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901.
Multi-component, regio-selective aldol addition of β-ketoesters to aldehydes: scope and applications
More V Di Mola A Croce G Tedesco C Petronzi C Peduto A De Caprariis P Filosa R Massa A 《Organic & biomolecular chemistry》2011,9(24):8483-8488
Simple and effective multi-component one-pot aldol addition/protection reactions of β-ketoesters to a series of aldehydes in the presence Me(3)SiCl and i-Pr(2)EtN have been described. The analysis of the scope of the reaction revealed a dramatic dependence of the reactivity on the substrates used. Thus the effect of a catalytic amount of DMF and different reaction conditions was widely investigated. Further transformations of the aldol adducts were particularly useful to give valuable diols and compounds with quaternary stereocenters, while X-ray structural analysis gave also important stereochemical information about this challenging reaction. 相似文献
902.
Forniés J Sicilia V Casas JM Martín A López JA Larraz C Borja P Ovejero C 《Dalton transactions (Cambridge, England : 2003)》2011,40(12):2898-2912
The mononuclear complexes [Pt(bzq)(S^S)] [S^S = pyrrolidinedithiocarbamate (pdtc 1), dimethyldithiocarbamate (dmdtc 2)] were prepared by reaction of [Pt(bzq)(NCMe)(2)]ClO(4) with an equimolecular amount of [NH(4)(pdtc)] and [Na(dmdtc)·2H(2)O] respectively in MeOH. Reactions of 1 and 2 with AgClO(4) in 1 : 1 and 2 : 1 molar ratios rendered the heteropolinuclear compounds [{Pt(bzq)(S^S)Ag}(2)](ClO(4))(2) (S^S = pdtc 3, dmdtc 4) and [{Pt(bzq)(S^S)}(2)Ag](ClO(4)) (S^S = pdtc 5, dmdtc 6) respectively. The X-ray studies on single crystals of 3 and 4 showed that both consist of tetranuclear [Pt(2)Ag(2)] clusters with the Pt-Ag and the Ag-Ag distances in the range of those corresponding to Pt-Ag dative bonds and argentophilic interactions. In 3 the tetranuclear [Pt(2)Ag(2)] clusters are connected into infinite polymeric chains by Pt···Pt metallophilic interactions (Pt···Pt = 3.1890(7) ?). The X-ray study on a single crystal of 5 showed that it is a polymer based on trinuclear [Pt(2)Ag] clusters containing two unsupported Pt-Ag dative bonds and connected by Ag-S bonds in such a way that the "Pt-Ag-S-Pt-Ag-S" atoms draw a zigzag polymeric chain. TD-DFT calculations carried out for 1 indicate that the lowest energy absorption band in CH(2)Cl(2) can be described as a mixture of (1)MLCT, (1)IL and (1)L'LCT transitions. Powdered samples of 1 at 298 K and 77 K show a green-yellow emission band coming mainly from a (3)LC excited state. However complex 2 shows "luminescence thermochromism": the colour of its luminescence changes from green-yellow at 77 K to orange-red at 298 K. The emission of the Pt-Ag clusters, 3-6, in the solid state, are due to excimeric (3)ππ and/or (3)MMLCT (dσ* →π*) low-lying excited states, indicating that the presence of silver in the clusters makes the "Pt(bzq)(S^S)" fragments interact to a large extent through Pt···Pt and/or π-π interactions. Solid 3 is a highly selective vapochromic compound towards acetonitrile although this behaviour is not fully reversible. 相似文献
903.
Caballero AB Maclaren JK Rodríguez-Diéguez A Vidal I Dobado JA Salas JM Janiak C 《Dalton transactions (Cambridge, England : 2003)》2011,40(44):11845-11855
Silver(I) coordination complexes with the versatile and biomimetic ligands 1,2,4-triazolo[1,5-a]pyrimidine (tp), 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp) and 7-amine-1,2,4-triazolo[1,5-a]pyrimidine (7atp) all feature dinuclear [Ag(2)(μ-tp)(2)](2+) building units (where tp is a triazolopyrimidine derivative), which are the preferred motif, independently of the counter-anion used. According to AIM (atoms in molecules) and ELF (electron localization function) analyses, this fact is due to the great stability of these dinuclear species. The complexes structures range from the dinuclear entities [Ag(2)(μ-tp)(2)(CH(3)CN)(4)](BF(4))(2) (1), [Ag(2)(μ-tp)(2)(CH(3)CN)(4)](ClO(4))(2) (2), [Ag(2)(μ-7atp)(2)](ClO(4))(2) (3) and [Ag(2)(μ-dmtp)(2)(CH(3)CN)](PF(6))(ClO(4)) (4) over the 1D polymer chain [Ag(2)(μ-CF(3)SO(3))(2)(μ-dmtp)(2)](n) (5) to the 3D net {[Ag(2)(μ(3)-tp)(2)](PF(6))(2)·~6H(2)O}(n) (6) with NbO topology. 相似文献
904.
Alonso PJ Arauzo AB García-Monforte MA García-Rubio I Martín A Menjón B Rillo C 《Dalton transactions (Cambridge, England : 2003)》2011,40(4):853-861
The homoleptic, square pyramidal organochromium(III) compound [NBu(4)](2)[Cr(C(6)F(5))(5)] (1) reacts with excess organic isocyanides, CNR [R = (t)Bu, 2,6-dimethylphenyl (Xy)], under dissociation of the apical C(6)F(5) ligand to give the more saturated, singly charged complexes [NBu(4)][trans-Cr(C(6)F(5))(4)(CNR)(2)] [R = (t)Bu (2), Xy (3)], containing six monodentate C-donor ligands. These compounds exhibit an axially distorted octahedral structure (single-crystal X-ray diffraction) with the four C(6)F(5) groups defining the equatorial positions and the CNR ligands occupying the axial ones. Compounds 2 and 3 both behave as spin quartet species (S = 3/2) at microscopic level (EPR spectroscopy), their macroscopic magnetic properties depending upon the nature of the terminal R group, as established by magnetisation measurements. When the R substituent is the saturated alkyl group (t)Bu, the compound (2) behaves as a simple paramagnet, with no magnetic interaction between individual Cr(III) centres along the whole temperature range measured (1.8-265 K). By contrast, a weak antiferromagnetic interaction is detected for compound 3 at low temperature with T(N) = 0.19(1) K. Since the closest intermetallic distances are similar in the crystals of 2·CH(2)Cl(2) and 3·1.75CH(2)Cl(2) (ca. 1.1 nm), we conclude that the insaturation of the aromatic Xy group together with the extended intermolecular π-π stacking interactions between Xy rings observed in the crystal lattice of 3·1.75CH(2)Cl(2) (centroid-to-centroid distance: 0.35 nm) favour magnetic interaction between the individual magnetic centres. 相似文献
905.
Carbone M Li Y Irace C Mollo E Castelluccio F Di Pascale A Cimino G Santamaria R Guo YW Gavagnin M 《Organic letters》2011,13(10):2516-2519
Two indole alkaloids, phidianidines A (1) and B (2), exhibiting an uncommon 1,2,4-oxadiazole ring linked to the indole system, have been isolated from the marine opisthobranch mollusk Phidiana militaris. The structures of the two metabolites have been elucidated by spectroscopic techniques. Phidianidines exhibit high cytotoxicity against tumor and nontumor mammalian cell lines in in vitro assays. 相似文献
906.
A convenient, general, and high yielding Pd-catalyzed cross-coupling of methanesulfonamide with aryl bromides and chlorides is reported. The use of this method eliminates concern over genotoxic impurities that can arise when an aniline is reacted with methanesulfonyl chloride. The application of this method to the synthesis of dofetilide is also reported. 相似文献
907.
Garrido Arteaga R Veloso Pita RC López López MA González Labaut JA Rodríguez Montero Mdel C Vélez Castro H Cremata Alvarez JA 《Analytical and bioanalytical chemistry》2011,400(10):3675-3680
Gangliosides are membrane-associated glycosphingolipids. N-Acetyl GM3 and N-glycolyl GM3 are two tumor-associated antigens expressed in cancer tissues such as melanoma and mammalian cancer. In order
to use these antigens in GM3-based vaccines for patients with early stage cancer, the synthetic version is recommended to
avoid the risk of animal virus transmission from the source. However, the isolation of natural gangliosides is of comparative
value for the structural characterization. The structures of N-acetyl and N-glycolyl GM3 extracted from dog and horse erythrocytes were evaluated by matrix-assisted laser desorption/ionization time-of-flight
mass spectrometry and nuclear magnetic resonance techniques; additionally, the natural N-acetyl ganglioside was compared to a synthetic one. In addition to the main compound with C24:0 fatty acid chain, a minor
component with an additional unsaturation in the ceramide chain was detected, in both the dog and the horse gangliosides.
This paper shows spectroscopic evidence of the aforementioned compounds. 相似文献
908.
There is currently a renewed focus aimed at understanding allosteric mechanisms at atomic resolution. This current interest
seeks to understand how both changes in protein conformations and changes in protein dynamics contribute to relaying an allosteric
signal between two ligand binding sites on a protein (e.g., active and allosteric sites). Both nuclear magnetic resonance
(NMR), by monitoring protein dynamics directly, and hydrogen/deuterium exchange, by monitoring solvent accessibility of backbone
amides, offer insights into protein dynamics. Unfortunately, many allosteric proteins exceed the size limitations of standard
NMR techniques. Although hydrogen/deuterium exchange as detected by mass spectrometry (H/DX-MS) offers an alternative evaluation
method, any application of hydrogen/deuterium exchange requires that the property being measured functions in both H2O and D2O. Due to the promising future H/DX-MS has in the evaluation of allosteric mechanisms in large proteins, we demonstrate an
evaluation of allosteric regulation in D2O. Exemplified using phenylalanine inhibition of rabbit muscle pyruvate kinase, we find that binding of the inhibitor is greatly
reduced in D2O, but the effector continues to elicit an allosteric response. 相似文献
909.
Erasmo?Caponio Miguel?ángel?Javaloyes Antonio?MasielloEmail author 《Mathematische Annalen》2011,351(2):365-392
In this paper we first study some global properties of the energy functional on a non-reversible Finsler manifold. In particular
we present a fully detailed proof of the Palais–Smale condition under the completeness of the Finsler metric. Moreover, we
define a Finsler metric of Randers type, which we call Fermat metric, associated to a conformally standard stationary spacetime.
We shall study the influence of the Fermat metric on the causal properties of the spacetime, mainly the global hyperbolicity.
Moreover, we study the relations between the energy functional of the Fermat metric and the Fermat principle for the light
rays in the spacetime. This allows one to obtain existence and multiplicity results for light rays, using the Finsler theory.
Finally the case of timelike geodesics with fixed energy is considered. 相似文献
910.
By applying a method due to Saint Raymond, we prove the existence of infinitely many weak solutions for a quasilinear elliptic
partial differential equation, involving the p-Laplacian operator, coupled with a nonlinear boundary condition. Our main assumption is a suitable oscillatory behaviour
of the nonlinearity either at infinity or at zero. 相似文献