全文获取类型
收费全文 | 2301篇 |
免费 | 67篇 |
国内免费 | 12篇 |
专业分类
化学 | 1661篇 |
晶体学 | 10篇 |
力学 | 35篇 |
数学 | 442篇 |
物理学 | 232篇 |
出版年
2023年 | 14篇 |
2022年 | 23篇 |
2021年 | 38篇 |
2020年 | 43篇 |
2019年 | 44篇 |
2018年 | 22篇 |
2017年 | 20篇 |
2016年 | 65篇 |
2015年 | 39篇 |
2014年 | 50篇 |
2013年 | 74篇 |
2012年 | 108篇 |
2011年 | 105篇 |
2010年 | 54篇 |
2009年 | 79篇 |
2008年 | 130篇 |
2007年 | 104篇 |
2006年 | 102篇 |
2005年 | 94篇 |
2004年 | 87篇 |
2003年 | 92篇 |
2002年 | 91篇 |
2001年 | 39篇 |
2000年 | 59篇 |
1999年 | 34篇 |
1998年 | 47篇 |
1997年 | 50篇 |
1996年 | 46篇 |
1995年 | 35篇 |
1994年 | 44篇 |
1993年 | 32篇 |
1992年 | 25篇 |
1991年 | 35篇 |
1990年 | 24篇 |
1989年 | 19篇 |
1988年 | 30篇 |
1987年 | 24篇 |
1986年 | 16篇 |
1985年 | 26篇 |
1984年 | 40篇 |
1983年 | 25篇 |
1982年 | 35篇 |
1981年 | 32篇 |
1980年 | 26篇 |
1979年 | 16篇 |
1978年 | 15篇 |
1977年 | 18篇 |
1976年 | 17篇 |
1975年 | 10篇 |
1973年 | 7篇 |
排序方式: 共有2380条查询结果,搜索用时 15 毫秒
61.
Stijn Dekeukeleire Matthias D’hooghe Matthieu Vanwalleghem Willem Van Brabandt Norbert De Kimpe 《Tetrahedron》2012,68(52):10827-10834
Chiral piperazine and 1,4-diazepane annulated β-lactams, prepared from the corresponding (3R,4S)-4-imidoyl-1-(ω-haloalkyl)azetidin-2-ones through reduction with sodium borohydride in ethanol, were transformed into novel methyl (R)-alkoxy-[(S)-piperazin-2-yl]acetates and methyl (R)-alkoxy-[(S)-1,4-diazepan-2-yl]acetates upon treatment with hydrogen chloride in methanol. On the other hand, bromination of (3R,4R)-1-allyl-4-formyl-β-lactams and (3R,4S)-1-allyl-4-imidoyl-β-lactams in dichloromethane, followed by sodium borohydride reduction of the resulting dibrominated azetidin-2-ones in ethanol, did not afford the envisaged bicyclic β-lactams but unexpectedly furnished (3R,4S)-1-(2-bromo-2-propenyl)azetidin-2-ones instead. 相似文献
62.
63.
Steffen Dachwitz Bjarne Scharkowski Prof. Norbert Sewald 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(72):18043-18046
Mild transition-metal catalysed cross-couplings enable direct functionalisation of biocatalytically halogenated tryptophans with alkyl iodides, representing a new alternative for late-stage derivatisations of halogenated aromatic amino acids. Moreover, this strategy enables preparation of (homo)tryptophan regioisomers in a simple two-step synthesis using a Pd-catalysed Negishi cross coupling. This method provides access to non-canonical constitutional surrogates of tryptophan, ready for use in peptide synthesis. 相似文献
64.
Dr. Mostakim SK Dr. Soumitra Barman Shounik Paul Ratnadip De Dr. S. S. Sreejith Dr. Helge Reinsch Dr. Maciej Grzywa Dr. Norbert Stock Prof. Dr. Dirk Volkmer Dr. Shyam Biswas Prof. Dr. Soumyajit Roy 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(12):4098-4107
A Zr-based metal-organic framework has been synthesized and employed as a catalyst for photochemical carbon dioxide reduction coupled with water oxidation. The catalyst shows significant carbon dioxide reduction property with concomitant water oxidation. The catalyst has broad visible light as well as UV light absorption property, which is further confirmed from electronic absorption spectroscopy. Formic acid was the only reduced product from carbon dioxide with a turn-over frequency (TOF) of 0.69 h−1 in addition to oxygen, which was produced with a TOF of 0.54 h−1. No external photosensitizer is used and the ligand itself acts as the light harvester. The efficient and selective photochemical carbon dioxide reduction to formic acid with concomitant water oxidation using Zr-based MOF as catalyst is thus demonstrated here. 相似文献
65.
Dr. Philipp Holtkamp Dario Poier Beate Neumann Dr. Hans-Georg Stammler Prof. Dr. Norbert W. Mitzel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(11):3793-3798
The reactivity of the geminal frustrated Lewis pair (FLP) (F5C2)3SnCH2P(tBu)2 ( 1 ) was explored by reacting it with a variety of small molecules (PhOCN, PhNCS, PhCCH, tBuCCH, H3CC(O)CH=CH2, Ph[C(O)]2Ph, PhN=NPh and Me3SiCHN2), featuring polar or non-polar multiple bonds and/or represent α,β-unsaturated systems. While most adducts are formed readily, the binding of azobenzene requires UV-induced photoisomerization, which results in the highly selective complexation of cis-azobenzene. In the case of benzil, the reaction does not lead to the expected 1,2- or 1,4-addition products, but to the non-stereoselective (tBu)2PCH2-transfer to a prochiral keto function of benzil. All adducts of 1 were characterised by means of multinuclear NMR spectroscopy, elemental analyses and X-ray diffraction experiments. 相似文献
66.
S. Jakobs Ulrike Schulz Angela Duparré Norbert Kaiser 《Analytical and bioanalytical chemistry》1997,358(1-2):242-244
SiO2 protective coatings have been deposited on polycarbonate substrates by plasma ion assisted deposition. The influence of ion energy on the water permeability and the surface topography of the coatings was studied by infrared spectroscopy and atomic force microscopy. Coatings deposited at sufficiently high ion energies show a barrier effect against moisture uptake and considerably reduced film roughness. Both effects are attributed to an increase of the packing densities of the coatings. 相似文献
67.
68.
69.
70.
Romeo D. Tadjouate Nago Paul Nayim Armelle T. Mbaveng James D. Simo Mpetga Gabin T. Mbahbou Bitchagno Badawe Garandi Pierre Tane Bruno N. Lenta Norbert Sewald Mathieu Tene Victor Kuete Augustin Silvere Ngouela 《Molecules (Basel, Switzerland)》2021,26(16)
The local botanical Imperata cylindrica in Cameroon was investigated for its antibacterial potency. The methanol extract afforded a total of seven compounds, including five hitherto unreported compounds comprising three flavonoids (1–3) and two C-15 isoprenoid analogues (4 and 5) together with known derivatives (6 and 7). The novelty of the flavonoids was related to the presence of both methyl and prenyl groups. The potential origin of the methyl in the flavonoids is discussed, as well as the chemophenetic significance of our findings. Isolation was performed over repeated silica gel and Sephadex LH-20 column chromatography and the structures were elucidated by (NMR and MS). The crude methanol extract and isolated compounds showed considerable antibacterial potency against a panel of multi-drug resistant (MDR) bacterial strains. The best MIC values were obtained with compound (2) against S. aureus ATCC 25923 (32 µg/mL) and MRSA1 (16 µg/mL). 相似文献