全文获取类型
收费全文 | 7176篇 |
免费 | 1093篇 |
国内免费 | 542篇 |
专业分类
化学 | 1521篇 |
晶体学 | 18篇 |
力学 | 525篇 |
综合类 | 61篇 |
数学 | 704篇 |
物理学 | 3154篇 |
无线电 | 2828篇 |
出版年
2024年 | 16篇 |
2023年 | 73篇 |
2022年 | 159篇 |
2021年 | 161篇 |
2020年 | 176篇 |
2019年 | 184篇 |
2018年 | 179篇 |
2017年 | 255篇 |
2016年 | 282篇 |
2015年 | 323篇 |
2014年 | 426篇 |
2013年 | 514篇 |
2012年 | 474篇 |
2011年 | 502篇 |
2010年 | 334篇 |
2009年 | 424篇 |
2008年 | 439篇 |
2007年 | 494篇 |
2006年 | 395篇 |
2005年 | 374篇 |
2004年 | 343篇 |
2003年 | 309篇 |
2002年 | 272篇 |
2001年 | 197篇 |
2000年 | 190篇 |
1999年 | 166篇 |
1998年 | 163篇 |
1997年 | 151篇 |
1996年 | 113篇 |
1995年 | 80篇 |
1994年 | 87篇 |
1993年 | 56篇 |
1992年 | 46篇 |
1991年 | 58篇 |
1990年 | 46篇 |
1989年 | 34篇 |
1988年 | 31篇 |
1987年 | 32篇 |
1986年 | 25篇 |
1985年 | 43篇 |
1984年 | 26篇 |
1983年 | 11篇 |
1982年 | 25篇 |
1981年 | 28篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1978年 | 13篇 |
1977年 | 14篇 |
1976年 | 14篇 |
1973年 | 8篇 |
排序方式: 共有8811条查询结果,搜索用时 0 毫秒
31.
Z.J. Liu H.H. Long W.C. Ye X.X. Zou Z.L. Qin E.P. Li J.S. Chen 《Journal of magnetism and magnetic materials》2006
In this paper, specific issues related to high-density perpendicular magnetic recording processes, such as transition noise properties and cross-track correlation lengths, were investigated with the help of micromagnetic analysis. The effects of media parameters were taken into consideration, including intergranular exchange coupling, and exchange distribution, irregular grain shapes, magnetization saturation distribution, and anisotropy distribution. The micromagnetic simulation results showed that the effect of anisotropy distribution on transition noise is more significant than magnetization saturation distribution, and it is crucial to reduce this effect to achieve a high signal-to-noise ratio. Additionally, a new method to further estimate the partial erasure threshold was proposed to approximate the partial erasure effects, and the relation between the microtrack jitter and total track jitter was investigated. 相似文献
32.
相关系数与相关性度量 总被引:2,自引:0,他引:2
研究了度量相关性的两个主要工具:线性相关系数和尾部相关系数.线性相关系数反映了变量间的线性相关性,这对于一般的椭圆型分布是合适的.但如果随机变量具有不对称的尾部变化特征时,要用尾部相关系数描述它们之间的相关性.通过相关函数C opu la,对沪深股市的尾部相关系数进行了定量分析.结果表明:沪深股市具有较强的相关性. 相似文献
33.
Applied Biochemistry and Biotechnology - 相似文献
34.
35.
联合功率谱的高频成份对相关峰识别具有重要作用,实验中记录的联合功率谱随着频率的增加其强度迅速降低。为增强联合功率谱的高频成分,改善其调制程度,可对功率谱进行对数变换,从而有效保留更多的高频成份,压低零级衍射光斑,提高联合变换相关器的识别能力。 相似文献
36.
A new microtensile tester for the study of MEMS materials with the aid of atomic force microscopy 总被引:4,自引:0,他引:4
An apparatus has been designed and implemented to measure the elastic tensile properties (Young's modulus and tensile strength)
of surface micromachined polysilicon specimens. The tensile specimens are “dog-bone” shaped ending in a large “paddle” for
convenient electrostatic or, in the improved apparatus, ultraviolet (UV) light curable adhesive gripping deposited with electrostatically
controlled manipulation. The typical test section of the specimens is 400 μm long with 2 μm×50 μm cross section. The new device
supports a nanomechanics method developed in our laboratory to acquire surface topologies of deforming specimens by means
of Atomic Force Microscopy (AFM) to determine (fields of) strains via Digital Image Correlation (DIC). With this tool, high
strength or non-linearly behaving materials can be tested under different environmental conditions by measuring the strains
directly on the surface of the film with nanometer resolution. 相似文献
37.
邱卫根 《数学的实践与认识》2006,36(1):227-231
提出了物元等价类概念,并利用子集合X和属性子集R对物元集合S(U,A,V,f)在集合论域U上构造了一类可拓集合A~,并讨论了A~关于X和R的一些相关性质. 相似文献
38.
39.
The fluorescence dynamics parameters of the fluorescent transient flavin-luciferase species from the typesVibrio fischeri andPhotobacterium leiognathi are presented. The fluorescence anisotropy decay is a single exponential function for both types. The correlation time is 70 ns for theP. leiognathi fluorescent transient intermediate (2°C, aqueous buffer, pH 7.0), consistent with the rotational correlation time of the luciferase macromolecule (77 kD) to which the flavin fluorophore is rigidly attached. In contrast, for theV. fischeri species the observed correlation time for the anisotropy decay function is 133 ns. This suggests that protein self-association occurs in theV. fischeri case and this is confirmed by filtration, where the fluorescent transient fromV. fischeri does not pass through a 100,000 molecular weight cutoff membrane, whereas theP. leiognathi species does. The filtration method also demonstrates self-association in the luciferase peroxyflavin and photoflavin fromV. fischeri. A monomer-dimer equilibrium also explains the previously reported high correlation times for theV. harveyi luciferase-flavin species. It is proposed that the self-association competes with the lumazine protein interaction in the bioluminescence reaction. 相似文献
40.
Solubility of carbon dioxide in aqueous solutions of sodium chloride: Experimental results and correlation 总被引:2,自引:0,他引:2
The solubility of carbon dioxide in aqueous solutions of sodium chloride was measured in the temperature range from 40 to 160°C, up to 6 mol-kg salt solutions and total pressures up to 10 MPa. Pitzer's(1) equations as well as the Chen and Evans(2) model were used to correlate the new data. Results are reported and compared to literature data and correlations. 相似文献