全文获取类型
收费全文 | 740篇 |
免费 | 33篇 |
国内免费 | 1篇 |
专业分类
化学 | 561篇 |
晶体学 | 2篇 |
力学 | 27篇 |
数学 | 81篇 |
物理学 | 103篇 |
出版年
2023年 | 6篇 |
2022年 | 7篇 |
2021年 | 14篇 |
2020年 | 15篇 |
2019年 | 20篇 |
2018年 | 10篇 |
2017年 | 14篇 |
2016年 | 22篇 |
2015年 | 31篇 |
2014年 | 22篇 |
2013年 | 28篇 |
2012年 | 52篇 |
2011年 | 55篇 |
2010年 | 28篇 |
2009年 | 34篇 |
2008年 | 50篇 |
2007年 | 47篇 |
2006年 | 42篇 |
2005年 | 32篇 |
2004年 | 37篇 |
2003年 | 21篇 |
2002年 | 17篇 |
2001年 | 6篇 |
2000年 | 6篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 18篇 |
1995年 | 5篇 |
1994年 | 8篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1979年 | 3篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1937年 | 5篇 |
1932年 | 3篇 |
1885年 | 4篇 |
1865年 | 3篇 |
排序方式: 共有774条查询结果,搜索用时 31 毫秒
31.
Vladislav S. Krasnoukhov Prof. Dr. Valeriy N. Azyazov Prof. Dr. Alexander M. Mebel Dr. Srinivas Doddipatla Dr. Zhenghai Yang Shane Goettl Prof. Dr. Ralf I. Kaiser 《Chemphyschem》2021,22(14):1497-1504
The chemical dynamics of the elementary reaction of ground state atomic silicon (Si; 3P) with germane (GeH4; X1A1) were unraveled in the gas phase under single collision condition at a collision energy of 11.8±0.3 kJ mol−1 exploiting the crossed molecular beams technique contemplated with electronic structure calculations. The reaction follows indirect scattering dynamics and is initiated through an initial barrierless insertion of the silicon atom into one of the four chemically equivalent germanium-hydrogen bonds forming a triplet collision complex (HSiGeH3; 3 i1 ). This intermediate underwent facile intersystem crossing (ISC) to the singlet surface (HSiGeH3; 1 i1 ). The latter isomerized via at least three hydrogen atom migrations involving exotic, hydrogen bridged reaction intermediates eventually leading to the H3SiGeH isomer i5 . This intermediate could undergo unimolecular decomposition yielding the dibridged butterfly-structured isomer 1 p1 (Si(μ-H2)Ge) plus molecular hydrogen through a tight exit transition state. Alternatively, up to two subsequent hydrogen shifts to i6 and i7 , followed by fragmentation of each of these intermediates, could also form 1 p1 (Si(μ-H2)Ge) along with molecular hydrogen. The overall non-adiabatic reaction dynamics provide evidence on the existence of exotic dinuclear hydrides of main group XIV elements, whose carbon analog structures do not exist. 相似文献
32.
We compare the plasma and cavitation dynamics underlying pulsed laser microsurgery in water and in fruit fly embryos (in vivo)--specifically for nanosecond pulses at 355 and 532 nm. We find two key differences. First, the plasma-formation thresholds are lower in vivo--especially at 355 nm--due to the presence of endogenous chromophores that serve as additional sources for plasma seed electrons. Second, the biological matrix constrains the growth of laser-induced cavitation bubbles. Both effects reduce the disrupted region in vivo when compared to extrapolations from measurements in water. 相似文献
33.
Conformational Control of Oligo(p‐phenyleneethynylene)s with Intrinsic Substituent Electronic Effects: Origin of the Twist in Pentiptycene‐Containing Systems
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)
Che‐Jen Lin Dr. Sandip Kumar Kundu Dr. Cheng‐Kai Lin Prof. Jye‐Shane Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(45):14826-14833
Dependence of the backbone planarity of oligo(p‐phenyleneethynylene)s (OPEs) on the intrinsic electronic character of substituents and on the nature of the solvent has been experimentally demonstrated with a series of center‐symmetrical five‐ring systems, pentiptycene‐pentiptycene‐arene‐pentiptycene‐pentiptycene, differing in the substituents on the central arene. In frozen 2‐methyltetrahydrofuran (MTHF), the adjacent pentiptycene units prefer to be in a mutually twisted orientation when the substituents are electron‐withdrawing (F and amido), resulting in a TPPT or TTTT conformation, whereas a planarized PPPP backbone is favored in the case of electron‐donating substituents (alkyl and alkoxy). The propensity to adopt the PPPP form is generally enhanced by replacing MTHF with either methylcyclohexane or mixed ethanol/methanol as solvent. These observations reveal that the twist between adjacent pentiptycene units in OPEs is a consequence of the electronic rather than steric effects of iptycenyl substituents. The electronic effect of iptycenyl substituents is manifested in decreased phenylene π polarizability as the net effect of both electron‐donating hyperconjugation and an electron‐withdrawing inductive effect. Variable‐temperature electronic absorption and emission spectroscopies are the critical tools for this work. Our findings provide important guidelines for conformational and electronic engineering of OPEs and for the design of novel iptycene‐based organic electronic materials. 相似文献
34.
35.
Chongqing Wang Christopher Lambert Maurice Hauser Adrian Deuschmann Dr. Carsten Zeilinger Prof. Dr. Klemens Rottner Prof. Dr. Theresia E. B. Stradal Prof. Dr. Marc Stadler Dr. Elizabeth J. Skellam Prof. Dr. Russell J. Cox 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(60):13578-13583
Mutasynthesis of pyrichalasin H from Magnaporthe grisea NI980 yielded a series of unprecedented 4′-substituted cytochalasin analogues in titres as high as the wild-type system (≈60 mg L−1). Halogenated, O-alkyl, O-allyl and O-propargyl examples were formed, as well as a 4′-azido analogue. 4′-O-Propargyl and 4′-azido analogues reacted smoothly in Huisgen cycloaddition reactions, whereas p-Br and p-I compounds reacted in Pd-catalysed cross-coupling reactions. A series of examples of biotin-linked, dye-linked and dimeric cytochalasins was rapidly created. In vitro and in vivo bioassays of these compounds showed that the 4′-halogenated and azido derivatives retained their cytotoxicity and antifungal activities; but a unique 4′-amino analogue was inactive. Attachment of larger substituents attenuated the bioactivities. In vivo actin-binding studies with adherent mammalian cells showed that actin remains the likely intracellular target. Dye-linked compounds revealed visualisation of intracellular actin structures even in the absence of phalloidin, thus constituting a potential new class of actin-visualisation tools with filament-barbed end-binding specificity. 相似文献
36.
In the first part of this paper an experimental setup using Fourier-transform infrared spectroscopy (FTIR) in combination with a photoelastic modulator (PEM) for linear dichroism measurements is described. The second part shows the influence of PEM-amplitude and scan-velocity on the sensitivity of the instrument. The third part deals with the fringe-problem in the baselines of absorbance spectra and its influence on the determination of the linear dichroic ratio. 相似文献
37.
38.
The straightforward synthesis of a polystyrene-arm-polybutadiene-arm-poly(methyl methacrylate) triarm star copolymer has been successfully realized by a sequence of reactions which involves the sequential addition of a living polybutadienyllithium to a polystyrene macromonomer with a terminal 1,1-diphenylethylene unit and subsequent polymerization of methyl methacrylate. The high-molecular-weight polystyrene-arm-polybutadiene-arm-poly(methyl methacrylate) star copolymer shows microphase separation into three phases. 相似文献
39.
40.