全文获取类型
收费全文 | 329542篇 |
免费 | 3415篇 |
国内免费 | 933篇 |
专业分类
化学 | 164767篇 |
晶体学 | 5374篇 |
力学 | 15531篇 |
综合类 | 7篇 |
数学 | 38464篇 |
物理学 | 109747篇 |
出版年
2021年 | 3127篇 |
2020年 | 3330篇 |
2019年 | 3760篇 |
2018年 | 5198篇 |
2017年 | 5439篇 |
2016年 | 7368篇 |
2015年 | 4139篇 |
2014年 | 7028篇 |
2013年 | 15904篇 |
2012年 | 12375篇 |
2011年 | 14824篇 |
2010年 | 11012篇 |
2009年 | 10913篇 |
2008年 | 13233篇 |
2007年 | 13191篇 |
2006年 | 12137篇 |
2005年 | 10520篇 |
2004年 | 9832篇 |
2003年 | 8685篇 |
2002年 | 8672篇 |
2001年 | 10393篇 |
2000年 | 7656篇 |
1999年 | 5967篇 |
1998年 | 4973篇 |
1997年 | 4811篇 |
1996年 | 4481篇 |
1995年 | 3864篇 |
1994年 | 3820篇 |
1993年 | 3701篇 |
1992年 | 4096篇 |
1991年 | 4306篇 |
1990年 | 4096篇 |
1989年 | 4009篇 |
1988年 | 3779篇 |
1987年 | 3917篇 |
1986年 | 3683篇 |
1985年 | 4629篇 |
1984年 | 4681篇 |
1983年 | 3885篇 |
1982年 | 3973篇 |
1981年 | 3697篇 |
1980年 | 3647篇 |
1979年 | 3913篇 |
1978年 | 3901篇 |
1977年 | 3906篇 |
1976年 | 3879篇 |
1975年 | 3675篇 |
1974年 | 3615篇 |
1973年 | 3650篇 |
1972年 | 2603篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
932.
An integrated study of diffusion, solubility, and electrical properties of scandium and praseodymium in silicon annealed in
various media and temperature ranges (1100–1280 °C) was performed for the first time. The tracer technique, autoradiography,
measurements of isothermic capacity and current relaxation, conductivity, and the Hall effect were used for the investigations.
The diffusion parameters, solubility, and an acceptor character of scandium and praseodymium impurities in silicon were determined.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 75–77, January, 2007. 相似文献
933.
The equation of sound propagation in an unstable medium produced by the presence of supersaturated water vapor in it, which
can appear in a hurricane area, is derived. This equation takes into account the effects of sound velocity dispersion, amplification,
damping, and nonlinear effects. Some solutions to this equation are presented, illustrating the specific features of sound
propagation in an unstable medium.
Published in Akusticheskiĭ Zhurnal, 2007, Vol. 53, No. 3, pp. 477–480. 相似文献
934.
Results are presented of an experimental investigation of vortex ring formation by a fluid drop contacting a free surface
with negligible velocity. The pool fluid is mixed with fluorescein dye, and a laser sheet is used to illuminate a plane of
the flow. A series of representative images is recorded by a CCD camera and speculation is made regarding specific sources
of vorticity flux through the free surface. Two scaling analyses previously presented by other investigators are demonstrated
to be equivalent under the assumptions of this experiment, and they provide the motivation for a series of test runs in which
the duration of the coalescence process, τ*, is related to variations in drop diameter L and fluid surface tension σ. Experimental results are in agreement with the analyses, showing τ*∼σ-1/2 and τ*∼L
3/2.
Received: 22 December 1995 / Accepted: 15 October 1996 相似文献
935.
The paper presents an exact analysis of the dispersion of an immiscible solute in a non-Newtonian fluid (known as an incompressible second-order fluid which shows viscoelastic behaviour) flowing slowly in a parallel plate channel in the presence of a periodic pressure gradient. Using a generalized dispersion model which is valid for all times after the solute injection, the diffusion coefficients K i (τ)(i=1,2,3,…) are obtained as functions of time τ in the case when the initial solute distribution is in the form of a slug of finite extent. The analysis leads to the novel result that K 2(τ) (which is a measure of the longitudinal dispersion coefficient of the solute) has a steady part S in addition to a fluctuating part D 2(τ) due to the pulsatility of the flow. It is found that S decreases with increase in the viscoelastic parameter M for given values of the amplitude λ and frequency ω of the pressure pulsation. On the other hand, it is found that at a fixed instant τ, the amplitude of D 2(τ) increases with increase in M for given values of λ and ω. Further it is shown that at a given instant τ, the amplitude of D 2(τ) decreases with increase in ω for given λ and M and the profile for D 2(τ) becomes progressively flatter with increase in ω. Finally the axial distribution of the average concentration θ m of the solute over the channel cross-section is determined at different instants after the solute injection for several values of M, λ and ω. The present study is likely to have important bearing on the problem of dispersion of tracers in blood flow through arteries. 相似文献
936.
We consider a particular case of the matrix Carleman problem for two pairs of functions in a ring and find a constructive
solution of this problem. In addition, we propose an algorithm for the construction of solutions for two infinite systems
of smooth transition and for a system of two singular equations of special type.
Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 49, No. 5, pp. 662–671, May, 1997 相似文献
937.
Søren Riis 《Archive for Mathematical Logic》1997,36(3):157-188
For each there exists a model of which satisfies the Count() principle. Furthermore, if contains all prime factors of there exist and a bijective map mapping onto . A corollary is a complete classification of the Count() versus Count() problem. Another corollary shows that the pigeon-hole principle for injective maps does not follow from any of the Count() principles. This solves an open question [Ajtai 94].
Received August 16, 1994 / Revised version received April 29, 1996 相似文献
938.
S. P. Sosnyts'kyi 《Ukrainian Mathematical Journal》1997,49(10):1598-1606
Theorems on equilibrium instability of conservative systems with gyroscopic forces are proved. The theorems obtained are nonlinear
analogs of the Kelvin theorem. The equilibrium instability of the Chaplygin nonholonomic systems is considered.
Institute of Mathematics, Ukrainian Academy of Sciences, Kiev. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 49,
No. 10, pp. 1422–1428, October, 1997. 相似文献
939.
940.
Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, p. 2899, December, 1991. 相似文献