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   63603篇
  免费   13965篇
  国内免费   4870篇
化学   58940篇
晶体学   689篇
力学   2461篇
综合类   299篇
数学   5811篇
物理学   14238篇
  2023年   565篇
  2022年   646篇
  2021年   1066篇
  2020年   2276篇
  2019年   3503篇
  2018年   1872篇
  2017年   1576篇
  2016年   4628篇
  2015年   4698篇
  2014年   4883篇
  2013年   6178篇
  2012年   5647篇
  2011年   5152篇
  2010年   4783篇
  2009年   4636篇
  2008年   4444篇
  2007年   3589篇
  2006年   3297篇
  2005年   3168篇
  2004年   2727篇
  2003年   2201篇
  2002年   1773篇
  2001年   1490篇
  2000年   1157篇
  1999年   709篇
  1998年   617篇
  1997年   537篇
  1996年   543篇
  1995年   489篇
  1994年   445篇
  1993年   400篇
  1992年   361篇
  1991年   299篇
  1990年   295篇
  1989年   235篇
  1988年   214篇
  1987年   148篇
  1986年   163篇
  1985年   179篇
  1984年   119篇
  1983年   110篇
  1982年   84篇
  1981年   67篇
  1980年   62篇
  1979年   42篇
  1977年   37篇
  1976年   37篇
  1975年   36篇
  1974年   50篇
  1973年   45篇
排序方式: 共有10000条查询结果,搜索用时 262 毫秒
1.
2.
Jin  Zhuochen  Cao  Nan  Shi  Yang  Wu  Wenchao  Wu  Yingcai 《显形杂志》2021,24(2):349-364
Journal of Visualization - The increasing availability of spatiotemporal data provides unprecedented opportunities for understanding the structure of an urban area in terms of people’s...  相似文献   
3.
During metal welding and cutting, large amounts of particulate matter (PM) are produced that might represent a significant health risk for the exposed workers. In the present pilot study, we performed an elemental analysis of fine PM collected in a metal workshop. Also, elemental analysis of the hair and nail samples collected from workers exposed to the workshop dust and control group was done. Concentrations of 15 elements in PM were measured with X‐Ray Fluorescence (XRF) and Particle Induced X‐ray Emission (PIXE), whereas inductively coupled plasma mass spectrometry (ICP‐MS) was used to determine 12 elements in hair and nail samples. Mean 8‐hr concentrations of PM2.5, Fe, and Mn in the vicinity of welders were up to 1803, 860, and 30 μg/m3, respectively, whereas in the nearby city, daily PM2.5 concentrations are on average 11 μg/m3. We found that several elements, especially Fe and Mn, had substantially higher concentrations in hair and nail samples of exposed workers than in the control group, which indicates the accumulation of metals in workers' tissues, although limit values were not exceeded.  相似文献   
4.
In this article a coupled version of the improved divergence‐free‐condition compensated method will be proposed to simulate time‐varying geometries by direct forcing immersed boundary method. The proposed method can be seen as a quasi‐multi‐moment framework due to the fact that the momentum equations are discretized by both cell‐centered and cell‐face velocity. For simulating time‐varying geometries, a semi‐implicit iterative method is proposed for calculating the direct forcing terms. Treatments for suppressing spurious force oscillations, calculating drag/lift forces, and evaluating velocity and pressure for freshly cells will also be addressed. In order to show the applicability and accuracy, analytical as well as benchmark problems will be investigated by the present framework and compared with other numerical and experimental results.  相似文献   
5.
Journal of Algebraic Combinatorics - APR tilts for path algebra kQ can be realized as the mutation of the quiver Q in $${\mathbb Z}Q$$ with respect to the translation. In this paper, we show that...  相似文献   
6.
Ding  Wei  Han  YongSheng  Zhu  YuePing 《Potential Analysis》2021,55(3):419-441
Potential Analysis - The purpose of this paper is to provide necessary and sufficient conditions of the boundedness for singular integrals on the local Hardy space and its dual. Particularly the...  相似文献   
7.
We generalize the P(N)-graded Lie superalgebras of Martinez-Zelmanov. This generalization is not so restrictive but suffcient enough so that we are able to have a classification for this generalized P(N)-graded Lie superalgebras. Our result is that the generalized P(N)-graded Lie super-algebra L is centrally isogenous to a matrix Lie superalgebra coordinated by an associative superalgebra with a super-involution. Moreover, L is P(N)-graded if and only if the coordinate algebra R is commutative and the super-involution is trivial. This recovers Martinez-Zelmanov's theorem for type P(N). We also obtain a generalization of Kac's coordinatization via Tits-Kantor-Koecher construction. Actually, the motivation of this generalization comes from the Fermionic-Bosonic module construction.  相似文献   
8.
柯荣住  张进 《运筹学学报》2021,25(3):87-104
本文首先对双层规划的一个特殊例子即道德风险模型中使用的一阶条件方法(FOA)做简要的梳理,然后提出一种更为一般的使FOA有效的原则与方法。新方法主要依赖于代理人对委托人设置的目标的最优反应映射是否存在不动点,这个性质不要求原问题与用一阶条件放松以后的问题之间的约束集等价,从而也不要求代理人的期望效用对行动具有全局凹性。在新方法下,可以用较为简单的方法证明FOA在以下两种情形之一有效,即如果分布函数是概率分布的凸组合或者分布函数来自某些特殊的指数族分布。  相似文献   
9.
Zheng  Xinyan  Hu  Po  Yao  Ruxian  cheng  Jinhe  Chang  Yiheng  Wu  Haitao  Mei  Hongying  Sun  Shuxiang  Chen  Qingtai  liu  Fang  Chen  Shujing  Wen  Hua 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(5):2217-2226
Journal of Radioanalytical and Nuclear Chemistry - Enhancement of U(VI) biomineralization by Saccharomyces cerevisiae through addition of inorganic phosphorus was studied in this work. The addition...  相似文献   
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