全文获取类型
收费全文 | 73510篇 |
免费 | 12777篇 |
国内免费 | 7298篇 |
专业分类
化学 | 50855篇 |
晶体学 | 657篇 |
力学 | 4740篇 |
综合类 | 310篇 |
数学 | 8196篇 |
物理学 | 28827篇 |
出版年
2024年 | 279篇 |
2023年 | 1601篇 |
2022年 | 2716篇 |
2021年 | 2836篇 |
2020年 | 3106篇 |
2019年 | 2907篇 |
2018年 | 2563篇 |
2017年 | 2335篇 |
2016年 | 3569篇 |
2015年 | 3475篇 |
2014年 | 4134篇 |
2013年 | 5307篇 |
2012年 | 6729篇 |
2011年 | 6725篇 |
2010年 | 4467篇 |
2009年 | 4251篇 |
2008年 | 4592篇 |
2007年 | 4107篇 |
2006年 | 3754篇 |
2005年 | 3129篇 |
2004年 | 2425篇 |
2003年 | 1919篇 |
2002年 | 1751篇 |
2001年 | 1470篇 |
2000年 | 1355篇 |
1999年 | 1533篇 |
1998年 | 1304篇 |
1997年 | 1292篇 |
1996年 | 1290篇 |
1995年 | 1053篇 |
1994年 | 921篇 |
1993年 | 763篇 |
1992年 | 675篇 |
1991年 | 582篇 |
1990年 | 501篇 |
1989年 | 384篇 |
1988年 | 335篇 |
1987年 | 274篇 |
1986年 | 249篇 |
1985年 | 204篇 |
1984年 | 143篇 |
1983年 | 102篇 |
1982年 | 80篇 |
1981年 | 67篇 |
1980年 | 65篇 |
1979年 | 33篇 |
1978年 | 30篇 |
1977年 | 40篇 |
1976年 | 30篇 |
1973年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
The magnetic property in neodymium gallium garnet (NdGaG) is studied by the quantum theory. The ground configuration split states are calculated taking into account the spin–orbit interaction and crystal field effect. Taking account of the Nd–Nd exchange interaction, a good agreement between experimental and theoretical values can be obtained for the variation of the magnetic moment with the external magnetic field under “extreme” conditions (low temperature and high magnetic field). Moreover, the temperature dependence of magnetic moment and the magnetic susceptibility χ is also discussed. Above 30 K, the magnetization (M) shows a linear field (He) dependence. 相似文献
122.
123.
Pingan Zeng Jiaquan Liu Yuxia Guo 《Journal of Mathematical Analysis and Applications》2004,300(1):102-128
In this paper, by using the Morse index theory for strongly indefinite functionals developed in [Nonlinear Anal. TMA, in press], we compute precisely the critical groups at the origin and at infinity, respectively. The abstract theorems are used to study the existence (multiplicity) of nontrivial periodical solutions for asymptotically wave equation and beam equation with resonance both at infinity and at zero. 相似文献
124.
Stability and bifurcation in a delayed predator-prey system with Beddington-DeAngelis functional response 总被引:1,自引:0,他引:1
Zhihua Liu 《Journal of Mathematical Analysis and Applications》2004,296(2):521-537
We consider a delayed predator-prey system with Beddington-DeAngelis functional response. The stability of the interior equilibrium will be studied by analyzing the associated characteristic transcendental equation. By choosing the delay τ as a bifurcation parameter, we show that Hopf bifurcation can occur as the delay τ crosses some critical values. The direction and stability of the Hopf bifurcation are investigated by following the procedure of deriving normal form given by Faria and Magalhães. An example is given and numerical simulations are performed to illustrate the obtained results. 相似文献
125.
Shu Fen Wang Wen Guo Zou Su Wen Liu Dong Xu Duo Rong Yuan Guang Jun Zhou 《Journal of Physics and Chemistry of Solids》2004,65(7):1243-1245
The photoluminescence properties of the Bi3+ in sol-gel derived ZnTiO3 nanocrystals have been investigated. An ultra-violet emission at 360 nm and a visible emission band at 506 nm have been observed, originating from two kinds of emission centers. The former is ascribed to the 3P1-1S0 transition of Bi3+ and the latter to the recombination of the electrons with the photo-generated holes trapped in the zinc vacancies. In all cases the latter contribution is predominant. 相似文献
126.
1D-nanostructural zinc oxide (ZnO) with different shapes have been synthesized on p-type Si(1 0 0) and glass substrates via vapor phase growth by heating pure zinc powder at temperatures between 480 and 570 °C. The different ZnO nanostructures depend on the substrates and the growth temperatures. Scanning electron microscopy and X-ray diffraction revealed that a well-aligned nanowires array, which are vertical to the substrate of Si(1 0 0) with 18 sides on their heads, but six sides on their stems, has been formed at 480 °C. Raman study on the ZnO nanostructures shows that the coupling strength between electron and phonon determined by the ratio of the second- to the first-order Raman scattering cross-sections declines with decreasing diameter of the nanowires. However, a little changes of the coupling strength in terms of the width of the nanobelts have been observed. 相似文献
127.
128.
Time-resolved electron transport studies on InGaAs/GaAs-QWIPs 总被引:1,自引:0,他引:1
S. Steinkogler H. Schneider R. Rehm M. Walther P. Koidl P. Grant R. Dudek H. C. Liu 《Infrared Physics & Technology》2003,44(5-6):355-361
Due to the short internal response time, quantum-well infrared photodetectors (QWIPs) are interesting for high-speed applications such as heterodyne spectroscopy or laser pulse monitoring. We studied the photocurrent transients of InGaAs/GaAs-QWIPs after irradiation with infrared laser pulses of 250 fs duration. The excitation wavelength of about 9 μm matches the peak wavelength of the QWIP structure. The photocurrent transient consists of two different dynamical components, representing the fast photoionization in the quantum-wells and the slow injection current that compensates the remaining space charge. The investigations of the different components as a function of temperature and bias voltage were performed on a nanosecond time-scale. The experimental separation of the two photocurrent contributions allows us to determine the photoconductive gain. The Fourier transform of the photocurrent transient was compared with other experimental methods including heterodyne detection and microwave rectification. The quantitative agreement between these different measurement techniques is excellent. 相似文献
129.
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
130.