全文获取类型
收费全文 | 10407篇 |
免费 | 2293篇 |
国内免费 | 1184篇 |
专业分类
化学 | 7250篇 |
晶体学 | 43篇 |
力学 | 1036篇 |
综合类 | 56篇 |
数学 | 477篇 |
物理学 | 5022篇 |
出版年
2024年 | 24篇 |
2023年 | 121篇 |
2022年 | 247篇 |
2021年 | 273篇 |
2020年 | 363篇 |
2019年 | 386篇 |
2018年 | 439篇 |
2017年 | 396篇 |
2016年 | 443篇 |
2015年 | 558篇 |
2014年 | 767篇 |
2013年 | 951篇 |
2012年 | 756篇 |
2011年 | 843篇 |
2010年 | 651篇 |
2009年 | 742篇 |
2008年 | 708篇 |
2007年 | 645篇 |
2006年 | 641篇 |
2005年 | 580篇 |
2004年 | 543篇 |
2003年 | 487篇 |
2002年 | 347篇 |
2001年 | 255篇 |
2000年 | 256篇 |
1999年 | 205篇 |
1998年 | 190篇 |
1997年 | 174篇 |
1996年 | 132篇 |
1995年 | 149篇 |
1994年 | 111篇 |
1993年 | 81篇 |
1992年 | 70篇 |
1991年 | 22篇 |
1990年 | 49篇 |
1989年 | 38篇 |
1988年 | 27篇 |
1987年 | 33篇 |
1986年 | 21篇 |
1985年 | 20篇 |
1984年 | 26篇 |
1982年 | 17篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1979年 | 16篇 |
1978年 | 8篇 |
1977年 | 11篇 |
1976年 | 7篇 |
1973年 | 7篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
High nuclearity paramagnetic, spin-coupled transition metal clusters and grids are fascinating chemists and physicists partly because of their structural beauty, and the challenge of creating them, but also because of their novel physical properties. Magnetic interactions between the spin centers are a primary focus. This review will examine a selection of Mn(II) polynuclear grids and clusters, with nuclearities in the range Mn4 to Mn9. Theoretical treatments of the magnetic properties are discussed, and approaches to solving the exchange problem for ‘large’ spin systems related to computational difficulties. A freely available software package (MAGMUN4.1) is presented as a means of dealing simply with spin-coupled clusters in general, and symmetry reduction methods are discussed briefly as a means of dealing with ‘large’ spin systems. 相似文献
133.
四(三苯基膦)化钯催化的若干菲啶类化合物的合成 总被引:1,自引:0,他引:1
邻甲酰基芳基硼酸与取代邻溴苯胺经四(三苯基膦)化钯催化偶联缩合, 合成了9个菲啶衍生物。邻溴苯胺的取代基无论是吸电子或供电子基团, 反应均可顺利进行。 相似文献
134.
135.
Guldi DM Hirsch A Scheloske M Dietel E Troisi A Zerbetto F Prato M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(20):4968-4979
Control over the interchromophore separation, their angular relationship, and the spatial overlap of their electronic clouds in several ZnP-C(60) dyads (ZnP=zinc porphyrin) is used to modulate the rates of intramolecular electron transfer. For the first time, a detailed analysis of the charge transfer absorption and emission spectra, time-dependent spectroscopic measurements, and molecular dynamics simulations prove quantitatively that the same two moieties can produce widely different electron-transfer regimes. This investigation also shows that the combination of ZnP and C(60) consistently produces charge recombination in the inverted Marcus region, with reorganization energies that are remarkably low, regardless of the solvent polarity. The time constants of electron transfer range from the mus to the ps regime, the electronic couplings from a few tens to several hundreds of cm(-1), and the reorganization energies remain below 0.54 eV and can be as low as 0.16 eV. 相似文献
136.
甲烷氧化偶联Na2WO4-Mn/SiO2催化剂热效应的研究 总被引:1,自引:2,他引:1
采用固定床微型反应装置,研究了甲烷氧化偶联反应过程中Na2WO4-Mn/S iO2催化剂床层的热效应和催化性能的关系,考察了反应炉温、CH4/O2比和反应气体空速对催化剂床层热点分布的影响.研究结果表明,甲烷氧化偶联催化剂床层的热效应强烈依赖于反应条件.反应炉温越高,CH4/O2比越低,反应气体空速越大,催化剂床层的热点温度越高.结合催化性能和热效应关系的研究,为优化甲烷氧化偶联的反应操作提供了实验依据. 相似文献
137.
Reaction of 2,3,7,8,12,13,17,18-octaethylporphyrin with LiR reagents containing functional groups readily yields meso substituted derivatives suitable for further transformations with residues such as -p-C6H5Br, -p-C6H5-CCH, -p-C6H5-NH2 or -(CH2)3-CHCH2. Similar reactions of tetrabenzoporphyrin with alkyllithium reagents afforded the first entry into meso mono- and dialkylsubstituted tetrabenzoporphyrins while reaction of bicyclo[2.2.2]oct-type masked isoindole precursors with LiR followed by in situ retro-Diels-Alder reaction also afforded the 5-phenyl and 5,10-diphenyltetrabenzoporphyrins in high purity. 相似文献
138.
Wei Wang Rongliang Wang Fan Wu Boshun Wan 《Reaction Kinetics and Catalysis Letters》2005,85(2):277-282
Summary A Ni-promoted ligand free palladium catalyst system for Suzuki coupling of aryl bromides has been developed in high efficiency under mild reaction conditions. It was obtained in situ by introducing NiCl2 to PdCl2/PVP using a parallel high-throughput screening technique. A wide range of aryl bromides bearing a variety of functional groups was evaluated. 相似文献
139.
Mohammad Ali Zolfigol Khodabakhsh Niknam Mojtaba Bagherzadeh Arash Ghorbani‐Choghamarani Nadiya Koukabi Maryam Hajjami Eskandar Kolvari 《中国化学会会志》2007,54(5):1115-1118
Tribromoisocyanuric acid (TBCA) and Oxone®‐MX systems were used as effective oxidizing agents for the oxidation of thiols to their corresponding disulfides under mild conditions at room temperature with good to excellent yields. 相似文献
140.
Zhende Liu 《Tetrahedron》2007,63(9):1931-1936
A flexible method for the synthesis of 5,6-disubstituted furo[2,3-d]pyrimidine derivatives is described. The key step is a palladium-catalyzed arylative cyclization of alkynylpyrimidinols with various aryl iodides, which gave the title compounds in 36-75% yield. 相似文献