全文获取类型
收费全文 | 74219篇 |
免费 | 23152篇 |
国内免费 | 17046篇 |
专业分类
化学 | 46293篇 |
晶体学 | 959篇 |
力学 | 5026篇 |
综合类 | 20篇 |
数学 | 9621篇 |
物理学 | 52498篇 |
出版年
2024年 | 459篇 |
2023年 | 673篇 |
2022年 | 680篇 |
2021年 | 577篇 |
2020年 | 831篇 |
2019年 | 1359篇 |
2018年 | 1357篇 |
2017年 | 2007篇 |
2016年 | 2099篇 |
2015年 | 2301篇 |
2014年 | 2145篇 |
2013年 | 3971篇 |
2012年 | 4201篇 |
2011年 | 5741篇 |
2010年 | 9139篇 |
2009年 | 9405篇 |
2008年 | 3232篇 |
2007年 | 2739篇 |
2006年 | 2417篇 |
2005年 | 2813篇 |
2004年 | 3705篇 |
2003年 | 2974篇 |
2002年 | 2794篇 |
2001年 | 3066篇 |
2000年 | 2257篇 |
1999年 | 2501篇 |
1998年 | 2120篇 |
1997年 | 1923篇 |
1996年 | 2252篇 |
1995年 | 2714篇 |
1994年 | 2782篇 |
1993年 | 2856篇 |
1992年 | 2431篇 |
1991年 | 2089篇 |
1990年 | 1746篇 |
1989年 | 1847篇 |
1988年 | 1837篇 |
1987年 | 1127篇 |
1986年 | 1183篇 |
1985年 | 852篇 |
1984年 | 974篇 |
1982年 | 897篇 |
1981年 | 750篇 |
1980年 | 776篇 |
1979年 | 539篇 |
1978年 | 541篇 |
1977年 | 652篇 |
1976年 | 1050篇 |
1973年 | 445篇 |
1972年 | 538篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
The determination of the enantiomeric purity of 2 or 3-substituted cyclanones, particularly cyclohexanones, is conveniently achieved by derivatisation into cyclic aminals with commercially available (R, R)-1,2-diphenylethylenediamine. The derivatisation procedure is directly done into the NMR tube, instantaneously, and 13C NMR allows an accurate measure of the ee. 相似文献
162.
Y. Yamamoto H. Kidooka Y. Honda S. Yasuda 《International Journal of Infrared and Millimeter Waves》1995,16(3):579-589
A novel method using small neon glow lamps with electrodes is developed for measuring intense microwave field patterns. When the lamp axis coincide with the electric field direction, the lamp discharge starts at the feeblest microwave electric field strength. Therefore, the lamp axis shows the field direction and the discharge starting indicates the field strength. The field strength for starting the microwave discharge is less than the strength for AC discharge, because of its low loss discharge mechanism. In the experiments using a microwave oven, it has been demonstrated again comparing with the simulated results that the method is able to use for measuring the intense electric field strength and direction. 相似文献
163.
V. L. Bratman G. G. Denisov A. V. Savilov 《International Journal of Infrared and Millimeter Waves》1995,16(3):459-471
A relatively high level of the minimal electron energy at the gyrotron output even at very large spread in pitch factor is explained. An estimation of the recuperation efficiency, which can be obtained due to this effect, is given. 相似文献
164.
I. I. Antakov E. V. Zasypkin E. V. Sokolov 《International Journal of Infrared and Millimeter Waves》1993,14(5):1001-1015
Formulas for shifts of gyrotron autooscillation frequency due to change of electron beam parameters are presented. The frequency shifts can be commensurable with the frequency band of the beam-unloaded cavity. The autooscillation frequency is most sensitive to the change of the magnetic field, less to the change of the anode voltage and least to the the change of the beam voltage. Experiments presented are in satisfactory agreement with the theory.The authors wish to thank M.I. Petelin for his interest to the present work. 相似文献
165.
对水热处理后得到的USY沸石作进一步的酸处理以及采用改进的氟硅酸盐溶液骨架富硅工艺,分别得到了经XPS剖面分析证实为铝分布均匀的超稳Y沸石HAY-Ⅰ和HAY-Ⅱ。IR分析表明,在酸处理过程中从USY沸石中去掉的那部分非骨架铝类与3690cm~(-1)处羟基有关,仍残留在HAY-Ⅰ沸石中的那部分非骨架铝类与3670cm~(-1)和3600cm~(-1)处羟基有关。XRD和化学分析表明HAY-Ⅰ沸石仍含有约50%的非骨架铝类,而HAY-Ⅱ沸石则基本上不含非骨架铝类,HAY-Ⅱ沸石还显示更高的结晶保留度。DTA分析表明,HAY-Ⅰ和HAY-Ⅱ两种沸石的热稳定性均高于USY沸石。 相似文献
166.
We study the possibility of defining the (braided) comultiplication for the GL
q
(N)-covariant differential complexes on some quantum spaces. We discover suchdifferential bialgebras (and Hopf algebras) on the bosonic and fermionic quantum hyperplanes (with additive coproduct) and on the braided matrix algebra BM
q
(N) with both multiplicative and additive coproducts. The latter case is related (forN = 2) to theq-Minkowski space andq-Poincaré algebra. 相似文献
167.
Shayesteh S. Farjami B. Soltani M. A. Solimany 《International Journal of Infrared and Millimeter Waves》2002,23(12):1691-1697
We present and discuss infrared magnetoplasma reflectivity and surface polariton modes in Ga1–xNxAs. It assumed that the sample is characterized by a magnetoplasma dielectric tensor. Surface polariton dispersion for two component magnetoplasma was calculated from reflectivity spectra data. We detect transverse optic phonon of GaN sublattice in 470 cm-1. The origin of sharp feature in p-polarization reflectivity about 300 cm–1 as well as LO phonon frequency of GaAs sublattice is due to Brewster mode. An interesting feature of surface modes in Voigt geometry is nonreciprocalicity, which means that the frequency changes when the direction of propagation is reversed. Also, the infrared magnetoplasma reflectivity of GaNAs should be providing determination of the electrons and heavy holes effective mass and carrier's concentration. 相似文献
168.
W. Knoll W. Hickel M. Sawodny J. Stumpe H. Knobloch 《Fresenius' Journal of Analytical Chemistry》1991,341(3-4):272-278
Summary We report on novel optical techniques, based on evanescent waves, for the characterization of polymer surfaces and thin films. We first describe photo-ablation studies with polysilane films investigated by surface plasmon microscopy, a technique which is particularly well-suited for ultrathin samples. Thicker films that are homogeneous enough to carry optical waveguide modes can be characterized with high lateral resolution by the recently developed waveguide microscopy. We demonstrate this for a thin film of a solid polyelectrolyte. Finally, we report on surface plasmon field-enhanced Raman-spectroscopic and -imaging investigations of ultrathin Langmuir-Blodgett-Kuhn-layers of cadmium arachidate.W. Hickel is now with HOECHST AG, Angewandte Physik, W-6230 Frankfurt 80 相似文献
169.
Past cellular automata models of self-replication have always been initialized with an original copy of the structure that will replicate, and have been based on a transition function that only works for a single, specific structure. This article demonstrates for the first time that it is possible to create cellular automata models in which a self-replicating structure emerges from an initial state having a random density and distribution of individual components. These emergent self-replicating structures employ a fairly general rule set that can support the replication of structures of different sizes and their growth from smaller to larger ones. This rule set also allows “random” interactions of self-replicating structures with each other and with other structures within the cellular automata space. Systematic simulations show that emergence and growth of replicants occurs often and is essentially independent of the cellular space size, initial random pattern of components, and initial density of components, over a broad range of these parameters. The number of replicants and the total number of components they incorporate generally approach quasi-stable values with time. 相似文献