全文获取类型
收费全文 | 11356篇 |
免费 | 2054篇 |
国内免费 | 2539篇 |
专业分类
化学 | 7967篇 |
晶体学 | 235篇 |
力学 | 695篇 |
综合类 | 226篇 |
数学 | 1390篇 |
物理学 | 5436篇 |
出版年
2024年 | 27篇 |
2023年 | 190篇 |
2022年 | 347篇 |
2021年 | 335篇 |
2020年 | 414篇 |
2019年 | 367篇 |
2018年 | 345篇 |
2017年 | 402篇 |
2016年 | 424篇 |
2015年 | 481篇 |
2014年 | 591篇 |
2013年 | 835篇 |
2012年 | 866篇 |
2011年 | 984篇 |
2010年 | 798篇 |
2009年 | 819篇 |
2008年 | 919篇 |
2007年 | 829篇 |
2006年 | 833篇 |
2005年 | 726篇 |
2004年 | 562篇 |
2003年 | 417篇 |
2002年 | 436篇 |
2001年 | 392篇 |
2000年 | 391篇 |
1999年 | 297篇 |
1998年 | 188篇 |
1997年 | 187篇 |
1996年 | 200篇 |
1995年 | 160篇 |
1994年 | 163篇 |
1993年 | 147篇 |
1992年 | 148篇 |
1991年 | 109篇 |
1990年 | 100篇 |
1989年 | 101篇 |
1988年 | 74篇 |
1987年 | 72篇 |
1986年 | 58篇 |
1985年 | 43篇 |
1984年 | 36篇 |
1983年 | 32篇 |
1982年 | 21篇 |
1981年 | 17篇 |
1980年 | 14篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1976年 | 5篇 |
1974年 | 4篇 |
1965年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
51.
In the presence of an applied static and uniform magnetic field, a cylindrical Kadomtsev-Petviashivili equation is derived for a relativistic electromagnetic solitary wave propagating in collisionless plasma consisting electrons, positrons, and ions in the case of weak relativistic limit. This equation is solved in a stationary frame to obtain explicit expression for the velocity, amplitude and width of solitons. The amplitude of the solitary wave has a maximum value at a critical αc of the ratio of the ion equilibrium density to the electron one, and it increases as the applied magnetic field becomes larger. 相似文献
52.
Safety considerations of TBM are part of the design process to ensure that the TBM do not adversely affect the safety of ITER. So accurate calculations of all radioactivity and potential harmfulness are very important for designing of device, selecting of blanket and shield material, analyzing of the safety and environment, disposing of nuclear waste and operation of the reactor. 相似文献
53.
Based on the generalized Huygens–Fresnel diffraction integral and the expansion of the hard aperture function into a finite sum of complex Gaussian functions, the approximate analytical expression of elegant Laguerre–Gaussian beams passing through a paraxial ABCD optical system with an annular aperture is derived. Meanwhile, the corresponding closed-forms for the unapertured, circular apertured or circular black screen cases are also given. The obtained results provide more convenience for studying their propagation and transformation than the usual way by using diffraction integral formula directly. Some numerical examples are given to illustrate the propagation properties of elegant Laguerre–Gaussian beams. 相似文献
54.
55.
56.
Gu De-shan Jing Shi-wei Sang Hai-feng Qiao Shuang Liu Yu-ren Liu Lin-mao 《Journal of Radioanalytical and Nuclear Chemistry》2004,262(2):493-496
This paper introduces the analysis method and principle of pulse fast-thermal neutron analysis (PFTNA). A system for the measurement
of low caloric power of coal by PFTNA is also presented. The 14 MeV pulse neutron generator and BGO detector and 4096 MCA
were applied in this system. A multiple linear regression method applied to the data solved the interferential problem of
multiple elements. The error of low caloric power between chemical analysis and experiment was less than 0.4 MJ/kg.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
57.
The effects of partial substitution of Mn for Co on the thermoelectric properties of Ca3MnxCo4−xO9 (x=0, 0.03, 0.9), prepared by sol-gel process, were investigated at the temperatures from 380 K down to 5 K. The results indicate that the substitution of Mn for Co results in increase in thermopower at temperatures >∼80 K, and substantial (23-31% at 300 K) decrease in lattice thermal conductivity in the whole temperature range investigated. The temperature behavior of ZT suggests that Ca3MnxCo4−xO9 with light Mn substitution would be a promising candidate for high-temperature thermoelectric applications. 相似文献
58.
59.
Optical characterization of bromo-alkoxyl-substituted copper phthalocyanine derivative thin films 总被引:2,自引:0,他引:2
A series of thin films of copper phthalocyanine derivatives with bromine and alkoxyl substituents [CuPc(OC8H17)4Brm, m=0,1,2,4] were prepared on single-crystal silicon substrates by spin coating. The ellipsometric spectra of the films have been studied on a rotating analyzer–polarizer type of scanning ellipsometer. The optical, dielectric constants and absorption coefficients of the films in 500–800 nm wavelength region were obtained. The results show that the complex refractive index, dielectric constants and absorption coefficient of these thin films are influenced regularly by bromine substituent on conjugated macrocycle. It was found that there are approximately linear relationships between the resonance absorption wavelengths of the films and the average number of bromine atoms substituted on the phthalocyanine ring. 相似文献
60.
The influence of hydrogen bonds on the physical and chemical properties of hydrogen bonding fluid system of A a D d type is investigated from two viewpoints by the principle of statistical mechanics. In detail, we proposed two new ways that can be used to obtain the equilibrium size distribution of the hydrogen bonding clusters, and derived the analytical expression of a relationship between the hydrogen bonding free energy and hydrogen bonding degree. For the nonlinear hydrogen bonding systems, it is shown that the sol-gel phase transition can take place under proper conditions, which is further proven to be a kind of geometrical phase transition rather than a thermodynamic one. Moreover, several problems associated with the geometrical phase transition and liquid-solid phase transition in nonlinear hydrogen bonding systems are discussed. 相似文献