全文获取类型
收费全文 | 1485篇 |
免费 | 191篇 |
国内免费 | 115篇 |
专业分类
化学 | 745篇 |
晶体学 | 4篇 |
力学 | 258篇 |
综合类 | 46篇 |
数学 | 69篇 |
物理学 | 669篇 |
出版年
2024年 | 6篇 |
2023年 | 15篇 |
2022年 | 52篇 |
2021年 | 60篇 |
2020年 | 63篇 |
2019年 | 48篇 |
2018年 | 30篇 |
2017年 | 60篇 |
2016年 | 65篇 |
2015年 | 68篇 |
2014年 | 60篇 |
2013年 | 157篇 |
2012年 | 99篇 |
2011年 | 84篇 |
2010年 | 69篇 |
2009年 | 75篇 |
2008年 | 55篇 |
2007年 | 86篇 |
2006年 | 87篇 |
2005年 | 54篇 |
2004年 | 51篇 |
2003年 | 56篇 |
2002年 | 43篇 |
2001年 | 47篇 |
2000年 | 45篇 |
1999年 | 37篇 |
1998年 | 36篇 |
1997年 | 27篇 |
1996年 | 20篇 |
1995年 | 28篇 |
1994年 | 24篇 |
1993年 | 12篇 |
1992年 | 11篇 |
1991年 | 11篇 |
1990年 | 16篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 3篇 |
1959年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有1791条查询结果,搜索用时 15 毫秒
1.
在综述光电对抗内涵的基础上,论述光电对抗在现代战争作战平台中的具体应用,并着重从电子战的角度论述了光电对抗在现代防空作战中的最新应用。最后指出光电对抗技术在未来电子战中的作用和发展方向。 相似文献
2.
湿度对绝缘体表面电导和气体电导有一定的影响,但通常在湿度传感器的研究中忽略了气体电导的贡献。本文通过特殊设计装置来区分表面电导和气体电导,并分别从实验和理论上进行了定性的研究。 相似文献
3.
4.
通过实验分析确立了把光纤电阻作为衡量气密性碳涂覆光纤通过2%应变筛选的过渡标准。要拉制2%应变筛选的碳涂覆光纤,其电阻值应小于30kΩ/cm。 相似文献
5.
M. Paluch 《Colloid and polymer science》1998,276(7):648-652
The results of experimental studies of the adsorption at the solution/air interface from an aqueous mixture: 2,4,6-trimethylphenol–2,4,6-trichlorophenol
are presented. The surface properties of the above-mentioned mixture were studied by surface potential and surface tension
measurements. These measurements were carried out as a function of the concentration of 2,4,6-trimethylphenol aqueous solution
at a constant concentration of 2,4,6-trichlorophenol.
Using the results obtained and based on the Gibbs equation, Helmholtz formula and Motomura’s method the relative surface excesses
of adsorbed substances, effective dipole moments, surface molar fractions of solutes and miscibility of adsorbed films were
determined.
Received: 7 November 1997 Accepted: 26 February 1998 相似文献
6.
A novel rapid pressure swing adsorption (RPSA) process is described for production of 25–50% oxygen enriched air. The embodiment consists of one or more pairs of adsorbent layers contained in a single adsorption vessel. The layers undergo simultaneous pressurization-adsorption and simultaneous depressurization-purge steps. A total cycle time of 6–20 seconds is used. The process yields a very large specific oxygen production rate and a reasonable oxygen recovery for production of 20–50 mole% oxygen enriched gas.It is demonstrated by a simple mathematical model of isothermal single adsorbate pressure swing ad(de)sorption concept on a single adsorbent particle that the specific production rate of a PSA process cannot be indefinitely increased by reducing the cycle time of operation when adsorbate mass transfer resistances are finite. 相似文献
7.
针对钝头机体用嵌入式大气数据传感(flush air data sensing,FADS)系统的4类攻角求解算法及算法的求解精度进行研究.针对典型的15°钝头体外形,在Mach数Ma=2.04,3.02,5.01,攻角α=-5°~30°,侧滑角β=0°的条件下,首先基于势流理论及修正的Newton流理论建立了钝头机体用... 相似文献
8.
Rotating-detonation-engines (RDE’s) represent an alternative to the extensively studied pulse-detonation-engines (PDE’s) for obtaining propulsion from the high efficiency detonation cycle. Since it has received considerably less attention, the general flow-field and effect of parameters such as stagnation conditions and back pressure on performance are less well understood than for PDE’s. In this article we describe results from time-accurate calculations of RDE’s using algorithms that have successfully been used for PDE simulations previously. Results are obtained for stoichiometric hydrogen–air RDE’s operating at a range of stagnation pressures and back pressures. Conditions within the chamber are described as well as inlet and outlet conditions and integrated quantities such as total mass flow, force, and specific impulse. Further computations examine the role of inlet stagnation pressure and back pressure on detonation characteristics and engine performance. The pressure ratio is varied between 2.5 and 20 by varying both stagnation and back pressure to isolate controlling factors for the detonation and performance characteristics. It is found that the detonation wave height and mass flow rate are determined primarily by the stagnation pressure, whereas overall performance is closely tied to pressure ratio. Specific impulses are calculated for all cases and range from 2872 to 5511 s, and are lowest for pressure ratios below 4. The reason for performance loss is shown to be associated with the secondary shock wave structure that sets up in the expansion portion of the RDE, which strongly effects the flow at low pressure ratios. Expansion to supersonic flow behind the detonation front in RDE’s with higher pressure ratios isolate the detonation section of the RDE and thus limit the effect of back pressure on the detonation characteristics. 相似文献
9.
This paper analytically investigates the interaction of light
filaments generated by a femtosecond laser beam in air. It obtains the
Hamiltonian of a total laser field and interaction force between two
filaments with different phase shifts and crossing angles. The
property of the interaction force, which leads the attraction or
repulsion of filaments, is basically dependent on the phase shift
between filaments. The crossing angle between two filaments can only
determine the magnitude of the interaction force, but does not
change the property of the force. 相似文献
10.