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991.
In many particle methods the accurate interpolation of a velocity field represented on a computational grid to arbitrary positions is crucial [2, 5]. Here, the importance of mass conservation and order of the interpolation scheme were analyzed. Initially equally distributed particles were tracked in a stationary, incompressible 2d flow field using different interpolation schemes. It could be demonstrated that especially mass conservation is of great importance, in particular in the case of complex flow patterns. The ideas presented in this paper are more general and the methods can be extended for unsteady, compressible 3d flow problems. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
992.
Andrei S. Batsanov Brian M. Bridgewater Judith A. K. Howard Andrew K. Hughes Claire Wilson 《Journal of organometallic chemistry》1999,590(2):1657-179
Reaction of phenyl magnesium bromide with the ,β-unsaturated ketone 3-methyl-2,3,4,5,6,7-hexahydroind-8(9)-en-1-one, followed by an aqueous work-up, generates the pro-chiral tetra-substituted cyclopentadiene, 1-phenyl-3-methyl-4,5,6,7-tetrahydroindene, Cp‡H, a precursor to the η5-cyclopentadienyl ligand in (Cp‡)2Fe and [(Cp‡)Fe(CO)]2(μ-CO)2. Both complexes were generated as mixtures of rac-(RR and SS)- and meso-(RS)-isomers, and in either case pure meso-isomer was isolated by crystallisation and characterised by single crystal X-ray structure, both molecules having crystallographic Ci symmetry. Reduction with Na/Hg cleaves meso-(RS)-[(Cp‡)Fe(CO)]2(μ-CO)2 and the resulting mixture of (R)- and (S)-[(Cp‡)Fe(CO)2]− anions reacts with MeI to give racemic (Cp‡)Fe(CO)2Me, which was characterised by the X-ray crystal structure. The Cp‡ ligand is more electron donating than (η-C5H5) as revealed by the reduction potential of the (Cp‡)2Fe+/(Cp‡)2Fe couple, E°=−0.127 V (vs. Ag AgCl). Reaction of LiCp‡ with ZrCl4 yields the zirconocene dichloride [Zr(Cp‡)2Cl2] as mixture of rac- and meso-isomers, from which pure rac-isomer is obtained as a mixture of RR and SS crystals by recrystallisation. The reaction of rac-[Zr(Cp‡)2Cl2] with LiMe gives rac-[Zr(Cp‡)2Me2]. The structures of RR-[Zr(Cp‡)2Cl2] and rac-[Zr(Cp‡)2Me2] have been determined by X-ray diffraction. The structural studies reveal the influence of the bulky substituted cyclopentadienyl ligand on the metal---Cp‡ distances and other metric parameters. 相似文献
993.
El Watik L. Claire Y. Zineddine H. Rossi C. Kaloustian J. Sergent M. Périchaud A. 《Journal of Thermal Analysis and Calorimetry》1999,58(1):19-28
The study of the thermal degradation of the fireproof polystyrene—butadiene copolymer by an intumescent system: ammonium polyphosphate (APP)—pentaerythritol (PER)—talc (TAL), was done through an experimental process. Thermogravimetry under air sweeping was used. We observed for the degradation rate of the mixture with fireproofing agents, in the field of 20 to 50% mass loss, a better linear increasing when this mixture contains more TAL and the ratio APP/PER is smaller.
This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
994.
We investigate the single-impurity Anderson model by means of the recently introduced modified perturbation theory. This approximation scheme yields reasonable results away from the symmetric case. The agreement with exactly known results for the symmetric case is checked, and results for the non-symmetric case are presented. With decreasing conduction band occupation, the breakdown of the screening of the local moment is observed. In the crossover regime between Kondo limit and mixed-valence regime, an enhanced zero-temperature susceptibility is found. 相似文献
995.
The TeV γ-ray sky displays at this time 9 sources comprising 6 supernova remnants (SNR) and 3 active galactic nuclei (AGN). They have been discovered with AIR
ERENKOV TELESCOPES since 1989, and more sources are sure to be found. They are related to violent astrophysical events and promise to be used as unique tools for cosmological questions like the universal infrared photon field and the intergalactic magnetic field strength. 相似文献
996.
M. Makrocka-Rydzyk S. Glowinkowski S. Jurga W. H. Meyer 《Applied magnetic resonance》2000,18(1):63-70
Proton and fluorine second moment and spin-lattice relaxation timesT 1 andT lρ have been employed to study molecular dynamics in the comb-like I-6,6-16-Me-BF4 ionene in the temperature range from 110 up to 300 K. The existence of motions of methyl groups, trans-gauche isomerization, and/or rotation of the main- and side-chain méthylene groups, as well as isotropic reorientation of tetrafluoroborate ions were established. The observed relaxation behaviors are explained by motional models which assume Davidson-Cole asymmetrical distribution of correlation times. The best-fit motional parameters are given. 相似文献
997.
P. Bakule P.E.G. Baird M.G. Boshier S.L. Cornish D.F. Heller K. Jungmann I.C. Lane V. Meyer P.H.G. Sandars W.T. Toner M. Towrie J.C. Walling 《Applied physics. B, Lasers and optics》2000,71(1):11-17
A Q-switched alexandrite laser suitable for high-resolution spectroscopy is described which produces pulses of 35 mJ energy in a 10 MHz bandwidth, with a high-purity TEM00 mode. The laser can be synchronised to external event to within 100 ns. The output pulse length is 120 ns and the repetition rate 25 Hz. The laser is injection-seeded by a Ti:sapphire laser operating around 730 nm. To preserve single-mode seeding under external triggering conditions, and to obtain small time-jitter, active cavity length control was used. In order to achieve the 10 MHz output bandwidth, intra-cavity electro-optic modulators were used to compensate for the frequency chirp. The refractive index of alexandrite was found to vary linearly with inversion density with a constant of proportionality equal to 1.6᎒-24 cm3. In pulsed operation at 730 nm, the index change due to this effect is only partially compensated by changes due to ground state phonon relaxation. 相似文献
998.
Michael Meyer Thomas Steinke Maria Brandl Jürgen Sühnel 《Journal of computational chemistry》2001,22(1):109-124
The structures and interaction energies of guanine and uracil quartets have been determined by B3LYP hybrid density‐functional calculations. The total interaction energy ΔET of the C4h‐symmetric guanine quartet consisting of Hoogsteen‐type base pairs with two hydrogen bonds between two neighbor bases is −66.07 kcal/mol at the highest level. The uracil quartet with C6 H6O4 interactions between the individual bases has only a small interaction energy of −20.92 kcal mol−1, and the interaction energy of −24.63 kcal/mol for the alternative structure with N3 H3O4 hydrogen bonds is only slightly more negative. Cooperative effects contribute between 10 and 25% to all interaction energies. Complexes of metal ions with G‐quartets can be classified into different structure types. The one with Ca2+ in the central cavity adopts a C4h‐symmetric structure with coplanar bases, whereas the energies of the planar and nonplanar Na+ complexes are almost identical. The small ions Li+, Be2+, Cu+, and Zn2+ prefer a nonplanar S4‐symmetric structure. The lack of coplanarity prevents probably a stacking of these base quartets. The central cavity is too small for K+ ions and, therefore, this ion favors in contrast to all other investigated ions a C4‐symmetric complex, which is 4.73 kcal/mol more stable than the C4h‐symmetric one. The distance 1.665 Å between K+ and the root‐mean‐square plane of the guanine bases is approximately half of the distance between two stacked G‐quartets. The total interaction energy of alkaline earth ion complexes exceeds those with alkali ions. Within both groups of ions the interaction energy decreases with an increasing row position in the periodic table. The B3LYP and BLYP methods lead to similar structures and energies. Both methods are suitable for hydrogen‐bonded biological systems. Compared with the before‐mentioned methods, the HCTH functional leads to longer hydrogen bonds and different relative energies for two U‐quartets. Finally, we calculated also structures and relative energies with the MMFF94 forcefield. Contrary to all DFT methods, MMFF94 predicts bifurcated C HO contacts in the uracil quartet. In the G‐quartet, the MMFF94 hydrogen bond distances N2 H22N7 are shorter than the DFT distances, whereas the N1 H1O6 distances are longer. © 2000 John Wiley & Sons, Inc. J Comput Chem 22: 109–124, 2001 相似文献
999.
Denise Barbier‐Baudry Claire‐Hlne Brachais Adina Cretu Andr Loupy Didier Stuerga 《Macromolecular rapid communications》2002,23(3):200-204
Poly(ε‐caprolactone) macromonomers were synthesized under microwave irradiation from commercial caprolactone, using commercial hydrated lanthanide halides as catalysts. The molecular weight of the polymers was in the range 3 000–5 000. Higher molecular weights (5 000–20 000) and lower polydispersity indices were obtained with THF adducts of the lanthanide halides as catalysts and also by applying longer reaction times or using diethylene glycol as a coupling reagent. 相似文献
1000.
Jochen Glaser Simone Dill Michael Marzini Hermann A. Mayer H.‐Jürgen Meyer 《无机化学与普通化学杂志》2001,627(5):1090-1094
(Meta)stable CaC2 One out of four modifications of CaC2 is the so‐called metastable Calcium Carbide, CaC2‐III, which was synthesized as pure material. It forms by heating monoclinic CaC2‐II (C2/c) above 150 °C and remains stable after cooling down to room temperature. The structure was refined from X‐ray powder patterns (C2/m, Z = 4, a = 722.6(1) pm, b = 385.26(7) pm, c = 737.6(1) pm, β = 107.345(2)°). After grinding CaC2‐III transforms back into CaC2‐II. Heating CaC2‐III induces a reversible phase transition into the cubic modification (CaC2‐IV) at 460 °C. Differences between the three different structures of CaC2 I–III, being stable at ambient conditions are also shown by 13C‐MAS‐NMR measurements, especially the presence of two distinct types of carbon atoms in the structure of the title compound. 相似文献