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   24539篇
  免费   60篇
  国内免费   103篇
系统科学   82篇
丛书文集   219篇
教育与普及   91篇
理论与方法论   71篇
现状及发展   10840篇
研究方法   984篇
综合类   12097篇
自然研究   318篇
  2012年   303篇
  2011年   604篇
  2009年   144篇
  2008年   382篇
  2007年   440篇
  2006年   406篇
  2005年   436篇
  2004年   475篇
  2003年   431篇
  2002年   424篇
  2001年   766篇
  2000年   775篇
  1999年   536篇
  1994年   326篇
  1992年   460篇
  1991年   379篇
  1990年   442篇
  1989年   397篇
  1988年   396篇
  1987年   424篇
  1986年   428篇
  1985年   526篇
  1984年   390篇
  1983年   372篇
  1982年   314篇
  1981年   314篇
  1980年   366篇
  1979年   758篇
  1978年   642篇
  1977年   566篇
  1976年   475篇
  1975年   531篇
  1974年   648篇
  1973年   562篇
  1972年   599篇
  1971年   768篇
  1970年   853篇
  1969年   714篇
  1968年   733篇
  1967年   631篇
  1966年   594篇
  1965年   427篇
  1964年   158篇
  1959年   233篇
  1958年   427篇
  1957年   320篇
  1956年   250篇
  1955年   246篇
  1954年   245篇
  1948年   218篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Chromosomal localization of human haemoglobin structural genes   总被引:15,自引:0,他引:15  
P M Price  J H Conover  K Hirschhorn 《Nature》1972,237(5354):340-342
  相似文献   
122.
RNA-DNA hybrids at the cytological level   总被引:37,自引:0,他引:37  
H A John  M L Birnstiel  K W Jones 《Nature》1969,223(5206):582-587
  相似文献   
123.
RNA synthesis during early development of the mouse   总被引:5,自引:0,他引:5  
H R Woodland  C F Graham 《Nature》1969,221(5178):327-332
  相似文献   
124.
Hominoid tali from East Africa   总被引:1,自引:0,他引:1  
M H Day  B A Wood 《Nature》1969,222(5193):591-592
  相似文献   
125.
Genetics of the alkaline phosphatase polymorphism of the human placenta   总被引:27,自引:0,他引:27  
E B Robson  H Harris 《Nature》1965,207(5003):1257-1259
  相似文献   
126.
Summary Tamoxifen is an anticancer drug widely used in the treatment of estrogen-dependent breast cancer. In hatchling alligators it acts as a pure antiestrogen in that it completely blocks the effect of estradiol-induced oviductal hypertrophy and completely blocks the estradiol-induced hepatic vitellogenin secretion. Paradoxically, when injected into alligator eggs incubated at 33°C, a temperature which would normally result in 100% male hatchlings, tamoxifen sex reverses the embryos into apparently normal female hatchlings.  相似文献   
127.
Summary Normal human spermatozoa were demonstrated by dot immunoblot analysis and immunohistochemistry to possess transglutaminase (TGase). The immunological identification of spermatozoal TGase is consistent with reports by others of its biochemical identification and suggested role in sperm motility,and provides, in view of the immunoregulatory properties of seminal plasma TGase, presumptive identification of a means whereby spermatozoa, under normal physiological conditions, may possibly be protected from immunological attack within the female reproductive tract.  相似文献   
128.
Summary The biochemical development of the fetal brain in relation to maternal vitamin A restriction was studied in rats. The vitamin A status of pregnant rats was varied by supplying low, medium and adequate amounts (6, 40, and 100 g retinol/day/kg body weight, respectively) of vitamin A during pregnancy and suckling. The maternal vitamin A restriction caused an altered brain development in terms of tissue weight, DNA, RNA and protein levels, and biosynthesis of DNA and protein from [3H]-thymidine and [3H]-leucine, respectively. A dose-dependent effect of maternal vitamin A restriction on the metabolism of DNA, RNA and protein was noticed in the developing fetal brain of rats.  相似文献   
129.
Summary The ability of liposomes composed of different kinds of phospholipid materials to adhere to the surface of the cornea was studied in the rabbit. The liposomes were labelled with tracer amounts of an I125-labelled phosphatidylethanolamine derivative and were instilled in 10 l drops onto the cornea. The retention of radioactivity was monitored. The results show that liposomes containing positively charged phospholipids are better retained than an albumin control. Thus, it may be possible to develop a drug delivery, liposome system which would permit long-term sustained release of ophthalmic drugs onto the cornea.  相似文献   
130.
Summary Histamine content in the rat hypothalamus was lower at 4°C and higher at 31°C compared to that at 21°C. Pretreatment with -fluoromethylhistidine, a suicide inhibitor of histidine decarboxylase, attenuated both the increased level of hypothalamic histamine and rat adaptive behavior at 31°C. Increase of histamine content in the hypothalamus appears to be an important factor contributing to rat adaptive behavior to high environmental temperature.  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