全文获取类型
收费全文 | 42963篇 |
免费 | 1213篇 |
国内免费 | 24篇 |
专业分类
化学 | 24634篇 |
晶体学 | 185篇 |
力学 | 859篇 |
数学 | 6809篇 |
物理学 | 11713篇 |
出版年
2023年 | 220篇 |
2021年 | 318篇 |
2020年 | 529篇 |
2019年 | 369篇 |
2018年 | 479篇 |
2017年 | 444篇 |
2016年 | 1074篇 |
2015年 | 933篇 |
2014年 | 1024篇 |
2013年 | 2258篇 |
2012年 | 1797篇 |
2011年 | 2179篇 |
2010年 | 1161篇 |
2009年 | 949篇 |
2008年 | 2078篇 |
2007年 | 2029篇 |
2006年 | 1815篇 |
2005年 | 1640篇 |
2004年 | 1287篇 |
2003年 | 1106篇 |
2002年 | 1036篇 |
2001年 | 836篇 |
2000年 | 785篇 |
1999年 | 551篇 |
1998年 | 489篇 |
1997年 | 506篇 |
1996年 | 592篇 |
1995年 | 546篇 |
1994年 | 558篇 |
1993年 | 662篇 |
1992年 | 543篇 |
1991年 | 401篇 |
1990年 | 441篇 |
1989年 | 369篇 |
1988年 | 378篇 |
1987年 | 393篇 |
1986年 | 350篇 |
1985年 | 552篇 |
1984年 | 511篇 |
1983年 | 477篇 |
1982年 | 507篇 |
1981年 | 480篇 |
1980年 | 461篇 |
1979年 | 408篇 |
1978年 | 462篇 |
1977年 | 446篇 |
1976年 | 387篇 |
1975年 | 350篇 |
1974年 | 339篇 |
1973年 | 353篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
Iodine(III)‐Catalyzed Rearrangements of Imides: A Versatile Route to α,α‐Dialkylated α‐Hydroxy Carboxylamides 下载免费PDF全文
Anna Ulmer Dr. Maciej Stodulski Stefanie V. Kohlhepp Christoph Patzelt Dr. Alexander Pöthig Dr. Wolfgang Bettray Dr. Tanja Gulder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(4):1444-1448
A tertiary hydroxy group α to a carboxyl moiety comprises a key structural motif in many bioactive substances. With the herein presented metal‐free rearrangement of imides triggered by hypervalent λ3‐iodane, an easy and selective way to gain access to such a compound class, namely α,α‐disubstituted‐α‐hydroxy carboxylamides, was established. Their additional methylene bromide side chain constitutes a useful handle for rapid diversification, as demonstrated by a series of further functionalizations. Moreover, the in situ formation of an iodine(III) species under the reaction conditions was proven. Our findings clearly corroborate that hypervalent λ3‐benziodoxolones are involved in these organocatalytic reactions. 相似文献
3.
Unexpected benzimidazole ring formation from a quinoneimide species in the presence of ammonium acetate as supporting electrolyte used in the coupling of electrochemistry with mass spectrometry 下载免费PDF全文
4.
5.
Timm Bergholz Dr. Benjamin Oelkers Dr. Benedikt Huber Prof. Bernhard Roling Prof. Dr. Jörg Sundermeyer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2613-2620
New salts based on imidazolium, pyrrolidinium, phosphonium, guanidinium, and ammonium cations together with the 5‐cyanotetrazolide anion [C2N5]? are reported. Depending on the nature of cation–anion interactions, characterized by XRD, the ionic liquids (ILs) have a low viscosity and are liquid at room temperature or have higher melting temperatures. Thermogravimetric analysis, cyclic voltammetry, viscosimetry, and impedance spectroscopy display a thermal stability up to 230 °C, an electrochemical window of 4.5 V, a viscosity of 25 mPa s at 20 °C, and an ionic conductivity of 5.4 mS cm?1 at 20 °C for the IL 1‐butyl‐1‐methylpyrrolidinium 5‐cyanotetrazolide [BMPyr][C2N5]. On the basis of these results, the synthesized compounds are promising electrolytes for lithium‐ion batteries. 相似文献
6.
Mechanistic Aspects of a Highly Active Dinuclear Zinc Catalyst for the Co‐polymerization of Epoxides and CO2 下载免费PDF全文
Stefan Kissling Peter T. Altenbuchner Dr. Maximilian W. Lehenmeier Dr. Eberhardt Herdtweck Dr. Peter Deglmann Dr. Uwe B. Seemann Prof. Dr. Bernhard Rieger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8148-8157
The dinuclear zinc complex reported by us is to date the most active zinc catalyst for the co‐polymerization of cyclohexene oxide (CHO) and carbon dioxide. However, co‐polymerization experiments with propylene oxide (PO) and CO2 revealed surprisingly low conversions. Within this work, we focused on clarification of this behavior through experimental results and quantum chemical studies. The combination of both results indicated the formation of an energetically highly stable intermediate in the presence of propylene oxide and carbon dioxide. A similar species in the case of cyclohexene oxide/CO2 co‐polymerization was not stable enough to deactivate the catalyst due to steric repulsion. 相似文献
7.
8.
9.
10.
Saleh Z. M. Nasser H. Özkol E. Günöven M. Abak K. Canli S. Bek A. Turan R. 《Journal of nanoparticle research》2015,17(10):1-12
Journal of Nanoparticle Research - Plasmonic interfaces consisting of silver nanoparticles of different sizes (50–100&;nbsp;nm) have been processed by the self-assembled dewetting... 相似文献