全文获取类型
收费全文 | 2362篇 |
免费 | 75篇 |
国内免费 | 20篇 |
专业分类
化学 | 1429篇 |
晶体学 | 11篇 |
力学 | 44篇 |
数学 | 425篇 |
物理学 | 548篇 |
出版年
2023年 | 17篇 |
2022年 | 51篇 |
2021年 | 65篇 |
2020年 | 48篇 |
2019年 | 67篇 |
2018年 | 63篇 |
2017年 | 54篇 |
2016年 | 79篇 |
2015年 | 90篇 |
2014年 | 78篇 |
2013年 | 160篇 |
2012年 | 140篇 |
2011年 | 162篇 |
2010年 | 114篇 |
2009年 | 115篇 |
2008年 | 166篇 |
2007年 | 141篇 |
2006年 | 173篇 |
2005年 | 137篇 |
2004年 | 92篇 |
2003年 | 82篇 |
2002年 | 92篇 |
2001年 | 37篇 |
2000年 | 29篇 |
1999年 | 28篇 |
1998年 | 22篇 |
1997年 | 25篇 |
1996年 | 33篇 |
1995年 | 17篇 |
1994年 | 11篇 |
1993年 | 13篇 |
1992年 | 10篇 |
1991年 | 9篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1969年 | 2篇 |
排序方式: 共有2457条查询结果,搜索用时 15 毫秒
141.
John C. Travers Andrei B. Rulkov Burly A. Cumberland Sergei V. Popov James Roy Taylor 《Optical and Quantum Electronics》2007,39(12-13):963-974
The enhancement of different non-linear processes in microstructured optical fibres can be achieved through manipulation of the dispersion characteristics of the fibre. This is demonstrated by extending the region of short wavelength operation of high power supercontinuum generation through four wave mixing in a cascaded fibre geometry where the dispersion of each fibre decreased on propagation. The technique is further refined in a demonstration utilizing long lengths of dispersion decreasing tapered microstructured fibres, where the supercontinuum extends to around 300 nm with spectral power densities in excess of 2 mW/nm in the uv. These long length tapers can also be utilized for adiabatic soliton pulse compression in new spectral regions, allowing the compression of 655 fs pulses to 45 fs. 相似文献
142.
We report on the first demonstration of nanodiamond (ND) as a scattering optical label in a biological environment. NDs were efficiently transfected into cells using cationic liposomes, and imaged using differential interference and Hoffman modulation ‘space’ contrast microscopy techniques. We have shown that 55 nm NDs are biologically inert and produce a bright signal compared to the cell background. ND as a scattering label presents the possibility for extended biological imaging with relatively little thermal or biochemical perturbations due to the optical transparency and biologically inert nature of diamond. 相似文献
143.
144.
Andrei V. Afonin Igor A. Ushakov Dmitry V. Pavlov Andrei V. Ivanov Al'bina I. Mikhaleva 《Magnetic resonance in chemistry : MRC》2010,48(9):685-692
The 1H, 13C and 15N NMR studies have shown that the E and Z isomers of pyrrole‐2‐carbaldehyde oxime adopt preferable conformation with the syn orientation of the oxime group with respect to the pyrrole ring. The syn conformation of E and Z isomers of pyrrole‐2‐carbaldehyde oxime is stabilized by the N? H···N and N? H···O intramolecular hydrogen bonds, respectively. The N? H···N hydrogen bond in the E isomer causes the high‐frequency shift of the bridge proton signal by about 1 ppm and increase the 1J(N, H) coupling by ~3 Hz. The bridge proton shows further deshielding and higher increase of the 1J(N, H) coupling constant due to the strengthening of the N? H···O hydrogen bond in the Z isomer. The MP2 calculations indicate that the syn conformation of E and Z isomers is by ~3.5 kcal/mol energetically less favorable than the anti conformation. The calculations of 1H shielding and 1J(N, H) coupling in the syn and anti conformations allow the contribution to these constants from the N? H···N and N? H···O hydrogen bondings to be estimated. The NBO analysis suggests that the N? H···N hydrogen bond in the E isomer is a pure electrostatic interaction while the charge transfer from the oxygen lone pair to the antibonding orbital of the N? H bond through the N? H···O hydrogen bond occurs in the Z isomer. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
145.
146.
147.
Edward W. Randall Andrei A. Samoilenko Riqiang Fu 《Solid state nuclear magnetic resonance》1999,14(3-4):173-179
We have observed Hahn-echoes resulting from Powles–Mansfield pulse-sequences for a variety of nitrogen containing solids which exhibit a range of 14N electric quadrupole coupling constants (Cq) from 0 to 4.9 MHz. Long echo-decays were frequently obtained which allowed the collection of many echoes in one echo-train, so that the method of Long Echo-Train Summation (LETS), could be used to accumulate signal. A one-dimensional STRAFI-profile is shown for solid ammonium nitrate. The spatial resolution is discussed as a function of Cq. 相似文献
148.
In this paper we analyse the vibrations of an N-stepped Rayleigh bar with sections of complex geometry, supported by end lumped masses and springs. Equations of motion and boundary conditions are derived from the Hamilton’s variational principal. The solutions for tapered and exponential sections are given. Two types of orthogonality for the eigenfunctions are obtained. The analytic solution to the N-stepped Rayleigh model is constructed in terms of Green function. 相似文献
149.
The dependence of the linear stability of two-time-level finite-difference semi-implicit schemes on the choice of reference temperature profile is studied. Particular vertical profiles of the temperature are considered to derive analytical conditions of stability. Analysis is made for general form of different model parameters such as the number of vertical levels and their distribution, the time step size, and the values of the viscosity coefficients. The derived conditions of stability are more restrictive than those for three-time-level schemes, but obtained necessary and sufficient condition for constant vertical lapse rates of the temperature has the form frequently applied to three-time-level schemes: the basic temperature profile should be warmer than the actual one. Performed numerical experiments show that the last restriction is neither necessary nor sufficient condition of stability for general temperature profiles. 相似文献
150.
Véronique Dupuis Nils Blanc Luis E. Diaz-Sanchez Arnaud Hillion Alexandre Tamion Florent Tournus Gustavo M. Pastor Andrei Rogalev Fabrice Wilhelm 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2013,67(2):1-4
In this paper, the one-way absorption property in one-dimensional dielectric/metal photonic crystal structure with a dielectric defect layer is studied. The effects of incident angle and state of polarization on one-way absorption behaviour of the anti-resonant (AR) mode are investigated. The normally incident wave from left to right propagation is totally allowed to penetrate to the structure but right to left propagation totally reflected at the same wavelength. It is found that, with increasing of the incident angle, the AR mode shifts to the lower wavelengths and its intensity decreases. Simultaneously, another AR mode with reversed one-way property appears at higher wavelength. The one-way behaviour on absorption is observed at the both states of polarizations but is localized on different wavelengths. Those effects, are suggesting that the proposed structure can be used as a direction sense polarization splitter or reflector/antireflector device. 相似文献