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   238258篇
  免费   2305篇
  国内免费   731篇
化学   131241篇
晶体学   3137篇
力学   9079篇
综合类   15篇
数学   26728篇
物理学   71094篇
  2021年   2107篇
  2020年   2333篇
  2019年   2568篇
  2018年   3592篇
  2017年   3470篇
  2016年   4870篇
  2015年   2893篇
  2014年   4406篇
  2013年   10200篇
  2012年   8092篇
  2011年   9754篇
  2010年   6829篇
  2009年   6656篇
  2008年   9254篇
  2007年   9309篇
  2006年   8655篇
  2005年   8325篇
  2004年   7593篇
  2003年   6621篇
  2002年   6169篇
  2001年   6483篇
  2000年   5210篇
  1999年   3792篇
  1998年   3277篇
  1997年   3302篇
  1996年   3175篇
  1995年   2620篇
  1994年   2743篇
  1993年   2781篇
  1992年   2932篇
  1991年   2916篇
  1990年   2772篇
  1989年   2734篇
  1988年   2638篇
  1987年   2620篇
  1986年   2534篇
  1985年   3266篇
  1984年   3404篇
  1983年   2742篇
  1982年   2974篇
  1981年   2826篇
  1980年   2624篇
  1979年   2843篇
  1978年   2962篇
  1977年   2965篇
  1976年   2938篇
  1975年   2780篇
  1974年   2763篇
  1973年   2906篇
  1972年   1910篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
Raman chemical imaging provides chemical and spatial information about pharmaceutical drug product. By using resolution methods on acquired spectra, the objective is to calculate pure spectra and distribution maps of image compounds. With multivariate curve resolution-alternating least squares, constraints are used to improve the performance of the resolution and to decrease the ambiguity linked to the final solution. Non negativity and spatial local rank constraints have been identified as the most powerful constraints to be used.  相似文献   
44.
By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A2L3 complexes (A represents anion, here orthophosphate PO43?), namely helicate, mesocate, and mono‐bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordination‐based structures as in transition‐metal complexes.  相似文献   
45.
Physics of Atomic Nuclei - We have studied the mechanisms influencing production of cumulative pions and protons in the fragmentation of the incident deuterons into cumulative pions and protons...  相似文献   
46.
47.
48.
Injection-moulding is one of the most common manufacturing processes used for polymers. In many applications, the mechanical properties of the product is of great importance. Injection-moulding of thin-walled polymer products tends to leave the polymer structure in a state where the mechanical properties are anisotropic, due to alignment of polymer chains along the melt flow direction. The anisotropic elastic-viscoplastic properties of low-density polyethylene, that has undergone an injection-moulding process, are therefore examined in the present work. Test specimens were punched out from injection-moulded plates and tested in uniaxial tension. Three in-plane material directions were investigated. Because of the small thickness of the plates, only the in-plane properties could be determined. Tensile tests with both monotonic and cyclic loading were performed, and the local strains on the surface of the test specimens were measured using image analysis. True stress vs. true strain diagrams were constructed, and the material response was evaluated using an elastic-viscoplasticity law. The components of the anisotropic compliance matrix were determined together with the direction-specific plastic hardening parameters.  相似文献   
49.
Erosion and sediments transport processes have a great impact on industrial structures and on water quality. Despite its limitations, the Saint‐Venant‐Exner system is still (and for sure for some years) widely used in industrial codes to model the bedload sediment transport. In practice, its numerical resolution is mostly handled by a splitting technique that allows a weak coupling between hydraulic and morphodynamic distinct softwares but may suffer from important stability issues. In recent works, many authors proposed alternative methods based on a strong coupling that cure this problem but are not so trivial to implement in an industrial context. In this work, we then pursue 2 objectives. First, we propose a very simple scheme based on an approximate Riemann solver, respecting the strong coupling framework, and we demonstrate its stability and accuracy through a number of numerical test cases. However, second, we reinterpret our scheme as a splitting technique and we extend the purpose to propose what should be the minimal coupling that ensures the stability of the global numerical process in industrial codes, at least, when dealing with collocated finite volume method. The resulting splitting method is, up to our knowledge, the only one for which stability properties are fully demonstrated.  相似文献   
50.
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