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   92511篇
  免费   462篇
  国内免费   397篇
化学   26366篇
晶体学   912篇
力学   6929篇
数学   32531篇
物理学   16469篇
无线电   10163篇
  2022年   88篇
  2021年   106篇
  2020年   130篇
  2019年   128篇
  2018年   11885篇
  2017年   11518篇
  2016年   7085篇
  2015年   1001篇
  2014年   504篇
  2013年   728篇
  2012年   4382篇
  2011年   11865篇
  2010年   6970篇
  2009年   6937篇
  2008年   7358篇
  2007年   9819篇
  2006年   395篇
  2005年   1730篇
  2004年   1873篇
  2003年   2248篇
  2002年   1169篇
  2001年   318篇
  2000年   356篇
  1999年   213篇
  1998年   249篇
  1997年   188篇
  1996年   255篇
  1995年   172篇
  1994年   147篇
  1993年   179篇
  1992年   133篇
  1991年   122篇
  1990年   121篇
  1989年   122篇
  1988年   132篇
  1987年   121篇
  1986年   103篇
  1985年   158篇
  1984年   163篇
  1983年   119篇
  1982年   112篇
  1981年   115篇
  1980年   121篇
  1979年   120篇
  1978年   109篇
  1977年   83篇
  1976年   80篇
  1975年   66篇
  1974年   63篇
  1973年   91篇
排序方式: 共有10000条查询结果,搜索用时 703 毫秒
1.
Journal of Optimization Theory and Applications - A framework for monitoring a target modeled as Dubins car using multiple UAVs is proposed. The UAVs are subject to minimum and maximum speed,...  相似文献   
2.
The health monitoring has been studied to ensure integrity of design of engine structure by detection, quantification, and prediction of damages. Early detection of faults may allow the downtime of maintenance to be rescheduled, thus preventing sudden shutdown of machines. In cylinder pressure developed, vibrations and noise emissions data provide a rich source of information about condition of engines. Monitoring of vibrations and noise emissions are novel non-intrusive methodologies for which positioning of various transducers are important issue. The presented work shows applicability of these diagnosis methodologies adopted in case of diesel engines. The effects of changing various fuel injection parameters was analyzed. Scope of using non-intrusive technique has been analyzed by changing locations of microphone. Novelty of this worklies in exploring signal processing methods for various locations around the engine test set up. Various frequency ranges of contributing noise and vibration sources were identified. Time-Frequency analysis showed the onset of various cyclic. Based on the identification of various frequency bands, it is possible to device suitable filters in order to extract more information.  相似文献   
3.
Wireless Personal Communications - The orthogonal frequency division multiplexing (OFDM) is the most encouraging multi-carrier modulation system chosen for the high data rates but the objective is...  相似文献   
4.
In the paper, the authors establish several integral representations for the generating functions of the large and little Schröder numbers and for the large and little Schröder numbers.  相似文献   
5.
6.
Mesoscopic modeling at the pore scale offers great promise in exploring the underlying structure transport performance of flow through porous media. The present work studies the fluid flow subjected to capillarity-induced resonance in porous media characterized by different porous structure and wettability. The effects of porosity and wettability on the displacement behavior of the fluid flow through porous media are discussed. The results are presented in the form of temporal evolution of percentage saturation and displacement of the fluid front through porous media. The present study reveals that the vibration in the form of acoustic excitation could be significant in the mobilization of fluid through the porous media. The dependence of displacement of the fluid on physicochemical parameters like wettability of the surface, frequency along with the porosity is analyzed. It was observed that the mean displacement of the fluid is more in the case of invading fluid with wetting phase where the driving force strength is not so dominant.  相似文献   
7.
8.
We prove that the group of diffeomorphisms of the interval [0, 1] contains surface groups whose action on (0, 1) has no global fix point and such that only countably many points of the interval (0, 1) have non-trivial stabiliser.  相似文献   
9.
10.
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