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51.
W. Gao M. Li R. Klie E.I. Altman 《Journal of Electron Spectroscopy and Related Phenomena》2006,150(2-3):136-149
Oxide catalysts are frequently used to convert toxic species to environmentally benign molecules, and to prevent the formation of toxic species in the first place. In this paper, growth and characterization of model oxide systems employed in both approaches is discussed. An example of the former approach is the selective catalytic reduction (SCR) of NO emitted from power plants by NH3, which employs tungsten and vanadium oxides supported on the anatase polymorph of TiO2. To model SCR catalysts, epitaxial titanium, vanadium and tungsten oxide films were grown using molecular beam epitaxy and magnetron sputtering. Two different anatase orientations were grown on LaAlO3 substrates and their interactions with vanadia were characterized. On LaAlO3 (0 0 1), anatase exposed a (4 × 1) reconstructed (0 0 1) surface. Vanadia lifted the reconstruction and at 1 ML a (1 × 1) surface with mostly V5+ was observed. Continued V2O5 growth led to loss of order, but at high temperatures epitaxial VO2 could be grown; vanadia behaved similarly on anatase films on LaAlO3 (1 1 0). Results suggested that the monolayer is pseudomorphic with O adsorption oxidizing the surface V to 5+, since the anatase structure cannot accommodate more bulk oxygen, only a monolayer can be pseudomorphic and have only V5+. Thus the vanadia monolayer has unique structural and chemical properties that can help explain why vanadia monolayers on TiO2 are much more active than bulk V2O5. For WO3, a series of added row reconstructions were observed as the epitaxial films were reduced. The effect of these structures on surface chemistry was characterized by studying 1-propanol adsorption. The results indicated that the structure of the WO3 surface did not alter its catalytic function but had a strong effect on reaction kinetics. As an example of a system where catalysts prevent the formation of toxic species, the reactivity of oxidized Pd surfaces used in CH4 catalytic combustion were studied. An ordered PdO-like monolayer was found to be less reactive towards CO than adsorbed O on Pd. On the other hand, the PdO layer favored a lower activation energy C3H6 oxidation pathway. The results indicated that Pd oxidation reduces the sticking coefficient of reactive species but once molecules adsorb, the oxide surface can reduce the activation energy for subsequent reaction. 相似文献
52.
The possibility that pairs of quarks will form diquark clusters in the regime above deconfinement transition for hadron matter
at finite density is revisited. Here we present the results on the diquark-diquark (dq-dq) interaction in the framework of
constituent quark model taking account of spin, isospin and color degrees of freedom in the spirit of generalized Pauli principle.
By constructing the appropriate spin and color states of the dq-dq clusters we compute the expectation values of the interaction
Hamiltonian involving pairwise quark—quark interaction. We find that the effective interaction between two diquark clusters
is quite sensitive to different configurations characterized by color and spin states, obtained after the coupling of two
diquark states. The value of the coupling parameter for a particular color—spin state, i.e., -3, 1 is compared to the one
obtained earlier by Donoghue and Sateesh,Phys. Rev.
D38, 360 (1988) based on the effective Φ4-theory. This new value of λ derived for different color-spin dq-dq states, may lead to several important implications in
the studies of diquark star and diquark gas. 相似文献
53.
N. Moslemzadeh G. Beamson P. Tsakiropoulos J.F. Watts S.R. Haines P. Weightman 《Journal of Electron Spectroscopy and Related Phenomena》2006
High-energy X-ray photoelectron spectroscopy (XPS) is of particular importance for minimizing the effects of surface contamination by increasing photoelectron escape depths. In this study high-resolution high-energy Cu Kα1 and soft Al Kα1 XPS and Auger electron spectroscopy were used to compare the electronic structure of Ti in TiO2 powder and Ti metal. The Ti 1s in TiO2 XPS line is narrower and more symmetric than in Ti metal. A comparison of the relative intensities of the L23M23M45 and L23M23M23 Auger transitions in Ti metal and TiO2 is consistent with the expected transfer of Ti 3d electrons away from the Ti site in the oxide. The satellites accompanying the Ti 1s XPS line excited by Cu Kα1 X-rays occur at the same energies as the satellites accompanying the Ti 2s and 2p XPS lines excited by Al Kα1 X-rays indicating that they do not depend on the core-level, the experimental resolution or inelastic scattering processes. 相似文献
54.
E. Liénard G. Ban J. Blieck D. Durand F. Duval X. Fléchard M. Herbane M. Labalme Y. Lemière F. Mauger A. Méry O. Naviliat-Cuncic D. Rodríguez J. C. Thomas 《Hyperfine Interactions》2006,172(1-3):29-33
We report on the status of the LPCTrap experiment, devoted to measure the β–ν angular correlation in the pure Gamow–Teller
decay of 6He. This measurement is motivated by the search for the presence of tensor type contributions to the weak interaction. The
6He ions are confined in a novel transparent Paul trap. The β particles and the recoil ions are detected in coincidence to
deduce the angular correlation parameter. The commissioning run performed in 2005 has given the proof of principle of this
experiment. Up to 105 coincidences were recorded during a second run in 2006. 相似文献
55.
养殖池塘沉积物的重金属分布及污染特征 总被引:3,自引:0,他引:3
浙江省淅西北地区淡水养殖池塘沉积物重金属调查研究表明,养殖池塘沉积物中7种重金属元素分布不均衡,差异也较大,除Hg和Cr元素外,其余重金属元素已大大超过土壤本底值.虽然其实测含量都未超出国家规定的标准值范围,但沉积物中重金属元素对养殖水环境、养殖品种存在的潜在污染与危害值得关注.污染指数评价显示,养殖池塘沉积物中主要污染物质为Cu和Cr,而Hg、Pb污染程度相对较轻. 相似文献
56.
Intermolecular Interactions in 8-Aza-D-Homogonane Crystals and their Manifestation in the IR Spectra
A. A. Akhrem A. A. Govorova O. V. Gulyakevich A. S. Lyakhov A. L. Mikhal'chuk I. V. Skornyakov G. B. Tolstorozhev 《Journal of Applied Spectroscopy》2004,71(2):156-163
Crystalline modifications of 8-aza-D-homogon-1,3,5(10),13-tetraen-12,17a-dione have been investigated by IR spectroscopy and x-ray structural analysis. It is shown that this compound crystallizes from solutions of chloroform with hexane in the form of a solvate comprised of chelate hydrogen bonds between the hydrogen atom of the chloroform molecule and the oxygen atoms of the carbonyl groups of the 8-azasteroid molecule. A relation between the changes in the characteristic absorption bands of the CH2-, C=O-, and I=C groups and the structure of the crystalline modifications has been established. 相似文献
57.
We study the elastic responses of double-(ds) and single-stranded (ss) DNA at external force fields. A double-strand-polymer
elastic model is constructed and solved by path integral methods and Monte Carlo simulations to understand the entropic elasticity,
cooperative extensibility, and supercoiling property of dsDNA. The good agreement with experiments indicates that short-ranged
base-pair stacking interaction is crucial for the stability and the high deformability of dsDNA. Hairpin-coil transition in
ssDNA is studied with generating function method. A threshold force is needed to pull the ssDNA hairpin patterns, stabilized
by base pairing and base-pair stacking, into random coils. This phase transition is predicted to be of first order for stacking
potential higher than some critical level, in accordance with experimental observations. 相似文献
58.
59.
I. Iovel L. Golomba J. Popelis S. Grinberga E. Lukevics 《Chemistry of Heterocyclic Compounds》2003,39(1):49-55
The addition of hydrosilanes (HSiEt3, HSiMe2Ph, H2SiPh2) to the CH=N bond of heterocyclic azomethines has been studied in the presence of monovalent complexes of rhodium and palladium. The effect on the reaction of the CF3 group of the aldimines, which were obtained from O-, S-, and N-heteroaromatic aldehydes and 2-trifluoromethylaniline, has been clarified, as were other regularities of the processes being studied. A series of corresponding furans, thiophenes, and pyridine amines has been synthesized. 相似文献
60.
The rotation-tunneling spectrum of the second most stable gGg′ conformer of ethylene glycol (1,2-ethanediol) in its ground vibrational state has been studied in selected regions between 77 and 579 GHz. Compared to the study of the more stable aGg′ conformer, a much larger frequency range was studied, resulting in a much extended frequency list covering similar quantum numbers, J?55 and Ka?19. While the input data were reproduced within experimental uncertainties up to moderately high values of J and Ka larger residuals remain at higher quantum numbers. The severe mixing of the states caused by the Coriolis interaction between the two tunneling substates is suggested to provide a considerable part of the explanation. In addition, a Coriolis interaction of the gGg′ ground vibrational state with an excited state of the aGg′ conformer may also contribute. Relative intensities of closely spaced lines have been investigated to determine the signs of the Coriolis constants between the two tunneling substates relative to the dipole moment components and to estimate the magnitudes of the dipole moment components and the energy difference between the gGg′ and the aGg′ conformers. Results of ab initio calculations on the total dipole moment and the vibrational spectrum were needed for these estimates. The current analysis is limited to transitions with quantum numbers J?40 and Ka?6 plus those having J?22 and Ka?17 which could be reproduced within experimental uncertainties. The results are aimed at aiding radioastronomers to search for gGg′ ethylene glycol in comets and in interstellar space. 相似文献