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   132474篇
  免费   7270篇
  国内免费   93篇
林业   5383篇
农学   4270篇
基础科学   831篇
  17044篇
综合类   21483篇
农作物   5394篇
水产渔业   6688篇
畜牧兽医   67961篇
园艺   1801篇
植物保护   8982篇
  2020年   1177篇
  2019年   1375篇
  2018年   2032篇
  2017年   2332篇
  2016年   2095篇
  2015年   1742篇
  2014年   2224篇
  2013年   5291篇
  2012年   4114篇
  2011年   5093篇
  2010年   3245篇
  2009年   3389篇
  2008年   4971篇
  2007年   4668篇
  2006年   4354篇
  2005年   4089篇
  2004年   3851篇
  2003年   3975篇
  2002年   3544篇
  2001年   4150篇
  2000年   4253篇
  1999年   3373篇
  1998年   1474篇
  1997年   1387篇
  1996年   1288篇
  1995年   1529篇
  1994年   1358篇
  1993年   1231篇
  1992年   2584篇
  1991年   2700篇
  1990年   2591篇
  1989年   2611篇
  1988年   2368篇
  1987年   2348篇
  1986年   2427篇
  1985年   2340篇
  1984年   1881篇
  1983年   1677篇
  1982年   1149篇
  1979年   1748篇
  1978年   1397篇
  1977年   1151篇
  1976年   1212篇
  1975年   1292篇
  1974年   1500篇
  1973年   1514篇
  1972年   1405篇
  1971年   1304篇
  1970年   1251篇
  1969年   1283篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
1. Mule ducks were produced by naturally mating Muscovy drakes and Khaki Campbell ducks. 2. Semen was collected from 6-month-old mule drakes via an artificial vagina. The fluid was clear without any spermatozoa or spermatids. 3. Testes from 27-week-old mule drakes were smaller in size than those of Khaki Campbell drakes but heavier than Muscovy males of the same age. Histological sections of these testes revealed that spermatogenesis was not complete. 4. Testosterone concentration in the mule drakes was higher than in Muscovy males but similar to Khaki Campbell drakes. 5. Mule drakes have strong sexual drives as a result of high concentrations of testosterone, but, because spermatogenesis is incomplete, their semen had no sperm.  相似文献   
992.
993.
This article describes the management of a complicated distal epiphyseal Salter–Harris type I fracture of the left tibia in a yearling horse. Closed reduction and internal fixation was attempted in the first surgery using tension band wires. Due to fracture instability 2 weeks after surgery, a full-limb transfixation pin cast was applied to the tibia and maintained for 7 weeks to prevent further fracture displacement and to achieve axial alignment. The full-limb cast was maintained for a total of 12 weeks, including the time with the transfixation pin cast. Cast sores and tendon laxity resolved without further complications. Ten months after the first surgery, the fracture had radiographically healed, and the horse was sound at the walk and trot in a straight line.  相似文献   
994.
995.
996.
Optimal patient care cannot be realized without effectively managing risks related to healthcare‐associated infections (HAI). Among human hospital admissions in the United States in 2002, there were approximately 4.5 HAI per 100 admissions, with surgical site infections (SSI) accounting for an estimated 20%, or approximately 2 SSI per 100 procedures. When considering the occurrence of disease in a population, it is important to remember that disease does not occur randomly in populations. Therefore, when thinking about managing risks associated with the occurrence of SSI, consideration should be given to key factors in disease development (the agent, the host, and the environment), and a multifaceted approach to prevention efforts should be considered, including the identification of high‐risk populations, adherence to aseptic principles, judicious use of antimicrobial drugs, and surveillance targeting SSI to better inform infection control practices within a facility. Although not all HAI are preventable, it is important to focus efforts on the preventable fraction and to take all reasonable precautions to mitigate foreseeable risks.  相似文献   
997.
998.
999.
The detection of 4-hydroxycoumarin rodenticides in poisoned domestic animals requires a highly sensitive method as tissue and serum levels of anticoagulants may be very low owing to rapid elimination, metabolism or post-mortem degradation. Thin-layer chromatography (TLC) and reversed-phase high-performance liquid chromatography (RP-HPLC) with fluorescence detection were used to identify the anticoagulants in spiked tissues and in suspicious samples. The analysis of ten suspicious samples highlighted the limitations of both methods. Only the three samples of baits were found positive by TLC whereas one of the five anticoagulants was detected in eight samples by RP-HPLC with fluorescence detection. Therefore, RP-HPLC with fluorescence detection proved to be the more sensitive method for detecting low levels of 4-hydroxycoumarins in blood serum, liver and ingesta, whereas TLC is usually sufficient for analysing baits.Abbreviations RP-HPLC reversed-phase high-performance liquid chromatography - TLC thin-layer chromatography  相似文献   
1000.
The hydroxylation and acetylation of 0.5 mM sulphadimidine (SDD) was studied in primary cultures of hepatocytes from male and female rats, and from castrated male and sham operated male rats. In addition, SDD metabolism was investigated in hepatocytes from castrated male rats treated with testosterone, prior to liver cell isolation. In male rat hepatocytes a significantly higher hydroxylation activity was observed than in hepatocytes from female and castrated male rats. Acetylation activity was higher in females. Testosterone induced hydroxylation but did not affect acetylation. These results correlate well with data from previous in vivo studies, showing the relevance of this in vitro model.  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