全文获取类型
收费全文 | 4334篇 |
免费 | 15篇 |
国内免费 | 10篇 |
专业分类
化学 | 3678篇 |
晶体学 | 22篇 |
力学 | 23篇 |
数学 | 70篇 |
物理学 | 366篇 |
综合类 | 200篇 |
出版年
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 1篇 |
2017年 | 6篇 |
2016年 | 4篇 |
2015年 | 2篇 |
2014年 | 10篇 |
2013年 | 10篇 |
2012年 | 12篇 |
2011年 | 24篇 |
2010年 | 26篇 |
2009年 | 29篇 |
2008年 | 33篇 |
2007年 | 37篇 |
2006年 | 33篇 |
2005年 | 20篇 |
2004年 | 9篇 |
2003年 | 16篇 |
2002年 | 17篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 14篇 |
1994年 | 3篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1985年 | 640篇 |
1984年 | 433篇 |
1983年 | 384篇 |
1982年 | 412篇 |
1981年 | 307篇 |
1980年 | 259篇 |
1979年 | 233篇 |
1978年 | 197篇 |
1977年 | 218篇 |
1976年 | 247篇 |
1975年 | 224篇 |
1974年 | 206篇 |
1973年 | 241篇 |
1960年 | 1篇 |
排序方式: 共有4359条查询结果,搜索用时 15 毫秒
41.
The kinetics of the reaction between organocobaloximes, RCo(DH)2H2O, and iodine have been investigated. They reveal the participation of an RCo(DH)2H2O · I2 intermediate which undergoes intramolecular transalkylation and acts as an electrophile towards a second organocobaloxime molecule. The trend in reactivity as the R group is varied is discussed. 相似文献
42.
The system copper-tellurium was investigated by DTA, DSC, and X-ray methods. A phase diagram with the phases Cu2?xTe (33.5–36.2 mole% Te), Cu3?xTe2 (40–41 mole%), and CuTe was constructed. In the homogeneity ranges of the nonstoichiometric phases several superstructures were observed. The lattice parameters and d values of some of these phases are given. 相似文献
43.
Molecular mechanics calculations on cycloheptadiene indicate that the molecule has a structure which undergoes a wide pseudorotational motion between two C1 forms, and a C1 form, and this structure is in equilibrium with the C2 form. It is shown that this equilibrium mixture is consistent with all of the available experimental data. 相似文献
44.
Galina Strand Reinhard Renneberg Frieder Scheller 《Journal of Electroanalytical Chemistry》1985,194(1):123-130
The enzyme α-amylase splits blue starch in fragments bearing electroactive groups which exhibit two waves in the pulse polarograms. This behaviour is the basis of the polagraphic determination of bacterial and human serum α-amylase activity. The differential pulse mode is more sensitive by a factor of 25 as compared with normal pulse polarography. With serum α-amylase, protein adsorption disturbs the determination of low activities. 相似文献
45.
With a view to the use of picolinealdehyde salicyloylhydrazone as analytical reagent, a study of the physical properties and chemical reactions of this substance has been carried out. It reacts with nickel (λmax = 375 nm, ? = 3.9 × 104M?1cm?1) or zinc (λmax = 365 nm, ? = 4.8 × 104M?1cm?1) to produce a yellow 1:2 complex in both cases. Spectrophotometric determinations of trace amounts of nickel and zinc have been established. 相似文献
46.
C.N.R. Rao Om Parkash D. Bahadur P. Ganguly S. Nagabhushana 《Journal of solid state chemistry》1977,22(3):353-360
Electronic and magnetic properties of Ln1?xSrxCoO3 (Ln = Pr, Nd, Sm, Eu, and Gd) systems show that above a critical value of x, the d electrons become itinerant while the materials become ferromagnetic at low temperatures. The ferromagnetic component increases with increase in x and decrease in temperature. The Curie temperature increases with x and decreases with decrease in the size of the rare-earth ion. Incorporation of Ba2+ in LaCoO3 favors itinerant electron ferromagnetism relative to Sr2+ while Ca2+ is less favorable than Sr2+. 相似文献
47.
A topological extrapolation method for the calculation of various properties (melting points, refractive indices, specific rotation, etc.) of infinite linear polymers is developed. The rapid convergence of the oligomer extrapolation series results in very good agreement between calculated and experimental values. Comparison between the proposed method and other empirical or semi-empirical methods (the group addition method and the Pade-approximation) is also presented. 相似文献
48.
49.
50.
Studies of the preparation of 1,8-dihydroazocines and transannular cyclization of hydroazocines to produce functionalized pyrrolizidines are described. Results are presented which demonstrate that unsymmetrically substituted acetylenes bearing at least one electron withdrawing groups undergo efficient cycloaddition to 1 - β - styryl - 1,2 - dihydropyridine producing in a regio-selective fashion 3,4 - disubstituted - 1,8 - dihydroazocines. The dihydroazocines generated in this manner can be converted to 1 - formyl - Δ4,5 - epoxyazocines which undergo interesting rearrangement reactions to form pyrrolizidines when subjected to methoxide deformylation followed by acid treatment. In addition, 1,6,7,8 - tetrahydroazocines can be converted to pyrrolizidines under bromination conditions. The intriguing chemical process which occur under the conditions outlined above are described. 相似文献