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991.
Pavel I Cota S Cînta-Pînzaru S Kiefer W 《The journal of physical chemistry. A》2005,109(44):9945-9952
The normal Raman and SERS spectra of 5-fluorouracil (5-FU) in water solution and attached to a biological artificial model (a silver colloid) at different pH values were recorded and discussed. The DFT calculation results helped us to establish for the first time the most stable resonance structure for each of the tautomeric forms (i.e., two enol and two enolate forms) and to interpret the Raman and SERS spectra. At alkaline pH, both deprotonated forms of 5-FU were found to be present in solution and to adsorb on the Ag surface in a perpendicular orientation or an orientation not significantly tilted from the surface normal. The N3-deprotonated form seems to be the dominant tautomer in the adsorbed state, more probably attached through the O7 atom. At acid pH values, the N3-deprotonated form was again found to be the mainly chemisorbed species adopting a similar orientation. The combination of these two approaches (i.e., the theoretical and experimental one) proved to be a viable candidate for inclusion in a rapid, sensitive biological method of detecting and studying such essential anticarcinogenic species or biological threats in different conditions. 相似文献
992.
From the aerial parts of Phlomis longifolia var. longifolia four iridoid glucosides, shanzhiside methyl ester (1), 5-deoxypulchelloside I (2), lamalbide (3), phlomiol (4) and three phenylethanoid glycosides, verbascoside (5), forsythoside B (6), leucosceptoside A (7) along with the caffeic acid ester, chlorogenic acid (8) were isolated. The structures of the isolated compounds were established by spectroscopic (UV, IR, 1D- and 2D-NMR, FABMS) and chemical evidence. The structure elucidation of the iridoid compounds 2 and 3 are discussed in detail. 相似文献
993.
The construction and basic characteristics of a new liquid-state Hg(2+)-selective membrane electrode are discussed. The membrane consists of the PAN chelate of Hg(II), dissolved in CHCl(3). The linear response range of the electrode is 10(-1) -10(-5)M Hg(2+) with a slope of 28.5 mV/decade of concentration. The response time of the electrode in dilute solutions is less than 3 min, and in concentrated solutions it is only a few sec. The electrode has been used in precipitation or complexation titrations in which Hg(2+) is involved (e.g., in the determination of some organic compounds in drug synthesis). 相似文献
994.
We study the Nash equilibria of a class of two-person nonlinear, deterministic differential games where the players are weakly coupled through the state equation and their objective functionals. The weak coupling is characterized in terms of a small perturbation parameter . With =0, the problem decomposes into two independent standard optimal control problems, while for 0, even though it is possible to derive the necessary and sufficient conditions to be satisfied by a Nash equilibrium solution, it is not always possible to construct such a solution. In this paper, we develop an iterative scheme to obtain an approximate Nash solution when lies in a small interval around zero. Further, after requiring strong time consistency and/or robustness of the Nash equilibrium solution when at least one of the players uses dynamic information, we address the issues of existence and uniqueness of these solutions for the cases when both players use the same information, either closed loop or open loop, and when one player uses open-loop information and the other player uses closed-loop information. We also show that, even though the original problem is nonlinear, the higher (than zero) order terms in the Nash equilibria can be obtained as solutions to LQ optimal control problems or static quadratic optimization problems.This research was supported in part by the US Department of Energy under Grant DE-FG-02-88-ER-13939.Paper presented at the 29th IEEE Conference on Decision and Control, Honolulu, Hawaii, 1990. 相似文献
995.
The effectiveness of the usual harmonic oscillator basis is demonstrated on a wide class of Schrödinger Hamiltonians with various spectral properties. More specifically, it is shown numerically that an appropriately scaled Hermite–Weber basis yields extremely accurate results not only for the energy eigenvalues which differ slighly from the harmonic oscillator levels, but also for the states which reflect a purely anharmonic character. 相似文献
996.
Oana Carp Luminita Patron G. Pascu Ioana Mindru N. Stanica 《Journal of Thermal Analysis and Calorimetry》2006,84(2):391-394
Nickel–zinc ferrites have been synthesized via thermal decomposition of polynuclear coordination compounds containing as ligand the anion of malic acid, namely (NH4)[Fe2NixZn1–x(C4H4O5)(OH)3]·nH2O (x =0.25, 0.5 and 0.75, n=3 and 5). A comparison between the thermal behaviour of the studied polynuclear coordination compounds is inferred. Fe2NixZn1–xO4 (n=0.25, 0.5 and 0.75) ferrites with mean particle sizes of 65–85 Å and free from other phases are formed after a heating treatment of only one hour at 500°C. 相似文献
997.
M. Elmastaş İ. Gülçin Ö. Işildak Ö. İ. Küfrevioğlu K. İbaoğlu H. Y. Aboul-Enein 《Journal of the Iranian Chemical Society》2006,3(3):258-266
Bay leaves (BL) (Laurus nobilis L., Family: Lauraceae) are traditionally used orally to treat the symptoms of gastrointestinal problems, such as epigastric bloating, impaired digestion, eructation, and flatulence. In this study, lyophilized extracts (both water and ethanol) of BL were studied for their antioxidant properties. The antioxidant activity, reducing power, free radical scavenging, superoxide anion radical scavenging, hydrogen peroxide scavenging and metal chelating activities were evaluated to determine the total antioxidant capacity of both BL extracts. Both extracts exhibited strong total antioxidant activity in linoleic acid emulsion. Concentrations of 20, 40, and 60 μg ml?1 showed 84.9, 95.7, 96.8, and 94.2, 97.7, and 98.6% inhibition of lipid peroxidation of linoleic acid emulsion, for water and ethanol extracts, respectively. On the other hand, 60 μg ml?1 of the standard antioxidants butylated hydroxyianisole (BHA), butylated hydroxytoluene (BHT), and α-tocopherol exhibited 96.6, 99.1, and 76.9% inhibition of lipid peroxidation in linoleic acid emulsion, respectively. In addition, the both BL extracts had effective reducing power, DPPH? free radical scavenging, superoxide anion radical scavenging, hydrogen peroxide scavenging and metal chelating activities at 20, 40, and 60 μg ml?1. The total amount of phenolic compounds in each BL extract was determined as gallic acid equivalents. 相似文献
998.
Ş. Turhan H. Yücel A. Demirbaş 《Journal of Radioanalytical and Nuclear Chemistry》2005,262(3):661-664
A prompt gamma neutron activation analysis (PGAA) setup installed at ANRTC has been used to analyze boron. It consists of a 22.6% REGe detector and a 740 GBq 241Am-Be neutron source moderated with water and paraffin. At the sample irradiation position, the thermal neutron fluence rate measured was 2.36·104 n·m–2· s–1 and the corresponding Cd-ratio was 22 for gold monitor. The absolute detection efficiency in the range of 120–1500 keV was determined using 152Eu standard solution. The sensitivity and detection limit for standard boric acid samples has been determined. The boron content in boric acid prepared from Turkish borate ores is measured to be 15.91±0.46% wt. 相似文献
999.
Faruk Kardaş 《Analytical letters》2019,52(9):1418-1431
A novel Schiff base designated as 5-[(3-methylthiophene-2-yl-methyleneamino)]-2-mercaptobenzimidazole was synthesized and characterized. A polyvinyl chloride-membrane potentiometric copper(II)-selective sensor was prepared by using the synthesized 5-[(3-methylthiophene-2-yl-methyleneamino)]-2-mercaptobenzimidazole compound. The prepared polyvinyl chloride-membrane copper(II)-selective sensor exhibited very good selectivity and sensitive potentiometric response towards copper(II) ions compared to a wide variety of other cations. The sensor had a fast response time of <5?s, and showed a linear Nerstian behavior to copper(II) ions over a wide concentration range from 1.0?×?10?5 to 1.0?×?10?1 mol L?1 with a slope of 29.2?±?0.7 and correlation coefficient of 0.9998. The prepared polyvinyl chloride-membrane copper(II)-selective sensor was used for 14 weeks without any significant change in its potentiometric response. The potentiometric response of the developed sensor was highly repeatable. Additionally, the developed sensor was used as an indicator electrode for the potentiometric titration of copper(II) ion with ethylenediaminetetraacetic acid. The sensor was also successfully applied to the direct determination of copper(II) ions in tap water, river water, and dam water samples. 相似文献
1000.
The hydrophobic effect is a major driving force in all chemical and biological events involving chain collapse in aqueous solution. Here, we show that the burial of nonpolar solvent-accessible surface area (NSASA) is a powerful criterion to predict the folding and misfolding behavior of small single-domain proteins as a function of chain elongation. This bears fundamental implications for co- and post-translational protein folding in the cell and for understanding the interplay between noncovalent interactions and formation of native-like structure and topology. Comparison between the fraction of NSASA in fully unfolded and folded elongating chains shows that efficient burial of nonpolar surface area is preferentially achieved only when the polypeptide chain is almost complete. This effect has no preferential vectorial character in that it is present upon elongation from both the N and C termini. For incomplete chains that do not have the ability to fold and bury nonpolar surface intramolecularly, the overall hydrophobic nature of the polypeptide chain (expressed as FBA, i.e., fractional buried surface area per residue) dictates the tendency toward misfolding and self-association. N-terminal chains characterized by FBA exceeding 0.73 are likely to misfold and aggregate, if unable to fold intramolecularly. 相似文献