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   185797篇
  免费   9858篇
  国内免费   182篇
林业   7760篇
农学   5637篇
基础科学   1153篇
  22711篇
综合类   33130篇
农作物   7503篇
水产渔业   8937篇
畜牧兽医   94736篇
园艺   2425篇
植物保护   11845篇
  2019年   1821篇
  2018年   2612篇
  2017年   2972篇
  2016年   2693篇
  2015年   2261篇
  2014年   2923篇
  2013年   6998篇
  2012年   5321篇
  2011年   6619篇
  2010年   4248篇
  2009年   4395篇
  2008年   6496篇
  2007年   6092篇
  2006年   5746篇
  2005年   5396篇
  2004年   5141篇
  2003年   5311篇
  2002年   4810篇
  2001年   5622篇
  2000年   5753篇
  1999年   4508篇
  1998年   1921篇
  1997年   1898篇
  1996年   1738篇
  1995年   2061篇
  1994年   1810篇
  1993年   1775篇
  1992年   3612篇
  1991年   3879篇
  1990年   3697篇
  1989年   3724篇
  1988年   3355篇
  1987年   3406篇
  1986年   3543篇
  1985年   3436篇
  1984年   2739篇
  1983年   2443篇
  1982年   1668篇
  1979年   2565篇
  1978年   2069篇
  1977年   1740篇
  1976年   1694篇
  1975年   1854篇
  1974年   2271篇
  1973年   2254篇
  1972年   2200篇
  1971年   2060篇
  1970年   1998篇
  1969年   1990篇
  1967年   1755篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Two dogs developed metacarpal pad ulceration subsequent to a motor vehicle accident. Evidence of ulnar nerve damage was found in both dogs. The ulcers were treated successfully by transferring neurovascular island flap grafts from the dorsum of the foot.  相似文献   
992.
993.
Phenol-water extraction of Megasphaera elsdenii, a predominant gram-negative coccus in rumens of cattle fed high-grain diets, yielded material that exhibited typical characteristics of endotoxin. The extract was lethal to mice and to chicken embryos, caused biphasic fever in rabbits, leukopenia in mice, and local and generalized Shwartzman reactions; and induced tolerance to the lethal effect of the endotoxin in mice. The material contained carbohydrate, protein, lipid, phosphorus, and 2-keto-3-deoxyoctonate, but no nucleic acid. The beta-hydroxymyristic acid was absent. Results imply that M elsdenii endotoxin has many biological and chemical characteristics common to enterobacterial endotoxin. However, the median lethal doses in mice and in chicken embryos, and minimal dose required to elicit a local Shwartzman reaction, indicate that M elsdenii endotoxin's potency is low, which may explain why the large gram-negative bacterial population in the rumen of cattle is generally innocuous.  相似文献   
994.
Fifty-seven cycling buffalo cows of the river type were treated with two doses of 0.5 mg cloprostenol intramuscularly given 11 days apart. Each animal was inseminated twice at 72 and 96 hours after the second injection of cloprostenol. The first service conception rate diagnosed by rectal palpation at 90 days was 38.6 per cent. At the time of insemination the cervix was easily penetrable on both days in only 39 (68.4 per cent) of the animals. They were inseminated at or beyond the internal cervical os, while the others were inseminated in the cervical canal. There was a marked difference in conception rate between those receiving deep inseminations (48.7 per cent) and the others (16.7 per cent). In relation to the interval from calving to insemination the conception rates for those which had calved 60 to 90, 90 to 120 and 120 to 150 days earlier were 16.6, 36.4 and 55.5 per cent respectively. The use of cloprostenol treatment and fixed-time insemination is a useful method of overcoming the problem of oestrus detection in buffaloes. Acceptable levels of fertility can be obtained in those animals which have a sufficiently relaxed cervix to permit semen deposition at the internal os, provided the interval from calving to insemination is more than 90 days.  相似文献   
995.
The peripheral plasma progesterone levels in bitches with spontaneously developed pyometra did not differ significantly from those in normally cycling or pregnant bitches. The macroscopic ovarian morphology gave no indication of an increased corpus luteum activity. Ovarian follicular cysts were found in 4 out of 31 cases. There was no detectable difference of results between 14 bitches that had received hormonal medication 10 years to 1 week previous to the pyometra diagnosis, and the other patients.  相似文献   
996.
Antidiuretic hormone (ADH) administration to a polyuric Miniature Poodle did not alter diuresis. Plasma ADH concentrations were high, and urine osmolality remained low during water deprivation. From these findings, it was concluded that the polyuria was of renal origin. In addition, the glomerular filtration rate was found to be high. Electron microscopic examination of the renal medulla revealed vacuoles containing myelinic figures and fingerprint structures in the cells of the Henle loops, blood vessels, and interstitium, similar to those in lysosomal lipid storage disease. Their absence in collecting duct epithelium indicated that the defect in concentrating ability was due to a disturbance of the counter-current multiplier mechanism rather than to a defect in ADH receptors.  相似文献   
997.
998.
Acute viral hepatitis was diagnosed in five California sea lions (Zalophus californianus) stranded along the Los Angeles coast. Light microscopy revealed large nuclear inclusion bodies in hepatocytes. Electron microscopy provided evidence that these inclusion bodies were composed of adenovirus-like virions. Attempts to grow the virus in cell culture systems were unsuccessful.  相似文献   
999.
1. The ladykiller (lk) gene has been located on the sex chromosome of the fowl. It is 4.2 map units distant from the feathering rate locus (k) and 11.2 map units distant from the dwarf (dw) locus. 2. Most of the embryonic mortalities associated with this gene occurred between 3 and 4 d of incubation.  相似文献   
1000.
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