全文获取类型
收费全文 | 3417篇 |
免费 | 541篇 |
国内免费 | 124篇 |
专业分类
化学 | 388篇 |
晶体学 | 3篇 |
力学 | 267篇 |
综合类 | 32篇 |
数学 | 1206篇 |
物理学 | 2186篇 |
出版年
2024年 | 8篇 |
2023年 | 32篇 |
2022年 | 63篇 |
2021年 | 68篇 |
2020年 | 73篇 |
2019年 | 78篇 |
2018年 | 62篇 |
2017年 | 91篇 |
2016年 | 96篇 |
2015年 | 106篇 |
2014年 | 203篇 |
2013年 | 244篇 |
2012年 | 162篇 |
2011年 | 229篇 |
2010年 | 164篇 |
2009年 | 197篇 |
2008年 | 251篇 |
2007年 | 252篇 |
2006年 | 219篇 |
2005年 | 173篇 |
2004年 | 146篇 |
2003年 | 143篇 |
2002年 | 125篇 |
2001年 | 108篇 |
2000年 | 104篇 |
1999年 | 96篇 |
1998年 | 96篇 |
1997年 | 56篇 |
1996年 | 56篇 |
1995年 | 47篇 |
1994年 | 38篇 |
1993年 | 33篇 |
1992年 | 31篇 |
1991年 | 26篇 |
1990年 | 15篇 |
1989年 | 16篇 |
1988年 | 14篇 |
1987年 | 18篇 |
1986年 | 17篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 14篇 |
1980年 | 10篇 |
1979年 | 17篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 8篇 |
排序方式: 共有4082条查询结果,搜索用时 46 毫秒
991.
1 Introduction Adouble beamsmutuallypumpedphaseconjugatorgeneratesthephase conjugatereplicaofeachoftwoincidentopticalbeams[1~ 7] .Thetwoincidentbeamsneednotbecoherentwitheachother,andtheycanevenbefromdifferentlasersoperatingatthesamenominalwavelength .Mut… 相似文献
992.
Irene Hueter 《Journal of Theoretical Probability》2000,13(4):939-950
Suppose that {(X t, Y t): t>}0 is a family of two independent Gaussian random variables with means m 1(t) and m 2(t) and variances σ 2 1(t) and σ 2 2(t). If at every time t>0 the first and second moment of the minimum process X t∧Y t are known, are the parameters governing these four moment functions uniquely determined ? We answer this question in the negative for a large class of Gaussian families including the “Brownian” case. Except for some degenerate situation where one variance function dominates the other, in which case the recovery of the parameters is fully successful, the second moment of the minimum process does not provide any additional clues on identifying the parameters. 相似文献
993.
Laser cavities with spherical mirrors and Gaussian diaphragms have been investigated. The influence of the parameters of mirrors
and Gaussian diaphragms on the stability conditions of such cavities is shown.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 465–468, July–August, 2000. 相似文献
994.
《Journal of mass spectrometry : JMS》2017,52(8):550-556
Amino acids are essential building blocks of life, and fluorinated derivatives have gained interest in chemistry and medicine. Modern mass spectrometry has enabled the study of oligo‐ and polypeptides as isolated entities in the gas phase, but predominantly as singly or even multiply charged species. While laser desorption of neutral peptides into adiabatically expanding supersonic noble gas jets is possible, UV–VIS spectroscopy, electric or magnetic deflectometry as well as quantum interferometry would profit from the possibility to prepare thermally slow molecular beams. This has typically been precluded by the fragility of the peptide bond and the fact that a peptide would rather ‘fry’, i.e. denature and fragment than ‘fly’. Here, we explore how tailored perfluoroalkyl functionalization can reduce the intermolecular binding and thus increase the volatility of peptides and compare it to previously explored methylation, acylation and amidation of peptides. We show that this strategy is essential and enables the formation of thermal beams of intact neutral tripeptides, whereas only fragments were observed for an extensively fluoroalkyl‐decorated nonapeptide. © 2017 The Authors. Journal of Mass Spectrometry Published by John Wiley & Sons Ltd. 相似文献
995.
A novel single-Gaussian-beam magneto-optical trap with a lens and spherical mirror is proposed. Our analysis and calculations show that it can trap as many as 106 atoms with a temperature of ~330 μK. Because of its extraordinary simplicity and much efficaciousness, the proposed single-beam trapping scheme will have many applications in the experiments of atom optics with cold and dense atoms. 相似文献
996.
On the measurement of the generalized degree of polarization 总被引:1,自引:0,他引:1
Movilla J.M. Piquero G. Mejías P.M. Martínez-Herrero R. 《Optical and Quantum Electronics》2000,32(12):1333-1342
On the basis of well-known methods to obtain the standard Stokes parameters, two simple experimental procedures are analysed to measure the so-called generalized degree of polarization, P, defined elsewhere [Opt. Commun., 149 (1998) 230]. After discussing the accuracy of the methods, the generalized degree of polarization of a non-uniformly polarized beam emerging from an optically pumped birefringent Nd:YAG rod optically pumped is experimentally investigated in terms of the pumped power. 相似文献
997.
Pankaj Kumar Gaurav 《Phase Transitions》2013,86(3):312-324
The compound 4-methyl (2′-hydroxy,4′-n-hexadecyloxy) azobenzene was synthesized by Prajapati and co-workers (Mol. Cryst. Liq. Cryst. 369 (2001), pp. 37–46). Subsequent experiments (D. Pal, [PhD thesis], University of Lucknow, Lucknow, India, 2007) confirmed that the compound exists in nematic phase for a small range of temperature (72°C–80°C). In the present work, optimization of molecular geometry has been carried out by employing the Gaussian 03 suit of programs without any constraint using density functional B3LYP along with 6-31G** basis set and checked for imaginary frequencies. A detailed investigation on intermolecular interaction energy at various interacting configurations has been carried out. In order to study the mesogenic characteristics of the molecule, an attempt has been made to estimate the variation of order parameter with respect to the change in temperature as well as degrees of freedom. These studies will be helpful to understanding the mesogenic character of any molecule prior to synthesis and promises future application in molecular engineering. 相似文献
998.
Boardman A. D. Marinov K. Pushkarov D. I. Shivarova A. 《Optical and Quantum Electronics》2000,32(1):49-62
Spatial solitary waves carried by a TE mode in planar optical waveguides with Kerr-type of nonlinearity are investigated based on a modified nonlinear (1 + 1) Schrödinger equation. Looking for effects instigated by the spatial inhomogeneity of the nonlinear polarization, the nonzero divE-term is taken into account in the nonlinear guided wave equation together with the nonparaxial approach and vector model. It is shown that, at self-focusing of beams in a (1 + 1) geometry, the effect coming out from the divergence term predominates over modifications related to the nonparaxial vector model. This term is interpreted as nonlinearly induced diffraction which plays the role of an effective saturation. Analytical solutions supported by numerical results are found. 相似文献
999.
负高斯曲率的曲面在建筑业、造船业及航空工业中都有广泛的应用。该文提出一种负高斯曲率双三次Bezier曲面的构造方法,简单直观,几何意义明显。 相似文献
1000.
Victor García David Zorrilla Manuel Fernández 《International journal of quantum chemistry》2013,113(18):2172-2179
We analyze some procedures to introduce the effect of confining the electrons of the hydrogen atoms in cavitation spheres like those used in the self‐consistent reaction field models for studying the solvent influence on molecular properties [as polarizable continuum model (PCM), or conductor screening model (COSMO)]. We have found that the boundary conditions to be applied have an important effect on the system energy that by no means should be neglected in this type of calculations. We have found as well that “‐nG” expansion technique could be applicable in this kind of calculations (even at the very simple “‐3G” level) and lead us to a relatively simple form of applying the theory. Moreover, we have found a way to define the cavitation radius of PCM calculations, by minimizing the system energy with respect to this parameter, which could be a more satisfactory procedure—at least from a theoretical point of view—than the use of empirical values characteristic of most of the PCM or COSMO standard calculations. © 2013 Wiley Periodicals, Inc. 相似文献