全文获取类型
收费全文 | 99908篇 |
免费 | 12596篇 |
国内免费 | 7509篇 |
专业分类
化学 | 60111篇 |
晶体学 | 910篇 |
力学 | 6029篇 |
综合类 | 323篇 |
数学 | 17051篇 |
物理学 | 35589篇 |
出版年
2024年 | 175篇 |
2023年 | 1541篇 |
2022年 | 2274篇 |
2021年 | 2650篇 |
2020年 | 3084篇 |
2019年 | 2856篇 |
2018年 | 3598篇 |
2017年 | 3649篇 |
2016年 | 4122篇 |
2015年 | 3840篇 |
2014年 | 4396篇 |
2013年 | 5764篇 |
2012年 | 9640篇 |
2011年 | 8961篇 |
2010年 | 6243篇 |
2009年 | 5758篇 |
2008年 | 5109篇 |
2007年 | 4678篇 |
2006年 | 4323篇 |
2005年 | 7450篇 |
2004年 | 6252篇 |
2003年 | 4142篇 |
2002年 | 2206篇 |
2001年 | 1751篇 |
2000年 | 1446篇 |
1999年 | 1702篇 |
1998年 | 1411篇 |
1997年 | 1361篇 |
1996年 | 1332篇 |
1995年 | 1090篇 |
1994年 | 962篇 |
1993年 | 784篇 |
1992年 | 844篇 |
1991年 | 732篇 |
1990年 | 637篇 |
1989年 | 492篇 |
1988年 | 434篇 |
1987年 | 328篇 |
1986年 | 291篇 |
1985年 | 240篇 |
1984年 | 171篇 |
1983年 | 127篇 |
1982年 | 98篇 |
1981年 | 85篇 |
1980年 | 77篇 |
1979年 | 61篇 |
1977年 | 58篇 |
1976年 | 109篇 |
1975年 | 60篇 |
1973年 | 76篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Kimmo Smolander Risto J?rnstr?m Annika Sajalinna 《Fresenius' Journal of Analytical Chemistry》1989,335(4):392-394
Summary The matric effect of boric acid was investigated in the determination of iron in the primary circuit coolant water of nuclear power plants by furnace atomic absorption spectrometry. The effect of boric acid was of particular interest. The method was applied during refuelling and maintenance periods and the results were used to interpret the chemical changes in the water.
Einfluß von Borsäure auf die Bestimmung von Eisen in Reaktorkühlwasser durch GF-AAS相似文献
992.
The title compound, (isopropylxanthato)(phenyl)mercury(I), was synthesized and characterized by elemental analysis, IR and thermogravimetric analysis. Density functional theory (DFT) method calculations were performed at B3LYP/CEP-121G and B3LYP/CEP-31G levels of theory, respectively. Vibrational frequencies were predicted, assigned, compared with the experimental values, and they are supported each other. The calculated results show that the strength of bond Hg—C is stronger than that of Hg—S, which is good agreement with the experimental data. The calculations of the second order optical nonlinearity and electronic absorption spectra are also performed. 相似文献
993.
994.
995.
不对称亚砜与1,10—双(1‘苯基—3’—甲基—5‘氧化吡唑—4’—基)癸二酮—[1,10]对… 总被引:1,自引:0,他引:1
996.
聚合物强化辐射交联研究进展 总被引:1,自引:0,他引:1
本文综述卫应用含有多个C=C不饱和基团的多官能团单体来强化辐射交联聚合物的研究进展,对强化交联的反应机理、多官能团单体的强化交联行为、强化交联的影响因素及强化交联的研究表征方法进行了介绍。 相似文献
997.
Host-guest complexes of cucubit[8]uril with phenanthrolines and some methyl derivatives 总被引:1,自引:0,他引:1
DAY Anthony I 《中国科学B辑(英文版)》2005,48(4):305-314
Cucurbituril a molecular container (or host) has a rigid hollow interior cavity which is large enough to accommodate, one or more, smaller molecules (or guests). The cavity is accessible through two carbonyl portal openings. Molecules or guests enter the … 相似文献
998.
999.
This paper reports the results of a variety of experiments carried out for understanding the solvation behavior of potassium thiocyanate in methanol–water mixtures. Electrical conductivity, speed of sound, viscosity, and FT-Raman spectra of potassium thiocyanate solutions in 5 and 10% methanol–water (w/w) mixtures were measured as functions of concentration and temperature. The conductivity and structural relaxation time suggest the ion–solvent and solvent-separated ion–ion associations increase as the salt concentration increases in the mixtures. The Raman band shifts due to the C–O stretching mode of methanol for the solvent mixtures reveal the formation of methanol–water complexes. The significant changes in the Raman bands for the C–N, C–S and O–H stretching modes indicate the presence of SCN−−solvent interactions through the N-end, “free” SCN− and the solvent-shared ion pairs as potassium thiocyanate is added to the methanol–water mixtures. The relative changes corresponding to H–O–H bending and C–O stretching frequencies indicate that K+ is preferentially solvated by water in these solvent mixtures. The appearance and increase of the intensity of a broad band at ≈940 cm−1 upon salt addition was attributed to the SCN−–H2O–K+ solvent-shared ion pairs. No Raman spectral evidence for K+(H2O)n species was observed. The preferential solvation of K+ and SCN− in the methanol−water mixtures was verified by the application of the Kirkwood−Buff theory of solutions. This theory confirms that K+ is strongly preferentially solvated by water, whereas SCN− is preferentially solvated by the methanol component. 相似文献
1000.
油莱甾醇内酯(Brassinolide)(1)是一种高效的植物生长激素,其生理活性与侧链中C_(22)、C_(23)的构型密切相关。当C_(22)、C_(23)为S、S构型时,其活性仅为1的十分之一。在1的 相似文献