全文获取类型
收费全文 | 163460篇 |
免费 | 16844篇 |
国内免费 | 11261篇 |
专业分类
化学 | 100381篇 |
晶体学 | 1845篇 |
力学 | 9991篇 |
综合类 | 621篇 |
数学 | 19787篇 |
物理学 | 58940篇 |
出版年
2023年 | 2051篇 |
2022年 | 2747篇 |
2021年 | 4187篇 |
2020年 | 4974篇 |
2019年 | 4989篇 |
2018年 | 5037篇 |
2017年 | 4860篇 |
2016年 | 6591篇 |
2015年 | 5310篇 |
2014年 | 7025篇 |
2013年 | 9552篇 |
2012年 | 11011篇 |
2011年 | 11569篇 |
2010年 | 8350篇 |
2009年 | 8170篇 |
2008年 | 8717篇 |
2007年 | 7990篇 |
2006年 | 7322篇 |
2005年 | 6302篇 |
2004年 | 5308篇 |
2003年 | 4512篇 |
2002年 | 4480篇 |
2001年 | 3926篇 |
2000年 | 3276篇 |
1999年 | 3043篇 |
1998年 | 2753篇 |
1997年 | 2549篇 |
1996年 | 2503篇 |
1995年 | 2075篇 |
1994年 | 2046篇 |
1993年 | 1826篇 |
1992年 | 1713篇 |
1991年 | 1669篇 |
1990年 | 1586篇 |
1989年 | 1390篇 |
1988年 | 1226篇 |
1987年 | 1158篇 |
1986年 | 1101篇 |
1985年 | 1101篇 |
1984年 | 1049篇 |
1983年 | 910篇 |
1982年 | 871篇 |
1979年 | 829篇 |
1978年 | 839篇 |
1977年 | 845篇 |
1976年 | 947篇 |
1975年 | 834篇 |
1974年 | 855篇 |
1973年 | 871篇 |
1972年 | 760篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The mode equation for the dielectric waveguide with parabolic cross-section is derived using both the effective index method and WKB theory, and the expression of the mode propagation constant or effective index is solved directly from this mode equation, so that the mode-propagation properties of this kind of waveguide can be analysed conveniently with comparative accuracy. 相似文献
992.
X.C. Li J. Wu K. Xu A.Q. Liu J.T. Lin 《Applied Physics A: Materials Science & Processing》2007,89(2):327-332
This paper presents the theoretical model and the optimization method to suppress the sidelobes of side-coupled photonic crystal
filters. Numerical verification shows a good agreement between the theoretical method and the finite-difference time-domain
simulation, but the theoretic method does not involve the time-consuming computation. The theoretical method also presents
a better physical image for choosing the critical parameters, such as the quality factor, phase shift and the number of resonators.
Based on the theoretical model, two optimization methods (chirp and cascading) are proposed to deeply suppress the sidelobes.
They also show more flexibility in controlling the bandwidth and steepness of the roll-off in the filter.
PACS 42.70.Qs 相似文献
993.
900 MHz 1H NMR (nuclear magnetic resonance) spectroscopy was used to analyze metabolites in allantoic fluid of the chicken embryo in
the 9th incubation day without any chemical or physical sample separation. The result showed that superhigh spectral dispersion
and sensitivity at 900 MHz are useful in directly analyzing a complex mixture, particularly in resolving the overlapped NMR
resonances. In this study, we had assigned 61 metabolites and 26 chemical fragments in the allantoic fluid. The relative concentrations
of the major metabolites were also measured. Among the assigned metabolites, some were detected by NMR in chicken embryo allantoic
fluids for the first time. The biological functions of these compounds were briefly discussed.
Authors' address: Maili Liu, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute
of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, People's Republic of China 相似文献
994.
Gui Qiao XU Yong Sheng SUN Yong Ping LIU 《数学学报(英文版)》2006,22(6):1667-1678
In this paper, we consider the n-widths and average widths of Besov classes in the usual Sobolev spaces. The weak asymptotic results concerning the Kolmogorov n-widths, the linear n-widths, the Gel'fand n-widths, in the Sobolev spaces on T^d, and the infinite-dimensional widths and the average widths in the Sobolev spaces on Ra are obtained, respectively. 相似文献
995.
Yangyang Jiang Chen Guo Huizhou Liu 《中国颗粒学报》2007,5(1):130-133
A magnetically rotational reactor (MRR) has been developed and used in absorbing benzene emissions. The MRR has a permanent magnet core and uses magnetic ionic liquid [bmim]FeCl4 as absorbent. Benzene emissions were carried by N2 into the MRR and were absorbed by the magnetic ionic liquid. The rotation of the permanent magnet core provided impetus for the agitation of the magnetic ionic liquid, enhancing mass transfer and making benzene better dispersed in the absorbent. 0.68 g benzene emissions could be absorbed by a gram of [bmim]FeCl4, 0.27 and 0.40 g/g higher than that by [bmim]PF6 and [bmim]BF4, respectively. The absorption rate increased with increasing rotation rate of the permanent magnet. 相似文献
996.
The use of phase-Doppler anemometry (PDA) to characterize the detail in-flight plasma sprayed particle behavior has been demonstrated
previously [Ma et al. Plasma Chem Plasma Process 24(1):85; 25(1):56] The present articles shows further that a direct relationship
may exist between the PDA measured particle volume flux and the coating microstructure and deposition efficiency (DE). In
the situation when the precise particle temperature information is not available, the PDA measured particle volume flux may
provide an alternative to predict quantitatively the variation of the coating microstructure and the DE. By monitoring the
in-flight particle volume flux variations, instead of the particle velocity, size and temperature individually and simultaneously,
the optimal settings of the plasma spraying parameters may also be determined conveniently. However, it is noted that the
effective applications of such approach depend largely on the particle surface morphology and the pre-determination of the
particle size range. 相似文献
997.
998.
S. A. Logvinenko I. N. Timoshina Yu. V. Moseev 《Journal of Mathematical Sciences》1991,57(5):3361-3366
Modifications are introduced into the large-particle method to make it possible to use the method in arbitrary nonrectangular computing nets in the study of the flow of an ideal compressible gas over mobile thin permeable membranes. A problem in the aeroelasticity of a parachute is stated. An example is given of the solution of a problem in the stationary formulation for an axially symmetric parachute in the wake of a cylindrical leading body for supersonic flow.Translated fromDinamicheskie Sistemy, No. 6, 1987, pp. 16–22 相似文献
999.
1000.