全文获取类型
收费全文 | 28813篇 |
免费 | 5308篇 |
国内免费 | 6639篇 |
专业分类
化学 | 21913篇 |
晶体学 | 861篇 |
力学 | 1784篇 |
综合类 | 570篇 |
数学 | 3519篇 |
物理学 | 12113篇 |
出版年
2024年 | 69篇 |
2023年 | 391篇 |
2022年 | 862篇 |
2021年 | 913篇 |
2020年 | 989篇 |
2019年 | 1153篇 |
2018年 | 904篇 |
2017年 | 1084篇 |
2016年 | 1214篇 |
2015年 | 1457篇 |
2014年 | 1735篇 |
2013年 | 2232篇 |
2012年 | 2679篇 |
2011年 | 2610篇 |
2010年 | 2266篇 |
2009年 | 2308篇 |
2008年 | 2572篇 |
2007年 | 2115篇 |
2006年 | 2147篇 |
2005年 | 1919篇 |
2004年 | 1556篇 |
2003年 | 1160篇 |
2002年 | 1206篇 |
2001年 | 1042篇 |
2000年 | 956篇 |
1999年 | 665篇 |
1998年 | 362篇 |
1997年 | 289篇 |
1996年 | 261篇 |
1995年 | 234篇 |
1994年 | 244篇 |
1993年 | 205篇 |
1992年 | 158篇 |
1991年 | 135篇 |
1990年 | 105篇 |
1989年 | 86篇 |
1988年 | 86篇 |
1987年 | 46篇 |
1986年 | 50篇 |
1985年 | 48篇 |
1984年 | 38篇 |
1983年 | 34篇 |
1982年 | 34篇 |
1981年 | 30篇 |
1980年 | 24篇 |
1979年 | 21篇 |
1978年 | 17篇 |
1977年 | 12篇 |
1959年 | 8篇 |
1936年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
71.
A new prediction technique is proposed for chaotic time series. The usefulness of the technique is thatit can kick off some false neighbor points which are not suitable for the local estimation of the dynamics systems. Atime-delayed embedding is used to reconstruct the underlying attractor, and the prediction model is based on the timeevolution of the topological neighboring in the phase space. We use a feedforward neural network to approximate thelocal dominant Lyapunov exponent, and choose the spatial neighbors by the Lyapunov exponent. The model is testedfor the Mackey-Glass equation and the convection amplitude of lorenz systems. The results indicate that this predictiontechnique can improve the prediction of chaotic time series. 相似文献
72.
73.
A new stochastic method of reconstructing porous media 总被引:1,自引:0,他引:1
We present a new stochastic method of reconstructing porous medium from limited morphological information obtained from two-dimensional
micro- images of real porous medium. The method is similar to simulated annealing method in the capability of reconstructing
both isotropic and anisotropic structures of multi-phase but differs from the latter in that voxels for exchange are not selected
completely randomly as their neighborhood will also be checked and this new method is much simpler to implement and program.
We applied it to reconstruct real sandstone utilizing morphological information contained in porosity, two-point probability
function and linear-path function. Good agreement of those references verifies our developed method’s powerful capability.
The existing isolated regions of both pore phase and matrix phase do quite minor harm to their good connectivity. The lattice
Boltzmann method (LBM) is used to compute the permeability of the reconstructed system and the results show its good isotropy
and conductivity. However, due to the disadvantage of this method that the connectivity of the reconstructed system’s pore
space will decrease when porosity becomes small, we suggest the porosity of the system to be reconstructed be no less than
0.2 to ensure its connectivity and conductivity. 相似文献
74.
75.
76.
Generation of UV laser light by stimulated Raman scattering in D2, D2/Ar and D2/He using a pulsed Nd:YAG laser at 355nm 下载免费PDF全文
A pulsed Nd:YAG laser at 355nm is used to pump Raman cell filled with D_2, D_2/Ar and D_2/He. With adequately adjusted parameters, the maximum photon conversion efficiency of the first-order Stokes light (S_1, 396.796nm) reaches 33.33% in D_2/Ar and the stability of S_1 in pure D_2 is fairly high, the energy drift being less than 10% when the pump energy drifts in the range of 5%. The conversion efficiency and stability, which are functions of the composition and pressure of the Raman medium and the energy of pump laser, are investigated. The result has been used to optimize the laser transmitter system for a differential absorption lidar system to measure NO_2 concentration profiles. 相似文献
77.
乌桕类可可脂结晶过程中表现体积变化 总被引:1,自引:0,他引:1
为了解乌桕类可可脂(CTCBE)缓冷结晶横向胀罐爆裂原因,研究CTCBE结晶过程中的膨胀特性,采用流体静力法测试了不同等温结晶条件下CTCBE结晶形成的表观密度和表观体积及其横纵向膨胀状况。结果表明,CTCBE缓冷结晶后形成外部和中部两个晶区。在5-25℃的各等温结晶范围内,当结晶温度增加时,外部结晶区域减小、表观密度变化不大;中部结晶区域增大、表观密度明显减小,CTCBE的表观体积、横向、纵向膨胀率均增大,膨胀横向大于纵向。进一步表明CTCBE在自然缓冷固化的表观体积根本上由其结晶温度决定。为有效防止横向胀罐,自然缓冷固化温度应低于10℃。 相似文献
78.
79.
80.