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   38497篇
  免费   2288篇
  国内免费   285篇
林业   1593篇
农学   1428篇
基础科学   328篇
  5543篇
综合类   5663篇
农作物   1502篇
水产渔业   1823篇
畜牧兽医   20035篇
园艺   465篇
植物保护   2690篇
  2021年   368篇
  2020年   436篇
  2019年   482篇
  2018年   795篇
  2017年   839篇
  2016年   753篇
  2015年   638篇
  2014年   790篇
  2013年   1844篇
  2012年   1324篇
  2011年   1552篇
  2010年   1067篇
  2009年   1094篇
  2008年   1502篇
  2007年   1343篇
  2006年   1275篇
  2005年   1095篇
  2004年   1045篇
  2003年   1034篇
  2002年   925篇
  2001年   1249篇
  2000年   1240篇
  1999年   935篇
  1998年   390篇
  1997年   421篇
  1996年   346篇
  1995年   392篇
  1994年   342篇
  1992年   663篇
  1991年   789篇
  1990年   691篇
  1989年   727篇
  1988年   666篇
  1987年   627篇
  1986年   670篇
  1985年   594篇
  1984年   462篇
  1983年   413篇
  1979年   553篇
  1978年   431篇
  1977年   359篇
  1976年   367篇
  1975年   399篇
  1974年   459篇
  1973年   474篇
  1972年   447篇
  1970年   366篇
  1969年   400篇
  1968年   357篇
  1967年   359篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
The activity of rat liver glutathione-insulin transhydrogenase (GIT) was measured by HPLC. The degradation of fluorescein isothiocyanate-I (FITC-I)-labeled insulin is separated into several peaks, which are bound different amount of FITC-I. We selected mono-fluorescein-thiocarbamylated insulin to estimate the decrease of insulin content and it became possible to assay GIT activity. This novel method was time-saving and simple, and this system could utilize instead of previous method.  相似文献   
22.
The effects of lipopolysaccharide ( Escherichia coli , O55:B5), administered 18 h after ovulation in the second oestrus after weaning on the hormonal profiles in 14 Swedish cross-bred (Landrace × Yorkshire) multiparous sows were studied. The endotoxin group (E-group) sows were administered with 300 ng/kg of lipopolysaccharide (LPS) whereas the control group (C-group) sows were administered 5 ml of saline intravenously via an indwelling jugular cannula. Blood samples for hormonal analyses were collected from all sows until slaughter. In the E-group, progesterone, cortisol and prostaglandin F metabolite levels increased significantly (p < 0.05) following LPS compared with the C-group. It can be concluded from this study that apart from elevating cortisol and prostaglandin F metabolite, LPS also elevates progesterone levels.  相似文献   
23.
24.
25.
2 groups of 20 cocks each were selected at random from non-dwarf White Leghorn (28 weeks post-hatch) and dwarf Krishna-J (38 weeks post-hatch) genotypes. The treated groups comprised 10 White Leghorn and 10 Krishna-J cocks. The remaining birds served as controls. 8 weeks prior to furazolidone treatment, semen was collected from both control groups at regular 4-day intervals, for 4 weeks. Cocks of the treated groups of both genotypes were administered furazolidone (0.14 g/bird/day) for 7 consecutive days. Semen was collected from all cocks at regular 4-day intervals for 4 weeks. Semen from the cocks of the same group was pooled. The pooled ejaculate volume and sperm density did not differ significantly in the 2 genotypes. The semen output as well as sperm density increased along with progressive attainment of sexual maturity. Furazolidone treatment caused significant reduction in semen volume as well as sperm concentration in either genotype.  相似文献   
26.
Abstract. Experiments were started in 1967 to investigate the effects of soil mixing on fen peat soil. Peaty topsoil was mixed with mineral subsoil to a maximum depth of 80 cm at two sites, one with a clay subsoil, the other sand. Mixing was done on a commercial scale with a range of implements. After initial increases, yields of arable crops on both mixed soils were subsequently similar to those on unmixed soil. Residual herbicide activity was enhanced on mixed soils, and evidence of peat conservation was obtained at one site. The practice has not been taken up commercially because of the high capital cost of mixing and lack of serious problems which had been predicted following peat wastage.  相似文献   
27.
28.
29.
30.
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