
儿科学   295篇
妇产科学   150篇
基础医学   1058篇
口腔科学   166篇
临床医学   1196篇
内科学   1756篇
皮肤病学   68篇
神经病学   567篇
特种医学   361篇
外国民族医学   2篇
外科学   1225篇
综合类   228篇
一般理论   5篇
预防医学   1016篇
眼科学   305篇
药学   807篇
中国医学   7篇
肿瘤学   437篇
  2023年   60篇
  2022年   77篇
  2021年   156篇
  2020年   91篇
  2019年   177篇
  2018年   163篇
  2017年   124篇
  2016年   143篇
  2015年   166篇
  2014年   237篇
  2013年   308篇
  2012年   460篇
  2011年   457篇
  2010年   286篇
  2009年   215篇
  2008年   356篇
  2007年   424篇
  2006年   398篇
  2005年   355篇
  2004年   311篇
  2003年   310篇
  2002年   292篇
  2001年   295篇
  2000年   292篇
  1999年   257篇
  1998年   125篇
  1997年   124篇
  1996年   119篇
  1995年   100篇
  1994年   89篇
  1993年   85篇
  1992年   216篇
  1991年   252篇
  1990年   194篇
  1989年   163篇
  1988年   144篇
  1987年   149篇
  1986年   161篇
  1985年   168篇
  1984年   116篇
  1983年   100篇
  1981年   66篇
  1980年   60篇
  1979年   103篇
  1978年   70篇
  1976年   70篇
  1974年   65篇
  1973年   68篇
  1972年   73篇
  1971年   62篇
排序方式: 共有9844条查询结果,搜索用时 15 毫秒
51.
Cell exfoliation in the gut is an important cell renewal mechanism. To approach its investigation we applied a novel immunomagnetic technique for isolation of exfoliated cells from human stool. Exfoliated colonocytes were isolated from 168 stool samples. The cells were assessed microscopically using conventional stains and immunohistochemistry. The technique allowed us to obtain well-preserved colonocytes displaying characteristic features of well-differentiated colonic epithelium and positive immunostaining for cytokeratin 5/8. No mucin-producing cells were found. Exfoliated cells did not produce inducible nitric oxide synthase, albeit cultured colon carcinoma cells HT-29 analysed in parallel showed strong immunostaining. Analysis of exfoliated cell numbers in consecutive stool samples from the same subjects revealed considerable interindividual variation. Overall exfoliated colonocyte numbers were relatively low, isolation being unaffected by addition during the procedure of excessive amounts of HT-29 cells. Apoptosis was extremely rare among exfoliated colonocytes. Well-preserved exfoliated colonocytes can be consistently isolated from human faeces using a simple procedure. Our findings suggest that the actual process of cell exfoliation in the human colon may be much less intense than is generally accepted. Exfoliated cell isolation from human stool constitutes a convenient non-invasive approach that can be used for diagnostic and research purposes.  相似文献   
52.
53.
Short-term exploratory activity was found to be significantly higher in C57BL/6By than in BALB/cBy inbred mice. Scopolamine reversed the activity levels in these strains. Basal exploratory activity levels and the effects of scopolamine on this behavioral measure assessed in these two strains, their reciprocal F1 hybrids, their recombinant inbred strains and three C57BL/6 congenic lines permitted characterization of a gene exerting a major effect on short-term exploratory activity [Exa, linked to H(w26), chromosome 4 (LG VIII)] and of a gene modulating the effects of scopolamine in this behavior, [Sco, linked to H-2, chromosome 17 (LG IX)]. Amphetamine exerted opposite effects in relation to those exerted by scopolamine on activity and its action was found to be determined by a polygenic system.  相似文献   
54.
55.
56.
Properties of a filamentous virus of the honey bee (Apis mellifera)   总被引:2,自引:0,他引:2  
An ellipsoidal particle, measuring 450 x 150 nm, from honey bees comprises a nucleocapsid measuring 3000 x 40 nm, containing double-stranded DNA with a molecular weight of approximately 12 x 10(6), which is coiled within a membrane. The buoyant densities in CsCl of the whole particle, nucleocapsid, DNA and DNA with ethidium bromide are 1.28, 1.36, 1.71 and 1.61 g/ml, respectively. The particle contains about 12 proteins, with molecular weights ranging from 13,000 to 70,000, which are distributed approximately equally between the membrane and the nucleocapsid.  相似文献   
57.
Determined the efficacy of profile analysis with a prison population (63 white, 63 black) of the Petersburg Federal Correctional Institution as Ss. By use of Veldman's Hierarchical Profile Analysis, five distinctive WAIS profile types were derived empirically for each racial group. Analyses of covariance that controlled for full-scale IQ differences revealed significant differences among the profile types within each race in terms of Stanford Achievement Test scores and MMPI T-scores. Further, partial correlations indepepdent of full-scale IQ revealed significant relationships between some of the profile types and the commission of rule infractions while incarcerated. These findings are interpreted as supportive of profile analysis with inmate populations. However, it is suggested that further research be effected to cross-validate these findings.  相似文献   
58.
We have previously shown that vitamin C supplementation affects recovery from an unaccustomed bout of demanding exercise, with the most pronounced effect being that on plasma interleukin-6 concentration. However, because of the proposed role of interleukin-6 in the regulation of metabolism, it was unclear whether this represented a reduced response to muscle damage or some form of interaction with the metabolic demands of the activity. Therefore, the aim of the present study was to investigate the effect of the same form of supplementation on a bout of exercise that initiated similar muscle damage but had a low metabolic cost. Fourteen male subjects were allocated to either a placebo (P) or a vitamin C (VC) group. The VC group consumed 200 mg of ascorbic acid twice a day for 14 days prior to a bout of exercise and for the 3 days after exercise. The P group consumed identical capsules that contained 200 mg lactose. Subjects performed 30 min of downhill running at a gradient of –18% and recovery was monitored for up to 3 days after exercise. Plasma VC concentrations in the VC group increased following supplementation. Nevertheless, downhill running provoked a similar increase in circulating markers of muscle damage (creatine kinase activity and myoglobin concentration) and muscle soreness in P and VC groups. Similarly, although downhill running increased plasma interleukin-6, there was no effect from VC supplementation. These results suggest that vitamin C supplementation does not affect interleukin-6 concentrations following eccentric exercise that has a low metabolic component.  相似文献   
59.
Sera from patients with St. Louis encephalitis were tested with an immunoglobulin M (IgM) antibody capture enzyme immunoassay (MAC ELISA). The assay used five reagents: antihuman IgM, test serum, sucrose-acetone-extracted mouse brain antigen, broadly cross-reactive flavivirus monoclonal antibody conjugated to alkaline phosphatase, and substrate (p-nitrophenyl phosphate). MAC ELISA endpoint titers correlated (r = 0.893) with the absorbance value of a 1:100 dilution of patient serum. Significant (fourfold or greater) changes in the endpoint titers between paired sera corresponded to a critical ratio (ratio of absorbance values at the 1:100 dilution) of greater than or equal to 1.3. IgM antibodies were detected in 71% of patients bled at 0 to 3 days after the onset of illness, in 99% bled at 4 to 21 days, and in 91% bled at 22 to 67 days. Thereafter, the IgM seropositivity rate declined; however, 29% of sera were still positive at 115 to 251 days after the onset of illness. MAC ELISA titers were significantly correlated with hemagglutination inhibition (r = 0.258) and neutralization (r = 0.711) titers. Because IgM antibodies appeared early and waned rapidly, a diagnosis was made on the basis of a decrease in titer more often by MAC ELISA than by hemagglutination inhibition, complement fixation, or neutralization tests. IgM antibodies generally showed a high degree of specificity; heterologous cross-reactions were, however, present in 4 of 14 sera examined. The MAC ELISA is useful for the rapid, early diagnosis of St. Louis encephalitis.  相似文献   
60.
Twelve IUDs that had been worn from 8 years 10 months to 24 years were examined by SEM. Photomicrographs of selected samples are shown, and a discussion of the nature of the surface encrustations is provided. The authors are of the opinion that surface encrustations are generic to different types of IUDs and that their clinical significance is presently unknown.
Resumen Doce DIU que fueron usados de 8 años 10 meses a 24 años, se examinaron por microscopio de barrido. Se muestran microfotografías de especímenes seleccionados y se especula sobre la naturaleza de las incrustaciones en la superficie. Los autores son de opinión que las incrustaciones en la superficie son comunes para los distintos tipos de DIU y que actualmente se desconoce su significado clínico.

Résumé Douze stérilets qui ont été utilisés pendant une période allant de 8 ans et 10 mois à 24 ans ont fait object 'dun examen sous microscope électronique. Des microphotographies de spécimens sélectionnés illustrent ce document. Après avoir examiné la nature des incrustations superficielles, les auterus en ont tiré la conclusion que les différents types de stérilets présentent tous les mêmes incrustations dont on ne connaît pas encore la signification clinique.


Presented at the 3rd International Meeting of the Society for the Advancement of Contraception, Bordeaux, France, September, 1985  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