全文获取类型
收费全文 | 79739篇 |
免费 | 7496篇 |
国内免费 | 7416篇 |
专业分类
化学 | 28571篇 |
晶体学 | 459篇 |
力学 | 7420篇 |
综合类 | 1365篇 |
数学 | 27565篇 |
物理学 | 29271篇 |
出版年
2023年 | 638篇 |
2022年 | 1255篇 |
2021年 | 1444篇 |
2020年 | 1606篇 |
2019年 | 1788篇 |
2018年 | 1521篇 |
2017年 | 1883篇 |
2016年 | 2159篇 |
2015年 | 1961篇 |
2014年 | 2849篇 |
2013年 | 5137篇 |
2012年 | 3360篇 |
2011年 | 3908篇 |
2010年 | 3477篇 |
2009年 | 4674篇 |
2008年 | 5039篇 |
2007年 | 5118篇 |
2006年 | 4813篇 |
2005年 | 4089篇 |
2004年 | 3838篇 |
2003年 | 3762篇 |
2002年 | 3447篇 |
2001年 | 2900篇 |
2000年 | 2817篇 |
1999年 | 2530篇 |
1998年 | 2330篇 |
1997年 | 1921篇 |
1996年 | 1703篇 |
1995年 | 1525篇 |
1994年 | 1401篇 |
1993年 | 1191篇 |
1992年 | 1141篇 |
1991年 | 891篇 |
1990年 | 750篇 |
1989年 | 667篇 |
1988年 | 594篇 |
1987年 | 464篇 |
1986年 | 415篇 |
1985年 | 459篇 |
1984年 | 449篇 |
1983年 | 220篇 |
1982年 | 361篇 |
1981年 | 418篇 |
1980年 | 315篇 |
1979年 | 300篇 |
1978年 | 232篇 |
1977年 | 212篇 |
1976年 | 160篇 |
1974年 | 112篇 |
1973年 | 107篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
V. I. Dashkevich 《Journal of Applied Spectroscopy》2002,69(6):862-870
Based on a semiclassical theory, investigations were made of the dynamics and spectral composition of pulsed generation with self-injection of priming radiation from the active part of a three-mirror linear resonator, the passive part of which contains an active loss modulator and serves as the output reflector of the laser. It is shown that there exists a range of resonator parameters at which pulsed lasing has virtually a single frequency irrespective of the detuning of the frequencies of the priming radiation and of the nearest eigenmode of the composite resonator. Considering graphically the phase conditions of generation, it is established that among pulsed lasers with self-injection of priming radiation which are constructed on the basis of three-mirror linear and branched resonators, the most efficient for creating single-frequency generation are those in which the length of the main resonator, where generation of the pulse occurs, is larger than the length of the additional one intended for forming the priming radiation. With an inverse ratio of the lengths of the resonators, the conditions of single-frequency pulsed generation becomes dependent on the priming radiation frequency. 相似文献
72.
一类机器人系统的最优控制 总被引:1,自引:1,他引:0
王辉 《数学的实践与认识》2002,32(3):455-459
本文通过把结构阻尼系数当作控制变量来讨论一类弹性机器人系统的最优控制问题 ,并利用Banach空间几何性质证明了最优控制元的存在唯一性 相似文献
73.
理想气体在热力学中的作用 总被引:1,自引:1,他引:0
指出热力学理论是普遍的,不依赖于理想气体.理想气体为热力学理论提供了一个简单的实例,为测量热力学温度提供了一种简单的温度计. 相似文献
74.
研究了V型三能级原子BEC与双模压缩光场相互作用系统中,忽略原子间相互作用和考虑原子间相互作用时光场的正交压缩和光子数压缩。结果表明,光场的正交压缩依赖于压缩参数,而光子数压缩与压缩参数、光场信号强度有关,在一定条件下,两种压缩可同时存在。原子间相互作用影响两种压缩的涨落随时间变化的周期,以及正交分量涨落随时间变化的幅度,而对光子数压缩涨落随时间变化的幅度几乎无影响。 相似文献
75.
(S)-2-[2-(p-Tolylsulfinyl)phenyl]acetaldehyde reacts with different O-silylated ketenethioacetals in the presence of Yb(OTf)3 yielding β-hydroxythioesters in high yields and diastereoselectivities. The obtained compounds were readily transformed into β-hydroxyacids and their corresponding diols. These Mukaiyama aldol reactions are a direct evidence of the ability of the sulfinyl group to control 1,5- and 1,6-asymmetric induction processes. 相似文献
76.
We consider the problem of maximizing a linear fractional function on the Pareto efficient frontier of two other linear fractional functions. We present a finite pivoting-type algorithm that solves the maximization problem while computing simultaneously the efficient frontier. Application to multistage efficiency analysis is discussed. An example demonstrating the computational procedure is included. 相似文献
77.
Franz H. Asthalter T. Dommach M. Ehnes A. Messel K. Sergueev I. 《Hyperfine Interactions》2002,141(1-4):131-134
The present status of the new nuclear resonance beamline PETRA 1 at HASYLAB, DESY, Hamburg is described. Besides an overview
of the experimental setup some examples of recent experiments are given. Those cover the main applications, i.e., inelastic
scattering from iron alloys and quasielastic scattering from glass-forming liquids.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
78.
We obtain a solution of the DGLAP equation for the gluon at low x first by expanding the gluon in a Taylor series and then using the method of characteristics. We test its validity by comparing
it with that of Glück, Reya and Vogt. The convergence criteria of the approximation used are also discussed. We also calculate
εF
2(x,Q)2/ε In Q
2 using its approximate relations with the gluon distribution at low x. The predictions are then compared with the HERA data. 相似文献
79.
We have obtained expressions of the accelerating effect in Kerr-Newman Kasuya field. These expressionsinclude four parameters: mass m, angular momentum a, electric charge q, and magnetic charge φ. Furthermore we studyits special case (vi = 0). We get the following conclusion. In the gravitation field of souse mass with electric charge qand magnetic charge b, the acceleration of test particle has not only radial component but also transverse component.When θ = 0, the acceleration is minimum, and when θ = π/2, the acceleration is maximum. Furthermore, we discussthe effects of electric charge q and magnetic charge φ respectively. 相似文献
80.
溴酸钾-亚甲蓝催化光度法测定硝酸盐和亚硝酸盐 总被引:16,自引:1,他引:15
用镉柱将NO-3 还原为NO-2 ,利用在磷酸介质中NO-2 对溴酸钾氧化亚甲蓝这一褪色反应具有强烈的催化作用而建立了同时测定痕量硝酸盐和亚硝酸盐的新方法。本方法简便、快速、灵敏 ,对亚硝酸盐和硝酸盐测定的线性范围分别为 0~ 2 0 0 μg·L-1和 0 0 0 3~ 310 μg·L-1,用于测定各种水样中痕量NO-2 和NO-3 的含量均获得满意结果 相似文献