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   58785篇
  免费   3368篇
  国内免费   37篇
林业   3054篇
农学   2231篇
基础科学   352篇
  7448篇
综合类   6831篇
农作物   2096篇
水产渔业   3206篇
畜牧兽医   32940篇
园艺   727篇
植物保护   3305篇
  2019年   499篇
  2018年   960篇
  2017年   1050篇
  2016年   1017篇
  2015年   873篇
  2014年   1017篇
  2013年   2330篇
  2012年   1810篇
  2011年   2205篇
  2010年   1442篇
  2009年   1378篇
  2008年   2037篇
  2007年   2046篇
  2006年   1937篇
  2005年   1790篇
  2004年   1686篇
  2003年   1668篇
  2002年   1537篇
  2001年   2332篇
  2000年   2186篇
  1999年   1724篇
  1998年   684篇
  1997年   625篇
  1996年   601篇
  1995年   671篇
  1994年   573篇
  1993年   558篇
  1992年   1264篇
  1991年   1397篇
  1990年   1450篇
  1989年   1333篇
  1988年   1243篇
  1987年   1230篇
  1986年   1167篇
  1985年   1105篇
  1984年   919篇
  1983年   725篇
  1982年   525篇
  1979年   793篇
  1978年   616篇
  1977年   470篇
  1976年   524篇
  1975年   504篇
  1974年   627篇
  1973年   605篇
  1972年   635篇
  1971年   602篇
  1970年   597篇
  1969年   541篇
  1967年   497篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
241.
Cloning of the canine yes oncogene was attempted from a c library derived from a healthy canine spleen using a human c-yes-1 probe. The nucleotide and amino acid sequences revealed that the canine yes gene contained an open reading frame consisting of 539 amino acids. Its product had a molecular mass of 60,368 Daltons and showed 95·9 per cent and 90·4 per cent homology with human and chick p61c-yes, respectively. Moreover, the product had a myristylation signal, src homology region (SH) 3, SH2, and tyrosine kinase domains showing 98·8 per cent and 96·0 per cent homology with those of human beings and chickens, respectively. These findings indicate that the products of the canine yes gene may have non-receptor-type tyrosine kinase activity on the cell membrane, as is the case in human and chick p61c-yes  相似文献   
242.
Experiments conducted m a phytotron on three rice varieties of different salinity tolerance revealed an increase in the content of endogenous abscisic acid (ABA) with increasing NaCl salinity in IR20 (semi salt-tolerant), but in Pokkali (salt-tolerant) and IR28 (salt-sensitive) the increase in ABA content was marginal. Under sahnity stress, in general, 5 weekly sprayings of ABA (10-4 mol L-1) decreased Na and K concentrations in the shoot to the extent of 29.5 % and 3.3 %, respectively. However, ABA application significantly improved the K/Na ratio as well as the chlorophyll fluorescence decrease ratio (Rfd, indicator for potential photosynthetic activity), the number of green leaves per plant and the shoot dry weight. The response of IR20 and IR28 to ABA application was significantly better than that of Pokkali. Increasing salinity caused marked nutrient imbalances, decreased Rfd values and shoot dry weight. The results are discussed in relation to possible mechanism of salinity tolerance.  相似文献   
243.
244.
245.
246.
247.
Rickets was diagnosed in a group of 80 yearling Angus steers wintered for three months on a crop of swedes (Brassica napus) in the Kimbolton area. Growth rate was poor and several steers developed lameness during the final three weeks on the crop. Five animals were euthanased after developing bone fractures. Necropsy of two animals revealed soft ribs, enlarged costochondral junctions and irregularly thickened growth plates in long bones. Histologically there were islands of hypertrophic cartilage within metaphyses and disruption of metaphyseal trabeculae. Thickened, irregular, trabeculae were sometimes lined by wide osteoid seams. Phosphorus deficiency was considered to be the most likely aetiology of the osteodystrophy. The dry matter content of the swedes was only six percent, and in order to satisfy their phosphorus requirements each steer would have had to ingest approximately 330 kg of swedes per day. Rickets is an uncommon disease of grazing animals in New Zealand and to our knowledge this is the first report of its occurrence in cattle.  相似文献   
248.
Thromboembolic meningoencephalitis (TEME) caused by Huemophilus somnus infection was diagnosed for the first time in New Zealand in an eight month old bull calf. Clinical signs included pyrexia, excessive salivation, recumbency, opisthotonus and rigidity of the front legs. Multiple red, malacic foci (1-10 mm in diameter) were visible grossly on the surface of the cerebrum and cerebellum, and were scattered throughout the brain parenchyma. Histologically these lesions consisted of focal haemorrhage, necrosis and neutrophilic infiltration. Fibrin thrombi and colonies of gram negative bacteria were present in many small blood vessels within necrotic foci. An organism with the morphological and biochemical characteristics of Haemophilus somnus was cultured from the brain. Although TEME is an important disease of feedlot cattle in North America and Europe it is relatively uncommon in cattle grazing pasture and is therefore unlikely to become a major problem in New Zealand.  相似文献   
249.
A field strain of Cooperia oncophora resistant to oxfendazole was isolated from a commercial cattle rearing property in Waikato, New Zealand. Resistance to oxfendazole was assessed by means of a faecal egg count depression test and an in vitro egg hatch test. This is the first documented case of anthelmintic resistance in Cooperia spp. and the first report of anthelmintic resistance in cattle in New Zealand.  相似文献   
250.
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