全文获取类型
收费全文 | 806篇 |
免费 | 25篇 |
专业分类
化学 | 626篇 |
晶体学 | 9篇 |
力学 | 8篇 |
数学 | 35篇 |
物理学 | 153篇 |
出版年
2023年 | 4篇 |
2022年 | 3篇 |
2021年 | 17篇 |
2020年 | 15篇 |
2019年 | 5篇 |
2018年 | 9篇 |
2016年 | 11篇 |
2015年 | 16篇 |
2014年 | 10篇 |
2013年 | 30篇 |
2012年 | 35篇 |
2011年 | 63篇 |
2010年 | 33篇 |
2009年 | 31篇 |
2008年 | 49篇 |
2007年 | 60篇 |
2006年 | 55篇 |
2005年 | 62篇 |
2004年 | 44篇 |
2003年 | 32篇 |
2002年 | 26篇 |
2001年 | 20篇 |
2000年 | 17篇 |
1999年 | 6篇 |
1997年 | 6篇 |
1996年 | 14篇 |
1995年 | 8篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 2篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 15篇 |
1974年 | 5篇 |
1973年 | 9篇 |
1972年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有831条查询结果,搜索用时 15 毫秒
151.
Albertus P. H. J. Schenning Michel Fransen E. W. Meijer 《Macromolecular rapid communications》2002,23(4):265-270
Stereospecific polymerizations of functionalized acetylenes were successfully performed using a Rh complex as the catalyst and triethylamine as a base yielding poly(3,4,5‐tridodecyloxyphenylacetylene) ( Poly5 ) and poly[3,4,5‐tris((S)‐3,7‐dimethyloctyloxy)phenylacetylene] ( Poly6 ). Poly5 and Poly6 are liquid crystalline with presumably a bilayer‐type architecture in which the mesogens are arranged in an antiparallel overlapping interdigitated manner. Poly6 showed unusual thermal stereomutation in solution in a very narrow temperature range. 相似文献
152.
153.
154.
155.
156.
André Fielicke Philipp Gruene Gerard Meijer David M. Rayner 《Surface science》2009,603(10-12):1427-1433
We present a discussion of recent experimental studies on the interaction of single CO molecules with transition metal clusters in the gas-phase, typically in the size range of 3 to more than 20 atoms, emphasizing specifically the insights gained from vibrational spectroscopy. Trends across the transition metals (TM) for molecular vs. dissociative chemisorption as well as for adsorption geometries are discussed and compared with the behaviour of CO adsorbed on extended surfaces. The dependence of the frequency of the internal CO stretch vibration on the size and charge of the cluster enables one to gauge quantitatively the effects of charge transfer between deposited nanoparticles and the substrate as well as of electron transfer due to the binding of co-adsorbed species. 相似文献
157.
158.
Peter Nockemann Dr. Ben Thijs Dr. Kyra Lunstroot Dr. Tatjana N. Parac‐Vogt Prof. Dr. Christiane Görller‐Walrand Prof. Dr. Koen Binnemans Prof. Dr. Kristof Van Hecke Dr. Luc Van Meervelt Prof. Dr. Sergey Nikitenko John Daniels Dr. Christoph Hennig Dr. Rik Van Deun Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(6):1449-1461
The dissolution process of metal complexes in ionic liquids was investigated by a multiple‐technique approach to reveal the solvate species of the metal in solution. The task‐specific ionic liquid betainium bis(trifluoromethylsulfonyl)imide ([Hbet][Tf2N]) is able to dissolve stoichiometric amounts of the oxides of the rare‐earth elements. The crystal structures of the compounds [Eu2(bet)8(H2O)4][Tf2N]6, [Eu2(bet)8(H2O)2][Tf2N]6?2H2O, and [Y2(bet)6(H2O)4][Tf2N]6 were found to consist of dimers. These rare‐earth complexes are well soluble in the ionic liquids [Hbet][Tf2N] and [C4mim][Tf2N] (C4mim=1‐butyl‐3‐methylimidazolium). The speciation of the metal complexes after dissolution in these ionic liquids was investigated by luminescence spectroscopy, 1H, 13C, and 89Y NMR spectroscopy, and by the synchrotron techniques EXAFS (extended X‐ray absorption fine structure) and HEXS (high‐energy X‐ray scattering). The combination of these complementary analytical techniques reveals that the cationic dimers decompose into monomers after dissolution of the complexes in the ionic liquids. Deeper insight into the solution processes of metal compounds is desirable for applications of ionic liquids in the field of electrochemistry, catalysis, and materials chemistry. 相似文献
159.
Willi A. Brand Tyler B. Coplen Anita T. Aerts‐Bijma J. K. Böhlke Matthias Gehre Heike Geilmann Manfred Gröning Henk G. Jansen Harro A. J. Meijer Stanley J. Mroczkowski Haiping Qi Karin Soergel Hilary Stuart‐Williams Stephan M. Weise Roland A. Werner 《Rapid communications in mass spectrometry : RCM》2009,23(7):999-1019
Internationally distributed organic and inorganic oxygen isotopic reference materials have been calibrated by six laboratories carrying out more than 5300 measurements using a variety of high‐temperature conversion techniques (HTC) a in an evaluation sponsored by the International Union of Pure and Applied Chemistry (IUPAC). To aid in the calibration of these reference materials, which span more than 125‰, an artificially enriched reference water (δ18O of +78.91‰) and two barium sulfates (one depleted and one enriched in 18O) were prepared and calibrated relative to VSMOW2 b and SLAP reference waters. These materials were used to calibrate the other isotopic reference materials in this study, which yielded:
The seemingly large estimated combined uncertainties arise from differences in instrumentation and methodology and difficulty in accounting for all measurement bias. They are composed of the 3‐fold standard errors directly calculated from the measurements and provision for systematic errors discussed in this paper. A primary conclusion of this study is that nitrate samples analyzed for δ18O should be analyzed with internationally distributed isotopic nitrates, and likewise for sulfates and organics. Authors reporting relative differences of oxygen‐isotope ratios (δ18O) of nitrates, sulfates, or organic material should explicitly state in their reports the δ18O values of two or more internationally distributed nitrates (USGS34, IAEA‐NO‐3, and USGS35), sulfates (IAEA‐SO‐5, IAEA‐SO‐6, and NBS 127), or organic material (IAEA‐601 benzoic acid, IAEA‐602 benzoic acid, and IAEA‐600 caffeine), as appropriate to the material being analyzed, had these reference materials been analyzed with unknowns. This procedure ensures that readers will be able to normalize the δ18O values at a later time should it become necessary. The high‐temperature reduction technique for analyzing δ18O and δ2H is not as widely applicable as the well‐established combustion technique for carbon and nitrogen stable isotope determination. To obtain the most reliable stable isotope data, materials should be treated in an identical fashion; within the same sequence of analyses, samples should be compared with working reference materials that are as similar in nature and in isotopic composition as feasible. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
Reference material | δ18O and estimated combined uncertainty c |
---|---|
IAEA‐602 benzoic acid | +71.28 ± 0.36‰ |
USGS35 sodium nitrate | +56.81 ± 0.31‰ |
IAEA‐NO‐3 potassium nitrate | +25.32 ± 0.29‰ |
IAEA‐601 benzoic acid | +23.14 ± 0.19‰ |
IAEA‐SO‐5 barium sulfate | +12.13 ± 0.33‰ |
NBS 127 barium sulfate | +8.59 ± 0.26‰ |
VSMOW2 water | 0‰ |
IAEA‐600 caffeine | ?3.48 ± 0.53‰ |
IAEA‐SO‐6 barium sulfate | ?11.35 ± 0.31‰ |
USGS34 potassium nitrate | ?27.78 ± 0.37‰ |
SLAP water | ?55.5‰ |
160.
We examine a recolouring scheme ostensibly used to assist in classifying geographic data. Given a drawing of a graph with bi-chromatic points, where the points are the vertices of the graph, a point can be recoloured if it is surrounded by neighbours of the opposite colour. The notion of surrounded is defined as a contiguous subset of neighbours that span an angle greater than 180 degrees. The recolouring of surrounded points continues in sequence, in no particular order, until no point remains surrounded. We show that for some classes of graphs the process terminates in a polynomial number of steps. On the other hand, there are classes of graphs with infinite recolouring sequences. 相似文献