全文获取类型
收费全文 | 131776篇 |
免费 | 28355篇 |
国内免费 | 9980篇 |
专业分类
化学 | 113464篇 |
晶体学 | 961篇 |
力学 | 7418篇 |
综合类 | 564篇 |
数学 | 12692篇 |
物理学 | 35012篇 |
出版年
2024年 | 599篇 |
2023年 | 5132篇 |
2022年 | 4363篇 |
2021年 | 5556篇 |
2020年 | 7541篇 |
2019年 | 5456篇 |
2018年 | 4891篇 |
2017年 | 3213篇 |
2016年 | 9113篇 |
2015年 | 9110篇 |
2014年 | 9419篇 |
2013年 | 11149篇 |
2012年 | 10904篇 |
2011年 | 8956篇 |
2010年 | 8654篇 |
2009年 | 8397篇 |
2008年 | 6795篇 |
2007年 | 5961篇 |
2006年 | 4903篇 |
2005年 | 4091篇 |
2004年 | 3325篇 |
2003年 | 2718篇 |
2002年 | 2648篇 |
2001年 | 2223篇 |
2000年 | 1907篇 |
1999年 | 1961篇 |
1998年 | 1573篇 |
1997年 | 1622篇 |
1996年 | 1566篇 |
1995年 | 1374篇 |
1994年 | 1167篇 |
1993年 | 1126篇 |
1992年 | 911篇 |
1991年 | 746篇 |
1990年 | 651篇 |
1989年 | 536篇 |
1988年 | 495篇 |
1987年 | 421篇 |
1986年 | 364篇 |
1985年 | 331篇 |
1977年 | 356篇 |
1976年 | 399篇 |
1975年 | 484篇 |
1974年 | 491篇 |
1973年 | 318篇 |
1972年 | 382篇 |
1971年 | 359篇 |
1970年 | 547篇 |
1969年 | 414篇 |
1968年 | 462篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
基于多站测向定位提供的目标辐射源方位角信息,提出了一种基于粒子滤波的测向定位跟踪算法.该算法采用序贯蒙特卡罗的粒子滤波技术,对目标辐射源方位信息进行粒子滤波融合处理,实现了对机动目标辐射源的无源定位跟踪.仿真实验表明,该算法适用于非线性模型和非高斯噪声的目标跟踪,与传统的基于卡尔曼滤波的多传感器融合跟踪算法相比,定位跟踪更为精确,从而对提高战场电子目标定位跟踪和精确打击具有广泛的应用价值. 相似文献
152.
This work reports a new synthetic approach for single‐phase TiO2 nanomaterials by solvothermal treatment of titanium tetrachloride in acetone at 80–110 °C. Small, uniform, and yet size‐tunable (5–10 nm) anatase titania nanocrystallites were obtained using a low concentration of TiCl4 in acetone (i.e., at molar ratios of TiCl4/acetone ≤ 1:15) in the temperature range of 80–110 °C, while rutile nanofibers were synthesized using a high concentration of TiCl4 (e.g., TiCl4/acetone = 1:10) at 110 °C. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
153.
An analytical method is presented to investigate the bending-torsion vibration characteristics of a cylinder with an arbitrary cross-section and partially submerged in water. The compressibility and the free surface waves of the water are considered simultaneously in the analysis. The exact solution of structure–water interaction is obtained mathematically. Firstly, the analytical expression of the velocity potential of the water is derived by using the method of separation of variables. The unknown coefficients in the velocity potential are determined by the longitudinal and circumferential Fourier expansions along the outer surface of the cylinder and are expressed in the form of integral equations including the unknown dynamic bending deflection and torsional angle of the cylinder. Secondly, the force and torque acting on the cylinder per unit length, provided by the water, are obtained by integrating the water dynamic pressure along the circumference of the cylinder. The general solution of bending-torsion vibration of the cylinder under the water dynamic pressure is derived analytically. The integral equations included in the velocity potential of the water can be solved exactly. Finally, the eigenfrequency equation of cylinder–water interaction is obtained by means of the boundary conditions of the cylinder. Some numerical examples for elliptical columns partially submerged in water are provided to show the application of the present method. 相似文献
154.
Fuzzy random vector is a measurable map from a probability space to a collection of fuzzy vectors. Our aim in this paper is
to discuss the measurability criteria for fuzzy random vectors, and show that under mild assumption, the measurability criteria
for upper semicontinuous fuzzy random vectors can be expressed in several different but equivalent formulations. Finally,
applying the obtained results, we resolve an open problem about the relationship between fuzzy random vectors and fuzzy random
variables. 相似文献
155.
The mode equation for the dielectric waveguide with parabolic cross-section is derived using both the effective index method and WKB theory, and the expression of the mode propagation constant or effective index is solved directly from this mode equation, so that the mode-propagation properties of this kind of waveguide can be analysed conveniently with comparative accuracy. 相似文献
156.
X.C. Li J. Wu K. Xu A.Q. Liu J.T. Lin 《Applied Physics A: Materials Science & Processing》2007,89(2):327-332
This paper presents the theoretical model and the optimization method to suppress the sidelobes of side-coupled photonic crystal
filters. Numerical verification shows a good agreement between the theoretical method and the finite-difference time-domain
simulation, but the theoretic method does not involve the time-consuming computation. The theoretical method also presents
a better physical image for choosing the critical parameters, such as the quality factor, phase shift and the number of resonators.
Based on the theoretical model, two optimization methods (chirp and cascading) are proposed to deeply suppress the sidelobes.
They also show more flexibility in controlling the bandwidth and steepness of the roll-off in the filter.
PACS 42.70.Qs 相似文献
157.
900 MHz 1H NMR (nuclear magnetic resonance) spectroscopy was used to analyze metabolites in allantoic fluid of the chicken embryo in
the 9th incubation day without any chemical or physical sample separation. The result showed that superhigh spectral dispersion
and sensitivity at 900 MHz are useful in directly analyzing a complex mixture, particularly in resolving the overlapped NMR
resonances. In this study, we had assigned 61 metabolites and 26 chemical fragments in the allantoic fluid. The relative concentrations
of the major metabolites were also measured. Among the assigned metabolites, some were detected by NMR in chicken embryo allantoic
fluids for the first time. The biological functions of these compounds were briefly discussed.
Authors' address: Maili Liu, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute
of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, People's Republic of China 相似文献
158.
Yangyang Jiang Chen Guo Huizhou Liu 《中国颗粒学报》2007,5(1):130-133
A magnetically rotational reactor (MRR) has been developed and used in absorbing benzene emissions. The MRR has a permanent magnet core and uses magnetic ionic liquid [bmim]FeCl4 as absorbent. Benzene emissions were carried by N2 into the MRR and were absorbed by the magnetic ionic liquid. The rotation of the permanent magnet core provided impetus for the agitation of the magnetic ionic liquid, enhancing mass transfer and making benzene better dispersed in the absorbent. 0.68 g benzene emissions could be absorbed by a gram of [bmim]FeCl4, 0.27 and 0.40 g/g higher than that by [bmim]PF6 and [bmim]BF4, respectively. The absorption rate increased with increasing rotation rate of the permanent magnet. 相似文献
159.
160.
在研究大量实验曲线的基础上,指出势阱所有能级均有一定的宽度,电子或空穴在各能级中出现的概率符合正态分布,从理论上分析了I类超晶格和双势垒单势阱的发光光谱与吸收光谱·解释了GaAs/Ga1-xAlxAs多量子阱和超晶格吸收光谱吸收边及量子阱变窄时各吸收峰的“蓝移现象”及GaAs/Ga1-xAlxAs双势垒单量子阱样品的电流—电压特性曲线及电导—电压特性曲线的特征和出现的“负阻效应”· 相似文献