全文获取类型
收费全文 | 18976篇 |
免费 | 3628篇 |
国内免费 | 1808篇 |
专业分类
化学 | 4503篇 |
晶体学 | 220篇 |
力学 | 2720篇 |
综合类 | 283篇 |
数学 | 3314篇 |
物理学 | 13372篇 |
出版年
2024年 | 37篇 |
2023年 | 179篇 |
2022年 | 441篇 |
2021年 | 519篇 |
2020年 | 567篇 |
2019年 | 470篇 |
2018年 | 471篇 |
2017年 | 627篇 |
2016年 | 756篇 |
2015年 | 672篇 |
2014年 | 1043篇 |
2013年 | 1389篇 |
2012年 | 1201篇 |
2011年 | 1281篇 |
2010年 | 1167篇 |
2009年 | 1241篇 |
2008年 | 1265篇 |
2007年 | 1160篇 |
2006年 | 1207篇 |
2005年 | 1025篇 |
2004年 | 1063篇 |
2003年 | 877篇 |
2002年 | 819篇 |
2001年 | 710篇 |
2000年 | 655篇 |
1999年 | 552篇 |
1998年 | 480篇 |
1997年 | 395篇 |
1996年 | 356篇 |
1995年 | 266篇 |
1994年 | 224篇 |
1993年 | 184篇 |
1992年 | 164篇 |
1991年 | 140篇 |
1990年 | 127篇 |
1989年 | 138篇 |
1988年 | 84篇 |
1987年 | 77篇 |
1986年 | 80篇 |
1985年 | 54篇 |
1984年 | 40篇 |
1983年 | 24篇 |
1982年 | 32篇 |
1981年 | 38篇 |
1980年 | 23篇 |
1979年 | 24篇 |
1978年 | 20篇 |
1977年 | 12篇 |
1976年 | 7篇 |
1975年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
A. N. Logunov 《Journal of Russian Laser Research》2004,25(4):331-348
A physical multidimensional local model of the propagation process of a laser pulse in air having no analogy to famous models in laser physics is constructed. It is based on the representations of classical wave mechanics characteristic of the theory of scalar wave fields. 相似文献
42.
Hongwei Hao Minsheng Wu Yifang Chen Jiaowen Tang Qingyu Wu 《Colloids and surfaces. B, Biointerfaces》2004,33(3-4):151-156
To prevent cyanobacterial bloom in eutrophic water by ultrasonic method, ultrasonic irradiations with different parameters were tested to inhibit Spirulina platensis from growth. The experimental result based on cyanobacterial growth, chlorophyll a and photosynthetic activity showed that, the ultrasonic irradiation inhibited cyanobacterial proliferation effectively, furthermore the inhibition effectiveness increased in the order: 200 kHz>1.7 MHz>20 kHz and became saturated with the increased power. The inhibition mechanism can be mainly attributed to the mechanical damage to the cell structures caused by ultrasonic cavitation, which was confirmed by light microscopy and differential interference microscopy. The optimal frequency of 200 kHz in cavition and sonochemistry was also most effective in cyanobacterial growth inhibition. The higher frequency of 1.7 MHz is weaker than 20 kHz in cavitation, but has more effective inhibition because it is nearer to the resonance frequency of gas vesicle. The inhibition saturation with ultrasonic power was due to the ultrasonic attenuation induced by the acoustic shielding of bubbles enclosing the radiate surface of transducer. 相似文献
43.
According to a multiphase mixture theory, we have mathematically developed a multiphysical model with chemoelectromechanical coupling considerations, termed the multieffect‐coupling electric‐stimulus (MECe) model, to simulate the responsive behavior of electric‐sensitive hydrogels immersed in a bath solution under an externally applied electric field. For solutions of the MECe model consisting of coupled nonlinear partial differential governing equations, a meshless Hermite–Cloud method with a hierarchical iteration technique has been used for a one‐dimensional steady‐state analysis of a hydrogel strip. The computed results are compared with the experimental data, and there is very good agreement. Simulations within the domains of both hydrogels and surrounding solutions also present distributions of the ionic concentrations and electric potential as well as the hydrogel displacement. The effects of various physical parameters on the response behavior of electric‐stimulus responsive hydrogels are discussed in detail. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1514–1531, 2004 相似文献
44.
45.
通过对非饱和土非线性本构方程和场方程的线性化,推导出了非饱和土的线性本构方程和场方程,把线性方程表示为与Biot饱和多孔介质方程相似的形式;证明了Darcy定律对非饱和土的适用性;说明了Biot饱和多孔介质方程是这些线性方程的特征。所有这些都表明用混合理论处理非饱和土本构问题的正确性。 相似文献
46.
本从第一性原理出发,计算了充磁线圈产生的磁场,脉冲充磁的超导圆盘中的感应电流密度和俘获场分布.以超导体中的电流运动方程为基础,通过磁通动力学方程E=Ec(J/Jc)^n和物质方程B=μ0H表示超导圆盘的超导特性.计算表明第一个脉冲充磁电流的峰值和磁通蠕动指数对于超导圆盘中的感应电流分布非常重要.同时研究了充磁电流的宽度,波形,第二个充磁电流的峰值和充磁线圈的形状对于俘获场的影响.计算表明不断减小脉冲充磁电流峰值的反复充磁可以保持超导圆盘中的感应电流密度的平台在一确定水平. 相似文献
47.
The electromagnetic (EM) energy flow near single spheres is investigated by applying Mie theory. From the patterns of the energy flow, the absorption and the scattering of light can be understood in the microscopic point of view. In the absorption profiles of metallic particles, most absorbed energy is consumed on the surface of the particles, which indicates that the resonance of surface plasmon is different from that of the bulk plasmon. Two mechanisms to enhanced local EM field are also distinguished. One is the surface plasmon resonance, and another one is the intensified energy flow. 相似文献
48.
49.
探讨了设计负动量压缩因子(αp<0)的正负电子对撞机储存环磁聚焦结构的可行性及方法.作为应用实例,说明了设计αp<0的τ–粲工厂磁聚焦结构的可能性. 相似文献
50.
具有奇异值分解性质的代数 总被引:4,自引:0,他引:4
设F为一个域,R为一个带有对合的F-代数,如果R上每一个矩阵都有奇异值分解(简称SVD),则称R为一个有SVD性质的F-代数.本文指出:R为一个有SVD性质的F-代数的充要条件是:R同构于R~+,或R~+上二次扩域,或R~+上四元数体((-1,-1)/R~+),其中R~+为R的对称元集合,并且R~+为一个Galois序闭域. 相似文献