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91.
Paul Gesche Franois Klinger Andreas Riesen Thophile Tschamber Margareta Zehnder Jacques Streith 《Helvetica chimica acta》1987,70(8):2087-2097
Saponification of homodiazepine 1a and 1b , in the absence of any proton donors, led to the formation of the 6π electron anionic species A which, by virtue of a 1,5-electrocyclization, is in equilibrium with the allylic anion B . This latter tricyclic species is thermodynamically less favoured than its bicyclic isomer A . Nevertheless, B could be trapped by acylation and led tupe- 2 compounds which are the major reaction products. This is due to the fact that B is more nucleophilic and, therefore, much more reactive than A . The transoid topology of the tricyclic products 2 was demonstrated by 1H-NMR and by an X-ray diagram of 2d . The transoid geometry of 2 is a consequence of a torquospecific 1,5-electrocyclization (of A ), which is due to a steric, and possibly even to an electronic factor. 相似文献
92.
In ternary aqueous solutions, hydrophobic solutes such as alcohols tend to aggregate with surfactants to form mixed micelles. These systems can be studied by meas of the functions of transfer of hydrophobic solutes from water to aqueous solutions of surfactant. These thermodynamic functions often go through extrema in the critical micellar concentration (CMC) region of the surfactant. A simple model based on interactions between surfactant and hydrophobic solute monomers, on the distribution of the hydrophobic solute between water and the micelles and on the shift in the CMC induced by the hydrophobic solute, can simulate the magnitude and trends of the transfer functions using parameters which are mostly derived from the binary systems. In order to check the model more quantitatively, volumes and heat capacities of transfer of alcohols from water to aqueous solutions of a nonionic surfactant, octyldimethylamine oxide, were measured. A quantitative agreement was achieved with three adjustable parameters. Good fits are also obtained for the transfers to the ionic surfactants, octylamine hydrobromide and sodium dodecylsulfate. When the equilibrium displacement contribution is small, the distribution constants and the partial molar properties of the alcohols in the micellar phase agree well with the parameters obtained with similar models. 相似文献
93.
Naveau A Monteil-Rivera F Dumonceau J Catalette H Simoni E 《Journal of colloid and interface science》2006,293(1):27-35
Understanding sorption processes is fundamental for the prediction of radionuclide migration in the surroundings of a deep geological disposal of high-level nuclear wastes. Pyrite (FeS2) is a mineral phase often present as inclusions in temperate soils. Moreover, it constitutes an indirect corrosion product of steel, a containment material that is candidate to confine radionuclides in deep geological disposals. The present study was thus initiated to determine the capacity of pyrite to immobilize Sr(II) and Eu(III). An air oxidized pyrite and a freshly acid-washed (non-oxidized) pyrite were used in background electrolytes of varying reducing-oxidizing ability (NaCl, NH3OHCl, and NaClO4) to study the sorption of both cationic species. The sorptive capacity of pyrite appeared directly correlated to the oxidation of the surface. Non-oxidized pyrite had nearly no affinity for the studied cations whereas Sr(II) and Eu(III) species were significantly retained by oxidized pyrite surface. Using the surface complexation theory, sorption mechanisms were modeled with the Fiteql v3.2 and the Jchess 2.0 codes. Sorption of both Sr and Eu was well fitted, assuming hydroxylated species as the major surface species. This study demonstrates that not only the components of a barrier but also the redox conditions and specifications should be well characterized to predict transport of contaminants in the surrounding of a nuclear wastes disposal. 相似文献
94.
This work presents a technique to simplify overcrowded proton spectra in chiral liquid crystal solvents using rotation of the sample near the magic angle, VASS, combined with homonuclear selective refocusing 2D NMR experiments, SERF. This methodology provides a powerful tool to visualise enantiomers out of unresolved proton spectra. A modified SERF sequence is presented where the resulting 2D spectrum can be phased to increase the resolution. Accurate enantiomeric excesses are determined that are not possible to measure on static samples. Two examples are presented. 相似文献
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The motivations to realize nuclear breeder reactors are developed in the present context of a strong growth in electronuclear power stations in many countries, using mostly moderated and water cooled reactors.The past studies can be of a substantial profit in France and, to a lesser degree, in other countries of the EU. However, to use fully the 238 uranium isotope, the materials for these breeders must withstand much harder radiation than those for water reactors. The power densities and thermal gradients will also be much more intense. The mechanical stresses, both static and dynamic, will be large and will act on materials with altered mechanical properties. Fuel elements will have to be produced with materials already irradiated several times and therefore showing such alterations.A field of studies concerning materials and their mechanical behavior in new and severe conditions is sketched here, both in construction and working conditions, together with proposed necessary instrumentation and research orientations. 相似文献
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Optimal performance laminar chromatography and automated multiple development chromatography are relatively recent techniques of planar chromatography that can be applied with success in plant material analysis. Therefore, these methods are used to study plant extracts and constituents belonging to different chemical classes of secondary metabolism: heterocyclic oxygen compounds (coumarins, flavonoids, and anthocyanins), alkaloids and quaternary ammonium salts, cannabinoids, essential oils, ginsenosides, and cardiac heterosides. Generally, the results obtained with these methods are good, and in most cases they compare with those of thin-layer chromatography. 相似文献
100.
Merdy P Guillon E Aplincourt M Dumonceau J Vezin H 《Journal of colloid and interface science》2002,245(1):24-31
Spectroscopic and physicochemical data, X-ray photoelectron spectroscopy (XPS), solid-state (13)C cross-polarization magic-angle-spinning NMR, GC/MS, specific surface area, site density, and surface acidity constants have been recorded or determined for a ligno-cellulosic substrate (LS) extracted from straw. Its copper(II)-bound ability has also been studied. The LS solid that exhibits two types of binding sites, carboxylic and phenolic groups, has a great affinity for copper(II), with a maximum of adsorption at around 4 mg g(-1) as early as the pH reaches 6. The structural characterization of the Cu(II) surface complexes has been investigated using EPR spectroscopy. The CuO(4) chromophore of the inner-sphere surface complexes is a slightly distorted square. A surface oxidation occurred simultaneously, which leads to semiquinonic radicals. Furthermore, our empirical approach, which used a correlation between thermodynamics data and EPR parameters, has led to a surface complexation constant log beta equal to 12.6. This indicates that copper(II) surface complexes are relatively stable. 相似文献