全文获取类型
收费全文 | 6207篇 |
免费 | 952篇 |
国内免费 | 466篇 |
专业分类
化学 | 979篇 |
晶体学 | 20篇 |
力学 | 884篇 |
综合类 | 48篇 |
数学 | 314篇 |
物理学 | 5380篇 |
出版年
2024年 | 7篇 |
2023年 | 31篇 |
2022年 | 105篇 |
2021年 | 104篇 |
2020年 | 124篇 |
2019年 | 87篇 |
2018年 | 97篇 |
2017年 | 253篇 |
2016年 | 265篇 |
2015年 | 239篇 |
2014年 | 408篇 |
2013年 | 384篇 |
2012年 | 377篇 |
2011年 | 435篇 |
2010年 | 315篇 |
2009年 | 384篇 |
2008年 | 451篇 |
2007年 | 455篇 |
2006年 | 378篇 |
2005年 | 308篇 |
2004年 | 311篇 |
2003年 | 282篇 |
2002年 | 236篇 |
2001年 | 252篇 |
2000年 | 208篇 |
1999年 | 170篇 |
1998年 | 151篇 |
1997年 | 147篇 |
1996年 | 112篇 |
1995年 | 97篇 |
1994年 | 63篇 |
1993年 | 71篇 |
1992年 | 47篇 |
1991年 | 46篇 |
1990年 | 37篇 |
1989年 | 34篇 |
1988年 | 29篇 |
1987年 | 24篇 |
1986年 | 12篇 |
1985年 | 23篇 |
1984年 | 18篇 |
1983年 | 12篇 |
1982年 | 16篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有7625条查询结果,搜索用时 593 毫秒
81.
在测量微安表内阻的众多方法中,替代法是最简单的方法。本文全面分析了影响测量结果不确定度的因素,求出了实验测量的最佳条件,计算了普通仪器组合下测量结果的相对不确定度。 相似文献
82.
Michael Höft Jochen Weinzierl Rolf Judaschke 《International Journal of Infrared and Millimeter Waves》2002,23(7):1127-1146
Holography is a promising technique for power combining applications in the frequency range of short millimeter and submillimeter waves. In this paper, quasi-optical holographic power combining circuits are investigated. An equivalent network is utilized which rigorously models horn arrays and biperiodic dielectric structures in order to design computer-generated holograms. We apply the network model to a 5-element quasi-optical power combiner and demonstrate its capability. The hologram is designed for 150 GHz and has an efficiency of 92.5 % with a 90 % bandwidth of 5.3 %. With the aid of a broadband waveguide power divider and a vector field measurement system, the circuit is analyzed. 相似文献
83.
Dieter Petrak 《Particle & Particle Systems Characterization》2002,19(6):391-400
The objective of this study was to compare the measuring results of a fiber‐optical probe based on a modified spatial filtering technique with given size distributions of different test powders and also with particle velocity values of laser Doppler measurements. Fiber‐optical spatial filtering velocimetry was modified by fiber‐optical spot scanning in order to determine simultaneously the size and the velocity of particles. The fiber‐optical probe system can be used as an in‐line measuring device for sizing of particles in different technical applications. Spherical test particles were narrow‐sized glass beads in the range 30–100 μm and irregularly shaped test particles were limestone particles in the range 10–600 μm. Particles were dispersed by a brush disperser and the measurements were carried out at a fixed position in a free particle‐laden air stream. Owing to the measurement of chord lengths and to the influence of diffraction and divergent angle, the probe results show differences from the given test particle sizes. Owing to the particle‐probe collisions, the mean velocity determined by the probe is smaller than the laser Doppler mean velocity. 相似文献
84.
Laser Doppler vibrometer (LVD) has been the most favorite instrument for precision dynamics measurement due to its non-contact, high accuracy and high resolution. However, LDV can only give the dynamic data of a particular location on the entire feature. In order to get the whole field data, a laser beam-scanning mechanism has to be implemented. Currently, motor-driven scanning mirror is used to move the measurement probe from one point to another. The mechanical vibrations of the scanning mirror will reduce the measurement accuracy. This paper introduces a novel scanning LDV optical system embodied in an acousto-optic deflector scanning mechanism. It can improve the measurement accuracy since there is no mechanical motion involved. One main advantage of this system is that it generates a laser scanning beam in parallel that is different from the beam scanning in the conventional scanning laser Doppler vibrometer (SLDV). The new system has a board scanning range. The measurement target size ranges from few tens of millimeters down to 10 μm. We have demonstrated the capability of the novel system on scanning measurements of features as big as ultra-precision cutting tool to features as tiny as AFM cantilever. We believe that the novel SLDV will find profound potential applications in the precision engineering field. 相似文献
85.
利用莫尔条纹的准正弦特性的三维轮廓术 总被引:5,自引:0,他引:5
分析了两个矩形光栅迭合产生的莫尔条纹的光强分布特性,通过选择适当的光栅参数,可得到一个近似的正弦分划板,并把它用于三维面形测量中,实验结果表明,这种方法简单,易于自动处理,有广泛的实用价值。 相似文献
86.
振动谱学研究中的光谱线型函数 总被引:3,自引:1,他引:2
本文讨论了在振动谱带计算拟合处理中的光谱线型函数问题,推导出适用于单道及多道拉曼光谱仪及色散型红外谱仪谱带线型公式。通过实验及拟合计算证实了它们的适用性并讨论了可能的误差源。理论计算和实验验证结果说明:在振动谱的谱带拟合计算中,应使用根据测谱条件计算求得的谱带线型函数,以保证拟合结果的可靠性。 相似文献
87.
Two extensions of the univariate Gini index are considered:RD, based on expected distance between two independent vectors from the same distribution with finite meanμ
d; andRV, related to the expected volume of the simplex formed fromd+1 independent such vectors. A new characterization ofRDas proportional to a univariate Gini index for a particular linear combination of attributes relates it to the Lorenz zonoid. TheLorenz zonoidwas suggested as a multivariate generalization of the Lorenz curve.RVis, up to scaling, the volume of the Lorenz zonoid plus a unit cube of full dimension. Whend=1, bothRDandRVequal twice the area between the usual Lorenz curve and the line of zero disparity. Whend>1, they are different, but inherit properties of the univariate Gini index and are related via the Lorenz zonoid:RDis proportional to the average of the areas of some two-dimensioned projections of the lift zonoid, whileRVis the average of the volumes of projections of the Lorenz zonoid over all coordinate subspaces. 相似文献
88.
89.
电磁继电器触点参数的测试 总被引:1,自引:0,他引:1
本文介绍了电磁继电器触点电参数的测试方法,包括接触电阻、绝缘电阻参数测试。 相似文献
90.
张正丽 《新疆大学学报(理工版)》2003,20(2):167-170
通过对气相色谱各项技术指标及意义的介绍,使应用者娴熟地掌握气相色谱的各项技术指标和测算方法,正确的表达分析检测结果。 相似文献