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   675篇
  免费   39篇
林业   39篇
农学   13篇
基础科学   2篇
  81篇
综合类   60篇
农作物   34篇
水产渔业   27篇
畜牧兽医   382篇
园艺   19篇
植物保护   57篇
  2023年   4篇
  2022年   9篇
  2021年   15篇
  2020年   16篇
  2019年   22篇
  2018年   15篇
  2017年   16篇
  2016年   27篇
  2015年   6篇
  2014年   14篇
  2013年   25篇
  2012年   28篇
  2011年   51篇
  2010年   27篇
  2009年   28篇
  2008年   41篇
  2007年   52篇
  2006年   44篇
  2005年   50篇
  2004年   48篇
  2003年   36篇
  2002年   40篇
  2001年   4篇
  2000年   3篇
  1999年   5篇
  1998年   4篇
  1997年   5篇
  1996年   6篇
  1995年   5篇
  1994年   5篇
  1993年   3篇
  1992年   5篇
  1991年   9篇
  1990年   6篇
  1989年   7篇
  1987年   2篇
  1986年   4篇
  1985年   4篇
  1983年   2篇
  1982年   2篇
  1981年   2篇
  1980年   1篇
  1979年   3篇
  1975年   4篇
  1973年   1篇
  1972年   2篇
  1970年   2篇
  1968年   1篇
  1940年   1篇
  1926年   1篇
排序方式: 共有714条查询结果,搜索用时 0 毫秒
1.
2.
We have come a long way in understanding and managing the FHL syndrome since it was first described nearly 30 years ago. Increased sensitivity of clinicians for recognizing the syndrome has improved case outcome by arresting this metabolic syndrome in its earliest stages. Simply ensuring adequate intake of a complete and balanced feline diet can rescue cats just developing clinical signs; however, full metabolic support as described herein provides the best chance for recovery of cats demonstrating the most severe clinicopathologic features. It remains possible that adjustments in recommended micronutrient and vitamin intake for healthy cats may pivotally change feline susceptibility to FHL over the coming years.  相似文献   
3.
4.
Vitamin A and provitamin A carotenoids are involved in the regulation of adipose tissue metabolism and inflammation. We examined the effect of dietary supplementation using all-trans and 9-cis β-carotene-rich Dunaliella bardawil alga as the sole source of vitamin A on obesity-associated comorbidities and adipose tissue dysfunction in a diet-induced obesity mouse model. Three-week-old male mice (C57BL/6) were randomly allocated into two groups and fed a high-fat, vitamin A-deficient diet supplemented with either vitamin A (HFD) or β-carotene (BC) (HFD-BC). Vitamin A levels in the liver, WATs, and BAT of the HFD-BC group were 1.5–2.4-fold higher than of the HFD group. BC concentrations were 5–6-fold greater in BAT compared to WAT in the HFD-BC group. The eWAT mRNA levels of the Mcp-1 and Cd68 were 1.6- and 2.1-fold lower, respectively, and the plasma cholesterol and triglyceride concentrations were 30% and 28% lower in the HFD-BC group compared with the HFD group. Dietary BC can be the exclusive vitamin A source in mice fed a high-fat diet, as shown by the vitamin A concentration in the plasma and tissues. Feeding BC rather than vitamin A reduces adipose tissue macrophage recruitment markers and plasma lipid concentrations.  相似文献   
5.
6.
7.
8.
Ediacara fossils [575 to 542 million years ago (Ma)] represent Earth's oldest known complex macroscopic life forms, but their morphological history is poorly understood. A comprehensive quantitative analysis of these fossils indicates that the oldest Ediacara assemblage-the Avalon assemblage (575 to 565 Ma)-already encompassed the full range of Ediacara morphospace. A comparable morphospace range was occupied by the subsequent White Sea (560 to 550 Ma) and Nama (550 to 542 Ma) assemblages, although it was populated differently. In contrast, taxonomic richness increased in the White Sea assemblage and declined in the Nama assemblage. These diversity changes, occurring while morphospace range remained relatively constant, led to inverse shifts in morphological variance. The Avalon morphospace expansion mirrors the Cambrian explosion, and both events may reflect similar underlying mechanisms.  相似文献   
9.
10.
Several Ponto‐Caspian gobiid species have recently expanded their ranges in Europe and North America. This is the first study to demonstrate passive downstream dispersal (drift) of the round goby (Neogobius melanostomus) and tubenose goby (Proterorhinus semilunaris) in newly colonised areas (River Dyje, Danube basin), a factor that could play an important role in their dispersal. Drift duration (i.e. number of dates on which the species was caught) in round goby was longer than that of both native species and tubenose goby, providing a possible advantage. Size of drifting fish was restricted to a narrow range of 6–8 mm and 5–8 mm for round and tubenose goby, respectively. Drift in both species occurred almost completely during hours of darkness (<1 lux) and fish size did not vary throughout the night. In both species, drift density increased significantly during the first hour after dusk. Round goby density gradually decreased up to dawn, while tubenose goby density varied throughout the night with no clear pattern. Drift of early life stages appears to be an important phenomenon that has not received adequate attention in studies of round and tubenose goby ecology and dispersal.  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