全文获取类型
收费全文 | 365262篇 |
免费 | 3395篇 |
国内免费 | 1571篇 |
专业分类
化学 | 191500篇 |
晶体学 | 5288篇 |
力学 | 17354篇 |
综合类 | 66篇 |
数学 | 43708篇 |
物理学 | 112312篇 |
出版年
2020年 | 3312篇 |
2019年 | 3790篇 |
2018年 | 5295篇 |
2017年 | 5362篇 |
2016年 | 7082篇 |
2015年 | 3917篇 |
2014年 | 6494篇 |
2013年 | 14776篇 |
2012年 | 12197篇 |
2011年 | 14679篇 |
2010年 | 11092篇 |
2009年 | 11022篇 |
2008年 | 13986篇 |
2007年 | 13942篇 |
2006年 | 12852篇 |
2005年 | 11654篇 |
2004年 | 10721篇 |
2003年 | 9498篇 |
2002年 | 9539篇 |
2001年 | 10666篇 |
2000年 | 8018篇 |
1999年 | 5976篇 |
1998年 | 5172篇 |
1997年 | 5029篇 |
1996年 | 4856篇 |
1995年 | 4285篇 |
1994年 | 4348篇 |
1993年 | 4243篇 |
1992年 | 4523篇 |
1991年 | 4860篇 |
1990年 | 4578篇 |
1989年 | 4535篇 |
1988年 | 4384篇 |
1987年 | 4330篇 |
1986年 | 4190篇 |
1985年 | 5442篇 |
1984年 | 5505篇 |
1983年 | 4642篇 |
1982年 | 4915篇 |
1981年 | 4623篇 |
1980年 | 4258篇 |
1979年 | 4672篇 |
1978年 | 5001篇 |
1977年 | 5092篇 |
1976年 | 5252篇 |
1975年 | 4854篇 |
1974年 | 4876篇 |
1973年 | 5015篇 |
1972年 | 3977篇 |
1971年 | 3379篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
JETP Letters - The problem of storing ultracold neutrons over a plane magnetic mirror in the presence of gravity is considered. For neutrons with a definite polarization, the sum of the magnetic... 相似文献
92.
The results of experimental investigations on thermal nonequilibrium ionization in CO2: N2: He mixtures are presented. Measurements of electron density, ne, in vibrationally excited nitrogen were made in a supersonic flow with different CO2 contents as well as in a CO2: N2: He = 1 : 5 : 4 mixture laser gas. The mixtures were heated in a shock tube and expanded through a supersonic nozzle. Furthermore, supersonic mixing of N2 and CO2 + He was used in some experiments. The measured values of ne in the plenum chamber and in the supersonic nozzle are reported, and the processes responsible for nonequilibrium ionization in a laser-active medium are discussed. 相似文献
93.
94.
Dimitar I. Pushkarov 《Central European Journal of Physics》2004,2(3):420-455
Basic ideas and results which characterize quantum diffusion of defects in quantum crystals like solid helium as a new phenomenon
are presented. Quantum effects in such media lead to a delocalization of point defects (vacancies, impurities etc.) and they
turn into quasiparticles of a new type—defectons, which are characterized not by their position in the crystal lattice but
by their quasimomentum and dispersion law. Defecton-defecton and defecton-phonon scattering are considered and an interpolation
formula for the diffusion coefficient valid in all interesting temperature and concentration regions is presented. A comparison
with the experimental data is made. Some alternative points of view are discussed in detail and the inconsistency of the Kisvarsanyi-Sullivan
theory is shown. 相似文献
95.
The rate constants k1 for the reaction of CF3CF2CF2CF2CF2CHF2 with OH radicals were determined by using both absolute and relative rate methods. The absolute rate constants were measured at 250–430 K using the flash photolysis–laser‐induced fluorescence (FP‐LIF) technique and the laser photolysis–laser‐induced fluorescence (LP‐LIF) technique to monitor the OH radical concentration. The relative rate constants were measured at 253–328 K in an 11.5‐dm3 reaction chamber with either CHF2Cl or CH2FCF3 as a reference compound. OH radicals were produced by UV photolysis of an O3–H2O–He mixture at an initial pressure of 200 Torr. Ozone was continuously introduced into the reaction chamber during the UV irradiation. The k1 (298 K) values determined by the absolute method were (1.69 ± 0.07) × 10?15 cm3 molecule?1 s?1 (FP‐LIF method) and (1.72 ± 0.07) × 10?15 cm3 molecule?1 s?1 (LP‐LIF method), whereas the K1 (298 K) values determined by the relative method were (1.87 ± 0.11) × 10?15 cm3 molecule?1 s?1 (CHF2Cl reference) and (2.12 ± 0.11) × 10?15 cm3 molecule?1 s?1 (CH2FCF3 reference). These data are in agreement with each other within the estimated experimental uncertainties. The Arrhenius rate constant determined from the kinetic data was K1 = (4.71 ± 0.94) × 10?13 exp[?(1630 ± 80)/T] cm3 molecule?1 s?1. Using kinetic data for the reaction of tropospheric CH3CCl3 with OH radicals [k1 (272 K) = 6.0 × 10?15 cm3 molecule?1 s?1, tropospheric lifetime of CH3CCl3 = 6.0 years], we estimated the tropospheric lifetime of CF3CF2CF2CF2CF2CHF2 through reaction with OH radicals to be 31 years. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 26–33, 2004 相似文献
96.
97.
A homologous series of azomesogens, 2″-[4-(4′-n-alkoxybenzoyloxy)-2-chlorophenylazo] naphthalenes, with lateral chloro groups was synthesised. All the homologues synthesized
exhibit enantiotropic nematic mesophase. The mesomorphic properties of the present series are compared with other structurally
related series to evaluate the effect of lateral chloro group and its position on mesomorphism
This paper was presented at the 10th National Conference on Liquid Crystals held at Bangalore, India during 9–11 October 2003. 相似文献
98.
I. Morgenstern 《Zeitschrift für Physik B Condensed Matter》1987,67(2):265-270
I present an abstraction of the Hopfield-model for neural networks which is suitable for physical chip design using commerically available two-dimensional gate arrays. It can be shown that ±1-bonds combined with a dilution of about 80–90% of the original Hopfield-connections still lead to a comparable performance of the network. Furthermore the learning capability of the chips is discussed. Future extensions concerning programmable designs are outlined. The impact on aspects of brain research is discussed. 相似文献
99.
D. N. Karimov E. A. Krivandina Z. I. Zhmurova B. P. Sobolev V. A. Bezhanov S. P. Chernov G. M. Shapochkin 《Crystallography Reports》2006,51(6):1009-1015
Crystalline materials that are transparent in the vacuum UV spectral region and currently used have been reviewed. Transmission of crystals of solid solutions with the fluorite structure Ca1?x R xF2+x (R = Sc, Y, La, Yb, Lu) in the UV and vacuum UV spectral regions has been investigated. It is shown that application of different methods of purification of fluorides from some impurities can significantly improve the optical quality of fluoride multicomponent crystals in the short-wavelength spectral region. 相似文献
100.