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   50912篇
  免费   2736篇
  国内免费   33篇
林业   2622篇
农学   1536篇
基础科学   217篇
  5743篇
综合类   10147篇
农作物   1949篇
水产渔业   2346篇
畜牧兽医   25432篇
园艺   559篇
植物保护   3130篇
  2019年   450篇
  2018年   734篇
  2017年   789篇
  2016年   687篇
  2015年   636篇
  2014年   767篇
  2013年   1758篇
  2012年   1485篇
  2011年   1665篇
  2010年   1074篇
  2009年   1161篇
  2008年   1632篇
  2007年   1645篇
  2006年   1536篇
  2005年   1462篇
  2004年   1377篇
  2003年   1345篇
  2002年   1281篇
  2001年   1529篇
  2000年   1484篇
  1999年   1215篇
  1998年   455篇
  1997年   474篇
  1996年   470篇
  1995年   523篇
  1994年   470篇
  1993年   481篇
  1992年   922篇
  1991年   916篇
  1990年   907篇
  1989年   916篇
  1988年   865篇
  1987年   899篇
  1986年   890篇
  1985年   894篇
  1984年   723篇
  1983年   652篇
  1979年   647篇
  1978年   540篇
  1977年   459篇
  1976年   462篇
  1975年   502篇
  1974年   691篇
  1973年   605篇
  1972年   675篇
  1971年   671篇
  1970年   598篇
  1969年   590篇
  1968年   450篇
  1967年   511篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
112.
113.
A 10-month-old male domestic short-haired cat was examined because of progressive lameness, a broad face with depressed nasal bridge, small ears, corneal clouding, and multiple bone dysplasia. The cat excreted excessive amounts of glycosaminoglycan (a component of connective tissue) in its urine and had evidence of lysosomal storage of glycosaminoglycans in fibroblasts and neurons. Activity of alpha-L-iduronidase, a lysosomal enzyme involved in glycosaminoglycan degradation, was deficient in cultured fibroblasts and leukocytes. The mucopolysaccharidosis was distinct from that seen in Siamese cats in terms of the pathologic changes and the specific enzyme deficiency.  相似文献   
114.
115.
116.
117.
The electrokinetic properties of feline blood lymphocytes isolated by centrifugation over Ficoll-Isopaque gradient were investigated. A biphasic electrophoretic mobility (EPM) distribution was regularly observed with a low-mobility (LM) population (mean EPM: 0.82) accounting for 32% of blood lymphocytes and a high-mobility (HM) population (mean EPM: 1.09) representing 68% of blood lymphocytes. Following fractionation on nylon-wool columns, lymphocytes with B-cell properties (64% sIg+; 9% guinea pig erythrocytes (GPE)-rosette+, PHA and Con A unresponsive) were enriched in the adherent fraction and belonged mainly (78%) to the LM population. In contrast, lymphocytes with T properties (5% sIg+, 42% GPE-rosette+, PHA and Con A responsive) were recovered in the effluent fraction and comprised 84% of HM elements.Thus, in cat blood, LM lymphocytes are likely to represent in majority B cells and HM lymphocytes T cells. This indicates that cell electrophoresis provides an interesting mean for differentiating B and T cells in the cat.  相似文献   
118.
Summary The activity of albendazole against gastrointestinal helminths in naturally infected calves in the Netherlands was tested. The calves were in their fist grazing season and kept in two groups of ten. One of these groups was grazed alternately with sheep. Five out of each group were drenched with albendazole (7.5 mg/kg) on the day they were housed (November 1). Before and 2, 14, and 28 days after treatment individual faecal samples were taken from all calves and larval cultures were made. Ten calves, six treated and four untreated, were killed for post mortem studies 14 days after treatment The remaining calves were slaughtered 14 days later. The drug was highly effective in reducing the egg output, measured as the number of larvae cultured per gram of faeces. Compared with the untreated calves, the reduction was more than 99% two days after treatment, 100% at 14 days, and 99% after 28 days. It was shown that egg output 28 days after treatment came from worms which had developed from arrested larvae of Ostertagia ostertagi that had survived treatment. Post mortem results showed an efficacy of 100% against adult O. ostertagi, of almost 100% against Trichostrongylus axei, and 100% against adult and larval Cooperia oncophora. Twenty-eight days after treatment, the reduction of arrested early fourth stages of O. ostertagi was 85% in comparison with the untreated calves. Apparently less effect was found against Trichuris ovis at the given dose rate.  相似文献   
119.
Ultrastructure of the cuticle and pseudobursa of adult males of four species of Trichinella has been studied by SEM. T. nativa differs markedly from T. spiralis, T. nelsoni and Trichinella sp. in the form of the pseudobursa. Trichinella sp. differs only slightly from T. spiralis and T. nelsoni. The ultrastructure of the cuticle revealed no characters suitable for the differentiation of the taxons under study.  相似文献   
120.
Astrophysics     
  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