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   23638篇
  免费   1910篇
  国内免费   1928篇
  27476篇
  2024年   60篇
  2023年   343篇
  2022年   775篇
  2021年   1258篇
  2020年   837篇
  2019年   1059篇
  2018年   995篇
  2017年   685篇
  2016年   1009篇
  2015年   1504篇
  2014年   1691篇
  2013年   1787篇
  2012年   2190篇
  2011年   1916篇
  2010年   1137篇
  2009年   1065篇
  2008年   1257篇
  2007年   1047篇
  2006年   935篇
  2005年   745篇
  2004年   601篇
  2003年   516篇
  2002年   453篇
  2001年   373篇
  2000年   359篇
  1999年   369篇
  1998年   231篇
  1997年   255篇
  1996年   207篇
  1995年   208篇
  1994年   182篇
  1993年   142篇
  1992年   201篇
  1991年   163篇
  1990年   161篇
  1989年   120篇
  1988年   94篇
  1987年   94篇
  1986年   67篇
  1985年   72篇
  1984年   47篇
  1983年   54篇
  1982年   26篇
  1981年   19篇
  1980年   17篇
  1979年   13篇
  1977年   12篇
  1976年   12篇
  1974年   12篇
  1965年   16篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Lung cancer is the leading cause of cancer-related mortality all over the world. In recent years, pulmonary adenocarcinoma has surpassed squamous cell carcinoma in frequency and is the predominant form of lung cancer in many countries. Epidemiological investigations have shown an inverse relationship between garlic (Allium sativum) consumption and death rate from many cancers. Diallyl trisulfide (DATS) is one of the garlic-derived compounds (also known as: organosulfer compounds, OSC). DATS can induce apoptosis and inhibit the growth of many cancer cell lines. Our study demonstrated that the apoptotic incidents induced by DATS were a mitochondria-dependent caspase cascade through a significant decrease of the anti-apoptotic Bcl-2 that resulted in up-regulation of the ratio of Bax/Bcl-2 and the activity of caspase-3, -8, and -9. Eventually, DATS induced the apoptosis and inhibited the proliferation in a concentration- and time-dependent manner. Furthermore, by establishing an animal model of female BALB/c nude mice with A549 xenografts, we found that oral gavage of DATS significantly retarded growth of A549 xenografts in nude mice without causing weight loss or any other side effects compared with the control group. All the evidence both in vitro and in vivo suggested that DATS could be an ideal anti-cancer drug.  相似文献   
52.
阿片类物质在中枢神经系统的免疫调控作用   总被引:5,自引:0,他引:5  
Sheng WS  Hu S  Chao CC 《生理科学进展》1998,29(2):125-129
内源及外源性阿片具有调节神经元与胶质细胞的功能,这些调节具有保护或损伤脑功能的双重作用。吗啡具有促进受病毒复制及继发感染的作用。另一方面,阿片受体中的kappa受体可能具有保护神经元的作用。更深层次的研究应是了解阿片通过什么机制作用在胶质细胞和神经元上,藉此以促进研制出具有明显疗效的新药。  相似文献   
53.

Background  

Understanding gene regulatory networks has become one of the central research problems in bioinformatics. More than thirty algorithms have been proposed to identify DNA regulatory sites during the past thirty years. However, the prediction accuracy of these algorithms is still quite low. Ensemble algorithms have emerged as an effective strategy in bioinformatics for improving the prediction accuracy by exploiting the synergetic prediction capability of multiple algorithms.  相似文献   
54.
Hu ZA  Tan YL  Luo J  Li HD  Li XC  Yu ZP 《生理学报》2004,56(1):89-94
既往研究发现,神经细胞粘附分子(neural cell adhesion molecules,NCAM)对海马CA1区突触传递长时程增强(longterm potentiation,LTP)的诱导和维持极为关键。本文采用原位杂交法和Western blot法,观察了大鼠海马腑片LTP诱导和维持过程中NCAM mRNA和蛋白水平的动态变化过程。结果显示,强直刺激诱发fEPSP斜率升高10 min时,海马CA1区NCAM mRNA染色阳性神经元数量显著增加(76.6±11.5个),NCAM蛋白水平亦明显升高(7.190±0.64任意单位/50μg蛋白)。强直刺激诱发fEPSP斜率升高1 h时,NCAM mRNA染色阳性神经元数量为73.3±14.0个,NCAM蛋白量为9.031±0.71任意单位/50 μg蛋白;与强直刺激后10 min比较,NCAM mRNA表达无显著变化,而NCAM蛋白水平变化明显。NMDA受体特异阻断剂AP-5在损害LTP的同时,显著抑制NCAM mRNA和蛋白的增加。实验结果表明,在大鼠海马LTP诱导和维持过程中,NCAM mRNA增强的表达相对稳定,而NCAM蛋白水平呈现先低后高的变化。  相似文献   
55.
Antibacterial and antifungal activity was investigated for strains of Acidovorax spp., Burkholderia spp., Herbaspirillum rubrisubalbicans and Ralstonia solanacearum ; strains representing 118 species and pathovars of Xanthomonas were also tested for phytotoxic capacity. Antibacterial activity was present in all Burkholderia spp. except B. andropogonis , in biovars II and III of R. solanacearum but not in biovars I and IV, and in two strains of Xanthomonas. Little antibacterial activity was recorded for Acidovorax spp. Antifungal activity was expressed by most strains of A. avenae ssp. avenae and A. avenae ssp. cattleyae. Weak or variable antifungal reactions were given by strains of A. avenae ssp. citrulli and no activity was expressed by A. konjaci. Most strains of B. caryophylli, B. cepacia, B. gladioli pv. agaricicola, B. gladioli pv. alliicola, B. gladioli pv. gladioli , B. glumae and B. plantari produced extensive inhibition zones against Rhodotorula mucilaginosa. Strains of H. rubrisubalbicans and R. solanacearum gave negative, weak or variable reactions. Strains of Xanthomonas spp. exhibited no antifungal activity. In all cases antifungal activity was caused by a low molecular weight toxin. Three Xanthomonas strains exhibited phytotoxic activity. The ecological implications of these data are discussed.  相似文献   
56.
Rat orthotopic liver transplantation (ROLT) remains a technically demanding procedure, especially regarding the reconstruction of the suprahepatic vena cava (SHVC). In this study, a new microsuture technique was developed for anastomosis of the SHVC, and a special single-groove cuff and blade-cut stent were introduced. With these modified techniques, we aimed to make a precise anastomosis of the SHVC and to provide optimal cuffs and stents for the reconstruction of the veins and bile ducts. According to different microsuture techniques for the SHVC and different types of cuffs and stents, three ROLT groups were created to compare the operation times and prognoses. Sham operations were performed as controls in the fourth group. The time expenditures with each step were compared among the transplantation groups. Biochemical parameters were tested at the end of a 1-month observation period. The short- and long-term survival rates of the transplantation groups were recorded and compared. Our new microsuture technique was faster than the conventional continuous suture technique for SHVC anastomosis (P < 0.05). The use of a single-groove cuff for reconstruction of the portal vein and the infrahepatic vena cava shortened the anastomotic time (P < 0.05). The use of blade-cut stents resulted in fewer biliary complications and better survival over the short and long terms (P < 0.05). Our new microsuture technique and the single-groove cuffs proved to be a precise method for venous reconstruction which shortened the anhepatic time and the anastomotic time significantly. The blade-cut stents apparently reduced the incidence of biliary complications. In summary, with this precise microsuture technique and delicate cuffs and stents, excellent long-term survival can be achieved easily and stably for ROLT.  相似文献   
57.
Genetic manipulation of antibiotic producers, such as Streptomyces species, is a rational approach to improve the properties of biologically active molecules. However, this can be a slow and sometimes problematic process. Red/ET recombination in an Escherichia coli host has permitted rapid and more versatile engineering of geldanamycin biosynthetic genes in a complementation plasmid, which can then be readily transferred into the Streptomyces host from which the corresponding wild type gene(s) has been removed. With this rapid Red/ET recombination and gene complementation approach, efficient gene disruptions and gene replacements in the geldanamycin biosynthetic gene cluster have been successfully achieved. As an example, we describe here the creation of a ketoreductase 6 null mutation in an E. coli high-copy-number plasmid carrying gdmA2A3 from Streptomyces hygroscopicus NRRL3602 and the subsequent complementation of a gdmA2A3 deletion host with this plasmid to generate a novel geldanamycin analog.  相似文献   
58.
MYH9-related diseases (MYH9-RD) are a group of autosomal dominant diseases caused by mutations in the MYH9 gene, which are featured by thrombocytopenia, giant platelets and granulocyte cytoplasmic inclusion bodies. MYH9-RD patients generally suffer from bleeding syndromes, progressive kidney disease, deafness, or cataracts. Here, we reported on a case of MYH9-RD. A novel heterozygous mutation of MYH9 (c.2344-2345delGTinsTA, p.T782Y) was discovered by targeted sequencing technology. Immunofluorescence analysis of neutrophils confirmed abnormal aggregation of MYH9 protein. The results of this study should expand the MYH9 gene mutation spectrum and provide reference for subsequent researchers and genetic counseling.  相似文献   
59.
Although cisplatin is one of the chemotherapeutics most frequently used in oral squamous cell carcinoma (OSCC) treatment,it exerts multiple side effects and poo...  相似文献   
60.
The molecular mechanisms underlying the involvement of oligodendrocytes in formation of the nodes of Ranvier (NORs) remain poorly understood. Here we show that oligodendrocyte-myelin glycoprotein (OMgp) aggregates specifically at NORs. Nodal location of OMgp does not occur along demyelinated axons of either Shiverer or proteolipid protein (PLP) transgenic mice. Over-expression of OMgp in OLN-93 cells facilitates process outgrowth. In transgenic mice in which expression of OMgp is down-regulated, myelin thickness declines, and lateral oligodendrocyte loops at the node-paranode junction are less compacted and even join together with the opposite loops, which leads to shortened nodal gaps. Notably, each of these structural abnormalities plus modest down-regulation of expression of Na(+) channel alpha subunit result in reduced conduction velocity in the spinal cords of the mutant mice. Thus, OMgp that is derived from glia has distinct roles in regulating nodal formation and function during CNS myelination.  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