全文获取类型
收费全文 | 3324篇 |
免费 | 932篇 |
国内免费 | 176篇 |
专业分类
化学 | 3976篇 |
晶体学 | 22篇 |
力学 | 46篇 |
综合类 | 15篇 |
数学 | 89篇 |
物理学 | 284篇 |
出版年
2024年 | 6篇 |
2023年 | 85篇 |
2022年 | 127篇 |
2021年 | 132篇 |
2020年 | 242篇 |
2019年 | 145篇 |
2018年 | 141篇 |
2017年 | 84篇 |
2016年 | 326篇 |
2015年 | 317篇 |
2014年 | 343篇 |
2013年 | 429篇 |
2012年 | 365篇 |
2011年 | 234篇 |
2010年 | 139篇 |
2009年 | 147篇 |
2008年 | 141篇 |
2007年 | 171篇 |
2006年 | 146篇 |
2005年 | 136篇 |
2004年 | 132篇 |
2003年 | 115篇 |
2002年 | 34篇 |
2001年 | 55篇 |
2000年 | 35篇 |
1999年 | 27篇 |
1998年 | 14篇 |
1997年 | 25篇 |
1996年 | 40篇 |
1995年 | 17篇 |
1994年 | 14篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 14篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1957年 | 1篇 |
排序方式: 共有4432条查询结果,搜索用时 15 毫秒
991.
Visible‐Light‐Mediated Decarboxylation/Oxidative Amidation of α‐Keto Acids with Amines under Mild Reaction Conditions Using O2 下载免费PDF全文
Jie Liu Dr. Qiang Liu Hong Yi Chu Qin Ruopeng Bai Xiaotian Qi Prof. Yu Lan Prof. Aiwen Lei 《Angewandte Chemie (International ed. in English)》2014,53(2):502-506
Photochemistry has ushered in a new era in the development of chemistry, and photoredox catalysis has become a hot topic, especially over the last five years, with the combination of visible‐light photoredox catalysis and radical reactions. A novel, simple, and efficient radical oxidative decarboxylative coupling with the assistant of the photocatalyst [Ru(phen)3]Cl2 is described. Various functional groups are well‐tolerated in this reaction and thus provides a new approach to developing advanced methods for aerobic oxidative decarboxylation. The preliminary mechanistic studies revealed that: 1) an SET process between [Ru(phen)3]2+* and aniline play an important role; 2) O2 activation might be the rate‐determining step; and 3) the decarboxylation step is an irreversible and fast process. 相似文献
992.
993.
One‐Pot Synthesis of N‐Acetyl‐ and N‐Glycolylneuraminic Acid Capped Trisaccharides and Evaluation of Their Influenza A(H1 N1) Inhibition 下载免费PDF全文
Dr. Yun Hsu Hsiu‐Hwa Ma Larry S. Lico Dr. Jia‐Tsrong Jan Prof. Dr. Koichi Fukase Dr. Yosuke Uchinashi Dr. Medel Manuel L. Zulueta Prof. Dr. Shang‐Cheng Hung 《Angewandte Chemie (International ed. in English)》2014,53(9):2413-2416
Human lung epithelial cells natively offer terminal N‐acetylneuraminic acid (Neu5Ac) α(2→6)‐linked to galactose (Gal) as binding sites for influenza virus hemagglutinin. N‐Glycolylneuraminic acid (Neu5Gc) in place of Neu5Ac is known to affect hemagglutinin binding in other species. Not normally generated by humans, Neu5Gc may find its way to human cells from dietary sources. To compare their influence in influenza virus infection, six trisaccharides with Neu5Ac or Neu5Gc α(2→6) linked to Gal and with different reducing end sugar units were prepared using one‐pot assembly and divergent transformation. The sugar assembly made use of an N‐phthaloyl‐protected sialyl imidate for chemoselective activation and α‐stereoselective coupling with a thiogalactoside. Assessment of cytopathic effect showed that the Neu5Gc‐capped trisaccharides inhibited the viral infection better than their Neu5Ac counterparts. 相似文献
994.
Ureidopeptide‐Based Brønsted Bases: Design,Synthesis and Application to the Catalytic Enantioselective Synthesis of β‐Amino Nitriles from (Arylsulfonyl)acetonitriles 下载免费PDF全文
Dr. Saioa Diosdado Dr. Rosa López Prof. Dr. Claudio Palomo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(21):6526-6531
The addition of cyanoalkyl moieties to imines is a very attractive method for the preparation of β‐amino nitriles. We present a highly efficient organocatalytic methodology for the stereoselective synthesis of β‐amino nitriles, in which the key to success is the use of ureidopeptide‐based Brønsted base catalysts in combination with (arylsulfonyl)acetonitriles as synthetic equivalents of the acetonitrile anion. The method gives access to a variety of β‐amino nitriles with good yields and excellent enantioselectivities, and broadens the stereoselective Mannich‐type methodologies available for their synthesis. 相似文献
995.
Palladium‐Catalyzed/Norbornene‐Mediated CH Activation/ N‐Tosylhydrazone Insertion Reaction: A Route to Highly Functionalized Vinylarenes 下载免费PDF全文
Dr. Ping‐Xin Zhou Lan Zheng Jun‐Wei Ma Yu‐Ying Ye Xue‐Yuan Liu Prof. Dr. Peng‐Fei Xu Prof. Dr. Yong‐Min Liang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(22):6745-6751
A straightforward method for the synthesis of highly functionalized vinylarenes through palladium‐catalyzed, norbornene‐mediated C?H activation/carbene migratory insertion is described. Extension to a one‐pot procedure is also developed. Furthermore, this method can also be used to generate polysubstituted bicyclic molecules. The reaction proceeds under mild conditions to give the products in satisfactory yields using readily available starting materials. This is a Catellani–Lautens reaction that incorporates different types of coupling partners. Additionally, this reaction is the first to demonstrate the possibility of combining Pd‐catalyzed insertion of diazo compounds and Pd‐catalyzed C?H activation. 相似文献
996.
Direct Synthesis of Benzofuro[2,3‐b]pyrroles through a Radical Addition/[3,3]‐Sigmatropic Rearrangement/Cyclization/Lactamization Cascade 下载免费PDF全文
Dr. Masafumi Ueda Yuta Ito Yuki Ichii Maiko Kakiuchi Hiroko Shono Prof. Dr. Okiko Miyata 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(22):6763-6770
A straightforward synthetic method for the construction of benzofuro[2,3‐b]pyrrol‐2‐ones by a novel domino reaction through a radical addition/[3,3]‐sigmatropic rearrangement/cyclization/lactamization cascade has been developed. The domino reaction of O‐phenyl‐conjugated oxime ether with an alkyl radical allows the construction of two heterocycles with three stereogenic centers as a result of the formation of two C?C bonds, a C?O bond, and a C?N bond in a single operation, leading to pyrrolidine‐fused dihydrobenzofurans, which are not easily accessible by existing synthetic methods. Furthermore, asymmetric synthesis of benzofuro[2,3‐b]pyrrol‐2‐one derivatives through a diastereoselective radical addition reaction to a chiral oxime ether was also developed. 相似文献
997.
Emil Lindbäck Sami Dawaigher Kenneth Wärnmark 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(42):13432-13481
Substrate selectivity is an important output function for the validation of different enzyme models, catalytic cavity compounds, and reaction mechanisms as demonstrated in this review. In contrast to stereo‐, regio‐, and chemoselective catalysis, the field of substrate‐selective catalysis is under‐researched and has to date generated only a few, but important, industrial applications. This review points out the broad spectrum of different reaction types that have been investigated in substrate‐selective catalysis. The present review is the first one covering substrate‐selective catalysis and deals with reactions in which the substrates involved have the same reacting functionality and the catalysts is used in catalytic or in stoichiometric amounts. The review covers real substrate‐selective catalysis, thus only including cases in which substrate‐selective catalysis has been observed in competition between substrates. 相似文献
998.
Recent Advances in Trifluoromethylation Reactions with Electrophilic Trifluoromethylating Reagents 下载免费PDF全文
Dr. Sebastián Barata‐Vallejo Prof.Dr. Beatriz Lantaño Prof. Dr. Al Postigo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(51):16806-16829
Electrophilic trifluoromethylation reactions have been the latest approach to achieve the fluoroalkylation of compounds with newly‐discovered reagents, such as the Togni’s (1‐trifluoromethyl‐1,2‐benziodoxol‐3‐(1 H)‐one), Umemoto’s (S‐(trifluoromethyl)dibenzothiophenium tetrafluoroborate), Yagupolskii’s (S‐(trifluoromethyldiarylsulfonium salts), Shreeve’s (S‐(trifluoromethyl)dibenzothiophenium triflate), and Shibata’s (trifluoromethylsulfoximine salts) reagents. All these reagents produce an electrophilic trifluoromethylating (CF3+) species that undergoes reaction with nucleophiles. In addition, these latter reactive species (i.e. CF3+) can undergo electron‐transfer (ET) processes affording CF3 ? radicals that expand the scope to substrates other than conventional nucleophiles that can undergo reaction. In this Review, we shall discuss the trifluoromethylation reactions of diverse families of organic substrates of biological interest as a means to comparing the reagents scope and best reaction conditions. Some, though not all, of these reactions require the assistance of metal or organometallic catalysts. Some require additives and catalysts to promote the fluoroalkylation reaction, but invariably all are initiated and carried out by electrophilic trifluoromethylating species. 相似文献
999.
Chemical Preparation of Graphene Materials Results in Extensive Unintentional Doping with Heteroatoms and Metals 下载免费PDF全文
Dr. Chun Kiang Chua Dr. Adriano Ambrosi Prof. Zdeněk Sofer Dr. Anna Macková Dr. Vladimír Havránek Dr. Ivo Tomandl Prof. Martin Pumera 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(48):15760-15767
Chemical synthesis of graphene relies on the usage of various chemical reagents. The initial synthesis step, in which graphite is oxidized to graphite oxide, is achieved by a combination of chemical oxidants and acids. A subsequent chemical reduction step eliminates/reduces most oxygen functionalities to yield graphene. We demonstrate here that these chemical treatments significantly contaminate graphene with heteroatoms/metals, depending on the procedures followed. Contaminations with heteroatoms (N, B, Cl, S) or metals (Mn, Al) were present at relatively high concentrations (up to 3 at %), with their chemical states dependent on the procedures. Such unintentional contaminations (unwanted doping) during chemical synthesis are rarely anticipated and reported, although the heteroatoms/metals may alter the electronic and catalytic properties of graphene. In fact, the levels of unintentionally introduced contaminants on graphene are often higher than typical levels found on intentionally doped graphene. Our findings are important for scientists applying chemical methods to prepare graphene. 相似文献
1000.
Gold‐Catalyzed C(sp3)H/C(sp)H Coupling/Cyclization/Oxidative Alkynylation Sequence: A Powerful Strategy for the Synthesis of 3‐Alkynyl Polysubstituted Furans 下载免费PDF全文
Yuanhong Ma Shuai Zhang Shiping Yang Dr. Feijie Song Prof. Dr. Jingsong You 《Angewandte Chemie (International ed. in English)》2014,53(30):7870-7874
In sharp contrast to the gold‐catalyzed reactions of alkynes/allenes with nucleophiles, gold‐catalyzed oxidative cross‐couplings and especially C? H/C? H cross‐coupling have been under represented. By taking advantage of the unique redox property and carbophilic π acidity of gold, this work realizes the first gold‐catalyzed direct C(sp3)? H alkynylation of 1,3‐dicarbonyl compounds with terminal alkynes under mild reaction conditions, with subsequent cyclization and in situ oxidative alkynylation. A variety of terminal alkynes including aryl, heteroaryl, alkenyl, alkynyl, alkyl, and cyclopropyl alkynes all successfully participate in the domino reaction. The protocol offers a simple and region‐defined approach to 3‐alkynyl polysubstituted furans. 相似文献