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   99091篇
  免费   9598篇
  国内免费   6240篇
耳鼻咽喉   717篇
儿科学   1687篇
妇产科学   1536篇
基础医学   11945篇
口腔科学   1905篇
临床医学   12615篇
内科学   14938篇
皮肤病学   1050篇
神经病学   5347篇
特种医学   3559篇
外国民族医学   38篇
外科学   10172篇
综合类   15988篇
现状与发展   17篇
一般理论   15篇
预防医学   6889篇
眼科学   2492篇
药学   10538篇
  95篇
中国医学   5233篇
肿瘤学   8153篇
  2024年   260篇
  2023年   1421篇
  2022年   2499篇
  2021年   4916篇
  2020年   3736篇
  2019年   3210篇
  2018年   3528篇
  2017年   3169篇
  2016年   2937篇
  2015年   4463篇
  2014年   5403篇
  2013年   5092篇
  2012年   7602篇
  2011年   7985篇
  2010年   5234篇
  2009年   4104篇
  2008年   5496篇
  2007年   5276篇
  2006年   4895篇
  2005年   4731篇
  2004年   3459篇
  2003年   3162篇
  2002年   2832篇
  2001年   2353篇
  2000年   2298篇
  1999年   2350篇
  1998年   1463篇
  1997年   1456篇
  1996年   1121篇
  1995年   1066篇
  1994年   909篇
  1993年   586篇
  1992年   757篇
  1991年   684篇
  1990年   581篇
  1989年   524篇
  1988年   456篇
  1987年   415篇
  1986年   360篇
  1985年   307篇
  1984年   225篇
  1983年   151篇
  1982年   119篇
  1981年   113篇
  1980年   79篇
  1979年   141篇
  1978年   74篇
  1974年   74篇
  1973年   90篇
  1972年   74篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
The bcl-2 proto-oncogene, which inhibits programmed cell death (apoptosis), has recently been found to be cyclically expressed in human endometrium. In order to investigate its role in endometrial hyperlasia and neoplasia, bcl-2 expression was studied in 25 cases of endometrial carcinoma and 20 cases of endometrial hyperplasia (eight simple, two complex, and ten atypical hyperplasias). Uniform intense cytoplasmic bcl-2 expression was found in all cases of non-atypical hyperplasia, and less strong positivity in eight out of ten cases of atypical hyperplasia. In well-differentiated carcinomas, nine out of ten showed weak to moderate bcl-2 expression, whereas six out of seven poorly differentiated carcinomas were bcl-2-negative. Moderately differentiated tumours were an intermediate group, with six out of eight being positive. Widespread localization of bcl-2 protein to the chromosomes of dividing cells was also demonstrated, regardless of cytoplasmic bcl-2 expression, with rare staining of interphase nuclei. Our findings suggest a role for bcl-2 in the natural history of endometrial neoplasia and studies are needed to determine its usefulness as a prognostic marker. The finding of bcl-2 localization to chromosomes has important implications for its mode and site of action.  相似文献   
992.
BACKGROUND: Blood vessel growth is necessary for normal tissue homeostatis and contributes to solid tumor growth. Methods to quantitate neovascularization should be useful in testing biological factors and drugs that regulate angiogenesis or to induce a vascular supply to promote wound healing. EXPERIMENTAL DESIGN: An extract of basement membrane proteins (Matrigel) was found to reconstitute into a gel when injected subcutaneously into C57/BL mice and to support an intense vascular response when supplemented with angiogenic factors. RESULTS: New vessels and von Willebrand factor antigen staining were apparent in the gel 2-3 days after injection, reaching a maximum after 3-5 days. Hemoglobin content of the gels was found to parallel the increase in vessels in the gel allowing ready quantitation. Angiogenesis was obtained with both acidic and basic fibroblast growth factors and was enhanced by heparin. Several substances were tested for angiostatic activity in this assay by coinjection in Matrigel with fibroblast growth factor and heparin. Platelet-derived growth factor BB, interleukin 1-beta, interleukin-6, and transforming growth factor-beta were potent inhibitors of neovascularization induced by fibroblast growth factor. Tumor necrosis factor-alpha did not alter the response but was alone a potent inducer of neovascularization when coinjected with Matrigel and heparin. Consistent with the previously demonstrated importance of collagenase in mediating endothelial cell invasion, a tissue inhibitor of metalloproteinases that also inhibits collagenases was found to be a potent inhibitor of fibroblast growth factor-induced angiogenesis. CONCLUSIONS: Our assay allows the ready quantitative assessment of angiogenic and anti-angiogenic factors and should be useful in the isolation of endothelial cells from the capillaries that penetrate into the gel.  相似文献   
993.
小腿前外侧筋膜皮瓣的显微外科解剖学   总被引:1,自引:0,他引:1  
在30例成人下肢标本上,观察了小腿前外侧筋膜皮瓣的血供。该部皮瓣血供来自腓浅动脉。该动脉在外踝尖上平均25.7±0.55cm处发自胫前动脉,与同名静脉、神经伴行,穿前外侧肌间隔浅出,沿小腿前外侧面下降,沿途向两侧发许多细小皮支,分别与小腿前,后皮动脉吻合,在深筋膜表面形成丰富的血管网。本文讨论了小腿前外侧筋膜皮瓣的应用解剖学要点。  相似文献   
994.
目的: 观测脑缺血再灌模型大鼠海马神经细胞CRF、PKC蛋白表达变化。方法: 采用免疫组化技术检测脑缺血模型大鼠于再灌2 h、6 h、24 h时海马神经细胞CRF、PKC蛋白表达量,CRF拮抗剂对照。结果: (1)CRF:假手术组海马区可见少量阳性细胞;模型组见大量阳性细胞,着色深,随时间延长增多。拮抗剂组阳性表达较少,着色较浅。模型组和盐水组CRF蛋白阳性表达面积均显著高于假手术组和CRF拮抗剂组(P<0.01)。(2)PKC:假手术组海马区阳性表达颗粒少,模型组和盐水组见大量阳性表达颗粒,拮抗剂组阳性表达颗粒稀疏。模型组和盐水组CRF蛋白阳性表达面积均显著高于假手术组和CRF拮抗剂组(P<0.01)。结论: 脑缺血再灌诱导CRF、PKC蛋白高表达是导致海马神经细胞迟发性死亡的重要因素;CRF蛋白激活PKC蛋白表达可能是CRF诱导缺血后神经组织损伤的机制。  相似文献   
995.
A key advantage in the conversion from film-based to digital radiology is the possibility of a long-term on line electronic archival of patient studies. The popular approach based on optical disk jukeboxes for the long-term archive and magnetic disk storage for data caching is not economically attractive because of the cost of both the jukebox and the medium. Strategies for extending the archival system design with a tape jukebox have been studied. The proposed strategy calls for the use of high-ratio lossy compression together with low-cost tape storage to make long-term on line archiving more affordable. An intelligent prefetching algorithm based on hospital information system and radiologic information system triggers, which in turn are augmented by manual case preparation, can effectively overcome the longer latency of ad hoc retrievals. This longer latency is caused by both system-level bottlenecks and the sequential access constraint of the tape drive. Strategies for image clustering and tape allocation by patient classification also enhance retrieval efficiency. This archival design using image compression, prefetching, and clustering could be implemented in many of the existing teleradiology and picture archiving and communication systems.  相似文献   
996.
nm23-H1、p53、PCNA表达与大肠癌浸润转移的关系   总被引:14,自引:1,他引:14  
目的:研究大肠癌中nm23-H1、p53、PCNA的表达与浸润转移的关系。方法:应用LSAB免疫组织化学方法检测74例大肠癌中nm23-H1、p53、PCNA和Ⅳ型原的表达。结果:大肠癌中nm23-H1、p53和PCNA的阳性率分别为71.6%、52.7%和81.1%。大肠癌中nm23-H1低表达与淋巴结转移有关(P<0.025),nm23-H1的表达在Ⅳ型胶原表达不同的肠癌中无明显差异(P>0.05);p53和PCNA过表达与浸润程度和淋巴结转移有关(P<0.05),p53和PCNA的表达在Ⅳ型胶原表达不同的肠癌中有非常显著的差异(P<0.005);大肠癌中p53过表达与nm23-H1低表达有关(P<0.01)。结论:实验结果揭示p53基因突变对于nm23-H1基因的失活有一定影响,其作用机制有待深入研究。nm23-H1低表达可能仅在大肠癌转移过程中发挥作用,p53过表达可在大肠癌浸润转移过程及细胞增殖中起重要作用。  相似文献   
997.
丹参对急性缺血后再灌注心肌磷脂肌醇系统变化的影响   总被引:5,自引:1,他引:5  
本文首镒报道采用大鼠在体心肌缺血后再灌注模型观察丹参对急性短时间缺血后再灌注心肌磷脂肌醇代谢的影响。结果显示:急性缺血10min后灌注10min,心肌磷脂肌醇信息传递系统功能明显增强,其磷脂酰肌醇-4,5-二磷酸和肌醇-1,4,5-三磷酸水平显著高于非缺血对照组和缺血组;丹参能显著抑制急性缺血后再灌注心肌磷脂肌醇系统的高功能状态,其PIP2和IP3水平明显低于缺血组和缺血再灌注组。  相似文献   
998.
七种中药小分子物质对淋巴细胞杀伤活性的影响   总被引:6,自引:0,他引:6  
用透析的方法从枸杞、槐籽、五谷虫(家蝇幼虫)、三七、小牛胸腺、白芍、茯苓,七种中药中获得小分子物质(分子量小于12000),系统地研究这些中药提取物对小鼠脾细胞杀伤活性的影响。结果发现枸杞、槐籽、五谷虫的透析外液不同程度地增强小鼠脾细胞杀伤活性。枸杞外液能抑制小鼠体内S180的生长;手术后乳腺癌病人使用枸杞小分子注射液,其外周血淋巴细胞的杀伤活性明显高于对照组。研究表明枸杞小分子成分经加热处理后,其有效性消失。  相似文献   
999.
In Vitro and In Vivo Characterization of MEMS Microneedles   总被引:1,自引:0,他引:1  
Transdermal drug delivery TDD systems have many advantages but are conventionally limited by the low permeability of skin. The idea of using microneedles to painlessly penetrate the topmost impermeable stratum corneum has previously been put forward. In this paper, the fabrication of solid and hollow silicon microneedles with straight side-walls and with the following dimensions: 20–100 m in diameter and 100–150 m in length is described. In vitro tests demonstrate that with prior solid microneedle application, transdermal drug transport is significantly increased by 10–20 times, with the degree of enhancement being related to needle diameter. In vivo tests in diabetic animals, however, were unable to demonstrate any delivery of insulin through the hollow microneedles. It is proposed that two factors, microneedle length and tip sharpness, have to be improved for systemic drug delivery to be seen in vivo.  相似文献   
1000.
The molecular epidemiological and clinical aspects of hepatitis D virus (HDV) in a unique HBV, HCV, and HDV triple virus endemic community in southern Taiwan were investigated. A total of 2,909 residents aged 45 or older were screened for hepatitis B surface antigen (HBsAg), anti-HCV antibody, and anti-HDV antibody (specifically for HBsAg-positive carriers). Factors that might be associated with HDV infection, viral nucleic acid detection, and genotyping of HBV, HCV, and HDV were investigated. The prevalence of HBsAg and anti-HCV were 12.6% (366/2,909) and 41.6% (1,227/2,909), respectively. For HBsAg carriers, 15.3% (56/366) were positive for anti-HDV assay. Living in a higher endemic district of HCV infection (odds ratio [OR] = 3.2; 95% confidence interval [CI] = 1.7-6.3), male gender (OR = 1.9; 95% CI = 1.1-3.6) and co-infection with HCV (OR = 1.8; 95% CI = 1.0-3.3) were significantly independent factors associated with HDV infection. The detection rate of HDV RNA among anti-HDV-positive patients was only 12.7% (7/55). The mean HBV titer of triple infection group was significantly lower than in the HBV/HDV co-infection group (2.23 vs 3.05 in log(10), copies/ml, P = 0.046). HCV RNA detection among the triple infection group showed 47.4% (9/19) viremia rate and viral loads of 579,121 IU/ml in median (16,803-1,551,190 IU/ml). The prevalent genotype of HBV was type B (23/25); HCV was 1b (7/9) and HDV was IIa/IIb (4/4). Only the presence of HCV RNA predicted the presence of elevated ALT significantly (OR = 25.0; 95% CI = 3.39-184.6). In conclusion, the geographical aggregation of HDV infection paralleled that of HCV infection in this community. HCV suppressed the replication of HBV among triple vital infection patients. HBV and HDV lapsed into a remission or nonreplicative phase in most cases, and HCV acted as a dominant factor in triple viral-infected individuals. Only the presence of HCV RNA was associated with elevated ALT values, but not HBV or HDV.  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