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201.
Johnny D. Reynolds Kelsey D. Cook 《Journal of the American Society for Mass Spectrometry》1990,1(2):149-157
The relative effects of adjustable fast atom bombardment (FAB) parameters (choice of matrix, primary atom flux, and primary atom energy) on the appearance of FAB spectra (including signal-to-noise, signal-to-background, and signal-to-matrix ratios) of several organic dyes have been investigated. Beam-induced chemical damage is minimized by lowering the primary atom flux, by raising the primary atom energy, and by selecting a matrix with radical scavenging properties (e.g., m-nitrobenzyl alcohol). The relative importance in minimizing this chemical damage is choice of matrix > primary atom flux > (nominal) primary atom energy, but optimization of the parameters involves a trade-off between sensitivity and damage. The effect of these parameters on thermal damage (fragmentation) is much less. It can be concluded from comparison of the dyes that the extent of beam damage does not depend simply on the standard reduction potential of the analyte. 相似文献
202.
David A. Babb Richard A. Bartsch James J. Collier Dhimant H. Desai Sadik Elshania Mi‐Ja Goo Johnny L. Hallman Gwi Suk Heo Xiaowu Huang Vincent J. Huber Hong‐Sik Hwang Russell J. Johnson Yung Liu Michael J. Pugia Qiang Zhao 《Journal of heterocyclic chemistry》2004,41(5):659-675
Structurally related dibenzo‐16‐crown‐5 lariat ethers with pendant ester and ether groups are prepared. Structural variations within the series of alkyl lariat ether esters include changes in the O‐alkyl group, attachment site and nature of the lipophilic group, and length of the spacer, which connects the ester group to the polyether framework. Also synthesized are bis(crown ether) diesters with two dibenzo‐16‐crown‐5 or two dicyclohexano‐16‐crown‐5 units and two ester groups connected to each other by a linker of varying length. Synthetic strategies for the preparation of these lariat ethers with pendant ester‐ and ether‐containing side arms are described. 相似文献
203.
Johnny L. Jackson 《Journal of heterocyclic chemistry》1991,28(1):109-111
The reaction of 2-lithiobenzo[b]thiophenes with ketones produced 2-hydroxyalkylbenzo[b]thiophenes which were cyclized in thionyl chloride to give novel thieno[3,2-b][1]benzothiophenes. Oxidation with peroxyacetic acid gave the S,S-dioxides whose regiochemistry was identified from 1H nmr model studies using substituted benzo[b]thiophenes and their corresponding-1,1-dioxides [1]. 相似文献
204.
This article analyzes the solvability of second-order, nonlinear dynamic boundary value problems (BVPs) on time scales. New Bernstein–Nagumo conditions are developed that guarantee an a priori bound on the delta derivative of potential solutions to the BVPs under consideration. Topological methods are then employed to gain solvability. 相似文献
205.
Paul W. Eloe Johnny Henderson 《Journal of Mathematical Analysis and Applications》2007,331(1):240-247
For the nth order differential equation, y(n)=f(x,y,y′,…,y(n−1)), we consider uniqueness implies existence results for solutions satisfying certain nonlocal (k+2)-point boundary conditions, 1?k?n−1. Uniqueness of solutions when k=n−1 is intimately related to uniqueness of solutions when 1?k?n−2. These relationships are investigated as well. 相似文献
206.
Bjarke Thomas Dalslet Martin Sgaard Henny J.M. Bouwmeester Peter Vang Hendriksen 《Solid State Ionics》2009,180(20-22):1173-1182
This paper is the first part of a two part series, where the effects of varying the A-site dopant on the defect chemistry, the diffusion coefficient and the surface catalytic properties of the materials (La0.6Sr0.4 − xMx)0.99Co0.2Fe0.8O3 − δ, M = Sr, Ca (x = 0.05, 0.1), Ba (x = 0.1, 0.2) (LSMFC) have been investigated. In part I, the findings on the defect chemistry are reported, while the transport properties are reported in part II. Substitution of Sr2+ ions with Ca2+ ions (smaller ionic radius) and Ba2+ ions (larger ionic radius) strains the crystal structure differently for each composition while keeping the average valence of the cations constant. The Ba2+ containing materials show the largest oxygen loss at elevated temperatures, while the purely Sr2+ doped material showed the smallest oxygen loss. This was reflected in the partial oxidation entropy of the materials. The measured oxygen loss was modelled with point defect chemistry models. Measurements at very low pO2 showed several phase transitions. 相似文献
207.
Florian Hastreiter Corinna Lorenz Johnny Hioe Stefanie Grtner Nanjundappa Lokesh Nikolaus Korber Ruth M. Gschwind 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(10):3165-3169
The existence of [μ‐HSi4]3? in liquid ammonia solutions is confirmed by 1H and 29Si NMR experiments. Both NMR and quantum chemical calculations reveal that the H atom bridges two Si atoms of the [Si4]4? cluster, contrary to the expectation that it is located at one vertex Si of the tetrahedron. The calculations also indicate that in the formation of [μ‐HSi4]3?, protonation is driven by a high charge density and an increase of electron delocalization compared to [Si4]4?. Additionally, [Si5]2? was detected for the first time and characterized by NMR. Calculations show that it is resistant to protonation, owing to a strong charge delocalization, which is significantly reduced upon protonation. Thus, our methods reveal three silicides in liquid ammonia: unprotonated [Si5]2?, terminally protonated [HSi9]3?, and bridge‐protonated [μ‐HSi4]3?. The protonation trend can be roughly predicted by the difference in charge delocalization between the parent compound and the product, which can be finely tuned by the presence of counter ions in solution. 相似文献
208.
José Delgado-Linares Nilo Morillo Mairis Guevara Johnny Bullón 《Journal of Dispersion Science and Technology》2019,40(1):74-81
Asphaltenes from three crudes were precipitated with a mixture of n-heptane and toluene, the size of the particles formed under different solvent mixtures and different agitation regimes were studied. The kinetic size reduction of aggregates formed with an excess of precipitant agent is followed, contrary to other published studies where the kinetic followed is of growing particles. It was found that the particle size of precipitated asphaltenes decreases as precipitant aromaticity increases and agitation energy rises, which indicates the formation of aggregates bonded by weak forces, since the agitation applied was not of high energy, except for the ultrasonic device. 相似文献
209.
Some properties related to the NUT--Taub-like spacetime,
such as the surface of infinite red-shift, horizon, singularity
and the area of the NUT--Taub-like black hole are discussed.
Furthermore, the geodesics in the NUT--Taub-like spacetime are
obtained in some special cases. Specifically, the circular orbits
for a massive particle are derived, which can reduce to the cases
of the Schwarzschild spacetime and the NUT--Taub spacetime when
m*=0 and m*\ll M, respectively. 相似文献
210.
Sufficient conditions are given for the existence of a solution of a fourth order nonlinear boundary value problem with nonlinear boundary conditions. The conditions assume the existence of a strong upper solution-lower solution pair, a concept that is defined in the paper. The differential equation has nonlinear dependence on all lower order derivatives of the unknown; in particular, appropriate Nagumo conditions are obtained and employed. 相似文献