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   72620篇
  免费   3480篇
  国内免费   204篇
林业   3935篇
农学   2281篇
基础科学   998篇
  9068篇
综合类   10273篇
农作物   2439篇
水产渔业   4637篇
畜牧兽医   36910篇
园艺   2047篇
植物保护   3716篇
  2023年   825篇
  2022年   745篇
  2021年   1141篇
  2020年   1403篇
  2019年   788篇
  2018年   1970篇
  2017年   2294篇
  2016年   1880篇
  2015年   1466篇
  2014年   1976篇
  2013年   2865篇
  2012年   3630篇
  2011年   4729篇
  2010年   2738篇
  2009年   2561篇
  2008年   4363篇
  2007年   4266篇
  2006年   4398篇
  2005年   4118篇
  2004年   4003篇
  2003年   3810篇
  2002年   3844篇
  2001年   3487篇
  2000年   3404篇
  1999年   2732篇
  1998年   903篇
  1997年   541篇
  1996年   508篇
  1995年   405篇
  1994年   426篇
  1993年   372篇
  1992年   277篇
  1991年   318篇
  1990年   251篇
  1989年   303篇
  1988年   215篇
  1987年   191篇
  1986年   153篇
  1985年   233篇
  1984年   248篇
  1983年   152篇
  1982年   160篇
  1981年   115篇
  1980年   130篇
  1979年   128篇
  1978年   130篇
  1977年   115篇
  1976年   95篇
  1975年   89篇
  1973年   127篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
畜禽产品的生产过程需要消耗大量水资源,对畜禽产品进行水足迹评价能够清楚地认识其对水资源的消耗情况。目前,人们对畜禽产品的需求日益增长,水资源消耗也在持续升高,因此研究如何缓解畜禽产品生产带来的水资源压力,已成为人们必须要面对的问题。评价畜禽产品的用水量和对不同生产阶段的用水分析,将有助于生产者和消费者确定用水量最大的过程,并针对性地实施提高用水效率的战略。本文介绍了国内外畜禽产品水足迹研究现状,对比分析了不同畜禽产品水足迹评价方法,展望了畜禽产品水足迹的发展,最终提出以下降低畜禽产品水足迹的主要措施:1)减少饲料生产的水足迹;2)提高饲料转化率;3)水资源管理和提高畜禽动物生产性能;4)改变人们的消费习惯。  相似文献   
53.
54.
55.
This study was aimed to evaluate the effect of 0.0015% preservative-free tafluprost (Zioptan®) and 0.005% preservative containing latanoprost ophthalmic solutions (Lataprost®) on intraocular pressure (IOP) in healthy male guinea pigs (Cavia porcellus). A total of 16 male guinea pigs were randomly assigned to receive one drop of tafluprost or one drop of latanoprost in the right eye. The contralateral eye served as control. IOP was measured using a rebound tonometer at time 0(baseline), after 30 minutes and every 60 minutes for the next three hours and then every three hours for the next 21 hours. Administration of tafluprost and latanoprost was not associated with changes in IOP in the treated eyes. The maximum IOP-lowering effect of the ophthalmic solutions was observed 30 minutes post-instillation in the treated eyes (-1.25 ± 1.50 mmHg, P-value = 0.194 in group A and -1.50 ± 1.29 mmHg, P-value = 0.103 in group B) and returned to normal after 9 and 12 hours in group A and B, respectively. There was no significant difference between the IOP measurements of the right and left eyes in neither groups during the study (repeated measure test and Generalized Linear Mixed Model). The administration of one drop of tafluprost and latanoprost had no significant effect on the IOP of healthy guinea pigs. Further studies are needed in guinea pigs affected by glaucoma to explore the effectiveness of these drugs.  相似文献   
56.
57.
Rather than a human-centric, the basic strategy of achieving Sustainable Development Goals must be focused on restoring and sustaining planetary processes. The urgency of meeting the demands of the humanity must be reconciled with the necessity of enhancing the environment. Increasing and restoring soil organic matter content of the degraded and depleted soils is critical to strengthening planetary processes.  相似文献   
58.
Melatonin (MT) influences lipid metabolism in animals; however, the mechanistic effect of melatonin on liver fat and abdominal adipose deposition requires further clarity. In order to study the effects of melatonin on lipid metabolism, and hepatic fat and abdominal adipose deposition in animals, twenty Sprague–Dawley (SD) rats of 6 weeks of age with similar bodyweight were randomly divided into two groups: control (CTL) and MT-treated (10 mg/kg/day). During a 60-day experiment, food intake and bodyweight were measured daily and weekly respectively. At the end of treatment, blood samples were collected to collect plasma to quantify hormones and metabolic indicators of lipid metabolism. In addition, organ and abdominal adipose depots including liver, and omental, perirenal, and epididymal fat were weighed. Liver tissue was sampled for sectioning, long-chain fatty acid (LCFA) quantification, and gene chip and Real-time quantitative PCR (qPCR) analyses. The results showed that liver weight and index (ratio of liver weight to body weight) in MT group reduced by 20.69% and 9.63% respectively; omentum weight and index reduced by 59.88% and 54.93% respectively, and epididymal fat weight reduced by 45.34% (p = 0.049), relative to CTL. Plasma lipid indices, triglyceride (TG), high-density lipoprotein (HDL), low-density lipoprotein (LDL) and total cholesterol (TC) with MT treatment decreased significantly compared with the control. Fat and 8 LCFA content in liver in MT group also decreased. Gene chip and qPCR demonstrated that there were 289 genes up-regulated and 293 genes down-regulated by MT. Further analysis found that the mRNA expression of lipolysis-related genes increased, while the mRNA expression of lipogenesis-related enzymes decreased (p < 0.05) with MT. This study concluded that melatonin greatly affected fat deposition, and hepatic LCFA supply and the expression of genes associated with lipogenesis and lipolysis.  相似文献   
59.
60.
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