全文获取类型
收费全文 | 298篇 |
免费 | 5篇 |
国内免费 | 5篇 |
专业分类
化学 | 190篇 |
晶体学 | 31篇 |
力学 | 7篇 |
数学 | 21篇 |
物理学 | 59篇 |
出版年
2022年 | 3篇 |
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 7篇 |
2016年 | 12篇 |
2015年 | 6篇 |
2014年 | 6篇 |
2013年 | 15篇 |
2012年 | 20篇 |
2011年 | 32篇 |
2010年 | 21篇 |
2009年 | 9篇 |
2008年 | 18篇 |
2007年 | 18篇 |
2006年 | 17篇 |
2005年 | 17篇 |
2004年 | 6篇 |
2003年 | 11篇 |
2002年 | 8篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1997年 | 1篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有308条查询结果,搜索用时 171 毫秒
1.
2.
The thermal decomposition of lead and manganese salts of mono(hydroxyethyl) phthalate was studied by thermogravimetry and differential scanning calorimetry. The kinetic parameters for the various stages of decomposition of these salts were calculated by different methods and mechanisms are proposed to explain the results. 相似文献
3.
4.
Stoltz C Ramesha K Sirchio SA Gönen ZS Eichhorn BW Salamanca-Riba L Gopalakrishnan J 《Journal of the American Chemical Society》2003,125(14):4285-4292
Anion metathesis reactions between ZrNCl and A(2)S (A = Na, K, Rb) in the solid state follow three different pathways depending on reaction temperature and reactant stoichiometry: (1) the reaction of ZrNCl with A(2)S in the 2:1 stoichiometry at 800 degrees C/72 h/in vacuo yields alpha-Zr(2)N(2)S with the expected layered structure of La(2)O(2)S. Above 850 degrees C, alpha-Zr(2)N(2)S (P3 macro m1; a = 3.605(1) A, c = 6.421(3) A) neatly transforms to beta-Zr(2)N(2)S (P6(3)/mmc: a = 3.602(1) A, c = 12.817(1) A). The structures of the alpha- and beta-forms are related by an a/2 shift of successive Zr(2)N(2) layers. (2) The same reaction at low temperatures (300-400 degrees C) yields ACl intercalated phases of the formula A(x)Zr(2)N(2)SCl(x) (0 < x < approximately 0.15), where alkali ions are inserted between the S/Cl.S/Cl van der Waals gap of a ZrNCl-type structure. The S and Cl ions are disordered and the c lattice parameters are alkali dependent (R3 macro m, a approximately 3.6 A, c approximately 28.4 (Na), 28.9 (K), and 30.5 A (Rb). A(x)Zr(2)N(2)SCl(x) phases are hygroscopic and reversibly absorb water to give monohydrates. (3) Reaction of ZrNCl with excess A(2)S at 400-1000 degrees C gives A(2)S intercalated phases of the formula A(2)(x)Zr(2)N(2)S(1+)(x) (0 < x < 0.5), where the alkali ions reside between the S.S van der Waals gap of a ZrNCl type structure (R3 macro m, a approximately 3.64 A, c approximately 29.48 A). Structural characterization of the new phases and implications of the results are described. 相似文献
5.
Some new metal-containing polyurethanes were synthesized from manganese and lead salts of mono(hydroxyethyl)phthalate by condensing them with hexamethylene diisocyanate and toluene diisocyanate in dimethylformamide as solvent. The polymers were characterized by viscometry, infrared spectroscopy and thermal analysis. The decomposition temperatures of these polymers were found to be significantly lower than those of metal-free polymers of similar structure. However, the rates of decomposition of metal-containing polyurethanes were lower than those of polyurethanes having no metal. Inherent viscosities in DMSO at 30° of these polyurethanes were low, ranging from 0.043 to 0.067. 相似文献
6.
Jin J Sioutis I Tarczay G Gopalakrishnan S Bezant A Miller TA 《The Journal of chemical physics》2004,121(23):11780-11797
Dispersed fluorescence (DF) spectra of 1-propoxy, 1-butoxy, 2-propoxy, and 2-butoxy radicals have been observed under supersonic jet cooling conditions by pumping different vibronic bands of the B-X laser induced fluorescence excitation spectrum. The DF spectra were recorded for both conformers of 1-propoxy, three conformers of the possible five of 1-butoxy, the one possible conformer of 2-propoxy, and two conformers of the possible three of 2-butoxy. Analysis of the spectra yields the energy separations of the vibrationless levels of the ground X and low-lying A electronic state as well as their vibrational frequencies. In all cases, the vibrational structure of the DF spectra is dominated by a CO stretch progression yielding the nuCO stretching frequency for the X state and in most cases for the A state. In addition to the experimental work, quantum chemical calculations were carried out to aid the assignment of the vibrational levels of the X state and for some conformers the A state as well. Geometry optimizations of the different conformers of the isomers were performed and their energy differences in the ground states were determined. The results of the calculation of the energy separations of the close-lying X and A states of the different conformations are provided for comparison with the experimental observations. 相似文献
7.
A series of hexacoordinated RuIII–PPh3 complexes of general formula [RuCl(PPh3)L] (L = tetradentate Schiff bases derived from the condensation of 2-furaldehyde or thiophene-2-carboxyaldehyde with alkyl and aryl diamines have been synthesized. The complexes were characterized by elemental analyses, spectroscopic and cyclic voltammetric studies. All of the complexes were paramagnetic. Coordination of the Schiff base appears to occur through the two nitrogen and two heterocyclic oxygen/sulphur atoms. 相似文献
8.
Mixed valency in the high-temperature phases of transition metal molybdates, A MoO4 ( A =Fe, Co, Ni)
Transition metal molybdates of the formulaAMoO4 whereA=Fe, Co or Ni exhibit a first-order phase transition between 670K–970K. An investigation of the lowtemperature (lt) and high-temperature (ht) phases by x-ray photoelectron spectroscopy, x-ray absorption spectroscopy, magnetic susceptibility and other physical methods
shows that the phase transition is associated with a valence change of the typeA
2++Mo6+αA
3++Mo5+ in the cases of iron and cobalt molybdates.
Contribution No. 311 from the Solid State and Structural Chemistry Unit. 相似文献
9.
G. Gopalakrishnan Nair 《Journal of Optimization Theory and Applications》1979,28(3):429-434
The convergence of the Luus-Jaakola search method for unconstrained optimization problems is established.Notation
E
n
Euclideann-space
- f
Gradient off(x)
- 2
f
Hessian matrix
- (·)
T
Transpose of (·)
-
I
Index set {1, 2, ...,n}
- [x
i1
*(j)
]
Point around which search is made in the (j + 1)th iteration, i.e., [x
1l
*(j)
,x
2l
*(j)
,...,x
n1
*(j)
]
-
r
i
(i)
Range ofx
il
*(i)
in the (j + 1)th iteration
-
l
1
mini {r
i
(0)
}
-
l
2
mini {r
i
(0)
}
-
A
j
Region of search in thejth iteration, i.e., {x E
n:x
il
*(j-1)
–0.5r
i
(j-1)
x
ix
il
*(j-1)
+0.5r
i
(j-1)
,i I}
-
S
j
Closed sphere with center origin and radius
j
-
Reduction factor in each iteration
-
1–
- (·)
Gamma function
Many discussions with Dr. S. N. Iyer, Professor of Electrical Engineering, College of Engineering, Trivandrum, India, are gratefully acknowledged. The author has great pleasure to thank Dr. K. Surendran, Professor, Department of Electrical Engineering, P.S.G. College of Technology, Coimbatore, India, for suggesting this work. 相似文献
10.