全文获取类型
收费全文 | 22849篇 |
免费 | 3823篇 |
国内免费 | 2253篇 |
专业分类
化学 | 5008篇 |
晶体学 | 253篇 |
力学 | 3865篇 |
综合类 | 208篇 |
数学 | 1715篇 |
物理学 | 9119篇 |
无线电 | 8757篇 |
出版年
2024年 | 51篇 |
2023年 | 215篇 |
2022年 | 525篇 |
2021年 | 621篇 |
2020年 | 632篇 |
2019年 | 537篇 |
2018年 | 554篇 |
2017年 | 759篇 |
2016年 | 970篇 |
2015年 | 1065篇 |
2014年 | 1557篇 |
2013年 | 1910篇 |
2012年 | 1780篇 |
2011年 | 1818篇 |
2010年 | 1448篇 |
2009年 | 1441篇 |
2008年 | 1571篇 |
2007年 | 1642篇 |
2006年 | 1435篇 |
2005年 | 1266篇 |
2004年 | 1076篇 |
2003年 | 950篇 |
2002年 | 811篇 |
2001年 | 703篇 |
2000年 | 584篇 |
1999年 | 496篇 |
1998年 | 522篇 |
1997年 | 336篇 |
1996年 | 279篇 |
1995年 | 248篇 |
1994年 | 223篇 |
1993年 | 178篇 |
1992年 | 122篇 |
1991年 | 115篇 |
1990年 | 86篇 |
1989年 | 78篇 |
1988年 | 64篇 |
1987年 | 46篇 |
1986年 | 35篇 |
1985年 | 48篇 |
1984年 | 28篇 |
1983年 | 11篇 |
1982年 | 29篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1976年 | 6篇 |
1959年 | 2篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 828 毫秒
91.
92.
93.
Quantitative H–Al distances in acid sites of two zeolites with MFI and IFR framework topology were obtained by numerical simulation of 1H{27Al} rotational echo adiabatic passage double resonance (REAPDOR) experiments. A 27Al offset-dependent data set yields for each resolved 1H NMR line a corresponding nuclear electric quadrupole coupling constant of the neighboring 27Al site. This information is used for analyzing a second data set for on-resonance irradiation, where the dipolar evolution time (number of rotor cycles) was varied, to yield the 1H–27Al dipolar coupling constant. Numerical simulations indicate that the REAPDOR method does not depend significantly on the polar angles, defining the orientation of the electric field gradient tensor of 27Al with respect to the Al–H dipolar vector. In contrast, the transfer of populations in double resonance sequence is sensitive to these angles, and it can be thus used to measure them. 相似文献
94.
用分子动力学方法模拟了空位在金刚石近(001)表面的扩散过程,研究了温度对空位扩散的影响.结果表明,当温度为1000K左右时,位于近表面第二层上的空位开始向表面运动;当温度在1400—2000K时,空位完全扩散到表面.这与实验结果和其他计算结果符合得很好.同时发现,温度为1400—1800K时,空位的扩散经历了两次迁移运动,其分别对应了均方位移图中的两个极大值.在不施加任何约束的条件下得到了空位的动态扩散路径,空位在金刚石近(001)表面的扩散势垒约为042eV.并探讨了一定温度下空位数目增多及其不同排列
关键词:
金刚石
空位
扩散
分子动力学 相似文献
95.
96.
A convergent-barrel (CB) cold spray nozzle was designed through numerical simulation. It was found that the main factors influencing significantly particle velocity and temperature include the length and diameter of the barrel section, the nature of the accelerating gas and its pressure and temperature, and the particle size. Particles can achieve a relatively low velocity but a high temperature under the same gas pressure using a CB nozzle compared to a convergent-divergent (CD) nozzle. The experiment results with Cu powder using the designed CB nozzle confirmed that particle deposition can be realized under a lower gas pressure with a CB nozzle. 相似文献
97.
This paper describes the performance and simulation of a compact integrated optical processor for the real-time reconstruction of two-dimensional images in airborne stripmap synthetic aperture radar applications. The functional behavior of the processor is explained in some detail. The design criteria are briefly given. The simulation step allowed the main processor characteristics and properties to be identified. A number of comparisons were obtained in airborne SAR mission scenarios between the predictions of the optical device and those achieved by the modern electronic digital approach, based on the wavefront reconstruction method by matched filtering. 相似文献
98.
本文针对一类非饱和土壤水流问题,提出了基于二次插值的特征差分格式,得到了严谨的L2模误差估计.并作了数值试验,指明方法的有效性. 相似文献
99.
Yukio Iida Masahiro Shibutani Katsuhiko Kobayashi Kazuhiko Ohnuma Yoichi Miyake Toru Noda 《Optical Review》2006,13(2):87-92
The double-pass method is thought to obtain the point spread function (PSF) in human eyes based on two techniques: the symmetric
double-pass method using the same pupil size and the asymmetric double-pass method using a different pupil size. The symmetric
double-pass method provides autocorrelation of the retinal PSF and, thus, the modulation transfer function. The asymmetric
double-pass method provides low-frequency partial-phase information and the partial phase-retrieval algorithm is applied to
obtain the complete-phase information, and to estimate the PSF. The partial phase-retrieval algorithm is based on the iteration
method proposed by Fineup and Kowalczyk and requires a lengthy computation. In this study, we propose a new high-speed phase-retrieval
algorithm based on the property that the real and imaginary parts of optical transfer functions (OTFs) continuously change
in value. 相似文献
100.
A one-dimensional nanodusty plasma was modeled by self-consistently coupling a plasma model with nanoparticle growth, charging,
and transport models. As nanoparticles grow from subnanometer to tens of nm in diameter, the numerical results predict a rich
spatiotemporal structure, including four distinct temporal phases: a charge-limited phase, a charge accumulation phase, an
early ion drag phase, and a sheath interaction phase. 相似文献