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141.
Let Ω be an open subset of , N ? 3, containing 0. We consider the solutions of ?Δu(x) + g(u(x)) = f(x) in Ω-{0}, where g is nondecreasing and f is bounded and we study the possible singularities at 0: when u(x) = o(|x|1 ? N) we prove that u is isotropic near 0 and show that either it is a C1 function in Ω (removable singularity) or |x|N ? 2u(x) → c, c ≠ 0 (weak singularity) or |x|N ? 2 |u(x) |→ + ∞ (strong singularity). We also characterize the g's for which solutions with a weak singularity exist and improve a previous removability result of H. Brézis and L. Véron (Arch. Rational Mech. Anal.23 (1979), 153–166). 相似文献
142.
143.
The substrate and field dependencies of surface SPINOE enhancements using optical pumping and magic angle spinning NMR were monitored. Relaxation rates and enhancements were examined to gain an understanding of the parameters that determine the SPINOE enhancement. (13)C-labeled deuterated methanol was adsorbed on three different substrates (SnO(2), TiO(2), Ti/SiO(2)) with heats of adsorption for xenon ranging from 14.2 to 22.6 kJ/mol. The different heats of adsorption led to a range of xenon coverages and xenon relaxation rates. Using a simple model along with experimental values for the xenon surface polarization and cross- and self-relaxation rates, the (13)C signal enhancement could be predicted and compared with experimental enhancement values. Magnetic field dependence studies were also made by monitoring the (13)C enhancements via SPINOE from hyperpolarized xenon at fields of 0.075, 4.7, and 9.4 T. The pertinent parameters necessary to achieve maximum SPINOE enhancement are discussed. 相似文献
144.
We report on a global potential energy hypersurface for the upper sheet of the lowest triplet state of H3+. The analytic representation is based on the double many-body expansion theory. The ab initio data points, calculated with a large cc-pV5Z basis, are represented with a root mean square deviation of only 5.54 cm(-1) in the energy region below the H(+)+2H(2S) dissociation threshold. The quasi-bound vibronic states supported by this surface have also been calculated. 相似文献
145.
In this work we have studied the stabilizing effect of a natural antioxidant, sugar cane bagasse-lignin, on the photo-oxidation of a commercial sample of butadiene rubber. This stabilizer was investigated in various concentrations, in the pure form, and associated with a diamine or a phosphite stabilizer. Stabilization of butadiene rubber with this lignin associated with the diamine produced a material with a photo-chemical stability comparable to that of a stabilized commercial sample. 相似文献
146.
Liu JA Petzold CJ Ramirez-Arizmendi LE Perez J Kenttämaa H 《Journal of the American Chemical Society》2005,127(37):12758-12759
Laser-induced acoustic desorption combined with mass spectrometry has been used to demonstrate that phenyl radicals can attack dinucleoside phosphates at both the sugar and base moieties, that purine bases are more susceptible to the attack than pyrimidine bases, and that the more electrophilic the radical, the more efficient the damage to dinucleoside phosphates. 相似文献
147.
Sarkar B Kaim W Klein A Schwederski B Fiedler J Duboc-Toia C Lahiri GK 《Inorganic chemistry》2003,42(20):6172-6174
The Ru(2)(III,II) mixed-valent state is strongly stabilized in [(bpy)(2)Ru(mu-bttz)Ru(bpy)(2)](5+) (3(5+), bttz = 3,6-bis(2-thienyl)-1,2,4,5-tetrazine, as evident from lowered oxidation potentials and isolability, a strongly increased comproportionation constant K(c) = 10(16.6), and a high-energy intervalence charge transfer band at 10100 cm(-1). Curiously, no such effects were observed for the diosmium(III,II) analogue, whereas the related systems [(bpy)(2)M(mu-bmptz)M(bpy)(2)](5+), bmptz = 3,6-bis(4-methyl-2-pyridyl)-1,2,4,5-tetrazine, exhibit conventional behavior, i.e., a slightly higher K(c) value of the Os(2)(III,II) analogue. EPR signals were observed at 4 K for 3(5+) but not for the other mixed-valent species, and high-frequency (285 GHz) EPR was employed to study the diruthenium(II) radical complexes 2(3+) and 3(3+). 相似文献
148.
Eulogio Jimenez Luis Romani Maria Inmaculada Paz Andrade Geneviève Roux-Desgranges Jean-Pierre E. Grolier 《Journal of solution chemistry》1986,15(11):879-890
Molar excess volumes V
E
at 25°C have been determined by vibrating-tube densimetry, as a function of mole fraction x for different series of an alkanoate (H
2m+1
C
m
COOC
n
H
2n+1
)+cyclohexane. Three types of alkanoates were investigated, i.e., methanoates (m=0, with n=3 and 4), ethanoates (m=1, with n=2, 3, and 4) and propanoates (m=2, with n=1, 2, and 3). In addition, a Picker flow calorimeter was used to obtain molar excess heat capacities C
p
E
at constant pressure at the same temperature. V
E
is positive for all systems and rather symmetric, with V
E
(x=0.5) amounting to almost identical values in a series of mixtures containing an alkanoate isomer of same formula (say C4H8O2, C5H10O2, or C6H12O2). The composition dependence of C
p
E
is rather unusual in that two more or less marked minima are observed for most of the mixtures, especially when the alkanoate is a methanoate or an ethanoate. These results are discussed in terms of possible changes in conformation of both the ester and cyclohexane. 相似文献
149.
Rezende MC Flores P Guerrero J Villarroel L 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(7):1637-1640
The 13C NMR of two solvatochromic dyes derived from a barbituric acid acceptor and dimethylaminophenyl donor fragments, compound 1 and the related merocyanine 2, were recorded in various solvents. The observed chemical-shift variations were used to interpret their structural differences and solvatochromic behavior in solution. 相似文献
150.
Hong SB Lee SH Shin CH Woo AJ Alvarez LJ Zicovich-Wilson CM Camblor MA 《Journal of the American Chemical Society》2004,126(42):13742-13751
Here, we report that synthetic gallosilicate molecular sieves with the NAT topology and Si/Ga ratios close to but slightly higher than 1.50 undergo an in situ transformation under their crystallization conditions. The materials have been studied ex situ by using powder X-ray diffraction, elemental and thermal analyses, and multinuclear MAS NMR. The transformation is characterized by a change in the distribution of Si and Ga of the NAT framework, from a quite (but not completely) disordered phase to a very highly (but not completely) ordered one, accompanied by a change from tetragonal to orthorhombic symmetry. During most of the solution-mediated transformation, no noticeable signs of fresh precipitation, phase segregation, or changes in the chemical composition are detected. Intermediate materials show variations in the degree of Si-Ga ordering and orthorhombic distortion and are not physical mixtures of the disordered and ordered phases. Ab initio calculations strongly suggest a preferential siting of Si in the tetrahedral sites involved in a smaller number of 4-rings in the NAT topology (i.e., the low multiplicity site). The cost of violations of Loewenstein's rule has also been calculated. For this topology and chemical composition the preferential siting and Loewenstein's rule drive together the system to the ordered configuration. A Monte Carlo sampling procedure affords a reasonable model for the initial, mainly disordered state, which fits well within the experimental disorder-order series. 相似文献