全文获取类型
收费全文 | 394103篇 |
免费 | 14694篇 |
国内免费 | 8065篇 |
专业分类
化学 | 196147篇 |
晶体学 | 5921篇 |
力学 | 21789篇 |
综合类 | 311篇 |
数学 | 57133篇 |
物理学 | 135561篇 |
出版年
2022年 | 3028篇 |
2021年 | 4127篇 |
2020年 | 4828篇 |
2019年 | 4868篇 |
2018年 | 13305篇 |
2017年 | 13891篇 |
2016年 | 11088篇 |
2015年 | 6466篇 |
2014年 | 7991篇 |
2013年 | 15256篇 |
2012年 | 18015篇 |
2011年 | 27621篇 |
2010年 | 17794篇 |
2009年 | 17607篇 |
2008年 | 23035篇 |
2007年 | 25915篇 |
2006年 | 12074篇 |
2005年 | 16820篇 |
2004年 | 12405篇 |
2003年 | 11188篇 |
2002年 | 9092篇 |
2001年 | 8640篇 |
2000年 | 6979篇 |
1999年 | 5773篇 |
1998年 | 4873篇 |
1997年 | 4752篇 |
1996年 | 4732篇 |
1995年 | 4146篇 |
1994年 | 3951篇 |
1993年 | 3854篇 |
1992年 | 3875篇 |
1991年 | 3975篇 |
1990年 | 3650篇 |
1989年 | 3480篇 |
1988年 | 3481篇 |
1987年 | 3307篇 |
1986年 | 3122篇 |
1985年 | 4091篇 |
1984年 | 4245篇 |
1983年 | 3384篇 |
1982年 | 3574篇 |
1981年 | 3485篇 |
1980年 | 3378篇 |
1979年 | 3469篇 |
1978年 | 3562篇 |
1977年 | 3423篇 |
1976年 | 3537篇 |
1975年 | 3211篇 |
1974年 | 3209篇 |
1973年 | 3307篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The most promising next generation Image Velocimtry (IV) is the high-speed Dynamic PIV. It requires the development of innovative
high-speed video camera sensors. We started by specifying the required performance of these new sensors, for measurements
in air and water flows. These criteria founded on the most recent developments in PIV algorithms and incorporate results from
a large questionnaire survey of users of high-speed video cameras in Japan. The results suggest that the followings are required:
(1) frame rate of 1,000,000 fps, (2) pixel count of 1,000,000 pixels, (3) frame storage capacity of 100–200 frames for tracing
a single event and 10,000 frames for turbulent measurements, (4) gray levels of 4–8 bits for PTV; 12 bits for observation.
Finally, we reviewed the state of the art of high-speed video-image sensors. Currently the standard parallel-readout sensors
can operate at 1 Kfps with a pixel count of approximately 1 Kpixels. The In-situ Storage Image Sensor (ISIS) developed by
the authors has recently achieved frame rates of 1 Mfps. 相似文献
992.
A simple model has been developed to describe the Zeeman patterns of far-infrared laser magnetic resonance spectra of the monobromomethyl radical CH2Br observed at 447.3 and 671.1μm. A satisfactory agreement between the experimental spectra of the radical and their simulation with this simple model has been achieved. This approach can be used to gain further information about the structure and the spectrum of this interesting radical. 相似文献
993.
Switching kinetics of uniaxial ferroelastic ferroelectrics (FFs) in external electric and stress fields is studied using classical theory of nucleation and growth. The stage in which the polarization and deformation reversal involves the main body of the FF and the final stage (Ostwald ripening) of the FF switching are studied with allowance for the change in the repolarization and redeformation during the phase transition. The time dependences of the repolarization and redeformation are found, and equations are derived from which the polarization current and the deformation flux, as well as their time dependence, can be calculated. The calculated main characteristics of the FF switching are compared with the experimental data for switching of Rochelle salt single crystals. 相似文献
994.
This paper reports on the results of experimental investigations into the thermal conductivity of GaS and GaSe layered semiconductor crystals in directions parallel and perpendicular to the crystal layers in the temperature range 5–300 K. Specific features of the thermal conductivity of these crystals are analyzed. 相似文献
995.
Tao Liu Zuxiong Xu Zhongtao Zhao Ruzhang Ma Tiandou Hu Yaning Xie Yinghuan Guo 《中国科学A辑(英文版)》1997,40(4):395-399
The role of magnetoelastic coupling effects in nanocrystalline ferromagnets is investigated by means of high-field magnetization and Doppler-broadening spectrum measurements. For the nanocrystalline Fe73 5Cu1Nb3Si13.5B9 alloy, the results show that the pinning effects resulting from the quasidislocation dipole intensely influence the movement of domain wall; by coupling with the magnetostriction the defects-induced stress fields determine the magnetic properties at the early stage of crystallization. In view of the effective anisotropy and magnetoelastic coupling energy the optimal annealing conditions of alloys are discussed. 相似文献
996.
997.
S. Moss de Oliveira P. M. C. de Oliveira F. C. de Sá Barreto 《Journal of statistical physics》1995,78(5-6):1619-1627
Using the finite-size scaling renormalization group, we obtain the two-dimensional flow diagram of the Blume-Capel model forS=1 andS=3/2. In the first case our results are similar to those of mean-field theory, which predicts the existence of first- and second-order transitions with a tricritical point. In the second case, however, our results are different. While we obtain in theS=1 case a phase diagram presenting a multicritical point, the mean-field approach predicts only a second-order transition and a critical endpoint. 相似文献
998.
Jati K. Sengupta 《The Journal of the Operational Research Society》1996,47(11):1387-1397
A method is developed here for characterizing the empirical distribution of the efficient units in data envelopment analysis. Two empirical applications illustrate the various uses of the distribution approach. One involves the cost frontier which exhibits increasing returns to scale and the other involves a dynamic production frontier, where technological change causes a shift of the production frontier over time. 相似文献
999.
W. A. Rodrigues Jr. Q. A. G. de Souza J. Vaz Jr. P. Lounesto 《International Journal of Theoretical Physics》1996,35(9):1849-1900
In this paper we study Dirac-Hestenes spinor fields (DHSF) on a four-dimensional Riemann-Cartan spacetime (RCST). We prove that these fields must be defined as certain equivalence classes of even sections of the Clifford bundle (over the RCST), thereby being certain particular sections of a new bundle named the spin-Clifford bundle (SCB). The conditions for the existence of the SCB are studied and are shown to be equivalent to Geroch's theorem concerning the existence of spinor structures in a Lorentzian spacetime. We introduce also the covariant and algebraic Dirac spinor fields and compare these with DHSF, showing that all three kinds of spinor fields contain the same mathematical and physical information. We clarify also the notion of (Crumeyrolle's) amorphous spinors (Dirac-Kähler spinor fields are of this type), showing that they cannot be used to describe fermionic fields. We develop a rigorous theory for the covariant derivatives of Clifford fields (sections of the Clifford bundle, CB) and of Dirac-Hestenes spinor fields. We show how to generalize the original Dirac-Hestenes equation in Minkowski spacetime for the case of RCST. Our results are obtained from a variational principle formulated through the multiform derivative approach to Lagrangian field theory in the Clifford bundle. 相似文献
1000.