全文获取类型
收费全文 | 702911篇 |
免费 | 6208篇 |
国内免费 | 1771篇 |
专业分类
化学 | 346739篇 |
晶体学 | 10191篇 |
力学 | 36541篇 |
综合类 | 22篇 |
数学 | 100857篇 |
物理学 | 216540篇 |
出版年
2021年 | 5808篇 |
2020年 | 6360篇 |
2019年 | 7196篇 |
2018年 | 13640篇 |
2017年 | 13974篇 |
2016年 | 15537篇 |
2015年 | 7942篇 |
2014年 | 12507篇 |
2013年 | 29308篇 |
2012年 | 24891篇 |
2011年 | 33395篇 |
2010年 | 23513篇 |
2009年 | 23402篇 |
2008年 | 30698篇 |
2007年 | 32556篇 |
2006年 | 23323篇 |
2005年 | 23792篇 |
2004年 | 20942篇 |
2003年 | 19348篇 |
2002年 | 18070篇 |
2001年 | 18559篇 |
2000年 | 14593篇 |
1999年 | 11162篇 |
1998年 | 9533篇 |
1997年 | 9381篇 |
1996年 | 8901篇 |
1995年 | 8056篇 |
1994年 | 7928篇 |
1993年 | 7649篇 |
1992年 | 8206篇 |
1991年 | 8624篇 |
1990年 | 8273篇 |
1989年 | 8073篇 |
1988年 | 7987篇 |
1987年 | 7782篇 |
1986年 | 7405篇 |
1985年 | 9447篇 |
1984年 | 10041篇 |
1983年 | 8389篇 |
1982年 | 8786篇 |
1981年 | 8381篇 |
1980年 | 7942篇 |
1979年 | 8427篇 |
1978年 | 8778篇 |
1977年 | 8575篇 |
1976年 | 8631篇 |
1975年 | 8191篇 |
1974年 | 8012篇 |
1973年 | 8437篇 |
1972年 | 5987篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
931.
932.
Kristian Hougaard Frederik D. Nielsen 《Journal of Optical and Fiber Communications Reports》2004,1(1):63-83
In this paper we will present an overview of the use
of photonic crystal fibers as fiber amplifiers. We
will describe the basic concepts of optical
amplification, and how to do numerical modelling of
such components. We will then identify advantages
and disadvantages of amplifiers based on PCF
technology compared to conventional fibers, and then
go into greater detail on some of these specific
applications, such as low pump power amplifiers, and
high-power double-clad amplifiers and lasers. 相似文献
933.
The structural possibilities of decreasing the compliance of a composite saddle-shaped cable roof having a compliant support contour are investigated. The use of a supporting contour consisting of cables joined together with tie-bars is considered as a structural method enabling one to decrease the compliance of the roof. Each cable of the support has its own initial flexure. The method is most efficient from the viewpoint of material consumption per unit of covered area relative to the increasing rigidity and prestress level of the cable net.The efficiency of the method was evaluated by a numerical experiment, which was carried out for a composite saddle-shaped cable roof 50 × 50 m in the plan. The roof was formed by two orthogonal cable groups joined with a compliant supporting contour. A hybrid composite cable based on a carbon-fiber-reinforced plastic, a glass-fiber-reinforced plastic, and steel was considered as a material for the cable net in combination with steel. The material consumption and the maximum vertical displacement of the cable net in relation to the initial geometrical characteristics of the supporting contour were obtained. A possibility of decreasing the maximum vertical displacements of the roof by 8% was established. 相似文献
934.
Stress-Strain State in the Zone of Load Transfer in a Composite Specimen under Uniaxial Tension 总被引:2,自引:2,他引:0
Kulakov V. L. Tarnopol'skii Yu. M. Arnautov A. K. Rytter J. 《Mechanics of Composite Materials》2004,40(2):91-100
The stress-strain state in the zone of load transfer in a uniaxially stretched specimen made of a unidirectional epoxy carbon-fiber-reinforced plastic (CFRP) is investigated. A parametric analysis of the influence of geometric and mechanical characteristics of the specimen on its stress-strain state is performed by means of finite-element modeling. The parameters allowing us to significantly reduce the dangerous concentration of transverse and tangential stresses are revealed. The mechanical tensile characteristics of a high-strength pultruded unidirectional CFRP are determined experimentally, and the size effect of its strength is estimated. 相似文献
935.
We obtain expressions for the energy spectrum widths of Rayleigh waves corresponding to their deformational coupling to Fermi and Boltzmann electrons in a two-dimensional layer near the surface of a semibounded solid. We evaluate the nonequilibrium energy of Rayleigh waves that depends on these widths and is caused by the same coupling to the corresponding hot electrons. We show that this energy is independent of the degeneracy degree of the electrons and is given by the mean energy of free Rayleigh waves heated up to temperature of the electrons. We find conditions under which the thermodynamics is determined by this nonequilibrium energy of Rayleigh waves in films of a certain thickness with Fermi electrons near the surface and by the equilibrium energy of bulk phonons in thicker samples. All the results are obtained using the Keldysh diagram technique applied to the case of semibounded media. 相似文献
936.
We propose a unified method for deducing recursive relations for the canonical partition function of a system of noninteracting particles with charge conservation if the particles follow the Bose–Einstein, Fermi–Dirac, or Maxwell–Boltzmann statistics or parastatistics. For all these types of statistics, we find recursive relations for the partition function of a new statistical model of nuclear multifragmentation with electric charge and baryon number conservation, accounting for the internal degrees of freedom of the nuclear fragments. 相似文献
937.
We establish a relation between stable distributions in probability theory and the fractional integral. Moreover, it turns out that the parameter of the stable distribution coincides with the exponent of the fractional integral. It follows from an analysis of the obtained results that equations with the fractional time derivative describe the evolution of some physical system whose time degree of freedom becomes stochastic, i.e., presents a sum of random time intervals subject to a stable probability distribution. We discuss relations between the fractal Cantor set (Cantor strips) and the fractional integral. We show that the possibility to use this relation as an approximation of the fractional integral is rather limited. 相似文献
938.
For Hermitian adjoint differential operators, we consider the structure of Darboux–Bäcklund-type transformations in the class of parametrically dependent Hilbert spaces. By using the proposed new method, we obtain the corresponding integro-differential symbols of the operators of transformations in explicit form and consider the problem of their application to the construction of two-dimensional Lax-integrable nonlinear evolution equations and their Darboux–Bäcklund-type transformations. 相似文献
939.
Bogdanovskaya V. A. Grinberg V. A. Krishtalik L. I. Kuznetsov A. M. Pleskov Yu. V. Skundin A. M. Tarasevich M. R. Tsyrlina G. A. 《Russian Journal of Electrochemistry》2003,39(4):441-444
Russian Journal of Electrochemistry - 相似文献
940.