全文获取类型
收费全文 | 26494篇 |
免费 | 3628篇 |
国内免费 | 2097篇 |
专业分类
化学 | 4969篇 |
晶体学 | 265篇 |
力学 | 8806篇 |
综合类 | 322篇 |
数学 | 8028篇 |
物理学 | 9829篇 |
出版年
2024年 | 51篇 |
2023年 | 250篇 |
2022年 | 598篇 |
2021年 | 612篇 |
2020年 | 736篇 |
2019年 | 602篇 |
2018年 | 625篇 |
2017年 | 850篇 |
2016年 | 1009篇 |
2015年 | 837篇 |
2014年 | 1347篇 |
2013年 | 2097篇 |
2012年 | 1376篇 |
2011年 | 1642篇 |
2010年 | 1366篇 |
2009年 | 1584篇 |
2008年 | 1616篇 |
2007年 | 1682篇 |
2006年 | 1551篇 |
2005年 | 1417篇 |
2004年 | 1213篇 |
2003年 | 1202篇 |
2002年 | 1056篇 |
2001年 | 963篇 |
2000年 | 877篇 |
1999年 | 831篇 |
1998年 | 798篇 |
1997年 | 602篇 |
1996年 | 485篇 |
1995年 | 433篇 |
1994年 | 351篇 |
1993年 | 266篇 |
1992年 | 273篇 |
1991年 | 224篇 |
1990年 | 185篇 |
1989年 | 117篇 |
1988年 | 81篇 |
1987年 | 80篇 |
1986年 | 59篇 |
1985年 | 78篇 |
1984年 | 52篇 |
1983年 | 35篇 |
1982年 | 38篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1957年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
91.
92.
B. M. Azizur Rahman A. K. M. Saiful Kabir Muttukrishnan Rajarajan Kenneth T. V. Grattan 《Optical and Quantum Electronics》2005,37(1-3):171-183
Modal solutions of planar photonic crystal waveguides with rectangular air-holes are presented by using a rigorous full-vectorial finite element-based approach. The effective indices, mode field profiles, spot-sizes, power confinements, modal hybridness, beat lengths and group velocity dispersions are shown for the fundamental and higher order modes of the quasi-TE and TM polarizations. 相似文献
93.
Yang Zuosheng 《国际流体数值方法杂志》2005,47(12):1423-1430
A complete boundary integral formulation for compressible Navier–Stokes equations with time discretization by operator splitting is developed using the fundamental solutions of the Helmholtz operator equation with different order. The numerical results for wall pressure and wall skin friction of two‐dimensional compressible laminar viscous flow around airfoils are in good agreement with field numerical methods. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
94.
95.
We consider the isothermal flow through a cylindrical flat chamber, a model of some particular heat exchanger, for which LDV measurements and a numerical simulation have been performed. Experimental results show the establishment of an important vortex zone, the secondary flow extending all along the chamber radius. This observation leads to an expected significant increase of the fluid mixing. Results issued from the numerical simulation appear to be in close agreement with experimental data. Nevertheless, the k–ε model used here must be improved to obtain a better approach near the vortex centre. To cite this article: S. Petitot et al., C. R. Mecanique 330 (2002) 593–599. 相似文献
96.
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
97.
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
98.
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
99.
Chen Hao 《中国科学A辑(英文版)》2006,49(5):715-720
In this paper, for the the primes p such that 3 is a divisor of p − 1, we prove a result which reduces the computation of the linear complexity of a sequence over GF(p
m) (any positive integer m) with the period 3n (n and p
m − 1 are coprime) to the computation of the linear complexities of three sequences with the period n. Combined with some known algorithms such as generalized Games-Chan algorithm, Berlekamp-Massey algorithm and Xiao-Wei-Lam-Imamura
algorithm, we can determine the linear complexity of any sequence over GF(p
m) with the period 3n (n and p
m
− 1 are coprime) more efficiently. 相似文献
100.
We have used x-ray fluorescence analysis to study the elemental composition of gunshot residues from smooth-bore and rifled-bore
guns. We have established that it is possible to differentiate between types of projectiles (jacketed/lead), types of primers
(corrosive/noncorrosive), and types of propellant powders (black/smokeless) by analysis of the elemental composition of the
gunshot residues. We have shown that the mercury content in gunshot residues on the surface of the object carrying the residues
steadily decreases as storage time increases. Despite this fact, mercury can be preserved as a component of gunshot residues
on the object (cotton cloth) under room conditions for more than 45 days.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 320–325, May–June, 2006. 相似文献