全文获取类型
收费全文 | 41493篇 |
免费 | 5344篇 |
国内免费 | 4225篇 |
专业分类
化学 | 11439篇 |
晶体学 | 967篇 |
力学 | 9776篇 |
综合类 | 566篇 |
数学 | 14736篇 |
物理学 | 13578篇 |
出版年
2024年 | 103篇 |
2023年 | 472篇 |
2022年 | 843篇 |
2021年 | 952篇 |
2020年 | 1206篇 |
2019年 | 1043篇 |
2018年 | 1069篇 |
2017年 | 1484篇 |
2016年 | 1671篇 |
2015年 | 1317篇 |
2014年 | 2131篇 |
2013年 | 2990篇 |
2012年 | 2546篇 |
2011年 | 2904篇 |
2010年 | 2457篇 |
2009年 | 2727篇 |
2008年 | 2622篇 |
2007年 | 2604篇 |
2006年 | 2420篇 |
2005年 | 2245篇 |
2004年 | 1914篇 |
2003年 | 1731篇 |
2002年 | 1537篇 |
2001年 | 1301篇 |
2000年 | 1218篇 |
1999年 | 1099篇 |
1998年 | 1017篇 |
1997年 | 854篇 |
1996年 | 708篇 |
1995年 | 594篇 |
1994年 | 549篇 |
1993年 | 450篇 |
1992年 | 460篇 |
1991年 | 346篇 |
1990年 | 276篇 |
1989年 | 212篇 |
1988年 | 177篇 |
1987年 | 128篇 |
1986年 | 87篇 |
1985年 | 115篇 |
1984年 | 111篇 |
1983年 | 54篇 |
1982年 | 70篇 |
1981年 | 50篇 |
1980年 | 27篇 |
1979年 | 43篇 |
1978年 | 33篇 |
1977年 | 37篇 |
1976年 | 13篇 |
1957年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Improving the membrane model by which the entropy of the black hole is studied, we study the entropy of the black hole in the non-thermal equilibrium state. To give the problem stated here widespread meaning, we discuss the (n 2)-dimensional de Sitter spacetime. Through discussion, we obtain that the black hole‘s entropy which contains two horizons (a black hole‘s horizon and a cosmological horizon) in the non-thermal equilibrium state comprises the entropy corresponding to the black hole‘s horizon and the entropy corresponding to the cosmological horizon. Furthermore, the entropy of the black hole is a natural property of the black hole. The entropy is irrelevant to the radiation field out of the horizon. This deepens the understanding of the relationship between black hole‘s entropy and horizon‘s area. A way to study the bosonic and fermionic entropy of the black hole in high non-thermal equilibrium spacetime is given. 相似文献
962.
Monte Carlo simulation of the dynamic evolution ofbinary lamellar eutectic in directional solidification 总被引:1,自引:0,他引:1 下载免费PDF全文
The dynamic evolution of the lamellar eutectic of binary alloys in directional solidification is studied in detail using the Monte Carlo technique. The simulated results can be summarized into two aspects: ({1}) the lamellar spacing λ is found to be inversely proportional to the chemical potential difference Δμ, predicting a linear relationship between the kinetic supercooling ΔT_k and total supercooling at the solid/liquid (S/L) interface; (2) as the solidifying velocity R is low, the dynamic product λ^{2}R shows a considerable dependence on temperature gradient G_T in the liquid in front of the S/L interface, although this dependence becomes much weaker at a high R. 相似文献
963.
Structural model and design technique are proposed for a polymer directional coupler electro-optic switch with rib waveguides and push-pull electrodes, of which the electric field distribution is analyzed by the conformal transforming method and image method. In order to get the minimum mode loss and the minimum switching voltage, the parameters of the waveguide and electrode are optimized, such as the core with, core thickness, buffer layer between the core and the electrode, coupling gap between the waveguides, electrode thickness, electrode width and electrode gap. Switching Characteristics are analyzed, which include the output power, insertion loss, and crosstalk. To realize normal switching function, the fabrication error, spectrum shift, and coupling loss between a single mode fiber (SMF) and the waveguide are discussed. Simulation results show that the coupling length is 3082 μm, push-pull switching voltage is 2.14 V, insertion loss is less than 1.17 dB, and crosstalk is less than −30 dB for the designed device. 相似文献
964.
Effects of unsymmetrical geometric confinements on depletion interactions in colloidal suspensions 下载免费PDF全文
The depletion interactions between two large-spheres immersed in a fluid of small spheres under unsymmetrical geometrical confinement are studied through the acceptance ratio method. The numerical results show that no matter whether the volume fraction is large or small, both the depletion potential and depletion force are affected by the presence of the two plates; the closer the two large spheres are to the plate, the larger the effects of the unsymmetrical confinements. 相似文献
965.
Simulating high Reynolds number flow in two-dimensional lid-driven cavity by multi-relaxation-time lattice Boltzmann method 总被引:3,自引:0,他引:3 下载免费PDF全文
By coupling the non-equilibrium extrapolation scheme for boundary condition with the
multi-relaxation-time lattice Boltzmann method, this paper finds that the stability
of the multi-relaxation-time model can be improved greatly, especially on
simulating high Reynolds number (Re) flow. As a discovery, the super-stability
analysed by Lallemand and Luo is verified and the complex structure of the cavity
flow is also exhibited in our numerical simulation when Re is high enough. To the
best knowledge of the authors, the maximum of Re which has been investigated by
direct numerical simulation is only around 50,000 in the literature; however,
this paper can readily extend the maximum to 1000,000 with the above combination. 相似文献
966.
967.
摄动有限体积法重构近似高精度的意义 总被引:3,自引:0,他引:3
研讨有限体积(FV)方法重构近似高精度的作用问题.FV方法中积分近似采用中点规则为二阶精度时,重构近似高精度(精度高于二阶)的意义和作用是一个有争议的问题.利用数值摄动技术[1,2]构造了标量输运方程的积分近似为二阶精度、重构近似为任意阶精度的迎风型和中心型摄动有限体积(PFV)格式.迎风PFV格式无条件满足对流有界准则(CBC),中心型PFV格式为正型格式,两者均不会产生数值振荡解.利用PFV格式求解模型方程的数值结果表明:与一阶迎风和二阶中心格式相比,PFV格式精度高、对解的间断分辨率高、稳定性好、雷诺数的适用范围大,数值地"证实"重构近似高精度和PFV格式的实际意义和好处. 相似文献
968.
Gjergj Dodbiba Hyun Seo ParkKatsunori Okaya Toyohisa Fujita 《Journal of magnetism and magnetic materials》2008
In this work, properties of a magnetorheological (MR) fluid, prepared by dispersing a mixture of two types of carbonyl iron powders (CIPs) of different sizes, in an ionic liquid (N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium tetrafluoroborate) that is stable from 9 °C to ca. 300 °C, have been investigated. At first, the random packing density of the mixture was computed as function of mixing ratio of CIP, in order to find out the tendency of the variation. Next, several mixtures, all having the same weight, were prepared at various mixing ratios and dispersed in the ionic liquid, in order to experimentally find the most suitable mixing ratio of CIP. Then, the magnetic clusters of the synthesized MR fluids were observed by using a digital microscope equipped with two permanent magnets, whereas the MR properties were investigated by using a rotation viscometer equipped with a solenoid coil. The experimental results pointed out that the MR fluid with 60 wt% fraction of large particles exhibited the highest MR response. 相似文献
969.
为了实现高双折射光子晶体光纤,提出了一种在纤芯中引入微小圆孔的方法.利用全矢量有限元方法和完美匹配层条件研究了基于圆孔微细结构纤芯的光子晶体光纤的双折射特性.讨论了纤芯圆孔数量、孔径、间隔距离对光纤双折射特性的影响;设计了一种双折射达到10-2量级的光子晶体光纤.模拟结果表明采用三个以上圆孔可以获得较大的双折射,增大外包层数目可以有效减小约束损耗. 相似文献
970.
在考虑组态相互作用的基础上,利用包含相对论修正的Hartree-Fock(HFR)理论对S8+-S13+离子的谱线波长及加权振子强度等有关原子参数进行了系统计算,并与最新的实验观测和其它理论计算结果进行了比较。计算结果表明:S8+-S11+的各个原子态在LS耦合下纯度很高,随着离化度的增大,S12+和S13+离子的部分原子态能级出现混合,组态相互作用逐渐增强。通过对实验结果的分析,识别出32条实验谱线,其中大多数谱线来自S8+-S13+离子的2s22pk-2s2pk+1和2s2pk+1-2s2pk+2(k=0,1,2,3,4)之间的跃迁,理论计算结果与实验谱线波长之间的绝对误差大多数都在实验的有效分辨力以内。 相似文献