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   76122篇
  免费   4336篇
  国内免费   35篇
林业   3303篇
农学   2454篇
基础科学   469篇
  9103篇
综合类   12510篇
农作物   2894篇
水产渔业   3736篇
畜牧兽医   39955篇
园艺   924篇
植物保护   5145篇
  2018年   1033篇
  2017年   1147篇
  2016年   1082篇
  2015年   899篇
  2014年   1122篇
  2013年   2864篇
  2012年   2069篇
  2011年   2442篇
  2010年   1622篇
  2009年   1645篇
  2008年   2448篇
  2007年   2364篇
  2006年   2170篇
  2005年   2086篇
  2004年   1975篇
  2003年   2122篇
  2002年   1933篇
  2001年   2302篇
  2000年   2269篇
  1999年   1805篇
  1998年   735篇
  1997年   789篇
  1996年   702篇
  1995年   891篇
  1994年   744篇
  1993年   744篇
  1992年   1528篇
  1991年   1674篇
  1990年   1631篇
  1989年   1631篇
  1988年   1513篇
  1987年   1478篇
  1986年   1565篇
  1985年   1480篇
  1984年   1289篇
  1983年   1091篇
  1982年   761篇
  1979年   1200篇
  1978年   898篇
  1977年   850篇
  1976年   805篇
  1975年   834篇
  1974年   1038篇
  1973年   1082篇
  1972年   1034篇
  1971年   971篇
  1970年   950篇
  1969年   909篇
  1968年   764篇
  1967年   856篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
Lethargic Crab Disease (LCD) caused extensive epizootic mortality of the mangrove land crab Ucides cordatus (Brachyura: Ocypodidae) along the Brazilian coast, mainly in the Northeastern region. The disease was named after the symptoms of slow movement of infected crabs. Causative agents were suspected to be two black yeast-like fungi of the family Herpotrichiellaceae (ascomycete order Chaetothyriales), judged by infected tissue biopsies from moribund U. cordatus. The aim of the present study is to prove that two species are involved in the disease: the recently described black yeast Exophiala cancerae, but also a less virulent, hitherto undescribed fonsecaea-like species, introduced here as the novel species Fonsecaea brasiliensis. Strains were identified by ITS rDNA sequencing, and species borderlines were established by multilocus sequencing and AFLP analysis. Fonsecaea brasiliensis proved to be closely related to the pathogenic species Cladophialophora devriesii which originally was isolated from a systemic infection in a human patient. The virulence of F. brasiliensis is lower than that of E. cancerae, as established by artificial inoculation of mangrove crabs.  相似文献   
993.
994.
Canine steroid-induced alkaline phosphatase (SIAP) has been measured quantitatively in an assay which depends on the finding that L-phenylalanine has a greater inhibitory effect on SIAP than on other plasma isoenzymes. The assay has advantages in precision, practicability and availability over other assays for SIAP. The steroid-induced isoenzyme was shown to contribute over 40 per cent of the total alkaline phosphatase (AP) activity in over 60 per cent of cases in which the level of AP was raised.  相似文献   
995.
Fourteen mature stallions were paired based on age and pretreatment spermatozoal output. One member of each pair was assigned to either 1) control (3 ml corn oil) or 2) treated (132,000 IU retinyl palmitate in 3 ml corn oil) experimental groups. Treatments were added to oat rations every other day. Seminal characteristics (gel free volume, gel volume, total seminal volume, percent progressively motile spermatozoa, number of spermatozoa per ml, percentage morphologically normal spermatozoa and spermatozoal membrane stability) and total scrotal width of each stallion were recorded before (February) and after three months of vitamin A supplementation (June). Plasma vitamin A was measured at 0,6,12,24, and 48 hours following the first and last treatments to document absorption. There were no treatment effects (p>.05) on seminal characteristics or scrotal width. Seasonal increases were recorded in gel-free volume, total seminal volume, percent spermatozoal motility, total spermatozoal output, percentage of morphologically normal spermatozoa, and total scrotal width. Plasma vitamin A was lower during the second collection period (June) than the first (February) in both treatment groups. Peak plasma vitamin A was observed 48 hours following ingestion of the first dose of the vitamin but at 12 hours following the last treatment.  相似文献   
996.
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