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Dr. S. James Ratnakar Dr. Sara Chirayil Dr. Alexander M. Funk Dr. Shanrong Zhang Prof. João F. Queiró Prof. Carlos F. G. C. Geraldes Prof. Zoltan Kovacs Prof. A. Dean Sherry 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(48):21855-21860
Paramagnetic chemical exchange saturation transfer (paraCEST) agents are well-suited for imaging tissue pH because the basis of CEST, chemical exchange, is inherently sensitive to pH. Several previous pH-sensitive paraCEST agents were based on an exchanging Ln3+-bound water molecule as the CEST antenna but this design often added additional line-broadening to the bulk water signal due to T2 exchange. We report herein a pH-sensitive paraCEST agent that lacks an inner-sphere water molecule but contains one Ln-bound −OH group for CEST activation. The Yb3+ complex, Yb( 1 ), displayed a single, highly shifted CEST peak originating from the exchangeable Yb-OH proton, the frequency of which changed over the biologically relevant pH range. CEST images of phantoms ranging in pH from 6 to 8 demonstrate the potential of this agent for imaging pH. Initial rodent imaging studies showed that Gd( 1 ) remains in the vascular system much longer than anticipated but is cleared slowly via renal filtration. 相似文献
24.
Dr. Dean Strotz Dr. Julien Orts Dr. Harindranath Kadavath Dr. Michael Friedmann Dhiman Ghosh Dr. Simon Olsson Dr. Celestine N. Chi Aditya Pokharna Prof. Dr. Peter Güntert Dr. Beat Vögeli Prof. Dr. Roland Riek 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(49):22316-22323
Protein allostery is a phenomenon involving the long range coupling between two distal sites in a protein. In order to elucidate allostery at atomic resoluion on the ligand-binding WW domain of the enzyme Pin1, multistate structures were calculated from exact nuclear Overhauser effect (eNOE). In its free form, the protein undergoes a microsecond exchange between two states, one of which is predisposed to interact with its parent catalytic domain. In presence of the positive allosteric ligand, the equilibrium between the two states is shifted towards domain–domain interaction, suggesting a population shift model. In contrast, the allostery-suppressing ligand decouples the side-chain arrangement at the inter-domain interface thereby reducing the inter-domain interaction. As such, this mechanism is an example of dynamic allostery. The presented distinct modes of action highlight the power of the interplay between dynamics and function in the biological activity of proteins. 相似文献
25.
Dr. Takaaki Mitsuhashi Dr. Lena Barra Zachary Powers Volga Kojasoy Andrea Cheng Feng Yang Dr. Yoshimasa Taniguchi Dr. Takashi Kikuchi Prof. Dr. Makoto Fujita Prof. Dr. Dean J. Tantillo Prof. Dr. John A. Porco Jr Prof. Dr. Ikuro Abe 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(52):23980-23989
Fungal meroterpenoids are a diverse group of hybrid natural products with impressive structural complexity and high potential as drug candidates. In this work, we evaluate the promiscuity of the early structure diversity-generating step in fungal meroterpenoid biosynthetic pathways: the multibond-forming polyene cyclizations catalyzed by the yet poorly understood family of fungal meroterpenoid cyclases. In total, 12 unnatural meroterpenoids were accessed chemoenzymatically using synthetic substrates. Their complex structures were determined by 2D NMR studies as well as crystalline-sponge-based X-ray diffraction analyses. The results obtained revealed a high degree of enzyme promiscuity and experimental results which together with quantum chemical calculations provided a deeper insight into the catalytic activity of this new family of non-canonical, terpene cyclases. The knowledge obtained paves the way to design and engineer artificial pathways towards second generation meroterpenoids with valuable bioactivities based on combinatorial biosynthetic strategies. 相似文献
26.
Linda Oberli Dean Caruso Colin Hall Manrico Fabretto Peter J. Murphy Drew Evans 《Advances in colloid and interface science》2014
Superhydrophobic coatings are reported as promising candidates for anti-icing applications. Various studies have shown that as well as having ultra water repellency the surfaces have reduced ice adhesion and can delay water freezing. However, the structure or texture (roughness) of the superhydrophobic surface is subject to degradation during the thermocycling or wetting process. This degradation can impair the superhydrophobicity and the icephobicity of those coatings. In this review, a brief overview of the process of droplet freezing on superhydrophobic coatings is presented with respect to their potential in anti-icing applications. To support this discussion, new data is presented about the condensation of water onto physically decorated substrates, and the associated freezing process which impacts on the freezing of macroscopic droplets on the surface. 相似文献
27.
He X Gui J Matthews TP Williams BB Swarts SG Grinberg O Sidabras J Wilcox DE Swartz HM 《Radiation measurements》2011,46(9):882-887
Rapid and accurate retrospective dosimetry is of critical importance and strategic value for the emergency medical response to a large-scale radiological/nuclear event. One technique that has the potential for rapid and accurate dosimetry measurements is electron paramagnetic resonance (EPR) spectroscopy of relatively stable radiation-induced signals (RIS) in fingernails and toenails. Two approaches are being developed for EPR nail dosimetry. In the approach using ex vivo measurements on nail clippings, accurate estimation of the dose-dependent amplitude of the RIS is complicated by the presence of mechanically-induced signals (MIS) that are generated during the nail clipping. Recent developments in ex vivo nail dosimetry, including a thorough characterization of the MIS and an appreciation of the role of hydration and the development of effective analytic techniques, have led to improvements in the accuracy and precision of this approach. An in vivo nail dosimetry approach is also very promising, as it eliminates the problems of MIS from the clipping and it has the potential to be an effective and efficient approach for field deployment. Two types of EPR resonators are being developed for in vivo measurements of fingernails and toenails. 相似文献
28.
Sylvestre P. J. T. Bachollet Dean C. Cocker Harry Adams Prof. Joseph P. A. Harrity 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(40):12889-12893
The aza‐Diels–Alder cycloaddition of 1,2,4‐triazines with alkynes offers a rapid and convenient method for the synthesis of highly substituted pyridines, but often requires harsh conditions and long reaction times. The present study offers a solution to these limitations by use of a temporary tether established by a Lewis acid–base complexation of in situ generated alkynylboranes and triazines bearing a Lewis basic donor. The cycloaddition reactions take place within 20 min at 40 °C and provide direct access to a broad range of pyridines with complete and predictable regiocontrol. The carbon?boron bond can be further functionalised by cross‐coupling allowing further functionality to be introduced after cycloaddition. 相似文献
29.
Giovannia A. Pereira Laura Ball A. Dean Sherry Joop A. Peters Carlos F. G. C. Geraldes 《Helvetica chimica acta》2009,92(11):2532-2551
The three‐dimensional structures in aqueous solution of the entire series of the Ln3+ complexes [Ln(DOTP*‐Et)]? (formed from the free ligand P,P′,P″,P′′′‐[1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetrayltetrakis(methylene)]tetrakis[P‐ethylphosphinic acid] (H4DOTP*‐Et) were studied by NMR techniques to rationalize the parameters governing the relaxivity of the Gd3+ complex and evaluate its potential as MRI contrast agent. From the 1H‐ and 31P‐NMR lanthanide‐induced‐shift (LIS) values, especially of the [Yb(DOTP*‐Et)]? complex, it was concluded that the [Ln(DOTP*‐Et)]? complexes adopt in solution twisted square antiprismatic coordination geometries which change gradually their coordination‐cage structure along the lanthanide series. These complexes have no inner‐sphere‐H2O coordination, and preferentially have the (R,R,R,R) configuration of the P‐atoms in the pendant arms. Self‐association was observed in aqueous solution for the tetraazatetrakisphosphonic acid ester complexes [Ln(DOTP*‐OEt)]? (=[Ln(DOTP‐Et)]?) and [Ln(DOTP*‐OBu)]? (=[Ln(DOTP‐Bu)]?) at and above 5 mM concentration, through analysis of 31P‐NMR, EPR, vapor‐pressure‐osmometry, and luminescence‐spectroscopic data. The presence of the cationic detergent cetylpyridinium chloride (CPC; but not of neutral surfactants) shifts the isomer equilibrium of [Eu(DOTP*‐OBu)]? to the (S,S,S,S) form which selectively binds to the cationic micelle surface. 相似文献
30.
Nari N. Talaty Kristina Beck Helene Citeau Kristin Kirschbaum Dean M. Giolando Prof. Dr. 《无机化学与普通化学杂志》2009,635(1):53-63
A new single‐source precursor, [SnCl4{OC(H)OC2H5}2], prepared by treating tin tetrachloride with ethyl formate (1:2 ratio) was developed for the deposition of tin oxide thin films on glass substrates. The compound [SnCl4{OC(H)OC2H5}2] is highly volatile and provides very high growth rates (up to 100Å s?1 at 560 °C) in an atmospheric pressure chemical vapor deposition (APCVD) reactor. More significantly, the compound does not decompose to tin oxide below 320 °C, thereby minimizing the formation of particles in the vapor above the growing tin oxide film. To prepare highly conducting fluorine doped tin oxide (SnO2:F) films 2,2,2‐trifluoroethyl trifluoroacetate was used as the source of fluoride. High quality SnO2:F films were deposited at 560 °C with a flow rate of 2 mL fluoride reagent hr?1; typical film properties are resistivity of 5.9 X 10?4 Ω cm, Hall mobility of 27.3 cm2 V?1 s?1, carrier concentration of 3.9 X 1020 cm?3 and percent transmission ranging from 86 to 88 %. The best films of SnO2:F possess transparencies as high as 90 % (750 nm), sheet resistances as low as 7 Ω sq?1 and Haacke's figure of merit as high as 29 X 10?3 (750 nm). The newly developed APCVD reactor and the chemistry were optimized with respect to structural, electrical and optical properties of the films by adjusting the substrate temperature, gas flow rates and the amount of fluoride present in the vapor stream. Growth rates with respect to deposition time, substrate temperature and flow rates of precursors were found to be similar for both undoped (SnO2) and doped (SnO2:F) samples. The SnO2:F films possess larger grains than the SnO2 which may account for the lower resistivity and the higher mobility in the SnO2:F samples. 相似文献