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71.
Chitosan is industrially acquired by the alkaline N-deacetylation of chitin. Chitin belongs to the β-N-acetyl-glucosamine polymers, providing structure, contrary to α-polymers, which provide food and energy. Another β-polymer providing structure is hyaluronan. A lot of studies have been performed on chitosan to explore its industrial use. Since chitosan is biodegradable, non-toxic, bacteriostatic, and fungistatic, it has numerous applications in medicine. Hyaluronan, one of the major structural components of the extracellular matrix in vertebrate tissues, is broadly exploited in medicine as well. This review summarizes the main areas where these two biopolymers have an impact. The reviewed areas mostly cover most medical applications, along with non-medical applications, such as cosmetics. 相似文献
72.
3T3 and VH10 cells were subjected to oxidative damage by hydroxyl radicals generated from Cu(II) ions and ascorbate. The presence of reactive oxygen and nitrogen species in cells was determined using fluorescent dyes. MitoQ—a mitochondrially targeted antioxidant—was examined to prevent cell death and was compared with trolox as a reference standard serving as an antioxidant. MitoQ at lower concentrations (up to 500 nM) prevented damage of mitochondria and thereby increased viability of cells. However, at higher concentrations (over 500 nM) MitoQ decreased the viability of both strains of cells. The last observation indicates that the application of MitoQ should be evaluated also from the point of its cell-destructive potential. 相似文献
73.
Ladislav Adamec 《Applications of Mathematics》1997,42(4):293-309
The aim of the paper is to give some preliminary information concerning a class of nonlinear differential equations often used in physical chemistry and biology. Such systems are often very large and it is well known that where studying properties of such systems difficulties rapidly increase with their dimension. One way how to get over the difficulties is to use special forms of such systems. 相似文献
74.
Ladislav ervinka 《Journal of Non》1992,150(1-3):136-139
Modeling studies were performed for a rigid rod polyester with flexible side-chains in order to simulate X-ray scattering features in the medium angle scattering region, i.e., for a scattering vector from 0.2 to 1.8 Å−1. A typical non-crystalline peak was observed at 1.46 Å−1 with a shoulder at 1.75 Å−1 and its position and intensity could be interpreted on the basis of a dense ordering (clustering) of flexible side chains. 相似文献
75.
Sychrovský V Budesínský M Benda L Spirko V Vokacova Z Sebestík J Bour P 《The journal of physical chemistry. B》2008,112(6):1796-1805
The l-alanyl-l-alanine (AA) molecule behaves differently in acidic, neutral, and basic environments. Because of its molecular flexibility and strong interaction with the aqueous environment, its behavior has to be deduced from the NMR spectra indirectly, using statistical methods and comparison with ab initio predictions of geometric and spectral parameters. In this study, chemical shifts and indirect spin-spin coupling constants of the AA cation, anion, and zwitterion were measured and compared to values obtained by density functional computations for various conformers of the dipeptide. The accuracy and sensitivity of the quantum methods to the molecular charge was also tested on the (mono)-alanine molecule. Probable AA conformers could be identified at two-dimensional potential energy surfaces and verified by the comparison of the computed parameters with measured NMR data. The results indicate that, whereas the main-chain peptide conformations of the cationic (AA+) and zwitterionic (AAZW) forms are similar, the anion (AA-) adopts also another, approximately equally populated conformer in the aqueous solution. Additionally, the NH2 group can rotate in the two main chain conformations of the anionic form AA-. According to a vibrational quantum analysis of the two-dimensional energy surfaces, higher-energy conformers might exist for all three charged AA forms but cannot be detected directly by NMR spectroscopy because of their small populations and short lifetimes. In accord with previous studies, the NMR parameters, particularly the indirect nuclear spin-spin coupling constants, often provided an excellent probe of a local conformation. Generalization to peptides and proteins, however, has to take into account the environment, molecular charge, and flexibility of the peptide chain. 相似文献
76.
The paper concerns with analysis of operational complexity of company supplier–customer relations. Well-known approach for measuring of operational complexity is based upon entropy. However, there are several approaches thereon. In the first part, we discuss various general measures of uncertainty of states, the power entropies in particular. In the second part, we use Shannon entropy as a base framework for our two case studies—the first, a supplier–customer system which implements managerial thresholds for processing product delivery term deviations, the second, a supplier system of the most important commodity in brewery industry, the malted barley. In both cases, we assume an existence of problem-oriented databases, which contain detailed records of all product orders, deliveries and forecasts in quantity and time having been scheduled and realized. Our general procedure elaborated consists of three basic steps—pre-processing of data with consistency checks in Java, calculation of histograms and empirical distribution functions, and finally, evaluation of conditional entropy. The last two steps are realized by Mathematica modules. Illustrative results of operational complexity measurement using entropy are provided for both case studies. 相似文献
77.
Ladislav Androvič Jan Bartáček Miloš Sedlák 《Research on Chemical Intermediates》2016,42(6):5133-5145
This mini-review describes recent developments and trends in the area of syntheses and applications of azo compounds, which are planned to act as initiators of radical reactions, particularly polymerizations. The paper reports chemical modifications of well-known initiators (AIBN, etc.) or variants of syntheses of new types of these compounds. The chemical modifications of basic skeletons of azo initiators are discussed in the context with their properties and applications. Also discussed are the contemporary trends in the development of these initiators, particularly in preparation of microparticles and nanoparticles of polymers or hybrid inorganic–organic microparticles and nanoparticles prepared for intentional studies and applications. 相似文献
78.
Jan Lokaj Jan Moncol Monika Polakova Ladislav Petru? 《Journal of chemical crystallography》2012,42(1):89-92
Abstract
The crystal structure of 2-cyclohexylethyl α-d-mannopyranoside (C14H26O6, Mr = 290.35) has been determined by single crystal X-ray diffraction analysis. The compound crystallizes in the monoclinic crystal system with space group C2 and unit cell parameters: a = 14.2420(2), b = 6.0320(1), c = 17.8065(3) ?, β = 102.131(2)° and Z = 4. The final reliability index is 0.0256 for 2,654 observed reflections. The one molecule of 2-cyclohexylethyl α-d-mannopyranoside is localized in independent part of unit cell. The molecules of 2-cyclohexylethyl α-d-mannopyranoside are linked through O–H···O hydrogen bond into bilayer. 相似文献79.
Ladislav Novotny 《Fresenius' Journal of Analytical Chemistry》1999,363(1):55-58
The adsorption of the polyether-antibiotic monensin from an aqueous solution on mercury was used to investigate the effect
of the decreasing size of a stationary mercury drop electrode on the shape of the voltammetric desorption peak of the surfactant.
The change of the i-E curve indicated an acceleration of the transport of the surfactant to the electrode as well as of time-dependent
changes in the adsorption layer. A decrease of the radius of the hanging mercury drop electrode from 220 μm to 80 μm at a
constant accumulation time of tac = 70 s resulted in an about 4-fold increase of the evaluated signal (i-E pre-wave) of monensin. A 7-fold increase of the
voltammetric desorption peak of monensin at conc. 5 · 10–7 mol/L was observed as result of a compressive accumulation of the surfactant due to a contraction of the mercury drop electrode.
A scheme of an apparatus for voltammetric/polarographic measurements by means of the contractible (compressible) mercury drop
electrode is described. The controlled contraction of the electrode surface is presented together with preliminary results
covering a new way of accumulation of surfactants, new accumulation effects, effective in adsorptive voltammetry, and other
electroanalytical techniques.
Received: 26 March 1998 / Revised: 14 July 1998 / Accepted: 15 July 1998 相似文献
80.
Grid convergence studies for subsonic and transonic flows over airfoils are presented in order to compare the accuracy of several spatial discretizations for the compressible Navier–Stokes equations. The discretizations include the following schemes for the inviscid fluxes: (1) second-order-accurate centered differences with third-order matrix numerical dissipation, (2) the second-order convective upstream split pressure scheme (CUSP), (3) third-order upwind-biased differencing with Roe's flux-difference splitting, and (4) fourth-order centered differences with third-order matrix numerical dissipation. The first three are combined with second-order differencing for the grid metrics and viscous terms. The fourth discretization uses fourth-order differencing for the grid metrics and viscous terms, as well as higher-order approximations near boundaries and for the numerical integration used to calculate forces and moments. The results indicate that the discretization using higher-order approximations for all terms is substantially more accurate than the others, producing less than two percent numerical error in lift and drag components on grids with less than 13,000 nodes for subsonic cases and less than 18,000 nodes for transonic cases. Since the cost per grid node of all of the discretizations studied is comparable, the higher-order discretization produces solutions of a given accuracy much more efficiently than the others. 相似文献