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951.
Maekawa H Toniolo C Broxterman QB Ge NH 《The journal of physical chemistry. B》2007,111(12):3222-3235
Two-dimensional infrared (2D IR) spectra of Calpha-alkylated model octapeptides Z-(Aib)8-OtBu, Z-(Aib)5-L-Leu-(Aib)2-OMe, and Z-[L-(alphaMeVal)]8-OtBu have been measured in the amide I region to acquire 2D spectral signatures characteristic of 3(10)- and alpha-helical conformations. Phase-adjusted 2D absorptive spectra recorded with parallel polarizations are dominated by intense diagonal peaks, whereas 2D rephasing spectra obtained at the double-crossed polarization configuration reveal cross-peak patterns that are essential for structure determination. In CDCl3, all three peptides are of the 3(10)-helix conformation and exhibit a doublet cross-peak pattern. In 1,1,1,3,3,3-hexafluoroisopropanol, Z-[L-(alphaMeVal)]8-OtBu undergoes slow acidolysis and 3(10)-to-alpha-helix transition. In the course of this conformational change, its 2D rephasing spectrum evolves from an elongated doublet, characteristic of a distorted 3(10)-helix, to a multiple-peak pattern, after becoming an alpha-helix. The linear IR and 2D absorptive spectra are much less informative in discerning the structural changes. The experimental spectra are compared to simulations based on a vibrational exciton Hamiltonian model. The through-bond and through-space vibrational couplings are modeled by ab initio coupling maps and transition dipole interactions. The local amide I frequency is evaluated by a new approach that takes into account the effects of hydrogen-bond geometry and sites. The static diagonal and off-diagonal disorders are introduced into the Hamiltonian through statistical models to account for conformational fluctuations and inhomogeneous broadening. The sensitivity of cross-peak patterns to different helical conformations and the chain length dependence of the spectral features for short 3(10)- and alpha-helices are discussed. 相似文献
952.
Reactive oxygen species (ROS) have important functions in cell signaling and, when present at overly high levels, may cause oxidation of important biological molecules. Kinetic models to study diffusion of ROS inside of mitochondria often assume dynamics similar to that in solution. However, it is well-known that separation of proteins in the cytosol or inside of mitochondria, where ROS are most predominant, can be smaller than 1 nm. Diffusion of small molecules can be better regarded as a percolation process. In this article, we report results of diffusivity and residence of water and hydrogen peroxide in the proximity of proteins. In carrying out this study, we found some issues with the conventional way of computing residence times by means of survival time correlation functions. The main problem is that particles remaining on the surface of a protein for long times and for which one has very poor statistics contribute significantly to the short time behavior of the survival time correlation function. We mathematically describe this problem and propose methodology to overcome it. 相似文献
953.
Espinoza Catalán L Carrasco Altamirano H Cuellar Fritis M Gallardo Araya C Catalán Marín K 《Molecules (Basel, Switzerland)》2007,12(3):318-327
A selective route for the degradation of the unsaturated side chain of ent-labdanes has been devised, giving two useful synthons: 2beta-acetoxy-14,15,17-trinor-ent-labdane-8,13- dione (5) and 2beta-acetoxy-14,15-dinor-ent-labd-8(17)-en-13-one (7), the use of which for the preparation of terpenylquinone derivatives shall be reported elsewhere. 相似文献
954.
Prof. Claudio Toniolo Dr. Marco Crisma Prof. Alessandro Moretto Dr. Cristina Peggion Prof. Fernando Formaggio Prof. Carlos Alemán Prof. Carlos Cativiela Prof. Chandrasekharan Ramakrishnan Prof. Padmanabhan Balaram 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(40):13866-13877
Among the various types of α‐peptide folding motifs, δ‐turn, which requires a central cis‐amide disposition, has been one of the least extensively investigated. In particular, this main‐chain reversal topology has been studied in‐depth neither in linear/cyclic peptides nor in proteins. This Minireview article assembles and critically analyzes relevant data from a literature survey on the δ‐turn conformation in those compounds. Unpublished results from recent conformational energy calculations and a preliminary solution‐state analysis on a small model peptide, currently ongoing in our laboratories, are also briefly outlined. 相似文献
955.
Prof. Steven V. Ley Daniel E. Fitzpatrick Dr. Rebecca M. Myers Dr. Claudio Battilocchio Dr. Richard. J. Ingham 《Angewandte Chemie (International ed. in English)》2015,54(35):10122-10136
In this Review we describe how the advent of machines is impacting on organic synthesis programs, with particular emphasis on the practical issues associated with the design of chemical reactors. In the rapidly changing, multivariant environment of the research laboratory, equipment needs to be modular to accommodate high and low temperatures and pressures, enzymes, multiphase systems, slurries, gases, and organometallic compounds. Additional technologies have been developed to facilitate more specialized reaction techniques such as electrochemical and photochemical methods. All of these areas create both opportunities and challenges during adoption as enabling technologies. 相似文献
956.
Differences in Dynamics between Crosslinked and Non‐Crosslinked Hyaluronates Measured by using Fast Field‐Cycling Relaxometry 下载免费PDF全文
Enrico Ravera Marco Fragai Giacomo Parigi Prof. Claudio Luchinat 《Chemphyschem》2015,16(13):2803-2809
The dynamic properties of water molecules in gels containing linear and crosslinked hyaluronic acid polymers are investigated by using an integrated approach that includes relaxometry, solid‐state NMR spectroscopy, and scanning electron microscopy. A model‐free analysis of field‐dependent nuclear relaxation is applied to obtain information on mobility and the population of different pools of water molecules in the gels. Differences between linear and crosslinked hyaluronic acid polymers are observed, indicating that crosslinking increases both the fraction and the correlation time of water molecules with slow dynamics. 相似文献
957.
Faramarz S. Gard Diego M. Santos María B. Daizo José L. Mijares Patricia B. Bozzano Claudio A. Danón María Reinoso Emilia B. Halac 《Surface and interface analysis : SIA》2020,52(11):755-769
Raman spectroscopy, optical microscopy, scanning electron microscopy (SEM), and electron probe microanalysis (EPMA) were used to study pigments on an Egyptian cartonnage from the Ptolemaic period (305–30 bc ). The surface morphology of each color region was examined using backscattering (BS) and secondary electron imaging. SEM X-ray energy dispersive spectrometry and EPMA wavelength dispersive spectroscopy provided semiquantitative chemical analysis of each pigment. Raman spectroscopy was used to identify the minerals associated with the pigments. This technique confirmed the presence of cinnabar (α-HgS) in the red part of the fragments. A mixture of orpiment (As2S3) and bonazziite (β-As4S4) and/or alacránite (As8S9) was detected in the yellow regions of the fragments. The orange pigment was confirmed to be a mixture of orpiment, uzonite (χ-As4S5), and pararealgar (As4S4). Egyptian blue (CaCuSi4O10) and Egyptian green ((Cu,Ca)SiO3) pigments were detected from blue/green dark-colored regions of the fragments. 相似文献
958.
Giuseppe Buscarnera Giuseppe Dattola Claudio di Prisco 《International Journal of Solids and Structures》2011,48(13):1867-1878
In this paper the onset of instabilities in elastoplastic materials is theoretically studied and a conceptual basis for understanding the physical implications of a loss of uniqueness and/or existence of the incremental response is provided. For this purpose, the concept of test controllability is reinterpreted and mixed stress–strain loading programmes are accounted for. A set of scalar indices, the moduli of instability, related with the inception of an unstable response is introduced and their dependency on the loading programme is explicitly illustrated. The paper shows that the use of these newly defined scalar measures provides support for an alternative definition for mechanical stability, which is closely related with the mathematical notions of existence and uniqueness of the predicted incremental response. In the final section, some mathematical properties of the moduli of instability are discussed, suggesting a novel reinterpretation of other well established theories and providing additional tools for the future application of the proposed framework. 相似文献
959.
We consider a suitable scaling, called the slow Markov walk limit, for a risk process with shot noise Cox claim number process and reserve dependent premium rate. We provide large deviation estimates for the ruin probability. Furthermore, we find an asymptotically efficient law for the simulation of the ruin probability using importance sampling. Finally, we present asymptotic bounds for ruin probabilities in the Bayesian setting. 相似文献
960.
Claudio Storck Raphael Gehrer Claude Fischer Markus Wolfensberger Flurin Honegger Gerhard Friedrich Markus Gugatschka 《Journal of voice》2011,25(5):632-637