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   155360篇
  免费   8902篇
  国内免费   413篇
林业   6369篇
农学   5545篇
基础科学   1296篇
  18783篇
综合类   25785篇
农作物   5935篇
水产渔业   7886篇
畜牧兽医   81480篇
园艺   1968篇
植物保护   9628篇
  2019年   1492篇
  2018年   2337篇
  2017年   2691篇
  2016年   2464篇
  2015年   2158篇
  2014年   2574篇
  2013年   6144篇
  2012年   4529篇
  2011年   5595篇
  2010年   3647篇
  2009年   3704篇
  2008年   5391篇
  2007年   5010篇
  2006年   4919篇
  2005年   4326篇
  2004年   4132篇
  2003年   4141篇
  2002年   3811篇
  2001年   5247篇
  2000年   5199篇
  1999年   4084篇
  1998年   1670篇
  1997年   1731篇
  1996年   1570篇
  1995年   1830篇
  1994年   1647篇
  1993年   1577篇
  1992年   3344篇
  1991年   3491篇
  1990年   3317篇
  1989年   3342篇
  1988年   3056篇
  1987年   3114篇
  1986年   3165篇
  1985年   3003篇
  1984年   2436篇
  1983年   2102篇
  1982年   1425篇
  1979年   2174篇
  1978年   1756篇
  1977年   1472篇
  1976年   1482篇
  1975年   1610篇
  1974年   1945篇
  1973年   1925篇
  1972年   1831篇
  1971年   1768篇
  1970年   1686篇
  1969年   1578篇
  1967年   1434篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
RNA was extracted from single or small groups of ovine ovarian follicles after treatment of ewes with FSH and/or LH. The content of mRNA for the alpha-inhibin and beta A-inhibin subunits was analyzed by hybridization with specific cDNA probes. All ewes were treated with progestin vaginal pessaries to suppress spontaneous preovulatory follicle maturation and ewes were given three intramuscular injections of gonadotropins at 8-hr intervals starting 24 hr prior to collection of ovaries. In experiment I, both Schering-FSH and NIDDK-oFSH-17 (oFSH) significantly increased alpha- and beta A-inhibin mRNA per ewe in 2-5 mm follicles and tended to increase alpha- and beta A-inhibin mRNA in large (greater than 5 mm) follicles. In experiment II, oFSH and NIDDK-oLH-25 (oLH) were administered in a 2X2 factorial arrangement. Separate administration of oFSH or oLH increased (P less than .05) the alpha-inhibin mRNA concentration in large follicles. alpha-inhibin mRNA concentration in 4-5 mm follicles was also increased by oFSH but was decreased by oLH. Concomitant treatment with oFSH and oLH did not change alpha-inhibin mRNA concentrations from those measured in oFSH treated ewes. In experiment II, beta A mRNA concentrations followed a pattern similar to that of alpha A mRNA, but the differences were not statistically significant. We conclude that, in the ewe, exogenous FSH increases the concentration of inhibin mRNA in the whole follicle. The ability of exogenous oLH to alter expression of the inhibin subunit genes may depend upon the stage of follicle maturation.  相似文献   
92.
The use of carbon dioxide and Nd:YAG lasers has expanded the capabilities of equine surgeons. These lasers are used to incise, vaporize, and coagulate tissue with minimal hemorrhage and reduced morbidity to the patient. In this article, practical fundamentals of laser surgery are briefly reviewed, and selected standing laser procedures of the head and neck are discussed.  相似文献   
93.
One-month-old Syrian hamsters of the APA and Std: golden strains were inoculated intraperitoneally with 10(5) PFU/head of the D variant of encephalomyocarditis (EMC) virus and examined virologically and pathologically up to 7 days after inoculation. APA hamsters developed apparent hyperglycemia due to pancreatic islet cell damage while Std:golden hamsters did not. Hamsters of both strains showed clear histopathologic changes in the testis with prominent viral replication as well as in the brain, heart and exocrine pancreas. The susceptibility to EMC virus-infection was higher in males than in females and in APA than in Std: golden hamsters.  相似文献   
94.
Samples of rapeseed from three Italian growing environments (Bologna, Perugia and Palermo) were analysed for glucose content and dry weight of 1000 seeds every three or four days starting from the end of flowering until complete ripening. In addition, the content of oil, soluble and total proteins, glucosinolates and myrosinase activity was determined in samples of mature seeds. The cultivars used were jet Neuf and Lingot (type 0) and Tandem, Jade and Santana (type 00). From the results it emerged that the point of intersection of the two branches of the linear regression plots for different glucose-consumption kinetics found during seed filling, in addition to being strongly affected by the climate of the test environment, is correlated with quantitative and qualitative production, independently of the genotype.  相似文献   
95.
96.
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   
97.
98.
99.
100.
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   
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