全文获取类型
收费全文 | 2953篇 |
免费 | 142篇 |
专业分类
化学 | 1819篇 |
晶体学 | 21篇 |
力学 | 47篇 |
数学 | 603篇 |
物理学 | 605篇 |
出版年
2021年 | 40篇 |
2020年 | 60篇 |
2019年 | 43篇 |
2018年 | 50篇 |
2017年 | 63篇 |
2016年 | 154篇 |
2015年 | 136篇 |
2014年 | 121篇 |
2013年 | 234篇 |
2012年 | 155篇 |
2011年 | 200篇 |
2010年 | 128篇 |
2009年 | 97篇 |
2008年 | 101篇 |
2007年 | 73篇 |
2006年 | 66篇 |
2005年 | 32篇 |
2004年 | 41篇 |
2003年 | 31篇 |
2002年 | 28篇 |
2001年 | 24篇 |
2000年 | 31篇 |
1999年 | 28篇 |
1998年 | 27篇 |
1997年 | 24篇 |
1990年 | 25篇 |
1988年 | 22篇 |
1987年 | 22篇 |
1986年 | 22篇 |
1985年 | 30篇 |
1984年 | 30篇 |
1983年 | 26篇 |
1982年 | 28篇 |
1981年 | 22篇 |
1978年 | 25篇 |
1977年 | 22篇 |
1976年 | 23篇 |
1973年 | 22篇 |
1969年 | 22篇 |
1968年 | 40篇 |
1966年 | 23篇 |
1965年 | 42篇 |
1964年 | 45篇 |
1963年 | 27篇 |
1962年 | 38篇 |
1961年 | 36篇 |
1960年 | 32篇 |
1959年 | 29篇 |
1958年 | 23篇 |
1957年 | 25篇 |
排序方式: 共有3095条查询结果,搜索用时 15 毫秒
91.
Mesoporous molecular sieve SBA‐15 and conventional silica gel were grafted with 3‐[2‐(diethylamino)ethylamino]propyl groups and used as supports for the preparation of deposited palladium catalysts, which were subsequently evaluated in Stille cross‐coupling reaction of aryl bromides. The highest conversions were achieved with the metal‐saturated catalyst resulting from the modified SBA‐15. Influence of various reaction parameters (solvent, additive, temperature, etc.) on the overall yield and selectivity was studied. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
92.
Expanding the Scope of Hypervalent Iodine Reagents for Perfluoroalkylation: From Trifluoromethyl to Functionalized Perfluoroethyl
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Václav Matoušek Jiří Václavík Peter Hájek Julie Charpentier Zsófia E. Blastik Ewa Pietrasiak Alena Budinská Prof. Dr. Antonio Togni Dr. Petr Beier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(1):417-424
A series of new hypervalent iodine reagents based on the 1,3‐dihydro‐3,3‐dimethyl‐1,2‐benziodoxole and 1,2‐benziodoxol‐3‐(1H)‐one scaffolds, which contain a functionalized tetrafluoroethyl group, have been prepared, characterized, and used in synthetic applications. Their corresponding electrophilic fluoroalkylation reactions with various sulfur, oxygen, phosphorus, and carbon‐centered nucleophiles afford products that feature a tetrafluoroethylene unit, which connects two functional moieties. A related λ3‐iodane that contains a fluorophore was shown to react with a cysteine derivative under mild conditions to give a thiol‐tagged product that is stable in the presence of excess thiol. Therefore, these new reagents show a significant potential for applications in chemical biology as tools for fast, irreversible, and selective thiol bioconjugation. 相似文献
93.
94.
Sreekar Wunnava Christina F. Dirscherl Jakub Výravský Dr. Aleš Kovařík Dr. Roman Matyášek Prof. Jiří Šponer Prof. Dieter Braun Dr. Judit E. Šponer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(70):17581-17585
The assembly of ancient informational polymers from nucleotide precursors is the central challenge of life's origin on our planet. Among the possible solutions, dry polymerization of 3’,5’-cyclic guanosine monophosphate (3’,5’-cGMP) has been proposed as a candidate to create oligonucleotides of 15–20 units in length. However, the reported sensitivity of the reaction to the presence of cations raised questions of whether this chemistry could be relevant in a geological context. The experiments in this study show that the presence of cations is not restrictive as long as the reaction is conducted in an acidic environment, in contrast to previous reports that suggested optimal conditions at pH 9. 相似文献
95.
96.
Lenka Blažková Lenka Malinová Václava Benešová Jan Roda Jiří Brožek 《Journal of polymer science. Part A, Polymer chemistry》2017,55(13):2203-2210
A successful preparation of polyamide 4 nanofibers via electrostatic spinning with diameters close to 100 nm is described. Polyamide 4 was prepared by the anionic ring‐opening polymerization of 2‐pyrrolidone and characterized. The effect of the system parameters (i.e., molar mass of the polymer, the solvent system) and the process parameters (i.e., the electrode‐to‐collector distance) during the electrostatic spinning have been studied. The morphology of the polyamide 4 fiber layers is given except molar mass of the polymer and the concentration of its solution primarily by the conformation of polyamide chains due to polyelectrolyte effect which was confirmed by viscosity measurements. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2203–2210 相似文献
97.
We consider one-dimensional Schrödinger-type operators in a bounded interval with non-self-adjoint Robin-type boundary conditions. It is well known that such operators are generically conjugate to normal operators via a similarity transformation. Motivated by recent interests in quasi-Hermitian Hamiltonians in quantum mechanics, we study properties of the transformations and similar operators in detail. In the case of parity and time reversal boundary conditions, we establish closed integral-type formulae for the similarity transformations, derive a non-local self-adjoint operator similar to the Schrödinger operator and also find the associated “charge conjugation” operator, which plays the role of fundamental symmetry in a Krein-space reformulation of the problem. 相似文献
98.
Miroslav Jelínek Petr Písařík Tomáš Kocourek Josef Zemek Jaroslav Lukeš 《Applied Physics A: Materials Science & Processing》2013,110(4):943-947
A hybrid PLD system with ion bombardment of films was developed. Growing DLC films were modified during the laser deposition (10 J?cm?2) by argon ions with energy in the range from 40 eV to 210 eV and cathode current of 0.15 A and 0.5 A. The content of sp2 “graphitic” and sp3 “diamond” bonds was measured using XPS. Sp3 bonds changed from 60 % to 81 %. We found the highest sp3 content for energy of 40 eV. Hardness (and reduced Young’s modulus) were determined by nanoindentation and reached 49 GPa (277 GPa). Film adhesion was studied using the scratch test and was up to 14 N for titanium substrates. Relations among deposition conditions and measured properties are presented. 相似文献
99.
100.
Zbyněk Brůža Dr. Jiří Kratochvíl Prof. Jeremy N. Harvey Dr. Lubomír Rulíšek Dr. Lucie Nováková Jana Maříková Dr. Jiří Kuneš Prof. Pavel Kočovský Prof. Milan Pour 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(34):8053-8060
Pyran-2-ones 3 undergo a novel Pd0-catalyzed 1,3-rearrangement to afford isomers 6 . The reaction proceeds via an η2-Pd complex, the pyramidalization of which (confirmed by quantum chemistry calculations) offers a favorable antiperiplanar alignment of the Pd−C and allylic C−O bonds ( C ), thus allowing the formation of an η3-Pd intermediate. Subsequent rotation and rate-limiting recombination with the carboxylate arm then gives isomeric pyran-2-ones 6 . The calculated free energies reproduce the observed kinetics semi-quantitatively. 相似文献