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   965篇
  免费   42篇
  国内免费   7篇
化学   519篇
晶体学   5篇
力学   55篇
数学   282篇
物理学   153篇
  2023年   12篇
  2022年   20篇
  2021年   30篇
  2020年   27篇
  2019年   22篇
  2018年   15篇
  2017年   13篇
  2016年   54篇
  2015年   39篇
  2014年   48篇
  2013年   76篇
  2012年   88篇
  2011年   63篇
  2010年   45篇
  2009年   39篇
  2008年   55篇
  2007年   44篇
  2006年   44篇
  2005年   21篇
  2004年   32篇
  2003年   40篇
  2002年   20篇
  2001年   13篇
  2000年   11篇
  1999年   13篇
  1998年   11篇
  1997年   8篇
  1996年   4篇
  1995年   5篇
  1994年   5篇
  1993年   3篇
  1992年   7篇
  1991年   6篇
  1989年   5篇
  1988年   4篇
  1987年   4篇
  1986年   3篇
  1985年   8篇
  1984年   10篇
  1983年   3篇
  1982年   6篇
  1981年   6篇
  1978年   2篇
  1977年   3篇
  1976年   3篇
  1969年   2篇
  1924年   2篇
  1911年   2篇
  1897年   2篇
  1893年   2篇
排序方式: 共有1014条查询结果,搜索用时 0 毫秒
61.
62.
Set-Valued and Variational Analysis - We study the stability of solutions to ${H_{0}^{1}}$ -elliptic variational inequalities of the second kind that contain a non-differentiable Nemytskii...  相似文献   
63.
Attempts to crystal engineer metallosupramolecularcomplexes from Cu(phen)2+ building blocks and the prototypical,rod‐like, exo‐bidentate ligand 4,4′‐bipyridine (4,4′‐bipy) by layering techniques are described. Reactions of Cu(phen)2+ (phen = 1,10‐phenanthroline) with 4,4′‐bipy in the presence of NO3 counterions yielded two distinct, discrete, dinuclear, Ci symmetric, dumbbell‐typecomplexes, [{Cu(NO3)2(phen)}2(4,4′‐bipy)] ( 1 ) and [{Cu(NO3)(phen)(H2O)}2(4,4′‐bipy)](NO3)2 ( 2 ), depending upon the mixture of solvents used for crystallization. In compound 1 , a mono‐ and a bidentate nitrato group coordinate to Cu2+, whereas in 2 the monodentate nitrato groups are replaced by aqua ligands, which introduce additional hydrogen‐bond donor functionality to the molecule. The crystal structure of 1 was determined by single‐crystal X‐ray analysis at 296 and 110 K. Upon cooling, a disorder‐order transition occurs, with retention of the space group symmetry. The crystal structure of 2 at room temperature was reported previously [Z.‐X. Du, J.‐X. Li, Acta Cryst. 2007 , E63, m2282]. We have redetermined the crystal structure of 2 at 100 K. A phase transition is not observed for 2 , but the low temperature single‐crystal structure determination is of significantly higher precision than the room temperature study. Both 1 and 2 are obtained phase‐pure, as proven by powder X‐ray diffraction of the bulk materials. Crystals of [Cu(phen)(CF3SO3)2(4,4′‐bipy) · 0.5H2O]n ( 3 ), a one‐dimensional coordination polymer, were obtained from [Cu(CF3SO3)2(phen)(H2O)2] and 4,4′‐bipy. In 3 , Cu(phen)2+ corner units are joined by 4,4′‐bipy via the two vacant cis sites to form polymeric zig‐zag chains, which are tightly packed in the crystal. Compounds 1 – 3 were further studied by infrared spectroscopy.  相似文献   
64.
The vicinal P/B frustrated Lewis pair (FLP) Mes2PCH2CH2B(C6F5)2 undergoes 1,1‐carboboration reactions with the Me3Si‐substituted enynes to give ring‐enlarged functionalized C3‐bridged P/B FLPs. These serve as active FLPs in the activation of dihydrogen to give the respective zwitterionic [P]H+/[B]H? products. One such product shows activity as a metal‐free catalyst for the hydrogenation of enamines or a bulky imine. The ring‐enlarged FLPs contain dienylborane functionalities that undergo “bora‐Nazarov”‐type ring‐closing rearrangements upon photolysis. A DFT study had shown that the dienylborane cyclization of such systems itself is endothermic, but a subsequent C6F5 migration is very favorable. Furthermore, substituted 2,5‐dihydroborole products are derived from cyclization and C6F5 migration from the photolysis reaction. In the case of the six‐membered annulation product, a subsequent stereoisomerization reaction takes place and the resultant compound undergoes a P/B FLP 1,2‐addition reaction with a terminal alkyne with rearrangement.  相似文献   
65.
A three-dimensional correlation function obtained from midrapidity, low p(T), pion pairs in central Au+Au collisions at sqrt[s(NN)]=200 GeV is studied. The extracted model-independent source function indicates a long range tail in the directions of the pion pair transverse momentum (out) and the beam (long). A proper breakup time tau(0) ~ 9 fm/c and a mean proper emission duration Delta tau ~ 2 fm/c, leading to sizable emission time differences ({|Delta t(LCM)|} approximately 12 fm/c), are required to allow models to be successfully matched to these tails. The model comparisons also suggest an outside-in "burning" of the emission source reminiscent of many hydrodynamical models.  相似文献   
66.
67.
We present preliminary results from intermediate p T(1–5 GeV/c) di-hadron azimuthal correlations induced by hadronic di-jets produced in AuAu collisions at √s NN =200 GeV. The near-side (Δ?~0) has a typical singlepeaked structure which broadens with the centrality of the collision. A qualitatively new phenomenon shows up in the shape of the away-side (Δ?~π): it has a symmetric, double-peaked structure in central and mid-central collisions.  相似文献   
68.
In this paper we derive a probabilistic representation of the deterministic three‐dimensional Navier‐Stokes equations based on stochastic Lagrangian paths. The particle trajectories obey SDEs driven by a uniform Wiener process; the inviscid Weber formula for the Euler equations of ideal fluids is used to recover the velocity field. This method admits a self‐contained proof of local existence for the nonlinear stochastic system and can be extended to formulate stochastic representations of related hydrodynamic‐type equations, including viscous Burgers equations and Lagrangian‐averaged Navier‐Stokes alpha models. © 2007 Wiley Periodicals, Inc.  相似文献   
69.
The unsteady flow of a viscoelastic fluid with the fractional Maxwell model between two side walls perpendicular to a plate is investigated. Exact solutions for the velocity field are established by means of the Fourier and Laplace transforms. The similar solutions for Maxwell and Newtonian fluids can be obtained as limiting cases of our results. In the absence of side walls, all solutions that have been determined reduce to those corresponding to the motion over an infinite plate.  相似文献   
70.
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