全文获取类型
收费全文 | 5575篇 |
免费 | 175篇 |
国内免费 | 998篇 |
专业分类
化学 | 2946篇 |
晶体学 | 11篇 |
力学 | 419篇 |
综合类 | 192篇 |
数学 | 1060篇 |
物理学 | 2120篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 4篇 |
2020年 | 13篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 13篇 |
2015年 | 29篇 |
2014年 | 20篇 |
2013年 | 62篇 |
2012年 | 87篇 |
2011年 | 988篇 |
2010年 | 518篇 |
2009年 | 554篇 |
2008年 | 85篇 |
2007年 | 95篇 |
2006年 | 143篇 |
2005年 | 326篇 |
2004年 | 943篇 |
2003年 | 558篇 |
2002年 | 442篇 |
2001年 | 332篇 |
2000年 | 110篇 |
1999年 | 109篇 |
1998年 | 137篇 |
1997年 | 99篇 |
1996年 | 79篇 |
1995年 | 55篇 |
1994年 | 55篇 |
1993年 | 202篇 |
1992年 | 168篇 |
1991年 | 110篇 |
1990年 | 102篇 |
1989年 | 102篇 |
1988年 | 84篇 |
1987年 | 6篇 |
1986年 | 63篇 |
1985年 | 8篇 |
1984年 | 20篇 |
1983年 | 3篇 |
1979年 | 1篇 |
1936年 | 2篇 |
排序方式: 共有6748条查询结果,搜索用时 31 毫秒
281.
YAO Tian-Ming YOU Xiao-ZengCoordination Chemistry Institute State Key Laboratory of Coordination Chemistry Nanjing University Nanjing ChinaYANG Qing-ChuanChemistry Department Beijing University Beijing China 《中国化学》1994,12(3):248-257
The reaction of CuCl2-2H2O or NiCl2.6H2O with K2(C5H6S4) [potassium salt of 6,7-dihydro-5H-1,4-dithiepin-2,3-dithiolate] under nitrogen atmosphere resulted in the isolation of [Cu(C5H6S4)2]- or [Ni(C5H6S4)2]- as the tetrabutylammonium salt. Both complexes show characteristic IR and UV-Vis absorptions of transition metal dithiolenes. Cyclic voltammograms contain two waves indicating a two step electrochemical procedure [M(C5H6S4)2]0 = [M(C5H6S4)2]1-= [M(C5H6S4)2]2-. Single crystal structure study has been carried out on the nickel complex. Crystal of [Bu4N][Ni(C5H6S4)2] belongs to monoclinic space group P21/c with a=17.576(5), 6=10.883(2), c=17.773(4) A,B=91.07(2)0, Z=4, and o(calcd.)=1.348 g/cm3. Final result is R=0.059 for 2959 reflections. The NiS4 core exhibits square planar coordination with average Ni-S bond length of 2.134(5) A. There are not anion pairs in crystal. The anions stack along a and c axes while the cations intercalate in them. The nearest S-S contact is 4.429 A. The solid powder ESR s 相似文献
282.
Feng Ke-Sheng Chen Ru-YuInstitute of Elemento-Organii Chemistry Nankai University Tianjin Wang Hong-Gen Wang Ru-JiCentral laboratory Nankai University Tianjin 《结构化学》1993,(5)
<正> Crystal of the title compound Mr=304. 80 belongs to the triclinic, space group P1, with a = 7. 282)2), b=9. 064(2), c=11. 737(5) A , α=75. 79 (3), β=78. 70(3), γ=88. 49(2)°, V-736. 21 A3, Z=2, Dx = l. 375 g/cm3. The final refinement is converged with R=0. 062 and Rw= 0. 069.The five-membered heterocycle is in envelope conformation. The P - N bond length (1. 68(1)) indicates that the dπ-Pπ bond between P and N of the title compound is stronger than that of the corresponding 4-phenyl compound. 相似文献
283.
铂(Ⅳ)—钼酸盐—丁基罗丹明B缔合显色反应的研究 总被引:7,自引:0,他引:7
本文研究在聚乙烯醇(PVA)存在下,铂与钼酸铵和丁基罗丹明B(BRB)形成离子缔合物,该缔合物的最大吸收位于570nm,摩尔吸光系数ε值为9.26×10~5L·mol~(-1)·cm~(-1),服从比耳定律范围0~3.0μg Pt/25ml,缔合物至少稳定3周。测定铂的条件为C_(HClO_4)=1.4mol/L,C_(MoO_4~(2-)=1.1×10~(-3)mol/L,C_(BRB)=3.8×10~(-5)mol/L,0.08%PVA。考察了40多种共存离子的影响,除形成杂多酸的元素外,大多数不干扰。本法已用于催化剂和某些铂矿中铂的测定,结果较满意。 相似文献
284.
285.
ShiGuoSUN XiaoJunPENG MingWenFAN YongQianXU LeiSHI LiChengSU 《中国化学快报》2004,15(8):965-968
Two novel rhenium(I) 2, 2′-bipyridyl complexes, [(4,4′-di-COOEt-bipy) Re(CO)3 (NCCH3)PF6] and [(4,4′-di-COOEt-bipy) Re (CO)3 (NCS)], a model complex [(4,4′-di-COOEt-bipy) Re (CO)3 (pyridine)PF6], were synthesized. Their ground state electronic spectra and emission spectra were measured in acetonitrile. The MLCT absorption maximum of the complex exhibited a considerable red shift as the ligand changed from pyridine to CNCH3, or SCN. 相似文献
286.
Tinghua Wu Mingqiao Zhu Zhenjiang Niu Yijun Zhong Yan Guan Ya Liu Qiangu Yan Zelin Li Huilin WanZhejiang Normal University Institute of Physical Chemistry Jinhua ChinaZhejiang University Department of Chemical Engineering Hangzhou ChinaXiamen University Department of Chemistry Xiamen China 《天然气化学杂志》2002,(Z2)
The catalytic properties of several supported metal catalysts on different carriers were studied in the partial oxidation of methane (POM) to syngas. In our experiment, supported noble metal catalysts exhibited better performance than the other supported transition metal catalysts. The catalyst performances were significantly influenced by the d-electron configuration of the active metal components and the dispersion of active metal components on the support. A catalyst with a moderate number of unpaired electrons in the d-orbital of the active metal support without obvious acidity or redox activity (e.g. MgO) was suitable for POM performance. The Rh/SiO2 catalyst was the best in the POM reaction, among those investigated. Reaction conditions apparently also affected the POM performance of the catalyst. The conversion of methane and the selectivity for CO increased with the reaction temperature, and a high CH4/O2 ratio was not beneficial for POM performance. 相似文献
287.
288.
Dan Zhu Yi-xiang Cheng Xiao-wei Zou Ling-wu Chen Jin-feng Song Zhi-liu Wang College of Chemistry Chemical Engineering Nanjing University Nanjing China 《高分子科学》2006,(6)
Chiral polymer was synthesized by the polymerization of (R)-6,6'-bistributylstannyl-2,2'-binaphtho-20-crown-6 (M-1) with 1,4-dibromo-2,3-bisbutoxy-naphthyl (M-2) by Pd(PPh3)4 catalyzed Stille coupling reaction. Both monomer and polymer were analyzed by NMR, MS, FT-IR, UV, polarimetry, DSC-TGA, CD, fluorescent spectroscopy and GPC. The major difference between monomer and polymer is that a long wavelength Cotton Effect was observed for the polymer due to its more extended conjugation in the repeating unit and a highly rigid backbone in the polymer chain. Polymer has strong blue fluorescence due to the efficient energy migration from the extended n-electronic structure of the repeating unit of the polymer to the chiral binaphthyl core and is expected to have potential application in the materials of fluorescent sensors and chiral chromatographic packing for resolution of racemic amino acid. 相似文献
289.
HONG Gong-Yi LI Le-MinCollege of Chemistry Molecular Engineering State Key Laboratory of Rare Earth Materials Chemistry Applications Peking University Beijing China 《中国化学》1996,14(4):289-296
Several numerical integration schemes for the evaluation of matrix elements in density functional theory calculations have been studied and compared by computational practice. The best scheme was found to be the combination of the atomic partition function proposed by Becke with the scaled generalized Gauss-Laguerre quadrature formula for radial integration suggested by Yang, which achieve the highest convergence rate to the numerical integration. With the same number of integration points, the accuracy of the calculated results by this scheme is higher by 1 to 2 orders of magnitudes than that by other schemes. The reason for achieving higher accuracy by this scheme has been proposed preliminarily. 相似文献
290.
本文提出了一种快速、简便、灵敏检测痕量多胺的新方法。用对酞内酰胺苯甲酰氯同多胺进行柱前衍生反应,以反相高效液相色谱定量测定多胺含量。在4~500 pmol范围内有良好的定量线性关系,腐胺、精脒和精胺的检测限均为0.1 pmol。 相似文献