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1.
Katharina Habermann Lutz Habermann Paul Rosenthal 《Calculus of Variations and Partial Differential Equations》2007,30(2):137-152
A Yang–Mills theory in a purely symplectic framework is developed. The corresponding Euler–Lagrange equations are derived
and first integrals are given. We relate the results to the work of Bourgeois and Cahen on preferred symplectic connections. 相似文献
2.
3.
A central problem that arises in evolutionary biology is that of displaying partitions of subsets of a finite set X on a tree whose vertices are partially labelled with the elements of X. Such a tree is called an X-tree and, for a collection of partitions of subsets of X, characterisations for the existence and uniqueness of an X-tree that displays have been previously given in terms of chordal graphs. In this paper, we obtain two closely related characterisations also in terms of chordal graphs. The first describes when identifies an X-tree, and the second describes when a compatible subset of is of maximum size. 相似文献
4.
Böcking T Kilian KA Hanley T Ilyas S Gaus K Gal M Gooding JJ 《Langmuir : the ACS journal of surfaces and colloids》2005,21(23):10522-10529
Surface modification with oligo(ethylene oxide) functionalized monolayers terminated with reactive headgroups constitutes a powerful strategy to provide specific coupling of biomolecules with simultaneous protection from nonspecific adsorption on surfaces for the preparation of biorecognition interfaces. To date, oligo(ethylene oxide) functionalized monolayer-forming molecules which can be activated for attachment of biomolecules but which can selectively form monolayers onto hydrogen terminated silicon have yet to be developed. Here, self-assembled monolayers (SAMs) containing tetra(ethylene oxide) moieties protected with tert-butyl dimethylsilyl groups were formed by thermal hydrosilylation of alkenes with single-crystal Si(111)-H. The protection group was used to avoid side reactions with the hydride terminated silicon surface. Monolayer formation was carried out using solutions of the alkene in the high-boiling-point solvent 1,3,5-triethylbenzene. The protecting group was removed under very mild acidic conditions to yield a free hydroxyl functionality, a convenient surface moiety for coupling of biological entities via carbamate bond formation. The chemical composition and structure of the monolayers before and after deprotection were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray reflectometry. To demonstrate the utility of this surface for covalent modification, two reagents were compared and contrasted for their ability to activate the surface hydroxyl groups for coupling of free amines, carbonyl diimidazole (CDI), and disuccinimidyl carbonate (DSC). Analysis of XP spectra before and after activation by CDI or DSC, and after subsequent reaction with glycine, provided quantitative information on the extent of activation and overall coupling efficiencies. CDI activated surfaces gave poor coupling yields under various conditions, whereas DSC mediated activation followed by aminolysis at neutral pH was found to be an efficient method for the immobilization of amines on tetra(ethylene oxide) modified surfaces. 相似文献
5.
Generalizing the work of Einstein and Mayer, it is assumed that at each point of space-time there exists a vector-spinor space with Nv vector dimensions and Ns spinor dimensions, where Nv=2k and Ns=2
k, k3. This space is decomposed into a tangent space with4 vector and4 spinor dimensions and an internal space with Nv–4 vector and Ns–4 spinor dimension. A variational principle leads to field equations for geometric quantities which can be identified with physical fields such as the electromagnetic field, Yang-Mills gauge fields, and wave functions of bosons and fermions. 相似文献
6.
{(MesGa)3[GaP(H)Mes](PMes)4}, a Phosphorus-substituted Ga? P-Heterocubane A mixture of MesGaCl2/GaCl3 (ratio 3:1) reacts with 5 equivalents of MesPLi2 in THF at ?78°C to the title compound {(MesGa)3[GaP(H)Mes](PMes)4} ( 1 ) by use of the “dilution principle”. 1 can be obtained in 30% yield. Recrystallization of 1 from DME and toluene, respectively, gives 1 · 0.5 DME and 1 · toluene. 1 was characterized by NMR-, IR-, and MS-techniques. According to the X-ray structure determination of 1 · toluene, 1 has a heterocubane structure, one corner of which is substituted with an P(H)Mes group. 相似文献
7.
Kopsirachine, an Unusual Alkaloid from the Apocynaceae Kopsia dasyrachis Ridl. From the leaves of Kopsia dasyrachis Ridl. a new type of alkaloid, kopsirachine ( 1 ), built up from catechin ( 2 ) and skytanthine ( 3 ) has been isolated. The structure elucidationis based on spectral and chemical evidence. Oxidative cleavage of its derivative 4 with KMnO4 afforded veratric acid wich was identified as its methylester by comparison with an authentic sample. Pyrolysis of 1 yielded δ-skytanthine ( 3 ). The stereochemistry of the skytanthine substituents in 1 could not yet be established. 相似文献
8.
The configurational isomers of astaxanthin (3,3′-dihydroxy-β,β-carotene-4,4′-dione) from the flesh of salmon (Salmo salar and Oncorhynchus) caught at different places in Europe and Canada were isolated and analyzed as (?)-camphanic acid diesters by means of HPLC. The biological variation in the composition of the configurational isomers in seven fish was surprisingly similar: 78 to 85% of (3S, 3′S)-astaxanthin, 12 to 17% (3R, 3′R)-astaxanthin and 2 to 6% meso-astaxanthin. 相似文献
9.
Katharina Schiedt Max Vecchi Ernst Glinz Trond Storebakken 《Helvetica chimica acta》1988,71(4):887-896
Diets supplemented with astaxanthin and canthaxanthin, respectively, and a control diet without carotenoid additions, were fed to 1½-year-old Atlantic salmon (Salmo salar, L.) for one year. The integuments were investigated as to their quantitative and qualitative carotenoid composition. Astaxanthin and canthaxanthin deposited in the skin amounted to 20 and 14% of the total carotenoids only. Seventy % must be considered as metabolites of astaxanthin and canthaxanthin and 10% as basic xanthophylls also present in the control groups. Astaxanthin apparently underwent the following metabolic pathway: astaxanthin→idoxanthin→adonixanthin→zeaxanthin→zeaxanthin 5,6-epoxides. Reduction of the 4′-carbonyl group was stereospecific leading to the (4′R)-idoxanthin. Canthaxanthin was obviously converted to β,β-carotene via 4′-hydroxyechinenone, echinenone, and 4-hydroxy-β,β-carotene. 相似文献
10.
The structure and thermodynamics of the hydrated electron are probed with resonance Raman spectroscopy of isotopic mixtures of H(2)O and D(2)O. The strongly enhanced intramolecular bends of e(-)(H(2)O) and e(-)(D(2)O) produce single downshifted bands, whereas the e(-)(HOD) bend consists of two components: one slightly upshifted from the 1,446 cm(-1) bulk frequency to 1,457 cm(-1) and the other strongly downshifted to approximately 1,396 cm(-1). This 60 cm(-1) split and the 200 (120) cm(-1) downshifts of the OH (OD) stretch frequencies relative to bulk water reveal that the water molecules that are Franck-Condon coupled to the electron are in an asymmetric environment, with one proton forming a strong hydrogen bond to the electron. The downshifted bend and librational frequencies also indicate significantly weakened torsional restoring forces on the water molecules of e(-)(aq), which suggests that the outlying proton is a poor hydrogen bond donor to the surrounding solvent. A 1.6-fold thermodynamic preference of the electron for H(2)O is observed based on the relative intensities of the e(-)(H(2)O) and e(-)(D(2)O) bands in a 50:50 isotopic mixture. This equilibrium isotope effect is consistent with the downshifted vibrational frequencies and a relative reduction of the zero-point energy of H(2)O bound to the electron. Our results enhance the cavity model of the solvated electron and support only those models that contain water monomers as opposed to other molecular species. 相似文献