全文获取类型
收费全文 | 5584篇 |
免费 | 90篇 |
国内免费 | 14篇 |
专业分类
化学 | 3663篇 |
晶体学 | 52篇 |
力学 | 79篇 |
数学 | 927篇 |
物理学 | 967篇 |
出版年
2019年 | 41篇 |
2016年 | 82篇 |
2015年 | 61篇 |
2014年 | 81篇 |
2013年 | 165篇 |
2012年 | 166篇 |
2011年 | 195篇 |
2010年 | 120篇 |
2009年 | 106篇 |
2008年 | 181篇 |
2007年 | 174篇 |
2006年 | 178篇 |
2005年 | 169篇 |
2004年 | 175篇 |
2003年 | 153篇 |
2002年 | 146篇 |
2001年 | 96篇 |
2000年 | 126篇 |
1999年 | 84篇 |
1998年 | 83篇 |
1997年 | 75篇 |
1996年 | 96篇 |
1995年 | 124篇 |
1994年 | 107篇 |
1993年 | 76篇 |
1992年 | 90篇 |
1991年 | 84篇 |
1990年 | 77篇 |
1989年 | 90篇 |
1988年 | 94篇 |
1987年 | 75篇 |
1986年 | 76篇 |
1985年 | 115篇 |
1984年 | 83篇 |
1983年 | 99篇 |
1982年 | 113篇 |
1981年 | 99篇 |
1980年 | 90篇 |
1979年 | 99篇 |
1978年 | 77篇 |
1977年 | 78篇 |
1976年 | 67篇 |
1975年 | 62篇 |
1974年 | 72篇 |
1973年 | 73篇 |
1972年 | 44篇 |
1971年 | 56篇 |
1970年 | 41篇 |
1968年 | 39篇 |
1966年 | 39篇 |
排序方式: 共有5688条查询结果,搜索用时 15 毫秒
91.
92.
A hybrid heterogeneous catalyst system, which has been synthesized by covalently anchoring oxodiperoxo molybdenum chelate complexes onto the surface of mesoporous MCM-41, is highly active and truly heterogeneous for the liquid-phase epoxidation of cyclooctene with tBuOOH as the oxygen source. 相似文献
93.
Winfried Mientus Hans-Georg Bartel Werner Haberditzl Hans-Joachim Spitzer 《Monatshefte für Chemie / Chemical Monthly》1980,111(3):597-606
A normalization of the wave functions by means of the theoretical exact Multiple-Scattering-(MS)-formalism is discussed within the framework of the SCF-X-SW-method. For the atomic and extramolecular regions the integrals of normalization can be easily determined and the results can be described by the corresponding electronic charges. The calculation of the integral of the interatomic region is problematic. The needful volume integration is only necessary to theGreen's functions of the wave functions and can be solved by means of the residual theory. The further analytical calculation of the surface integrals leads to a complicated formalism which can be numerically evaluated. 相似文献
94.
A synthesis of all possible N-alkylated 2-n-butyl-imidazo[4,5]pyridine isomers is described as well as their structural assignment by 1H NMR spectroscopy. One of these derivatives, 2,-n-butyl-3-[2′- (1H-tetrazol-5-yl)-4-biphenylylmethyl]-3H-imidazo[4,5-b]pyridine 9 is a potent angiotensin II receptor antagonist. 相似文献
95.
Robert Werner Lang 《Helvetica chimica acta》1986,69(4):881-886
The title compound 1 , which can be regarded as a synthetic equivalent of substituted 1,1,1-trifluoroacetone 2 , is prepared by Zn-induced reductive addition of 1,1,1-trichloro-2,2,2-trifluoroethane ( 3 ) to formaldehyde ( 4 ). A brief survey of the scope of this C? C-bond formation leading to a variety of new CF3-containing synthetic building blocks is also given. 相似文献
96.
97.
Diphenylphosphorylazide N3P(O)(OPh)2 reacts with Pt(PPh3)3, Pt(PPh3)2(C2H4), trans-RhCl(CO)(PPh3)2, Ru(CO)3(PPh3)2, CoCl2(PPh3)2 and CuCl(PPh3)2 to give the azido complexes Pt(PPh3)2(N3)R, Pt(PPh3)2(N3)2R2, the urylene complex RhCl(PPh3)2(RNCONR) and the phosphine imine complexes Ru(CO)3(RPPh3)2, CoCl2(RNPPh3)2, CuCl(RNPPh3)2, respectively, (RP(O)(OPh)2). The oxidative addition of n-C6F13SO2N3 to Pt(PPh3)4 and Pt(PPh3)2(C2H4) affords the complexes Pt(PPh3)2(N3)R and Pt(PPh3)2(N3)2R2, respectively, (RSO2C6F13. The compounds are characterized by elemental analysis and by their IR spectra. 相似文献
98.
The dialkylgallium chlorides R2GaCl (R = Me, Et, CMe3) reacted with hydrazines H2N-N(H)R′ (R′ = CMe3, C6H5) to form the adducts R2ClGa ← NH2-N(H)R′ (1-4), in which the gallium atoms are coordinated by the NH2 nitrogen atoms of the hydrazine ligands. Treatment of these adducts with tert-butyllithium as a base afforded dialkylgallium hydrazides (R2Ga-N2H2R′)2 [5 (R = R′ = CMe3) and 6 (R = CMe3, R′ = C6H5)] by deprotonation of the hydrazine ligands and precipitation of LiCl in two cases only. The remaining adducts gave a substitution reaction at gallium or an unclear reaction course. The hydrazides 5 and 6 adopt different structures in the solid state. The tri(tert-butyl) compound 5 possesses a four-membered Ga2N2 heterocycle in its molecular core with two exocyclic N-N bonds, which represents the structural motif usually observed for dialkylgallium hydrazides. 6 has a five-membered Ga2N3 heterocycle with one endocyclic and one exocyclic N-N bond. That structure is preserved in solution as clearly shown by NMR spectroscopy. The behaviour of 5 in solution is more complicated, which may be caused by cis/trans isomerization. 相似文献
99.
We present analytical expressions to calculate the gradient of the water-accessible surface area of proteins with respect to Cartesian coordinates and dihedral angles. A detailed mathematical analysis leads to corrected equations for the gradient calculation used previously in the ANAREA program. To study the hydrophobic effect of solvent-protein interactions, our expressions have been implemented to further improve the program package FANTOM. We used this version of FANTOM to minimize the ECEPP/2 and the hydrophobic energy of tendamistat. © 1993 John Wiley & Sons, Inc. 相似文献
100.
Photoelectron spectroscopic investigations indicate that (i) monocyclic diaziridines prefer a trans-conformation of the nitrogen-lone pairs, and (ii) the interaction between these is comparable to that exhibited by open-chain analogues, i.e. alkyl-substituted hydrazines. The chemical experience concerning the particular case of ? NH? NH? →? N?N? oxidation of diaziridines can therefore not be accounted for by a prevailing unfavorable ‘lone pair’ interaction. Thermochemical as well as entropy arguments may serve as an explanation. A rather unsatisfactory agreement between predictions from various theoretical procedures and experimental results for the ionization potentials of ‘lone pair’ MO electrons is noted. 相似文献