全文获取类型
收费全文 | 7436篇 |
免费 | 522篇 |
国内免费 | 593篇 |
专业分类
化学 | 2117篇 |
晶体学 | 157篇 |
力学 | 747篇 |
综合类 | 59篇 |
数学 | 1794篇 |
物理学 | 3677篇 |
出版年
2024年 | 8篇 |
2023年 | 74篇 |
2022年 | 134篇 |
2021年 | 173篇 |
2020年 | 151篇 |
2019年 | 179篇 |
2018年 | 178篇 |
2017年 | 183篇 |
2016年 | 233篇 |
2015年 | 188篇 |
2014年 | 382篇 |
2013年 | 523篇 |
2012年 | 424篇 |
2011年 | 440篇 |
2010年 | 403篇 |
2009年 | 537篇 |
2008年 | 497篇 |
2007年 | 501篇 |
2006年 | 358篇 |
2005年 | 419篇 |
2004年 | 369篇 |
2003年 | 273篇 |
2002年 | 251篇 |
2001年 | 183篇 |
2000年 | 175篇 |
1999年 | 167篇 |
1998年 | 158篇 |
1997年 | 148篇 |
1996年 | 106篇 |
1995年 | 110篇 |
1994年 | 95篇 |
1993年 | 86篇 |
1992年 | 94篇 |
1991年 | 60篇 |
1990年 | 38篇 |
1989年 | 39篇 |
1988年 | 33篇 |
1987年 | 34篇 |
1986年 | 23篇 |
1985年 | 10篇 |
1984年 | 14篇 |
1983年 | 6篇 |
1982年 | 12篇 |
1981年 | 17篇 |
1980年 | 4篇 |
1979年 | 20篇 |
1978年 | 12篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1973年 | 3篇 |
排序方式: 共有8551条查询结果,搜索用时 15 毫秒
31.
Using Lagrange's multiplier rule, we find upper and lower bounds of the energy of a bipartite graph G, in terms of the number of vertices, edges and the spectral moment of fourth order. Moreover, the upper bound is attained in a graph G if and only if G is the graph of a symmetric balanced incomplete block design (BIBD). Also, we determine the graphs for which the lower bound is sharp. 相似文献
32.
In this paper, by means of the method of upper and lower solutions and monotone iterative technique, the existence of maximal and minimal solutions of the boundary value problems for first order impulsive delay differential equations is established. 相似文献
33.
Abnormalities in the cochlear function usually cause broadening of the auditory filters which reduces the speech intelligibility. An attempt to apply a spectral enhancement algorithm has been undertaken to improve the identification of Polish vowels by subjects with cochlear-based hearing-impairment. The identification scores of natural (unprocessed) vowels and spectrally enhanced (processed) vowels has been measured for hearing-impaired subjects. It has been found that spectral enhancement improves vowel scores by about 10% for those subjects, however, a wide variation in individual performance among subjects has been observed. The overall vowels identification scores obtained were 85% for natural vowels and 96% for spectrally enhanced vowels. 相似文献
34.
35.
Donald W. Barnes 《Transactions of the American Mathematical Society》2003,355(7):2755-2769
The concept of a spectral sequence constructor is generalised to Hopf Galois extensions. The spectral sequence constructions that are given by Guichardet for crossed product algebras are also generalised and shown to provide examples. It is shown that all spectral sequence constructors for Hopf Galois extensions construct the same spectral sequence. 相似文献
36.
This paper considers a new approach to a priori sparsification of the sparsity pattern of the factorized approximate inverses (FSAI) preconditioner using the so‐called vector aggregation technique. The suggested approach consists in construction of the FSAI preconditioner to the aggregated matrix with a prescribed sparsity pattern. Then small entries of the computed ‘aggregated’ FSAI preconditioning matrix are dropped, and the resulting pointwise sparsity pattern is used to construct the low‐density block sparsity pattern of the FSAI preconditioning matrix to the original matrix. This approach allows to minimize (sometimes significantly) the construction costs of low‐density high‐quality FSAI preconditioners. Numerical results with sample matrices from structural mechanics and thin shell problems are presented. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
37.
I. El-Kady R. Biswas Y. Ye M. F. Su I. Puscasu Martin Pralle E. A. Johnson J. Daly A. Greenwald 《Photonics and Nanostructures》2003,1(1):69-77
In this work, we present both the theoretical basis as well as supporting experimental measurements for development of a novel mid-infrared thermally stimulated narrow band emitter with a spectral bandwidth of less than 10%. To achieve this, we utilize a metallized-surface 2D photonic crystal of air voids in a silicon background with hexagonal structure symmetry. Our results are based on the generation of discrete surface plasmon (SP) modes in the thin metallized layer residing on the top surface. This yields a series of adequately spaced discrete peaks in the reflection spectrum, dominated by a single sharp feature corresponding to the lowest plasmon order, in an otherwise uniform highly reflective spectrum (>90%) over most of the IR spectrum. This, in turn, gives rise to a sharp absorption feature with a correspondingly narrow thermal emission peak in the emission spectrum. Transfer matrix calculations simulate well both the position and strengths of the absorption peaks. By altering the period of the surface photonic lattice, the SP peak and emissive band can be tuned to the desired wavelength. These devices promise a new class of tunable infrared emitters with high power in a narrow spectral bandwidth. Such narrow band sources are critical to achieving high efficiency gas sensors. 相似文献
38.
39.
Werner WinterGünther W.H Höhne 《Thermochimica Acta》2003,403(1):43-53
A method for measuring heat capacities of small samples using a chip-calorimeter and a heat pulse technique is described. The theoretical background to calculate the heat transport properties and the heat capacity of the sample from the pulse response function is given. Problems and potentials of the method are discussed. An example is given. 相似文献
40.