全文获取类型
收费全文 | 202711篇 |
免费 | 2251篇 |
国内免费 | 501篇 |
专业分类
化学 | 110928篇 |
晶体学 | 3650篇 |
力学 | 8005篇 |
综合类 | 11篇 |
数学 | 19276篇 |
物理学 | 63593篇 |
出版年
2020年 | 1728篇 |
2019年 | 1922篇 |
2018年 | 2240篇 |
2017年 | 2358篇 |
2016年 | 3526篇 |
2015年 | 2199篇 |
2014年 | 3549篇 |
2013年 | 9108篇 |
2012年 | 6528篇 |
2011年 | 8032篇 |
2010年 | 5713篇 |
2009年 | 5670篇 |
2008年 | 7179篇 |
2007年 | 7092篇 |
2006年 | 6730篇 |
2005年 | 6091篇 |
2004年 | 5549篇 |
2003年 | 5126篇 |
2002年 | 4896篇 |
2001年 | 6163篇 |
2000年 | 4641篇 |
1999年 | 3535篇 |
1998年 | 2762篇 |
1997年 | 2709篇 |
1996年 | 2598篇 |
1995年 | 2448篇 |
1994年 | 2344篇 |
1993年 | 2179篇 |
1992年 | 2835篇 |
1991年 | 2734篇 |
1990年 | 2680篇 |
1989年 | 2701篇 |
1988年 | 2723篇 |
1987年 | 2730篇 |
1986年 | 2598篇 |
1985年 | 3317篇 |
1984年 | 3325篇 |
1983年 | 2606篇 |
1982年 | 2718篇 |
1981年 | 2773篇 |
1980年 | 2544篇 |
1979年 | 2885篇 |
1978年 | 2870篇 |
1977年 | 2992篇 |
1976年 | 2823篇 |
1975年 | 2559篇 |
1974年 | 2516篇 |
1973年 | 2471篇 |
1972年 | 1709篇 |
1968年 | 1705篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
R. Silvennoinen K. -E. Peiponen T. Asakura Yan-Fang Zhang Cong Gu K. Ikonen E. J. Morley 《Optics and Lasers in Engineering》1992,17(2)
The specular reflectance of cold-rolled aluminum surface is studied using a fiber optic system. An approximation for the determination of surface roughness is presented. 相似文献
993.
M. K. Sparavalo 《Ukrainian Mathematical Journal》1995,47(1):152-156
The definitions of homogeneous and mosaic attractors of codimension one are given. A topological method for their purposeful formation by using the feedback control laws of controlled dynamical systems is suggested.Published in Ukrainskii Matematicheskii Zhurnal, Vol. 47, No. 1, pp. 129–132, January, 1995. 相似文献
994.
The positron annihilation lifetime method (PAL) has been applied to study the characteristics of polyethylenes (PEs) at low temperatures between 273 and 100 K. It has been found that the intensity (I
3) of the long-lived component of positronium (Ps) showed an increase in non-annealed PE and annealed PE in vacuo. However, PAL in PEs annealed in an atmosphere containing oxygen did not show such an increase. It has been indicated that the latter effect is due to formation of carbonyl groups through oxidation during the annealing. 相似文献
995.
The role of filamentation instability of quark-gluon plasma, in explaining collective phenomena in relativistic heavy-ion
collisions, has been analyzed. Using equations of SU(2) two fluid color hydrodynamics it is shown that this instability can
significantly enhance nuclear stopping and might contribute to collective sideward flows. 相似文献
996.
Two previously unknown metabolites of halofantrine, a candidate anti-malarial drug, have been isolated by thin-layer chromatography from the plasma of dogs administered a single oral dose of 60 mg/kg. Their identifies were investigated after trimethylsilylation by gas chromatography-mass spectrometry under electron-impact and negative-ion chemical ionization conditions. The structural assignment was further confirmed by using a combination of elemental composition analysis of all the isotope peaks at low mass resolution and isotope pattern matching. These two metabolites were formed by modification of the dibutylaminopropyl side-chain of the parent compound involving deamination and oxidation or reduction. 相似文献
997.
By time-resolved electron paramagnetic resonance (TREPR), four (tetraphenylporphinato) zinc (ZnTPP) complexes coordinated by an axial ligand containing a nitroxide radical (NRX; X=4, 5, 8, and 10, denotes the bond number from zinc to nitroxide nitrogen) have been studied in terms of magnetic interactions between the photoexcited triplet state of ZnTPP and NRX. The TREPR spectrum of ZnTPP coordinated by NR10 is almost the same as the one of ZnTPP coordinated by pyridine, indicating that the electron exchange interaction,J, between ZnTPP and the doublet nitroxide is negligibly small. On the other hand, TREPR spectra of the NR4 and NR5 complexes are assigned to the Q1 state constituted by the ZnTPP and the nitroxide radical. In the case of the ZnTPP-NR8 complex, both T1 and Q1 TREPR signals are seen, which may originate from two conformations or degenerate T1 states of ZnTPP. This EPR study is useful for understanding the photophysical and photochemical properties of chromophores. 相似文献
998.
Three four-step enantiospecific syntheses of different diastereomers of AES, a new biodegradable chelating agent, are described. The stereocenters in each of the isomers are accessible from l- and d-malic and aspartic acids. 相似文献
999.
1000.