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   413517篇
  免费   37851篇
  国内免费   1015篇
  452383篇
  2018年   14275篇
  2017年   12963篇
  2016年   11135篇
  2015年   5832篇
  2014年   6556篇
  2013年   9380篇
  2012年   13925篇
  2011年   22473篇
  2010年   18289篇
  2009年   13962篇
  2008年   18206篇
  2007年   20120篇
  2006年   9032篇
  2005年   8901篇
  2004年   9369篇
  2003年   9211篇
  2002年   8787篇
  2001年   14648篇
  2000年   14600篇
  1999年   11581篇
  1998年   4078篇
  1997年   4166篇
  1996年   3946篇
  1995年   3815篇
  1994年   3815篇
  1993年   3730篇
  1992年   9832篇
  1991年   9434篇
  1990年   9228篇
  1989年   8953篇
  1988年   8370篇
  1987年   8007篇
  1986年   7221篇
  1985年   7340篇
  1984年   6070篇
  1983年   5332篇
  1982年   4190篇
  1981年   3701篇
  1980年   3521篇
  1979年   6109篇
  1978年   4563篇
  1977年   4286篇
  1976年   3974篇
  1975年   4307篇
  1974年   4659篇
  1973年   4720篇
  1972年   4598篇
  1971年   4326篇
  1970年   3440篇
  1969年   3336篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
103.
104.
105.
Six hundred foramina transversaria (FT) of the axis vertebrae of 4 population groups were examined for the presence of erosion of the lateral articular mass. Of these, 127 (21%) and 72 (12%) presented with moderate and marked erosion, respectively. Evidence is presented incriminating the tortuosity of the vertebral artery as well as congenital factors in the etiology of the erosion of the FT. Attention is drawn to the possible correlation between angulation of the transverse process of the axis and erosion of the FT.  相似文献   
106.
Two internal herinias of the intestines were found in adult males. One was a large translucent avascular membranous sac contining the small intestine from the duodenojejunal flexure to a point 6 in. proximal to the ileocaecal junction. The other was a peritoneal sac enclosing the small intestine, appendix, caecum and 6 in. of the ascending colon. The mesenteric and colic vessels were normal. Both hernias conformed to PAPEZ's concept of the so-called paraduodenal hernia that the hernial sac is derived from the umbilical coelom. The authors suggest that most of the so-called paraduodenal hernias are derived from the embryonic umbilical peritoneal diverticulum rather than from the peritoneal recesses or mesentery of the colon.  相似文献   
107.
108.
The liver and kidney of rat underwent severe histopathological lesions when treated with a single bolus dose of carbendazim, a fungicide, particularly affecting the hepatocytes and the renal corpuscles, respectively. The effects appear to be manifestations of the microtubule-disrupting activity of carbendazim. Treatment of carbendazim-treated rats with the powder of tuberous root of Withania somnifera (Ashwagandha) for 48 days resulted in complete cure of these organs. The results indicate that Withania somnifera would be an effective curative for carbendazim-induced histopathological changes in the liver and kidney.  相似文献   
109.
Biomass of bottom and near-bottom fishes in the eastern Sea of Okhotsk has been calculated using results of a bottom trawl survey performed in the summer 2010 through depths of 200?C1000 m. Obtained data are compared with the results of investigations performed in compatible water areas during the same season of 1989 and 1997. Biomass variability patterns of major species have been revealed for the period of more than two recent decades. The bathymetric and spatial distribution of major fish species has been revealed using the modern information. Species are listed whose commercial catches could be enlarged.  相似文献   
110.
Food availability is important to the dynamics of animal social organizations or populations. However, the role of winter food availability in animal population dynamics is still controversial. We carried out an experimental study to test Lack’s hypothesis that reduced food in winter limits survival and spring numbers of breeding individuals of social groups, using the Mongolian gerbil (Meriones unguiculatus) as model species. We established 24 gerbil social groups in 24, 10 × 10 m, pens in September 2008. We provided wheat seeds as supplemental food in 12 enclosures from September 2008 to March 2009; the other 12 enclosures, not provided with supplemental food, served as controls. We live-trapped gerbils at a 2-week interval from September to April. Supplemental food during winter increased biweekly survival by 10% relative to that in control groups. Only four control social groups survived to the end of our study whereas all 12 food-supplemented social groups survived through our study period. Supplemental food also increased cumulative numbers of recruits and group sizes of gerbils. We conclude that winter food availability limits winter survival and spring social groups or population sizes of Mongolian gerbils.  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