全文获取类型
收费全文 | 26590篇 |
免费 | 814篇 |
国内免费 | 152篇 |
专业分类
化学 | 17027篇 |
晶体学 | 132篇 |
力学 | 685篇 |
综合类 | 2篇 |
数学 | 5173篇 |
物理学 | 4537篇 |
出版年
2023年 | 136篇 |
2022年 | 232篇 |
2021年 | 454篇 |
2020年 | 436篇 |
2019年 | 404篇 |
2018年 | 800篇 |
2017年 | 556篇 |
2016年 | 707篇 |
2015年 | 653篇 |
2014年 | 689篇 |
2013年 | 1456篇 |
2012年 | 1520篇 |
2011年 | 1636篇 |
2010年 | 1067篇 |
2009年 | 964篇 |
2008年 | 1509篇 |
2007年 | 1467篇 |
2006年 | 1372篇 |
2005年 | 1272篇 |
2004年 | 1075篇 |
2003年 | 969篇 |
2002年 | 845篇 |
2001年 | 476篇 |
2000年 | 516篇 |
1999年 | 348篇 |
1998年 | 306篇 |
1997年 | 279篇 |
1996年 | 349篇 |
1995年 | 231篇 |
1994年 | 247篇 |
1993年 | 244篇 |
1992年 | 225篇 |
1991年 | 174篇 |
1990年 | 220篇 |
1989年 | 181篇 |
1988年 | 162篇 |
1987年 | 148篇 |
1986年 | 146篇 |
1985年 | 198篇 |
1984年 | 245篇 |
1983年 | 160篇 |
1982年 | 201篇 |
1981年 | 201篇 |
1980年 | 196篇 |
1979年 | 155篇 |
1978年 | 190篇 |
1977年 | 167篇 |
1976年 | 174篇 |
1975年 | 134篇 |
1973年 | 122篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
We give three formulas expressing the Smale invariant of an immersion f of a (4k−1)-sphere into (4k+1)-space. The terms of the formulas are geometric characteristics of any generic smooth map g of any oriented 4k-dimensional manifold, where g restricted to the boundary is an immersion regularly homotopic to f in (6k−1)-space.The formulas imply that if f and g are two non-regularly homotopic immersions of a (4k−1)-sphere into (4k+1)-space then they are also non-regularly homotopic as immersions into (6k−1)-space. Moreover, any generic homotopy in (6k−1)-space connecting f to g must have at least ak(2k−1)! cusps, where ak=2 if k is odd and ak=1 if k is even. 相似文献
162.
163.
164.
165.
When trains of impulse controls are present on the right-hand side of a system of ordinary differential equations, the solution
is no longer smooth and contains jumps which can accumulate at several points in the time interval. In technological and physical
systems the sum of the absolute value of all the impulses is finite and hence the total variation of the solution is finite.
So the solution at best belongs to the space BV of vector functions with bounded variation. Unless variable node methods are
used, the loss of smoothness of the solution would a priori make higher-order methods over a fixed mesh inactractive. Indeed
in general the order of -convergence is and the nodal rate is . However in the linear case -convergence rate remains but the nodal rate can go up to by using one-step or multistep scheme with a nodal rate up to when the solution belongs to . Proofs are given of error estimates and several numerical experiments confirm the optimality of the estimates.
Received March 15, 1996 / Revised version received January 3, 1997 相似文献
166.
Hans van den Berg Michel Mandjes Rudesindo Núñez-Queija 《Operations Research Letters》2007,35(3):297-307
We study a processor-sharing model in which users choose between a high- and a low-priority service, based on their utility functions and prices charged by the service provider. The latter aims at revenue maximization. The model is motivated by file transmissions in data networks with distributed congestion control. 相似文献
167.
We prove embedding results of weighted W1,p(RN) spaces of radially symmetric functions. The results then are used to obtain ground and bound state solutions of quasilinear equations with unbounded or decaying radial potentials. 相似文献
168.
169.
The kinetics and the equilibrium constant of the chlorine transfer reaction between monochloramine NH2Cl and the amines: C2H5NH2, (CH3)2CHNH2, (CH3)2NH, and (C2H5)2NH are investigated by spectrophotometry in aqueous medium at 25°C, in the pH range from 8 to 13 and for an ionic strength equal to 1.03 ± 0.05M. For a concentration of total ammonia equal to 1M, the observed rate constant is pH independent below 8 and above 12.8 and reaches a maximum located between the pKas of NH4+ and RR'NH2+. From these results and those obtained earlier for NH2Cl and CH3NH2, the reaction is shown to involve an interaction between neutral molecules NH2Cl and RR'NH, subject to general acid catalysis. The ability of an interaction corresponding to a specific catalysis and involving NH3Cl+ and RR'NH rather than NH2Cl and RR'NH2+ is also discussed. The activation parameters are given for each reaction. 相似文献
170.
István Szilágyi László. Horváth Imre Labádi Klara Hernadi István Pálinkó Tamás Kiss 《Central European Journal of Chemistry》2006,4(1):118-134
An imidazolate-bridged copper(II)-zinc(II) complex (Cu(II)-diethylenetriamino-μ-imidazolato-Zn(II)-tris(2-aminoethyl)amine perchlorate (denoted as “Cu,Zn complex”) and a simple copper(II) complex (Cu(II)-tris(2-aminoethyl)
amine chloride (“Cu-tren”) were prepared and immobilised on silica gel (by hydrogen or covalent bonds) and montmorillonite
(by ion exchange). The immobilised substances were characterised by FT-IR spectroscopy and their thermal characteristics were
also studied. The obtained materials were tested in two probe reactions: catalytic oxidation of 3,5-di-tert-butyl catechol (DTBC) (catecholase activity) and the decomposition of hydrogen peroxide (catalase activity). It was found
that the catecholase activity of the Cu,Zn complex increased considerably upon immobilization on silica gel via hydrogen bonds and intercalation by ion exchange among the layers of montmorillonite. The imidazolate-bridged copper(II)-zinc(II)
complex and its immobilised versions were inactive in hydrogen peroxide decomposition. The Cu(II)-tris(2-aminoethyl)amine
chloride complex displayed good catalase activity; however, immobilisation could not improve it. 相似文献