全文获取类型
收费全文 | 11067篇 |
免费 | 1538篇 |
国内免费 | 943篇 |
专业分类
化学 | 6561篇 |
晶体学 | 65篇 |
力学 | 493篇 |
综合类 | 154篇 |
数学 | 1140篇 |
物理学 | 5135篇 |
出版年
2024年 | 43篇 |
2023年 | 168篇 |
2022年 | 431篇 |
2021年 | 437篇 |
2020年 | 414篇 |
2019年 | 360篇 |
2018年 | 311篇 |
2017年 | 485篇 |
2016年 | 527篇 |
2015年 | 509篇 |
2014年 | 719篇 |
2013年 | 723篇 |
2012年 | 749篇 |
2011年 | 663篇 |
2010年 | 579篇 |
2009年 | 680篇 |
2008年 | 662篇 |
2007年 | 645篇 |
2006年 | 562篇 |
2005年 | 594篇 |
2004年 | 524篇 |
2003年 | 400篇 |
2002年 | 300篇 |
2001年 | 220篇 |
2000年 | 246篇 |
1999年 | 212篇 |
1998年 | 185篇 |
1997年 | 180篇 |
1996年 | 146篇 |
1995年 | 142篇 |
1994年 | 83篇 |
1993年 | 92篇 |
1992年 | 78篇 |
1991年 | 49篇 |
1990年 | 63篇 |
1989年 | 57篇 |
1988年 | 60篇 |
1987年 | 50篇 |
1986年 | 35篇 |
1985年 | 35篇 |
1984年 | 27篇 |
1983年 | 17篇 |
1982年 | 35篇 |
1981年 | 14篇 |
1980年 | 6篇 |
1979年 | 12篇 |
1978年 | 4篇 |
1971年 | 4篇 |
1969年 | 2篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
A new method for rotation and brightness invariant pattern recognition was proposed by applying multiple circular harmonic expansions to the joint transform correlator. The amplitudes of the multiple orders of circular harmonic expansions made from a detecting image were synthetically modified to respond to the same auto-correlation peaks. These modified circular harmonic expansions were arranged in the input plane as reference patterns together with an arbitrary target pattern, and the correlation signals between them were calculated in the subtracted joint transform correlator. The fraction of the correlation-peak intensities between the target and the references were extracted as a new discrimination parameter. This new parameter performs pattern recognition under rotation and brightness invariance with good discriminability. Its high discriminability has been proved in computer simulations using the face image patterns of many individuals. 相似文献
43.
以Nd:MgO:LiNbO_3同时兼作激活介质和非线性光学材料,研究自倍频激光器。用小型氙灯泵浦,在室温下获得二次谐波激光(0.547μm) 阈值小于4.8'J,最大输出400μJ/shot,工作温度范围大于20℃~45℃,无光损伤。 相似文献
44.
Using the appropriate harmonic oscillator states and reasonable approximations, we construct coherent wavepackets corresponding
to the solutions of the Klein-Gordon equation for the attractive potentialV(r)=−k/r, k>0, in two and three space dimensions. We deduce the corresponding classical limit in two dimension by requiring that the
expectation value 〈r〉 of the radial variable is large. In the case of three dimensions, besides the condition of large 〈r〉, we make the uncertainty Δr=[〈r
2〉 − 〈r〉2]1/2 a minimum with respect to certain parameter of the wavepacket. We then investigate the trajectory traversed by the wavepacket
in the classical limit. We find that the classical limit of this relativistic quantal problem gives, in the leading order,
the same expression for the rate of motion of the perihelion as that given by the solution of the corresponding special relativistic
classical dynamical problem. We also briefly discuss some of the subtle aspects of the classical limit of the relativistic
quantal system, in general. 相似文献
45.
尹传存 《数学物理学报(A辑)》1997,17(2):145-151
设中的角域.该文绘出了A上正调和函数的Martin表示,讨论了极小调和函数与条件Brown运动的一个0—1律之间的关系,并给出了A上极小调和函数的表现形式, 相似文献
46.
微腔激光器的发展与应用 总被引:1,自引:0,他引:1
本文探讨了微腔激光器的分类、基本原理及特点,并简单介绍了目前几种微型激光器的发展及应用。 相似文献
47.
Liquid chromatography-electrospray ionisation mass spectrometry was evaluated in the high-throughput analysis of microcystins and nodularins, cyanobacterial peptide hepatotoxins. Extracts originating from cyanobacterial strains and field material were separated on a 30 mm × 4 mm I.D. Merck Purospher STAR RP-18e column using a rapid gradient of aqueous formic acid and acetonitrile, ionised by electrospray technique and analysed on a Micromass Quattro II triple-quadrupole mass spectrometer operated in the selected ion recording (SIR) mode. The total analysis time per sample was 2.8 min corresponding to 514 samples a day. The system showed good robustness during a series of 320 repetitive injections of a field sample containing three major microcystins. 相似文献
48.
49.
T. Rietmann S. Sohn M. Schröder D. Lipinsky H.F. Arlinghaus 《Applied Surface Science》2006,252(19):6640-6643
In order to improve quantification of high mass ions, the influence of cluster composition on detection efficiencies has been studied using a TOF-SIMS IV with the extended capability of postaccelerating ions up to 20 keV. In this experimental study, we focus on the comparison of detection efficiencies for three types of negatively charged secondary cluster ions: gold-alkanethiolate-clusters (AuxMy), gold-sulfur-clusters (AuxSy) and gold-clusters (Aux). The clusters were sputtered from self-assembled monolayers of hexadecanethiols on gold substrates using 10 keV Ar+ primary ions. The detection efficiencies were derived on the basis of a function for the secondary electron yield and a fourth-order approximated Poisson probability distribution for electron propagation and amplification within the microchannel plate.In addition to the well-known dependence of detection efficiencies on ion mass and energy, which has already been studied for positively charged ions, we were able to show a similar behaviour for the investigated negatively charged secondary ions. We have observed major variations among the three types of clusters at similar mass and energy as predicted in a theoretical approach. The observed differences are due to the different composition of the investigated clusters which has a major influence on the kinetic ion induced electron emission within the microchannel plate. For the first time it was possible to experimentally verify these predictions for detection efficiencies. 相似文献
50.
用线性插值法求单摆运动周期的近似解 总被引:6,自引:1,他引:5
利用线性插值的方法,提出了一个任意摆角条件下的单摆运动周期的近似公式.并利用Mathematica软件将该公式与精确解进行了比较,还与其他近似公式进行了对比.结果表明,该公式的近似程度相当好. 相似文献