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   198430篇
  免费   10780篇
  国内免费   124篇
林业   8393篇
农学   6150篇
基础科学   1360篇
  23536篇
综合类   34192篇
农作物   7661篇
水产渔业   9871篇
畜牧兽医   101702篇
园艺   2533篇
植物保护   13936篇
  2018年   2491篇
  2017年   2817篇
  2016年   2652篇
  2015年   2386篇
  2014年   2835篇
  2013年   7335篇
  2012年   5332篇
  2011年   6411篇
  2010年   4046篇
  2009年   4060篇
  2008年   6179篇
  2007年   5858篇
  2006年   5636篇
  2005年   5920篇
  2004年   5657篇
  2003年   5558篇
  2002年   5001篇
  2001年   6001篇
  2000年   5789篇
  1999年   4751篇
  1998年   1930篇
  1997年   1969篇
  1995年   2289篇
  1994年   2037篇
  1993年   1951篇
  1992年   4044篇
  1991年   4273篇
  1990年   4384篇
  1989年   4329篇
  1988年   4039篇
  1987年   4090篇
  1986年   4164篇
  1985年   4029篇
  1984年   3466篇
  1983年   3046篇
  1982年   2095篇
  1981年   1897篇
  1980年   1861篇
  1979年   3144篇
  1978年   2550篇
  1977年   2269篇
  1976年   2063篇
  1975年   2235篇
  1974年   2879篇
  1973年   2902篇
  1972年   2824篇
  1971年   2555篇
  1970年   2398篇
  1969年   2285篇
  1967年   2061篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
Abstract. The ability of two nitrogen cycle models, of contrasting complexity, to predict N mineralization from a range of grassland soils in the UK, was evaluated. These were NCYCLE, a simple mass balance model of the N cycle in UK grasslands, and CENTURY, a more complex model simulating long-term C, N, P & S dynamics in grassland ecosystems. The models were tested using field measurements of net N mineralization from a range of grassland soils (differing in soil type, history & management practice), obtained over a 2 year period using a soil core incubation technique. This method was considered to measure the total net release of mineral N from the soil organic matter over a specified time, including N which may have been recycled several times. NCYCLE consistently under-estimated mineralization rates at all sites. By contrast, there was some correlation between CENTURY predictions of net N mineralization and field measurements. This may have reflected the different abilities of the two models to simulate N recycling. Neither model, however, was able to predict adequately the effect of cultivation and reseeding on net N mineralization.  相似文献   
72.
Since the International Society of Veterinary Acupuncture (IVAS) was founded in 1974, acupuncture (AP) has received greater acceptance by veterinary professionals throughout the world. This article introduces some important animal diseases that respond well to AP therapy. These include resuscitation of small animals, treatment of anoestrous gilts and sows, bovine reproductive disease, canine vertebral problems and equine backpain, etc. Conventional medicine considers these to be difficult cases to treat. Veterinarians have become more aware of the benefits of AP especially for those diseases, thanks to the efforts of experienced practitioners and scientists, and the many published reports on veterinary AP that have introduced some good indications for AP therapy in veterinary practice. Possible mechanisms behind the effectiveness of AP are discussed. This article aims to introduce veterinarians to good indications for AP to initiate their interest in the practice of AP. Although this is a rapidly expanding field, a long march must begin with one step. We wish this article to be the shoes for such a march. For more information on veterinary AP, contact IVAS , P.O. Box 1478, Longmont, CO.. 80502, USA (http://www.ivas.org), or your national veterinary acupuncture society (http://www.komvet.at/ ivadkom/vapsocs.htm).  相似文献   
73.
74.
Two serological tests (indirect immunofluorescence and enzyme-linked immunosorbent assay) were developed for the detection of fetal antibody to Chlamydia psittaci. Fetal blood and thoracic fluid from 126 field cases of suspected ovine chlamydial abortion were examined using both tests. Placenta and fetal tissues (lung, liver, and kidney) from the same animals were also examined by the following conventional diagnostic methods: isolation in McCoy cells, detection of chlamydial lipopolysaccharide (LPS), modified Ziehl-Nielsen staining, and direct fluorescent antibody staining of chlamydia in frozen cryostat sections. Seventy cases were positive by fetal serology, and of these, 68 were also positive by isolation and/or LPS detection. The remaining 56 cases had negative fetal serology, and of these, 39 were positive by isolation and/or LPS detection. Results indicate that fetal serology, although less sensitive than either isolation in McCoy cells or detection of chlamydial LPS antigen, may be of particular use when placenta is not available.  相似文献   
75.
76.
77.
78.
79.
80.
The feet of three two-humped camels (Camelus bactrianus), one lama (Lama glama) and four alpacas (Lama pacos) from zoos and a circus in the Netherlands were examined for the mange-mite Choroptes bovis. Mites were found on two of the camels, the lama, and three of the alpacas. On one camel and one alpaca small mange lesions on the feet were present. This is the first report of Chorioptes bovis and chorioptic mange in the two-humped camel.  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