全文获取类型
收费全文 | 47120篇 |
免费 | 2691篇 |
国内免费 | 3608篇 |
专业分类
化学 | 30820篇 |
晶体学 | 329篇 |
力学 | 516篇 |
综合类 | 689篇 |
数学 | 6662篇 |
物理学 | 14403篇 |
出版年
2023年 | 348篇 |
2022年 | 846篇 |
2021年 | 1563篇 |
2020年 | 811篇 |
2019年 | 996篇 |
2018年 | 773篇 |
2017年 | 884篇 |
2016年 | 1058篇 |
2015年 | 1118篇 |
2014年 | 1436篇 |
2013年 | 2869篇 |
2012年 | 2158篇 |
2011年 | 2286篇 |
2010年 | 2009篇 |
2009年 | 2711篇 |
2008年 | 2779篇 |
2007年 | 3010篇 |
2006年 | 2414篇 |
2005年 | 1664篇 |
2004年 | 1538篇 |
2003年 | 1475篇 |
2002年 | 3891篇 |
2001年 | 1564篇 |
2000年 | 1112篇 |
1999年 | 997篇 |
1998年 | 915篇 |
1997年 | 728篇 |
1996年 | 784篇 |
1995年 | 689篇 |
1994年 | 672篇 |
1993年 | 689篇 |
1992年 | 735篇 |
1991年 | 468篇 |
1990年 | 390篇 |
1989年 | 322篇 |
1988年 | 353篇 |
1987年 | 265篇 |
1986年 | 249篇 |
1985年 | 348篇 |
1984年 | 265篇 |
1983年 | 174篇 |
1982年 | 311篇 |
1981年 | 482篇 |
1980年 | 444篇 |
1979年 | 475篇 |
1978年 | 372篇 |
1977年 | 288篇 |
1976年 | 242篇 |
1974年 | 80篇 |
1973年 | 154篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
We investigate separability questions for the mapping class group of a surface. While this group is not subgroup separable in general, we prove a large family of interesting subgroups are separable. This includes many classically studied subgroups such as solvable subgroups, Heegaard and Handlebody groups, geometric subgroups, and all the terms in the Johnson filtration. 相似文献
152.
New criteria are provided for determining whether an integral representation of a stable process is minimal. These criteria are based on various nonminimal sets and their projections, and have several advantages over and shed light on already available criteria. In particular, they naturally lead from a nonminimal representation to the one which is minimal. Several known examples are considered to illustrate the main results. The general approach is also adapted to show that the so-called mixed moving averages have a minimal integral representation of the mixed moving average type. 相似文献
153.
High-resolution Fourier transform spectra of CH3OH have been investigated in the infrared region from 930 to 1450 cm−1 in order to map the torsion-rotation energy manifolds associated with the ν7 in-plane CH3 rock, the ν11 out-of-plane CH3 rock, and the ν6 OH bend. Upper-state term values have been determined from the assigned spectral subbands, and have been fitted to power-series expansions to obtain substate origins and effective B-values for the three modes. The substate origins have been grouped into related families according to systematic trends observed in the torsion-vibration energy map, but there are substantial differences from the traditional torsional patterns. There appears to be significant torsion-mediated spectral mixing, and a variety of “forbidden” torsional combination subbands with |Δυt|>1 have been observed, where υt denotes the torsional quantum number (equivalent to υ12). For example, coupling of the (υ6,υt)=(1,0) OH bend to nearby torsionally excited (υ7,υt)=(1,1) CH3-rock and (υ8,υt)=(1,1) CO-stretch states introduces (υ6,υt)=(1,0)←(0,1) subbands into the spectrum and makes the ν7+ν12−ν12 torsional hot band stronger than the ν7 fundamental. The results suggest a picture of strong coupling among the OH-bending, CH3-rocking, and CO-stretching modes that significantly modifies the traditional energy structure and raises interesting and provocative questions about the torsion-vibration identity of a number of the observed states. 相似文献
154.
U. Turgut 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,86(4):353-359
The Coster-Kronig transition, f23, was determined using differential fluorescence cross sections of Ll X-ray for Th and U. The targets were irradiated an Am-241 radioisotope at the different incident angle. The Ll X-rays were counted with a Si (Li) detector at the different scattering angle varying from 60° to 90° at 10° intervals. For each angle, the Coster-Kronig transition probability, f23, was found. An obtained Coster-Kronig transition probability value was fitted versus emission angle. According to present results we can say that the Coster-Kronig transition probability, f23, shows isotropic distribution. 相似文献
155.
P.S Erdman M Fajardo K.M Sando W.C Stwalley 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,88(4):447-481
Experimental results are reported for a unique spectroscopic device called the Plasma Spectroscopy Cell. Optical absorption of lithium metal vapor was observed at high density and temperature. Absorption spectra are analyzed using theoretical calculations of absorption cross sections for lithium-helium interactions, and singlet and triplet state transitions of diatomic lithium in the visible spectral range. This is believed to be the most complex example yet calculated in which absolute bound-bound, bound-free, free-bound, and free-free contributions for all possible optically allowed transitions are all included, in quite respectable agreement with experiment. 相似文献
156.
L. K. Seah U. S. Dinish S. K. Ong Z. X. Chao V. M. Murukeshan 《Optics & Laser Technology》2004,36(5):371-376
Imaging of latent fingerprints using time-resolved (TR) method offers a broader platform to eliminate the unwanted background emission. In this paper, a novel TR imaging technique is demonstrated and implemented, which facilitates the detection of latent fingerprints with nanosecond resolution. Simulated experiments were carried out with two overlapping fingerprints treated with two fluorescent powders having different lifetimes in nanosecond range. The dependence of the fluorescence emission intensity in nanosecond resolution of TR imaging is also revealed. 相似文献
157.
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
158.
159.
160.