全文获取类型
收费全文 | 21432篇 |
免费 | 3335篇 |
国内免费 | 4106篇 |
专业分类
化学 | 17419篇 |
晶体学 | 338篇 |
力学 | 1029篇 |
综合类 | 310篇 |
数学 | 2320篇 |
物理学 | 7457篇 |
出版年
2024年 | 36篇 |
2023年 | 342篇 |
2022年 | 566篇 |
2021年 | 714篇 |
2020年 | 815篇 |
2019年 | 852篇 |
2018年 | 667篇 |
2017年 | 693篇 |
2016年 | 927篇 |
2015年 | 1060篇 |
2014年 | 1249篇 |
2013年 | 1690篇 |
2012年 | 1833篇 |
2011年 | 2040篇 |
2010年 | 1534篇 |
2009年 | 1433篇 |
2008年 | 1633篇 |
2007年 | 1472篇 |
2006年 | 1362篇 |
2005年 | 1185篇 |
2004年 | 954篇 |
2003年 | 782篇 |
2002年 | 766篇 |
2001年 | 693篇 |
2000年 | 572篇 |
1999年 | 457篇 |
1998年 | 366篇 |
1997年 | 270篇 |
1996年 | 282篇 |
1995年 | 279篇 |
1994年 | 236篇 |
1993年 | 197篇 |
1992年 | 139篇 |
1991年 | 161篇 |
1990年 | 131篇 |
1989年 | 96篇 |
1988年 | 101篇 |
1987年 | 57篇 |
1986年 | 54篇 |
1985年 | 43篇 |
1984年 | 35篇 |
1983年 | 31篇 |
1982年 | 18篇 |
1981年 | 13篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Zhengqian Luo Guoyong Sun Zhiping Cai Miaoling Si Qibo Li 《Optics Communications》2007,277(1):118-124
In this paper, continuous wave Yb3+-doped double-clad fiber lasers (DCFLs) with linear-cavity are investigated theoretically and numerically using the rate equations. Under the steady state conditions, the simplified analytic solutions of Yb3+-doped DCFLs under considering the scattering loss are deduced in the strongly pump condition. Compared with the known analytic solutions in published literatures, our analytic solutions are more accurate, especially, at higher reflectivity of output mirror. In addition, a fast and stable algorithm based on the Newton-Raphson method is proposed to simulate numerically Yb3+-doped DCFLs. The results by simplified analytic solutions are in good agreement with those by the numerical simulation. Moreover, we have performed the optimization of an Yb3+-doped DCFL using the simplified analytic solutions and the numerical simulations, respectively. 相似文献
92.
De Ming ZHU Ying SUN 《数学学报(英文版)》2007,23(8):1495-1504
In this paper, we study the dynamical behavior for a 4-dimensional reversible system near its heteroclinic loop connecting a saddle-focus and a saddle. The existence of infinitely many reversible 1-homoclinic orbits to the saddle and 2-homoclinic orbits to the saddle-focus is shown. And it is also proved that, corresponding to each 1-homoclinic (resp. 2-homoclinic) orbit F, there is a spiral segment such that the associated orbits starting from the segment are all reversible 1-periodic (resp. 2-periodic) and accumulate onto F. Moreover, each 2-homoclinic orbit may be also accumulated by a sequence of reversible 4-homoclinic orbits. 相似文献
93.
94.
95.
Ping-xing Chen Jian-ming Cai Zheng-wei Zhou Guang-can Guo 《量子光学学报》2006,12(B08):72-73
The second law of thermodynamics is one of the most fundamental and for-reaching laws of physics. It teaches us that when a closed system undergoes a thermodynamic process the entropy of the system never decreases; it increases, or at least remains constant. If the entropy increases the thermodynamic process is irreversible, otherwise it is reversible. Only ideal thermal process is reversible. In classical world a great number of facts have proved the second law is true. But in quantum world since the quantum coherence and correlations exist we are not sure the second law is still true, at least in principle. This is because that: 1. on the microscopic level the irreversibility is conflict with the reversibility of all fundamental physical laws ; 2. there are not enough evidences to show it is true in quantum world. 相似文献
96.
The melting curve of MgSiO分子动力学 MgSiO3钙钛矿 熔化温度 高压 melting temperature, molecular dynamics, high pressure Project supported by the National Natural Science Foundation of China (Grant Nos 10274055 and 10376021),the Natural Science Foundation of Gansu Province, China (Grant No 3ZS051-A25-027) and the Scientific Research Foundation of Education Bureau of Gansu Province, China (Grant No 0410-01). 2005-01-12 5/8/2005 12:00:00 AM The melting curve of MgSiO3 perovskite is simulated using molecular dynamics simulations method at high pressure. It is shown that the simulated equation of state of MgSiO3 perovskite is very successful in reproducing accurately the experimental data. The pressure dependence of the simulated melting temperature of MgSiO3 perovskite reproduces the stability of the orthorhombic perovskite phase up to high pressure of 130GPa at ambient temperature, consistent with the theoretical data of the other calculations. It is shown that its transformation to the cubic phase and melting at high pressure and high temperature are in agreement with recent experiments. 相似文献
97.
提出了将哈密顿算符对角化的一种方法.围绕一维谐振子讨论了如何将哈密顿算符对角化、引进的是玻色算符还是费米算符的问题,并分析了能量量子化的原因及能量子与声子的区别. 相似文献
98.
99.
100.
The contrast of interference pattern formed by two circularly polarized waves and by a linearly polarized wave and a circularly polarized one is discussed. The results are compared with that by two linear beams. It shows that the use of circular light in holographic fabrication of three-dimensional periodic microstructures may remove the necessity of beam ratio and polarization optimization needed in the interference of three linear noncoplanar beams and improve the uniform contrast of resultant pattern simultaneously. 相似文献