全文获取类型
收费全文 | 7037篇 |
免费 | 190篇 |
国内免费 | 38篇 |
专业分类
化学 | 3623篇 |
晶体学 | 72篇 |
力学 | 266篇 |
数学 | 1052篇 |
物理学 | 2252篇 |
出版年
2023年 | 32篇 |
2022年 | 134篇 |
2021年 | 190篇 |
2020年 | 164篇 |
2019年 | 217篇 |
2018年 | 221篇 |
2017年 | 217篇 |
2016年 | 308篇 |
2015年 | 178篇 |
2014年 | 249篇 |
2013年 | 372篇 |
2012年 | 434篇 |
2011年 | 445篇 |
2010年 | 286篇 |
2009年 | 304篇 |
2008年 | 391篇 |
2007年 | 356篇 |
2006年 | 327篇 |
2005年 | 266篇 |
2004年 | 223篇 |
2003年 | 172篇 |
2002年 | 183篇 |
2001年 | 119篇 |
2000年 | 86篇 |
1999年 | 89篇 |
1998年 | 81篇 |
1997年 | 78篇 |
1996年 | 66篇 |
1995年 | 43篇 |
1993年 | 35篇 |
1992年 | 31篇 |
1991年 | 47篇 |
1990年 | 36篇 |
1989年 | 38篇 |
1987年 | 36篇 |
1986年 | 34篇 |
1985年 | 38篇 |
1984年 | 32篇 |
1983年 | 35篇 |
1982年 | 41篇 |
1980年 | 37篇 |
1979年 | 36篇 |
1978年 | 37篇 |
1977年 | 48篇 |
1976年 | 50篇 |
1975年 | 45篇 |
1973年 | 46篇 |
1972年 | 31篇 |
1971年 | 35篇 |
1970年 | 31篇 |
排序方式: 共有7265条查询结果,搜索用时 15 毫秒
81.
L. N. Vakhitova A. V. Skrypka K. V. Bogutskaya N. A. Taran A. F. Popov 《Theoretical and Experimental Chemistry》2007,43(6):389-395
The reactivity of hydroxide and peroxide anions with 4-nitrophenyl N,N-dimethylcarbamate in aqueous-alcoholic detergent media
and in “oil in water” microemulsions has been studied. Aqueous-alcoholic solutions of cationic (CTAB) and neutral (Triton
X-100) surface active substances have promise for decomposition of substrates by a nucleophilic mechanism.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 6, pp. 358–363, November–December, 2007. 相似文献
82.
V. F. Lukinykh S. A. Myslivets A. K. Popov V. V. Slabko 《Optical and Quantum Electronics》1987,19(5):319-322
Direct eighth-harmonic generation ( = 134.4 nm) of Nd-laser radiation has been studied experimentally in Hg vapour. An electric field produced by free electrons created by photoionization is shown to be reasonable for even-order harmonic generation in a centrosymmetric medium. 相似文献
83.
Yellowish crystals of K2[(UO2)As2O7] ( 1 ) have been synthesized by solid‐state reactions method. The structure of 1 [orthorhombic, Pmmn, a = 12.601(2), b = 13.242(2), c = 5.621(1) Å, V = 937.9(3) Å3, Z = 4] has been solved by direct methods and refined to R1 = 0.049, wR2 = 0.1060 for 1059 observed reflections. The structure of 1 is based upon [(UO2)As2O7]2? sheets formed by corner sharing between [UO6]6? distorted octahedra and [As2O7]4? polyarsenate groups. The K+ cations are either in eightfold or tenfold coordination and are located between the sheets. The topology of the uranyl arsenate sheet is related to silicate minerals of the melilite group and related synthetic silicate, aluminate and germanate compounds. 相似文献
84.
Babij C Farrar DH Koshevoy IO Poë AJ Tunik SP 《Dalton transactions (Cambridge, England : 2003)》2005,(1):116-122
Reactions of the halides X- (X- = chloride, bromide or iodide) with the substituted cluster Rh6(CO)15(PPh3) in oxygen-free chloroform lead to [Rh5(CO)14(PPh3)]-, Rh(CO)2(PPh3)2X and [Rh(CO)2X2]- in the molar ratios 2:1: approximately 13. Oxidation by the solvent is assumed to lead to most of the Rh(I) product, and the stoichiometry for reactions with I- can be defined as 4Rh6(CO)15(PPh3) + 27I- + 12CHCl3 --> 2[Rh5(CO)14(PPh3)]- + Rh(CO)2(PPh3)2I + 13[Rh(CO)2I2]- + 6C2H2Cl4 + 4CO + 12Cl-. This can be rationalized quite simply with the aid of a few generally justifiable assumptions. Rate constants for reactions with bromide increase to a limiting value with increasing [Br-] in a way that shows that breaking of one Rh-Rh bond, with an unusual closo to nido structural change, is rate determining. This opening of the cluster might be spontaneous or solvent induced. To complete the reaction, the bromide has to compete with the reverse nido to closo change. The same closo to nido change is also a major rate determining step for reactions with P(OPh)3 in oxygen-free solutions, and for reactions with bromide in oxygenated solutions in the presence of trifluoroacetic and some other acids. The limiting rates increase slightly with increasing basicity of the ligands P(p-XC6H4)3 along the series X = F3C, Cl, F, H and MeO. Activation parameters for these reactions are reported. 相似文献
85.
T. N. Solomoichenko Yu. S. Sadovskii T. M. Prokop’eva E. A. Karpichev I. V. Kapitanov Zh. P. Piskunova V. A. Savelova A. F. Popov 《Theoretical and Experimental Chemistry》2006,42(6):364-370
We have studied the nucleophilicity of the hydroperoxide anion relative to 4-nitrophenyl diethyl phosphonate (NPDEPS) in the
presence of cetyltrimethylammonium bromide (water, 25 °C) while varying the acidity of the medium and the hydroperoxide anion
concentration over a broad range. The increase in the reaction rate when the reaction is transferred to a micellar pseudophase
is as high as ∼10-fold, which is explained by concentration effects. In CTAB micelles, as in water, the hydroperoxide ion
is one of the most effective α-nucleophiles, and the size of the α-effect, characterized by the ratio of the second-order rate constants for reactions of HOO− and OH− anions with NPDEPS, remains practically constant and reaches a value of ∼50-fold.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 6, pp. 357–363, November–December, 2006. 相似文献
86.
Yu. S. Simanenko E. A. Karpichev T. M. Prokop’eva V. A. Savelov A. F. Popov 《Theoretical and Experimental Chemistry》1998,34(2):76-80
A detailed extrathermodynamic analysis of the behavior of oximate ions (pKa≈7–13) in reactions with various types of substrate was undertaken. For oximate ions with pKa≥9.0, irrespective of the nature of the acyl group, the reactivity of the oximes tends toward that of the alcoholate ions,
and their α-effect disappears. The reason for this is the unfavorable solvation effects of the solvent.
Institute of Physical Organic Chemistry and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg ul.,
Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 34, No. 2, pp. 86–90, March–April,
1998. 相似文献
87.
Popov A. F. Lobanova O. V. Savelova V. A. Sadovskii Yu. S. Solomoichenko T. N. Piskunova Zh. P. 《Russian Journal of Organic Chemistry》2002,38(11):1624-1628
For amides belonging to series RCONH2 (I), RCONHMe (II), RCONHPh (III), and RCONMe2 (IV) rate constants k1 (l mol-1 s-1) were determined (in acetonitrile at 25°C) specifying the nucleophilic reactivity of the oxygen atom in amides toward benzoyl chloride and diphenyl chlorophosphate. The lack of substrate selectivity in the reactions in question was established. For equal values of inductive constants * of the R substituents the reactivity sequence of amides with respect to both substrates is the same (I >>
IV >
II, and III >
II), and it does not follow the corresponding sequence of basicities. A conclusion was drawn that both groups of reactions proceed through cyclic transition states resembling reagents: six-membered with amides I and III, and five-membered with amides II and IV. 相似文献
88.
[reaction: see text]. We have previously described a diastereofacially selective 1,3-dipolar cycloaddition reaction of isomünchnones with vinyl ethers. While adapting this methodology for solid phase synthesis, we discovered a chemoselective and self-promoted linker aminolysis that provides liberated product in high purity, at a significantly enhanced rate. Herein we describe the implementation of a chiral auxiliary as a solid-phase linker, the detailed investigation of its unique aminolysis, and the utility of this cleavage within a chemical diversity format. 相似文献
89.
An influence of tensile stress on the rate of oxidative destruction of polydienes and polyolefins under the action of ozone has been found; the influence of molecular and submolecular parameters and macrochain segmental mobility on the kinetics of oxidation of polymers is discussed. It is shown that chemical processes, with sp3 to sp2 carbon atom rehybridization in the main chain, can change the reactivity of molecules under the action of structural deformations. Both acceleration and deceleration of bimolecular reactions have been found. 相似文献
90.
The standard enthalpies of formation ΔfHo (liq. or cr.) at the temperature T = 298.15 K were measured using combustion calorimetry for benzophenone (A), 1-indanone (B), -tetralone (C), 9-fluorenone (D), anthrone (E) and dibenzosuberone (F). The standard enthalpies of vaporization ΔvHo or sublimation ΔsHo of A-F and 5,7-dihydro-6H-dibenzo[a,c]cyclohepten-6-one (G) were obtained from the temperature function of the vapor pressure measured in a flow system. Enthalpies of fusion ΔmH of solid compounds were measured by DSC. From the enthalpies of formation of the gaseous compounds of A-G the values of their strain enthalpies were derived and structural effects discussed.