全文获取类型
收费全文 | 1023篇 |
免费 | 42篇 |
国内免费 | 4篇 |
专业分类
化学 | 699篇 |
晶体学 | 4篇 |
力学 | 13篇 |
数学 | 162篇 |
物理学 | 191篇 |
出版年
2023年 | 8篇 |
2022年 | 27篇 |
2021年 | 34篇 |
2020年 | 18篇 |
2019年 | 30篇 |
2018年 | 20篇 |
2017年 | 17篇 |
2016年 | 29篇 |
2015年 | 41篇 |
2014年 | 33篇 |
2013年 | 60篇 |
2012年 | 65篇 |
2011年 | 57篇 |
2010年 | 56篇 |
2009年 | 42篇 |
2008年 | 77篇 |
2007年 | 62篇 |
2006年 | 79篇 |
2005年 | 47篇 |
2004年 | 54篇 |
2003年 | 53篇 |
2002年 | 38篇 |
2001年 | 14篇 |
2000年 | 19篇 |
1999年 | 13篇 |
1998年 | 10篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 3篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1968年 | 1篇 |
排序方式: 共有1069条查询结果,搜索用时 12 毫秒
961.
962.
963.
Inside Cover: Recyclable Ligands for the Non‐Enzymatic Dynamic Kinetic Resolution of Challenging α‐Amino Acids (Angew. Chem. Int. Ed. 44/2015) 下载免费PDF全文
964.
965.
Min Wen William Erb Florence Mongin Yury S. Halauko Oleg A. Ivashkevich Vadim E. Matulis Thierry Roisnel 《Molecules (Basel, Switzerland)》2022,27(6)
The purpose of the study is to design synthetic methodologies, especially directed deprotometalation using polar organometallic reagents, to access polysubstituted ferrocenesulfoxides. From enantiopure 2-substituted (SiMe3, PPh2) S-tert-butylferrocenesulfoxides, a third substituent was first introduced at the 5 position (SiMe3, I, D, C(OH)Ph2, Me, PPh2, CH2NMe2, F) and removal of the trimethylsilyl group then afforded 2-substituted ferrocenesulfoxides unreachable otherwise. Attempts to apply the “halogen dance” reaction to the ferrocenesulfoxide series led to unexpected results although rationalized in light of calculated pKa values. Further functionalizations were also possible. Thus, new enantiopure, planar chiral di- and trisubstituted ferrocenes have been obtained, in addition to several original 2-substituted, 2,3- and 2,5-disubstituted, 2,3,5-trisubstituted and even 2,3,4,5-tetrasubstituted ferrocenesulfoxides, also enantiopure. 相似文献
966.
967.
Vadim E Matulis Alexander S Lyakhov Pavel N Gaponik Sergei V Voitekhovich Oleg A Ivashkevich 《Journal of Molecular Structure》2003,649(3):309-314
The crystal and molecular structures of 1,5-diamino-1H-1,2,3,4-tetrazolium picrate (DATP) were determined by X-ray diffraction analysis. The tetrazolium cation in DATP has a structure with protonated N4 atom of the ring. Two amino groups in the cation are found to be rather different. The 5-amino group lies in the plane of the tetrazole ring and valence angles around the N atom are close to 120°, which indicates sp2 hybridization of atomic orbital of the nitrogen atom. In contrast, valence angles around the N atom of the 1-amino group are close to tetrahedral angle, which suggests sp3 hybridization. The exocyclic C-N bond in the cation is substantially shorter than that in 1,5-diaminotetrazole. The obtained results indicate a conjugation between the π-system of the tetrazole ring and the 5-amino group. The results of ab initio calculations of electronic structure and relative stability for various tautomeric forms of protonated 1,5-diaminotetrazole using MP2/6-31G* and B3LYP/6-31G* levels of theory are in a good agreement with X-ray data and show that there are differences in σ-electron overlap populations for the C-N bonds in the cation in DATP, while π-electrons are delocalized. 相似文献
968.
969.
Sergey E. Lyubimov Andrey A. Tyutyunov Valery N. Kalinin Ernest E. Said-Galiev Alexey R. Khokhlov Pavel V. Petrovskii Vadim A. Davankov 《Tetrahedron letters》2007,48(46):8217-8219
Novel monodentate phosphites containing ortho- and meta-closo-dodecarboranyl groups have been synthesized and applied in the asymmetric Rh-catalyzed hydrogenation of dimethyl itaconate, providing excellent enantioselectivities (up to 99.8% ee in CH2Cl2 and up to 93% ee in supercritical CO2). 相似文献
970.
Vadim G. Kessler Gerald I. Spijksma Gulaim A. Seisenbaeva Sebastian Håkansson Dave H. A. Blank Henny J. M. Bouwmeester 《Journal of Sol-Gel Science and Technology》2006,40(2-3):163-179
This paper summarizes recent literature data and presents new experimental data on the mechanisms of chemical modification,
hydrolysis and polycondensation of the alkoxides and demonstrates possibilities to approach new classes of materials, exploiting
these mechanisms. Low reactivity of silicon alkoxides is improved by either basic catalysis exploiting an SN2 mechanism or acidic catalysis facilitating a proton-assisted SN1 mechanism as well as by modification with chelating ligands. Metal alkoxides are much stronger Lewis bases compared to silicon
alkoxides and the acidity of water is strong enough to achieve their rapid hydrolysis via proton-assisted SN1 pathway even in the absence of additional catalysts. Introduction of the modifying chelating ligands is leading generally
to increased charge distribution in the precursor molecules. Modifying chelating ligands are also appreciably smaller than
the alkoxide ligands they replace. The modification with chelating ligands is thus facilitating the kinetics of hydrolysis
and polycondensation. The size and shape of the primary particles formed in sol-gel treatment of metal alkoxides are defined
not by kinetic factors in their hydrolysis and polycondensation but by the interactions on the phase boundary, which is in
its turn directed by the ligand properties. The products of the fast hydrolysis and condensation sequence consist of micelles
templated by self-assembly of ligands (mainly oxo-species). This concept provides explanations for commonly observed material
properties and allows for the development of new strategies for the preparation of materials. We discuss the formation of
inverted micelles, obtained by the appropriate choice of solvents, which allows for the formation of hollow spheres. The modifying
β-diketonate ligands act as the surfactant and form an interface between the hollow sphere and the solvent. Retention of ligands
inside the gel particles is possible only if ligands possessing both chelating and bridging properties are applied. Application
of such ligands, for example, diethanolamine, permits to prepare new transition metal oxide based microporous membranes. 相似文献