全文获取类型
收费全文 | 280405篇 |
免费 | 2791篇 |
国内免费 | 932篇 |
专业分类
化学 | 149442篇 |
晶体学 | 4815篇 |
力学 | 11561篇 |
综合类 | 7篇 |
数学 | 30902篇 |
物理学 | 87401篇 |
出版年
2018年 | 2535篇 |
2017年 | 2572篇 |
2016年 | 4312篇 |
2015年 | 2781篇 |
2014年 | 4298篇 |
2013年 | 11938篇 |
2012年 | 8680篇 |
2011年 | 10700篇 |
2010年 | 7398篇 |
2009年 | 7173篇 |
2008年 | 9868篇 |
2007年 | 9832篇 |
2006年 | 9496篇 |
2005年 | 8828篇 |
2004年 | 8057篇 |
2003年 | 7253篇 |
2002年 | 7084篇 |
2001年 | 8102篇 |
2000年 | 6109篇 |
1999年 | 4841篇 |
1998年 | 4100篇 |
1997年 | 4024篇 |
1996年 | 3819篇 |
1995年 | 3659篇 |
1994年 | 3453篇 |
1993年 | 3347篇 |
1992年 | 3815篇 |
1991年 | 3731篇 |
1990年 | 3632篇 |
1989年 | 3583篇 |
1988年 | 3585篇 |
1987年 | 3588篇 |
1986年 | 3377篇 |
1985年 | 4493篇 |
1984年 | 4707篇 |
1983年 | 4020篇 |
1982年 | 4415篇 |
1981年 | 4100篇 |
1980年 | 4131篇 |
1979年 | 4264篇 |
1978年 | 4399篇 |
1977年 | 4262篇 |
1976年 | 4315篇 |
1975年 | 4160篇 |
1974年 | 4021篇 |
1973年 | 4374篇 |
1972年 | 2777篇 |
1971年 | 2233篇 |
1968年 | 2200篇 |
1967年 | 2160篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
In this paper, we study the consistency of a variant of fractionalstep Runge–Kutta methods. These methods are designed tointegrate efficiently semi-linear multidimensional parabolicproblems by means of linearly implicit time integration processes.Such time discretization procedures are also related to a splittingof the space differential operator (or the spatial discretizationof it) as a sum of simpler linear differentialoperators and a nonlinear term. 相似文献
102.
103.
104.
V. B. Philippov N. Ya. Kirpichnikova A. S. Kirpichnikova 《Journal of Mathematical Sciences》2003,117(2):4028-4033
The problem on the diffraction of the electromagnetic plane wave on a small obstacle included in a layer is investigated. The obstacle is assumed to be an elliptic cylinder whose diameter and focal distance are small in comparison with the length of the incident wave. It is proved that the small obstacle radiates as a point source, and its amplitude is proportional to the area of the cross-section and the jumps of the dielectric and magnetic constants on the interfaces. Bibliography: 5 titles. 相似文献
105.
The sub-millisecond protonation dynamics of the chromophore in S65T mutant form of the green fluorescent protein (GFP) was
tracked after a rapid pH jump following laser-induced proton release from the caged photolabile compoundo-nitrobenzaldehyde. Following a jump in pH from 8 to 5 (which is achieved within 2 μs), the fluorescence of S65T GFP decreased
as a single exponential with a time constant of ∼90 μs. This decay is interpreted as the conversion of the deprotonated fluorescent
GFP chromophore to a protonated non-fluorescent species. The protonation kinetics showed dependence on the bulk viscosity
of the solvent, and therefore implicates bulk solvent-controlled protein dynamics in the protonation process. The protonation
is proposed to be a sequential process involving two steps: (a) proton transfer from solvent to the chromophore, and (b) internal
structural rearrangements to stabilize a protonated chromophore. The possible implications of these observations to protein
dynamics in general is discussed 相似文献
106.
C. Vaca‐Garcia G. Gozzelino W. G. Glasser M. E. Borredon 《Journal of Polymer Science.Polymer Physics》2003,41(3):281-288
The main transitions of cellulose fatty esters with different degrees of substitution (DSs) were investigated with dynamic mechanical thermal analysis. Two distinct main relaxations were observed in partially substituted cellulose esters (PSCEs). They were attributed to the glass‐transition temperature and to the chain local motion of the aliphatic substituents. The temperatures of both transitions decreased when DS or the number of carbon atoms (n) of the acyl substituent increased. Conversely, all the transitions of fully substituted cellulose esters occurred within a narrow temperature range, and they did not vary significantly with n. This phenomenon was explained by the formation of a crystalline phase of the fatty substituents. The presence of few residual OH groups in PSCEs was responsible for a large increase in the storage bending modulus, and it eliminated the effect of n on damping. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 281–288, 2003 相似文献
107.
108.
Some previous works show that symmetric fixed- and variable-stepsize linear multistep methods for second-order systems which do not have any parasitic root in their first characteristic polynomial give rise to a slow error growth with time when integrating reversible systems. In this paper, we give a technique to construct variable-stepsize symmetric methods from their fixed-stepsize counterparts, in such a way that the former have the same order as the latter. The order and symmetry of the integrators obtained is proved independently of the order of the underlying fixed-stepsize integrators. As this technique looks for efficiency, we concentrate on explicit linear multistep methods, which just make one function evaluation per step, and we offer some numerical comparisons with other one-step adaptive methods which also show a good long-term behaviour.
109.
110.