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161.
J. M. Quintela M. C. Veiga S. Conde C. Peinador 《Monatshefte für Chemie / Chemical Monthly》1996,127(6-7):739-745
Summary A facile synthesis of 8-substituted pyrimido[4,5:4,5]thieno[2,3-c]pyridazines (6a–i) has been accomplished. The sequence involves the ring closure of a heterocyclic aminonitrile precursor (3) after reaction with (dichloromethylene)-dimethylammonium chloride.
Eine allgemeine Synthese von Pyrimido[4,5:4,5]thieno[2,3-c]pyridazin-Derivaten
Zusammenfassung Es wurde ein einfacher Syntheseweg für 8-substituierte Pyrimido[4,5:4,5]thieno-[2,3-c]pyridazine entwickelt. Die Reaktion verläuft über den Ringschluß eines heterocyclischen Aminonitrilvorläufers (3) nach Umsetzung mit Dichlormethylen-dimethylammoniumchlorid.相似文献
162.
Pereira-Meirelles Fatima Ventura Rocha-LeãO Maria Helena Miguez Anna Geraldo Lippel Santť 《Applied biochemistry and biotechnology》1997,(1):73-85
Although Upases have been intensively studied, some aspects of enzyme production like substrate uptake, catabolite repression,
and enzyme stability under long storage periods are seldom discussed in the literature. This work deals with the production
of lipase by a new selected strain ofCandida lipolytica. Concerning nutrition, it was observed that inorganic nitrogen sources were not as effective as peptone, and that oleic acid
or triacylglycerides (TAG) were essential carbon sources. Repression by glucose and stimulation by oleic acid and long chain
TAG (triolein and olive oil) were observed. Extracellular lipase activity was only observed at high levels at late stationary
phase, whereas intracellular lipase levels were constant and almost undetectable during the cultivation period, suggesting
that the produced enzyme was attached to the cell wall, mainly at the beginning of cultivation. The crude lipase produced
by this yeast strain shows the following optima conditions: pH 8.0–10.0, temperature of 55°C. Moreover, this preparation maintains
its full activity for at least 370 d at 5°C. 相似文献
163.
H. Beirão da Veiga 《Communications in Mathematical Physics》1987,109(2):229-248
In this paper we study the system (1.1), (1.3), which describes the stationary motion of a given amount of a compressible heat conducting, viscous fluid in a bounded domain ofR
n, n2. Hereu(x) is the velocity field, (x) is the density of the fluid, (x) is the absolute temperature,f(x) andh(x) are the assigned external force field and heat sources per unit mass, andp(, ) is the pressure. In the physically significant case one hasg=0. We prove that for small data (f, g, h) there exists a unique solution (u, , ) of problem (1.1), (1.3)1, in a neighborhood of (0,m, 0); for arbitrarily large data the stationary solution does not exist in general (see Sect. 5). Moreover, we prove that (for barotropic flows) the stationary solution of the Navier-Stokes equations (1.8) is the incompressible limit of the stationary solutions of the compressible Navier-Stokes equations (1.7), as the Mach number becomes small. Finally, in Sect. 5 we will study the equilibrium solutions for system (4.1). For a more detailed explanation see the introduction. 相似文献
164.
Pedro Linares Sara Lumbreras Alberto Santamaría Andrea Veiga 《Annals of Operations Research》2016,246(1-2):227-251
We consider the 1-median problem with euclidean distances with uncertainty in the weights, expressed as possible changes within given bounds and a single budget constraint on the total cost of change. The upgrading (resp. downgrading) problem consists of minimizing (resp. maximizing) the optimal 1-median objective value over these weight changes. The upgrading problem is shown to belong to the family of continuous single facility location-allocation problems, whereas the downgrading problem reduces to a convex but highly non-differentiable optimization problem. Several structural properties of the optimal solution are proven for both problems, using novel planar partitions, the knapsack Voronoi diagrams, and lead to polynomial time solution algorithms. 相似文献
165.
José W. da Cruz Jr. Lucas R. de Moraes Marcelo H. dos Santos Geraldo Alves da Silva Maisa R. P. L. Brigagão Javier Ellena Antonio C. Doriguetto 《Helvetica chimica acta》2008,91(1):144-154
The crystalline structure of mangiferin (=2‐β‐D ‐glucopyranosyl‐1,3,6,7‐tetrahydroxy‐9H‐xanthen‐9‐one; 1 ), a biologically active xanthenone C‐glycoside, isolated from the stem bark of Mangifera indica (Anacardiaceae), was unambiguously determined by single‐crystal X‐ray diffraction (XRD). The crystal structure is summarized as follows: triclinic, P1, a=7.6575(5), b=11.2094(8), c=11.8749(8) Å, α=79.967(5), β=87.988(4), γ=72.164(4)°, V=955.3(1) Å3, and Z=2. The structure also shows two molecules in the asymmetric unit cell and five crystallization H2O molecules. The packing is stabilized by several intermolecular H‐bonds involving either the two symmetry‐independent mangiferin molecules 1a and 1b , or the H2O ones. 相似文献
166.
167.
In this work we present some advances towards full digitization of the detection subsystem of a Mössbauer transmission spectrometer. We show how, using adequate instrumentation, preamplifier output of a proportional counter can be digitized with no deterioration in spectrum quality, avoiding the need of a shaping amplifier. A pipelined architecture is proposed for a digital processor, which constitutes a versatile platform for the development of pulse processing techniques. Requirements for minimization of the analog processing are considered and experimental results are presented. 相似文献
168.
Geraldo M. de Lima Solange M. S. V. Wardell James L. Wardell Edward R. T. Tiekink 《Journal of chemical crystallography》2010,40(12):1159-1162
Abstract
The title molecule, 4-acetamidobenzaldehyde 4-nitrophenylhydrazone, is essentially planar with the maximum deviations from the least-squares plane through the 22 non-hydrogen atoms being 0.176(1) ? (nitro-O) and −0.152(1) ? (amide-O). The dihedral angle between the benzene rings is 6.93(7)°. The conformation about the C=N bond is E. The presence of amide-H···O-nitro and hydrazine-H···O-amide hydrogen bonding leads to the formation of zigzag 2-D arrays with a pseudo three-connected brick-wall network when viewed normal to the plane of the layer. The layers are sustained by 38-membered {···OCNC5N2C4NO···HNCO···HN2C5NH···ONC4NH} synthons and the rather large voids defined by these are occupied by a centrosymmetrically related layer to result in the formation of a doubly interpenetrated network. These stack along the b direction being connected by C–H···O interactions. The compound crystallizes in the monoclinic space group P21/c with a = 10.8152(3) ?, b = 10.9469(2) ?, c = 12.9198(4) ?, β = 113.679(1)°, and Z = 4. 相似文献169.
Geraldo D. Matos Edmagno B. dos Reis Antonio C.S. Costa Sergio L.C. Ferreira 《Microchemical Journal》2009,92(2):135-139
In the present work, a cloud point extraction (CPE) system has been proposed for determination of species de chromium in the natural water samples, Cr(III) and Cr(VI). The procedure was based on the reaction of Cr(III) with 1-(2-pyridilazo)-2-naphtol (PAN) in a surfactant solution (Triton X-114) yielding a hydrophobic complex, which then is entrapped “in situ” in the surfactant micelles. When the temperature of the system was higher than the cloud point of Triton X-114, the complex of Cr(III)-PAN entered the surfactant-rich phase and thus separation of the analyte from the matrix was achieved. Separation of the two phases was accomplished by centrifugation for 15 min at 2500 rpm. The Cr(VI) assay is based on its reduction to Cr(III) by ascorbic acid which subsequently reacts with PAN in a similar manner. The main factors affecting the cloud point extraction, such as complexation pH (7.7), buffer concentration (0.025 mol L− 1) and microwave irradiation time (10 min) were optimized by response surface methodology (RSM) using Box–Behnken design. Under the optimized conditions, the preconcentration system (50 mL sample) permitted an enrichment factor of 48, linear range of 2.5–80 μg L− 1, limit of detection and quantification of 0.7 and 2.5 μg L− 1, respectively, and the relative standard deviation (n = 10) of 2.0% for 50 μg L− 1 Cr(III) solution and (n = 10) 5.5% for 10 μg L− 1. The proposed procedure was applied to the speciation of chromium in river water samples. The procedure affords recoveries of 84–115% and a relative standard deviation lower than 4.2%. The analytical results of total chromium in the river water samples under study agreed well with those by electrothermal atomic absorption spectrometry (ET AAS). It is proved that the procedure can be successfully employed as an alternative to the commonly used preconcentration and speciation analytical techniques. 相似文献