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   68267篇
  免费   10188篇
  国内免费   1551篇
化学   60415篇
晶体学   540篇
力学   1035篇
综合类   4篇
数学   8670篇
物理学   9342篇
  2023年   249篇
  2022年   218篇
  2021年   714篇
  2020年   1779篇
  2019年   3133篇
  2018年   1702篇
  2017年   1291篇
  2016年   4474篇
  2015年   4354篇
  2014年   4351篇
  2013年   6178篇
  2012年   5106篇
  2011年   4574篇
  2010年   4268篇
  2009年   4140篇
  2008年   4514篇
  2007年   3856篇
  2006年   3375篇
  2005年   3404篇
  2004年   2943篇
  2003年   2299篇
  2002年   1711篇
  2001年   1443篇
  2000年   1121篇
  1999年   571篇
  1998年   425篇
  1997年   434篇
  1996年   506篇
  1995年   401篇
  1994年   421篇
  1993年   379篇
  1992年   372篇
  1991年   337篇
  1990年   316篇
  1989年   254篇
  1988年   249篇
  1987年   252篇
  1986年   244篇
  1985年   322篇
  1984年   333篇
  1983年   216篇
  1982年   238篇
  1981年   239篇
  1980年   236篇
  1979年   166篇
  1978年   161篇
  1977年   164篇
  1976年   146篇
  1975年   130篇
  1973年   133篇
排序方式: 共有10000条查询结果,搜索用时 123 毫秒
1.
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   
2.
Set-Valued and Variational Analysis - In a Hilbert framework ℌ, we study the convergence properties of a Newton-like inertial dynamical system governed by a general maximally monotone...  相似文献   
3.
Archiv der Mathematik - In this note, we introduce a criterion to detect vanishing of essential algebras of a Green biset functor by means of morphisms. We introduce the inflation morphism and...  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.
Set-Valued and Variational Analysis - The production correspondence associated with a technology maps every input vector into the set of output vectors that may be obtained by means of those...  相似文献   
6.
Journal of Solid State Electrochemistry - A study of poly(3-hexylthiophene) (P3HT) thin films by spin-coating process, deposited on conducting glass substrates of fluorine-doped tin oxide (FTO), is...  相似文献   
7.
Meccanica - In this work we study, from the numerical point of view, a one-dimensional thermoelastic problem where the thermal law is of type III. Quasi-static microvoids are also assumed within...  相似文献   
8.
9.
Mathematical Programming - Let G be a digraph where every node has preferences over its incoming edges. The preferences of a node extend naturally to preferences over branchings, i.e., directed...  相似文献   
10.
Central European Journal of Operations Research - Sustainability practice within supply chains remains in an early development phase. Enterprises still need tools that support the integration of...  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