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   259篇
  免费   1篇
  国内免费   5篇
教育与普及   1篇
理论与方法论   5篇
现状及发展   31篇
研究方法   45篇
综合类   174篇
自然研究   9篇
  2019年   1篇
  2018年   2篇
  2017年   2篇
  2016年   5篇
  2015年   1篇
  2014年   3篇
  2013年   5篇
  2012年   23篇
  2011年   38篇
  2010年   5篇
  2009年   2篇
  2008年   21篇
  2007年   16篇
  2006年   24篇
  2005年   33篇
  2004年   22篇
  2003年   26篇
  2002年   18篇
  1999年   1篇
  1993年   1篇
  1990年   1篇
  1989年   1篇
  1987年   1篇
  1986年   2篇
  1984年   3篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1980年   1篇
  1969年   1篇
  1965年   1篇
  1961年   1篇
排序方式: 共有265条查询结果,搜索用时 0 毫秒
61.
62.
A national scientific community developed in the United States following the American Revolution. The independent scientific societies, journals and other institutions that formed the basis of this community were, however, centred in the North. An analysis of the work of four leading natural historians of the Southern tidewater (two from before the Revolution and two from after it) suggests that their region participated in this development by shifting scientific ties and allegiances from Europe to the North rather than by creating national or regional scientific institutions.  相似文献   
63.
Twenty-three species of spider mites (Tetranychidae) are recognized for Utah and Idaho; three of these are described as new: Bryobia neoribis, Pseudobryobia knowltoni, and Schizotetranychus agropyron. Eleven species of Tenuipalpidae are recorded.  相似文献   
64.
This paper explores various metaphysical aspects of Leibniz's concepts of space, motion, and matter, with the intention of demonstrating how the distinctive role of force in Leibnizian physics can be used to develop a theory of relational motion using privileged reference frames. Although numerous problems will remain for a consistent Leibnizian relationist account, the version developed within our investigation will advance the work of previous commentators by more accurately reflecting the specific details of Leibniz's own natural philosophy, especially his handling of the dynamical interactions of plenum bodies.  相似文献   
65.
66.
The decline and fate of an iron-induced subarctic phytoplankton bloom   总被引:2,自引:0,他引:2  
Iron supply has a key role in stimulating phytoplankton blooms in high-nitrate low-chlorophyll oceanic waters. However, the fate of the carbon fixed by these blooms, and how efficiently it is exported into the ocean's interior, remains largely unknown. Here we report on the decline and fate of an iron-stimulated diatom bloom in the Gulf of Alaska. The bloom terminated on day 18, following the depletion of iron and then silicic acid, after which mixed-layer particulate organic carbon (POC) concentrations declined over six days. Increased particulate silica export via sinking diatoms was recorded in sediment traps at depths between 50 and 125 m from day 21, yet increased POC export was not evident until day 24. Only a small proportion of the mixed-layer POC was intercepted by the traps, with more than half of the mixed-layer POC deficit attributable to bacterial remineralization and mesozooplankton grazing. The depletion of silicic acid and the inefficient transfer of iron-increased POC below the permanent thermocline have major implications both for the biogeochemical interpretation of times of greater iron supply in the geological past, and also for proposed geo-engineering schemes to increase oceanic carbon sequestration.  相似文献   
67.
The silhouette of women's garment is diversified in its design. In this paper,a new model was developed to predict the silhouette of jacket for the given girth measurements. Sixty-three princess-seam women's jackets with seven styles and nine girth dimensions of each style were produced. Their ease distribution was investigated at bustline,waistline,and hipline,respectively. The widths of the cross-sections for bustline,waistline,and hipline were formulated by multiple linear regressions. Then the silhouette was captured from the ratio of waist width to bust width of a designed jacket,together with that of waist width to hip width.  相似文献   
68.
69.
70.
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