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   15768篇
  免费   735篇
  国内免费   378篇
耳鼻咽喉   36篇
儿科学   144篇
妇产科学   296篇
基础医学   1950篇
口腔科学   245篇
临床医学   1035篇
内科学   2101篇
皮肤病学   214篇
神经病学   853篇
特种医学   264篇
外国民族医学   6篇
外科学   769篇
综合类   2384篇
现状与发展   1篇
预防医学   756篇
眼科学   227篇
药学   3498篇
  6篇
中国医学   1331篇
肿瘤学   765篇
  2023年   202篇
  2022年   316篇
  2021年   563篇
  2020年   635篇
  2019年   453篇
  2018年   390篇
  2017年   624篇
  2016年   639篇
  2015年   576篇
  2014年   1400篇
  2013年   2126篇
  2012年   1783篇
  2011年   1574篇
  2010年   1156篇
  2009年   946篇
  2008年   792篇
  2007年   406篇
  2006年   364篇
  2005年   343篇
  2004年   266篇
  2003年   182篇
  2002年   134篇
  2001年   56篇
  2000年   37篇
  1999年   26篇
  1998年   46篇
  1997年   39篇
  1996年   36篇
  1995年   28篇
  1994年   15篇
  1993年   14篇
  1992年   9篇
  1990年   17篇
  1989年   11篇
  1988年   15篇
  1987年   13篇
  1986年   8篇
  1985年   64篇
  1984年   77篇
  1983年   87篇
  1982年   85篇
  1981年   55篇
  1980年   58篇
  1979年   42篇
  1978年   36篇
  1977年   28篇
  1976年   23篇
  1975年   24篇
  1974年   20篇
  1973年   24篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
41.
42.
The Thy-1 antigens or rat brain and thymus have been isolated and chemically characterized, but those of mice have not been identified. Moreover, it is uncertain whether the antigens are glycolipids or glycoproteins. This study with highly purified preparations of gangliosides GM1, 1GD1a, GD1b and GT1b from bovine brain and several ganglioside fractions from mouse brain showed that Thy-1 activity does not reside in gangliosides, but rather in the chloroform-methanol-insoluble residue of brain remaining after extraction of gangliosides. The antigen could be solubilized from this residue with a non-ionic detergent. The antigenic activity of the solubilized preparation was heat-labile but resistant to periodate. The chemical properties of the Thy-1 antigen of mouse brain are discussed.  相似文献   
43.
AIMS: To elucidate the mechanism of marked stromal fibrosis in strictured colorectal carcinomas (SC) that cause complete ileus. METHODS AND RESULTS: Sixteen cases of SC and 29 cases of non-strictured colorectal carcinoma (NSC) were studied. These carcinomas showed similar clinicopathological features except for bowel stricture. The stricture index (SI) showing the degree of bowel stricture was 59.8 +/- 12.1% in SC versus 20.8 +/- 24.6% in NSC (P < 0.001). The fibrosis index (FI), defined to reflect the extent of stromal fibrosis, was 56.3 +/- 8.8% in SC versus 21.9 +/- 10.6% in NSC (P < 0.001). COX-2+ myofibroblasts were detected in 13 cases (81.3%) in SC versus eight cases (27.6%) in NSC (P < 0.01). The COX-2+ myofibroblast density was 276.7 +/- 181.1 cells/mm(2) in SC versus 26.6 +/- 52.7 cells/mm(2) in NSC (P < 0.001). When all cases were divided into two groups with and without COX-2+ myofibroblasts, the SI was 48.8 +/- 19.1% in those with COX-2+ myofibroblasts versus 24.8 +/- 29.3% in those with COX-2- myofibroblasts (P < 0.001). CONCLUSION: COX-2+ myofibroblasts may play an important role in extensive bowel stricture in colorectal carcinomas.  相似文献   
44.
目的:探讨了妊高征患者治疗前后血清TNF-α、IL-6和IL-8水平的变化及意义。方法:采用放射免疫分析对36例妊高征患者进行了血清TNF-α、IL-6和IL-8水平检测并与35名正常孕妇作比较。结果:在治疗前血清TNF-α、IL-6和IL-8水平非常显著地高于正常孕妇组(P〈0.01),经治疗后2周,血清TNF-α、IL-6和IL-8水平与正常孕妇组比较,无显著性差异(P〉0.05)。结论:炎性细胞因子TNF-α、IL-6和IL-8在妊高征的发病机理中具有重要的作用,有一定的临床价值。  相似文献   
45.
Liposomes could bind and fuse efficiently to human erythrocytes in the presence of HVJ when they contained gangliosides isolated from human erythrocytes. Sialosylparagloboside, which has a terminal sequence of NeuAcα2?3Ga1β1?4GlcNac, has a much higher receptor activity to the virus than GD1a, GD1b, GT1b, and GT1a, all of which contain the terminal sequence of NeuAcα2?3Galβ1?3GalNAc or NeuAcα2?8NeuAcα2?3Galβ1?3GalNAc. The activity of sialosylparagloboside is comparable to that of glycophorin, a major sialoglycoprotein of human erythrocytes, when compared on the basis of the required amount (as sialic acid) of compounds. The high affinity of sialosylparagloboside to the viral HANA protein is also suggested by the finding that it showed high inhibitory activity against HVJ-mediated binding of glycophorin liposomes to erythrocytes. Sialosylparagloboside was also highly susceptible to the viral sialidase, the other biological function of HANA protein.  相似文献   
46.
C W Coen  M C Coombs 《Neuroscience》1983,10(1):187-206
The preovulatory surge of luteinizing hormone reaches a maximum at 18.00 h on the day of pro-oestrus in female rats maintained with regular lighting from 06.00 to 20.00 h. This surge is initiated by a discharge of luteinizing hormone-releasing hormone into hypophysial portal blood. In this study, drugs which affect catecholamine-mediated neurotransmission were administered on the day of pro-oestrus and the effects on serum concentrations of luteinizing hormone and on subsequent ovulation were observed. alpha-Methyl-p-tyrosine, diethyldithiocarbamate and SKF 64139 inhibit catecholamine synthesis at the level of tyrosine hydroxylase, dopamine beta-hydroxylase and phenylethanolamine N-methyltransferase, respectively. Although alpha-methyl-p-tyrosine suppressed ovulation, it had a negligible effect on the incidence of the preovulatory surge. In contrast, the various treatments with diethyldithiocarbamate and SKF 64139 resulted in a minimal occurrence of the 18.00 h surge; at relatively low doses, however, these drugs frequently elicited a surge at 22.00 or 24.00 h which invariably resulted in ovulation. The failure of the surge after diethyldithiocarbamate or SKF 64139 was not associated with a loss of pituitary sensitivity to luteinizing hormone-releasing hormone. In terms of the hypothalamic concentration of dopamine, noradrenaline, adrenaline and 5-hydroxytryptamine at 18.00 h on pro-oestrus, the only common effect of diethyldithiocarbamate and SKF 64139, given in a dose which blocks the surge, was a severe depletion of adrenaline; alpha-methyl-p-tyrosine failed to produce this effect despite inducing a marked depression of dopamine and a moderate loss of noradrenaline. Neither the increase in hypothalamic dopamine after diethyldithiocarbamate, nor the alpha 2 receptor blocking properties of SKF 64139 appear to be relevant in this context since injections of L-dopa or piperoxane, an alpha 2 receptor antagonist, were without effect on the surge or ovulation. The failure of the surge after prazosin, an alpha 1 receptor antagonist, indicates that the function of adrenaline may be mediated postsynaptically by alpha 1 receptors. Clonidine, an alpha 2 receptor agonist which reduces the turnover rate of hypothalamic adrenaline, had effects of the surge and ovulation which were comparable to those of diethyldithiocarbamate and SKF 64139, the relatively low doses causing some of the surges to occur at 24.00 instead of 18.00 h and higher doses suppressing the surge at both times and thus preventing ovulation.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   
47.
Mianserin (5-20 mg/kg), like chlordiazepoxide (2.5-10 mg/kg), inhibits the shock-induced suppression of drinking (SSD) in rats. However, in contrast to chlordiazepoxide, the effect of mianserin is not blocked by the benzodiazepine antagonist, Ro 15-1788 (10 mg/kg). Although mianserin does not inhibit [3H]diazepam binding in vitro it has now been found to enhance [3H]flunitrazepam binding to mouse whole brain in vivo at 10-100 mg/kg p.o. These results suggest that mianserin does influence central benzodiazepine receptors, but the mechanism by which it does so differs from that of chlordiazepoxide.  相似文献   
48.
Susceptibility to apoptosis changes with age and most of the available data on lymphocytes refer to mitogen stimulated cells. We studied this susceptibility in quiescent, purified CD4+ or CD8+ T cells from a group of Italian old people compared with a group of young people. We found that an apoptotic agent such as 2-deoxy-D-ribose (dRib), which acts via glutathione depletion and oxidative stress, was more effective in CD4+ T cells from young donors, while no difference was found in CD8+ T cells. On the contrary, another agent such as TNF-alpha, which acts via receptor engagement, was more effective in CD8+ T cells from old subjects, and no difference was found in CD4+ T cells. When marker of activation-memory were investigated, no difference between young and old subjects was found when dRib was used. Differently, when TNF-alpha was used, memory and activated CD4+ T cells from old donors were less sensitive than younger counterparts, while memory CD8+ T cells from old donors were more sensitive than younger counterparts. This suggests that age-related changes in susceptibility to apoptosis of resting T cells largely depend on the type of the apoptotic stimulus which is used as well as on the memory phenotype of the cells. These results may also account, at least in part, for the deep remodelling of T cell repertoire that occurs during ageing.  相似文献   
49.
同种器官移植成功率的提高导致了供体器官的严重短缺.采用解剖学上与人类相近的动物,比如猪的器官可以解决这种危机.但从猪到人的器官移植需要克服很多障碍,包括免疫学,生理学及其伦理道德问题.超急性排斥反应是猪到人异种器官移植的首要免疫学障碍,目前主要通过敲除半乳糖α1,3半乳糖(galactose-α1,3-galactose,Gal)抗原来克服超急性排斥反应.除此之外,仍有其它的非-Gal抗原可能引起猪到人的移植物的失功,例如N-羟乙酰神经氨酸等.除了免疫学障碍,猪器官携带的病毒及可能引起的异种移植的潜在风险也不容忽视.虽然现在还没有明显的实验数据显示猪到人的病原体的感染,但当猪到人的免疫学障碍被克服后,感染将成为又一研究热点.  相似文献   
50.
The tripartite motif (TRIM) protein, TRIM5alpha, restricts infection by particular retroviruses. Many TRIM proteins form cytoplasmic bodies of unknown function. We investigated the relationship between cytoplasmic body formation and the structure and antiretroviral activity of TRIM5alpha. In addition to diffuse cytoplasmic staining, the TRIM5alpha proteins from several primate species were located in cytoplasmic bodies of different sizes; by contrast, TRIM5alpha from spider monkeys did not form cytoplasmic bodies. Despite these differences, all of the TRIM5alpha proteins exhibited the ability to restrict infection by particular retroviruses. Treatment of cells with geldanamycin, an Hsp90 inhibitor, resulted in disappearance or reduction of the TRIM5alpha-associated cytoplasmic bodies, yet exerted little effect on the restriction of retroviral infection. Studies of green fluorescent protein-TRIM5alpha fusion proteins indicated that no TRIM5alpha domain is specifically required for association with cytoplasmic bodies. Apparently, the formation of cytoplasmic bodies is not required for the antiretroviral activity of TRIM5alpha.  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