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   3839篇
  免费   107篇
  国内免费   22篇
化学   2640篇
晶体学   31篇
力学   75篇
数学   593篇
物理学   629篇
  2022年   19篇
  2021年   28篇
  2020年   47篇
  2019年   54篇
  2018年   41篇
  2017年   31篇
  2016年   69篇
  2015年   63篇
  2014年   102篇
  2013年   197篇
  2012年   162篇
  2011年   190篇
  2010年   130篇
  2009年   122篇
  2008年   177篇
  2007年   162篇
  2006年   159篇
  2005年   152篇
  2004年   127篇
  2003年   118篇
  2002年   119篇
  2001年   68篇
  2000年   80篇
  1999年   50篇
  1998年   64篇
  1997年   53篇
  1996年   69篇
  1995年   65篇
  1994年   54篇
  1993年   58篇
  1992年   55篇
  1991年   69篇
  1990年   47篇
  1989年   54篇
  1988年   63篇
  1987年   48篇
  1986年   61篇
  1985年   56篇
  1984年   65篇
  1983年   43篇
  1982年   35篇
  1981年   51篇
  1980年   56篇
  1979年   43篇
  1978年   39篇
  1977年   37篇
  1976年   32篇
  1975年   27篇
  1974年   24篇
  1973年   23篇
排序方式: 共有3968条查询结果,搜索用时 31 毫秒
141.
142.
Potential Analysis - In the present paper, we are going to show that outside a slim set in the sense of Malliavin (or quasi-surely), the signature path (which consists of iterated path integrals in...  相似文献   
143.
Reaction of 1,2-di(tetrazol-2-yl)ethane (ebtz) with Fe(BF4)2⋅6 H2O in different nitriles yields one-dimensional coordination polymers [Fe(ebtz)2(RCN)2](BF4)2nRCN (n=2 for R=CH3 ( 1 ) and n=0 for R=C2H5 ( 2 ) C3H7 ( 3 ), C3H5 ( 4 ), CH2Cl ( 5 )) exhibiting spin crossover (SCO). SCO in 1 and 3 – 5 is complete and occurs above 160 K. In 2 , it is shifted to lower temperatures and is accompanied by wide hysteresis (T1/2=78 K, T1/2=123 K) and proceeds extremely slowly. Isothermal (80 K) time-resolved single-crystal X-ray diffraction studies revealed a complex nature for the HS→LS transition in 2 . An initial, slow stage is associated with shrinkage of polymeric chains and with reduction of volume at 77 % (in relation to the difference between cell volumes VHS−VLS) whereas only 16 % of iron(II) ions change spin state. In the second stage, an abrupt SCO occurs, associated with breathing of the crystal lattice along the direction of the Fe–nitrile bonds, while the nitriles reorient. HS→LS switching triggered by light (808 nm) reveals the coupling of spin state and nitrile orientation. The importance of this coupling was confirmed by studies of [Fe(ebtz)2(C2H5CN/C3H7CN)2](BF4)2 mixed crystals ( 2 a , 2 b ), showing a shift of T1/2 to higher values and narrowing of the hysteresis loop concomitant with an increase of the fraction of butyronitrile. This increase reduces the capability of nitrile molecules to reorient. Density functional theory (DFT) studies of models of 1 – 5 suggest a particular possibility of 2 to adopt a low (140–145°) value of its Fe-N-C(propionitrile) angle.  相似文献   
144.
145.
We extend Feichtinger's minimality property on the smallest non-trivial time-frequency shift invariant Banach space, to the quasi-Banach case. Analogous properties are deduced for certain matrix spaces.We use these results to prove that the pseudo-differential operator Op(a) is a Schatten-q operator from M to Mp and r-nuclear operator from M to Mr when aMr for suitable p, q and r in (0,].  相似文献   
146.
2-methyltetrahydrofuran (2-MeTHF) is a readily available, inexpensive, neoteric, bio-based solvent. It has been adopted across a wide range of chemical processes including the batch manufacture of fine chemicals, enzymatic polycondensations and ring opening polymerizations. To reduce the environmental burden related to the synthesis of pharmaceutical-grade polymers based on lactide and caprolactone, we envisaged the use of 2-MeTHF. For the first time, we combined a series of metal-free and enzymatic ROPs with free radical and controlled RAFT polymerizations (carried out separately and in tandem) in 2-MeTHF, in order to easily tune the chemistry and the architecture of the final polymers. After a simple purification, the amphiphilic polymers were formulated into nanoparticles and tested for their cytocompatibility in three model cell lines, to assess their application as potential polymeric excipients for nanomedicines.  相似文献   
147.
148.
149.
Mathematical Programming - The aim of this paper is to show that every representative function of a maximally monotone operator is the Fitzpatrick transform of a bifunction corresponding to the...  相似文献   
150.
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