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851.
Under the influence of guanidine, 1,3-benzodioxolane, 1,4-benzodioxane, and 1,5-benzodioxepane analogs of isoflavone are converted into 2-aminopyrimidine derivativesTranslated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 636–640, September–October, 1994. 相似文献
852.
S. S. Mochalov F. M. Abdel'razek T. P. Surikova Yu. S. Shabarov 《Chemistry of Heterocyclic Compounds》1980,16(4):339-344
In the nitration of 5-formyl-substituted 2-cyclopropylfurans and the corresponding thiophenes, in addition to the formation of the corresponding 3-nitro derivative the replacement of the formyl group by a nitro group takes place. For a thiophene derivative the latter direction of the reaction is observed to a substantially smaller degree. Under nitration conditions, 5-formylsylvane is converted only into 5-nitrosylvane, while the corresponding formylmethylthiophene is nitrated exclusively in position 3. The difference observed in the behavior on nitration of the furans and thiophenes studied is explained by the different degrees of participation of the heteroatom in the delocalization of the charges in the heterocyclic ipso-ions formed as intermediates.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 455–460, April, 1980. 相似文献
853.
S.P. So 《Chemical physics letters》1979,61(1):83-84
Ab initio Hartree—Fock calculations with STO-3G functions have been performed to determine the structure (1.371 Å and 95.33°) of SH+3 and the proton affinity (≈196 kcal/mol) of H2S. Inclusion of a sulphur 3d function in the basis has been found essential to give a better geometry of SH+3. 相似文献
854.
The valency of the ions Fe, Cr, Cu, Sb, incorporated in PZT 95/5 ceramics, is evaluated from the viewpoint of a correlation between the mean radius of the ions at the octahedral site and the two parameters: the temperature of the antiferroelectric-ferroelectric phase transition, and the volume of the unit cubic cell. It is found that Fe and Cr enter as Fe2+ and Cr2+ at the B site. Experiments suggest that Cu is incorporated at the B site as Cu+ and Cu2+ and that Sb enters partly at the A site as Sb3+ and mainly at the B site as Sb5+. 相似文献
855.
Yu. I. Yermakov Yu. P. Grabovskii A. M. Lazutkin 《Reaction Kinetics and Catalysis Letters》1974,1(3):345-349
The kinetics of 1,4-cis polymerization of butadiene on a catalyst formed by reacting bis(-allyl) nickel with silica have been studied. The rate of polymerization is first order with respect to the monomer concentration. The apparent activation energy is 9.5±0.5 kcal/mol. The possible structure of the active center and the scheme of polymer chain growth have been discussed.
I,4- , -- . . 9,5±0,5 /. .相似文献
856.
Examination of a large number of spectra indicates that bis-unsaturated compounds commonly undergo a skeletal rearrangement in which part or all or the bridging moiety is eliminated, often with concomitant loss of hydrogen atoms. The spectra of labeled azobenzene, diphenyl sulfide, and their p,p′-dimethyl derivatives show that scrambling of hydrogen atoms precedes or accompanies such rearrangements, in contrast to the loss of a p-methyl group from the latter derivatives. These results are rationalized in terms of the radical site formed on one unsaturated functional group attacking the polarizable π-electrons of the other unsaturated group. 相似文献
857.
V. P. Sheverdov O. V. Ershov A. V. Eremkin O. E. Nasakin I. N. Bardasov V. A. Tafeenko 《Russian Journal of Organic Chemistry》2005,41(12):1757-1763
β,β,γ,γ-Tetracyanoalkanones react with acrolein at a high rate to afford the corresponding 2-substituted 4-formyl-3-cyclopentene-1,1,2-tricarbonitriles in high yields. The reaction occurs under mild conditions and is quite applicable for modification of natural and biologically active compounds possessing an R′CHC(O)CR3 fragment to obtain their derivatives containing three cyano groups. 相似文献
858.
Tzanetos NP Dracopoulos V Kallitsis JK Deimede VA 《Langmuir : the ACS journal of surfaces and colloids》2005,21(20):9339-9345
A detailed study of the self-assembly ability of triblock coil-rod-coil copolymers containing a rigid di(styryl)-anthracene segment covalently linked to oxadiazole-based blocks and their binary blends with oxadiazole-based homopolymers is presented here. The self-organized microdomains seem to pack into a fascinating ordered hexagonal structure obtained at a critical concentration without any significant influence of the sample preparation method, based on evidence obtained by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and fluorescence microscopy studies. The compatibilization efficiency of these coil-rod-coil copolymers in polymer blends composed of an electron-accepting polyoxadiazole and a luminescent polyanthracene-based pair was studied by atomic force microscopy (AFM). The common feature of all observed morphologies is the compatibilizing function of the rod-coil molecule, which intercalates between the incompatible domains to prevent the formation of well-defined phase separated nanostructured surfaces. 相似文献
859.
Lerbret A Bordat P Affouard F Descamps M Migliardo F 《The journal of physical chemistry. B》2005,109(21):11046-11057
The structural properties resulting from the reciprocal influence between water and three well-known homologous disaccharides, namely, trehalose, maltose, and sucrose, in aqueous solutions have been investigated in the 4-66 wt % concentration range by means of molecular dynamics computer simulations. Hydration numbers clearly show that trehalose binds to a larger number of water molecules than do maltose or sucrose, thus affecting the water structure to a deeper extent. Two-dimensional radial distribution functions of trehalose solutions definitely reveal that water is preferentially localized at the hydration sites found in the trehalose dihydrate crystal, this tendency being enhanced when increasing trehalose concentration. Over a rather wide concentration range (4-49 wt %), the fluctuations of the radius of gyration and of the glycosidic dihedral angles of trehalose indicate a higher flexibility with respect to maltose and sucrose. At sugar concentrations between 33 and 66 wt %, the mean sugar cluster size and the number of sugar-sugar hydrogen bonds formed within sugar clusters reveal that trehalose is able to form larger clusters than sucrose but smaller than maltose. These features suggest that trehalose-water mixtures would be more homogeneous than the two others, thus reducing both desiccation stresses and ice formation. 相似文献
860.
By mapping the interactions of colloidal particles onto the problem of minimizing areas, the physics of foams can be used to understand the phase diagrams of both charged and fuzzy colloids. We extend this analogy to study the elastic properties of such colloidal crystals and consider the face-centered cubic, body-centered cubic and A15 lattices. We discuss two types of soft interparticle potentials corresponding to charged and fuzzy colloids, respectively, and we analyze the dependence of the elastic constants on density as well as on the parameters of the potential. We show that the bulk moduli of the three lattices are generally quite similar, and that the shear moduli of the two non-close-packed lattices are considerably smaller than in the face-centered cubic lattice. We find that in charged colloids, the elastic constants are the largest at a finite screening length, and we discuss a shear instability of the A15 lattice. 相似文献