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   27069篇
  免费   2964篇
  国内免费   1381篇
耳鼻咽喉   133篇
儿科学   469篇
妇产科学   479篇
基础医学   4886篇
口腔科学   357篇
临床医学   2206篇
内科学   4858篇
皮肤病学   449篇
神经病学   1453篇
特种医学   646篇
外国民族医学   20篇
外科学   2271篇
综合类   4128篇
现状与发展   7篇
预防医学   1091篇
眼科学   815篇
药学   2267篇
  16篇
中国医学   503篇
肿瘤学   4360篇
  2024年   72篇
  2023年   602篇
  2022年   995篇
  2021年   1674篇
  2020年   1209篇
  2019年   1147篇
  2018年   1012篇
  2017年   985篇
  2016年   1132篇
  2015年   1255篇
  2014年   1689篇
  2013年   1877篇
  2012年   1653篇
  2011年   1754篇
  2010年   1567篇
  2009年   1509篇
  2008年   1446篇
  2007年   1398篇
  2006年   1217篇
  2005年   974篇
  2004年   783篇
  2003年   688篇
  2002年   528篇
  2001年   535篇
  2000年   436篇
  1999年   356篇
  1998年   322篇
  1997年   313篇
  1996年   234篇
  1995年   217篇
  1994年   225篇
  1993年   183篇
  1992年   158篇
  1991年   118篇
  1990年   108篇
  1989年   119篇
  1988年   102篇
  1987年   76篇
  1986年   69篇
  1985年   105篇
  1984年   69篇
  1983年   52篇
  1982年   53篇
  1981年   70篇
  1980年   73篇
  1979年   42篇
  1978年   47篇
  1977年   32篇
  1976年   44篇
  1975年   20篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
小横切口手术治疗小儿腹股斜疝   总被引:1,自引:1,他引:0  
王新生  黄兴建 《河北医学》2002,8(8):709-711
目的:探讨小儿腹股沟斜疝手术方法。方法:经外环小横切口行疝囊高位结扎加修补术。结果:全组126例,平均手术时间12min,无一例出现并发症。结论:此方法有切口小、时间短、创伤轻、恢复快、费用低、疤痕不明显等优点,值得推广。  相似文献   
42.
The purpose of this study was to validate the hypothesis of neural histogenesis of Ewing's sarcoma of bone and related tumors by light microscopic, electron microscopic, and immunohistochemical analysis. We studied 32 round-cell sarcomas (19 cases of Ewing's sarcoma of bone, 3 extraskeletal Ewing's sarcomas, 5 peripheral primitive neuroectodermal tumors (PNET) and 5 cases of unclassified small round-cell type of neurogenic sarcoma (NS). Immunoreactivity for MIC2 was observed in all cases of Ewing's sarcoma and PNET, and in 1 cases of NS. Positive immunoreactivity for neural markers (NSE, synaptophysin, S-100) was found frequently in some tumors. Ultrastructurally, some specific features of neural differentiation, such as a fragmented basal lamina and neurosecretory granule-like particles, were found even in typical cases of Ewing's sarcoma of bone, which presented without a rosette arrangement and were almost negative for neural immuno-markers, but positive for MIC2. These ultrastructural neural features were observed less frequently in Ewing's sarcoma of bone than in PNET and NS. However, no significant correlation was demonstrated between the immunoreactivity for neural markers and the ultrastructural and histological neural features. These results support the hypothesis of a neural origin of Ewing's sarcoma and related neoplasms, and suggest that some overlapping entity could persist in PNET and Ewing's sarcoma and that this entity could be seen in histological and immunohistochemical studies of both tumors.  相似文献   
43.
Ischemia-reperfusion injury by free radicals and lipid peroxides is observed in various organs. Ascorbic acid (AsA) or glutathione (GSH) in various doses (AsA:2, 0.5, 0.1 mmol/kg, GSH:2 mmol/kg) was intraperitoneally administered to male Wistar rats. The entire small intestines were resected just before ischemia, after ischemia, and after 20 min of reperfusion (n = 7–10 at each time point). At each time point, the specimens were subjected to assays of lipid peroxides, GSH, and glutaminase activity of the tissues; they were also examined histologically. In the AsA group, the production of lipid peroxides after reperfusion was significantly suppressed in a dose-dependent manner, and the ratio of oxidized GSH to total GSH was also significantly low. Tissue glutaminase activity decreased to a lesser extent, and the degree of injury was apparently less marked in the AsA group. This study indicates that AsA acts as an antioxidant against peroxidative tissue injury, possibly by scavenging radicals, preserving reduced GSH, and reducing the peroxidative reaction. Received: 21 June 1996 Received after revision: 8 October 1996 Accepted: 12 November 1996  相似文献   
44.
Intestinal ischaemia-reperfusion (IR) injury has largely been attributed to cellular necrosis. Apoptosis, a distinct form of cell death has been observed following IR to the brain, heart, adrenals and the kidneys. In order to characterize the role of apoptosis in intestinal IR, small bowel grafts were stored in saline ( n  = 6) or modified University of Wisconsin solution ( n  = 6) at 4 °C for 12 h and reperfused for 6 h in syngeneic rats. Samples of normal, stored and reperfused intestines at 1, 3 and 6 h were analysed by light and electron microscopy. Following reperfusion, there was crypt and villous epithelial apoptosis, loss of crypt and villous structures, and an increase in mucosal inflammatory cell infiltration. Ongoing apoptosis was maximum at 1 h, its degree decreasing with increasing reperfusion intervals. Large numbers of apoptotic bodies dominated the picture from 3 h of reperfusion. This study has demonstrated the induction of apoptosis by intestinal IR injury, which begins within an hour of reperfusion and is probably responsible for the observed crypt and villous loss. This has potential therapeutic implications as, opposed to necrosis, apoptosis is an active process with genetic regulators and biochemical effectors, which can be specifically targeted to prevent or alleviate IR injury.  相似文献   
45.
Dipeptidyl peptidase IV (DPP-IV) is a cell surface ectopeptidase that has been implicated in cell-extracellular matrix interactions, lymphocyte growth and the regulation of biological peptides. Previous studies have shown that immunostaining for DPP-IV and DPP-IV enzyme levels is decreased in hepatoma cells and levels have been correlated with the ability of such cells to adhere in vitro. The aim of this paper was to measure DPP-IV enzyme levels in rat hepatoma cells and to examine whether changes were associated with alterations at the mRNA level. The results indicate a greater than 90% reduction in DPP-IV enzyme levels in two rat hepatoma cell lines, HTC and H35, compared with rat hepatocytes. Enzyme levels of the control enzyme leucine aminopeptidase (LAP) were not decreased. mRNA studies indicated that these changes were associated with similar reductions in rat DPP-IV mRNA. It is concluded that DPP-IV is markedly reduced at the protein, enzyme and mRNA levels in rat hepatoma cells. The significance of these changes is unclear but may lead to decreased extracellular matrix interactions by such cells.  相似文献   
46.
大鼠肝细胞Ⅰ,Ⅲ型前胶原基因表达及PDGF的影响   总被引:3,自引:1,他引:2  
目的观察大鼠肝细胞Ⅰ,Ⅲ型前胶原基因的表达及PDGF对其表达的影响.方法应用原位杂交技术检测分离培养的SD大鼠肝细胞(n=30)内Ⅰ,Ⅲ型前胶原基因的表达.同时观察10μg/L(n=30)和30μg/L(n=30)PDGF促进前胶原基因表达的作用.测定基因表达颗粒总面积占细胞总面积的百分比,并作比较分析.结果无论正常肝细胞或是在两种浓度的PDGF存在时,肝细胞内均可见到Ⅰ,Ⅲ型前胶原基因的表达.正常肝细胞Ⅰ,Ⅲ型前胶原基因表达面积的百分比(%)为77±19和75±21;加10μg/LPDGF后为115±19和112±10,而加30μg/L后为152±34及181±28,且在后者中表达明显增强(P<005及P<001).结论PDGF在转录水平上促进肝细胞胶原的合成.  相似文献   
47.
本文报道我院1981年8月~1986年10月间收治的41例原发性小肠肿瘤,所有病例均经手术切除并经病理检查证实。本组男性24例,女性17例;年龄最小9个月,最大68岁。其中良性肿瘤5例,恶性肿瘤36例。肿瘤位于十二指肠者7例,空肠10例,回肠24例。 原发性小肠肿瘤的临床表现无一定规律,早期多无明显症状,且目前尚缺乏简便可靠的诊断措施,往往导致诊断延误。本文就本病的发生率,临床表现与诊断,误诊原因及辅助诊断等进行了讨论。  相似文献   
48.
用AGPC法抽提幼年家兔视网膜总RNA,并应用了地高辛标记核酸探针的方法。经斑点杂交显示幼年家兔视网膜出现C—sis原癌基因表达。对实验方法以及C-sis原癌基因表达的意义进行了探讨。认为此方法快速、灵敏,检测C-sis原癌基因表达对深入研究视网膜生长发育及肿瘤等病变有一定意义。  相似文献   
49.
用体外培养的人的伪表皮作为模型,进行药物毒理学作用的研究,观察了二甲亚砜(DMSO)在不同浓度和不同接触时间条件下,对人的伪表皮细胞脱氧核糖核酸(DNA)、核糖核酸(RNA)和蛋白质合成的影响:随着接触时间的延长,DNA、RNA和蛋白质合成均受抑制。低浓度条件下(1%),DNA、RNA和蛋白质合成增加;在15~50%浓度下,DNA和蛋白质合成抑制,而RNA合成仍增加;在高浓度条件下(70%~100%),DNA、RNA和蛋白质合成均明显抑制。  相似文献   
50.
目的 探讨参附注射液对大鼠缺血再灌注小肠细胞Bax、Bcl 2及c myc蛋白表达的影响及它们与肠细胞凋亡的内在联系。方法 健康SD大鼠 36只随机分为 3组 ,空白对照组 (S组 )、缺血再灌注 +生理盐水组 (IR +NS组 )、缺血再灌注 +参附注射液组 (IR +SF组 ) ,每组 12只。采用钳闭肠系膜前动脉制备小肠缺血再灌注模型。免疫组化检测Bax、Bcl 2及c myc蛋白的表达 ,每组选 2 4个视野分别测量光密度值 (OD值 )。TUNEL法检测凋亡的小肠细胞并计算凋亡指数。结果 IR +NS组BaxOD值明显高于S组 (P <0 .0 1) ,IR +SF组BaxOD值明显低于IR +NS组 (P <0 .0 1) ,且低于S组 (P <0 .0 5 )。IR +NS组Bcl 2OD值高于S组 (P <0 .0 5 ) ,且IR +SF组Bcl 2OD值高于S组 (P <0 .0 1) ,但IR +NS组与IR +SF组比较无显著差异。IR +NS组c mycOD值明显高于S组 (P<0 .0 1) ,且明显高于IR +SF组 (P <0 .0 1)。IR +NS组细胞凋亡指数明显高于S组和IR +SF组 (P <0 .0 1) ,而IR +SF组高于S组 (P <0 .0 5 )。结论 参附注射液增加小肠组织Bcl 2蛋白的表达 ,降低Bax及c myc蛋白的表达 ,抑制小肠细胞凋亡 ,保护缺血再灌注小肠。  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