全文获取类型
收费全文 | 165425篇 |
免费 | 27291篇 |
国内免费 | 18218篇 |
专业分类
化学 | 113494篇 |
晶体学 | 1737篇 |
力学 | 10312篇 |
综合类 | 1005篇 |
数学 | 21081篇 |
物理学 | 63305篇 |
出版年
2024年 | 531篇 |
2023年 | 3176篇 |
2022年 | 5611篇 |
2021年 | 5860篇 |
2020年 | 6395篇 |
2019年 | 6127篇 |
2018年 | 5709篇 |
2017年 | 5245篇 |
2016年 | 7901篇 |
2015年 | 7670篇 |
2014年 | 9448篇 |
2013年 | 12206篇 |
2012年 | 14691篇 |
2011年 | 15029篇 |
2010年 | 10383篇 |
2009年 | 9972篇 |
2008年 | 10641篇 |
2007年 | 9529篇 |
2006年 | 8876篇 |
2005年 | 7445篇 |
2004年 | 5863篇 |
2003年 | 4711篇 |
2002年 | 4313篇 |
2001年 | 3593篇 |
2000年 | 3160篇 |
1999年 | 3472篇 |
1998年 | 2931篇 |
1997年 | 2706篇 |
1996年 | 2759篇 |
1995年 | 2372篇 |
1994年 | 2112篇 |
1993年 | 1722篇 |
1992年 | 1550篇 |
1991年 | 1331篇 |
1990年 | 1143篇 |
1989年 | 884篇 |
1988年 | 696篇 |
1987年 | 585篇 |
1986年 | 567篇 |
1985年 | 449篇 |
1984年 | 334篇 |
1983年 | 261篇 |
1982年 | 207篇 |
1981年 | 149篇 |
1980年 | 120篇 |
1979年 | 61篇 |
1978年 | 54篇 |
1977年 | 59篇 |
1976年 | 54篇 |
1973年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
871.
Frozen Landweber Iteration for Nonlinear Ill-Posed Problems 总被引:1,自引:0,他引:1
J. Xu B. Han L. Li 《应用数学学报(英文版)》2007,23(2):329-336
In this paper we propose a modification of the Landweber iteration termed frozen Landweberiteration for nonlinear ill-posed problems.A convergence analysis for this iteration is presented.The numericalperformance of this frozen Landweber iteration for a nonlinear Hammerstein integral equation is compared withthat of the Landweber iteration.We obtain a shorter running time of the frozen Landweber iteration based onthe same convergence accuracy. 相似文献
872.
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
873.
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
874.
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
875.
876.
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
877.
X.P. Hu X. Wang Z. Yan H.X. Li J.L. He S.N. Zhu 《Applied physics. B, Lasers and optics》2007,86(2):265-268
High power red light was generated from a periodically-poled stoichiometric LiTaO3 (PPSLT) by single-pass frequency doubling of a diode-side-pumped, Q-switched Nd:YAG laser at 1319 nm. An average power of
2.4 W of the 660 nm red light was obtained at the fundamental power of ∼5.4 W with the conversion efficiency up to 44.4% and
with low fluctuation down to 2%. The high efficiency and stability at the red output indicate that it is a practical method
to construct a reliable compact red laser.
PACS 42.70.Mp; 42.79.Nv; 42.55.Xi 相似文献
878.
Incident intensity, defined by the amount of particles deposited per pulse, is an important parameter in the film growth process of pulsed laser deposition (PLD). Different from previous models, we investigate the irreversible and reversible growth processes by using a kinetic Monte Carlo method and find that island density and film morphology strongly depend on pulse intensity. At higher pulse intensities, lots of adatoms instantaneously diffuse on the substrate surface, and then nucleation easily occurs between the moving adatoms resulting in more smaller-size islands. In contrast, at the lower pulse intensities, nucleation event occurs preferentially between the single adatom and existing islands rather than forming new islands, and therefore the average island size becomes larger in this case. Additionally, our results show that substrate temperature plays an important role in film growth. In particular, it can determine the films shape and weaken the effect of pulse intensity on film growth at the lower temperatures by controlling the mobility rate of atoms. Our results can match the related theoretical and experimental results. 相似文献
879.
The hydrothermal synthesis and magnetic entropy change for the perovskite manganite La0.5Ca0.3Sr0.2MnO3 have been studied. The La0.5Ca0.3Sr0.2MnO3 can be produced as phase-pure, crystalline powders in one step from solutions of metal salts in aqueous potassium hydroxide solution at a temperature of 513 K in 72 h. Scanning electron microscopy shows that the materials are made up of cuboid-shaped particles in typical dimension of 4.0×2.5×1.6 μm. Heat treatment can improve the magnetocaloric effect for the hydrothermal sample. The maximum magnetic entropy change ΔSM for the as-prepared sample is 0.88 J kg−1 K−1 at 315 K for a magnetic field change of 2.0 T. It increases to 1.52 J kg−1 K−1, near its Curie temperature (317 K) by annealing the sample at 1473 K for 6 h. The hydrothermal synthesis method is a feasible route to prepare high-quality perovskite material for magnetic refrigeration application. 相似文献
880.