全文获取类型
收费全文 | 39229篇 |
免费 | 5460篇 |
国内免费 | 4065篇 |
专业分类
化学 | 27573篇 |
晶体学 | 435篇 |
力学 | 2081篇 |
综合类 | 315篇 |
数学 | 4716篇 |
物理学 | 13634篇 |
出版年
2024年 | 115篇 |
2023年 | 679篇 |
2022年 | 1170篇 |
2021年 | 1280篇 |
2020年 | 1304篇 |
2019年 | 1325篇 |
2018年 | 1142篇 |
2017年 | 1088篇 |
2016年 | 1640篇 |
2015年 | 1644篇 |
2014年 | 1926篇 |
2013年 | 2684篇 |
2012年 | 3187篇 |
2011年 | 3465篇 |
2010年 | 2367篇 |
2009年 | 2357篇 |
2008年 | 2561篇 |
2007年 | 2295篇 |
2006年 | 2077篇 |
2005年 | 1808篇 |
2004年 | 1432篇 |
2003年 | 1166篇 |
2002年 | 1130篇 |
2001年 | 939篇 |
2000年 | 828篇 |
1999年 | 778篇 |
1998年 | 708篇 |
1997年 | 626篇 |
1996年 | 609篇 |
1995年 | 565篇 |
1994年 | 530篇 |
1993年 | 463篇 |
1992年 | 418篇 |
1991年 | 357篇 |
1990年 | 317篇 |
1989年 | 251篇 |
1988年 | 207篇 |
1987年 | 161篇 |
1986年 | 174篇 |
1985年 | 174篇 |
1984年 | 119篇 |
1983年 | 84篇 |
1982年 | 83篇 |
1981年 | 59篇 |
1980年 | 61篇 |
1979年 | 60篇 |
1978年 | 44篇 |
1976年 | 38篇 |
1974年 | 42篇 |
1973年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
用一维混合粒子编码研究了具有电子旋转方向的对称和非对称旋转间断的稳定性。发现在相对窄的过渡层厚度下,具有电子旋转方向的旋转间断是不稳定的,它趋向于发展成离子旋转方向的旋转间断和一些MHD波。这个发展过程部分地受到电子温度的限制。当过渡层厚度增加到足够宽时,电子旋转方向的旋转间断变成稳定的。本文简单地讨论了导致这种旋转间断不稳定的可能原因。 相似文献
992.
Huang YW Hu ST Yang SY Horng HE Hung JC Hong CY Yang HC Chao CH Lin CF 《Optics letters》2004,29(16):1867-1869
When an external magnetic field is applied parallel to the film surface of a magnetic fluid film, a high-quality one-dimensional periodic chain structure is formed when the field strength reaches a certain level. With a periodic chain structure in the magnetic fluid film, an incident light is diffracted onto the magnetic thin film. The results show that the one-dimensional periodic chain structure in the magnetic fluid film can serve as an optical grating. Further investigations reveal the feasibility of developing tunable coarse wavelength-division multiplexing by utilizing a periodic chain structure. 相似文献
993.
We present a positive-negative refraction effect in which, under certain conditions, an incident plane wave launched into a photonic crystal excites a positive-refracted Bloch wave and a negative-refracted Bloch wave simultaneously, both of which maintain the polarization. By utilizing this phenomenon, wide-angle beam splitting can be realized at the microscale level. Numerical simulations are employed to demonstrate this anomalous refraction behavior. 相似文献
994.
Convergence of the fractional step Lax-Friedrichs scheme and Godunov scheme for the isentropic system of gas dynamics 总被引:3,自引:0,他引:3
A convergence theorem of the fractional step Lax-Friedrichs scheme and Godunov scheme for an inhomogeneous system of isentropic gas dynamics (1<5/3) is established by using the framework of compensated compactness. Meanwhile, a corresponding existence theorem of global solutions with large data containing the vacuum is obtained.Partially supported by U.S. NSF Grant # DMS-850403 相似文献
995.
Suoyuan Lian Lei Gao Zhenhui Kang Di Wu Yang Lan Lin Xu 《Solid State Communications》2004,132(6):375-378
Single-crystal magnetite nanowires with average diameter of ca. 20 nm and length of up to several micrometers were prepared by a simple alkaline surfactant-free hydrothermal process. The crystallinity, purity, morphology, and structural features of the as-prepared magnetite nanowires were investigated by powder X-ray diffraction, transmission electron microscopy (TEM) and selected area electron diffraction. The composition and length of nanowires depends on the pH, with higher pH favoring longer nanowires composed entirely of Fe3O4. A mechanism for nanowire growth is proposed. 相似文献
996.
Huang DJ Chang CF Jeng HT Guo GY Lin HJ Wu WB Ku HC Fujimori A Takahashi Y Chen CT 《Physical review letters》2004,93(7):077204
We present measurements of the spin and orbital magnetic moments of Fe3O4 by using SQUID and magnetic circular dichroism in soft x-ray absorption. The measurements show that Fe3O4 has a noninteger spin moment, in contrast to its predicted half-metallic feature. Fe3O4 also exhibits a large unquenched orbital moment. Calculations using the local density approximation including the Hubbard U method and the configuration interaction cluster-model suggest that strong correlations and spin-orbit interaction of the 3d electrons result in the noninteger spin and large orbital moments of Fe3O4. 相似文献
997.
A new design is presented for Bragg fibers that allows low-loss propagation for linearly polarized light. Predictions based on a simple ray model show that approximately doubling the thickness of the first wall layer results in low losses at TM-like boundaries while keeping TE-like boundary losses manageable. This contrasts sharply with conventional quarter-wave designs that are extremely low loss for TE01 modes but very high loss for linear polarization. We fabricate Bragg fibers based on this design concept in a Si/SiO2 system and verify experimentally that they propagate linearly polarized light with losses less than 6 dB/cm over a 60-nm spectral range. 相似文献
998.
In the course of an extensive investigation aimed at understanding the detailed mechanisms of a prototypical polyatomic reaction, several remarkable observations were uncovered. To interpret these findings, we surmise the existence of a reactive resonance in this polyatomic reaction. The reaction of concern is F+CH4-->HF+CH3, and the abnormal attributes were revealed only near the reaction threshold. The discovery of reactive resonance in a polyatomic reaction is more than just an extension from a typical atom+diatom reaction. As shown here, it holds great promise to disentangle the elusive intramolecular vibrational dynamics of transient collision complex in the critical transition-state region. 相似文献
999.
To simplify the reconstruction calculation of a large-aperture digital hologram we propose a novel Fourier-transformation reconstruction algorithm. When the reconstructed wave is the same as or similar to the reference wave, the higher-order phase term of reconstruction can be compensated for. For example, the variation between the higher-order phase term and the aperture angle with a different field of view in in-line phase-shifting digital holography is analyzed. 相似文献
1000.
Optical seeding of plasma waves and the injection of electrons are key issues in self-modulated laser-wakefield accelerators. By implementing a copropagating laser prepulse with proper timing, we are able to control the growth of Raman forward scattering and the production of accelerated electrons. The dependence of the Raman intensity on prepulse timing indicates that the seeding of Raman forward scattering is dominated by the ionization-induced wakefield, and the dependence of the divergence and number of accelerated electrons further reveals that the stimulated Raman backward scattering of the prepulse plays the essential role of injecting hot electrons into the fast plasma wave driven by the main pulse. 相似文献