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   151643篇
  免费   13214篇
  国内免费   6904篇
耳鼻咽喉   1182篇
儿科学   4592篇
妇产科学   3294篇
基础医学   19520篇
口腔科学   5915篇
临床医学   15177篇
内科学   22559篇
皮肤病学   2437篇
神经病学   10309篇
特种医学   3932篇
外国民族医学   44篇
外科学   14922篇
综合类   23516篇
现状与发展   27篇
预防医学   10461篇
眼科学   3720篇
药学   13090篇
  45篇
中国医学   5229篇
肿瘤学   11790篇
  2024年   327篇
  2023年   1872篇
  2022年   3706篇
  2021年   5238篇
  2020年   4819篇
  2019年   4479篇
  2018年   4410篇
  2017年   4867篇
  2016年   5182篇
  2015年   5308篇
  2014年   9285篇
  2013年   11253篇
  2012年   9056篇
  2011年   10266篇
  2010年   8398篇
  2009年   8091篇
  2008年   8420篇
  2007年   8571篇
  2006年   7642篇
  2005年   6941篇
  2004年   5872篇
  2003年   5092篇
  2002年   4182篇
  2001年   3709篇
  2000年   3092篇
  1999年   2680篇
  1998年   2274篇
  1997年   2070篇
  1996年   1874篇
  1995年   1676篇
  1994年   1438篇
  1993年   1162篇
  1992年   1077篇
  1991年   908篇
  1990年   845篇
  1989年   676篇
  1988年   555篇
  1987年   494篇
  1986年   422篇
  1985年   610篇
  1984年   486篇
  1983年   338篇
  1982年   444篇
  1981年   342篇
  1980年   297篇
  1979年   208篇
  1978年   177篇
  1977年   142篇
  1976年   154篇
  1975年   84篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
162.
糖尿病大鼠视网膜血管内皮生长因子与一氧化氮的变化   总被引:4,自引:1,他引:3  
目的:探讨糖尿病大鼠视网膜血管内皮生长因子(VEGF)与一氧化氮(NO)的变化及其在糖尿病视网膜病变(DR)发生发展过程中的作用。方法:选择健康成年SD大鼠,随机分成正常对照组,糖尿病1月(DM1),糖尿病3月(DM3)和糖尿病5月(DM5)组,一次性腹腔注射链佐菌素(STZ)诱发糖尿病模型,应用免疫组织化学方法观察各组视网膜组织VEGF的表达情况,并检测各组视网膜组织中一氧化氮合酶(NOS)活性和NO含量变化。结果:3个月时,糖尿病大鼠视网膜VEGF表达增强,NOS活性增强,NO含量增高,5个月时,糖尿病大鼠视网膜表达进一步增强,而NOS活性开始减弱,NO含量减少,结论:糖尿病大鼠视网膜VEGF的过度表达和NOS活性,NO含量的变化在DR的发生发展过程中起重要作用。  相似文献   
163.
Intravenous administration of human bone marrow stromal cells (hMSCs) after middle cerebral artery occlusion (MCAo) in rats provides functional benefit. We tested the hypothesis that these functional benefits are derived in part from hMSC production of growth and trophic factors. Quantitative sandwich enzyme‐linked immunosorbent assay (ELISA) of hMSCs cultured with normal and MCAo brain extracts were performed. hMSCs cultured in supernatant derived from ischemic brain extracts increased production of brain‐derived neurotrophic factor (BDNF), nerve growth factor (NGF), vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF). These neurotrophins and angiogenic growth factors increased in a post‐ischemia time‐dependent manner. The hMSC capacity to increase expression of growth and trophic factors may be the key to the benefit provided by transplanted hMSCs in the ischemic brain.  相似文献   
164.
In order to further investigate the effect of annexin Ⅱ (Ann- Ⅱ ) on tissue plasminogen activator (t-PA)-dependent plasminogen (PLG) activation and its interactive mechanism, recombinant native Ann- Ⅱ bound t-PA, PLG and plasmin with high affinity was examined. The flow cytometric assay showed that the ann- Ⅱ expression rate was higher in the human umbilical vein endothelial cell (HUVEC) (87. 65 %) than in the HL-60 cells as controls (35. 79 %). Two irrelevant proteins,bovine serum albumin (BSA) and equine IgG (EIG) had no effect on the production of plasmin.Ann- Ⅱ -mediated enhancement of t-PA-dependent PLG activation was inhibited by ε-aminocaproic acid or by pretreatment of Ann- Ⅱ with carboxypeptidase B with the inhibitive rate being 77.8 % and 77. 0 %, respectively. It was revealed that the effect of Ann- Ⅱ on PLG activation was specific for tPA. Urokinase didn‘t bind to Ann- Ⅱ , demonstrating the role of receptor-related lysine residues on activation of PLG, showing that the Ann- Ⅱ -PLG interaction was dependent upon carboxyl-terminal lysine residues. These findings suggest that annexin Ⅱ -mediated co-assembly of t-PA and PLG may promote plasmin generation and play a key role in modulating fibrinolysis on the endothelial surface.  相似文献   
165.
SUMMARY: In patients with chronic renal failure (CRF), hyperleptinaemia has been widely reported, but the exact mechanisms leading to elevated leptin levels are unclear. Impaired renal clearance of leptin and the influence of other hormones may be important. In this study, we measured serum leptin levels in 150 patients on haemodialysis, peritoneal dialysis or in the predialysis phase of CRF. Furthermore, we measured plasma levels of insulin, growth hormone (GH) and insulin-like growth factor 1 (IGF-1), as well as plasma levels of triacylglycerols and total low density lipoprotein (LDL)- and high density lipoprotein (HDL)-cholesterol. We observed significantly elevated levels of leptin, particularly in female patients, and leptin was shown to correlate significantly with insulin, total and LDL-cholesterol and log triacylglycerols. Leptin was inversely correlated with GH concentrations, but was not correlated with IGF-1 levels. Despite the multiple correlations established between leptin levels and other variables, only hyperinsulinaemia in CRF seems to be important as a determinator of leptin levels.  相似文献   
166.
儿童髓母细胞瘤中VEGFR-2的表达   总被引:3,自引:0,他引:3  
目的:探讨血管内皮生长因子受体VEGFR-2在儿童髓母细胞瘤中的表达及临床意义。方法:采用免疫组化LSAB法检测84例获随访的儿童髓母细胞瘤中的VEGFR-2表达,按术后生存期3,5,10年分为A,B,C三组,使用Cox回归统计分析。结果:84例儿童髓母细胞瘤中,VEGFR-2阳性表达74例(88.09%),A,B,C三组间VEGFR-2阳性表达分别为100%,88.89%,55.33%(P<0.01),Cox回归分析显示VEGFR-2是影响生存时间的一个独立的预后因子,它与预后存在负相关关系。结论:VEGFR-2表达水平可作为儿童髓母细胞瘤的预后指标之一。  相似文献   
167.
不稳定型心绞痛患者内皮素及血管性假血友病因子的改变   总被引:2,自引:0,他引:2  
王国彬  胡申江  孙坚 《浙江医学》2002,24(4):203-204
目的 观察不稳定型心绞痛 (Unstableanginapectoris,UAP)患者内皮素 (Endothelin,ET)及血管性假血友病因子 (vonWillebrandfactor,vWF)的变化。方法 不稳定型心绞痛患者34例、正常人21名分别在清晨采血测定ET及vWF值。 结果 不稳定型心绞痛患者ET(129.3±26.4) pg/ml及vWF(185.4±32.4) %值明显高于正常人(85.2±39.6)pg/ml及(142.1±42.0) % ,两者之间不具有显著相关性 (r=0.15,P>0.05)。结论 ET及vWF的改变可能参与了不稳定型心绞痛的病理生理过程。  相似文献   
168.
Platelet factor 4 ( PF4) is a negativehematopoietic factor.It can inhibit the prolifera-tion of endothelial cells and hematopoietic stem/progenitor cells,particularly megakaryoryocyticcells,reversibly[1] ,inhibit DNA synthesis,blockcell cycle progression during S phase and reducethe sensibility of normal hematopoietic stem/pro-genitor cells,but not some cancer or leukemia celllines,to cytotoxic drugs and ionizing radia-tion[2 - 3] ,and it also can cause a population in-crease of the stem cel…  相似文献   
169.
目的 :观察天然碱性脂 (Stearylamine,SA)脂质体介导绿色荧光蛋白 /碱性成纤维细胞生长因子(GFP/bFGF)基因于不同时间段豚鼠耳蜗中的表达 ,为进一步研究耳聋的基因治疗提供实验基础。方法 :取豚鼠 1 6只 ,分成 4组 ,每组 4只。其中 3只右耳圆窗内注入SA -GFP/bFGF复合物 ,1只同法注入生理盐水作为对照。分别于术后第 2、7、1 4、2 1天取材。在荧光显微镜下观察GFP的表达 ,用免疫组化法检测bFGF的转导情况。结果 :荧光显微镜下见双侧耳蜗于术后第 2天开始部分细胞发出绿色荧光 ,第 7天达到高峰 ,支持细胞及内外毛细胞均显荧光 ,细胞轮廓清晰 ;第 1 4天开始减弱 ,第 2 1天消失。免疫组化染色显示 ,除血管纹外 ,耳蜗各回Corti器、螺旋韧带、螺旋缘及螺旋神经节细胞均有高浓度的表达产物 ,对照动物呈阴性表达。结论 :SA脂质体介导的GFP/bFGF基因单耳给药双侧耳蜗均有高效表达 ,为进一步研究基因治疗耳聋提供了可能。  相似文献   
170.
In a large study on 1,220 patients with ovarian carcinoma in FIGO stages I-IV, the prognostic importance of the time factor for start of postoperative chemotherapy was studied together with other important factors for long-term survival. The patient series was a total geographic material of ovarian carcinoma patients treated during the years 1975-1993. All patients were followed up for 10 years or until death. The 5-year cancer-specific survival rate of the complete series was 50%. Significant and independent prognostic factors with regard to long-term cancer-specific survival were FIGO stage, histology, tumor grade, and completeness of the primary surgery. Special attention was paid to the prognostic importance of the time interval between primary surgery and the first course of chemotherapy. Patient groups with intervals shorter or longer than the median value were compared. In early-stage disease, no significant difference was noted. In advanced and bulky disease, an interval longer than the median value seemed to be beneficial compared with a shorter interval. However, after correction for other prognostic factors, the interval was not a significant factor (P = 0.647) with regard to the cancer-specific survival rate. Therefore, the time factor should not be an important argument for how to best organize the gynecologic oncology service.  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