全文获取类型
收费全文 | 18591篇 |
免费 | 2728篇 |
国内免费 | 2674篇 |
专业分类
化学 | 13186篇 |
晶体学 | 232篇 |
力学 | 1058篇 |
综合类 | 257篇 |
数学 | 2480篇 |
物理学 | 6780篇 |
出版年
2024年 | 45篇 |
2023年 | 242篇 |
2022年 | 448篇 |
2021年 | 540篇 |
2020年 | 546篇 |
2019年 | 610篇 |
2018年 | 539篇 |
2017年 | 529篇 |
2016年 | 822篇 |
2015年 | 851篇 |
2014年 | 1106篇 |
2013年 | 1397篇 |
2012年 | 1516篇 |
2011年 | 1649篇 |
2010年 | 1282篇 |
2009年 | 1284篇 |
2008年 | 1446篇 |
2007年 | 1277篇 |
2006年 | 1227篇 |
2005年 | 1083篇 |
2004年 | 879篇 |
2003年 | 741篇 |
2002年 | 847篇 |
2001年 | 611篇 |
2000年 | 500篇 |
1999年 | 360篇 |
1998年 | 247篇 |
1997年 | 202篇 |
1996年 | 192篇 |
1995年 | 136篇 |
1994年 | 122篇 |
1993年 | 100篇 |
1992年 | 84篇 |
1991年 | 67篇 |
1990年 | 63篇 |
1989年 | 57篇 |
1988年 | 51篇 |
1987年 | 34篇 |
1986年 | 30篇 |
1985年 | 36篇 |
1984年 | 29篇 |
1983年 | 20篇 |
1982年 | 17篇 |
1981年 | 10篇 |
1980年 | 22篇 |
1979年 | 19篇 |
1978年 | 21篇 |
1976年 | 12篇 |
1975年 | 6篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Yong Zhang 《Order》1996,13(4):365-367
G. Grätzer, H. Lakser, and E. T. Schmidt proved that every distributive lattice with n join-irreducible elements can be represented as the congruence lattice of a small lattice L, that is, a lattice L with O(n
2
) elements. G. Grätzer, I. Rival, and N. Zaguia proved that, for any <2, O(n
2
) can not be improved to O(n
). In this note we show that the theorem about small representation can be improved further to get a more delicate result. 相似文献
82.
Gallium(III) triflate catalyzed the rearrangement of 2-substituted vinylepoxides into beta,gamma-unsaturated carbonyl compounds with high regio- and chemoselectivity (>97/3) in low catalyst loading (1-5 mol %). The alkyl-substituted trimethylsilylvinyl epoxides gave beta,gamma-unsaturated ketone, but aryl-substituted vinylepoxides gave the aldehydes instead. 相似文献
83.
2型糖尿病患者血清钙镁与甲状腺激素含量变化及临床意义 总被引:1,自引:0,他引:1
为了监测 2型糖尿病人血清钙、镁和甲状腺激素含量 ,分析其临床意义及相关性 ,应用放射免疫分析法测定了 1 1 5例 2型糖尿病及 1 5 0例健康人血清甲状腺激素含量。同时用美国杜邦RXL自动生化仪测定了其血清钙、镁含量。结果表明 ,在 2型糖尿病伴有明显并发症者血镁、FT3水平明显降低 (P <0 0 5 ) ,钙镁两种元素与甲状腺激素水平无明显相关性。 2型糖尿病患者适当补镁对预防其并发症是有益的 ,测定FT3 等可作为判断 2型糖尿病严重程度和估计预后的参考指标。 相似文献
84.
85.
Using the method of diagonalization, in which zero-field wavefunctions from a potential model are chosen as a basis, we calculate positions and widths of anticrossings for highly excited Stark states of Rb with principal quantum number n up to 49. We obtain the theoretical positions and widths in good agreement with available experimental values, and we present scaling laws of the field positions and widths of anticrossings that can be used to provide information for future experiments. 相似文献
86.
Kang MS Kim JH Kim YJ Won J Park NG Kang YS 《Chemical communications (Cambridge, England)》2005,(7):889-891
The ionic conductivity of polymer electrolytes and their interfacial contact with dye-attached TiO2 particles were enhanced markedly by the addition of amorphous oligomer into polymer electrolytes, resulting in very high overall energy conversion efficiency. 相似文献
87.
Stasko DJ Perzynski KJ Wasil MA Brodbeck JK Kirschbaum K Kim YW Lind C 《Inorganic chemistry》2004,43(13):3786-3788
The acid H(2)B(12)(OH)(12) can be isolated as a crystalline solid by protonation of the hydroxylated borane anion, B(12)(OH)(12)(2)(-). This acidic compound has low solubility in water, conducts protons in the solid state, and has thermal stability to a temperature of 400 degrees C. The conductivity mechanism is a Grotthuss mechanism with a low activation enthalpy (9-13 kcal/mol). This new acid represents an addition to the class of oxoacids, of which sulfuric and phosphoric acid are the most prominent examples. 相似文献
88.
N-Alkyl acryloylamides derived from o-aminobenzaldehyde derivatives react with N-alkyl glycine derivatives to provide cis-fused pyrrole[3,2-c]quinolones in moderate yield and high diastereoselectivity. These same substrates engage in a tandem Michael-Mannich pathway on treatment with a secondary amine, providing corresponding quinolone derivatives. The elaboration of a pyrroloquinolone derivative via addition of an in situ generated functionalized copper acetylide to an in situ generated iminium ion provided the C2-substituted derivative. Global deprotection and reduction of the alkyne afford the tricyclic triamine core (as the HCl salt) found in martinellic acid. 相似文献
89.
Yong Qiang TU 《中国化学快报》1992,3(8):625-628
Three new β-dihydroagarofuran sesquiterpene polyol esters,one alkaloid andtwo non-alkaloids,were isolated from the MeOH extract of seed oil of Celastrus angulatus.Their structures were elucidated on the basis of UV,IR,mass,NOE difference,~1H-NMR,~(13)C-NMR and ~1H-~(13)C long-range correlation spectroscopy. 相似文献
90.
The complex species of UO2(HA)(H2A)+ and UO2(HA)2 were identified in the ascorbic acid solution of uranyl ion at pH<2.1 and pH>2.1, respectively. Polarographic wave was proved to be the simultaneous reduction of UO2+2 and UO2(HA)(H2A)+ at pH <2.1. However, at pH>2.1, the wave is due to the reduction of U02(HA)2 The stability constants of the two complex species were found to be 5.1×10+ and 1.0×105, respectively. The hydrolysis constant of uranyl ion in the solution of ascorbic acid was determined. 相似文献