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   3195篇
  免费   216篇
  国内免费   10篇
  2023年   27篇
  2022年   50篇
  2021年   128篇
  2020年   105篇
  2019年   220篇
  2018年   159篇
  2017年   106篇
  2016年   148篇
  2015年   176篇
  2014年   148篇
  2013年   253篇
  2012年   269篇
  2011年   254篇
  2010年   143篇
  2009年   153篇
  2008年   170篇
  2007年   144篇
  2006年   135篇
  2005年   111篇
  2004年   101篇
  2003年   86篇
  2002年   65篇
  2001年   26篇
  2000年   19篇
  1999年   17篇
  1998年   14篇
  1997年   17篇
  1996年   4篇
  1995年   10篇
  1994年   12篇
  1993年   7篇
  1992年   9篇
  1991年   8篇
  1990年   7篇
  1989年   7篇
  1988年   6篇
  1987年   13篇
  1986年   9篇
  1985年   4篇
  1984年   6篇
  1982年   7篇
  1981年   4篇
  1979年   4篇
  1978年   11篇
  1977年   10篇
  1976年   5篇
  1974年   5篇
  1973年   7篇
  1972年   3篇
  1971年   4篇
排序方式: 共有3421条查询结果,搜索用时 15 毫秒
41.
Heparin was found to be the most potent inhibitor of rat ovarian luteinizing hormone-sensitive adenylate cyclase (I50 = 2 μg/ml) when compared to other naturally occurring glycosaminoglycans. This inhinibition was also appparent when this enzyme was stimulated by follicle-stimulating hormone or prostaglandin E 2. Heparin was also found to inhibit glucagon-sensitive rat hepatice adenylate cyclase, and the prostaglandin E1-sensitive enzyme from rat ileum and human platelets. In contrast, heparin stimulated the dopamine sensitive adenylate cyclase from rat caudate nucleus. The sulfade polysugar dextran sulfate exerts similar effects on adenylate cyclase activity of the rat ovary was shown to inhibit hormone binding to rat ovarian plasma membrane in a manner similar to that exerted by heparin. In contrast to heparin, dextran sulfate inhibited dopamine-sensitive adenylate cyclase from rat caudate nucleus.  相似文献   
42.
43.
Water stress is one of the main abiotic factors that reduces plant growth, mainly due to high evaporative demand and low water availability. In order to evaluate the effects of drought stress on certain morphological and physiological characteristics of two canola cultivars, we conducted a factorial experiment based on a completely randomized design. The findings show that drought stress exacerbations result in the plant's response to stress due to increased canola resistance caused by changes in plant pigments, proline, catalase, ascorbate peroxidase, peroxidase, superoxide dismutase and malondialdehyde, glucose, galactose, rhamnose and xylose. These in turn ultimately influence the morphological characteristics of canola. Drought stress reduces the concentration of carotenoids, chlorophyll a, chlorophyll b, total chlorophylls; however, glucose, galactose, rhamnose, xylose, proline, catalase, ascorbate peroxidase, peroxidase, superoxide dismutase, malondialdehyde (in leaves and roots) and the chlorophyll a and b ratios were increased. Reduction of plant height, stem height, root length, fresh and dry weight of canola treated with 300 g/l PEG compared to non‐treatment were 0.264, 0.236, 0.394, 0.183 and 0.395, respectively. From the two canola cultivars, the morphological characteristics of the NIMA increased compared to the Ks7 cultivar. Interaction effects of cultivar and drought stress showed that NIMA cultivar without treatment had the highest number of morphological characteristics such as carotenoid concentration, chlorophyll a, chlorophyll b, total chlorophylls a and b, whereas the cultivar with 300 g/l PEG (drought stress) had the highest amount of proline, malondialdehyde, soluble sugars and enzymes in leaves and roots. Increasing activity of oxidative enzymes and soluble sugars in canola under drought stress could be a sign of their relative tolerance to drought stress.  相似文献   
44.
Sleep and Biological Rhythms - To examine the psychometric properties of the Sleep Condition Indicator (SCI) using different psychometric approaches [including classical test theory, Rasch models,...  相似文献   
45.
46.
Rapid urbanization, global trade, and the exceptionally great numbers of worldwide visitors during Hajj and Umrah have all placed the Kingdom of Saudi Arabia at a significant risk of introducing several vector-borne tropical diseases, such as dengue fever virus (DENV) infection. In this study we estimated DENV infection cost of illness (COI) in Saudi Arabia in the period 2013–2017, by processing national data including all declared cases recorded in referral centers in the western region, being the endemic region of the country. Using a statistically validated predictive model that was built on a representative sample of 717 laboratory-confirmed cases of DENV infection, direct costs, due to care-related expenditures, were estimated by applying the predictive equation to national data. However, indirect costs, which are due to productivity loss, were estimated using the human capital model based on gross domestic product adjusted for invalidity duration. Further, under-reporting was adjusted by using an expansion factor EF = 3. We observed highest estimated costs in 2016 with over US$168.5 Million total costs, including direct (US$29.0 Million) and indirect (US$139.5 Million) costs, for a total 4415 confirmed cases. The total DENV COI for the five years was estimated as US$551.0 Million for a total 15,369 patients (59.7%) out of 25,745 declared cases, resulting in an average cost of US$11 947.6 by patient. Depending on the year, productivity years loss costs accounted for 63.3% to 83.8% of the estimated total costs. Dengue has a substantial local economic burden that costs US$110.2 Million per year, stressing the urgent need for an effective national prevention strategy to perform considerable cost-savings besides reducing morbidity.  相似文献   
47.
48.
Molecular Biology Reports - Both extreme usage of water in agriculture i.e., drought and flooding affect physiological and growth aspects of the plant as well as gene expression undertaken in water...  相似文献   
49.
Journal of Plant Growth Regulation - Plants require optimum amounts of nutrients for suitable growth and yield production. Accordingly, the most efficient methods of fertilization, including the...  相似文献   
50.
Journal of Plant Growth Regulation - Plant biofibers are of great economic and commercial importance. Among various fiber producing crops, cotton (Gossypium hirsutum L.), hemp (Cannabis sativa L.),...  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