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   875902篇
  免费   94792篇
  国内免费   602篇
  971296篇
  2021年   7407篇
  2018年   8763篇
  2017年   8128篇
  2016年   11982篇
  2015年   16988篇
  2014年   19751篇
  2013年   27359篇
  2012年   31454篇
  2011年   31852篇
  2010年   21472篇
  2009年   19652篇
  2008年   27972篇
  2007年   28573篇
  2006年   27037篇
  2005年   26137篇
  2004年   25959篇
  2003年   24887篇
  2002年   23939篇
  2001年   39070篇
  2000年   39100篇
  1999年   31425篇
  1998年   11705篇
  1997年   11876篇
  1996年   11136篇
  1995年   10382篇
  1994年   10071篇
  1993年   9891篇
  1992年   25245篇
  1991年   24483篇
  1990年   23821篇
  1989年   23140篇
  1988年   21514篇
  1987年   20056篇
  1986年   18573篇
  1985年   18479篇
  1984年   15498篇
  1983年   12896篇
  1982年   9959篇
  1981年   8913篇
  1980年   8316篇
  1979年   13750篇
  1978年   10779篇
  1977年   9678篇
  1976年   8774篇
  1975年   9681篇
  1974年   10354篇
  1973年   10167篇
  1972年   9059篇
  1971年   8255篇
  1970年   7043篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
Home range, dispersal and the clan system of impala   总被引:1,自引:0,他引:1  
  相似文献   
922.
A sugar-binding component was shown to be present at the surface of endoerythrocytic Plasmodium berghei and P. chabaudi stages and merozoites by means of a panel of neoglycoproteins using fluorescence microscopy and flow cytofluorometry. The protein nature of this material was ascertained by the loss of sugar-binding capacity upon trypsin treatment. This lectin-like protein primarily bound neoglycoprotein-borne N-acetylglucosamine and secondarily bound neoglycoprotein-borne alpha-D-glucose, beta-D-galactose and alpha-L-fucose. These results suggest the presence of at least one type of lectin-like protein with an extended binding site accomodating several sugar units, and define its localization on the parasite surface.  相似文献   
923.
924.
In vitro directly micropropagated plantlets from three selected five-year-old Eucalyptus grandis Hill ex. Maiden hybrids were compared to their related half-sib seedlings for growth and growth pattern parameters under greenhouse conditions used for operational seedling production. The oven dry weights were determined from stem, leaf, and root samples collected every 40 days for four times. Relative growth rate, net assimilation rates and shoot:root ratio were calculated. Survival was 98% and 95% for plantlets and seedlings, respectively. Significant differences were observed between parents in terms of shoot and root dry weights and their ratios with similar ranking among plantlets and seedlings, suggesting genetic control over these traits. Plantlets started with significantly higher root: shoot ratios and stem, leaf, root, and total dry weight. Although seedlings had higher relative growth and net assimilation rates, all the initial differences decreased sharply over time.  相似文献   
925.
Identification of bacteria of dairy origin using miniaturized test-systems   总被引:1,自引:1,他引:0  
One hundred and forty-four isolates of dairy origin were identified using a number of commercially available test kits. Agreement between these kits was acceptable for assignment of isolates to genera, but there was some variation between the kits for the identification of the isolates at specific level. The reasons for these variations are discussed. In terms of cost, ease of performance and accuracy, the identification systems manufactured by Roche Products Ltd (viz. the Oxi/Ferm tube and the Enterotube) are considered to be the best suited to the routine identification of dairy micro-organisms.  相似文献   
926.
927.
The study of the effect of gamma globulin introduced in different doses (0.5 and 0.25 ml/mg) in combination with Fermi rabies vaccine (observations on humans were made) and with cerebral rabies vaccine inactivated by UV irradiation (in animal experiments) demonstrated that the injection of the higher doses of gamma globulin resulted in lower geometrical mean of antibody titers. Therefore, in combined administration of rabies vaccine and gamma globulin for postexposure rabies prevention it is advisable to reduce the dose of gamma globulin by one-half.  相似文献   
928.
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   
929.
930.
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   
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