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   2896篇
  免费   157篇
林业   243篇
农学   333篇
基础科学   33篇
  634篇
综合类   142篇
农作物   248篇
水产渔业   353篇
畜牧兽医   757篇
园艺   82篇
植物保护   228篇
  2023年   40篇
  2022年   71篇
  2021年   83篇
  2020年   110篇
  2019年   134篇
  2018年   168篇
  2017年   168篇
  2016年   138篇
  2015年   92篇
  2014年   141篇
  2013年   264篇
  2012年   201篇
  2011年   182篇
  2010年   157篇
  2009年   109篇
  2008年   133篇
  2007年   113篇
  2006年   93篇
  2005年   68篇
  2004年   58篇
  2003年   45篇
  2002年   37篇
  2001年   53篇
  2000年   39篇
  1999年   32篇
  1998年   21篇
  1997年   18篇
  1996年   11篇
  1995年   7篇
  1994年   10篇
  1993年   7篇
  1992年   12篇
  1991年   15篇
  1990年   13篇
  1989年   11篇
  1988年   12篇
  1987年   17篇
  1986年   9篇
  1985年   10篇
  1984年   8篇
  1983年   11篇
  1981年   10篇
  1979年   16篇
  1974年   8篇
  1973年   8篇
  1971年   11篇
  1970年   8篇
  1968年   11篇
  1967年   8篇
  1966年   7篇
排序方式: 共有3053条查询结果,搜索用时 250 毫秒
1.
2.
Two outbreaks of the egg drop syndrome were observed in quail flocks maintained on a farm together with chickens. The decrease in egg production ranged from 10.6 per cent to 50.6 per cent, and the number of soft-shelled eggs increased with the decline in egg production. In both the outbreaks haemagglutination inhibiting antibodies to EDS-76 virus were detected. Fluorescent viral antigen specific to EDS-76 virus was also detected in the lining epithelial and glandular cells of the uterus.  相似文献   
3.
The relative amounts of primary and secondary sulfates in atmospheric aerosols and precipitation can be estimated from measurements of the stable oxygen isotope ratios. The oxygen-18 content of sulfates formed in power plant stack gases before emission into the atmosphere is significantly higher than that of sulfates formed from sulfur dioxide after emission. Results show that 20 to 30 percent of the sulfates in rain and snow at Argonne, Illinois, are of primary origin.  相似文献   
4.
The independent modes of action of diuron and atrazine on the photochemical activities of chloroplasts (In vivo and in vitro) from the leaves of crop plants Pisum sativum and Pennisetum typhoides and the weeds Amaranthus viridis and Cyperus rotundus were investigated. Hill reaction activity (DCPIP photoreduction) of in vivo chloroplasts (chloroplasts isolated from herbicide-sprayed plants) was unaffected by treatment at sublethal or intermediate levels of diuron or atrazine while that of in vitro chloroplasts (chloroplasts incubated in the required herbicidal concentration) was severely inhibited. The ferricyanide catalyzed noncyclic photophosphorylation was markedly reduced in both the in vivo and in vitro chloroplast systems. N-Methyl phenozonium sulfate (PMS)-mediated cyclic photophosphorylation was inhibited in the in vivo system while a pronounced enhancement of activity was noticed in the in vitro chloroplasts. The rate of NADP+ photoreduction was severely inhibited in the in vitro chloroplasts. The unaffected in the in vivo system. The herbicidal effects on the photoreactions of isolated chloroplasts were compared with chloroplasts isolated from herbicide-sprayed plants.  相似文献   
5.
6.
Trace minerals feeding had significant effects on sperm production and fertility with better absorption and proper utilization within the body for optimum reproductive function. Several studies have shown that more influenced trace elements in the diets of animals are copper (Cu) and zinc (Zn). Bucks showing deficiency of this mineral might affect the quality of semen production which in turn would affect the fertility. This experiment was thus designed to test the effects of organic Cu and Zn supplementation on antioxidants enzyme activities and sperm functional attributes in fresh semen of bucks. Forty bucks (n = 40, Aged 5 months) were assigned to ten groups of four animals in each group, supplemented (for a period of 8 months) with different levels of organic Zn: 20 mg (T2), 40 mg (T3) and 60 mg (T4), organic Cu: 12.5 mg (T5), 25 mg (T6), 37.5 mg (T7) and combined organic Zn and Cu: 20 + 12.5 mg (T8), 40 + 25 mg (T9), 60 + 37.5 mg (T10), respectively, per kg dry matter and no additional mineral diet (control; T1). One hundred and sixty semen samples were collected through electro‐ejaculator and analysed for sperm quantity, quality, acrosome intactness and plasma membrane integrity and correlated with the catalase, superoxide dismutase, glutathione peroxidase and glutathione reductase enzyme activities in seminal plasma. The results indicated organic Cu and zinc supplemented bucks produced more sperm cells, had higher sperm concentrations, maintained higher (< .01) sperm livability, plasma membrane and acrosome integrities, more motility and velocity. The increased antioxidant enzyme activities, reduced oxidative stress and lowered lipid peroxidation were positively correlated (< .05) with the sperm functional attributes. In conclusion, organic Cu and Zn supplement to male goats showed protective roles against oxidative damage and maintained better fresh semen characteristics.  相似文献   
7.
8.
9.
10.
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