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971.
A recently developed calorimetric method has been employed to estimate the thermodynamic functions for transfer of 1-propanol, 1-butanol, 1-pentanol, 1-hexanol and 1-heptanol from n-octane to water at 25°C. A linear correlation for G
t
o
as a function of the number of carbon atoms of the alchohol molecule has been found but for H
t
o
and S
t
o
the dependence gave well defined minima. 相似文献
972.
Giovanni Minghetti Angelino Doppiu Antonio Zucca Sergio Stoccoro Maria Agostina Cinellu Mario Manassero Mirella Sansoni 《Chemistry of Heterocyclic Compounds》1999,35(8):992-1000
Reaction of Pd(OAc)2 with HL1 and HL2 (HL1=6-iso-propyl-2,2-bipyridine; HL2=6-neo-pentyl-2,2-bipyridine), followed by treatment with LiCl or KI, gives [PdCl(L1)]2, (1), [PdCl(L2)]2 (2), and [PdI(L2)]2 (3), respectively. The chloride bridge in complexes1 and2 is split by PPh3 to give the mononuclear species PdCl(L1)(PPh3) (4) and PdCl(L2)(PPh3) (5). Spectroscopic data provide evidence for coordination of the deprotonated ligands through a nitrogen and the C(3) atom of the 6-substituted pyridine. An analogous platinum complex PtCl(L3)(SMe2) (6) (HL3=6-tert-butyl-2,2-bipyridine) was obtained from trans-PtClMe(SMe2)2 and HL3. The crystal structures of compounds1 and6 have been solved by X-ray diffraction analysis.Dipartimento di Chimica, Universita di Sassari, via Vienna 2, I-07100 Sassari, Italy; Dipartimento di Chimica Strutturale e Stereochimica Inorganica, Universita di Milano, Centro CNR, I-20133 Milano, Italy; Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1127–1137, August, 1999. 相似文献
973.
Szczepina MG Johnston BD Yuan Y Svensson B Pinto BM 《Journal of the American Chemical Society》2004,126(39):12458-12469
The syntheses of N-alkylated deoxynojirimycin and 1,5-dideoxy-1,5-iminoxylitol derivatives having either a D- or an L-erythritol-3-sulfate functionalized N-substituent are reported. The alkylating agent used was a cyclic sulfate derivative, whereby selective attack of the nitrogen atom at the least hindered primary center afforded the desired ammonium salt. In aqueous solution, these salts were configurationally labile at the ammonium center. Sulfonium and/or selenonium analogues of the ammonium salts were prepared by analogous reactions. The chalcogen salts were obtained as mixtures of diastereomers, separable in some cases, differing only in the stereochemistry at the configurationally stable sulfur or selenium atoms. Proof of configuration and conformation of each compound was obtained by detailed NMR experiments. The compounds are six-membered ring analogues of salacinol, a known sulfonium-salt glucosidase inhibitor. Evaluation of the target compounds for enzyme inhibition of the glucosidase enzyme glucoamylase G2 indicated that these compounds were either inactive or, at best, only weak inhibitors of maltose hydrolysis. 相似文献
974.
Paolo Cabella Massimo Barbeni Marcella Conterno Daniela Talarico Emilio Marengo Mario Marsili 《Analytica chimica acta》1990
Computer-assisted methods for improving research and production in a food-flavour company are described. Methods of experimental design are used in planning experiments. Special programs are used for identification of components through correlation of mass spectra and gas chromatographic retention indices, and for the design of new synthetic routes. In flavour creation, a data base containing qualitative and quantitative information on flavours, relevant legislation and organoleptic properties of components, can be searched selectively in attempts to improve flavours and to identify better combinations of substances. A computer-assisted production system is described which ensures complete qualitative and quantitative control. 相似文献
975.
Roberta Galeazzi Silvano Geremia Giovanna Mobbili Mario Orena 《Tetrahedron: Asymmetry》1996,7(12):3573-3584
(R)- and (S)-N-allyl-N-(1-phenylethyl)methoxycarbonylacetamide, 5 and 6, underwent oxidative cyclisation mediated by Mn(III), to give easily separable diastereomeric mixtures of 3-aza-2-oxobicyclo[3.1.0]hexanes 8a,b and 9a,b, respectively, whose structures were assigned on the basis of 1H NMR spectra and then confirmed by X-ray diffraction analysis of the derivatives 11b and 14. 相似文献
976.
Giampiero Pagani Zecchini Mario Paglialunga Paradisi 《Journal of heterocyclic chemistry》1979,16(8):1589-1597
Treatment of protected dipeptides containing 1,2,3,4-tetrahydroquinoline-2-carboxylic acid with acetic anhydride affords only 1H,3H,5H-oxazolo[3,4-a]quinolin-3-one derivatives. The formation of a-acylaminomethylketones, arising from the competitive Dakin-West reaction, was generally observed when the cyclization procedure was extended to some amides of the cyclic imino acid. The preferential stabilization of one of two probable mesoionic intermediates seems to determine the preferred pathway. 相似文献
977.
Calorimetric and dielectric results for crystallizable poly(n-alkyl methacrylates) (PnAMA) with C=12, 16 and 18 alkyl carbons per side chain are presented. Degree of crystallization Dcal and melting peak temperature TM are estimated from conventional DSC measurements. For poly(n-hexadecyl methacrylate) (C=16) the influence of isothermal crystallization is studied by DSC as well as TMDSC. Changes in dielectric relaxation strength Δε and α peak shape during crystallization are investigated. Effects of side chain crystallization on the complex dynamics of PnAMA are discussed. The results are related to the relaxation behavior of lower nanophase-separated PnAMA with two co-existing glass transitions, the conventional glass transition (a or α) and the polyethylene-like glass transition (αPE) within alkyl nanodomains formed by aggregated alkyl rests. It is shown that amorphous as well as semicrystalline PnAMA can be understood as nanophase-separated polymers with alkyl nanodomains having a typical dimension of 1-2 nm. The results are compared with the predictions of simple morphological pictures for side chain polymers. X-ray scattering data for the amorphous and semicrystalline PnAMA are included in the discussion. Common aspects of nanophase-separated systems in both states as well as differences caused by crystallization are discussed. Indications for the existence of rigid amorphous regions are compiled. Different approaches to explain a similar increase of Tg(αPE)—the glass temperature of the amorphous alkyl nanodomains—and TM—the melting temperature of crystalline alkyl nanodomains—with side chain length are considered. Pros and cons of both approaches, based on increasing order within the alkyl nanodomains and confinement effects in nanophase-separated systems, are discussed. Main trends concerning crystallization and cooperative dynamics are compared with those in other systems with self-assembled nanometer confinements like microphase-separated blockcopolymers or semicrystalline main chain polymers. 相似文献
978.
Abstract— The fact that most proteins contain several tryptophans hinders the investigation of the photochemistry of a particular indole residue. A method is presented here that can be used to investigate the photochemistry of specific tryptophan residues in proteins. It consists simply of separating the peptides of a proteolytically digested protein by TLC and then scanning the peptides at the fluorescent maximum of tryptophan. The assignment of the resultant peaks to a particular peptide is based on the chromatographic comparison of the scans with peptide maps.
Using this method, the photochemistry of the tryptophan residues in alpha crystallin, a major protein of lenses, was investigated. Under photolytic conditions that mimic the transmission characteristics of the cornea (>293 nm), it was found that there is a differential photolysis of the tryptophan residues in the protein; with Trp-9 in the N-terminal peptide photolyzing at a considerably faster rate than Trp-60. In addition to tryptophan, photolytic losses of tyrosine were assessed by scanning the peptide maps at the tyrosine fluorescent maximum. Only one tyrosine residue photolyzes under these conditions. The differential photolysis of the tryptophan residues is explained in part by the presence of residues in the vicinity of the indole moieties. 相似文献
Using this method, the photochemistry of the tryptophan residues in alpha crystallin, a major protein of lenses, was investigated. Under photolytic conditions that mimic the transmission characteristics of the cornea (>293 nm), it was found that there is a differential photolysis of the tryptophan residues in the protein; with Trp-9 in the N-terminal peptide photolyzing at a considerably faster rate than Trp-60. In addition to tryptophan, photolytic losses of tyrosine were assessed by scanning the peptide maps at the tyrosine fluorescent maximum. Only one tyrosine residue photolyzes under these conditions. The differential photolysis of the tryptophan residues is explained in part by the presence of residues in the vicinity of the indole moieties. 相似文献
979.
Sooboo Singh J.A. Nevines Moganavelli Singh Mario Ariatti Munessar Sankar 《Journal of solution chemistry》2003,32(5):435-450
The second dissociation constants pK
2of the NH3
+charge center of the alanylpeptides, alanylglutamine (Ala–Gln), alanylleucine (Ala–Leu), alanylglycine (Ala–Gly), and DL-alanyl–DL-methionine (DL-Ala–DL-Met) were determined at ten temperatures in the range, 5–50°C. These pK
2values were calculated from the emf of cells containing buffer solutions of these dipeptides. A cell of the type described by Harned and Ehlers,(1)utilizing hydrogen and silver–silver bromide electrodes was used. The thermodynamic quantities, Ho, So, and Cp
owere derived from the temperature coefficients of the dissociation constants. The pK
2values at 25°C, 8.2105 ( Ala–Gln), 8.2668 ( Ala–Leu), 8.2940 ( Ala–Gly), and 8.3054 ( DL-Ala–DL-Met). These values show that different substituent groups on the -carbon atom (which include polar and nonpolar groups), have a small effect on the dissociation of the NH3
+charge center. These compounds were also found to be suitable as buffers in the pH range(7–9). The thermodynamics of the solute–solvent interaction is interpreted in terms of the mixture model.(2) 相似文献
980.
Carlo Bicchi Angela D'amato Valeria Manzin Anna Galli Mario Galli 《Journal of separation science》1995,18(5):295-298
In pre vious papers, 2,6-di-O-methyl-3-O-pentyl-β-cyclodextrin (CD) was demonstrated to be successful in separating volatile compounds, while avoiding the drawbacks of 2,3,6-tri-O-methyl-O-methyl-β-CD in terms of column stability and operating temperature. Since a CD chiral selector of universal use has not yet been found, and at least two (or more) columns coated with different CD derivatives are therefore necessary for routine work, the performance of 2,6-di-O-methyl-3-O-pentyl-γ-CD, 2,6-di-O-methyl-3-O-(4-oxopentyl)-γ-CD, 2,6-di-O-pentyl-3-O-(4-oxo-pentyl)-β-CD, and 2,6-di-O-pentyl-3-O-(-4-oxo-pentyl)-γ-CD diluted in polysiloxanes for the separation of volatile compounds in aromas and essential oils will be illustrated; each column coated with each of the newly synthesized CD derivatives was evaluated by analyzing more than 150 different recemates with different structures. 相似文献