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   84425篇
  免费   4780篇
  国内免费   198篇
林业   3770篇
农学   2307篇
基础科学   522篇
  10182篇
综合类   15701篇
农作物   3473篇
水产渔业   4142篇
畜牧兽医   43377篇
园艺   976篇
植物保护   4953篇
  2020年   761篇
  2019年   915篇
  2018年   1331篇
  2017年   1487篇
  2016年   1308篇
  2015年   1109篇
  2014年   1443篇
  2013年   3026篇
  2012年   2608篇
  2011年   3083篇
  2010年   1954篇
  2009年   2007篇
  2008年   2929篇
  2007年   2718篇
  2006年   2543篇
  2005年   2410篇
  2004年   2288篇
  2003年   2347篇
  2002年   2105篇
  2001年   2492篇
  2000年   2527篇
  1999年   1940篇
  1998年   752篇
  1997年   745篇
  1996年   732篇
  1995年   831篇
  1993年   754篇
  1992年   1564篇
  1991年   1765篇
  1990年   1649篇
  1989年   1665篇
  1988年   1481篇
  1987年   1539篇
  1986年   1602篇
  1985年   1554篇
  1984年   1194篇
  1983年   1063篇
  1979年   1155篇
  1978年   895篇
  1977年   757篇
  1975年   775篇
  1974年   1024篇
  1973年   1024篇
  1972年   1045篇
  1971年   995篇
  1970年   988篇
  1969年   906篇
  1968年   809篇
  1967年   800篇
  1966年   733篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
991.
A 2‐year‐old Lipizzaner colt presented for removal of a mass over the left eye. The colt had no blepharospasm or significant ocular discharge, but the cornea underlying the mass was mildly oedematous. The mass protruded from the conjunctiva at the dorsotemporal aspect of the globe and was covered in normal conjunctiva. It had a gross appearance similar to the cartilaginous flap of a nictitating membrane, but in an aberrant location. It was moveable to cover the dorsal aspect of the cornea when the globe was retropulsed. Excision of the mass under general anaesthesia was elected. Histopathology supported a diagnosis of an accessory nictitating membrane, consisting of a cartilaginous band surrounded by glandular epithelium. The colt recovered from surgery without complication and no problems were reported by the owner at 8.5 months post‐operatively. To the author's knowledge, there have not been previous reports of accessory or ectopic nictitating membranes in equine or other species.  相似文献   
992.
Veterinary medicine is marching forward with genomics grasped firmly in one fist. Genomics has been part of our veterinary tool bag for some time in various guises, but the breadth and depth of its ramifications can be daunting. This article is designed to provide toe‐holds for veterinarians to enjoy a better understanding of genomics – a truly fascinating area of science.  相似文献   
993.
New Rice for Africa (NERICA) is a general name for interspecific rice varieties derived from a cross between the high‐yielding Asian rice (Oryza sativa L.) between locally adapted African rice (Oryza glaberrima Steud.). Eight NERICAs were evaluated for cold tolerance (CT) at the reproductive stage and compared with their O. sativa parents and three Japanese standard rice varieties over 3 years. Cold tolerance was evaluated based on the filled grain ratio (FGR) after cold water irrigation. The FGR was greatly reduced by cold water irrigation. NERICA 1, 2 and 7 had higher FGR (51.9–57.9 %), while NERICA 6, 15 and 16 had lower FGR (6.2–14.5 %). NERICA 1, 2 and 7 were less affected by cold stress, with a 31 % mean reduction in FGR, while NERICA 6, 15 and 16 were greatly affected, with their FGRs being reduced by more than 80 %. NERICA 3 and 4 were moderately affected by cold stress, with about 45 % reduction rate in FGR. FGR significantly influenced the grain weights of the varieties with strong positive correlations (r = 0.83–0.91; P < 0.001), and thus, similar trends in grain weights were observed. Grain weights were reduced by 61.7–96.4 % under cold stress. NERICA 1, 2 and 7 showed significantly better performance than NERICA 3 and 4, while NERICA 6, 15 and 16 performed poorly under cold water irrigation. The Japanese varieties Koshihikari (very tolerant) and Ozora (moderately tolerant) were more affected by cold water irrigation than NERICA 1, 2 and 7. On the basis of the mean reduction rate (%) in FGR under cold stress, the varieties were classified as follows: NERICA 1, 2 and 7 as tolerant; NERICA 3 and 4 as moderately tolerant; and NERICA 6, 15 and 16 as susceptible to cold stress. However, NERICA 7 grain yields were lower under cold stress due to both greatly reduced number of panicles per plant and number of spikelets per panicle. Therefore, NERICA 1 and 2 are suitable candidates for production in the highland regions of East Africa and should be promoted for production.  相似文献   
994.
995.
We studied the black carbon (BC) content of ca. 405 samples from French topsoil and artificial soil and carbonate mixtures. Our protocol involved three main steps: (i) decarbonation by HCl, (ii) elimination of non‐pyrogenic organic carbon in a furnace at 375 °C, and (iii) quantification of residual carbon by CHN analysis. BC content increased for calcareous soils according to their carbonates content. Subsequent analyses confirmed the existence of a methodological artefact for BC determination only in calcareous soils. Decarbonation changes the thermal properties of organic matter, creating more recalcitrant carbon than in the initial sample. Higher CaCO3 and organic carbon content results in a more pronounced artefact. The reversal of the first two steps of the chemo‐thermal oxidation method (i.e. thermal oxidation before soil decarbonation) eliminates this artefact. Overall, our results suggest that BC content may have been overestimated in a large number of studies on calcareous soils.  相似文献   
996.
997.
In Bolivia, one of the world’s most important centres of plant domestication, there is growing awareness of the value of native Andean crops, both for domestic consumption and for market sale – notably the virtually boom‐like consumer demand for quinoa around the world. The southern altiplano of Bolivia, south of Oruro, relies almost purely on the production of quinoa and breeding of llamas, which have also been selected as the two commodities of priority to the government to increase the income of the country. Presently, however, quinoa is facing increasing problems in production, owing to its increasing export market and price. The flat areas around the salt desert of the southern altiplano, previously characterized by natural vegetation fed by the llamas, are being increasingly sown with quinoa, hence transformed into deserts, because intensive cultivation methods make the soil loose its fertility. Possible solutions to these problems will require extensive efforts in the south, in addition to various strategies, which also include other parts of the Bolivian altiplano and a strengthened focus on other Andean crops.  相似文献   
998.
A 12‐year‐old spayed English pointer dog developed multiple skin lesions including pigmented viral plaques, basal cell carcinomas, squamous cell carcinomas and trichoblastomas. Canine papillomavirus type 3 was detected in multiple lesions suggesting common aetiology.

  相似文献   

999.
1000.
The materials for studying the development of muscle tissue and particular skeletal muscles at the anatomical regions of the body in the red steppe young stock are presented in comparative aspects. Agerelated changes in the muscle tissue growth rates in different periods of rearing and fattening the animals were caused by both the unequal intensities of its development in different body parts and the increasing process of lipogenesis associated with aging.  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