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   102406篇
  免费   5665篇
  国内免费   68篇
林业   3929篇
农学   3280篇
基础科学   537篇
  11779篇
综合类   17268篇
农作物   3495篇
水产渔业   5146篇
畜牧兽医   55225篇
园艺   1222篇
植物保护   6258篇
  2018年   1525篇
  2017年   1577篇
  2016年   1442篇
  2015年   1281篇
  2014年   1465篇
  2013年   4048篇
  2012年   2785篇
  2011年   3403篇
  2010年   2245篇
  2009年   2187篇
  2008年   3277篇
  2007年   3184篇
  2006年   3033篇
  2005年   2702篇
  2004年   2685篇
  2003年   2708篇
  2002年   2486篇
  2001年   3456篇
  2000年   3490篇
  1999年   2759篇
  1998年   1131篇
  1997年   1039篇
  1996年   948篇
  1995年   1159篇
  1994年   1045篇
  1993年   964篇
  1992年   2230篇
  1991年   2398篇
  1990年   2274篇
  1989年   2195篇
  1988年   2069篇
  1987年   2074篇
  1986年   2066篇
  1985年   2006篇
  1984年   1668篇
  1983年   1481篇
  1982年   957篇
  1979年   1447篇
  1978年   1154篇
  1977年   1079篇
  1976年   1052篇
  1975年   1115篇
  1974年   1329篇
  1973年   1276篇
  1972年   1276篇
  1971年   1125篇
  1970年   1147篇
  1969年   1134篇
  1968年   965篇
  1967年   979篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
The validation of a liquid chromatographic procedure suitable for the determination of calcitriol and alfacalcidol in their respective formulations labeled to contain at least 0.25 micrograms drug per unit is described. The capsule content is diluted and chromatographed in 15-20 min on silica columns (5 micron) with a mobile phase of hexane-tetrahydrofuran-methylene dichloride-isopropanol (72 + 12 + 12 + 4, v/v) with detection at 254 nm. The calibration curve is linear. Recoveries of "spikes" averaged 101% with a standard deviation of 2%. Precision was better than 1.5%.  相似文献   
152.
153.
On a property in the Nelson District, blood and urine samples were taken from red deer (Cervus elaphus) from which low (<1:100) antibody titres to serovar copenhageni and suspected leptospiral abortions had previously been reported. A total of 27 hinds were sampled. Microscopic agglutination test (MAT) titres in sera ranging from 1:32 to 1:128 were found in six animals. Thirteen leptospiral isolations were made from nine of the 27 urine samples. Four of these were typed as copenhageni and nine as hardjo. Two cultures were prepared from each urine sample and hardjo and copenhageni were both isolated from single urine samples from two animals. None of the 27 deer had serum MAT titres at 1:32 or above to copenhageni.  相似文献   
154.
155.
156.
157.
158.
159.
Practitioners commonly submit samples from dogs for partial thromboplastin time and prothrombin time determinations. Controversy exists as to the necessity for rapid separation of plasma and cells, and submission of the plasma on ice (or frozen). The purpose of this study was to address three questions. First, is it better to submit plasma or is whole blood satisfactory? Second, is it necessary to refrigerate the sample or is maintenance at room temperature (20° C) adequate? Third, does the sample have to arrive at the laboratory within a few hours of collection or can reliable partial thromboplastin time/prothrombin time determinations be made on samples up to 48 hours old?It has been shown by this study that reliable partial thromboplastin time and prothrombin time determinations can be carried out on canine plasma for up to 48 hours after collection regardless of whether or not the plasma is separated immediately; however the samples must be kept at 4°C. If the samples are maintained at room temperature, reliable prothrombin time determinations can be obtained for up to six hours after collection regardless of whether or not the plasma is separated immediately. Reliable partial thromboplastin time determinations can be made on plasma stored at 20°C for up to 24 hours after collection and possibly longer (up to 48 hours) if the plasma has been separated immediately.  相似文献   
160.
Caprine β-mannosidosis, a fatal inherited deficiency of the lysosomal enzyme β-mannosidase, was diagnosed in neonatal female Nubian crossbred twin kids from a small herd near Guelph, Ontario. The kids had been tetraplegic since birth, with whole body tremors, abnormal nystagmus and an intention tremor of the head.  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