全文获取类型
收费全文 | 6720篇 |
免费 | 287篇 |
国内免费 | 14篇 |
专业分类
化学 | 3925篇 |
晶体学 | 23篇 |
力学 | 138篇 |
数学 | 849篇 |
物理学 | 2086篇 |
出版年
2023年 | 46篇 |
2021年 | 69篇 |
2020年 | 107篇 |
2019年 | 104篇 |
2018年 | 80篇 |
2017年 | 83篇 |
2016年 | 203篇 |
2015年 | 178篇 |
2014年 | 177篇 |
2013年 | 306篇 |
2012年 | 342篇 |
2011年 | 389篇 |
2010年 | 219篇 |
2009年 | 172篇 |
2008年 | 326篇 |
2007年 | 314篇 |
2006年 | 271篇 |
2005年 | 311篇 |
2004年 | 218篇 |
2003年 | 183篇 |
2002年 | 143篇 |
2001年 | 99篇 |
2000年 | 86篇 |
1999年 | 77篇 |
1998年 | 64篇 |
1997年 | 98篇 |
1996年 | 94篇 |
1995年 | 101篇 |
1994年 | 87篇 |
1993年 | 88篇 |
1992年 | 91篇 |
1991年 | 63篇 |
1990年 | 60篇 |
1989年 | 50篇 |
1988年 | 51篇 |
1987年 | 58篇 |
1986年 | 55篇 |
1985年 | 57篇 |
1984年 | 71篇 |
1983年 | 55篇 |
1982年 | 64篇 |
1981年 | 59篇 |
1980年 | 45篇 |
1979年 | 55篇 |
1978年 | 54篇 |
1977年 | 52篇 |
1976年 | 52篇 |
1975年 | 56篇 |
1973年 | 45篇 |
1956年 | 45篇 |
排序方式: 共有7021条查询结果,搜索用时 234 毫秒
1.
Mathematical Programming - We study the computation and efficiency of pure Nash equilibria in combinatorial congestion games, where the strategies of each player i are given by the binary vectors... 相似文献
2.
Oxidative dehydrogenation (ODH) of n-octane was carried out over a vanadium–magnesium oxide catalyst in a continuous flow fixed bed reactor. The catalyst was characterized by ICP–OES, powder XRD and SEM. The catalytic tests were carried out at different gas hourly space velocities (GHSVs), viz. 4000, 6000, 8000, and 10,000 h?1. The best selectivity for octenes was obtained at the GHSV of 8000 h?1, while that for C8 aromatics was attained at the GHSV of 6000 h?1 at high temperatures (500 and 550 °C). The catalytic testing at the GHSV of 10,000 h?1 showed the lowest activity, while that at the GHSV of 4000 h?1 consistently showed the lowest ODH selectivity. Generally, the best ODH performance was obtained by the catalytic testing at the GHSVs of 6000 and 8000 h?1. No phasic changes were observed after the catalytic testing. 相似文献
3.
Michael Meier Dr. Lei Ji Dr. Jörn Nitsch Dr. Ivo Krummenacher Andrea Deißenberger Dr. Dominic Auerhammer Dr. Marius Schäfer Prof. Dr. Todd B. Marder Prof. Dr. Holger Braunschweig 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(18):4707-4712
A novel thiophene-bridged donor–acceptor system was synthesized with a carbazole as donor and a borole as acceptor unit. The borole group was successfully installed via the tin–boron exchange reaction of 1,1-dimethyl-2,3,4,5-tetraphenylstannole with 9-(5-(dibromoboryl)thiophen-2-yl)carbazole. The effect of the borole on the optoelectronic properties of the donor–acceptor system was explored by spectroscopic (UV/Vis and fluorescence spectroscopy), electrochemical (cyclic voltammetry) and theoretical (TD-DFT) methods as well as by modifying its structure. The corresponding donor–acceptor compound bearing the widely employed dimesitylboryl acceptor group was also synthesized for comparison. 相似文献
4.
Designs, Codes and Cryptography - We study security functions which can serve to establish semantic security for the two central problems of information-theoretic security: the wiretap channel, and... 相似文献
5.
Lana K. Hiscock Brooke M. Raycraft Monika Wałęsa-Chorab Coralie Cambe Alexandre Malinge Prof. Dr. W. G. Skene Hi Taing Prof. Dr. S. Holger Eichhorn Prof. Dr. Louise N. Dawe Prof. Dr. Kenneth E. Maly 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(4):1018-1028
A series of new tetrakis(dialkoxyphenyl) dicyanotetraoxapentacene derivatives ( 1 a – c ) were prepared by reaction of the appropriate terphenyl diols with tetrafluoroterephthalonitrile in good yields. Compounds 1 b and 1 c , which bear hexyloxy and decyloxy side chains, exhibited columnar hexagonal mesophases, as shown by polarized optical microscopy, variable-temperature powder X-ray diffraction, and differential scanning calorimetry. Single-crystal X-ray diffraction of methoxy-substituted 1 a revealed that the dicyanotetraoxapentacene core is highly planar, consistent with the notion that these molecules are able to stack in columnar mesophases. A detailed photophysical characterization showed that these compounds exhibit aggregation-induced emission in solution, emission in nonpolar solvents, weak emission in polar solvents, and strong emission in the solid state both as powder and in thin films. These observations are consistent with a weakly emissive charge-transfer state in polar solvents and a more highly emissive locally excited state in nonpolar solvents. 相似文献
6.
We discuss the motion of substance in a channel containing nodes of a network. Each node of the channel can exchange substance with: (i) neighboring nodes of the channel, (ii) network nodes which do not belong to the channel, and (iii) environment of the network. The new point in this study is that we assume possibility for exchange of substance among flows of substance between nodes of the channel and: (i) nodes that belong to the network but do not belong to the channel and (ii) environment of the network. This leads to an extension of the model of motion of substance and the extended model contains previous models as particular cases. We use a discrete-time model of motion of substance and consider a stationary regime of motion of substance in a channel containing a finite number of nodes. As results of the study, we obtain a class of probability distributions connected to the amount of substance in nodes of the channel. We prove that the obtained class of distributions contains all truncated discrete probability distributions of discrete random variable which can take values . Theory for the case of a channel containing infinite number of nodes is presented in Appendix A. The continuous version of the discussed discrete probability distributions is described in Appendix B. The discussed extended model and obtained results can be used for the study of phenomena that can be modeled by flows in networks: motion of resources, traffic flows, motion of migrants, etc. 相似文献
7.
Back Cover: Activation of Elemental Sulfur at a Two‐Coordinate Platinum(0) Center (Chem. Eur. J. 36/2016) 下载免费PDF全文
8.
Solubility and Crystallizability: Facile Access to Functionalized π‐Conjugated Compounds with Chlorendylimide Protecting Groups 下载免费PDF全文
Dr. Jan Gebers Damien Rolland Dr. Roman Marty Dr. Stéphane Suàrez Luca Cervini Dr. Rosario Scopelliti Dr. Jan Cornelius Brauer Prof. Dr. Holger Frauenrath 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(4):1542-1553
Functional π‐conjugated molecules are relevant for the preparation of new organic electronic materials with improved performance. However, their synthesis is often rendered difficult by their inherently low solubility, and the permanent attachment of solubilizing groups may change the properties of the material. Here, we introduced the chlorendylimidyl moiety as a new temporary protecting group for the straightforward large‐scale synthesis of protected quarter‐, sexi‐, octathiophene, and perylene bisimide diamine and dicarboxylic acid derivatives. The obtained chlorendylimides and chlorendylimidyl active esters were highly soluble in organic solvents, and optical spectroscopy confirmed the low tendency of the compounds to aggregate in solution. At the same time, they could be conveniently purified by recrystallization or precipitation. Single‐crystal X‐ray structures obtained for most compounds showed supramolecular motifs highlighting the role of the rigid, polychlorinated chlorendyl moieties in their crystallization. The obtained protected diamine and dicarboxylic acid derivatives were easily deprotected and converted into various amide‐substituted oligothiophenes and perylene bisimides that are of interest as new functional materials for organic electronic thin film or nanowire devices. 相似文献
9.
Corrigendum: Labeling and Selective Inactivation of Gram‐Positive Bacteria Employing Bimodal Photoprobes with Dual Readouts 下载免费PDF全文
Dr. Anzhela Galstyan Dr. Desiree Block Dr. Silke Niemann Dr. Malte C. Grüner Prof.Dr. Stefania Abbruzzetti Michele Oneto Dr. Constantin G. Daniliuc Dr. Sven Hermann Prof.Dr. Cristiano Viappiani Prof.Dr. Michael Schäfers Prof.Dr. Bettina Löffler Priv.‐Doz.Dr. Cristian A. Strassert Dr. Andreas Faust 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(27):9051-9051
10.
Cover Picture: A new topological insulator built from quasi one‐dimensional atomic ribbons (Phys. Status Solidi RRL 2/2015) 下载免费PDF全文