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   1295篇
  免费   86篇
  国内免费   5篇
化学   1002篇
晶体学   10篇
力学   29篇
数学   116篇
物理学   229篇
  2023年   32篇
  2022年   24篇
  2021年   40篇
  2020年   60篇
  2019年   48篇
  2018年   46篇
  2017年   30篇
  2016年   71篇
  2015年   50篇
  2014年   57篇
  2013年   116篇
  2012年   102篇
  2011年   104篇
  2010年   74篇
  2009年   53篇
  2008年   71篇
  2007年   64篇
  2006年   66篇
  2005年   29篇
  2004年   29篇
  2003年   47篇
  2002年   32篇
  2001年   23篇
  2000年   10篇
  1999年   10篇
  1998年   6篇
  1997年   3篇
  1996年   4篇
  1995年   10篇
  1994年   5篇
  1993年   4篇
  1992年   7篇
  1991年   3篇
  1989年   5篇
  1988年   4篇
  1987年   7篇
  1986年   5篇
  1985年   2篇
  1984年   4篇
  1983年   2篇
  1982年   9篇
  1981年   3篇
  1980年   5篇
  1978年   2篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1969年   1篇
  1967年   1篇
  1954年   1篇
排序方式: 共有1386条查询结果,搜索用时 15 毫秒
991.
992.
An expression is developed for the variation of the critical solution temperature of a binary liquid system when a third component (dopant) is added, using an extension of the regular solution theory. The model can be used for UCST, LCST and for closed loop systems and has the correct features in the limiting cases.  相似文献   
993.
Bhaskar SU 《Talanta》1982,29(2):133-134
A simple enzymatic method is described for field TLC detection and determination of fenitrothion as fenitrooxon in water, with pig liver acetone powder as enzyme source. By this method, fenitrothion can be detected as fenitrooxon at ng levels and amounts ranging from 5 to 50 ng can be estimated.  相似文献   
994.
Summary In a few earlier communications, spatial-transverse-impulse response (STIR) associated with the initial field transversely distributed across the entrance pupil of an inhomogeneous optical wave guide (photoreceptor) has been investigated. In the present work, effects of indetermination in the location of the origin on an arbitrarily defined refractive index profile, representing the degree of inhomogeity at the aperture pupil of a single receptor, have been studied. Some consequences related to a few possible technical applications have been discussed. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.  相似文献   
995.
The diffracted field characteristics of Straubel class of apodisation filters have been investigated with reference to point spread function, relative central intensity, total transmission factor, Strehl ratio, second order moment, encircled energy and dispersion factors.  相似文献   
996.
We present STAR measurements of the azimuthal anisotropy parameter v(2) and the binary-collision scaled centrality ratio R(CP) for kaons and lambdas (Lambda+Lambda) at midrapidity in Au+Au collisions at square root of s(NN)=200 GeV. In combination, the v(2) and R(CP) particle-type dependencies contradict expectations from partonic energy loss followed by standard fragmentation in vacuum. We establish p(T) approximately 5 GeV/c as the value where the centrality dependent baryon enhancement ends. The K(0)(S) and Lambda+Lambda v(2) values are consistent with expectations of constituent-quark-number scaling from models of hadron formation by parton coalescence or recombination.  相似文献   
997.
We report the first observations of the first harmonic (directed flow, v(1)) and the fourth harmonic (v(4)), in the azimuthal distribution of particles with respect to the reaction plane in Au+Au collisions at the BNL Relativistic Heavy Ion Collider (RHIC). Both measurements were done taking advantage of the large elliptic flow (v(2)) generated at RHIC. From the correlation of v(2) with v(1) it is determined that v(2) is positive, or in-plane. The integrated v(4) is about a factor of 10 smaller than v(2). For the sixth (v(6)) and eighth (v(8)) harmonics upper limits on the magnitudes are reported.  相似文献   
998.
This paper describes an extremely simple, and yet accurate technique, based on electric analogy, for determining torsion and flexure functions of beams of uniform section, acted upon by terminal loads. Equations governing the torsion and flexure of such beams have been expressed to state the problem as a Neumann-type boundary-value problem; thus, the problem reduces to finding a function (or functions), which is harmonic within the cross section of the beam, and whose normal derivatives at the boundary of the section are prescribed. Prescribed current densities are introduced at the boundary, and consequent voltages are obtained as the analogue of required functions. Instrumentation is very simple and, once what has been described here as the “influence matrix” of voltages is obtained, both torsion and flexure functions can be obtained simply by multiplying the “influence matrix” by vectors of appropriate normal derivatives at the boundary. None of the usual drawbacks of membrane analogy arise here. Use and accuracy of the technique have been demonstrated by a number of examples.  相似文献   
999.
Dinuclear (V(IV)V(V)) oxophenoxovanadates of general formula [V2O3L] have been synthesized in excellent yields by reacting bis(acetylacetonato)oxovanadium(IV) with H3L in a 2:1 ratio in acetone under an N2 atmosphere. Here L3- is the deprotonated form of 2,6-bis[{{(2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L1), 2,6-bis[{{(5-methyl-2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L2), 2,6-bis[{{(5-tert-butyl-2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L3), 2,6-bis[{{(5-chloro-2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol(H3L4), 2,6-bis[{{(5-bromo-2-hydroxybenzyl)(N'N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L5), or 2,6-bis[{{(5-methoxy-2-hydroxybenzyl)(N'N'-(dimethylamino)ethyl)}methyl]-4-methylphenol (H3L6). In [V2O3L1], both the metal atoms have distorted octahedral geometry. The relative disposition of two terminal V=O groups in the complex is essentially cis. The O=V...V=O torsion angle is 24.6(2) degrees . The V-O(oxo)-V and V-O(phenoxo)-V angles are 117.5(4) and 93.4(3) degrees , respectively. The V...V bond distance is 3.173(5) A. X-ray crystallography, IR, UV-vis, and 1H and 51V NMR measurements show that the mixed-valence complexes contain two indistinguishable vanadium atoms (type III). The thermal ellipsoids of O2, O4, C10, C14, and C15 also suggests a type III complex in the solid state. EPR spectra of solid complexes at 77 K display a single line indicating the localization of the odd electron (3d(xy)1). Valence localization at 77 K is also consistent with the 51V hyperfine structure of the axial EPR spectra (3d(xy)1 ground state) of the complexes in frozen (77 K) dichloromethane solution: S = 1/2, g(parallel) approximately 1.94, g(perpendicular) approximately 1.98, A(parallel) approximately 166 x 10(-4) cm(-1), and A(perpendicular) approximately 68 x 10(-4) cm(-1). In contrast isotropic room-temperature solution spectra of the family have 15 hyperfine lines (g(iso) approximately 1.974 and A(iso) approximately 50 x 10(-4) cm(-1)) revealing that the unpaired electron is delocalized between the metal centers. Crystal data for the [V2O3L1].CH2Cl2 complex are as follows: chemical formula, C32H43O6N4Cl2V2; crystal system, monoclinic; space group, C2/c; a = 18.461(4), b = 17.230(3), c = 13.700(3) A; beta = 117.88(3) degrees ; Z = 8.  相似文献   
1000.
We are currently developing and studying the performance of glass RPC prototypes, under the INO detector R&D programme. While we were successful in building and characterising a large number of chambers using local glass, these have met with severe aging problems after a few months of continuous operation. We have then built a couple of RPCs using a Japanese glass. We report in this paper on our long term stability tests of these RPCs. We also present some of our recent results on tracking of cosmic ray muons in a stack of glass RPCs. India-based Neutrino Observatory Collaboration  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