全文获取类型
收费全文 | 5990篇 |
免费 | 682篇 |
国内免费 | 1066篇 |
专业分类
化学 | 6346篇 |
晶体学 | 165篇 |
力学 | 54篇 |
综合类 | 20篇 |
数学 | 140篇 |
物理学 | 1013篇 |
出版年
2024年 | 11篇 |
2023年 | 80篇 |
2022年 | 135篇 |
2021年 | 238篇 |
2020年 | 265篇 |
2019年 | 247篇 |
2018年 | 218篇 |
2017年 | 223篇 |
2016年 | 249篇 |
2015年 | 248篇 |
2014年 | 310篇 |
2013年 | 522篇 |
2012年 | 380篇 |
2011年 | 361篇 |
2010年 | 266篇 |
2009年 | 345篇 |
2008年 | 403篇 |
2007年 | 385篇 |
2006年 | 348篇 |
2005年 | 308篇 |
2004年 | 301篇 |
2003年 | 243篇 |
2002年 | 484篇 |
2001年 | 179篇 |
2000年 | 142篇 |
1999年 | 121篇 |
1998年 | 114篇 |
1997年 | 78篇 |
1996年 | 81篇 |
1995年 | 82篇 |
1994年 | 80篇 |
1993年 | 50篇 |
1992年 | 53篇 |
1991年 | 41篇 |
1990年 | 25篇 |
1989年 | 16篇 |
1988年 | 14篇 |
1987年 | 12篇 |
1986年 | 16篇 |
1985年 | 18篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 6篇 |
1974年 | 4篇 |
1973年 | 4篇 |
排序方式: 共有7738条查询结果,搜索用时 187 毫秒
31.
32.
The central zinc(II) atom in the title complex is tetrahedrally coordinated by four nitrogen atoms derived from 4‐methyl‐5‐imidazolecarboxyaldehyde ligands with Zn? N in the range 2.007(3) to 2.026(4) Å. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
33.
A new hydrophilic copolymer having three kinds of hydroxyl groups, i.e. primary OH on -hydroxy allyl alcohol component, secondary OH on cyclic hemiacetal component and tertiary OH on -hydroxy acrylate component, was prepared by reducing a ‘polylactone’, poly(1-oxa-2-oxobutane-1,4:3,3-tetrayl), with NaBH4 in mixed solvents containing an alcohol. The structural analyses were performed by the solution 1H NMR and the solid state 13C NMR spectroscopies of the reduced samples. The composition of the three components turned out to be variable to the alcohol species used for the mixed solvent. 相似文献
34.
采用PM 3半经验方法对肾上腺素和二甲亚砜与肾上腺素形成的 1∶1复合物的结构进行了几何优化 .在此基础上用密度泛函理论 (DFT)的B3LYP方法 ,分别在 6 31G、6 31G 、6 31+G 基组水平上进行了精确计算 ,并通过单点能计算考察了它们之间在形成各种复合物前后的能量和分子结构参数变化特点 .在各基组水平上所有物种的能量均进行零点振动能 (ZPVE)校正 .计算结果表明 ,二甲亚砜与肾上腺素能形成 6种稳定的复合物 ,在这些复合物中都具有较强的氢键作用 .计算结果能够解释有关实验现象 相似文献
35.
36.
A. Filarowski A. Koll A. Kochel J. Kalenik P. E. Hansen 《Journal of Molecular Structure》2004,700(1-3):67-72
The crystal structures of two ortho-hydroxy ketones (5-chloro-2-hydroxyacetophenone (I K) and 3,5-dichloro-2-hydroxyacetophenone (II K)) have been determined with X-ray diffraction at 100 K. A comparison of steric effects on properties of pseudoaromatic hydrogen bonds in ortho-hydroxy acetophenone and ortho-hydroxy ketimines have been carried out with the application of crystallographic data.
Nuclear quadrupole resonance (NQR) spectra have been measured and interpreted. 相似文献
37.
Xu Zhang Dongfeng Xue Meinan Liu Henryk Ratajczak Dongli Xu 《Journal of Molecular Structure》2005,754(1-3):25-30
On the basis of the crystallographic characteristics of lithium niobate (LN) crystals, Law of Bravais and Pauling's third rule (i.e. Polyhedral Sharing Rule) are employed with the aim to find the relationship between the crystal structure and morphological faces of LN powders. In order to validate our analytical results, we have successfully synthesized LN powders and measured the corresponding X-ray powder diffraction. Our results show that the structural analysis is consistent with the experimental data and is helpful and effective for us to control the single-crystal growth and to design superstructures at the specific plane, starting from the viewpoint of the microscopic behaviors of constituent chemical bonds and polyhedra in the crystallographic frame. 相似文献
38.
ZHU Hai-Xia YAN Shi-Lei 《理论物理通讯》2004,42(11)
We study the ferromagnetic properties of spin-1 system, which is considered in the frame of the bond dilution and random positive or negative anisotropy Blume-Capel model in the effective field theory and a cutting approximation. The investigation of phase diagrams displays some rich properties of the trajectory of tricritical point, reentrant henomena at low temperatures. Under certain both bond concentrations and random negative anisotropy, there are new transition lines of double tricritical points. So special emphasis is placed on the influence of the bond dilution and random anisotropy on phase diagrams. The magnetizations of the system are also discussed. Some results have not been evealed in previous reports. 相似文献
39.
E.C. Reynhardt L. Latanowicz 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):195-208
Equations for the temperature dependence of proton and deuteron spin–lattice relaxation rates and second moments due to a complex motion consisting of classical jumps over a potential barrier and quantum mechanical tunneling through the barrier have been derived. Asymmetric double and triple potential wells are considered. These equations have been employed to analyze proton spin–lattice relaxation data for solid naphthazarin in the laboratory and rotating frames as a function of temperature. It is shown that tunneling plays an important role in the proton transfer dynamics of this compound. 相似文献
40.
Cyclic and acyclic β-bromovinyl aldehydes are cyclized with an array of arylhydrazines in toluene at 125 °C in the presence of a palladium catalyst and a phosphorus chelating ligand together with NaOtBu to give 1-aryl-1H-pyrazoles in moderate to good yields. 相似文献