全文获取类型
收费全文 | 4367篇 |
免费 | 750篇 |
国内免费 | 287篇 |
专业分类
化学 | 1632篇 |
晶体学 | 14篇 |
力学 | 311篇 |
综合类 | 61篇 |
数学 | 918篇 |
物理学 | 2468篇 |
出版年
2024年 | 7篇 |
2023年 | 41篇 |
2022年 | 98篇 |
2021年 | 94篇 |
2020年 | 100篇 |
2019年 | 98篇 |
2018年 | 138篇 |
2017年 | 173篇 |
2016年 | 167篇 |
2015年 | 115篇 |
2014年 | 242篇 |
2013年 | 679篇 |
2012年 | 247篇 |
2011年 | 278篇 |
2010年 | 222篇 |
2009年 | 253篇 |
2008年 | 264篇 |
2007年 | 274篇 |
2006年 | 222篇 |
2005年 | 186篇 |
2004年 | 206篇 |
2003年 | 157篇 |
2002年 | 157篇 |
2001年 | 145篇 |
2000年 | 130篇 |
1999年 | 95篇 |
1998年 | 113篇 |
1997年 | 80篇 |
1996年 | 73篇 |
1995年 | 59篇 |
1994年 | 35篇 |
1993年 | 40篇 |
1992年 | 34篇 |
1991年 | 29篇 |
1990年 | 21篇 |
1989年 | 19篇 |
1988年 | 15篇 |
1987年 | 15篇 |
1986年 | 14篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1971年 | 2篇 |
排序方式: 共有5404条查询结果,搜索用时 15 毫秒
91.
92.
设$ G $ 是一个$ n $ 阶$ k $ 圈图, $ k $ 圈图为边数等于顶点数加$ k-1 $ 的简单连通图。$ \mu_{1}(G) $ 、$ \mu_{2}(G) $ 分别记为图$ G $ 的Laplace矩阵的最大特征值和次大特征值, 图$ G $ 的Laplace分离度定义为$ S_{L}(G)=\mu_{1}(G)-\mu_{2}(G) $ 。本文研究了给定阶数的$ k $ 圈图的最大Laplace分离度, 并刻画了相应的极图, 其结果推广了已有当$ k=1, 2, 3 $ 时的结论。 相似文献
93.
94.
95.
A potentiometric method using a glass electrode has been applied to determination of ionization constants for deuterium oxide (D2O) in binary mixtures of D2O with dioxane, tetrahydrofuran, acetone, dimethylsulfoxide, CH3CH2OD, and CH3OD at 25°C. The results are compared with values of ionization constants for H2O obtained previously in the corresponding H2O-organic mixtures, and the isotope effect is shown to be small. Further calculations with the D2O results show that the first five solvents mentioned above are neither appreciably acidic nor basic in D2O solution, but that CH3OD shows slightly acidic behavior (pKa=16.0±0.3). 相似文献
96.
19F and 1H NMR spectra of halocarbons 总被引:1,自引:0,他引:1
Foris A 《Magnetic resonance in chemistry : MRC》2004,42(6):534-555
19F NMR chemical shifts and coupling constants are reported for 215 compounds. For 77 of these compounds, 1H NMR spectral data are also given. Long-range couplings, including 8J(F,F) and 5J(F,H), are reported. The complexity of halocarbon spectra owing to the presence of rotational isomers, asymmetric centers, long-range couplings, and chlorine isotope effects are illustrated, and the methods used for analyzing such complex spectra are briefly discussed. 相似文献
97.
Samuel O. Asekomhe Janet A. W. Elliott 《Colloids and surfaces. A, Physicochemical and engineering aspects》2003,220(1-3):271-278
Much research has been done on line tension measurement and interpretation, and attempts have also been made to measure line tension with simple, cheap and reliable methods that do not require excessive sophistication. Of particular interest is the method of determining line tensions of solid–liquid–vapor systems from the capillary rise in a conical tube. This simple and relatively inexpensive method gives line tension values comparable to those reported in the literature obtained via highly sophisticated instruments or techniques such as the well known axisymmetric drop shape analysis technique. The absolute value of line tension obtained using the conical tube method and assuming a spherical liquid–vapor interface is larger but of the same order of magnitude (1 μJ m−1) as that reported in the literature. A theoretical analysis presented herein shows that by including the deformation of the liquid–vapor interface due to gravity in the conical capillary analysis, the line tension value inferred from the experimental data is reduced by approximately 50% and compares better with values in the literature obtained using other sophisticated methods. Thus a relatively simple, cheap, accurate and reliable method of line tension measurement has been advanced. 相似文献
98.
Rosenberg Edward Freeman William Carlos Zinnia Hardcastle Kenneth Yong Jin Yoo Milone Luciano Gobetto Roberto 《Journal of Cluster Science》1992,3(4):439-457
The general relationships between trinuclear cluster reactivity and the ligand dynamical processes in these systems are explored. Three specific mechanistic studies are presented: (1) the rate and stereochemistry of ligand addition to 3-imidoyl complexes, (2) the factors influencing the rate of carbon-hydrogen bond activation in 3-alkyne complexes, and (3) the origin of anomalously large kinetic deuterium isotope effect in metal to ligand and ligand to metal hydrogen transfer in trinuclear and binuclear complexes. In all three cases, the current state of the mechanistic studies are summarized and the possible rate of specific ligand dynamical processes in controlling the mechanism are put forth. 相似文献
99.
Sm2+-doped glasses in the system of Al2O3-SiO2 were prepared by sol-gel processing of metal alkoxides and reacting with H2 gas at 800°C. The hole burning properties of these glasses were investigated. The holes were burned in the 7F0 5D0 line of the Sm2+ ions using a DCM dye laser at 77 K. The hole depth increased with increasing the laser irradiation time, reaching up to 15% of the total intensity within a few hundred seconds. The hole width was 3 cm–1 full width at half maximum. Fluorescence line narrowing spectra of the 5D0 7 F1 transition were analyzed to study the local structure surrounding the Sm2+ ion. It is concluded that the Sm2+ ions are closely coordinated with nine oxygens of the AlO6 group in aluminosilicate glasses and that the addition of Al3+ ions into glass induces an increase in the coordination number of the Sm2+. 相似文献
100.