全文获取类型
收费全文 | 630003篇 |
免费 | 5064篇 |
国内免费 | 1634篇 |
专业分类
化学 | 319301篇 |
晶体学 | 9241篇 |
力学 | 32039篇 |
综合类 | 27篇 |
数学 | 83001篇 |
物理学 | 193092篇 |
出版年
2021年 | 5837篇 |
2020年 | 6290篇 |
2019年 | 7176篇 |
2018年 | 9686篇 |
2017年 | 9814篇 |
2016年 | 13575篇 |
2015年 | 7288篇 |
2014年 | 12339篇 |
2013年 | 27946篇 |
2012年 | 21636篇 |
2011年 | 25757篇 |
2010年 | 19418篇 |
2009年 | 19377篇 |
2008年 | 24371篇 |
2007年 | 24130篇 |
2006年 | 21905篇 |
2005年 | 19564篇 |
2004年 | 18337篇 |
2003年 | 16516篇 |
2002年 | 16338篇 |
2001年 | 17518篇 |
2000年 | 13468篇 |
1999年 | 10444篇 |
1998年 | 8979篇 |
1997年 | 8900篇 |
1996年 | 8333篇 |
1995年 | 7470篇 |
1994年 | 7550篇 |
1993年 | 7272篇 |
1992年 | 7830篇 |
1991年 | 8223篇 |
1990年 | 7943篇 |
1989年 | 7856篇 |
1988年 | 7649篇 |
1987年 | 7385篇 |
1986年 | 7110篇 |
1985年 | 9110篇 |
1984年 | 9525篇 |
1983年 | 7959篇 |
1982年 | 8190篇 |
1981年 | 7750篇 |
1980年 | 7325篇 |
1979年 | 7958篇 |
1978年 | 8187篇 |
1977年 | 8163篇 |
1976年 | 8141篇 |
1975年 | 7776篇 |
1974年 | 7570篇 |
1973年 | 7931篇 |
1972年 | 5833篇 |
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
981.
982.
The diffraction of a plane wave incident on a thick hologram at the first and second Bragg angles in the process of nonlinear recording is analyzed using the coupled-wave equations. It is shown that, in this case, the two-wave approximation with the use of effective modulation amplitudes of the refractive index, n 1ef and n 2ef, can be applied. Analytical dependences of n 1ef and n 2ef on the modulation amplitudes of the refractive index n 1 and n 2 at the fundamental and doubled spatial frequencies are obtained and the criteria of their applicability are determined. The dependences found are used to calculate the parameters of gratings recorded in a photopolymeric material. 相似文献
983.
The cross section of absorption of electromagnetic radiation by an inhomogeneous spherical particle is calculated. The general case of an arbitrary value of the ratio of the particle radius to the radius of the dielectric core is considered. The condition of diffuse reflection of electrons from the inner and outer surfaces of the metal layer of the particle is taken as the boundary condition of the problem. The limiting cases are considered and the results obtained are discussed. 相似文献
984.
N. A. Borisevich S. L. Dziarzhytski V. A. Povedailo D. L. Yakovlev 《Optics and Spectroscopy》2004,96(6):819-823
The spectra of the fluorescence excitation within the rotational contours of the bands of the pure electronic long-wavelength S 0-S 1 transitions of jet-cooled indole and carbazole molecules and their complexes with water are measured. For the carbazole-water complex, a contour with three maxima is registered, which is possibly related to the occurrence of two isomers, differing in a slight displacement of hydrogen between the nitrogen atom of the imine group of carbazole and the oxygen atom of the water molecule. The degrees of polarization of integral fluorescence upon excitation within the rotational contours of the S 0-S 1 electronic transition bands of the above molecules and their complexes with water are determined for the first time. The coincidence of the calculated (7.7%) and measured (7.3%) values of the degree of polarization upon excitation in the rotational Q branch of the b L 1-A electronic transition of indole confirms the accepted intramolecular orientation of the transition dipole moment at an angle of 38.3° with respect to the principal axis of inertia A. Upon excitation of indole, its complex with water, and carbazole into the P and R branches, the measured and calculated degrees of polarization are also close to each other and amount to 2–3%. This confirms the occurrence of contributions to the fluorescence polarization due to the rotations of the indole molecules around the principal axes of inertia A and C. 相似文献
985.
986.
It is experimentally demonstrated that second-order polarizability gratings preliminarily recorded using bichromatic light in a phosphate glass can be amplified under the action of monochromatic radiation. The amplification effect takes place irrespective of the polarization and direction of propagation of the amplifying radiation and is achieved at various wavelengths. The phenomenon is related to the asymmetry of optical transitions between local centers in an isotropic medium in the presence of electric field. It is theoretically shown that this system may feature the formation of alternating electric field domains with dimensions depending on the grating amplitude. 相似文献
987.
The process of muon (pion) pair production with small invariant mass in electron-positron high-energy annihilation, accompanied by emission of a hard photon at large angles, is considered. We find that the Drell-Yan picture for the differential cross section is valid in the charge-even experimental setup. Radiative corrections both for the electron block and for the final-state block are taken into account. 相似文献
988.
A. J. Nurmagambetov 《JETP Letters》2004,79(5):191-195
In this letter, we describe how to string together the doubled field approach by Cremmer, Julia, Lü, and Pope with the Pasti-Sorokin-Tonin technique to construct the sigma-model-like action for type IIA supergravity. The relation of the results with those obtained in the context of searching for superstring/M-theory hidden symmetry group is discussed. 相似文献
989.
S. N. Molotkov 《JETP Letters》2004,80(8):563-567
A “collective” attack on the key is considered, and its connection with the classical capacity of a quantum communication channel is analyzed. It has been shown that the allowable error probability for legitimate users to which the secure key can be extracted is less than half the value for “translucent” eavesdropping and individual measurements. 相似文献
990.
A scheme of nuclear excitation by the ionic X-ray lines in laser plasma using two femtosecond laser pulses is proposed. The first pulse produces plasma with a given degree of ionization, allowing the X-ray line energies of the target ions to be tuned to resonance with the nuclear transition, while the second pulse generates hot electrons that are necessary for X-ray generation. 相似文献