全文获取类型
收费全文 | 390篇 |
免费 | 23篇 |
专业分类
化学 | 304篇 |
晶体学 | 1篇 |
力学 | 4篇 |
数学 | 29篇 |
物理学 | 75篇 |
出版年
2023年 | 5篇 |
2022年 | 6篇 |
2021年 | 6篇 |
2020年 | 13篇 |
2019年 | 5篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 8篇 |
2015年 | 15篇 |
2014年 | 14篇 |
2013年 | 29篇 |
2012年 | 25篇 |
2011年 | 18篇 |
2010年 | 18篇 |
2009年 | 19篇 |
2008年 | 28篇 |
2007年 | 21篇 |
2006年 | 27篇 |
2005年 | 18篇 |
2004年 | 22篇 |
2003年 | 26篇 |
2002年 | 21篇 |
2001年 | 6篇 |
2000年 | 9篇 |
1999年 | 8篇 |
1998年 | 9篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1943年 | 1篇 |
1912年 | 1篇 |
排序方式: 共有413条查询结果,搜索用时 0 毫秒
41.
Seguin J Moutiez M Li Y Belin P Lecoq A Fonvielle M Charbonnier JB Pernodet JL Gondry M 《Chemistry & biology》2011,18(11):1362-1368
Cyclodipeptide synthases (CDPSs) are small enzymes structurally related to class-I aminoacyl-tRNA synthetases (aaRSs). They divert aminoacylated tRNAs from their canonical role in ribosomal protein synthesis, for cyclodipeptide formation. All the CDPSs experimentally characterized to date are?bacterial. We show here that a predicted CDPS from the sea anemone Nematostella vectensis is an active CDPS catalyzing the formation of various cyclodipeptides, preferentially containing tryptophan. Our findings demonstrate that eukaryotes encode active CDPSs and suggest that all CDPSs have?a similar aminoacyl-tRNA synthetase-like architecture and ping-pong mechanism. They also raise questions about the biological roles of the cyclodipeptides produced in bacteria and eukaryotes. 相似文献
42.
Aubert V Ordronneau L Escadeillas M Williams JA Boucekkine A Coulaud E Dragonetti C Righetto S Roberto D Ugo R Valore A Singh A Zyss J Ledoux-Rak I Le Bozec H Guerchais V 《Inorganic chemistry》2011,50(11):5027-5038
A series of cationic Ir(III) substituted bipyridyl ()(N(∧)N (N(∧)N-bpy) complexes incorporating electron-donor and -acceptor substituents, [Ir(C(∧)N-ppy-R')(2)(N(∧)N-bpy-CH═CH-C(6)H(4)-R)][X] (X(-) = PF(6)(-) or C(12)H(25)SO(3)(-)), 2 (a, R = NEt(2) and R' = Me; b, R = O-Oct and R' = Me; c, R = NO(2) and R' = C(6)H(13); C(∧)N-ppy = cyclometalated 2-phenylpyridine, [Ir(C(∧)N-ppy-Me)(2)(N(∧)N-bpy-CH═CH-thienyl-Me)][PF(6)], 2d, and the dithienylethene (DTE)-containing complex 2e have been synthesized and characterized, and their absorption, luminescence, and quadratic nonlinear optical (NLO) properties are reported. Density functional theory (DFT) and time-dependent-DFT (TD-DFT) calculations on the complexes facilitate a detailed assignment of the excited states involved in the absorption and emission processes. All five complexes are luminescent in a rigid glass at 77 K, displaying vibronically structured spectra with long lifetimes (14-90 μs), attributed to triplet states localized on the styryl-appended bipyridines. The second-order NLO properties of 2a-d and related complexes 1a-d with 1,10-phenanthrolines have been investigated by both electric field induced second harmonic generation (EFISH) and harmonic light scattering (HLS) techniques. They are characterized by high negative EFISH μβ values which decrease when the ion pair strength between the cation and the counterion (PF(6)(-), C(12)H(25)SO(3)(-)) increases. The EFISH response is mainly controlled by metal-to-ligand charge-transfer/ligand-to-ligand charge-transfer (MLCT/L'LCT) processes. A combination of HLS and EFISH techniques is used to evaluate both the dipolar and octupolar contributions to the total quadratic hyperpolarizability, demonstrating that the major contribution is controlled by the octupolar part. The incorporation of a photochromic DTE unit into the N(∧)N-bpy ligand (complex 2e) allows the luminescence to be switched ON or OFF. The photocyclisation of the DTE unit can be triggered by using either UV (365 nm) or visible light (430 nm), leading to an efficient quenching of the ligand-based 77 K luminescence, which can be restored upon irradiation of the closed form at 715 nm. In contrast, no significant modification of the EFISH μβ value is observed upon photocyclization, suggesting that the quadratic NLO response is dominated by the MLCT/L'LCT processes, rather than by the intraligand excited states localized on the substituted bipyridine ligand. 相似文献
43.
R. Grau S. W. Moissejew A. P. Georgijewski A. M. Michailowa A. Miermeister G. Buogo Maria Maitilasso C. Wilhelm G. Steiner F. Th. van Voorst J. Peltzer J. H. Glynn G. L. Taylor G. S. Adair Muriel E. Adair G. Kieselbach H. Diller und R. Stäsche 《Fresenius' Journal of Analytical Chemistry》1943,125(7-8):306-309
Ohne Zusammenfassung 相似文献
44.
Muriel Jz Rbert Vrdai Andrs Bartos Jnos Mcz Bla Puknszky 《Molecules (Basel, Switzerland)》2022,27(19)
Biocomposites were prepared from poly(lactic acid) and two natural reinforcements, a native starch and sugarcane bagasse fibers. The strength of interfacial adhesion was estimated by model calculations, and local deformation processes were followed by acoustic emission testing. The results showed that the two additives influence properties differently. The strength of interfacial adhesion and thus the extent of reinforcement are similar because of similarities in chemical structure, the large number of OH groups in both reinforcements. Relatively strong interfacial adhesion develops between the components, which renders coupling inefficient. Dissimilar particle characteristics influence local deformation processes considerably. The smaller particle size of starch results in larger debonding stress and thus larger composite strength. The fracture of the bagasse fibers leads to larger energy consumption and to increased impact resistance. Although the environmental benefit of the prepared biocomposites is similar, the overall performance of the bagasse fiber reinforced PLA composites is better than that offered by the PLA/starch composites. 相似文献
45.
Pomestchenko IE Luman CR Hissler M Ziessel R Castellano FN 《Inorganic chemistry》2003,42(5):1394-1396
Room temperature phosphorescence has been observed in a synthetically facile Pt(II) complex, Pt(dbbpy)(CtriplebondC-pyrene)(2) (dbbpy = 4,4'-di(tert-butyl)-2,2'-bipyridine; CtriplebondC-pyrene = 1-ethynylpyrene), in fluid solution. The static and time-resolved absorption and luminescence data are consistent with phosphorescence emerging from the appended CtriplebondC-pyrenyl units following excitation into the low energy dpi Pt --> pi* dbbpy metal-to-ligand charge transfer absorption bands. 相似文献
46.
47.
W. J. Firth C. T. Seaton E. M. Wright S. D. Smith M. E. Prise G. Litfin J. Mlynek F. Mitschke R. Deserno W. Lange H. J. Eichler F. Maßmann C. Zaki J. Heritage F. V. Karpushko G. V. Simitsyn J. A. Martin-Pereda M. A. Muriel P. W. Smith W. J. Tomlinson Ch. Harder K. Y. Lau A. Yariv J. C. Khoo S. Shepard S. Nahar S. L. Zhuang 《Applied physics. B, Lasers and optics》1982,28(2-3):131-141
48.
An electrochemical sensor with two soluble enzymes allows assay of 0.1–10 mM, l- carnitine with an accuracy of 2%. The assay takes about 2 min. The first enzyme, carnitine dehydrogenase, catalyzes the oxidation of l-carnitine by NAD+. The NADH formed is oxidized by hexacyanoferrate(III) in a reaction catalyzed by diaphorase, and the hexacyanoferrate(II) produced is oxidized by electrolysis at 0.3 V. The sensor can be used for several days. 相似文献
49.
van der Eerden AM Visser T Nijhuis TA Ikeda Y Lepage M Koningsberger DC Weckhuysen BM 《Journal of the American Chemical Society》2005,127(10):3272-3273
Atomic XAFS is a very attractive technique for probing electronic properties of supported metal nanoclusters. For platinum nanoparticles on different supports, the technique is found to be in good agreement with infrared CO adsorption measurements. The advantages of AXAFS, however, are that no probe molecule is required and that real-time measurements under reaction conditions are possible. 相似文献
50.
We consider the two-dimensional motion of a rigid structure immersed in an incompressible fluid governed by Navier–Stokes equations. The control force acts on a fixed subset of the fluid domain. We prove that our system is null controllable; that is, for small initial data, the system can be driven at rest and the structure can be driven to the origin at a given . The result holds for a structure symmetric with respect to the center of mass and for initial conditions satisfying strong compatibility conditions. To cite this article: M. Boulakia, A. Osses, C. R. Acad. Sci. Paris, Ser. I 343 (2006). 相似文献