全文获取类型
收费全文 | 1105篇 |
免费 | 49篇 |
国内免费 | 4篇 |
专业分类
化学 | 718篇 |
晶体学 | 23篇 |
力学 | 12篇 |
数学 | 146篇 |
物理学 | 259篇 |
出版年
2023年 | 9篇 |
2022年 | 13篇 |
2021年 | 29篇 |
2020年 | 21篇 |
2019年 | 21篇 |
2018年 | 19篇 |
2017年 | 15篇 |
2016年 | 39篇 |
2015年 | 28篇 |
2014年 | 39篇 |
2013年 | 54篇 |
2012年 | 66篇 |
2011年 | 68篇 |
2010年 | 53篇 |
2009年 | 51篇 |
2008年 | 77篇 |
2007年 | 61篇 |
2006年 | 49篇 |
2005年 | 49篇 |
2004年 | 36篇 |
2003年 | 29篇 |
2002年 | 41篇 |
2001年 | 20篇 |
2000年 | 28篇 |
1999年 | 19篇 |
1998年 | 14篇 |
1997年 | 4篇 |
1996年 | 19篇 |
1995年 | 16篇 |
1994年 | 19篇 |
1993年 | 20篇 |
1992年 | 23篇 |
1991年 | 22篇 |
1990年 | 18篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 10篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有1158条查询结果,搜索用时 771 毫秒
71.
Daniel E. Vicentes Andrea L. Romero Ricuarte Rodríguez Justo Cobo Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2020,76(5):446-453
An efficient synthesis of 1‐arylisochromeno[3,4‐d][1,2,3]triazol‐5(1H)‐ones, involving the diazotization of 3‐amino‐4‐arylamino‐1H‐isochromen‐1‐ones in weakly acidic solution, has been developed and the spectroscopic characterization and crystal structures of four examples are reported. The molecules of 1‐phenylisochromeno[3,4‐d][1,2,3]triazol‐5(1H)‐one, C15H9N3O2, (I), are linked into sheets by a combination of C—H…N and C—H…O hydrogen bonds, while the structures of 1‐(2‐methylphenyl)isochromeno[3,4‐d][1,2,3]triazol‐5(1H)‐one, C16H11N3O2, (II), and 1‐(3‐chlorophenyl)isochromeno[3,4‐d][1,2,3]triazol‐5(1H)‐one, C15H8ClN3O2, (III), each contain just one hydrogen bond which links the molecules into simple chains, which are further linked into sheets by π‐stacking interactions in (II) but not in (III). In the structure of 1‐(4‐chlorophenyl)isochromeno[3,4‐d][1,2,3]triazol‐5(1H)‐one, (IV), isomeric with (III), a combination of C—H…O and C—H…π(arene) hydrogen bonds links the molecules into sheets. When compound (II) was exposed to a strong acid in methanol, quantitative conversion occurred to give the ring‐opened transesterification product methyl 2‐[4‐hydroxy‐1‐(2‐methylphenyl)‐1H‐1,2,3‐triazol‐5‐yl]benzoate, C17H15N3O3, (V), where the molecules are linked by paired O—H…O hydrogen bonds to form centrosymmetric dimers. 相似文献
72.
A semiempirical approch for calculation of pAl0.7Ga0.3As-pGaAs-nGaAs concentrator solar cell behaviour in a very wide range of operating temperatures (77 K – 490 K) is developed. Experimental values of cell collection efficiency, short circuit current and open circuit voltage are given, while cell fill factor and overall conversion efficiency are calculated. Optimum cell operating conditions are found both for AM 1 and AM 0 radiation. 相似文献
73.
Thick window pAl0.7Ga0.3As-pGaAs-nGaAs solar cells are reported being grown by forced cooling LPE. Device evaluation shows an 18% maximum conversion efficiency at room temperature. A method for calculating cell conversion efficiency upon knowledge of internal collection efficiency, open circuit voltage and short circuit current is also devised. 相似文献
74.
75.
76.
F. J. Romero M. C. Gallardo A. Czarnecka M. Koralewski J. del Cerro 《Journal of Thermal Analysis and Calorimetry》2007,87(2):357-363
The specific heat
and the enthalpy variation of a highly deuterated crystal of ferroelectric
triglycine selenate have been measured around its first-order phase transition
using the technique square modulated differential thermal analysis (SMDTA).
The low temperature variation rate has allowed analyzing the kinetics of the
phase transition. Due to an internal crack in the sample, the transition is
carried out in two steps and an intermediate region where the transition is
blocked and both phases coexist without transformation has been found. The
latent heat on cooling (L
c=1.32±0.02
J g–1) is higher than on heating (L
h=1.08±0.02 J g–1)
due to the thermal hysteresis and the great difference between the specific
heat in both phases. Nevertheless, the enthalpy balance is fulfilled on heating
and on cooling. 相似文献
77.
Noe Oña Antonio Romero Carmen Assiego Claudia Bello Pierre Vogel M. Soledad Pino-González 《Tetrahedron: Asymmetry》2010,21(17):2092-2099
An approach to the synthesis of polyhydroxyazepane derivatives from sugar-based epoxyamides or epoxyalcohols, in which the total regioselective epoxide opening by nitrogen nucleophiles is the key step, is described. Thus, novel polyhydroxyazepane carboxamides and aminomethyl polyhydroxyazepanes, with potential pharmacological interest, are synthesized from diacetone d-mannose. Configurational assignments of the obtained products were determined. 相似文献
78.
79.
Langlet A Latypov NV Wellmar U Bemm U Goede P Bergman J Romero I 《The Journal of organic chemistry》2002,67(22):7833-7838
Nitration of some 2-substituted pyrimidine-4,6-diones in sulfuric acid was studied, which afforded previously unknown 5,5-gem-dinitropyrimidine-4,6-diones in high yields. The gem-dinitro products were easily attacked by nucleophiles with concomitant formation of gem-dinitroacetyl derivatives, which in turn could be further hydrolyzed to salts of dinitromethane and triureas. 相似文献
80.
In the interaction of molecules with light endowed with orbital angular momentum, an exchange of orbital angular momentum in an electric dipole transition occurs only between the light and the center of mass motion; i.e., internal "electronic-type" motion does not participate in any exchange of orbital angular momentum in a dipole transition. A quadrupole transition is the lowest electric multipolar process in which an exchange of orbital angular momentum can occur between the light, the internal motion, and the center of mass motion. This rules out experiments seeking to observe exchange of orbital angular momentum between light beams and the internal motion in electric dipole transitions. 相似文献