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   108774篇
  免费   3912篇
  国内免费   3717篇
  2024年   123篇
  2023年   598篇
  2022年   1417篇
  2021年   2317篇
  2020年   1599篇
  2019年   2020篇
  2018年   8565篇
  2017年   8083篇
  2016年   6516篇
  2015年   2880篇
  2014年   3401篇
  2013年   3709篇
  2012年   6501篇
  2011年   11211篇
  2010年   8770篇
  2009年   8345篇
  2008年   8702篇
  2007年   10075篇
  2006年   2284篇
  2005年   2898篇
  2004年   2409篇
  2003年   2599篇
  2002年   2247篇
  2001年   1237篇
  2000年   1114篇
  1999年   658篇
  1998年   410篇
  1997年   374篇
  1996年   340篇
  1995年   343篇
  1994年   313篇
  1993年   268篇
  1992年   325篇
  1991年   298篇
  1990年   232篇
  1989年   229篇
  1988年   136篇
  1987年   188篇
  1986年   150篇
  1985年   139篇
  1984年   126篇
  1983年   124篇
  1982年   106篇
  1981年   85篇
  1979年   71篇
  1978年   82篇
  1975年   63篇
  1973年   72篇
  1972年   667篇
  1971年   573篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
生态意识及其主要特点   总被引:7,自引:0,他引:7  
一、生态意识产生的时代背景生态意识作为人类思想的先进观念,产生于20世纪后半叶。产业革命以来二百多年,人类依据先进科学技术武装的强大生产力,无限制地向自然进  相似文献   
132.
Analysis of parameters of metabolic function of lungs with respect to lipid metabolism was performed in rats under conditions of acute experimental emotional-nociceptive stress. Study of the stress-sensitivity of lungs in the comparative-age aspect has shown different extent of changes of several parameters of lipid metabolism in pulmonary tissue in animals of different age. The results of the study demonstrate areactivity and high stress-stability of lungs with respect to surface-active properties, free-radical processes, and lipase activity in early postnatal ontogenesis.  相似文献   
133.
134.
135.
Sexual selection has driven the evolution and elaboration of a wide variety of displays and ornaments in male nonhuman primates, including capes, cheek flanges, and sexual coloration. Among the most sexually dimorphic of all primates is the drill (Mandrillus leucophaeus), the males of which can be 3 times the mass of females, possess large canines, and exhibit extremely bright sexual skin coloration. However, the function of male coloration in this species has never been examined. Here, we present data on male color (measured objectively using digital photography), dominance rank, measures of male-female association, and key sexual behaviors, of adult male drills (n = 17) living in four semi free-ranging enclosures at the Drill Rehabilitation and Breeding Center in Nigeria. We test the hypothesis that male coloration is a badge of status, indicating dominance rank, and the hypothesis that male coloration attracts females. We found that male coloration did indicate rank, and that high ranking, strongly colored males were more likely to associate with adult females, and more specifically with fully tumescent females. These males also engaged in more sexual activity. However, measures of male-female association and sexual behaviors were not related to male color once rank had been taken into consideration; i.e., for males of a given rank, females did not prefer those that were more colorful. We discuss the results in light of what is known about the wild drill social system, in which unfamiliar individuals may come together in “supergroups,” and in which quality indicators of competitive ability may be particularly important.  相似文献   
136.
137.
138.
139.
The trophic structure of benthic communities in the Sea of Okhotsk and Bering Sea was analyzed based on the results of macrobenthic survey catches conducted in the Far Eastern seas in the 2000s. The production of trophic levels and entire communities was determined. It was shown that production of benthic communities is still at a high level and has almost not changed since the 1980s. The arrangement of the communities of some shelf areas by productivity characteristics was made.  相似文献   
140.
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