全文获取类型
收费全文 | 332篇 |
免费 | 9篇 |
专业分类
化学 | 211篇 |
晶体学 | 1篇 |
力学 | 4篇 |
数学 | 37篇 |
物理学 | 46篇 |
无线电 | 42篇 |
出版年
2021年 | 2篇 |
2019年 | 1篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 3篇 |
2015年 | 10篇 |
2014年 | 9篇 |
2013年 | 11篇 |
2012年 | 18篇 |
2011年 | 24篇 |
2010年 | 17篇 |
2009年 | 8篇 |
2008年 | 26篇 |
2007年 | 31篇 |
2006年 | 29篇 |
2005年 | 21篇 |
2004年 | 25篇 |
2003年 | 20篇 |
2002年 | 12篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 2篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1986年 | 1篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有341条查询结果,搜索用时 15 毫秒
201.
Intramolecular Frustrated Lewis Pair with the Smallest Boryl Site: Reversible H2 Addition and Kinetic Analysis
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Konstantin Chernichenko Bianka Kótai Dr. Imre Pápai Dr. Vladimir Zhivonitko Dr. Martin Nieger Prof. Markku Leskelä Prof. Timo Repo 《Angewandte Chemie (International ed. in English)》2015,54(6):1749-1753
Ansa‐aminoborane 1 (ortho‐TMP? C6H4? BH2; TMP=2,2,6,6‐tetramethylpiperid‐1‐yl), a frustrated Lewis pair with the smallest possible Lewis acidic boryl site (? BH2), is prepared. Although it is present in quenched forms in solution, and BH2 represents an acidic site with reduced hydride affinity, 1 reacts with H2 under mild conditions producing ansa‐ammonium trihydroborate 2 . The thermodynamic and kinetic features as well as the mechanism of this reaction are studied by variable‐temperature NMR spectroscopy, spin‐saturation transfer experiments, and DFT calculations, which provide comprehensive insight into the nature of 1 . 相似文献
202.
Diverting Hydrogenations with Wilkinson's Catalyst towards Highly Reactive Rhodium(I) Species
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Jesus E. Perea‐Buceta Dr. Israel Fernández Dr. Sami Heikkinen Dr. Kirill Axenov Dr. Alistair W. T. King Teemu Niemi Dr. Martin Nieger Prof. Markku Leskelä Prof. Timo Repo 《Angewandte Chemie (International ed. in English)》2015,54(48):14321-14325
The addition of Barton's base has a dramatic effect on the classic rhodium(III)‐mediated hydrogenations promoted by Wilkinson′s catalyst. Following the initial oxidative addition, a barrierless reductive elimination of HCl from the traditional rhodium(III) intermediates instantly produces a rhodium(I) monohydride species, which is remarkably reactive in the hydrogenation of several internal alkynes and functionalized trisubstituted alkenes. The direct formation of this species is unprecedented upon addition of molecular hydrogen and its catalytic potential has been hitherto barely explored. 相似文献
203.
Pehkonen S Marushkevich K Khriachtchev L Räsänen M Grigorenko BL Nemukhin AV 《The journal of physical chemistry. A》2007,111(45):11444-11449
Productive photochemical synthesis of hydrogen peroxide, H(2)O(2), from the H(2)O...O((3)P) van der Waals complex is studied in solid krypton. Experimentally, we achieve the three-step formation of H(2)O(2) from H(2)O and N(2)O precursors frozen in solid krypton. First, 193 nm photolysis of N(2)O yields oxygen atoms in solid krypton. Upon annealing at approximately 25 K, mobile oxygen atoms react with water forming the H(2)O...O complex, where the oxygen atom is in the triplet ground state. Finally, the H(2)O...O complex is converted to H(2)O(2) by irradiation at 300 nm. According to the complete active space self-consistent field modeling, hydrogen peroxide can be formed through the photoexcited H(2)O+-O- charge-transfer state of the H(2)O...O complex, which agrees with the experimental evidence. 相似文献
204.
Tuula Kuivalainen Risto Kostiainen Rolf Uggla Markku R. Sundberg Heikki Björk 《Journal of the American Society for Mass Spectrometry》1996,7(2):189-197
The gas-phase ion chemistry of protonated O,O-diethyl O-aryl phosphorothionates was studied with tandem mass spectrometric and ab initio theoretical methods. Collision-activated dissociation (CAD) experiments were performed for the [M+H]+ ions on a triple quadrupole mass spectrometer. Various amounts of internal energy were deposited into the ions upon CAD by variation of the collision energy and collision gas pressure. In addition to isobutane, deuterated isobutane C4D10 also was used as reagent gas in chemical ionization. The daughter ions [M+H?C2H4]+ and [M+H?2C2H4]+ dominate the CAD spectra. These fragments arise via various pathways, each of which involves γ-proton migration. Formation of the terminal ions [M+H?2C2H4?H2O]+, [M+H?2C2H4?H2S]+, [ZPhOH2]+, [ZPhSH2]+, and [ZPhS]+ [Z = substituent(s) on the benzene ring] suggests that (1) the fragmenting [M+H]+ ions of O,O-diethyl O-aryl phosphorothionates have protons attached on the oxygen of an ethoxy group and on the oxygen of the phenoxy group; (2) thiono-thiolo rearrangement by aryl migration to sulfur occurs; (3) the fragmenting rear-ranged [M+H]+ ions have protons attached on the oxygen of an ethoxy group and on the sulfur of the thiophenoxy group. To get additional support for our interpretation of the mass spectrometric results, some characteristics of three protomers of O,O-diethyl O-phenyl phosphorothionate were investigated by carrying out ab initio molecular orbital calculations at the RHF/3–21G* level of theory. 相似文献
205.
206.
207.
Multiuser detectors for asynchronous multirate code-division multiple-access (CDMA) systems are considered. A multirate CDMA system model able to fit several system concepts in the same framework is presented. The performance of the multi-code (MC) system with one processing gain and the multiple processing gain (MPG) system is compared. Upper bounds for the expected value of the asymptotic multiuser efficiency of the decorrelating detector for a synchronous multirate CDMA system with three effective users are derived for a system with one and two processing gains. The numerical results show that the performance of the decorrelating detector for MC and MPG systems do not differ significantly. The bit error rates (BER) of the decorrelating, parallel interference canceler (PIC) and groupwise serial interference canceler (GSIC) with either PIC or decorrelator within the group are compared. The results show that the decorrelating and the GSIC detectors yield the best performance. For all interference cancellation schemes the BER saturates at high SNRs due to decision errors degrading the multiple-access interference (MAI) estimates. 相似文献
208.
Markku S. Hannula 《ZDM》2012,44(1):83-90
This commentary paper analyses and discusses the conceptual analysis of values and the methodological choices made for its study, as presented in the separate papers of this special issue. As a foundation, the first part of the paper presents a metatheoretical framework for the affective domain, where stability (state vs. trait), functionality (truths, feelings and preferences) and level of analysis (individual vs. social) are its specific dimensions. The subsequent conceptual analysis identifies values as motivational traits. However, it was not possible to identify values exclusively as a social or as an individual construct, as the concept is used with both meanings, even by the same author. Further analysis elaborates how values develop, both on a cultural and an individual level, and how values can be studied. 相似文献
209.
210.
Tsuge M Berski S Stachowski R Räsänen M Latajka Z Khriachtchev L 《The journal of physical chemistry. A》2012,116(18):4510-4517
We investigate the conditions when noble-gas hydrides can be found in real environments and report on the preparation and identification of the HXeBr···CO(2) complex in a xenon matrix and HXeBr in a carbon dioxide matrix. The H-Xe stretching mode of the HXeBr···CO(2) complex in a xenon matrix is observed at 1557 cm(-1), showing a spectral shift of +53 cm(-1) from the HXeBr monomer. The calculations at the CCSD(T)/aug-cc-pVTZ-PP(Xe,Br) level of theory give two stable structures for the HXeBr···CO(2) complex with frequency shifts of +55 and +103 cm(-1), respectively. On the basis of the calculations, the experimentally observed band is assigned to the more stable structure with a "parallel" geometry. The HXeBr molecule was prepared in a carbon dioxide matrix and has the H-Xe stretching frequency of 1646 cm(-1), meaning a strong matrix shift and stabilization of the H-Xe bond. The deuterated species DXeBr in a carbon dioxide matrix absorbs at 1200 cm(-1). This is the first case where a noble-gas hydride is prepared in a molecular solid. The thermal stabilities of HXeBr and HXeBr···CO(2) complex in a xenon matrix and HXeBr in a carbon dioxide matrix were examined. We have found a high thermal stability of HXeBr in carbon dioxide ice (at least up to 100 K), i.e., under conditions that may occur in nature. 相似文献