全文获取类型
收费全文 | 14310篇 |
免费 | 1554篇 |
国内免费 | 866篇 |
专业分类
化学 | 10042篇 |
晶体学 | 160篇 |
力学 | 558篇 |
综合类 | 47篇 |
数学 | 1243篇 |
物理学 | 4680篇 |
出版年
2023年 | 173篇 |
2022年 | 326篇 |
2021年 | 334篇 |
2020年 | 385篇 |
2019年 | 384篇 |
2018年 | 338篇 |
2017年 | 300篇 |
2016年 | 475篇 |
2015年 | 500篇 |
2014年 | 604篇 |
2013年 | 932篇 |
2012年 | 1047篇 |
2011年 | 1040篇 |
2010年 | 705篇 |
2009年 | 674篇 |
2008年 | 862篇 |
2007年 | 714篇 |
2006年 | 741篇 |
2005年 | 641篇 |
2004年 | 600篇 |
2003年 | 457篇 |
2002年 | 467篇 |
2001年 | 350篇 |
2000年 | 297篇 |
1999年 | 239篇 |
1998年 | 206篇 |
1997年 | 218篇 |
1996年 | 212篇 |
1995年 | 153篇 |
1994年 | 180篇 |
1993年 | 177篇 |
1992年 | 148篇 |
1991年 | 126篇 |
1990年 | 122篇 |
1989年 | 95篇 |
1988年 | 100篇 |
1987年 | 94篇 |
1986年 | 106篇 |
1985年 | 132篇 |
1984年 | 116篇 |
1983年 | 58篇 |
1982年 | 80篇 |
1981年 | 87篇 |
1980年 | 83篇 |
1979年 | 70篇 |
1978年 | 74篇 |
1977年 | 74篇 |
1976年 | 65篇 |
1975年 | 47篇 |
1974年 | 61篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
This paper presents a new scheduling method for manufacturing system based on the Timed Petri Net model and a reactive fast graph search algorithm. The following two typical problems are addressed in this paper. (1) Minimization of the maximum completion time. (2) Minimization of the total tardiness. As for the problem (1), a new search algorithm which combines the RTA∗ and a rule-based supervisor is proposed. As for problem (2), the original Petri Net model is converted to its reverse model and the algorithm developed for the problem (1) is applied, regarding the due date as the starting time in the reverse model. Some numerical experiments are carried out to demonstrate usefulness of our algorithm. 相似文献
12.
HaiHuiXIE XiaoYiWEI JiDongWANG MeiFangLIU RenZhouYANG 《中国化学快报》2003,14(6):588-590
A New Annonaceous acetogenin,squamostolide(1),was isolated from the seeds of Annona squamosa.Its structure was elucidated based on spectroscopic methods and comparison with known compounds.It is the first example of Annonaceous acetogenin with each of the two ends of the aliphatic chain bearing a γ-lactone.Thenew compound exhibited cytotoxic activity in vitro against bel-7402 and CNE2 human tumor cell lines. 相似文献
13.
本文使用变分方法证明了三维标准切触球的标准勒让德扭结,至少存在一个弦连结适应于标准切触结构的任何选定切触形式,这部分证明了著名的阿诺德弦猜想。 相似文献
14.
René Meziat Diego Patiño Pablo Pedregal 《Computational Optimization and Applications》2007,38(1):147-171
We propose an alternative method for computing effectively the solution of non-linear, fixed-terminal-time, optimal control
problems when they are given in Lagrange, Bolza or Mayer forms. This method works well when the nonlinearities in the control
variable can be expressed as polynomials. The essential of this proposal is the transformation of a non-linear, non-convex
optimal control problem into an equivalent optimal control problem with linear and convex structure. The method is based on
global optimization of polynomials by the method of moments. With this method we can determine either the existence or lacking
of minimizers. In addition, we can calculate generalized solutions when the original problem lacks of minimizers. We also
present the numerical schemes to solve several examples arising in science and technology. 相似文献
15.
In the present paper, some types of general solutions of a first-order nonlinear ordinary differential equation with six degree are given and a new generalized algebra method is presented to find more exact solutions of nonlinear differential equations. As an application of the method and the solutions of this equation, we choose the (2 + 1) dimensional Boiti Leon Pempinelli equation to illustrate the validity and advantages of the method. As a consequence, more new types and general solutions are found which include rational solutions and irrational solutions and so on. The new method can also be applied to other nonlinear differential equations in mathematical physics. 相似文献
16.
Zhen‐Feng Chen Hong‐Li Zhou Hong Liang Yan Li Ren‐Gen Xiong Xiao‐Zeng You 《应用有机金属化学》2003,17(11):883-884
The centrosymmetric binuclear structure of [Pb2(H‐Norf)2(ONO2)4]shows the geometry around each lead(II) atom to be distorted trigonal bipyramidal with Pb–O distances ranging from 2.357(3) to 2.769(4) Å. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
17.
18.
19.
Lasing conditions for He I in a cold recombining helium plasma are numerically discussed including optical thicknesses. A collisional radiative model is used to calculate population densities. We discuss the effect of self absorptions by the background residual gas on the lasing conditions quantitatively. The optical thickness is essential in the calculation and affects the population inversions between level pairs of the singlet state drastically, while those of the triplet state are not affected very much. In the optically thin plasma, the laser lower levels of the singlet state depopulate mainly through radiative transitions. On the other hand, they depopulate mainly through electron collisional deexcitations in the optically thick plasma. Results of the calculations are verified by the spectroscopic observations of an arc-heated magnetically trapped expanding plasma jet generator which we developed. The requirement for the background pressure in which the lasing is possible is discussed quantitatively. 相似文献
20.
All-optical wavelength conversion of 10-Gb/s signal based on four-wave mixing is experimentally demonstrated in a 30-m-long dispersion-flattened microstructure fiber with small positive dispersion. For an average pump power of 26 dBm, the conversion efficiency was around -19.5 dB with the fluctuation less than ±1.4 dB, covering a conversion bandwidth of 20 nm. The eye diagram of the converted signal shows good eye opening. 相似文献