全文获取类型
收费全文 | 14604篇 |
免费 | 2334篇 |
国内免费 | 1439篇 |
专业分类
化学 | 10720篇 |
晶体学 | 180篇 |
力学 | 822篇 |
综合类 | 67篇 |
数学 | 1784篇 |
物理学 | 4804篇 |
出版年
2024年 | 31篇 |
2023年 | 310篇 |
2022年 | 402篇 |
2021年 | 540篇 |
2020年 | 675篇 |
2019年 | 571篇 |
2018年 | 505篇 |
2017年 | 434篇 |
2016年 | 698篇 |
2015年 | 727篇 |
2014年 | 763篇 |
2013年 | 1100篇 |
2012年 | 1265篇 |
2011年 | 1284篇 |
2010年 | 859篇 |
2009年 | 866篇 |
2008年 | 1002篇 |
2007年 | 863篇 |
2006年 | 755篇 |
2005年 | 721篇 |
2004年 | 533篇 |
2003年 | 426篇 |
2002年 | 414篇 |
2001年 | 329篇 |
2000年 | 294篇 |
1999年 | 301篇 |
1998年 | 201篇 |
1997年 | 155篇 |
1996年 | 200篇 |
1995年 | 168篇 |
1994年 | 138篇 |
1993年 | 126篇 |
1992年 | 102篇 |
1991年 | 88篇 |
1990年 | 92篇 |
1989年 | 68篇 |
1988年 | 63篇 |
1987年 | 49篇 |
1986年 | 40篇 |
1985年 | 42篇 |
1984年 | 38篇 |
1983年 | 17篇 |
1982年 | 16篇 |
1981年 | 20篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1976年 | 10篇 |
1975年 | 11篇 |
1971年 | 7篇 |
1969年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
971.
The nonlinear behavior of a probe pulse propagating in a medium with electromagnetically induced transparency is studied both numerically and analytically. A new type of nonlinear wave equation is proposed in which the noninstantaneous response of nonlinear polarization is treated properly. The resulting nonlinear behavior of the propagating probe pulse is shown to be fundamentally different from that predicted by the simple nonlinear Schr?dinger-like wave equation that considers only instantaneous Kerr nonlinearity. 相似文献
972.
Colored conical emission was observed experimentally in a thick beta-barium borate crystal as a result of spatiotemporal modulational instability. In the presence of both dispersion and diffraction, colored conical emission showed specific features that were characteristic of the nonlinear dynamics of the strongly coupled fundamental and harmonic fields. Experimental observation directly demonstrated that beam angular spectra were substantially modified as a result of exponential growth of perturbations by means of parametric wave mixing. Seeded amplification of colored conical emission was demonstrated to support ultrabroadband up-conversion. 相似文献
973.
Entangled-photon coincidence imaging is a method to nonlocally image an object by transmitting a pair of entangled photons through the object and a reference optical system, respectively. The image of the object can be extracted from the coincidence rate of these two photons. From a classical perspective, the image is proportional to the fourth-order correlation function of the wave field. Using classical statistical optics, we study a particular aspect of coincidence imaging with incoherent sources. As an application, we give a proposal to realize lensless Fourier-transform imaging, and discuss its applicability in x-ray diffraction. 相似文献
974.
975.
976.
The mechanism for SEU simulation by pulsed laser 总被引:2,自引:0,他引:2
HUANG Jianguo & HAN Jianwe Center for Space Science Applied Research Chinese Academy of Sciences Beijing China 《中国科学G辑(英文版)》2004,47(5):540-549
~~The mechanism for SEU simulation by pulsed laser~~ 相似文献
977.
An "arrested" chloride abstraction occurs in the reaction of trans-RuCl(2)(DMeOPrPE)(2) with TlPF(6); the product is a 1-D coordination polymer in which the Tl(I) centers have an unusual octahedral coordination geometry with a stereochemically active 6s(2) lone pair. 相似文献
978.
He Liu Bo-Hua Zhong Li-Ping Liu Shi-Tian Han 《Journal of chemical crystallography》2004,34(4):265-268
Crystals of 2,3-bis(2-pyridyl)-5,8-dimethoxyquinoxaline (bpdmq) were examined using X-ray diffraction analysis: Monoclinic, space group P2
1/n with a = 6.9362(14) Å, b =17.285(4) Å, c =13.583(3) Å, =96.21(3)°, V =1619.0(6) Å3, Z = 4. The crystal structure indicates that the title compound consists of quinoxaline ring system substituted with two pyridine rings and two methoxy groups. Two pyridine rings form dihedral angles of 39.8 and 44.1° with the mean planar quinoxaline ring, and a dihedral angle of 67.1° with each other. The orientation of the pyridine rings is such that their N atoms face each other. There exist significant – interactions responsible for the formation of the stacks along the a-axis of the crystal packing. 相似文献
979.
We propose the remote multiplexing of holograms with random patterns from a multimode fiber bundle used as the reference beams. The random pattern reference beam is characterized by the superposition and concatenation of propagation modes of multimode fiber and free space. For angle, shift, and wavelength remote multiplexing we compare two methods of laser coupling to the fiber bundle, i.e., direct coupling and lens coupling. A theoretical discussion that uses mode orthogonality is provided to describe multiplexing characteristics, and the theory is verified by experimental results. These remote-multiplexing methods can be applied to general multimode waveguide arrays for construction of compact and integrated optical systems in which multiplexing can be controlled remotely. 相似文献
980.
Zhang D Wu LZ Zhou L Han X Yang QZ Zhang LP Tung CH 《Journal of the American Chemical Society》2004,126(11):3440-3441
1,4-Dihydropyridines have been photocatalytically oxidized to pyridines by platinum(II) terpyridyl complexes with the generation of hydrogen in homogeneous solution. The hydrogen production proceeds in quantitative yield and with great catalytic turnover. 相似文献