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   50907篇
  免费   2742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   25433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   1075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 15 毫秒
191.
192.
Elderly migration and development in small communities   总被引:1,自引:0,他引:1  
"This paper develops a conceptual model of the process of community change [in the United States] in response to elderly inmigration. Analysis of intra-regional variation in elderly migration patterns in Appalachia, and synthesis of an emergent literature on the benefits and costs of attracting elderly migrants, serve as a backdrop for case studies, based on field observations and interviews, of three contrasting Appalachian communities at different stages of development as retirement destinations."  相似文献   
193.
194.
Fan FR  Bard AJ 《Science (New York, N.Y.)》1995,267(5199):871-874
The electrochemical behavior of a single molecule can be observed by trapping a small volume of a dilute solution of the electroactive species between an ultramicroelectrode tip with a diameter of approximately 15 nanometers and a conductive substrate. A scanning electrochemical microscope was used to adjust the tip-substrate distance ( approximately 10 nanometers), and the oxidation of [(trimethylammonio)methyl] ferrocene (Cp(2)FeTMA(+)) to Cp(2)FeTMA(2+) was carried out. The response was stochastic, and anodic current peaks were observed as the molecule moved into and out of the electrode-substrate gap. Similar experiments were performed with a solution containing two redox species, ferrocene carboxylate (Cp(2)FeCOO(-)) and Os(bpy)(3)(2+) (bpy is 2,2'-bipyridyl).  相似文献   
195.
A study was undertaken to determine the efficacy of the novel avermectin, doramectin, against experimental larval and adult infections of three species of nematode parasite important to cattle production in New Zealand. Eighteen worm-free dairy bull beef calves were randomly allocated on live weight to three similar treatment groups. Each calf was given 30,000 Ostertagia ostertagi, 20,000 Cooperia spp. and 10,000 Trichostrongylus axei infective larvae as a single dose. One group was treated with doramectin 6 days after infection while the remaining groups received saline or doramectin 27 days after infection. Given as a single subcutaneous injection behind the ear, doramectin at 200 microg/kg removed 99.9-100% of adult and larval stages of O. ostertagi, Cooperia spp. and T. axei when compared to infections established in untreated controls (p<0.001). No adverse reactions were observed following treatment in the doramectin-treated animals. No injection site lesions were found by palpation following treatment or by injection site examination at necropsy.  相似文献   
196.
197.
198.
199.
1. Treatment of rapeseed meal with calcium hydroxide suspension decreased the sinapine content by up to 90%. Smaller decreases were obtained by autolysis, steaming and treatment with ammonia.

2. When this treated meal was fed to susceptible ("tainting") hens the concentration of trimethylamine in the eggs was decreased to much less than that required to cause taint.  相似文献   

200.
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   
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