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   23164篇
  免费   658篇
  国内免费   82篇
系统科学   1132篇
丛书文集   173篇
教育与普及   73篇
理论与方法论   337篇
现状及发展   8559篇
研究方法   807篇
综合类   12547篇
自然研究   276篇
  2018年   764篇
  2017年   764篇
  2016年   470篇
  2012年   524篇
  2011年   1477篇
  2010年   924篇
  2009年   554篇
  2008年   834篇
  2007年   1123篇
  2006年   349篇
  2005年   394篇
  2004年   525篇
  2003年   498篇
  2002年   400篇
  2001年   471篇
  2000年   492篇
  1999年   339篇
  1994年   309篇
  1992年   271篇
  1991年   229篇
  1990年   280篇
  1989年   254篇
  1988年   263篇
  1987年   283篇
  1986年   291篇
  1985年   339篇
  1984年   236篇
  1983年   261篇
  1982年   214篇
  1981年   204篇
  1980年   245篇
  1979年   509篇
  1978年   438篇
  1977年   391篇
  1976年   316篇
  1975年   386篇
  1974年   475篇
  1973年   423篇
  1972年   436篇
  1971年   565篇
  1970年   610篇
  1969年   535篇
  1968年   534篇
  1967年   461篇
  1966年   409篇
  1965年   295篇
  1958年   323篇
  1957年   253篇
  1956年   202篇
  1955年   200篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The participation of non-state actors in implementation processes is often understood as a means to increase compliance efficiency. But the implementation of spatial policies frequently focuses on pre-established goals, processes and instruments and thus renders difficult open discourse and shared decision-making. This paper introduces conflict pattern analysis (CPA) as a tool that supports the analysis of the actual actor constellation in order to define efficient approaches that avoid common problems of participatory processes. CPA is a semi-formalised method that helps to identify key-actors, their relations and interaction amongst each other as well as their core beliefs, interests and resources. It aggregates this information to interaction patterns that can be compared, classified and linked to different participatory methods on a theoretically informed basis. Particularly on the local and regional level, this could be the first step for successful (participatory) implementation strategies.  相似文献   
72.
In this paper, we introduce a new class of generalized convex function, namely, a-pseudounivex function, by combining the concepts of pseudo-univex and α-invex functions. Further, we establish some relationships between vector variational-like inequality problems and vector optimization problems under the assumptions of α-pseudo-univex functions. Results obtained in this paper present a refinement and improvement of previously known results.  相似文献   
73.
74.
The geomagnetic fields, which play important roles in the ionospheric dynamo, can greatly affect the global distribution of ionospheric electric fields, currents and other ionospheric electrodynamics phenomena. In the study of ionospheric electrodynamics phenomena, such as the longitudinal variations of ionospheric electric fields, the non-dipolar component of the geomagnetic fields must be taken into account. In this paper, we deduce a theoretical electric field model for ionospheric dynamo at mid- and low-latitude which adopt a modified magnetic apex coordinates system. In the new electric field model, the geomagnetic fields can be calculated from either the IGRF model or the dipole field model, and the neutral winds and conductivities are calculated based on empirical models. Then the dynamo equation for the electric potential is finally solved in terms of the line-by-line iteration method, and the ionospheric electric fields and currents are derived from the calculated potential. Our model can reproduce the main features of the ionospheric electrodynamics processes, so it will be a useful tool for the investigation of the upper atmosphere and ionosphere.  相似文献   
75.
76.
77.
On going trend of miniaturization in electronic rel at ed parts, which is an average of two times in every 5~7 years introduce grindin g challenges. In grinding process, the surface waviness control of thin parts is an ardent task due to its warpage, induced by the high specific grinding energy (2~10 J/mm 3). Therefore, coolant is often used to avoid thermal damage, obtai n better surface integrity and to prolong wheel life. However coolant, the incomp ressibility media introduce high forces at the gri...  相似文献   
78.
79.
研究以水泥处理固体有机物时,有机物对水泥水化的影响。以膜流模式说明水份在水泥浆体内传输的现象。水膜存在半干之水泥浆体,其厚度小于100nm,膜流由离分压所驱动,而离分压来自分子间作用力。膜拟结果发现,水泥浆体内局部位置可用以进行水化之水量为Q=-Aslv/6vπ。当有机物添加在水泥浆体内时,会影响Hamaker常数,Aslv因此可能使膜流不稳定或完全抑制膜流,因而使水泥浆体内局部缺水,影响水化进行,造成成品强度降低,影响品质。  相似文献   
80.
T Matsuda  Y Yabushita  T Doi  H Iwata 《Experientia》1985,41(7):924-925
The highest specific activity of thiamin pyrophosphokinase was found in the cerebellum, and lower activity in cerebral cortex and midbrain. The regional difference in the enzyme activity was similar to that in thiamin content and the influx rate in rat brain, suggesting that the enzyme is involved in the thiamin transport.  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