全文获取类型
收费全文 | 180643篇 |
免费 | 3838篇 |
国内免费 | 1950篇 |
专业分类
化学 | 99108篇 |
晶体学 | 2570篇 |
力学 | 8261篇 |
综合类 | 74篇 |
数学 | 18890篇 |
物理学 | 57528篇 |
出版年
2021年 | 1355篇 |
2020年 | 1530篇 |
2019年 | 1567篇 |
2018年 | 1530篇 |
2017年 | 1526篇 |
2016年 | 2827篇 |
2015年 | 2402篇 |
2014年 | 3052篇 |
2013年 | 8455篇 |
2012年 | 7112篇 |
2011年 | 8842篇 |
2010年 | 5511篇 |
2009年 | 5588篇 |
2008年 | 7994篇 |
2007年 | 7857篇 |
2006年 | 7524篇 |
2005年 | 6917篇 |
2004年 | 6194篇 |
2003年 | 5311篇 |
2002年 | 5253篇 |
2001年 | 6222篇 |
2000年 | 4749篇 |
1999年 | 3720篇 |
1998年 | 2796篇 |
1997年 | 2742篇 |
1996年 | 2703篇 |
1995年 | 2406篇 |
1994年 | 2252篇 |
1993年 | 2131篇 |
1992年 | 2429篇 |
1991年 | 2392篇 |
1990年 | 2098篇 |
1989年 | 2062篇 |
1988年 | 2069篇 |
1987年 | 1992篇 |
1986年 | 1888篇 |
1985年 | 2804篇 |
1984年 | 2767篇 |
1983年 | 2219篇 |
1982年 | 2401篇 |
1981年 | 2277篇 |
1980年 | 2230篇 |
1979年 | 2176篇 |
1978年 | 2245篇 |
1977年 | 2200篇 |
1976年 | 2131篇 |
1975年 | 2120篇 |
1974年 | 2023篇 |
1973年 | 2107篇 |
1972年 | 1201篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
64.
Zhang Kailun Wu Hongjuan Wang Tian Yao Meng Xie Jixing Jiao Yunhong 《Journal of Thermal Analysis and Calorimetry》2021,145(6):3067-3075
Journal of Thermal Analysis and Calorimetry - A phosphazene-based flame retardant (PBFA) was synthesized by hexachlorocyclotriphosphazene and N-aminoethylpiperazine. To improve the flame retardancy... 相似文献
65.
π-Extended molecules are key components for the development of materials science. In fact, polyaromatic structures are fundamental for the scientific and technological progress of fields such as organic electronics and bio-applications. Beneficial properties of π-extended structures are absorption in the visible region, often luminescence, high electron mobilities and stability. Common approaches to adjust the properties of polyaromatic structures to functional setups involve changes in shape and size at the molecular level. Recently, incorporating hetero-elements emerged as successful approach. In this regard, organophosphorus conjugated molecules are new materials holding great promise for potential applications. In this review, we comprehensively discuss the design/development of polyaromatic phosphorus materials and their applicability. We establish structure/property/applicability relationships to provide key guidelines for the engineering of newer, future applications. This article thus provides a source of information for the further development of this rapidly evolving field of research. 相似文献
66.
Experimental Mechanics - There have been relatively few studies on mechanical properties of nanomaterials under high strain rates, mainly due to the lack of capable nanomechanical testing devices.... 相似文献
67.
Immobilized Catalysts for Iridium‐Catalyzed Allylic Amination: Rate Enhancement by Immobilization 下载免费PDF全文
Dr. Chandi C. Malakar Prof. Dr. Günter Helmchen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(19):7127-7134
The first immobilized catalyst for Ir‐catalyzed asymmetric allylic aminations is described. The catalyst is a cationic (π‐allyl)Ir complex bound by cation exchange to an anionic silica gel support. Preparation of the catalyst is facile, and the supported catalyst displayed considerably enhanced activity compared with the parent homogeneous catalyst. Up to 43 consecutive amination runs were possible in recycling experiments. 相似文献
68.
69.
Chunhong Wang Qi Cui Zhixin Zhang Prof. Zhu-Jun Yao Dr. Shaozhong Wang Prof. Zhi-Xiang Yu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(42):9821-9826
1,3-Azaprotio transfer of propargylic α-ketocarboxylate oximes, a new type of alkynyl oximes featuring an ester tether, has been explored by taking advantage of gold catalysis. The incorporation of an oxygen atom to the chain of alkynyl oximes led to the formation of two different oxa-cyclic nitrones. It was found that internal alkynyl oximes with an E-configuration deliver five-membered nitrones, whereas terminal alkynyl oximes with an E-configuration afford six-membered nitrones. DFT calculations on four possible pathways supported a stepwise formation of C−N and C−H bonds, in which a 1,3-acyloxy-migration competes with the 1,3-azaprotio-transfer, especially in the case of internal alkynyl oximes. The relative nucleophilic properties of oxygen in the carbonyl group and the nitrogen in the oxime, the electronic effects of alkynes, and the influence of the ring system have been investigated computationally. 相似文献
70.