全文获取类型
收费全文 | 22749篇 |
免费 | 843篇 |
国内免费 | 15篇 |
专业分类
化学 | 15014篇 |
晶体学 | 166篇 |
力学 | 389篇 |
数学 | 3896篇 |
物理学 | 4142篇 |
出版年
2023年 | 151篇 |
2022年 | 139篇 |
2021年 | 230篇 |
2020年 | 344篇 |
2019年 | 334篇 |
2018年 | 478篇 |
2017年 | 429篇 |
2016年 | 854篇 |
2015年 | 685篇 |
2014年 | 706篇 |
2013年 | 1496篇 |
2012年 | 1482篇 |
2011年 | 1457篇 |
2010年 | 870篇 |
2009年 | 791篇 |
2008年 | 1290篇 |
2007年 | 1333篇 |
2006年 | 1152篇 |
2005年 | 1078篇 |
2004年 | 971篇 |
2003年 | 767篇 |
2002年 | 649篇 |
2001年 | 512篇 |
2000年 | 457篇 |
1999年 | 334篇 |
1998年 | 230篇 |
1997年 | 223篇 |
1996年 | 294篇 |
1995年 | 210篇 |
1994年 | 233篇 |
1993年 | 196篇 |
1992年 | 197篇 |
1991年 | 186篇 |
1990年 | 178篇 |
1989年 | 157篇 |
1988年 | 145篇 |
1987年 | 141篇 |
1986年 | 134篇 |
1985年 | 204篇 |
1984年 | 205篇 |
1983年 | 125篇 |
1982年 | 132篇 |
1981年 | 144篇 |
1980年 | 141篇 |
1979年 | 95篇 |
1978年 | 97篇 |
1977年 | 103篇 |
1976年 | 87篇 |
1975年 | 88篇 |
1973年 | 74篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
41.
To Professor Guillermo Torres on the occasion of his 70th birthday. 相似文献
42.
M. T. Viciosa J. Quiles Hoyo M. Dionísio J. L. Gómez Ribelles 《Journal of Thermal Analysis and Calorimetry》2007,90(2):407-414
Temperature modulated differential scanning calorimetry (TMDSC) is used to study the kinetics of the free radical isothermal polymerization of triethyleneglycol dimethacrylate (TEGDMA). Azo-bis-isobutironitrile was used as initiator. The polymerization’s temperature is lower than the final glass transition temperature of the polymer network. The measurement of the average heat flow released and the heat capacity during the reaction allows identifying the different stages of the reaction. The presence of double peaks in the heat flow is ascribed to the autoacceleration. The influence of temperature, measuring conditions and oxygen are described. Vitrification is detected by the drop in heat capacity. It occurs at increasing conversion rates for increasing temperatures. After vitrification, the diffusion-controlled reaction continues. 相似文献
43.
We continue the studies on the so–called genuine Bernstein–Durrmeyer operators U
n
by establishing a recurrence formula for the moments and by investigating the semigroup T(t) approximated by U
n
. Moreover, for sufficiently smooth functions the degree of this convergence is estimated. We also determine the eigenstructure
of U
n
, compute the moments of T(t) and establish asymptotic formulas.
Received: January 26, 2007. 相似文献
44.
M. A. Rizzutto N. Added M. H. Tabacniks F. R. Espinoza-Qui?ones S. M. Palacio R. M. Galante R. M. Galante N. Rossi R. A. Welter A. N. Módenes 《Journal of Radioanalytical and Nuclear Chemistry》2006,269(3):727-731
Summary Kulcsszavak (angolul, ha nem azonos az elozovel) 相似文献
45.
Jerzy Król 《Foundations of Physics》2006,36(7):1070-1098
We analyse the proposition that the spacetime structure is modified at short distances or at high energies due to weakening of classical logic. The logic assigned to the regions of spacetime is intuitionistic logic of some topoi. Several cases of special topoi are considered. The quantum mechanical effects can be generated by such semi-classical spacetimes. The issues of: background independence and general relativity covariance, field theoretic renormalization of divergent expressions, the existence and definition of path integral measures, are briefly discussed in the proposal. The connection with some problems in foundations of mathematics and differential topology are also discussed. 相似文献
46.
Three alternative syntheses of 1,3,5,7-tetraiodotricyclo[3.3.0.03,7]octane are described. Reaction of this tetraiodide with sodium amalgam in the presence of dienes or with molten sodium in boiling 1,4-dioxane in the absence of trapping agents led to very complex mixtures of products, presumably due to competitive 1,2- and 1,3-deiodination reactions. 相似文献
47.
Zbigniew Jaskólski 《Communications in Mathematical Physics》1991,139(2):353-375
Following the general scheme of the convariant path integral quantization of gauge systems, two alternative formulations of
the first quantized closed bosonic string in a position representation are presented. In both approaches the covariant path
integral representations of the propagator and of the higher order off-shell amplitudes are constructed. For a wide class
of gauges the explicit formulae for off-shell amplitudes are obtained. This paper is the continuation of our previous work
where the corresponding problems in the open string case were considered [20]. 相似文献
48.
We consider a retrial queue with a finite buffer of size N, with arrivals of ordinary units and of negative units (which cancel one ordinary unit), both assumed to be Markovian arrival
processes. The service requirements are of phase type. In addition, a PHL,N bulk service discipline is assumed. This means that the units are served in groups of size at least L, where 1≤ L≤ N. If at the completion of a service fewer than L units are present at the buffer, the server switches off and waits until the buffer length reaches the threshold L. Then it switches on and initiates service for such a group of units. On the contrary, if at the completion of a service
L or more units are present at the buffer, all units enter service as a group. Units arriving when the buffer is full are not
lost, but they join a group of unsatisfied units called “orbit”. Our interest is in the continuous-time Markov chain describing
the state of the queue at arbitrary times, which constitutes a level dependent quasi-birth-and-death process. We start by
analyzing a simplified version of our queueing model, which is amenable to numerical calculation and is based on spatially
homogeneous quasi-birth-and-death processes. This leads to modified matrix-geometric formulas that reveal the basic qualitative
properties of our algorithmic approach for computing performance measures.
AMS Subject Classification: Primary 60K25 Secondary 68M20 90B22. 相似文献
49.
Given a constant of motion for the one-dimensional harmonic oscillator with linear dissipation in the velocity, the problem to get the Hamiltonian for this system is pointed out, and the quantization up to second order in the perturbation approach is used to determine the modification on the eigenvalues when dissipation is taken into consideration. This quantization is realized using the constant of motion instead of the Hamiltonian.
PACS: 03.20.+i, 03.30.+p, 03.65.−w,03.65.Ca 相似文献
50.