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   1348627篇
  免费   30050篇
  国内免费   7735篇
化学   676756篇
晶体学   20315篇
力学   74701篇
综合类   104篇
数学   244389篇
物理学   370147篇
  2021年   13682篇
  2020年   16164篇
  2019年   16362篇
  2018年   12581篇
  2016年   28286篇
  2015年   21227篇
  2014年   30988篇
  2013年   75475篇
  2012年   39078篇
  2011年   35828篇
  2010年   37408篇
  2009年   39616篇
  2008年   34940篇
  2007年   30307篇
  2006年   37069篇
  2005年   28662篇
  2004年   30051篇
  2003年   28441篇
  2002年   29674篇
  2001年   28497篇
  2000年   24923篇
  1999年   22650篇
  1998年   21102篇
  1997年   21127篇
  1996年   21283篇
  1995年   19313篇
  1994年   18760篇
  1993年   18358篇
  1992年   18231篇
  1991年   18478篇
  1990年   17662篇
  1989年   17747篇
  1988年   17270篇
  1987年   17224篇
  1986年   16159篇
  1985年   22597篇
  1984年   23846篇
  1983年   20017篇
  1982年   21704篇
  1981年   20922篇
  1980年   20272篇
  1979年   20448篇
  1978年   21748篇
  1977年   21344篇
  1976年   21126篇
  1975年   19780篇
  1974年   19499篇
  1973年   19978篇
  1972年   14426篇
  1967年   12595篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Designs, Codes and Cryptography - Given an integer $$k\ge 3$$ and a group G of odd order,  if there exists a 2-(v, k, 1)-design and if v is sufficiently large then there...  相似文献   
142.
Journal of Analytical Chemistry - Silver nanoparticles modified with Eu3+ ions increase the intensity of the fluorescence signal by a factor of 125 in an analytical system containing doxycycline as...  相似文献   
143.
Computational Optimization and Applications - We consider a continuous-time optimization method based on a dynamical system, where a massive particle starting at rest moves in the conservative...  相似文献   
144.
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   
145.
Herein, we report a Mott-Schottky catalyst by entrapping cobalt nanoparticles inside the N-doped graphene shell (Co@NC). The Co@NC delivered excellent oxygen evolution activity with an overpotential of merely 248 mV at a current density of 10 mA cm–2 with promising long-term stability. The importance of Co encapsulated in NC has further been demonstrated by synthesizing Co nanoparticles without NC shell. The synergy between the hexagonal close-packed (hcp) and face-centered cubic (fcc) Co plays a major role to improve the OER activity, whereas the NC shell optimizes the electronic structure, improves the electron conductivity, and offers a large number of active sites in Co@NC. The density functional theory calculations have revealed that the hcp Co has a dominant role in the surface reaction of electrocatalytic oxygen evolution, whereas the fcc phase induces the built-in electric field at the interfaces with N-doped graphene to accelerate the H+ ion transport.  相似文献   
146.
Crystallography Reports - Two LiInSe2 single crystals, grown under different conditions, have been studied. Characteristics of these crystals for neutron detection have been compared using...  相似文献   
147.
Journal of Radioanalytical and Nuclear Chemistry - In this paper a study for the selection of an NPE (nonylphenol ethoxylates)—free cocktail is discussed in order to be used for our routine...  相似文献   
148.
Central European Journal of Operations Research - Digital competences are among the most important competences in modern society, with the education system playing a key role in the acquisition of...  相似文献   
149.
150.
Radiophysics and Quantum Electronics - A well-known simplified model of turbulent convection from local sources of buoyancy and/or momentum acting for a short time has been developed and...  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