全文获取类型
收费全文 | 3260篇 |
免费 | 939篇 |
国内免费 | 480篇 |
专业分类
化学 | 2606篇 |
晶体学 | 8篇 |
力学 | 200篇 |
综合类 | 26篇 |
数学 | 229篇 |
物理学 | 1610篇 |
出版年
2023年 | 26篇 |
2022年 | 74篇 |
2021年 | 77篇 |
2020年 | 98篇 |
2019年 | 124篇 |
2018年 | 109篇 |
2017年 | 148篇 |
2016年 | 147篇 |
2015年 | 281篇 |
2014年 | 269篇 |
2013年 | 404篇 |
2012年 | 329篇 |
2011年 | 321篇 |
2010年 | 266篇 |
2009年 | 280篇 |
2008年 | 276篇 |
2007年 | 196篇 |
2006年 | 190篇 |
2005年 | 157篇 |
2004年 | 142篇 |
2003年 | 142篇 |
2002年 | 95篇 |
2001年 | 85篇 |
2000年 | 75篇 |
1999年 | 57篇 |
1998年 | 67篇 |
1997年 | 46篇 |
1996年 | 41篇 |
1995年 | 35篇 |
1994年 | 32篇 |
1993年 | 24篇 |
1992年 | 12篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有4679条查询结果,搜索用时 15 毫秒
61.
A Convenient Palladium‐Catalyzed Carbonylative Suzuki Coupling of Aryl Halides with Formic Acid as the Carbon Monoxide Source 下载免费PDF全文
Dr. Xinxin Qi Li‐Bing Jiang Hao‐Peng Li Prof. Dr. Xiao‐Feng Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(49):17650-17656
A practical palladium‐catalyzed carbonylative Suzuki coupling of aryl halides under carbon monoxide gas‐free conditions has been developed. Here, formic acid was utilized as the carbon monoxide source for the first time with acetic anhydride as the additive. A variety of diarylketones were produced in moderate to excellent yields from the corresponding aryl halides and arylboronic acids. 相似文献
62.
63.
Rapid and Efficient Copper‐Catalyzed Finkelstein Reaction of (Hetero)Aromatics under Continuous‐Flow Conditions 下载免费PDF全文
Dr. Mao Chen Saki Ichikawa Prof. Dr. Stephen L. Buchwald 《Angewandte Chemie (International ed. in English)》2015,54(1):263-266
A general, rapid, and efficient method for the copper‐catalyzed Finkelstein reaction of (hetero)aromatics has been developed using continuous flow to generate a variety of aryl iodides. The described method can tolerate a broad spectrum of functional groups, including N‐H and O‐H groups. Additionally, in lieu of isolation, the aryl iodide solutions were used in two distinct multistep continuous‐flow processes (amidation and Mg–I exchange/nucleophilic addition) to demonstrate the flexibility of this method. 相似文献
64.
Z‐Selective Cross Metathesis with Ruthenium Catalysts: Synthetic Applications and Mechanistic Implications 下载免费PDF全文
Dr. Myles B. Herbert Prof. Dr. Robert H. Grubbs 《Angewandte Chemie (International ed. in English)》2015,54(17):5018-5024
Olefin cross metathesis is a particularly powerful transformation that has been exploited extensively for the formation of complex products. Until recently, however, constructing Z‐olefins using this methodology was not possible. With the discovery and development of three families of ruthenium‐based Z‐selective catalysts, the formation of Z‐olefins using metathesis is now not only possible but becoming increasingly prevalent in the literature. In particular, ruthenium complexes containing cyclometalated NHC architectures developed in our group have been shown to catalyze various cross metathesis reactions with high activity and, in most cases, near perfect selectivity for the Z‐isomer. The types of cross metathesis reactions investigated thus far are presented here and explored in depth. 相似文献
65.
Direct C(sp2)C(sp3) Cross‐Coupling of Diaryl Zinc Reagents with Benzylic,Primary, Secondary,and Tertiary Alkyl Halides 下载免费PDF全文
Dr. Jay J. Dunsford Dr. Ewan R. Clark Dr. Michael J. Ingleson 《Angewandte Chemie (International ed. in English)》2015,54(19):5688-5692
The direct C(sp2)? C(sp3) cross‐coupling of diaryl zinc reagents with benzylic, primary, secondary, and tertiary alkyl halides proceeded in the absence of coordinating ethereal solvents at ambient temperature without the addition of a catalyst. The C(sp2)? C(sp3) cross‐coupling showed excellent functional‐group tolerance, and products were isolated in high yields, generally without the requirement for purification by chromatography. This process represents an expedient, operationally simple method for the construction of new C(sp2)? C(sp3) bonds. 相似文献
66.
A Simple,High‐Yield Synthesis of DNA Duplexes Containing a Covalent,Thermally Cleavable Interstrand Cross‐Link at a Defined Location 下载免费PDF全文
Jacqueline Gamboa Varela Prof. Kent S. Gates 《Angewandte Chemie (International ed. in English)》2015,54(26):7666-7669
Interstrand DNA–DNA cross‐links are highly toxic to cells because these lesions block the extraction of information from the genetic material. The pathways by which cells repair cross‐links are important, but not well understood. The preparation of chemically well‐defined cross‐linked DNA substrates represents a significant challenge in the study of cross‐link repair. Here a simple method is reported that employs “post‐synthetic” modifications of commercially available 2′‐deoxyoligonucleotides to install a single cross‐link in high yield at a specified location within a DNA duplex. The cross‐linking process exploits the formation of a hydrazone between a non‐natural N4‐amino‐2′‐deoxycytidine nucleobase and the aldehyde residue of an abasic site in duplex DNA. The resulting cross‐link is stable under physiological conditions, but can be readily dissociated and re‐formed through heating–cooling cycles. 相似文献
67.
Nickel‐Catalyzed Dehydrogenative Cross‐Coupling: Direct Transformation of Aldehydes into Esters and Amides 下载免费PDF全文
Dr. Aaron M. Whittaker Prof.Dr. Vy M. Dong 《Angewandte Chemie (International ed. in English)》2015,54(4):1312-1315
By exploring a new mode of nickel‐catalyzed cross‐coupling, a method to directly transform both aromatic and aliphatic aldehydes into either esters or amides has been developed. The success of this oxidative coupling depends on the appropriate choice of catalyst and organic oxidant, including the use of either α,α,α‐trifluoroacetophenone or excess aldehyde. Mechanistic data that supports a catalytic cycle involving oxidative addition into the aldehyde C? H bond is also presented. 相似文献
68.
Rhodium(I)‐Catalyzed Regiospecific Dimerization of Aromatic Acids: Two Direct CH Bond Activations in Water 下载免费PDF全文
Dr. Hang Gong Dr. Huiying Zeng Dr. Feng Zhou Prof. Dr. Chao‐Jun Li 《Angewandte Chemie (International ed. in English)》2015,54(19):5718-5721
2,2′‐Diaryl acids are key building blocks for some of the most important and high‐performance polymers such as polyesters and polyamides (imides), as well as structural motifs of MOFs (metal–organic frameworks) and biological compounds. In this study, a direct, regiospecific and practical dimerization of simple aromatic acids to generate 2,2′‐diaryl acids has been discovered, which proceeds through two rhodium‐catalyzed C? H activations in water. This reaction can be easily scaled up to gram level by using only 0.4–0.6 mol % of the rhodium catalyst. As a proof‐of‐concept, the natural product ellagic acid was synthesized in two steps by this method. 相似文献
69.
Rebecca A. Green Prof. John F. Hartwig 《Angewandte Chemie (International ed. in English)》2015,54(12):3768-3772
The nickel‐catalyzed amination of aryl chlorides to form primary arylamines occurs with ammonia or ammonium sulfate and a well‐defined single‐component nickel(0) precatalyst containing a Josiphos ligand and an η2‐bound benzonitrile ligand. This system also catalyzes the coupling of aryl chlorides with gaseous amines in the form of their hydrochloride salts. 相似文献
70.
Tandem Chemoselective Suzuki–Miyaura Cross‐Coupling Enabled by Nucleophile Speciation Control 下载免费PDF全文
Ciaran P. Seath James W. B. Fyfe John J. Molloy Dr. Allan J. B. Watson 《Angewandte Chemie (International ed. in English)》2015,54(34):9976-9979
Control of boronic acid speciation is presented as a strategy to achieve nucleophile chemoselectivity in the Suzuki–Miyaura reaction. Combined with simultaneous control of oxidative addition and transmetalation, this enables chemoselective formation of two C? C bonds in a single operation, providing a method for the rapid preparation of highly functionalized carbogenic frameworks. 相似文献