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   859122篇
  免费   92676篇
  国内免费   492篇
  952290篇
  2018年   7732篇
  2016年   10231篇
  2015年   13379篇
  2014年   15912篇
  2013年   23491篇
  2012年   25746篇
  2011年   26438篇
  2010年   17854篇
  2009年   16517篇
  2008年   23290篇
  2007年   24342篇
  2006年   22899篇
  2005年   21885篇
  2004年   21807篇
  2003年   20992篇
  2002年   20455篇
  2001年   39743篇
  2000年   39767篇
  1999年   31419篇
  1998年   10542篇
  1997年   11266篇
  1996年   10495篇
  1995年   9773篇
  1994年   9519篇
  1993年   9606篇
  1992年   25970篇
  1991年   25127篇
  1990年   24625篇
  1989年   24050篇
  1988年   22343篇
  1987年   21023篇
  1986年   19511篇
  1985年   19768篇
  1984年   16282篇
  1983年   13949篇
  1982年   10549篇
  1981年   9488篇
  1980年   8942篇
  1979年   15507篇
  1978年   11996篇
  1977年   11196篇
  1976年   10393篇
  1975年   11401篇
  1974年   12333篇
  1973年   12080篇
  1972年   11150篇
  1971年   10170篇
  1970年   8749篇
  1969年   8559篇
  1968年   7968篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
991.
Summary Viral leukemogenesis in mice is frequently initiated by proviral activation of a highly conserved cellular gene called Pim-1. Here we report the chromosomal localization of the human homologue by Southern blot analyses of DNAs obtained from human-rodent somatic cell hybrids. The single copy human homologue was assigned to the 6pter-q12 segment.  相似文献   
992.
993.
We examined the relationships among reproductive hormone concentrations and bone mineral density (BMD) in 43 women runners classified as eumenorrheic (n = 24), oligomenorrheic (n = 8), or amenorrheic (n = 11). Results were compared with a eumenorrheic nonrunner control group (n = 11). Serum 17 beta-estradiol, progesterone, and dehydroepiandrosterone sulfate concentrations were determined in daily blood samples for 21 days, and integrated concentrations (areas under the curve) were calculated. BMD was assessed at the lumbar spine and proximal femur by dual-photon absorptiometry. As expected, 17 beta-estradiol, progesterone, and lumbar spine BMD were higher in the control and eumenorrheic runner groups than in the oligomenorrheic and amenorrheic runner groups (P less than 0.05). Progesterone concentration was significantly correlated with lumbar spine BMD in the eumenorrheic runners (r = 0.61). None of the steroid hormones was significantly related to BMD in the oligomenorrheic/amenorrheic group. The present data suggest that circulating levels of gonadal steroid hormones affect axial BMD in eumenorrheic runners.  相似文献   
994.
Oxidation of thymine with O2 was promoted by copper(I) ion generated from reaction of L-ascorbic acid (AA) with copper (II) ion. The main oxidation products were thymine glycol (TG) and N-formyl-N'-pyruvylurea (FPU). At higher concentration of O2, formation of FPU was favored, while TG was dominant at higher Cu(II) ion and lower O2 concentrations. Reaction mechanism involving hydroxy thyminyl radical was proposed.  相似文献   
995.
Fractionation of human erythrocyte membrane proteins was performed using a modification of two-dimensional gel electrophoresis described by P. O'Farrel with isoelectric point plotted against molecular mass. All major erythrocyte proteins, including high molecular weight proteins, such as spectrin and band 3 protein, identified by one-dimensional sodium dodecyl sulfate gel electrophoresis, were visualized by silver staining of two-dimensional gels. All in all about 50 polypeptides were distinguished on two-dimensional electrophoretic patterns. Preliminary protein map was developed.  相似文献   
996.
A method is proposed for assessing the biocidal efficacy of water-dispersed nanoparticles of silver. It is based on negative chemotaxis of the plasmodia of the slime mold Physarum polycephalum. Biocidal and repellent effects were compared for silver nanoparticles, Ag+ ions, and AOT in solution and in the agar gel. In such characteristics as increasing the period of auto-oscillations of contractile activity, decreasing the area of spreading on substrate, and substrate preference in spatial tests, silver nanoparticles proved to be substantially more effective than Ag+ and AOT. The lethal concentrations of the nanoparticles were close to those found earlier for bacteria and viruses. The chemotactic tests allow quantitative assessment of the biological reaction and monitoring its dynamics; in resolution, they are superior to the tests based on the lethal action of biocidal agents.  相似文献   
997.
998.
During an ultrastructural study of small-intestinal mucosa from a patient suffering from alpha-chain disease organisms were identified within the epithelial cytoplasm which showed the fine structural features of the coccidian group. Though coccidiosis is well recognized as causing a diarrhoeal and often lethal illness in animals it has been neglected as a cause of disease in man. Thus this finding may be significant and warrants further investigation into its possible role in the pathogenesis of alpha-chain disease.  相似文献   
999.
1000.
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