全文获取类型
收费全文 | 20896篇 |
免费 | 3361篇 |
国内免费 | 1853篇 |
专业分类
化学 | 14270篇 |
晶体学 | 525篇 |
力学 | 845篇 |
综合类 | 175篇 |
数学 | 655篇 |
物理学 | 9640篇 |
出版年
2024年 | 27篇 |
2023年 | 135篇 |
2022年 | 336篇 |
2021年 | 417篇 |
2020年 | 577篇 |
2019年 | 583篇 |
2018年 | 578篇 |
2017年 | 720篇 |
2016年 | 927篇 |
2015年 | 873篇 |
2014年 | 936篇 |
2013年 | 2213篇 |
2012年 | 1243篇 |
2011年 | 1269篇 |
2010年 | 1063篇 |
2009年 | 1140篇 |
2008年 | 1211篇 |
2007年 | 1211篇 |
2006年 | 1169篇 |
2005年 | 1032篇 |
2004年 | 1028篇 |
2003年 | 903篇 |
2002年 | 988篇 |
2001年 | 679篇 |
2000年 | 693篇 |
1999年 | 581篇 |
1998年 | 493篇 |
1997年 | 403篇 |
1996年 | 360篇 |
1995年 | 386篇 |
1994年 | 292篇 |
1993年 | 251篇 |
1992年 | 235篇 |
1991年 | 167篇 |
1990年 | 154篇 |
1989年 | 111篇 |
1988年 | 118篇 |
1987年 | 104篇 |
1986年 | 97篇 |
1985年 | 80篇 |
1984年 | 78篇 |
1983年 | 36篇 |
1982年 | 54篇 |
1981年 | 30篇 |
1980年 | 31篇 |
1979年 | 37篇 |
1978年 | 12篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
The aim of this paper is to highlight the added value of the generalized Gouy phase shift introduced by Siegman. Although suited for optical systems study, including those more complex than free space, we note that it did not meet the use that it deserves so far. The analysis of the whole of the ideas and analytical approaches associated to the important concept of the Gouy phase proves its effectiveness.
Usually, the resonance condition is systematically built on the basis of the equivalent empty cavity. Unfortunately, this approach does not cover some of the useful parameters of the real resonator. By means of the generalized Gouy phase and the self-consistent complex parameter q, we derive here a new approach for the calculation of the resonance condition for the real cavity. Moreover, the use of the generalized Gouy phase clearly simplifies the study of resonators, while making it possible to avoid the use of the Huygens’ Fresnel integral. 相似文献
102.
Aït Hmaïdouch L. Mançour Billah S. El Hadek M. 《Journal of Thermal Analysis and Calorimetry》2002,69(2):659-667
The solid—liquid equilibria of the ternary system H2O—Al(NO3)3—Mg(NO3)2 were studied at –30, –20, –10 and 0°C by using a synthetic method which allows to detemine all the characteristic points of isothermal sections. The stable solid phases which appear are respectively: ice, Al(NO3)3·9H2O, Mg(NO3)2·9H2O and Mg(NO3)2·6H2O. Neither double salts nor mixed crystals are observed in the temperature and composition field studied. Polytherm diagram layout show two invariant transformations correspond with an eutectic point and a peritectic point.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
103.
Traveling wave Ti:LiNbO3 Mach-Zehnder optical modulators with buried electrodes and etched grooves in the SiO2 buffer layer are analyzed by the finite element method. The tradeoff between the bandwidth BW and the half-wave voltage Vπ is discussed. The value of BW/Vπ is used to weight the total performance of the modulator. Taking a thick buffer layer and etching deep grooves in the buffer layer are demonstrated as two effective methods to improve the performance of the modulator. A 3-dB optical bandwidth of 18 GHz with half-wave voltage 5V at a wavelength of 1.55 pm could be obtained even though the electrode is not very thick. When the requirement of half-wave voltage is not very critical, a bandwidth of more than 100 GHz can be obtained. 相似文献
104.
Hans C. Fogedby 《Journal of statistical physics》1992,69(1-2):411-425
We elaborate in some detail on a new phase space approach to complexity, due to Y.-C. Zhang. We show in particular that the connection between maximal complexity and power law noise or correlations can be derived from a simple variational principle. For a 1D signal we find 1/f noise, in accordance with Zhang. 相似文献
105.
本文采用高压X光衍射方法在金刚石对顶压砧中在位地(in situ)研究了Fe68Co24Ni8(wt%)合金在室温下的压致bcc→hcp结构相变和直到40.5 GPa的等温压缩行为。实验结果表明该合金在常压下为bcc结构,晶格常数a0=(0.287 0±0.000 1) nm,体积V0=(7.119±0.007) cm3/mol,密度ρ0=(7.981±0.008) g/cm3;在20.9 GPa附近出现bcc→hcp结构相变,两相共存压力区约10 GPa,在此区域内有晶面间距d(002)hcp=d(110)bcc,且原子平面(002)hcp//(110)bcc,hcp相比bcc相体积减小(0.33±0.02) cm3/mol;高压相hcp结构的晶格参数比值c/a=1.608±0.004;相变后原子配位数的增加使得hcp相(002)平面内及(002)平面间的最近邻原子间距比bcc相最近邻原子间距分别增大约1.6%和0.5%;用Murnaghan状态方程对实验数据进行最小二乘法拟合,得到bcc相B0=(130±13) GPa,B0'=12.6±0.5;hcp相V0=(6.62±0.04) cm3/mol,B0=(243±21) GPa,B0'=6.8±0.3;对于该合金的bcc→fcp相变时的结构转变机制做了详细的讨论。 相似文献
106.
107.
用粒子(PIC,Particle-in-Cell)模拟方法研究了当前颇感兴趣的高功率振荡器的锁相问题。给出了模拟计算结果。讨论了锁相(Phase Locking)、Priming和InjectionSeeding等概念的区别。 相似文献
108.
Poly (n-butylisocyanate)-benzene solutions prepared by solubilization at 45°C, followed by aging at room temperature were found to be metastable for months, although, eventually, they separated into a birefringent polymer-rich phase and an isotropic solution. These metastable solutions, as well as isothermally phase-separated biphasic samples, flowed and exhibited dynamic moduli indicative of low polymer connectivity. By contrast samples prepared by a freeze-thaw cycle were uniformly and highly birefringent and showed network (gel) behavior at room temperature. The mechanism of gel formation is most likely the exclusion of the polymer from the benzene crystal during crystallization, forcing the polymer to align and exist at grain boundaries. Films formed from solutions have different moduli than those formed from gels, and are consistent with the proposed mechanism. 相似文献
109.
The structural phase transition from orthorhombic (T) phase to tetragonal (T′) phase in substituted La2−x
R
x
CuO4 (R = Pr, Nd, Sm, Eu and Gd) and T′ to T-phase in Pr2−x
M
x
CuO4−y
(M = Sr, Ca) has been studied by X-ray diffraction technique. The T-phase of La2CuO4 is transferred to T′ phase abruptly atx=0.8, 0.4, 0.4, 0.3 and 0.4 respectively for substitution of Pr, Nd, Sm, Eu and Gd for La in La2CuO4 without evidence of the T* phase. The T′ structure of Pr2CuO4 (x = 0.0) gets transformed to the T* structure at 30% Ca doping (x=0.6) and then to the T structure at 50% Ca doping (x=1.0), while for Sr-contentx=0.0, 0.4 and 1.0 it shows T′, T* and T structure respectively. 相似文献
110.
B. V. Derjaguin 《Progress in Surface Science》1992,40(1-4):240-251
A review is presented about research on surface forces and surface interactions conducted over the past half-century, with some emphasis on the pioneering contributions of the Department of Surface Phenomena at the Institute of Physical Chemistry of the USSR Academy of Sciences. 相似文献