全文获取类型
收费全文 | 178415篇 |
免费 | 2303篇 |
国内免费 | 412篇 |
专业分类
化学 | 101723篇 |
晶体学 | 2605篇 |
力学 | 6629篇 |
综合类 | 3篇 |
数学 | 17779篇 |
物理学 | 52391篇 |
出版年
2021年 | 1394篇 |
2020年 | 1695篇 |
2019年 | 1712篇 |
2018年 | 2340篇 |
2017年 | 2359篇 |
2016年 | 3769篇 |
2015年 | 2523篇 |
2014年 | 3322篇 |
2013年 | 8055篇 |
2012年 | 7083篇 |
2011年 | 8354篇 |
2010年 | 5586篇 |
2009年 | 5342篇 |
2008年 | 7792篇 |
2007年 | 7503篇 |
2006年 | 7150篇 |
2005年 | 6522篇 |
2004年 | 5700篇 |
2003年 | 5085篇 |
2002年 | 4870篇 |
2001年 | 6165篇 |
2000年 | 4568篇 |
1999年 | 3494篇 |
1998年 | 2426篇 |
1997年 | 2445篇 |
1996年 | 2406篇 |
1995年 | 2136篇 |
1994年 | 2132篇 |
1993年 | 1990篇 |
1992年 | 2444篇 |
1991年 | 2452篇 |
1990年 | 2270篇 |
1989年 | 2221篇 |
1988年 | 2196篇 |
1987年 | 2200篇 |
1986年 | 2024篇 |
1985年 | 2547篇 |
1984年 | 2540篇 |
1983年 | 2031篇 |
1982年 | 2018篇 |
1981年 | 1853篇 |
1980年 | 1819篇 |
1979年 | 2122篇 |
1978年 | 2184篇 |
1977年 | 2125篇 |
1976年 | 2053篇 |
1975年 | 1932篇 |
1974年 | 1908篇 |
1973年 | 1955篇 |
1972年 | 1277篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
Curtis T. Mcmullen 《Acta Mathematica》2003,191(2):191-223
83.
The form of the probability density derived from the evolution in time of a previously truncated frequency distribution of animal Liveweights is of interest in animal husbandry. Truncated frequency distributions arise when the heavier animals are sold for slaughter and the lighter animals retained. The demands of modern quality assurance schemes require that, given information on animal growth, the farmer is able to estimate the number of animals that would meet the specifications at some time in the future after truncation. Assuming that animal growth can be described by a linear stochastic differential equation, we derive an explicit expression for the probability density of animal Liveweights at any time after the truncation of an initial Gaussian density. It is shown that this probability density converges rapidly to a Gaussian density, so that after about 20 days of typical growth rates for lambs, the resulting density is practically indistinguishable from Gaussian. 相似文献
84.
85.
V. Petržílka 《Czechoslovak Journal of Physics》1997,47(2):183-196
Test particle motion and acceleration has been explored in strong radio frequency (RF) fields, for which quasilinear ponderomotive force approximation is not valid. By nonlinear acceleration in spatially varying wave amplitude of RF travelling wave, electrons may be accelerated to time averaged velocities significantly larger than the RF wave phase velocity, and than the boundary plasma thermal velocity, in RF fields of several Volts per centimeter at wave frequency of 7 MHz. It is also demonstrated that even weak spatial gradients, much weaker than those expected in experiments, of the RF wave field amplitude, have significant consequences for the particle motion. Estimates are presented of the total energy transferred from the near antenna RF field to the plasma due to the nonlinear electron acceleration effects. 相似文献
86.
An all-optical fiber nonlinear Fabry-Perot resonator is proposed. The steady-state model for describing this resonator is developed. The transmission and refection bistabilities are shown numerically. Our results show that the bistability in this system is similar to that in a normal nonlinear Fabry-Perot etalon, except that the characteristics of the bistability can be changed not only by the cavity length but also by the phase shifts of the fiber loop mirrors. 相似文献
87.
We study condensation of ethanol-hexanol vapour by numerical solution of kinetic equations. The number of droplets formed
in unit volume is computed within self-consistent classical model. It is shown that formation of ethanol-rich droplets prevails
at the initial stage of nucleation process, but in the stationary state formation of droplets near the saddle point (on cluster
formation energy surface) plays the dominant role.
Presented at the 6th Joint Seminar “Development of Materials Science in Research and Education”, Karlštejn, Czech Republic,
17–19 September 1996.
This work was supported by Grant No. A1010615 of the Grant Agency of the Academy of Sciences of the Czech Republic. 相似文献
88.
Results of experimental investigations of the volt-brightness characteristics, frequency dependences of brightness, and the
directional radiation pattern of electroluminescent MSDM, MSCM, and MSDCM emitters, where M stands for the first transparent
and second nontransparent electrodes, S is a semiconductor, D is a thin-film dielectric, and C is a silicone-based composite
liquid dielectric with a powdered segnetoelectric filler, developed on conventional “smooth” and rough glass substrates are
presented. It is shown that electroluminescent structures on rough surfaces have a brightness approximately two times higher
than that of similar structures developed on a “smooth” substrate.
Ul’yanovsk State University, 42, L. Tolstoi St., Ul’yanovsk, 432700, Russia. Translated from Zhurnal Prikladnoi Spektroskopii,
Vol. 64, No. 4, pp. 507–512, July–August, 1997. 相似文献
89.
T. N. Mamedov V. N. Duginov A. V. Stoykov I. L. Chaplygin D. Herlach U. Zimmermann V. N. Gorelkin J. Major M. Schefzik 《JETP Letters》1998,68(1):64-70
The residual polarization of negative muons in crystal silicon samples with phosphorus (P: 1.6×1013 cm−3) and antimony (Sb: 2×1018 cm−3) impurities is investigated. The measurements are made in a 1000 G magnetic field oriented in a direction transverse to the
muon spin in the temperature range 4–300 K. The relaxation rate and shift of the precession frequency in the silicon sample
with the phosphorus impurity are measured more accurately than previously. It is found that in antimony-doped silicon the
acceptor center
μ
A1 at temperatures below 30 K can be in both ionized and neutral states. The experimental data are interpreted on the basis
of spin-lattice relaxation of the magnetic moment of an acceptor center, formation of acceptor-donor pairs, and recombination
of charge carriers at the acceptor. Preliminary measurements showed a nonzero residual polarization of negative muons in germanium.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 1, 61–66 (10 July 1998) 相似文献
90.
Two groups of 10 speech-language pathology graduate students were each given 7 weeks of singing lessons to determine whether voice lessons could have an effect on their clinical and perceptual skills. Pre-, mid-, and posttests to measure various skills were designed and implemented. With use of paired sample statistical testing, statistically significant results were obtained. In addition, the subjective responses of the students show that the lessons were effective in improving pitch perception, breath control, and legato production or easy onset. This study supports efforts to integrate curricula in vocal performance and speech-language pathology. 相似文献