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Conjugated block copolymers are potentially useful for organic electronic applications and the study of interfacial charge and energy transfer processes; yet few synthetic methods are available to prepare polymers with well‐defined conjugated blocks. Here, we report the synthesis and thin film morphology of a series of conjugated poly(3‐hexylthiophene)‐block‐poly(9,9‐dioctylfluorene) (P3HT‐b‐PF) and poly(3‐dodecylthiophene)‐block‐poly(9,9‐dioctylfluorene) (P3DDT‐b‐PF) block copolymers prepared by functional external initiators and click chemistry. Functional group control is quantified by proton nuclear magnetic resonance spectroscopy, size‐exclusion chromatography, and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. The thin film morphology of the resulting all‐conjugated block copolymers is analyzed by a combination of grazing‐incidence X‐ray scattering, atomic force microscopy, and transmission electron microscopy. Crystallization of the P3HT or P3DDT blocks is present in thin films for all materials studied, and P3DDT‐b‐PF films exhibit significant PF/P3DDT co‐crystallization. Processing conditions are found to impact thin film crystallinity and orientation of the π–π stacking direction of polymer crystallites. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 154–163  相似文献   
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A geometric graph is a simple graph drawn on points in the plane, in general position, with straightline edges. A geometric homomorphism from to is a vertex map that preserves adjacencies and crossings. This work proves some basic properties of geometric homomorphisms and defines the geochromatic number as the minimum n so that there is a geometric homomorphism from to a geometric n‐clique. The geochromatic number is related to both the chromatic number and to the minimum number of plane layers of . By providing an infinite family of bipartite geometric graphs, each of which is constructed of two plane layers, which take on all possible values of geochromatic number, we show that these relationships do not determine the geochromatic number. This article also gives necessary (but not sufficient) and sufficient (but not necessary) conditions for a geometric graph to have geochromatic number at most four. As a corollary, we get precise criteria for a bipartite geometric graph to have geochromatic number at most four. This article also gives criteria for a geometric graph to be homomorphic to certain geometric realizations of K2, 2 and K3, 3. © 2011 Wiley Periodicals, Inc. J Graph Theory 69:97‐113, 2012  相似文献   
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Abstract

A method was developed and validated to measure octamethylcyclotetrasiloxane (D4)? quantitatively by gas chromatography-mass spectrometry (GC-MS) at low level in extracts of several biological matrices that include plasma, liver, lung, feces and fat from rats. The key to the successful determination lay in the use of extracts dried with anhydrous magnesium sulfate. This was necessary in view of the propensity of the methyl siloxane based GC-stationary phase to generate D4 by its reaction with water present in the extracts. To enable quantiiation of D4 at parts per billion (μg/L) levels, the base ion m/z 281 resulting from the loss of a methyl group from the parent molecule was selected for monitoring by SIM mode in GC-MS. The recovery of D4 from any of the biological matrices was determined to be greater than 90% in three extractions. The D4 response for the standards in GC-MS was linear (R2 > 0.9900) and reproducible at concentrations ranging from 1—16,000 ng D4/g solvent. Precision was less than 5%.  相似文献   
6.

In this paper, we study nonlinear discrete boundary value problems of the form x ( t +1)= A ( t ) x ( t )+ h ( t )+ k f ( t , x ( t ), k ) subject to Bx (0)+ Dx ( J )= u + k g ( x (0), x ( J ), k ) where k is a "small" parameter. Our main concern is the case of resonance, that is, the situation where the associated linear homogeneous boundary value problem x ( t +1)= A ( t ) x ( t ), Bx (0)+ Dx ( J )=0 admits nontrivial solutions. We establish conditions for the solvability of the nonlinear boundary value problem when k is "small". We also establish qualitative properties of these solutions.  相似文献   
7.
The purpose of the study was to examine the effectiveness of the Iowa Chautauqua Professional Development Program in terms of changes in concept mastery, use of process skills, application of science concept and skills, student attitudes toward science, student creativity, and student perceptions regarding their science classrooms. Participants were 12 teachers who agreed to participate in an experimental study where an inquiry approach was utilized with one section and traditional strategies in another section. A total of 24 sections of students were enrolled in inquiry sections (365 students) and traditional sections (359 students). The data collected were analyzed using quantitative methods. The results are tabulated and contrasted for students enrolled in the two sections for each teacher. The results indicate that student use and understanding of science skills and concepts in the inquiry sections increased significantly more than they did for students enrolled in typical sections in terms of process skills, creativity skills, ability to apply science concepts, and the development of more positive attitudes.  相似文献   
8.
Prioritized OWA aggregation   总被引:2,自引:0,他引:2  
We indicate that the problem of prioritized criteria arises in situations in which there exists a relationship between the criteria so that lack of satisfaction by the higher priority criteria cannot be readily compensated for by satisfaction by lower priority criteria. Typical of this situation is the relationship between safety and cost. We consider the problem of criteria aggregation in this environment. Central to our approach is the use of importance weights to enforce this prioritization imperative. We apply our use of priority based importance weights to the case where the scope of the criteria aggregation is an OWA type aggregation.  相似文献   
9.
We review the theoretical underpinning of nonequilibrium umbrella sampling. We provide its historical context and show how it relates to other important results in nonequilibrium statistical mechanics. Its relationships to the generalised Yamada-Kawasaki distribution function is explored. A new functional version of the Crooks Fluctuation Theorem is also presented.  相似文献   
10.
Our prediction that phase II of dipotassium hydrogen chromatoarsenate, K2[HCr2AsO10], is ferroelectric, based on the analysis of the atomic coordinates by Averbuch‐Pouchot, Durif & Guitel [Acta Cryst. (1978), B 34 , 3725–3727], led to an independent redetermination of the structure using two separate crystals. The resulting improved accuracy allows the inference that the H atom is located in the hydrogen bonds of length 2.555 (5) Å which form between the terminal O atoms of shared AsO3OH tetrahedra in adjacent HCr2AsO102− ions. The largest atomic displacement of 0.586 Å between phase II and the predicted paraelectric phase I is by these two O atoms. The H atoms form helices of radius ∼0.60 Å about the 31 or 32 axes. Normal probability analysis reveals systematic error in seven or more of the earlier atomic coordinates.  相似文献   
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