全文获取类型
收费全文 | 9290篇 |
免费 | 1318篇 |
国内免费 | 775篇 |
专业分类
化学 | 6854篇 |
晶体学 | 127篇 |
力学 | 437篇 |
综合类 | 50篇 |
数学 | 860篇 |
物理学 | 3055篇 |
出版年
2024年 | 27篇 |
2023年 | 185篇 |
2022年 | 272篇 |
2021年 | 308篇 |
2020年 | 368篇 |
2019年 | 335篇 |
2018年 | 256篇 |
2017年 | 237篇 |
2016年 | 446篇 |
2015年 | 388篇 |
2014年 | 460篇 |
2013年 | 664篇 |
2012年 | 850篇 |
2011年 | 859篇 |
2010年 | 521篇 |
2009年 | 518篇 |
2008年 | 596篇 |
2007年 | 583篇 |
2006年 | 493篇 |
2005年 | 458篇 |
2004年 | 308篇 |
2003年 | 207篇 |
2002年 | 225篇 |
2001年 | 190篇 |
2000年 | 186篇 |
1999年 | 162篇 |
1998年 | 147篇 |
1997年 | 120篇 |
1996年 | 113篇 |
1995年 | 136篇 |
1994年 | 122篇 |
1993年 | 91篇 |
1992年 | 80篇 |
1991年 | 73篇 |
1990年 | 68篇 |
1989年 | 36篇 |
1988年 | 45篇 |
1987年 | 35篇 |
1986年 | 37篇 |
1985年 | 31篇 |
1984年 | 23篇 |
1983年 | 9篇 |
1982年 | 20篇 |
1981年 | 14篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The kinetic behaviour of aluminum naphthenate/benzene system in the process of gelation and degradation was systematically studied. The results obtained from the kinetic experiments indicated that the gelation stage was in accordance with a kinetic model of an auto-catalytic first-order reaction, and the degradation stage was a simple first-order reaction. The rate constants in these two stages at various temperaturs were measured. And the determined apparent activation energies for the gelation stage and for the degradation stage are 27.5±2.0 and 37.7±2.3 kJ/mol, respectively. 相似文献
52.
53.
54.
Wei Gang SU Huai Jie ZHONG 《数学学报(英文版)》2006,22(2):515-522
This paper introduces the concept of the generalized Riesz operators and the concept of the generalized West decomposition of a general operator which generalizes the definition of the West decomposition of Riesz operators, and proves that the following three statements are equivalent on a general Banach space:
(a) Every generalized Riesz operator has the generalized West decomposition;
(b) Every operator makes strong Stampfli theorem true; Every operator has Apostol's compact correction. 相似文献
55.
Ching-Cherng Sun You-Nian Lin Shih-Po Yeh Wei-Chia Su Yuh Ouyang 《Optics & Laser Technology》2002,34(7):523-526
High longitudinal selectivity of the shifting multiplexing with spherical reference wave is proposed and demonstrated. A simplified method based on wave optics is used for calculating the selectivity, and the result fits well the experimental measurement. Under the paraxial condition, a simple formula for the longitudinal selectivity is introduced. With use of an object lens with effective NA=0.817, we obtain that an FWHM of selectivity is as small as 1 μm. 相似文献
56.
57.
We describe the formation of a narrow beam for intensity-modulated electromagnetic radiation propagating through highly scattering materials. We propose to use this beam to reconstruct images, similar to X-ray back-projection techniques. For sufficiently high modulation frequency, the photon density wave is primarily carried by photons that suffer small or no large-angle scattering, which gives rise to the beam’s narrow divergence. The beam-narrowing concept is supported by large-scale numerical simulations to examine the quality of the imaging. 相似文献
58.
关于B值随机和的完全收敛性的进一步讨论 总被引:1,自引:0,他引:1
该文在深入揭示B值非随机和完全收敛性中的一系列等价关系的基础上,给出了随机和完全收敛的充分条件,改进和完善了有关文献中的既有成果,并对矩条件的必要性问题做了初步讨论. 相似文献
59.
Isabel Echeverria Ping-Chung Su Sindee L. Simon Donald J. Plazek 《Journal of Polymer Science.Polymer Physics》1995,33(17):2457-2468
Creep and differential scanning calorimetry (DSC) measurements have been used to study the physical aging behavior of a polyetherimide. Isothermal aging temperatures ranged from 160°C to Tg with aging times ranging from 10 min to 8 days. The only measurable effect of physical aging on the short-time creep curves is a shift of the creep compliance to longer times. Andrade plots of the compliance versus the cube root of time are linear at short times with the slope β decreasing with increasing aging time to a constant value once equilibrium is reached. Log β3 is related directly to the degree to which the creep curves shift to longer times with physical aging, and is used in this work as a measure of physical aging. A reduced curve of log β3 versus log aging time is obtained for the aging temperatures investigated by appropriate vertical and horizontal shifts. The enthalpy change during aging increases linearly with the logarithm of the aging time, ta, leveling off at equilibrium at values which increase with decreasing aging temperature. Hence, both nonequilibrium and equilibrium temperature shift factors can be calculated from the DSC data. Good agreement is observed between the equilibrium temperature shift factors obtained from the creep and DSC data. The temperature dependence of the nonequilibrium temperature shift factors is found to be an order of magnitude smaller than that of the equilibrium shift factors. The time scales to reach equilibrium for enthalpy and for mechanical measurements are found to be the same within experimental error. © 1995 John Wiley & Sons, Inc. 相似文献
60.
奇异类内离差矩阵条件下的Fisher最优判据 总被引:1,自引:0,他引:1
特征提取是模式分类与识别的重要环节,Fisher最优判据是特征提取的基本方法之一.本文提出了一种计算奇异类内离差矩阵条件下Fisher最优判据的新方法,并给出了计算步骤. 相似文献