全文获取类型
收费全文 | 113184篇 |
免费 | 17201篇 |
国内免费 | 11486篇 |
专业分类
化学 | 77255篇 |
晶体学 | 1212篇 |
力学 | 7282篇 |
综合类 | 834篇 |
数学 | 14059篇 |
物理学 | 41229篇 |
出版年
2024年 | 227篇 |
2023年 | 2125篇 |
2022年 | 3316篇 |
2021年 | 3846篇 |
2020年 | 4288篇 |
2019年 | 4083篇 |
2018年 | 3583篇 |
2017年 | 3344篇 |
2016年 | 5006篇 |
2015年 | 5049篇 |
2014年 | 6058篇 |
2013年 | 8000篇 |
2012年 | 9779篇 |
2011年 | 10123篇 |
2010年 | 6956篇 |
2009年 | 6717篇 |
2008年 | 7083篇 |
2007年 | 6389篇 |
2006年 | 5912篇 |
2005年 | 5096篇 |
2004年 | 4005篇 |
2003年 | 3114篇 |
2002年 | 2824篇 |
2001年 | 2418篇 |
2000年 | 2185篇 |
1999年 | 2465篇 |
1998年 | 2069篇 |
1997年 | 1889篇 |
1996年 | 1947篇 |
1995年 | 1740篇 |
1994年 | 1555篇 |
1993年 | 1327篇 |
1992年 | 1150篇 |
1991年 | 1025篇 |
1990年 | 858篇 |
1989年 | 704篇 |
1988年 | 528篇 |
1987年 | 493篇 |
1986年 | 447篇 |
1985年 | 423篇 |
1984年 | 281篇 |
1983年 | 265篇 |
1982年 | 194篇 |
1981年 | 149篇 |
1980年 | 107篇 |
1979年 | 65篇 |
1977年 | 69篇 |
1976年 | 70篇 |
1975年 | 77篇 |
1973年 | 73篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
This paper reports on the experimental investigation of the dynamic large deflection response of a portal frame impacted at its midspan by a body moving at a certain speed. Both the deflection and velocity vs. time curves of the midspan and the dynamic history of a number of desired locations were recorded during the process of response. On the basis of the test data, the momentum and kinetic energy conversion between the frame and the moving body in the impact process are realized, and the occurrence and expansion of plastic regions are described. Investigation results show that the initial collision is approximately ideally inelastic, and that the elastic deformation plays a considerable role in the response though the input energy is much larger than the maximum elastic energy capacity of the beam member; therefore, in a general impact, the energy ratio should not be regarded as a sufficient criterion for a rigid—plastic solution. The ratios of the impulse transferred to and the energy absorbed by the frame in the initial collision to that carried by the moving body before impact is only related to the ratiobetween the equivalent mass of the frame paticipating in the initial collision and the mass of the impacting body, having nothing to do with the impacting velocity to a certain extent. 相似文献
952.
The complete convergence theorem implies that starting from any initial distribution the one dimensional contact process converges to a limit ast. In this paper we give a necessary and sufficient condition on the initial distribution for the convergence to occur with exponential rapidity.This work was discussed while the authors were visiting the Nankai Mathematics Institute in Tianjin.Partially supported by the National Science Foundation, the Army Research Office through the Mathematical Sciences Institute at Cornell University, and a Guggenheim fellowship.Research supported by the National Science Foundation of China. 相似文献
953.
Based on special relativity, we introduce a way to develop a new field theory from (1) the relativistic property of the particle coupling coefficient with the field, and (2) the field due to a static point source. As an example, we discuss a theory of electromagnetic and gravitational fields. The results of this special relativistic gravitational theory for the redshift and the deflection of light are the same as those deduced from general relativity. The results of experiments on the planetary perihelion procession shift and on an additional short-range gravity are more favorable to the special relativistic gravitational theory than to general relativity. We put forward a new idea to test experimentally whether the equivalence principle of general relativity is correct.Plovdiv University Paissii Hilendarskii.Moscow Institute of Railway Transport Engineers. 相似文献
954.
955.
956.
Tiehui Liu Zhijiang Chen Tao Huang 《Zeitschrift fur Physik C Particles and Fields》1990,46(1):133-140
The various properties of quarkonium systems have been studies in the framework of a recently proposed potential model, which combines the asymptotic freedom at the largeQ 2 and the multigluon effect at the lowerQ 2 regions with the confinement at the large distance. Good agreements with experiments are found, including \(c\bar c\) and \(b\bar b\) energy levels, leptonic decay widths, and in particular the fine and hyperfine splittings. We also analyze the Lorentz structure of the confinement potential with reference to the charmonium and bottomium fine and hyperfine splittings. Our analyses conclude that almost pure scalar confinement is favored. The properties of \(t\bar t\) spectroscopies are studied over a wide range of \(M_{t\bar t}\) values (from 80 GeV to 200 GeV). 相似文献
957.
Xiang-Qian Luo Qi-Zhou Chen Shuo-Hong Guo 《Zeitschrift fur Physik C Particles and Fields》1990,47(4):635-639
The physical vacuum state and general expression for the Hamiltonian ofd+1 dimensional lattice gauge theory are given by incorporating the exact ground state of pure gauge theory and the variational fermion vacuum state. The applications toSU(2) andSU(3) gauge theories in 2+1 and 3+1 dimensions are demonstrated and the fermion condensates \(\left\langle {\bar \psi \psi } \right\rangle \) as functions of 1/g 2 are calculated. 相似文献
958.
959.
960.
We have measured the resistivity of the YBa2Cu3O7–Ag composite system with Ag volume fraction,p
Ag ranging from 0–100%. The percolation behavior and the normal-state resistivity are studied. We find a three-dimensional threshold for the Ag matrix occurring atp
Ag 20% and a threshold for the superconducting matrix occurring at 1–p
Ag30%. The electrical resistivity is interpreted in terms of a resistivity model for granular YBa2Cu3O7 proposed by Halbritter et al. [Z. Phys. B —Condensed Matter71, 411 (1988)]. Based on this model, we show that the resistivities between the YBa2Cu3O7 grains and flaws in the grains are greatly diminished in the samples, indicating significantly improved grain growth behavior of the YBa2Cu3O7 phase resulting from the addition of Ag. With the diminishing of the grain boundary resistivities, an intrinsic value for the temperature coefficient of resistivity, (1/gr)(d/dT), can be inferred, which is 3.3×10–3/K at 300 K. This value is very close to that observed in the Cu–O2 planes in single crystals and epitaxial films of YBa2Cu3O7. 相似文献