全文获取类型
收费全文 | 2266篇 |
免费 | 59篇 |
国内免费 | 4篇 |
专业分类
化学 | 1717篇 |
晶体学 | 4篇 |
力学 | 18篇 |
数学 | 346篇 |
物理学 | 244篇 |
出版年
2023年 | 29篇 |
2022年 | 19篇 |
2021年 | 23篇 |
2020年 | 61篇 |
2019年 | 50篇 |
2018年 | 28篇 |
2017年 | 17篇 |
2016年 | 41篇 |
2015年 | 28篇 |
2014年 | 41篇 |
2013年 | 71篇 |
2012年 | 72篇 |
2011年 | 99篇 |
2010年 | 41篇 |
2009年 | 45篇 |
2008年 | 73篇 |
2007年 | 64篇 |
2006年 | 72篇 |
2005年 | 71篇 |
2004年 | 56篇 |
2003年 | 46篇 |
2002年 | 39篇 |
2001年 | 20篇 |
2000年 | 23篇 |
1999年 | 18篇 |
1998年 | 18篇 |
1995年 | 22篇 |
1994年 | 21篇 |
1991年 | 22篇 |
1990年 | 15篇 |
1987年 | 17篇 |
1986年 | 19篇 |
1985年 | 27篇 |
1984年 | 29篇 |
1983年 | 27篇 |
1982年 | 39篇 |
1981年 | 24篇 |
1980年 | 28篇 |
1979年 | 43篇 |
1978年 | 27篇 |
1977年 | 36篇 |
1976年 | 30篇 |
1975年 | 28篇 |
1974年 | 23篇 |
1973年 | 22篇 |
1970年 | 15篇 |
1967年 | 19篇 |
1965年 | 16篇 |
1956年 | 20篇 |
1934年 | 23篇 |
排序方式: 共有2329条查询结果,搜索用时 15 毫秒
991.
Ab initio investigation of the stability of Si3C3 clusters and their structural and bonding features
Max Mühlhäuser Georgios Froudakis Aristides Zdetsis Bernd Engels Nikos Flytzanis Sigrid D. Peyerimhoff 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1994,32(1):113-123
Various structural possibilities for Si3C3 clusters are investigated by ab initio calculations employing basis sets of double- and triple-zeta quality augmented by d polarization functions. Correlation effects are included by a second-order Moeller Plesset perturbation treatment. For the two lowest-lying structures higher-order correlation corrections and multi-reference effects are also included. Bonding features are investigated by two different types of population analyses to obtain insight into the nature of chemical bonding. A total of 17 stationary points were investigated, 14 of which correspond to local minima and three being transition states. The energetically lowest-lying structures are: A “pyramidlike” structure with various multicenter bonds, followed by a Cs symmetric isomer closely related to the ground state Si6 structure. Planar structures, favoured in small carbon clusters, lie higher in energy and are transition states. The lowest-lying triplet system is found to be the linear nonsymmetric Si-C-C-C-Si-Si structure, which is calculated to lie about 38 kcal/mole above the singlet ground state. A building-up principle based on bonding criteria is suggested for the occurence of the various structural possibilities. 相似文献
992.
A high resolution infra-red PbSe diode laser spectrometer has been developed for application in air pollution monitoring and mineral prospecting. This instrument possesses three cells for measurement and calibration. Correlation techniques have been applied to increase the sensitivity. SO2 concentrations of around 5 ppm have been monitored at 7.3m with the diode operating at 77 K. 相似文献
993.
994.
995.
M. Sc. Esther von Grotthuss Dr. Martin Diefenbach Dr. Michael Bolte Dr. Hans‐Wolfram Lerner Prof. Dr. Max C. Holthausen Prof. Dr. Matthias Wagner 《Angewandte Chemie (International ed. in English)》2016,55(45):14067-14071
A new approach to main‐group H2 activation combining concepts of transition‐metal and frustrated Lewis pair chemistry is reported. Ambiphilic, metal‐like reactivity toward H2 can be conferred to 9,10‐dihydro‐9,10‐diboraanthracene (DBA) acceptors by the injection of two electrons. The resulting [DBA]2? ions cleave the H?H bond with the formation of hydridoborates under moderate conditions (T=50–100 °C; p<1 atm). Depending on the boron‐bonded substituents R, the addition is either reversible (R=C≡CtBu) or irreversible (R=H). The reaction rate is strongly influenced by the nature and the coordination behavior of the countercation (Li+ slower than K+). Quantum‐chemical calculations support the experimental observations and suggest a concerted, homolytic addition of H2 across both boron atoms. As proven by the successful conversion of Me3SiCl into Me3SiH, the system Li2[DBA]/H2 appears generally relevant for the hydrogenation of element–halide bonds. 相似文献
996.
Julia I. Schweizer Dr. Markus G. Scheibel Dr. Martin Diefenbach Felix Neumeyer Dr. Christian Würtele Dr. Natalia Kulminskaya Dr. Rasmus Linser Prof. Dr. Norbert Auner Prof. Dr. Sven Schneider Prof. Dr. Max C. Holthausen 《Angewandte Chemie (International ed. in English)》2016,55(5):1782-1786
An experimental and theoretical study of the base‐stabilized disilene 1 is reported, which forms at low temperatures in the disproportionation reaction of Si2Cl6 or neo‐Si5Cl12 with equimolar amounts of NMe2Et. Single‐crystal X‐ray diffraction and quantum‐chemical bonding analysis disclose an unprecedented structure in silicon chemistry featuring a dative Si→Si single bond between two silylene moieties, Me2EtN→SiCl2→Si(SiCl3)2. The central ambiphilic SiCl2 group is linked by dative bonds to the amine donor and the bis(trichlorosilyl)silylene acceptor, which leads to push–pull stabilization. Based on experimental and theoretical examinations a formation mechanism is presented that involves an autocatalytic reaction of the intermediately formed anion Si(SiCl3)3? with neo‐Si5Cl12 to yield 1 . 相似文献
997.
Isabel V. L. Wilkinson Max Bottlinger Yassmine El Harraoui Stephan A. Sieber 《Angewandte Chemie (International ed. in English)》2023,62(9):e202212111
Heme is a cofactor with myriad roles and essential to almost all living organisms. Beyond classical gas transport and catalytic functions, heme is increasingly appreciated as a tightly controlled signalling molecule regulating protein expression. However, heme acquisition, biosynthesis and regulation is poorly understood beyond a few model organisms, and the heme-binding proteome has not been fully characterised in bacteria. Yet as heme homeostasis is critical for bacterial survival, heme-binding proteins are promising drug targets. Herein we report a chemical proteomics method for global profiling of heme-binding proteins in live cells for the first time. Employing a panel of heme-based clickable and photoaffinity probes enabled the profiling of 32–54 % of the known heme-binding proteomes in Gram-positive and Gram-negative bacteria. This simple-to-implement profiling strategy could be interchangeably applied to different cell types and systems and fuel future research into heme biology. 相似文献
998.
Ulrike Wirth Julia Erl Saphia Azzam Dr. Carina Höring Dr. Michael Skiba Ritu Singh Kathrin Hochmuth PD Dr. Max Keller Prof. Dr. Joachim Wegener Prof. Dr. Burkhard König 《Angewandte Chemie (International ed. in English)》2023,62(21):e202215547
G protein-coupled cell surface receptors (GPCR) trigger complex intracellular signaling cascades upon agonist binding. Classic pharmacological assays provide information about binding affinities, activation or blockade at different stages of the signaling cascade, but real time dynamics and reversibility of these processes remain often disguised. We show that combining photochromic NPY receptor ligands, which can be toggled in their receptor activation ability by irradiation with light of different wavelengths, with whole cell label-free impedance assays allows observing the cell response to receptor activation and its reversibility over time. The concept demonstrated on NPY receptors may be well applicable to many other GPCRs providing a deeper insight into the time course of intracellular signaling processes. 相似文献
999.