全文获取类型
收费全文 | 134篇 |
免费 | 14篇 |
国内免费 | 37篇 |
专业分类
化学 | 156篇 |
力学 | 9篇 |
综合类 | 4篇 |
数学 | 7篇 |
物理学 | 9篇 |
出版年
2022年 | 5篇 |
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 4篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 4篇 |
2015年 | 1篇 |
2014年 | 6篇 |
2013年 | 26篇 |
2012年 | 3篇 |
2011年 | 9篇 |
2010年 | 8篇 |
2009年 | 3篇 |
2008年 | 10篇 |
2007年 | 9篇 |
2006年 | 13篇 |
2005年 | 12篇 |
2004年 | 6篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1985年 | 1篇 |
1979年 | 1篇 |
1978年 | 4篇 |
排序方式: 共有185条查询结果,搜索用时 15 毫秒
1.
The reaction of a new fluorinated unsymmetrical allenylazine with dimethyl acetylenedicarboxylate and phenylacetylene affords the combined intra-intermolecular criss-cross cycloaddition products, 2,3-disubstituted-1,10-diazatricyclo[5.2.1.04,10]deca-2,6-diene derivatives. The products contain three fused five-membered rings with two nitrogen atoms within an unsaturated heterocyclic system. The structures were assigned using 2D NMR correlations and in the case of the phenylacetylene adduct by X-ray structure analysis. 相似文献
2.
Vladimir B. Arion Alexey A. Nazarov Christian G. Hartinger Gerald Giester Bernhard K. Keppler 《应用有机金属化学》2003,17(9):723-724
For the unsymmetrical title compound, 1‐bromo‐1′‐[(2S)‐N‐(1‐hydroxy‐3‐methylbutane‐2‐yl)]‐ferroceneamide, two independent molecules were found in the asymmetric unit. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
3.
Z. X. Li L. Q. Lin W. M. Zhang T. Wu J. L. Pu 《Journal of polymer science. Part A, Polymer chemistry》2006,44(3):1291-1298
A series of new polyimides were prepared via the polycondensation of (3‐amino‐2,4,6‐trimethylphenyl)‐(3′‐aminophenyl)methanone and aromatic dianhydrides, that is, 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), 4,4′‐oxydiphthalic anhydride, 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride, and 2,2′‐bis(3,4‐dicarboxyphenyl) hexafluoropropane dianhydride. The structures of the polyimides were characterized by Fourier transform infrared and NMR measurements. The properties were evaluated by solubility tests, ultraviolet–visible analysis, differential scanning calorimetry, and thermogravimetric analysis. The two different meta‐position‐located amino groups with respect to the carbonyl bridge in the diamine monomer provided it with an unsymmetrical structure. This led to a restriction on the close packing of the resulting polymer chains and reduced interchain interactions, which contributed to the solubility increase. All the polyimides except that derived from BPDA had good solubility in strong aprotic solvents, such as N‐methyl‐2‐pyrrolidinone, N,N′‐dimethylacetamide, N,N‐dimethylformamide, and dimethyl sulfone, and in common organic solvents, such as cyclohexanone and chloroform. In addition, these polyimides exhibited high glass‐transition values and excellent thermal properties, with an initial thermal decomposition temperature above 470 °C and glass‐transition temperatures in the range of 280–320 °C. The polyimide films also exhibited good transparency in the visible‐light region, with transmittance higher than 80% at 450 nm and a cutoff wavelength lower than 370 nm. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1291–1298, 2006 相似文献
4.
The differential equations and the boundary conditions for the nonequilibrium binary distribution function of an unsymmetrical binary electrolyte are derived from the Ebeling-Falkenhagen continuity equation. The connection between the Onsager reciprocal relation and the binary distribution functions is shown. Further, Feistel's result for thec logc contribution to the conductance is extended to unsymmetrical binary electrolytes. The reason for the difference between Feistel's and Chen'sc logc term is explained, and the significance of Onsager's reciprocal relation for the calculation ofc logc and higher-concentration contributions of the conductance is discussed. 相似文献
5.
The heat of formation (H
f) of unsymmetrical ketone phenylhydrazones and their enehydrazine tautomers was calculated by the semi-empirical quantum-chemical AM1 method. It is concluded that from H
f values it is possible to judge the regioselectivity of indolization of unsymmetrical ketone phenylhydrazones.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 220–221, January, 1993. 相似文献
6.
7.
8.
The relaxation field for solutions of mixed electrolytes of any type is calculated. the calculation is based on the well-known
treatment due to Fuoss-Onsager with the same distance parameter for all the ions in solution. A general conductance-continuity
equation has been established and an improved iterative method of calculation, using Laplace transforms, is proposed. The
relaxation-field results are derived to the second iteration in the perturbation method of integration. 相似文献
9.
Ming BaoMasao Shimizu 《Tetrahedron》2003,59(48):9655-9659
N-Trifluoroacetyl arenesulfenamides (3) were effective precursors for the synthesis of unsymmetrical disulfides (4) and sulfenamides (5). Reactions of 3 with a variety of aromatic thiols at room temperature were generally complete within 5 min and gave unsymmetrical diaryl disulfides in high yields. Aralkyl disulfides were isolated in high yields from the reaction of 3 with aliphatic thiols. The nucleophilic substitution reactions of 3 with amines proceeded smoothly and provided N-substituted sulfenamides in good to excellent yields. 相似文献