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   19804篇
  免费   632篇
  国内免费   114篇
化学   14198篇
晶体学   189篇
力学   378篇
综合类   1篇
数学   2988篇
物理学   2796篇
  2022年   166篇
  2021年   201篇
  2020年   294篇
  2019年   291篇
  2018年   187篇
  2017年   182篇
  2016年   407篇
  2015年   360篇
  2014年   453篇
  2013年   932篇
  2012年   981篇
  2011年   1271篇
  2010年   621篇
  2009年   531篇
  2008年   1025篇
  2007年   1103篇
  2006年   1081篇
  2005年   1045篇
  2004年   885篇
  2003年   748篇
  2002年   735篇
  2001年   255篇
  2000年   260篇
  1999年   234篇
  1998年   225篇
  1997年   260篇
  1996年   287篇
  1995年   230篇
  1994年   213篇
  1993年   250篇
  1992年   205篇
  1991年   187篇
  1990年   166篇
  1989年   142篇
  1988年   143篇
  1987年   159篇
  1986年   135篇
  1985年   205篇
  1984年   250篇
  1983年   178篇
  1982年   223篇
  1981年   241篇
  1980年   181篇
  1979年   183篇
  1978年   215篇
  1977年   161篇
  1976年   157篇
  1975年   150篇
  1974年   166篇
  1973年   142篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
In a 2:2 reaction with silver(I) chloride or bromide, 1,5-bis(1-phospholano)pentane ( 1a ) afforded frame-like macrocyclic structures, with intra- ( 2 , Cl) or intermolecular ( 3 , Br) halido bridges. In contrast, 1,7-bis(1-phospholano)heptane ( 1b ) formed coordination polymers 4a (Cl) and 4b (Br) with bridging bis-phospholane and halido ligands. A unique paddle wheel-type metallacryptand structure 5 was obtained from 1a and silver(I) bromide in a 2:3 reaction (M:L). All complexes were fully characterized by NMR, IR spectroscopy, mass spectrometry, and X-ray crystallography.  相似文献   
2.
3.
4.
Daylight photodynamic therapy (DPDT) is an effective and patient preferred treatment for the management of field change actinic keratosis. An important factor in DPDT is light dosimetry, to ensure that patients receive sufficient daylight for effective treatment, and this is the focus of the contribution to this issue by (La Rochelle et al. [2019] Photochem. Photobiol., https://doi.org/10.1111/php.13170 ). In this work, the authors present an easy-to-use method for obtaining real-time information about patient received light dose during treatment and for determining indoor locations best suited to DPDT.  相似文献   
5.
Transition‐metal complexes containing stimuli‐responsive systems are attractive for applications in optical devices, photonic memory, photosensing, as well as luminescence imaging. Amongst them, photochromic metal complexes offer the possibility of combining the specific properties of the metal centre and the optical response of the photochromic group. The synthesis, the electrochemical properties and the photophysical characterisation of a series of donor–acceptor azobenzene derivatives that possess bipyridine groups connected to a 4‐dialkylaminoazobenzene moiety through various linkers are presented. DFT and TD‐DFT calculations were performed to complement the experimental findings and contribute to their interpretation. The position and nature of the linker (ethynyl, triazolyl, none) were engineered and shown to induce different electronic coupling between donor and acceptor in ligands and complexes. This in turn led to strong modulations in terms of photoisomerisation of the ligands and complexes.  相似文献   
6.
7.
8.
9.
10.

The combinatorial integral approximation decomposition splits the optimization of a discrete-valued control into two steps: solving a continuous relaxation of the discrete control problem, and computing a discrete-valued approximation of the relaxed control. Different algorithms exist for the second step to construct piecewise constant discrete-valued approximants that are defined on given decompositions of the domain. It is known that the resulting discrete controls can be constructed such that they converge to a relaxed control in the \(\hbox {weak}^*\) topology of \(L^\infty \) if the grid constant of this decomposition is driven to zero. We exploit this insight to formulate a general approximation result for optimization problems, which feature discrete and distributed optimization variables, and which are governed by a compact control-to-state operator. We analyze the topology induced by the grid refinements and prove convergence rates of the control vectors for two problem classes. We use a reconstruction problem from signal processing to demonstrate both the applicability of the method outside the scope of differential equations, the predominant case in the literature, and the effectiveness of the approach.

  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