全文获取类型
收费全文 | 38303篇 |
免费 | 449篇 |
国内免费 | 141篇 |
专业分类
化学 | 19193篇 |
晶体学 | 683篇 |
力学 | 1658篇 |
综合类 | 2篇 |
数学 | 3935篇 |
物理学 | 13422篇 |
出版年
2022年 | 315篇 |
2021年 | 368篇 |
2020年 | 347篇 |
2019年 | 350篇 |
2018年 | 545篇 |
2017年 | 471篇 |
2016年 | 778篇 |
2015年 | 459篇 |
2014年 | 775篇 |
2013年 | 1693篇 |
2012年 | 1586篇 |
2011年 | 1953篇 |
2010年 | 1413篇 |
2009年 | 1394篇 |
2008年 | 1644篇 |
2007年 | 1601篇 |
2006年 | 1464篇 |
2005年 | 1261篇 |
2004年 | 1190篇 |
2003年 | 1048篇 |
2002年 | 992篇 |
2001年 | 1372篇 |
2000年 | 992篇 |
1999年 | 830篇 |
1998年 | 633篇 |
1997年 | 603篇 |
1996年 | 530篇 |
1995年 | 484篇 |
1994年 | 459篇 |
1993年 | 409篇 |
1992年 | 476篇 |
1991年 | 483篇 |
1990年 | 467篇 |
1989年 | 427篇 |
1988年 | 454篇 |
1987年 | 441篇 |
1986年 | 383篇 |
1985年 | 461篇 |
1984年 | 485篇 |
1983年 | 353篇 |
1982年 | 396篇 |
1981年 | 389篇 |
1980年 | 336篇 |
1979年 | 410篇 |
1978年 | 391篇 |
1977年 | 408篇 |
1976年 | 396篇 |
1975年 | 348篇 |
1974年 | 326篇 |
1973年 | 342篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
Supposa that f(x) is a quasidifferentiable function, defined on S(?)R~n where S is an open set, with a -equivalent bounded quasidifferential subfam ily. Lenma I 相似文献
24.
In the study of the behaviors of barriers in an enclosed field, one should take into account such phenomena as sound energy reflection, absorption, scattering and diffraction. Therefore, the study is much more difficult than that in free field. In this paper, sound barriers are classified into four kinds according to their size, number and shape. Each kind of barriers is modelled by a corresponding method based on a computer program—SOFIS. The program combines the ray-tracing technique and statistical method. The impulse response and some acoustical parameters such as sound pressure level at different positions can be calculated by the program, no matter there are a certain kind of barriers in the field or the field is empty. The ray-tracing program and the algorithms for various barriers are validated by the comparison between measurement and prediction of the reverberation room and the anechoic room of the Northwestern Polytechnic University. 相似文献
25.
许多实验对用CsI(Tl)闪烁晶体作为探测器来寻找和探测暗物质的可行性进行了研究.本工作利用8MeV单能中子轰击CsI(Tl)晶体探测器来研究Cs核和I核的QuenchingFactor.在数据处理中,运用脉冲形状甄别(PSD)方法来分辨反冲核信号和本底信号.实验结果表明,在7keV到132keV的能区中,Quench ingFactor随着反冲核能量的减少而增加.在探测暗物质的实验中,这一性质对于CsI(Tl)晶体探测器获得较低的能量阈值是很有利的. 相似文献
26.
F. Chen L. Liu Z. Shen G.Q. Xu T.S.A. Hor 《Applied Physics A: Materials Science & Processing》2002,74(2):317-319
Free-standing and supported hydrogenated amorphous carbon films (a:C–H) were prepared upon pyrolysis of the polymer formed
by ethanolamine (EA) and citric acid (CA), under an ambient atmosphere at 300 °C. EA facilitates the formation of the macroscopic
films, while CA is essential for obtaining the a:C–H microstructure, which comprises a mixture of sp2 and sp3 carbon.
Received: 29 May 2001 / Accepted: 17 August 2001 / Published online: 20 December 2001 相似文献
27.
This paper is concerned with the implementation and testing of an algorithm for solving constrained least-squares problems. The algorithm is an adaptation to the least-squares case of sequential quadratic programming (SQP) trust-region methods for solving general constrained optimization problems. At each iteration, our local quadratic subproblem includes the use of the Gauss–Newton approximation but also encompasses a structured secant approximation along with tests of when to use this approximation. This method has been tested on a selection of standard problems. The results indicate that, for least-squares problems, the approach taken here is a viable alternative to standard general optimization methods such as the Byrd–Omojokun trust-region method and the Powell damped BFGS line search method. 相似文献
28.
The revival of the nondiffracting vortex beam after its interaction with the 2D on axis obstacle is examined. We show that the phase topology and the spatial distribution of the orbital angular momentum of the beam transmitted through the obstacle regenerate to the initial form during further free propagation. We verify that the healing effect appears even if the interaction is accompanied by the exchange of the orbital angular momentum. 相似文献
29.
Bond covalency and valence of elements in HgBa2Can−1CunO2n+2+δ (n=1, 2, 3, 4) were calculated and their relationship with Tc was discussed. For both oxygen and argon annealed samples, the results indicated that with the increase of n, the trend of bond covalency of Hg-O and Cu-O was the same or opposite compared with that of superconducting temperature. This may suggest that the magnitudes of Cu-O and Hg-O bond covalency are important in governing the superconducting temperature. For the highest Tc sample, Hg had the lowest valence, implying that lower valence of Hg was preferred in order to produce higher Tc. For fixed n, the valence of Cu in oxygen annealed samples was larger than that in argon annealed samples, indicating that oxygen annealed samples produced more carriers than argon annealed samples. 相似文献
30.
An experimental study of the aerodynamic damping of oscillating plates has been undertaken. Plates of various shapes were placed into an air flow normal to the plate and excited to oscillate parallel to the flow direction by electromagnetic forces of equal amplitudes and random frequencies. The aerodynamic damping of oscillating plates, evaluated in terms of a quality Q-factor from a frequency response resonance curve, was found to vary linearly with the absolute pressure in stationary surrounding air and with the air flow velocity in moving air. The flow velocity was also found to affect the aerodynamic damping more than the absolute pressure. A simple empirical model has been developed to predict the variation of the aerodynamic damping with the flow velocity. 相似文献