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   77772篇
  免费   3822篇
  国内免费   55篇
林业   3706篇
农学   2360篇
基础科学   409篇
  8197篇
综合类   15686篇
农作物   3176篇
水产渔业   3471篇
畜牧兽医   39044篇
园艺   932篇
植物保护   4668篇
  2018年   881篇
  2017年   944篇
  2016年   895篇
  2015年   801篇
  2014年   989篇
  2013年   2659篇
  2012年   1729篇
  2011年   2146篇
  2010年   1397篇
  2009年   1330篇
  2008年   2088篇
  2007年   2126篇
  2006年   1960篇
  2005年   1913篇
  2004年   1811篇
  2003年   1858篇
  2002年   1756篇
  2001年   2244篇
  2000年   2244篇
  1999年   1862篇
  1998年   707篇
  1997年   718篇
  1995年   830篇
  1993年   704篇
  1992年   1508篇
  1991年   1565篇
  1990年   1680篇
  1989年   1665篇
  1988年   1534篇
  1987年   1490篇
  1986年   1538篇
  1985年   1527篇
  1984年   1255篇
  1983年   1152篇
  1982年   780篇
  1981年   731篇
  1979年   1261篇
  1978年   987篇
  1977年   855篇
  1976年   809篇
  1975年   923篇
  1974年   1212篇
  1973年   1249篇
  1972年   1263篇
  1971年   1188篇
  1970年   1108篇
  1969年   1008篇
  1968年   865篇
  1967年   913篇
  1966年   841篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Cellular alterations in level of expression of mRNA encoding for prostaglandin endoperoxide synthase were quantified within ovarian tissues of sheep obtained before, during and after induction of the preovulatory surge of LH and ovulation with LHRH. This was accomplished by isotopic in situ hybridization using a selective cRNA probe to ovine prostaglandin endoperoxide synthase mRNA. A significant elevation in mRNA was detected within the theca interna of the preovulatory follicle at 8, 16 and 24 hr following administration of LHRH. Very close to the time of ovulation (ie., at 24 hr post-LHRH) a marked rise in mRNA was observed in association with epithelial cells covering the apical surface of the follicle. Ovarian cyclooxygenase metabolites of arachidonic acid produced during the ovulatory process in the ewe originate within the thecal layer and germinal epithelium of the follicle destined to ovulate.  相似文献   
62.
63.
64.
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   
65.
66.
67.
68.
Thyroidal 99mTcO4(pertechnetate) uptake percentages were determined in unanesthetized euthyroid (n = 13) and hyperthyroid (n = 18) cats. Maximal uptakes were observed 60 minutes after IV injection of the radionuclide and ranged from 0.3 to 3.9% of the dose in euthyroid cats (median 2.23%) and from 5.2% to 23.9% of the dose in hyperthyroid cats (median 14.8%) ( P < .05). There were no overlaps in pertechnetate uptake percentages during any of the intervals evaluated. It is concluded that the optimal time for visualization of the thyroid by 99mTcO4-scanning is 60 minutes after IV injection of the radionuclide. Calculation of the percentage uptake is of additional diagnostic value.  相似文献   
69.
70.
A 2-year-old female Japanese domestic cat weighing 3.6 kg was presented due to marked abdominal distention and was diagnosed as hepatic cyst. The bile acid concentration of the hepatic cyst was as low as the serum bile acid concentration. The membrane of the cysts was excised from the edge of the compressed hepatic tissue and no other surgical manipulation was performed. This surgical procedure is simple and quick compared to hepatic lobectomy, however, it is necessary to evaluate the fluid of the cyst before performing this procedure.  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