全文获取类型
收费全文 | 519篇 |
免费 | 39篇 |
专业分类
化学 | 485篇 |
力学 | 3篇 |
数学 | 16篇 |
物理学 | 54篇 |
出版年
2023年 | 10篇 |
2022年 | 6篇 |
2021年 | 14篇 |
2020年 | 18篇 |
2019年 | 27篇 |
2017年 | 4篇 |
2016年 | 22篇 |
2015年 | 16篇 |
2014年 | 20篇 |
2013年 | 15篇 |
2012年 | 33篇 |
2011年 | 31篇 |
2010年 | 14篇 |
2009年 | 19篇 |
2008年 | 28篇 |
2007年 | 21篇 |
2006年 | 25篇 |
2005年 | 24篇 |
2004年 | 9篇 |
2003年 | 14篇 |
2002年 | 21篇 |
2001年 | 14篇 |
2000年 | 7篇 |
1999年 | 13篇 |
1998年 | 9篇 |
1997年 | 16篇 |
1996年 | 13篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1972年 | 2篇 |
1918年 | 4篇 |
1909年 | 3篇 |
1903年 | 2篇 |
排序方式: 共有558条查询结果,搜索用时 15 毫秒
431.
Different polymers were investigated with respect to the sorption of solvents and gases. Depending on the chemical nature of the polymers this sorption leads to polymer swelling. The degree of swelling D/D0 was measured utilizing Small angle X-ray scattering (SAXS) as well as Surface plasmon resonance (SPR). From the change in film thickness after swelling in different solvents Hildebrand parameters of the polymers were determined. By crosslinking of the polymer films the degree of swelling can be controlled. In the case of ultra-thin polyimide films a higher degree of crosslinking led to a decreased selectivity of the transport of gases through the membrane. Reptation of macromolecules was also investigated and the influence of polymer swelling in different solvents has a great influence on the selectivity and diffusion coefficient. 相似文献
432.
433.
The polyiminophosphazene bases Et-P2 and t-Bu-P4 were used as a promoter for ethylene oxide and siloxane polymerizations. Initiation by an alcohol in combination with t-Bu-P4 lead to an extremely rapid polymerization reaction of octamethylcyclotetrasiloxane. In the case of ethylene oxide, well-defined polymers were obtained, however the rate of polymerization decreased during the polymerization reaction due to decomposition of the counterion. In combination with organolithium compounds, the phosphazene bases lead to well-defined polymers in the case of cyclotrisiloxanes as well as in the case of ethylene oxide. 相似文献
434.
Waldemar Hoffmann Jennifer Langenhan Susanne Huhmann Johann Moschner Rayoon Chang Matteo Accorsi Jongcheol Seo Jrg Rademann Gerard Meijer Beate Koksch Michael T. Bowers Gert vonHelden Kevin Pagel 《Angewandte Chemie (International ed. in English)》2019,58(24):8216-8220
More than 100 hydrophobicity scales have been introduced, with each being based on a distinct condensed‐phase approach. However, a comparison of the hydrophobicity values gained from different techniques, and their relative ranking, is not straightforward, as the interactions between the environment and the amino acid are unique to each method. Here, we overcome this limitation by studying the properties of amino acids in the clean‐room environment of the gas phase. In the gas phase, entropic contributions from the hydrophobic effect are by default absent and only the polarity of the side chain dictates the self‐assembly. This allows for the derivation of a novel hydrophobicity scale, which is based solely on the interaction between individual amino acid units within the cluster and thus more accurately reflects the intrinsic nature of a side chain. This principle can be further applied to classify non‐natural derivatives, as shown here for fluorinated amino acid variants. 相似文献
435.
Abdelaaty Hamed Marwa Y. Issa Mohamed A. Ghani Marcel Frese Beate Neumann Hans Georg Stammler 《Natural product research》2019,33(20):3029-3032
Herein, we report the isolation and stereo-structure of rare pyrane-based cembranoid diterpenes, 9-hydroxy-7,8-dehydro-sarcotrocheliol (1) and sarcotrocheliol (2), from Sarcophyton trocheliophorum collected from Red Sea. Absolute configurations of both compounds were revised based on single crystal X-ray analyses. 相似文献
436.
Philipp Holtkamp Felix Friedrich Erik Stratmann Andreas Mix Beate Neumann Hans‐Georg Stammler Norbert W. Mitzel 《Angewandte Chemie (International ed. in English)》2019,58(15):5114-5118
The geminal frustrated Lewis pair (FLP) (F5C2)3SnCH2P(tBu)2 ( 2 ) was prepared by reacting (F5C2)3SnCl with LiCH2P(tBu)2. It is neutral and contains an extremely electronegatively substituted, but relatively soft (hard–soft acid–base, HSAB) acidic tin function. Its FLP‐type reactivity was proven by reaction with a variety of small molecules (CO2, SO2, CS2, PhNCO, HCl, (Ph3P)AuCl). However, it shows no reaction in H/D scrambling experiments with H2/D2 mixtures and binds CO2 reversibly, as was observed by VT‐NMR spectroscopy. Compound 2 and all its adducts were completely characterized by means of multinuclear NMR spectroscopy, elemental analysis, and X‐ray diffraction experiments. 相似文献
437.
438.
439.
440.
Dennis Rottschäfer Beate Neumann Dr. Hans-Georg Stammler Dr. Ryohei Kishi Prof. Dr. Masayoshi Nakano PD Dr. Rajendra S. Ghadwal 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(13):3244-3247
Para-quinodimethane (pQDM) is a fundamental structural component in many π-conjugated organic molecules and materials. The incorporation of phosphorus atom into π-conjugated frameworks offers unique opportunities for controlling the properties of derived species. A phosphorus analogue of p-quinodimethane (pQDM), (IPrC)2P4 [ 5 , IPr=C{N(Ar)CH2}2; Ar=2,6-iPr2C6H3] featuring a planar P4 ring, was readily accessible by KC8-reduction of (IPrC)(PCl2)2 ( 2 ). Base-mediated C−H functionalization of IPrCH2 ( 1 ) with PCl3 afforded 2 . The formation of 5 was expected to occur through a dimerization of the transient 3H-diphosphirene (IPrC)P2 ( 4 ), which was theoretically suggested to have an intermediate diradical character. Compound 5 underwent photo-induced ring-contraction reaction to form the singlet diradicaloid (IPrCP)2 VI and white phosphorus (P4). The formation of and VI and P4 suggested the formal diphosphorus (P2) elimination from 5 . Indeed, photolysis of a mixture of 1,3-cyclohexadiene (CHD) and 5 led to the formation of P2-entrapped product (CHD)2P2 ( 6 ). The compound 5 represents the first organophosphorus species that functions as a P2 source. 相似文献