全文获取类型
收费全文 | 1159篇 |
免费 | 32篇 |
国内免费 | 3篇 |
专业分类
化学 | 744篇 |
晶体学 | 1篇 |
力学 | 67篇 |
数学 | 215篇 |
物理学 | 167篇 |
出版年
2023年 | 9篇 |
2022年 | 11篇 |
2021年 | 11篇 |
2020年 | 29篇 |
2019年 | 27篇 |
2018年 | 9篇 |
2017年 | 13篇 |
2016年 | 38篇 |
2015年 | 30篇 |
2014年 | 31篇 |
2013年 | 41篇 |
2012年 | 56篇 |
2011年 | 61篇 |
2010年 | 41篇 |
2009年 | 41篇 |
2008年 | 72篇 |
2007年 | 68篇 |
2006年 | 59篇 |
2005年 | 59篇 |
2004年 | 46篇 |
2003年 | 52篇 |
2002年 | 36篇 |
2001年 | 23篇 |
2000年 | 27篇 |
1999年 | 21篇 |
1998年 | 13篇 |
1997年 | 14篇 |
1996年 | 16篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 12篇 |
1992年 | 13篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 11篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1982年 | 10篇 |
1981年 | 12篇 |
1979年 | 11篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1975年 | 6篇 |
1973年 | 6篇 |
1972年 | 5篇 |
1970年 | 8篇 |
1967年 | 5篇 |
排序方式: 共有1194条查询结果,搜索用时 15 毫秒
41.
We studied the orientational relaxation of the OD-stretch vibration of HDO molecules in concentrated solutions of alkali-halide salts (NaCl, NaI, CsCl and KI) in isotopically diluted water (4% D(2)O in H(2)O), using polarization-resolved femtosecond infrared pump-probe spectroscopy (fs-IR). We were able to distinguish the orientational dynamics of the water molecules solvating the halide ions from the dynamics of the bulk water and the water solvating the cations. We found that the reorientation of the halide-bound molecules shows two strongly different components (2.0 ± 0.3 ps and 9 ± 1 ps), related to a wiggling motion of the OD group hydrogen-bonded to the anion, and rotational diffusion of the molecule over the charged anion surface, respectively. The relative amplitudes of the two components are dependent on the nature of both the anion and cation, and on the concentration. These results show that cations can have a profound effect on the solvation shell dynamics of their counter-ions. 相似文献
42.
Dr. Damien Hudry Dr. Christos Apostolidis Dr. Olaf Walter Dr. Thomas Gouder Dr. Eglantine Courtois Dr. Christian Kübel Dr. Daniel Meyer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(17):5297-5305
Very little is known about the size and shape effects on the properties of actinide compounds. As a consequence, the controlled synthesis of well‐defined actinide‐based nanocrystals constitutes a fundamental step before studying their corresponding properties. In this paper, we report on the non‐aqueous surfactant‐assisted synthesis of thorium and uranium oxide nanocrystals. The final characteristics of thorium and uranium oxide nanocrystals can be easily tuned by controlling a few experimental parameters such as the nature of the actinide precursor and the composition of the organic system (e.g., the chemical nature of the surfactants and their relative concentrations). Additionally, the influence of these parameters on the outcome of the synthesis is highly dependent on the nature of the actinide element (thorium versus uranium). By using optimised experimental conditions, monodisperse isotropic uranium oxide nanocrystals with different sizes (4.5 and 10.7 nm) as well as branched nanocrystals (overall size ca. 5 nm), nanodots (ca. 4 nm) and nanorods (with ultra‐small diameters of 1 nm) of thorium oxide were synthesised. 相似文献
43.
Olaf Böge Eckhart Nietzschmann Joachim Heinicke 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):25-29
Abstract 2-Bromoaryloxy-chloromethyldiorganosilanes react with sodium in a one-pot-reaction via metallation, [1,3]-carbanionic rearrangement and cyclization to give diorgano-1,3-benzoxasilolenes. The title compounds have been characterized by n.m.r. spectroscopic data and an alternative independent synthesis. 相似文献
44.
Karim Fahmy Olaf Weidlich Martin Engelhard Jörg Tittor Dieter Oesterhelt Friedrich Siebert † 《Photochemistry and photobiology》1992,56(6):1073-1083
Abstract— In order to assign the proton acceptor for Schiff base deprotonation in bacteriorhodopsin to a specific Asp residue, the photoreaction of the Asp85 → Glu mutant, as expressed in Halobacterium sp . GRB, was investigated by static low-temperature and time-resolved infrared difference spec-troscopy. Measurements were also performed on the mutant protein labeled with [4-13 C]Asp which allowed discrimination between Asp and Glu residues. 14,15-di13 C-retinal was incorporated to distinguish amide-II absorbance changes from changes of the ethylenic mode of the chromophore. In agreement with earlier UV-VIS measurements, our data show that from both the 540 and 610 nm species present in a pH-dependent equilibrium, intermediates similar to K and L can be formed. The 14 ms time-resolved spectrum of the 540 nm species shows that a glutamic acid becomes protonated in the M-like intermediate, whereas the comparable difference spectrum of the 610 nm species demonstrates that in the initial state a glutamic acid is already protonated. In conjunction with earlier observations of protonation of an Asp residue in wild-type M, the data provide direct evidence that the proton acceptor in the deprotonation reaction of the Schiff base is Asp85. 相似文献
45.
Abdul Majid Jim Tunney Steve Argue Mike Post 《Journal of Sol-Gel Science and Technology》2004,32(1-3):323-326
We have investigated the synthesis of perovskite-type SrFeOx (2.5 x 3.0) using three preparative methods: sol-gel, mechanochemical processing and solid state reactions at high temperature of the corresponding oxides. The sample obtained after calcination of the gel from sol-gel method, contained the least amount of strontium carbonate impurity. The amount of strontium carbonate impurity decreased with the increase in calcination temperature. Perovskites obtained have been characterized by X-ray diffraction (XRD) and nitrogen adsorption isotherms. Samples obtained from three methods have been compared with respect to calcination temperature, crystallite size and specific surface area.Issued as NRCC No. 46479. 相似文献
46.
Wiest O Harrison CB Saettel NJ Cibulka R Sax M König B 《The Journal of organic chemistry》2004,69(24):8183-8185
Two new artificial photolyase models that recognize pyrimidine dimers in protic and aprotic organic solvents as well as in water through a combination of charge and hydrogen-bonding interactions and use a mimic of the flavine to achieve repair through reductive photoinduced electron transfer are presented. Fluorescence and NMR titration studies show that it forms a 1:1 complex with pyrimidine dimers with binding constants of approximately 10(3) M(-1) in acetonitrile or methanol, while binding constants in water at pH 7.2 are slightly lower. Excitation of the complex with visible light leads to clean and rapid cycloreversion of the pyrimidine dimer through photoinduced electron transfer catalysis. The reaction in water is significantly faster than in organic solvents. The reaction slows down at higher conversions due to product inhibition. 相似文献
47.
T. Rampke W. -D. Emmerich E. Post L. Giersig 《Journal of Thermal Analysis and Calorimetry》1996,47(2):633-642
The decomposition reactions of polystyrene, phenolic resin and a protective undercoating material for automobiles which contains PVC were tested using a new type of thermal analysis — mass spectrometry coupling system for measurements to 1500C or 2000C, which is based on the principle of a two-step skimmer orifice system. The results will be presented, with particular emphasis on the detection sensitivity of the new system for the products of decomposition.The capability of this coupling system to detect even heavy metals such as lead and silver in the waste gases from decomposition or after evaporation at high temperatures will also be demonstrated. 相似文献
48.
49.
Saravanakumar Shanmuganathan Olaf Kühl Peter G. Jones Joachim Heinicke 《Central European Journal of Chemistry》2010,8(5):992-998
The reaction of chloroethyltrimethylsilylether with 1-methylimidazole furnishes an ionic liquid that undergoes methanolysis
to crystalline 2-hydroxyethylimidazolium chloride (crystal structure presented). Conversion to defined hydroxyethylimidazol-2-ylidene
nickel complexes failed, but was accomplished with 1-methyl-3-acetophenyl-imidazolium bromide. The bis(NHC⋂O−) nickel(II) chelate is formed, rather than a methallylnickel monochelate, but with nickelocene a monochelate NiCp complex
was detected. The bulky 1-(2,6-diisopropylphenyl)-3-(2’-phenyl-enolato)-imidazol-2-ylidene allylpalladium chloride was obtained
in pure form. Attempts to generate catalysts for ethylene oligomerization by in situ techniques have failed so far whereas P⋂O− ligands, comparable by the P-C diagonal relationship, provide active catalysts.
相似文献
50.
Biologically Inspired C−H and C=C Oxidations with Hydrogen Peroxide Catalyzed by Iron Coordination Complexes 下载免费PDF全文
The development of catalysts for the selective oxidation of readily available hydrocarbons or organic precursors into oxygenated products is a long‐standing goal in organic synthesis. In the last decade, some iron coordination complexes have shown the potential to fit this role. These catalysts can mimic the O?O activation mode of far more sophisticated iron oxygenase enzymes, generating powerful yet selective oxidants. In this review, we report state‐of‐the‐art C?H and C=C oxidations catalyzed by non‐heme iron complexes and H2O2 as the oxidant. Finally, we briefly describe some novel oxidative reactivity and the perspectives of this chemistry. 相似文献