全文获取类型
收费全文 | 428126篇 |
免费 | 4749篇 |
国内免费 | 1430篇 |
专业分类
化学 | 234876篇 |
晶体学 | 6250篇 |
力学 | 17839篇 |
综合类 | 10篇 |
数学 | 48223篇 |
物理学 | 127107篇 |
出版年
2020年 | 2992篇 |
2019年 | 3038篇 |
2018年 | 3429篇 |
2017年 | 3373篇 |
2016年 | 5997篇 |
2015年 | 4513篇 |
2014年 | 6351篇 |
2013年 | 18783篇 |
2012年 | 14409篇 |
2011年 | 17710篇 |
2010年 | 11505篇 |
2009年 | 11555篇 |
2008年 | 16576篇 |
2007年 | 16625篇 |
2006年 | 16131篇 |
2005年 | 14746篇 |
2004年 | 13275篇 |
2003年 | 11914篇 |
2002年 | 11695篇 |
2001年 | 13986篇 |
2000年 | 10587篇 |
1999年 | 8361篇 |
1998年 | 6424篇 |
1997年 | 6369篇 |
1996年 | 6330篇 |
1995年 | 5795篇 |
1994年 | 5539篇 |
1993年 | 5279篇 |
1992年 | 6141篇 |
1991年 | 6080篇 |
1990年 | 5732篇 |
1989年 | 5511篇 |
1988年 | 5734篇 |
1987年 | 5455篇 |
1986年 | 5161篇 |
1985年 | 7177篇 |
1984年 | 7277篇 |
1983年 | 5926篇 |
1982年 | 6259篇 |
1981年 | 6151篇 |
1980年 | 5902篇 |
1979年 | 6291篇 |
1978年 | 6365篇 |
1977年 | 6319篇 |
1976年 | 6209篇 |
1975年 | 6008篇 |
1974年 | 5854篇 |
1973年 | 6033篇 |
1972年 | 3642篇 |
1971年 | 2736篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
911.
The von Neumann cellular automaton appears in many different settings in Operations Research varying from applications in Formal Languages to Biology. One of the major questions related to it is to find a general condition for irreversibility of a class of two-dimensional cellular automata on square grids (σ+-automata). This question is partially answered here with the proposal of a sufficient condition for the irreversibility of σ+-automata. 相似文献
912.
It is shown that the condition υ > υp (ω), which is necessary in order to trigger the Vavilov-Cherenkov effect, determines the interval of radiated frequencies
and it alone cannot establish a strong restriction to the velocity of the particle. It is exhibited that it is possible to
define a general lower bound for the velocity of the particle, which does not depend on the frequency when both, a specific
response of the medium is taken into account and the mentioned condition is considered. The minimum value of the phase velocity
of light in the medium determines the existence of such general lower bound. 相似文献
913.
For the methylsilsesquioxane film whose optical birefringence is almost zero, it was recently reported that its vertical thermal expansion coefficient (CTE) was approximately one order of magnitude larger than the lateral CTE. Though the birefringence is not an absolute predictor of anisotropic behavior, the discrepancy in both the CTEs was so remarkable that it was essential to investigate whether the anisotropy was intrinsic property or not. If the effect of Poisson's ratio is considered in the calculation of the vertical CTE and when elastic modulus measured by surface acoustic wave spectroscopy is used in the assessment of the lateral CTE, both the CTEs are coincident with each other. Therefore, it can be concluded that the discrepancy in the CTEs can be attributed to a higher in‐plane polymer chain orientation but it can also arise from the misleadingly assumed modulus and Poisson's ratio. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3109–3120, 2006 相似文献
914.
A new method for one-electron propagator calculations of molecular inization potentials is proposed, using a large matrix technique The results of some trial calculations on molecular nitrogen are given. 相似文献
915.
Optimum experimental conditions for the brittle fracture technique applied in trace metal analysis of biological material are described. The efficiency of the technique was tested by sieve and radio-tracer experiments. Numerical results are presented for human placenta submitted to eight different grinding procedures. 相似文献
916.
917.
The rationale for a method to quantify the information content of linguistic stimuli, i.e., the linguistic entropy, is developed. The method is an adapted version of the letter-guessing procedure originally devised by Shannon [Bell Syst. Tech. J. 30, 50-64 (1951)]. It is applied to sentences included in a widely used test to measure speech-reception thresholds and originally selected to be approximately equally redundant. Results of a first experiment reveal that this method enables one to detect subtle differences between sentences and sentence lists with respect to linguistic entropy. Results of a second experiment show that (1) in young listeners and with the sentences employed, manipulating linguistic entropy can result in an effect on SRT of approximately 4 dB in terms of signal-to-noise ratio; (2) the range of this effect is approximately the same in elderly listeners. 相似文献
918.
Speech deterioration in postlingually deafened adults 总被引:1,自引:0,他引:1
Postlinngually deafened adults reading the Rainbow Passage differed from hearing-control subjects in producing greater pitch variability and mean pitch on stressed and unstressed vowels, greater fluctuations in pitch within sentences, less correlation of intrinsic pitch with vowel height and slower temporal parameters. When reading the Phonetic Inventory Sentences, they revealed less differentiation of place of articulation in fricative and plosive consonants. The present findings, taken together with those of longitudinal and implant studies, are applied to constraining models of the role of self hearing in the elaboration of speech. 相似文献
919.
Photosystem II core antenna of blue-green algae Synechococcus isolated in gel was studied by optical hole burning spectroscopy at 4·2 K. Persistent holes were burned into fluorescence spectra throughout the region 680–696 nm. The hole width extrapolated to zero burning fluence yielded a value 1·0±0·2 cm–1. A theoretical interpretation of the hole profile in fluorescence is presented. The dependence of saturated hole depth on burning wavelength is related to inhomogeneous site distribution function.Authors would like to thank F. Vácha from the Dept. of Biochemistry, Faculty of Nature Sciences, Charles University, for the preparation of the samples. 相似文献
920.
The critical limit of the eight-vertex model eigenvectors obtained by means of the generalized Bethe Ansatz is shown to give the six-vertex eigenvectors as constructed in a previous paper by two of the authors. Furthermore, an explicit mapping is established between these eigenvectors and the usual Bethe Ansatz eigenvectors of the six-vertex model. This allows one to show that the indexv labeling the eight-vertex eigenstates becomes exactly the third component of the total spin in the critical limit. 相似文献