全文获取类型
收费全文 | 6481篇 |
免费 | 1414篇 |
国内免费 | 624篇 |
专业分类
化学 | 1478篇 |
晶体学 | 85篇 |
力学 | 622篇 |
综合类 | 88篇 |
数学 | 1131篇 |
物理学 | 5115篇 |
出版年
2024年 | 11篇 |
2023年 | 65篇 |
2022年 | 90篇 |
2021年 | 158篇 |
2020年 | 149篇 |
2019年 | 123篇 |
2018年 | 162篇 |
2017年 | 185篇 |
2016年 | 227篇 |
2015年 | 153篇 |
2014年 | 271篇 |
2013年 | 825篇 |
2012年 | 335篇 |
2011年 | 424篇 |
2010年 | 340篇 |
2009年 | 465篇 |
2008年 | 477篇 |
2007年 | 463篇 |
2006年 | 421篇 |
2005年 | 378篇 |
2004年 | 328篇 |
2003年 | 314篇 |
2002年 | 322篇 |
2001年 | 222篇 |
2000年 | 220篇 |
1999年 | 181篇 |
1998年 | 202篇 |
1997年 | 151篇 |
1996年 | 118篇 |
1995年 | 103篇 |
1994年 | 106篇 |
1993年 | 99篇 |
1992年 | 86篇 |
1991年 | 59篇 |
1990年 | 46篇 |
1989年 | 37篇 |
1988年 | 22篇 |
1987年 | 23篇 |
1986年 | 20篇 |
1985年 | 25篇 |
1984年 | 19篇 |
1983年 | 17篇 |
1982年 | 17篇 |
1981年 | 5篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1973年 | 5篇 |
排序方式: 共有8519条查询结果,搜索用时 15 毫秒
111.
112.
Yirang Yuan 《Numerical Methods for Partial Differential Equations》2003,19(5):665-681
For the coupled system of multilayer fluid dynamics in porous media, the modified characteristic finite difference fractional steps method applicable to parallel arithmetic is put forward and two‐dimensional and three‐dimensional schemes are used to form a complete set. Some techniques, such as calculus of variations, energy method, piecewise biquadratic interpolation, multiplicative commutation rule of difference operators, decomposition of high order difference operators and prior estimates are adopted. Optimal order estimates in L2 norm are derived to determine the error in the approximate solution. This method has already been applied to the numerical simulation of multilayer fluid dynamics in porous media. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 19: 665–681, 2003. 相似文献
113.
A. S. Yasyukevich V. G. Shcherbitskii V. É. Kisel' A. V. Mandrik N. V. Kuleshov 《Journal of Applied Spectroscopy》2004,71(2):202-208
A new method of determining the stimulated emission cross-section spectra from the absorption cross-section spectra, which we call the integral method of reciprocity, is suggested it does not require knowledge of the structure of the impurity-center electron levels. Based on this method, formulas for calculating the radiation lifetime of impurity centers in crystals have been derived. The effectiveness of the integral method of reciprocity was demonstrated in determining the stimulated emission cross sections and radiation lifetime of an ytterbium ion in the laser crystals Yb3+:KYW and Yb3+:KGW. 相似文献
114.
115.
北京同步辐射装置3B1B生物光谱实验站 总被引:1,自引:0,他引:1
本文介绍北京同步辐射装置(BSRF)3B1B光束线、生物光谱实验站和圆二色谱仪的基本情况。报道北京正负电子对撞机(BEPC)同步辐射专用光期间,我们在站测量了11种手征性生物和药物样品的圆二色(CD)谱,首次在国内利用同步辐射光获取了D-苯丙氨酸等样品的CD谱和D-及L-亮氨酸对称的CD曲线。 相似文献
116.
脉冲染料激光器的可见光波段辐射通过共线倍频和非共线混频实现紫外波段的连续可调谐输出.本文报道了一种闭环跟踪方法;在调谐起始波长处,将取样光束在垂直相位匹配方向分割成等光强的两部分,然后在波长调谐时比较和平衡这两部分光强.对该方法在理论上作了分析并在实验中得到成功的验证.获得的自动跟踪效率大于90%. 相似文献
117.
A formula is given to calculate the last n number of symplectic characteristic classes of the tensor product of the vector Spin(3)- and Sp(n)-bundles through its first 2n number of characteristic classes and through characteristic classes of Sp(n)-bundle. An application of this formula is given in symplectic cobordisms and in rings of symplectic cobordisms of generalized quaternion groups. 相似文献
118.
Takanari Yasui Takeshi Ohtsuka Tetsu Suzuki Shigeki Okajima Kazuya Nakayama Mitsuru Tomioka Katsuhiro Kamimura Takeo Namekata Hiroaki Minamide Hiromasa Ito 《International Journal of Infrared and Millimeter Waves》2006,27(2):199-210
A new, wide-band, high-speed and high-sensitivity THz detector has been developed. The prototype detector consists of a parabolic
cylindrical mirror, a long wire antenna and a Schottky barrier diode. Direct detection measurements have shown a stable sensitivity
of 150 ± 50 V/W for 1–2 THz without any adjustments. The long wire antenna was fixed at the focus of parabolic cylindrical
mirror then it has been realized less operation steps, easy coupling to the external THz signals and a dramatic enhancement
in the practicality of this system. The optically polished mirror and frosted surface one showed comparable sensitivities,
thus easy polishing and less cost mirror fabrication can be applied for this system. The radiation pattern showed a maximum
radiation angle of approximately 23° with its dominant main lobe, which was attributed to the wire antenna character and confirmed
good agreements with classical antenna theory. 相似文献
119.
In this paper, we discuss the detailed optical design of a beam line that is under construction on the synchrotron radiation source, Indus-1. Toroidal mirrors are used as pre-and post- focusing elements and a toroidal grating monochromator as a dispersing element. Using three interchangeable gratings, this monochromator will give, at a moderate resolution, a good throughput on the sample in the wavelength range 40 to 1000 Å. Effect of various parameters and their optimization on the resolution and throughput characteristics have been studied by ray tracing calculations, and presented. 相似文献
120.
Spherically symmetric static cosmological models filled with black-body radiation are considered. The models are isotropic
about a central observer but inhomogeneous. It is suggested that the energy density of the free gravitational field, which
is coupled to the isotropic radiation energy density, might play an important role in generating sufficient field (vacuum)
energy (when converted into thermal energy) and initiate processes like inflation. On the central world line the energy density
of the free gravitational field vanishes whereas the proper pressure and density of the isotropic black-body radiation are
constants. Further, it is shown that the cosmological constant is no more arbitrary but given in terms of the central pressure
and density. Also, at its maximum value the energy density of the free gravitational field is proved to be equal to one third
of the combined value of radiation pressure and density. 相似文献