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   208610篇
  免费   7604篇
  国内免费   110篇
林业   8141篇
农学   6803篇
基础科学   1502篇
  24919篇
综合类   34582篇
农作物   7732篇
水产渔业   10555篇
畜牧兽医   105357篇
园艺   2614篇
植物保护   14119篇
  2018年   2819篇
  2017年   3174篇
  2016年   2967篇
  2015年   2543篇
  2014年   3114篇
  2013年   8008篇
  2012年   5687篇
  2011年   7023篇
  2010年   4536篇
  2009年   4493篇
  2008年   6890篇
  2007年   6483篇
  2006年   6349篇
  2005年   5678篇
  2004年   5542篇
  2003年   5593篇
  2002年   5335篇
  2001年   6631篇
  2000年   6454篇
  1999年   5146篇
  1998年   2087篇
  1997年   2190篇
  1996年   1983篇
  1995年   2388篇
  1994年   2165篇
  1993年   2073篇
  1992年   4252篇
  1991年   4422篇
  1990年   4451篇
  1989年   4413篇
  1988年   4010篇
  1987年   4094篇
  1986年   4159篇
  1985年   4017篇
  1984年   3353篇
  1983年   2966篇
  1982年   2065篇
  1981年   1900篇
  1979年   3035篇
  1978年   2465篇
  1977年   2087篇
  1976年   1954篇
  1975年   2129篇
  1974年   2698篇
  1973年   2704篇
  1972年   2606篇
  1971年   2399篇
  1970年   2268篇
  1969年   2140篇
  1967年   1876篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Examinations were made of three sections of trachea obtained from eight dogs. The sections examined were at the regions of the second ring caudal to the larynx, the thoracic inlet, and the origin of the brachiocephalic trunk. Measurements were made of the lateral and ventrodorsal diameters, the lumen area of the trachea, the width and thickness of the tracheal cartilages, and the thickness of the trachealis muscle. Cell counts-per-square-micrometer of the cartilage and trachealis muscle were made. The results of these measurements were subjected to statistical analyses by means of one-way and two-way analyses of variance. The tracheal diameters, cartialge thickness, muscle thickness, and tracheal lumen area had significantly different measurements among the areas compared with both statistical methods. Ventrodorsal tracheal diameter and lumen area were not found to have significantly different measurements between the levels of the thoracic inlet and the brachiocephalic trunk. The cell counts did not have significantly different values among the areas considered when body weight was not a factor, but the values were significant when weight was a factor.  相似文献   
993.
SUMMARY: Modern treatment of hydatid disease of man depends on confirmation of active disease by use of modern serological tests, accurate identification of anatomical sites followed by complete removal of the parasite without spillage, and sterilisation of the remaining cavity. To avoid spillage use of a hydatid cone is recommended.  相似文献   
994.
SURGICAL repair of the patent ductus arteriosus (PDA) is one of the most common cardiovascular procedures performed in veterinary and human medicine.1–3 The techniques have been well documented and used successfully.2–5  相似文献   
995.
Five Boxer dogs with a new neurological disease are described. There is a progressive ataxia and weakness, initially in the hind-legs but later involving forelegs. The onset of signs is usually around 6 months of age although an older dog was affected. Proprioceptive function, muscle tone and tendon reflexes are diminished or absent while pedal reflexes and pain sensation are preserved. Muscle atrophy is minimal. The peripheral nerves are depleted in myelinated fibres. Nerve roots and, to a lesser extent, peripheral nerves show demyelination/remyelination changes and in the cervical ventral roots in particular, regenerative clusters are present. Forelimb muscles show evidence of re-innervation. In the CNS numerous swollen axons are present. The dorsolateral and ventral columns of the spinal cord are affected throughout their length. In the brain a number of nuclei and tracts, particularly in the lower brain stem, are affected and the superior olives are severely involved. The cerebral cortex and subcortical white matter appear normal. Various portions of the auditory and optic pathways are affected pathologically as are a number of cranial nerves. The axonal swellings contain a number of organelles including smooth endoplasmic reticulum, disordered neurofilaments, vesicles and mitochondria. The disease may be specific to Boxer dogs and may be inherited.  相似文献   
996.
Bile samples were collected from 477 Iowa dairy cows and were cultured for thermophilic campylobacters. The prevalence of thermophilic campylobacters in the bile was 15.5%. Campylobacter jejuni and C coli from dairy cattle, chickens, pigs, sheep, and human beings were serotyped to develop host-species profiles. Human and cattle serologic profiles were the most similar, and human and chicken profiles shared several similarities. Epidemiologic data from 168 human cases of campylobacteriosis indicated that 23% of the cases were associated with consumption of unpasteurized milk.  相似文献   
997.
998.
999.
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