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121.
Aldehydes are produced in water disinfected primarily by ozone treatment, and are generally present in treated water below the limit of detection (<5 μg L−1) of commonly proposed methods. Formaldehyde is the most studied along with acetaldehyde due to their mutagenic character, and because it causes chromosomal aberrations. This paper reports the first miniaturised system for the simultaneous determination of thirteen aldehydes (aliphatic and aromatic) which are selected based on their frequent or suspected presence in water, mainly as disinfection by-products (DBPs). The micro liquid–liquid extraction (MLLE) method is a miniaturisation of EPA Method 556.1 for carbonyl compounds that includes some innovations, such as performing the derivatising reaction in a strong acidic medium (pH 1.1), and the addition of magnesium sulphate to the aqueous layer as the heating agent, which allows to carry out the whole simultaneous derivatisation/microextraction process in only 1 min. Large-volume sample injection (50 μL) coupled to programmed temperature vaporiser–gas chromatography–mass spectrometry is also used to improve both sensitivity and selectivity. The MLLE method demonstrated high extraction efficiency (96%) with low limits of detection, between 0.7 and 80 ng L−1, and good precision (RSD below 10%, n = 11). The proposed method was evaluated by determining aldehydes in water. Our study demonstrated that the selection of the target aldehydes was appropriate since all were found (at average concentrations from 8.0 to 1.4 μg L−1 for aliphatic and aromatic aldehydes, respectively) in swimming pool waters as DBPs. 相似文献
122.
The growing use of markers in analytical literature in the 10 years, 1991-2000, is presented and discussed because of their relevance in modern analytical chemistry. The complementary and contradictory aspects of markers and others related words, such as tracer, indicator, index, labelling compound, etc., are clarified. To offer a general overview, several classifications of markers are outlined. The main distinction between markers is their internal or external fitness for purpose. Selected examples are assessed on this basis. 相似文献
123.
124.
Eduardo Gallego 《Differential Geometry and its Applications》2005,22(3):315-325
Using results from integral geometry, we find inequalities involving mean curvature integrals of convex hypersurfaces in hyperbolic space. Such inequalities generalize the Minkowski formulas for euclidean convex sets. 相似文献
125.
Summary Free-energy diagrams of amorphous alloys are constructed using Miedema's semiempirical model of heats of formation. These
diagrams account for the experimental glass-forming concentration range in binary alloys of transition metals. One of the
main factors controlling glass formation is the elastic contribution to the heat of mixing of the solid solution phase. Free-energy
diagrams of this kind are also useful for interpreting some characteristic processes occurring in amorphous systems, such
as the spontaneous vitrification observed by Von Allmen and coworkers in several Ti-based and Nb-based alloys.
The authors have agreed not to receive proofs for correction. 相似文献
126.
127.
Amorphous films of NbO2.00 have been prepared by sputtering solid targets of NbO2 in an atmosphere of 10% vol. of H and 90% vol. of Ar. Measurements of the conductivity at high electric fields show that the high field conductivity σ(F) can be described by: where d represents the hopping distance between defect centres having a density of ~ 3 × 1019cm?3. Similar behaviour has been observed previously in other transition metal oxides with the defect centres attributed to oxygen vacancies. 相似文献
128.
129.
In this work, a framework to boost the efficiency of Bayesian inference in probabilistic models is introduced by embedding a Markov chain sampler within a variational posterior approximation. We call this framework “refined variational approximation”. Its strengths are its ease of implementation and the automatic tuning of sampler parameters, leading to a faster mixing time through automatic differentiation. Several strategies to approximate evidence lower bound (ELBO) computation are also introduced. Its efficient performance is showcased experimentally using state-space models for time-series data, a variational encoder for density estimation and a conditional variational autoencoder as a deep Bayes classifier. 相似文献
130.
Faustino Aguilera‐Granja Jesús Carrete Andrés Vega Luis J. Gallego 《International journal of quantum chemistry》2015,115(8):523-528
We performed density‐functional‐theoretic calculations to investigate the structural, magnetic and vibrational properties of the stoichiometric clusters (CrN)n ( ). We show that the building block of the ground‐state structures of these clusters is a square CrNCrN unit; the only exception with n > 2 occurs for (CrN)3, but this cluster has an isomer not very far in energy from the ground state consisting of a pair of CrNCrN squares sharing a CrN bond. In the smaller CrN, (CrN)2, and (CrN)3 clusters the magnetic moments of the N atoms are non‐negligible and antiparallel to those of the Cr atoms, but for the larger species (CrN)4, (CrN)5, (CrN)6, and (CrN)9 the cluster magnetic moments are almost entirely due to the Cr atoms. Lack of imaginary vibrational frequencies in the predicted ground‐state structures of (CrN)n ( ) confirms that they are mechanically stable equilibrium states. © 2015 Wiley Periodicals, Inc. 相似文献