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991.
992.
The modes of fragmentation of perchlorylbenzene (C6H5ClO3) and its perdeutero derivative under electron impact are reported and discussed. The occurrence of the [C6H5O]? and [C6H5O]+ ions is accounted for in terms of a novel phenyl migration from chlorine to oxygen. 相似文献
993.
Carmona D Sáez J Granados H Pérez E Blair S Angulo A Figadere B 《Natural product research》2003,17(4):275-280
Dichloromethane extracts of both the roots and the leaves of Raimondia cf. monoica showed in vitro antiplasmodial and leishmanicidal activities against Plasmodium falciparum and Leishmania panamensis, respectively. Three 6-substituted 5,6-dihydro-2H-pyran-2-ones were isolated. (1) and (2) were identified as (6S)-(5'-oxohepten-1'E,3'E-dienyl)-5,6-dihydro-2H-pyran-2-one (1) and (6R)-(5'-oxohepten-1'Z,3'E-dienyl)-5,6-dihydro-2H-pyran-2-one (2), respectively. (-)-Arentilactone (3) was also isolated. The structure of the new compound (1) was determined by spectroscopic methods; additional spectroscopic data for (2) are reported for the first time. 相似文献
994.
De Gregorio A Battistutta R Arena N Panzalorto M Francescato P Valentini G Bruno G Zanotti G 《Organic & biomolecular chemistry》2003,1(18):3178-3185
Ornithine transcarbamoylase from ovine liver has been purified to homogeneity. Like all anabolic OTCs, the ovine enzyme is a trimer, constituted by identical subunits of 34 kDa. Sequence analysis of the 54 N-terminal residues of ovine OTC shows a high degree of homology with the human enzyme. The optimum pH and the Michaelis constants for the catalytic reaction were determined. The ovine enzyme is the most thermostable one among mammals OTCs, its critical temperature being 6 degrees C higher than those measured for the other enzymes. The enzyme has been crystallised and the structure determined at 3.5 A resolution. Crystals belong to the cubic P4(3)32 space group, with a = b = c = 184.7 A and a solvent content of about 80%. There is no evidence of any ligand in the active site cavity, indicating that the crystals contain an unliganded or T state of the enzyme. The unliganded OTCase enzyme adopts a trimeric structure which, in the crystal, presents a three-fold axis coincident with the crystallographic one. The conformation of each monomer in the trimer is quite similar to that of the liganded human protein, with the exception of a few loops, directly interacting with the substrate(s), which are able to induce a rearrangement of the quaternary organisation of the trimer, that accounts for the cooperative behaviour of the enzyme following the binding of the substrates. 相似文献
995.
The Z- and E-γ-alkylthio-allylboronates and were found to add aldehydes forming diastereoselectively the adducts and respectively in high yield. 相似文献
996.
A conformational study of new diversely substituted 14-membered diketal dilactam macrocycles was conducted by NMR spectroscopy in liquid and solid states, molecular mechanics calculations and, for one compound, a previous X-ray analysis. The results obtained by the different techniques show that the conformations depend closely on whether the molecules are chiral or achiral and on the stereochemistry of the ketal OMe groups. In achiral compounds, the most stable conformation of each compound has, in both the liquid and solid states, the two NH-CO links positioned perpendicular to the macrocycle plane, lending to the trans-7,7′-OMe macrocycles 6b and 7b a rectangular [3434]-type structure. In contrast, in chiral compounds, the most stable conformations are not the same in the liquid and solid phases. In the liquid state the conformations are set by the presence of one or two N4-H?O1′, N4′-H?O1 intramolecular hydrogen bonds that position the amide group parallel to the macrocycle plane, whereas in the solid state the amide moieties again adopt a perpendicular position which can be stabilized, when the 3-R substituent is not too bulky, by intermolecular N-H?OC bonds between parallel sheets, and exceptionally, in the cis-7,7′-OMe-3,3′-Ph compound 1c, by a π-π stacking effect between the phenyl groups. 相似文献
997.
Erich Widmer Milan Soukup Reinhard Zell Emil Broger Bruno Lohri Roman Marbet Teodor Luk
《Helvetica chimica acta》1982,65(3):944-957
Technical Procedures for the Synthesis of Carotenoids and Related Compounds from 6-Oxo-isophorone, VI. Synthesis of Rhodoxanthin and (3RS, 3′RS)-Zeaxanthin; Routes to the C15-Ring Component via 3-Oxo-ionone Derivatives The C15-ring component 4 , key intermediate of a new scheme for the synthesis of rhodoxanthin ( 1 ) and (3RS, 3RS)-zeaxanthin ( 3 ), has been synthesized starting from 6-oxo-isophorone ( 7 ) via 3-oxo-cyclocitral and 3-oxo-ionone derivatives. 相似文献
998.
Xifra R Ribas X Llobet A Poater A Duran M Solà M Stack TD Benet-Buchholz J Donnadieu B Mahía J Parella T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(17):5146-5156
A family of highly stable organometallic Cu(III) complexes with monoanionic triazamacrocyclic ligands (L(i)) with general formula [CuL(i)]+ have been prepared and isolated, and their structural, spectroscopic, and redox properties thoroughly investigated. The HL(i) ligands have been designed in order to understand and quantify the electronic effects exerted by electron donor and electron-withdrawing groups on either the aromatic ring or the central secondary amine or on both. In the solid state the Cu(III) complexes were mainly characterized by single-crystal X-ray diffraction analysis, whereas in solution their structural characterization was mainly based on 1H NMR spectroscopy given the diamagnetic nature of the d(8) square-planar Cu(III) complexes. Cyclic voltammetry together with 1H NMR and UV/Vis spectroscopy have allowed us to quantify the electronic effects exerted by the ligands on the Cu(III) metal center. A theoretical analysis of this family of Cu(III) complexes has also been undertaken by DFT calculations to gain a deeper insight into the electronic structure of these complexes, which has in turn allowed a greater understanding of the nature of the UV/Vis transitions as well as the molecular orbitals involved. 相似文献
999.
Cirilli R Ferretti R Gallinella B La Torre F La Regina G Silvestri R 《Journal of separation science》2005,28(7):627-634
The enantiomeric separation of a series of imidazole analogues of Fluoxetine and Miconazole endowed with potent antifungal activity was performed using cellulose tris(4-methylbenzoate) (Chiralcel OJ) and cellulose tris(3,5-dimethylphenylcarbamate) (Chiralcel OD) as chiral stationary phases. Binary mixtures of n-hexane and alcohol as well as pure alcohols (ethanol or 2-propanol) were used as eluents. The enantiomer elution order was monitored by chiroptical detectors based on on-line optical rotation and circular dichroism measurements. For some of the compounds studied very high enantioseparation factor values (alpha > 7) on Chiralcel OJ CSP were observed. In order to study the chiroptical characteristics of the two most biologically active compounds, chromatographic resolutions were carried out on a semipreparative scale. Assignment of the absolute configuration was empirically established by comparing the CD spectra of the separated enantiomers with those obtained from the enantiomers of Miconazole. 相似文献
1000.
A gas chromatographic investigation of the steam distilled oil of the herb of Artemisia vulgaris led to the identification of 21 irregular monoterpenes of non-head-to-tail isoprenoid skeleton. The spectral data of some of these compounds are discussed. The structures of eight new irregular monoterpenes are given. 相似文献