全文获取类型
收费全文 | 33596篇 |
免费 | 1646篇 |
国内免费 | 6518篇 |
专业分类
化学 | 36117篇 |
晶体学 | 456篇 |
力学 | 182篇 |
综合类 | 311篇 |
数学 | 1358篇 |
物理学 | 3336篇 |
出版年
2024年 | 12篇 |
2023年 | 336篇 |
2022年 | 471篇 |
2021年 | 868篇 |
2020年 | 938篇 |
2019年 | 981篇 |
2018年 | 834篇 |
2017年 | 1042篇 |
2016年 | 1200篇 |
2015年 | 1099篇 |
2014年 | 1299篇 |
2013年 | 2947篇 |
2012年 | 2251篇 |
2011年 | 2044篇 |
2010年 | 1757篇 |
2009年 | 2199篇 |
2008年 | 2243篇 |
2007年 | 2357篇 |
2006年 | 2206篇 |
2005年 | 2054篇 |
2004年 | 1891篇 |
2003年 | 1506篇 |
2002年 | 1307篇 |
2001年 | 936篇 |
2000年 | 907篇 |
1999年 | 690篇 |
1998年 | 574篇 |
1997年 | 617篇 |
1996年 | 552篇 |
1995年 | 588篇 |
1994年 | 526篇 |
1993年 | 442篇 |
1992年 | 418篇 |
1991年 | 304篇 |
1990年 | 234篇 |
1989年 | 248篇 |
1988年 | 169篇 |
1987年 | 113篇 |
1986年 | 100篇 |
1985年 | 70篇 |
1984年 | 80篇 |
1983年 | 38篇 |
1982年 | 62篇 |
1981年 | 55篇 |
1980年 | 41篇 |
1979年 | 40篇 |
1978年 | 40篇 |
1977年 | 12篇 |
1976年 | 16篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The aim of this work has been to study the influence of modified hole‐extraction layers on the performance of organic solar cells (OSCs) based on blends of poly (3‐hexylthiophene) and [6,6]‐phenyl‐C61‐butyric acid methyl ester. The hole‐extraction layers consist of poly (3,4‐ethylene dioxythiophene):polystyrene sulfonic acid (PEDOT:PSS) doped with different concentrations of bromine. Compared with pristine OSC without adding bromine to the hole‐extraction layer, the bromine‐doped OSCs show a 49% increase in the power conversion efficiency (from 2.12 to 3.16%), which could be attributed to the increase of electrical and optical properties of PEDOT:PSS films after the addition of bromine. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 50: 125–128, 2012 相似文献
992.
993.
《Analytical letters》2012,45(1):57-61
Abstract A new method for the determination of the titre of ascorbic acid standard solutions employing potassium dichromate as a primary standard has been developed. In a pyrophosphate medium, the pyrophosphate complex of divalent manganese is oxidized by dichromate to the pyrophosphate complex of tervalent manganese; the latter oxidizes o-tolidine reversibly with formation of the corresponding quinonediimine, which is visually titrated by the ascorbic acid standard solution. 相似文献
994.
《Analytical letters》2012,45(8):491-495
Abstract An ion selective electrode is described for measuring the unreacted salicylate ion concentration during the electroreduction of salicylic acid. Conditions for making measurements are discussed. 相似文献
995.
《Analytical letters》2012,45(12):995-1001
Abstract Correlations between extraction distribution ratios, bond types, and common solvent physical properties were determined for 19 extraction systems. Different types of bonding are involved in the water adduct formation on different types of chelates. 相似文献
996.
Kiyoshi Tanemura 《Tetrahedron letters》2018,59(49):4293-4298
Silica gel-mediated hydrochlorination of unactivated alkenes using 35% hydrochloric acid under organic solvent-free conditions proceeded to give the corresponding chlorides in good yields. Hydrobromination or hydriodination using 47% hydrobromic acid or 55% hydriodic acid afforded the corresponding halides, respectively. Silica gel could be recycled five times without any significant loss of activities. 相似文献
997.
998.
Low dielectric constant apolar aprotic solvents, although employed on a limited scale for studying proton transfer reactions as compared with commonly used polar protic or dipolar aprotic ones, offer some particular advantages, namely, specific solute–solvent interactions are virtually eliminated and proton transfer occurs directly in an apolar aprotic solvent. An intriguing feature of these reactions is their general acid‐catalyzed/base‐catalyzed kinetics with a time scale over microseconds to minutes. In fact, the true or intrinsic relative strengths of acids/bases when measured in such solvents come to the fore much more clearly than those obtained in other classes of solvents. Recently, a review documenting the post‐1980 developments relating to proton transfer reactions in apolar aprotic solvents has been published. The present article is a commentary of the pre‐1980 developments in this area since the 1920s Brønsted–Lowry's “proton cult” of acid–base theory. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
999.
Will R. Gutekunst Athina Anastasaki Sungbaek Seo Alaina J. McGrath David J. Lunn Paul G. Clark Craig J. Hawker 《Journal of polymer science. Part A, Polymer chemistry》2017,55(5):801-807
A new di‐tert‐butyl acrylate (diTBA) monomer for controlled radical polymerization is reported. This monomer complements the classical use of tert‐butyl acrylate (TBA) for synthesis of poly(acrylic acid) by increasing the density of carboxylic acids per repeat unit, while also increasing the flexibility of the carboxylic acid side‐chains. The monomer is well behaved under Cu(II)‐mediated photoinduced controlled radical polymerization and delivers polymers with excellent chain‐end fidelity at high monomer conversions. Importantly, this new diTBA monomer readily copolymerizes with TBA to further the potential for applications in areas such as dispersing agents and adsorbents. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 801–807 相似文献
1000.
Mandipogula Mahesh Veladi Panduranga Girish Prabhu Roopesh Kumar L P. Venkata Ramana 《合成通讯》2017,47(7):716-721
A simple protocol involving metal-free oxidative amidation of benzyl alcohols with amino acid esters has been presented. The amidation proceeds in a radical pathway unlike in conventional metal-mediated extrusion of dihydrogen. The method is advantageous in terms of metal-free conditions, nonexpensive commercial starting substrates. Also various substituents in the starting materials are tolerated and sterically hindered amino acid side chains could provide good yields of amide products. 相似文献