全文获取类型
收费全文 | 181515篇 |
免费 | 3820篇 |
国内免费 | 1886篇 |
专业分类
化学 | 99808篇 |
晶体学 | 2551篇 |
力学 | 8257篇 |
综合类 | 88篇 |
数学 | 18845篇 |
物理学 | 57672篇 |
出版年
2021年 | 1333篇 |
2020年 | 1456篇 |
2019年 | 1484篇 |
2018年 | 1409篇 |
2017年 | 1422篇 |
2016年 | 2767篇 |
2015年 | 2293篇 |
2014年 | 3086篇 |
2013年 | 8388篇 |
2012年 | 7143篇 |
2011年 | 8876篇 |
2010年 | 5527篇 |
2009年 | 5650篇 |
2008年 | 8015篇 |
2007年 | 7899篇 |
2006年 | 7555篇 |
2005年 | 7074篇 |
2004年 | 6260篇 |
2003年 | 5396篇 |
2002年 | 5314篇 |
2001年 | 6323篇 |
2000年 | 4825篇 |
1999年 | 3702篇 |
1998年 | 2831篇 |
1997年 | 2791篇 |
1996年 | 2743篇 |
1995年 | 2414篇 |
1994年 | 2324篇 |
1993年 | 2145篇 |
1992年 | 2478篇 |
1991年 | 2415篇 |
1990年 | 2113篇 |
1989年 | 2094篇 |
1988年 | 2078篇 |
1987年 | 1996篇 |
1986年 | 1913篇 |
1985年 | 2819篇 |
1984年 | 2781篇 |
1983年 | 2237篇 |
1982年 | 2415篇 |
1981年 | 2293篇 |
1980年 | 2242篇 |
1979年 | 2184篇 |
1978年 | 2261篇 |
1977年 | 2218篇 |
1976年 | 2144篇 |
1975年 | 2132篇 |
1974年 | 2036篇 |
1973年 | 2119篇 |
1972年 | 1205篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Jigneshkumar P. Patel Zou Guo Xiang Shaw Ling Hsu Andrew B. Schoch Sena Ada Carleen Dean Matsumoto 《Journal of Polymer Science.Polymer Physics》2015,53(21):1519-1526
A uniform dispersion of reactants is necessary to achieve a complete reaction involving multicomponents. In this study, we have examined the role of plasticizer in the reaction of two seemingly unlikely reactants: a highly crystalline hexamethylenetetramine (HMTA) and a strongly hydrogen bonded phenol formaldehyde resin. By combining information from NMR, infrared spectroscopy and differential scanning calorimetry, we were able to determine the role of specific intermolecular interactions necessary for the plasticizer to dissolve the highly crystalline HMTA and to plasticize the phenol formaldehyde resin in this crosslinking reaction. The presence of the plasticizer increased the segmental mobility, disrupted the hydrogen bonded matrix, and freed the hydroxyl units, which further increased the solubility of the HMTA. Both the endothermic and exothermic transitions are accounted for in the calorimetric data obtained. For the first time, it is possible to obtain the effective molar ratio of each component needed to complete the crosslinking reaction efficiently. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1519–1526 相似文献
52.
Claudia Poloni Marc C. A. Stuart Pieter van der Meulen Wiktor Szymanski Ben L. Feringa 《Chemical science》2015,6(12):7311-7318
The external photocontrol over peptide folding, by the incorporation of molecular photoswitches into their structure, provides a powerful tool to study biological processes. However, it is limited so far to switches that exhibit only a rather limited geometrical change upon photoisomerization and that show thermal instability of the photoisomer. Here we describe the use of an overcrowded alkene photoswitch to control a model β-hairpin peptide. This photoresponsive unit undergoes a large conformational change and has two thermally stable isomers which has major influence on the secondary structure and the aggregation of the peptide, permitting the phototriggered formation of amyloid-like fibrils. 相似文献
53.
54.
55.
56.
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
57.
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
58.
59.
Ling-Yang Hsu Qiumin Liang Zhiheng Wang Hsin-Hung Kuo Wun-Shan Tai Shi-Jian Su Xiuwen Zhou Yi Yuan Yun Chi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(67):15375-15386
Iridium complexes bearing chelating cyclometalates are popular choices as dopant emitters in the fabrication of organic light-emitting diodes (OLEDs). In this contribution, we report a series of blue-emitting, bis-tridentate IrIII complexes bearing chelates with two fused five-six-membered metallacycles, which are in sharp contrast to the traditional designs of tridentate chelates that form the alternative, fused five-five metallacycles. Five IrIII complexes, Px-21 – 23 , Cz-4 , and Cz-5 , have been synthesized that contain a coordinated dicarbene pincer chelate incorporating a methylene spacer and a dianionic chromophoric chelate possessing either a phenoxy or carbazolyl appendage to tune the coordination arrangement. All these tridentate chelates afford peripheral ligand–metal–ligand bite angles of 166–170°, which are larger than the typical bite angle of 153–155° observed for their five-five-coordinated tridentate counterparts, thereby leading to reduced geometrical distortion in the octahedral frameworks. Photophysical measurements and TD-DFT studies verified the inherent transition characteristics that give rise to high emission efficiency, and photodegradation experiments confirmed the improved stability in comparison with the benchmark fac-[Ir(ppy)3] in degassed toluene at room temperature. Phosphorescent OLED devices were also fabricated, among which the carbazolyl-functionalized emitter Cz-5 exhibited the best performance among all the studied bis-tridentate phosphors, showing a maximum external quantum efficiency (EQEmax) of 18.7 % and CIEx,y coordinates of (0.145, 0.218), with a slightly reduced EQE of 13.7 % at 100 cd m−2 due to efficiency roll-off. 相似文献
60.