全文获取类型
收费全文 | 1309638篇 |
免费 | 39955篇 |
国内免费 | 14683篇 |
专业分类
化学 | 654680篇 |
晶体学 | 15669篇 |
力学 | 77409篇 |
综合类 | 408篇 |
数学 | 244005篇 |
物理学 | 372105篇 |
出版年
2021年 | 15414篇 |
2020年 | 18073篇 |
2019年 | 18358篇 |
2018年 | 12710篇 |
2016年 | 29547篇 |
2015年 | 23021篇 |
2014年 | 33472篇 |
2013年 | 78282篇 |
2012年 | 39737篇 |
2011年 | 33809篇 |
2010年 | 38404篇 |
2009年 | 41247篇 |
2008年 | 32312篇 |
2007年 | 26656篇 |
2006年 | 34757篇 |
2005年 | 25438篇 |
2004年 | 27443篇 |
2003年 | 26374篇 |
2002年 | 27842篇 |
2001年 | 25365篇 |
2000年 | 23301篇 |
1999年 | 22628篇 |
1998年 | 21687篇 |
1997年 | 21751篇 |
1996年 | 22019篇 |
1995年 | 19950篇 |
1994年 | 19262篇 |
1993年 | 18595篇 |
1992年 | 18034篇 |
1991年 | 17685篇 |
1990年 | 16871篇 |
1989年 | 16852篇 |
1988年 | 16379篇 |
1987年 | 16416篇 |
1986年 | 15256篇 |
1985年 | 21781篇 |
1984年 | 23188篇 |
1983年 | 19354篇 |
1982年 | 21137篇 |
1981年 | 20369篇 |
1980年 | 19661篇 |
1979年 | 19742篇 |
1978年 | 21188篇 |
1977年 | 20789篇 |
1976年 | 20471篇 |
1975年 | 19135篇 |
1974年 | 18747篇 |
1973年 | 19298篇 |
1972年 | 13823篇 |
1967年 | 12255篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Hideaki Murasugi Dr. Shohei Kumagai Dr. Hiroaki Iguchi Prof. Dr. Masahiro Yamashita Dr. Shinya Takaishi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(42):9885-9891
Crystal structures of a series of organic–inorganic hybrid gold iodide perovskites, formulated as A2[AuII2][AuIIII4] [A=methylammonium (MA) ( 1 ) and formamidinium (FA) ( 2 )], A′2[I3]1−x[AuII2]x[AuIIII4] [A′=imidazolium (IMD) ( 3 ), guanidinium (GUA) ( 4 ), dimethylammonium (DMA) ( 5 ), pyridinium (PY) ( 6 ), and piperizinium (PIP) ( 7 )], systematically changed depending on the cation size. In addition, triiodide (I3−) ions were partly incorporated into the AuI2− sites of 3 – 7 , whereas they were not incorporated into those of 1 and 2 . Such a difference comes from the size of the organic cation. Optical absorption spectra showed characteristic intervalence charge-transfer bands from AuI to AuIII species, and the optical band gap increased as the size of the cation became larger. 相似文献
942.
Minoru Koyama Dr. Takafumi Kawakami Dr. Takashi Okazoe Prof. Dr. Kyoko Nozaki 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(46):10913-10917
Methacrylic esters, represented by methyl methacrylate (MMA), are widely used as commodity chemicals. Here, the one-pot synthesis of methacrylic esters from acetone, a haloform and alcohols in the presence of an organic base is described. Using DBU as the organic base for the reaction of acetone, chloroform and methanol in acetonitrile afforded MMA in 66 % yield. When the solvent was replaced by benzonitrile, the product MMA was successfully purified by distillation. Applicability of this process to various alcohols was also investigated to show ethyl, phenyl, CF3CH2, and n-C6F13CH2CH2 esters were obtained in moderate yields. The use of bromoform instead of chloroform resulted in the improvement of the yield, for example, methyl and n-C6F13CH2CH2 esters up to 81 and 70 %, respectively. The reaction with deuterated starting materials acetone-d6 and MeOH-d4, with DBU in acetonitrile afforded deuterated MMA (MMA-d8) in 70 % yield. 相似文献
943.
944.
Pan Huang Dawen Xu Robert M. Reich Felix Kaiser Boping Liu Fritz E. Kühn 《Tetrahedron letters》2019,60(24):1574-1577
A first example of an Et2Zn mediated silylation of 1-aklynes is reported. A series of functional groups are tolerated in this reaction. Mechanistic studies support Zn alkynilides as intermediates in the reaction. This reaction protocol provides a practical method for the preparation of alkynylsilanes and expands the application of organometallic zinc in organic synthesis. 相似文献
945.
Journal of Global Optimization - In this paper, we propose a novel algorithm that is based on quadratic-piecewise-linear approximations of DC functions to solve nonnegative sparsity-constrained... 相似文献
946.
近年来,基于透射电子显微技术、微纳加工技术和薄膜制造技术的发展,原位液相透射电子显微技术产生,为构建多种纳米级分辨率尺度下的微实验平台,发展新型纳米表征技术和众多领域的相关研究提供了途径.本文首先介绍了应用于原位液相透射电子显微技术的液体腔设计要求,然后介绍了液体腔的发展和典型的制备工艺,最后综述了近年来液体腔透射电子显微镜在纳米粒子成核和生长方面的应用研究,并探讨了该技术前沿发展面临的机遇和挑战.本文将为提高我国先进纳米表征技术和原子精准构筑技术提供相关讨论和支持. 相似文献
947.
Siberian Mathematical Journal - Under study are the right-symmetric algebras over a field $ F $ which possess a “unital” matrix subalgebra $... 相似文献
948.
Doklady Mathematics - Integro-differential equations with unbounded operator coefficients in a Hilbert space are studied. The equations under consideration are abstract hyperbolic equations... 相似文献
949.
Science China Mathematics - We prove that if a compact Riemannian 4-manifold with positive sectional curvature satisfies a strengthened Kato type inequality, then it is definite. We also discuss... 相似文献
950.
Stadnyk V. Yo. Shchepanskyi P. A. Rudysh M. Ya. Kogut Z. A. 《Journal of Applied Spectroscopy》2021,88(4):831-837
Journal of Applied Spectroscopy - The temperature dependence of the refractive indices of K2SO4 with copper impurity was investigated. It was found that introduction of the copper impurity leads to... 相似文献