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41.
Influence of Solution Volume on the Dissolution Rate of Silicon Dioxide in Hydrofluoric Acid 下载免费PDF全文
Boris Shvartsev Danny Gelman Ilia Komissarov Alon Epshtein Dr. David Starosvetsky Prof. Yair Ein‐Eli 《Chemphyschem》2015,16(2):370-376
Experimental data and modeling of the dissolution of various Si/SiO2 thermal coatings in different volumes of hydrofluoric acid (HF) are reported. The rates of SiO2‐film dissolution, measured by means of various electrochemical techniques, and alteration in HF activity depend on the thickness of the film coating. Despite the small volumes (0.6–1.2 mL) of the HF solution, an effect of SiO2‐coating thickness on the dissolution rate was detected. To explain alterations detected in HF activity after SiO2 dissolution, spectroscopic analyses (NMR and FTIR) of the chemical composition of the solutions were conducted. This is associated with a modification in the chemical composition of the HF solution, which results in either the formation of an oxidized species in solution or the precipitation of dissolution products. HF2? accumulation in the HF solution, owing to SiO2 dissolution was identified as the source of the chemical alteration. 相似文献
42.
43.
A novel iodide-catalyzed reduction method using hypophosphorous and/or phosphorus acids was developed to reduce both diaryl ketones and nitroarenes chemoselectively in the presence of chloro and bromo substituents in high yield. This efficient and practical method has been successfully applied to a large scale production of a potential anticancer agent. 相似文献
44.
In this paper, we study the problems of (approximately) representing a functional curve in 2-D by a set of curves with fewer
peaks. Representing a function (or its curve) by certain classes of structurally simpler functions (or their curves) is a
basic mathematical problem. Problems of this kind also find applications in applied areas such as intensity-modulated radiation
therapy (IMRT). Let f\bf f be an input piecewise linear functional curve of size n. We consider several variations of the problems. (1) Uphill–downhill pair representation (UDPR): Find two nonnegative piecewise
linear curves, one nondecreasing (uphill) and one nonincreasing (downhill), such that their sum exactly or approximately represents
f\bf f. (2) Unimodal representation (UR): Find a set of unimodal (single-peak) curves such that their sum exactly or approximately
represents f\bf f. (3) Fewer-peak representation (FPR): Find a piecewise linear curve with at most k peaks that exactly or approximately represents f\bf f. Furthermore, for each problem, we consider two versions. For the UDPR problem, we study its feasibility version: Given ε>0, determine whether there is a feasible UDPR solution for f\bf f with an approximation error ε; its min-ε version: Compute the minimum approximation error ε
∗ such that there is a feasible UDPR solution for f\bf f with error ε
∗. For the UR problem, we study its min-k version: Given ε>0, find a feasible solution with the minimum number k
∗ of unimodal curves for f\bf f with an error ε; its min-ε version: given k>0, compute the minimum error ε
∗ such that there is a feasible solution with at most k unimodal curves for f\bf f with error ε
∗. For the FPR problem, we study its min-k version: Given ε>0, find one feasible curve with the minimum number k
∗ of peaks for f\bf f with an error ε; its min-ε version: given k≥0, compute the minimum error ε
∗ such that there is a feasible curve with at most k peaks for f\bf f with error ε
∗. Little work has been done previously on solving these functional curve representation problems. We solve all the problems
(except the UR min-ε version) in optimal O(n) time, and the UR min-ε version in O(n+mlog m) time, where m<n is the number of peaks of f\bf f. Our algorithms are based on new geometric observations and interesting techniques. 相似文献
45.
Stefan Krause Danny Kowerko Richard Börner Prof. Christian G. Hübner Prof. Christian von Borczyskowski 《Chemphyschem》2011,12(2):303-312
Spectral diffusion as a result of both the transitions between different molecular conformers and the ′′molecular softness′′ of quasi‐free perylene diimides on a SiO2 surface is investigated by means of single‐molecule spectroscopy, which reveals the time dependence of both the fluorescence spectra and the three‐dimensional orientation. Spectral wavelengths of all single emitters cover a wide energy range of about 0.27 eV, which is due to different types of conformers with large differences in optical transition energy. Time‐dependent spectral trajectories of single emitters within this wavelength manifold are evaluated with a model transcribed from the analysis of spatial diffusion. Spectral diffusion processes are closely correlated with fluorescence emission and excitation power. The overall analysis of spectral diffusion reveals, similar to proteins, a hierarchy of energy barriers in a broad energy landscape. 相似文献
46.
School STEM Culture—an aspect of culture within a school community—is defined as the beliefs, values, practices, and resources in STEM fields as perceived by students, parents, teachers, and administrators and counselors within a school. This study validates the STEM Culture Assessment Tool (STEM‐CAT), an instrument intended to advance the use of the School STEM Culture construct within the research community. Internal consistency was determined through the use of Cronbach's alpha and factor analyses, and the instrument was found to be a reliable measure of School STEM Culture. The instrument can be used in future research to quantify School STEM Culture to determine if interventions change the culture of a school to further STEM education. 相似文献
47.
Danny Z. Chen 《Journal of Algorithms in Cognition, Informatics and Logic》1996,20(3):459-478
Given ann-vertex simple polygonP, the problem of computing the shortest weakly visible subedge ofPis that of finding a shortest line segmentson the boundary ofPsuch thatPis weakly visible froms(ifsexists). In this paper, we present new geometric observations that are useful for solving this problem. Based on these geometric observations, we obtain optimal sequential and parallel algorithms for solving this problem. Our sequential algorithm runs inO(n) time, and our parallel algorithm runs inO(log n) time usingO(n/log n) processors in the CREW PRAM computational model. Using the previously best known sequential algorithms to solve this problem would takeO(n2) time. We also give geometric observations that lead to extremely simple and optimal algorithms for solving, both sequentially and in parallel, the case of this problem where the polygons are rectilinear. 相似文献
48.
Experimental results are presented for rotating Couette flows with and without circumferential pressure gradients between a rotating disk and a stationary fluid chamber. The spinning disk and the top of the C-shaped fluid chamber are separated by a μ-scale gap that forms the fluid chamber passage with inner and outer radii of 1.19 and 2.38 mm, respectively. Ranges of experimental conditions are presented to demonstrate the fluid dynamics of the test arrangement, and for determination of fluid viscosity, and gas slip flow accommodation coefficients. As such, the test arrangement provides means to determine such fluid and flow properties using microliter sample sizes, with relatively low magnitudes of experimental uncertainty. 相似文献
49.
The central result of this paper is an explicit computation of the Hochschild and cyclic homologies of a natural smooth subalgebra of stable continuous trace algebras having smooth manifolds X as their spectrum. More precisely, the Hochschild homology is identified with the space of differential forms on X, and the periodic cyclic homology with the twisted de Rham cohomology of X, thereby generalising some fundamental results of Connes and Hochschild-Kostant-Rosenberg. The Connes-Chern character is also identified here with the twisted Chern character. 相似文献
50.
We study a class of subdivision invariant lattice models based on the gauge groupZ
p
, with particular emphasis on the four dimensional example. This model is based upon the assignment of field variables to both the 1- and 2-dimensional simplices of the simplicial complex. The property of subdivision invariance is achieved when the coupling parameter is quantized and the field configurations are restricted to satisfy a type of mod-p flatness condition. By explicit computation of the partition function for the manifoldRP
3×S
1, we establish that the theory has a quantum Hilbert space which differs from the classical one.Supported by Stichting voor Fundamenteel Onderzoek der Materie (FOM) 相似文献