全文获取类型
收费全文 | 79281篇 |
免费 | 8855篇 |
国内免费 | 12246篇 |
专业分类
化学 | 49591篇 |
晶体学 | 2118篇 |
力学 | 2915篇 |
综合类 | 781篇 |
数学 | 16175篇 |
物理学 | 28802篇 |
出版年
2024年 | 85篇 |
2023年 | 1154篇 |
2022年 | 1254篇 |
2021年 | 2349篇 |
2020年 | 2540篇 |
2019年 | 2378篇 |
2018年 | 2033篇 |
2017年 | 2548篇 |
2016年 | 2710篇 |
2015年 | 2408篇 |
2014年 | 3585篇 |
2013年 | 6517篇 |
2012年 | 4578篇 |
2011年 | 5720篇 |
2010年 | 4677篇 |
2009年 | 5481篇 |
2008年 | 5571篇 |
2007年 | 5467篇 |
2006年 | 5034篇 |
2005年 | 4423篇 |
2004年 | 4167篇 |
2003年 | 3534篇 |
2002年 | 3135篇 |
2001年 | 2449篇 |
2000年 | 2350篇 |
1999年 | 1979篇 |
1998年 | 1691篇 |
1997年 | 1418篇 |
1996年 | 1199篇 |
1995年 | 1137篇 |
1994年 | 1080篇 |
1993年 | 855篇 |
1992年 | 792篇 |
1991年 | 636篇 |
1990年 | 475篇 |
1989年 | 440篇 |
1988年 | 364篇 |
1987年 | 276篇 |
1986年 | 244篇 |
1985年 | 261篇 |
1984年 | 230篇 |
1983年 | 115篇 |
1982年 | 171篇 |
1981年 | 179篇 |
1980年 | 138篇 |
1979年 | 126篇 |
1978年 | 111篇 |
1977年 | 93篇 |
1976年 | 68篇 |
1973年 | 51篇 |
排序方式: 共有10000条查询结果,搜索用时 29 毫秒
131.
The breakthrough and stoichiometric SO2 adsorption efficiencies of a biomass supported Na2CO3 system (80 wt %Na2CO3/straw) have reached 48.9% and 80.6% respectively at a desulfurization temperature of 80℃. 相似文献
132.
A construction for Segal operations for K-theory of categories with cofibrations, weak equivalences and a biexact pairing is given and coherence properties of the operations are studied. The model for K-theory, which is used, allows coherence to be studied by means of (symmetric) monoidal functors. In the case of Waldhausen A-theory it is shown how to recover the operations used in Waldhausen (Lecture Notes in Mathematics, Vol. 967, Springer, Berlin, 1982, pp. 390-409) for the A-theory Kahn-Priddy theorem. The total Segal operation for A-theory, which assembles exterior power operations, is shown to carry a natural infinite loop map structure. The basic input is the un-delooped model for K-theory, which has been developed from a construction by Grayson and Gillet for exact categories in Gunnarsson et al. (J. Pure Appl. Algebra 79 (1992) 255), and Grayson's setup for operations in Grayson (K-theory (1989) 247). The relevant material from these sources is recollected followed by observations on equivariant objects and pairings. Grayson's conditions are then translated to the context of categories with cofibrations and weak equivalences. The power operations are shown to be well behaved w.r.t. suspension and are extended to algebraic K-theory of spaces. Staying close with the philosophy of Waldhausen (1982) Waldhausen's maps are found. The Kahn-Priddy theorem follows from splitting the “free part” off the equivariant theory. The treatment of coherence of the total operation in A-theory involves results from Laplaza (Lecture Notes in Mathematics, Vol. 281, Springer, Berlin, 1972, pp. 29-65) and restriction to spherical objects in the source of the operation. 相似文献
133.
F.E. SalmanN. Shash H. Abou El-HadedM.K. El-Mansy 《Journal of Physics and Chemistry of Solids》2002,63(11):1957-1966
AC conductivity and dielectric studies on vanadium phosphate glasses doped with lithium have been carried out in the frequency range 0.2-100 kHz and temperature range 290-493 K. The frequency dependence of the conductivity at higher frequencies in glasses obeys a power relationship, σac=Aωs. The obtained values of the power s lie in the range 0.5≤s≤1 for both undoped and doped with low lithium content which confirms the electron hopping between V4+ and V5+ ions. For doped glasses with high lithium content, the values of s≤0.5 which confirm the domination of ionic conductivity. The study of frequency dependence of both dielectric constant and dielectric loss showed a decrease with increasing frequency while they increase with increasing temperature. The results have been explained on the basis of frequency assistance of electron hopping besides the ionic polarization of the glasses. The bulk conductivity increases with increasing temperature whereas decreases with increasing lithium content which means a reduction of the V5+. 相似文献
134.
135.
A Dirac picture perturbation theory is developed for the time evolution operator in classical dynamics in the spirit of the Schwinger–Feynman–Dyson perturbation expansion and detailed rules are derived for computations. Complexification formalisms are given for the time evolution operator suitable for phase space analyses, and then extended to a two-dimensional setting for a study of the geometrical Berry phase as an example. Finally a direct integration of Hamilton's equations is shown to lead naturally to a path integral expression, as a resolution of the identity, as applied to arbitrary functions of generalized coordinates and momenta. 相似文献
136.
A Garcia-Quiroz David L AzevedoE.C da Silva 《Journal of Physics and Chemistry of Solids》2002,63(10):1863-1866
Properties of oxygenated carbon nitride films have attracted the attention of physics researchers due to their magnetic and physical properties, as well as for their usefulness in the industry. The free radicals were investigated using electron paramagnetic resonance applied in the study of spin concentration due to the different mechanism of preparation of carbon nitride films by RF-discharge with different kinds of plasma. Unpaired spin concentrations, in the order of 1020 per cm3, were measured and their time recombination dependency was important in those films. The films were grown by plasma enhanced chemical vapor deposition using mixtures of hydrocarbons, N2 and O2 in different proportions. 相似文献
137.
A simple simulation scheme that simultaneously describes the growth kinetics of SiO2 films at the nanometer scale and the SiOx/Si interface dynamics (its extent, and spatial/temporal evolution) is presented. The simulation successfully applies to experimental data in the region above and below 10 nm, reproduces the Deal and Grove linear-parabolic law and the oxide growth rate enhancement in the very thin film regime (the so-called anomalous region). According to the simulation, the oxidation is governed mainly by two processes: (a) the formation of a transition suboxide layer and (b) its subsequent drift towards the silicon bulk. We found that it is the superposition of these two processes that produces the crossover from the anomalous oxidation region behavior to the linear-parabolic law. 相似文献
138.
陈泽乾 《数学物理学报(B辑英文版)》2002,22(3)
A new framework of Gaussian white noise calculus is established, in line with generalized expansion in [3, 4, 7]. A suitable frame of Fock expansion is presented on Gaussian generalized expansion functionals being introduced here, which provides the integral kernel operator decomposition of the second quantization of Koopman operators for chaotic dynamical systems, in terms of annihilation operators dt and its dual, creation operators t*. 相似文献
139.
通过数值模拟的方法,对高斯孤子在对数型饱和非线性介质中的相互作用进行了研究,考查了两光束间的相对振幅和相对相位对其相互作用的影响。结果表明:高斯孤子之间的相互作用敏感地依赖于两光束间的相对振幅和相对相位。在不同的振幅差异范围内,光束间的主要作用交替地表现为相互排斥和相互吸引,并由于高斯孤子的不稳定性,导致了光束在碰撞后以一种尺寸周期性变化的呼吸模式传输。随着相对相位的增大,两光束间始终持续地表现出强烈的排斥作用,直到相对相位增加到一个2π周期之后。而且碰撞之后,光束也都以呼吸模式进行传输,其分离的角度越大,呼吸就越明显。 相似文献
140.
采用固相法在较低温度下合成了Eu2+激活的Ca2SiO3Cl2高亮度蓝白色发光材料,并对其发光性质进行了研究。其发射光谱由两个谱带组成,峰值分别位于420,498nm处,归结为Ca2SiO3Cl2晶体中占据两种不同Ca2+格位的Eu2+离子的5d→4f跃迁发射。改变Eu2+浓度,可以使样品的发光在蓝白色和绿白色之间变化。当Eu2+浓度为0.005mol-1时,样品呈现很亮的蓝白色发光。两个发射峰的激发光谱均分布在250~410nm的波长范围内,峰值分别位于333,369nm处。Ca2SiO3Cl2:Eu2+可被InGaN管芯产生的近紫外辐射有效激发,是一种性能良好的白光LED用单一基质蓝白色荧光粉。 相似文献