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71.
Hauke Harms Julien Rime Olivier Leupin Stephan J. Hug Jan Roelof van der Meer 《Mikrochimica acta》2005,151(3-4):217-222
A luminescent bacterial biosensor was used to quantify bioavailable arsenic in artificial groundwater. Its light production
above the background emission was proportional to the arsenite concentration in the toxicologically relevant range of 0 to
0.5 μM. Effects of the inorganic solutes phosphate, Fe(II) and silicate on the biosensor signal were studied. Phosphate at
a concentration of 0.25 g L−1 phosphate slightly stimulated the light emission, but much less than toxicologically relevant concentrations of the much
stronger inducer arsenite. No effect of phosphate was oberved in the presence of arsenite. Freshly prepared sodium silicate
solution at a concentration of 10 mg L−1 Si reduced the arsenite-induced light production by roughly 37%, which can be explained by transient polymerization leading
to sequestration of some arsenic. After three days of incubation, silicate did not have this effect anymore, probably because
depolymerization occurred. In the presence of 0.4 mg L−1 Fe(II), the arsenite-induced light emission was reduced by up to 90%, probably due to iron oxidation followed by arsenite
adsorption on the less soluble Fe(III) possibly along with some oxidation to the stronger adsorbing As(V). Addition of 100 μM
EDTA was capable of releasing all arsenic from the precipitate and to transform it into the biologically measurable, dissolved
state. The biosensor also proved valuable for monitoring the effectiveness of an arsenic removal procedure based on water
filtration through a mixture of sand and iron granules. 相似文献
72.
Hans-Oscar Stephan 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》1994,106(1):135-136
73.
Klaus Burger Elisabeth Windeisen Elisabeth Heistracher Torsten Lange Abdel-Aleem H. Abdel-Aleem 《Monatshefte für Chemie / Chemical Monthly》2002,2(3):41-58
The synthesis of homochiral heterocyclic α-hydroxy acids starting from (S)- and (R)-malic acid using hexafluoroacetone as protecting and activating agent is described. The new compounds are useful building
blocks for peptide and depsipeptide modification. 相似文献
74.
Photocycloadditlon of (+)-isoplperltenone and cyclobutene-1-carboxylic acid gives an adduct which upon reduction with NaCNBH3 followed by thermolysis yields an isomer of isoaristolactone in an overall yield of 26%. 相似文献
75.
Summary The paper deals with mixed boundary value problems and transmission problems for elliptic differential and pseudo-differential operators. These problems are considered as elements of an algebra (where is the considered domain, x=, YX a submanifold of codimension 1, where the conditions have a jump, and x is a certain compactification of X/Y), the elements of which are described on a symbolic level. By means of additional conditions (of trace and potential type, with respect to Y) a given mixed problem is extended to an operator, and the Fredholm property of is established under an ellipticity condition, the parametrix is constructed on symbolic level and ind is expressed. In the second part the authors also study classes of special cases, namely differential operators of second and higher order with mixed boundary conditions for dim 2, where explicit index expressions are derived. 相似文献
76.
Three different methods for the preparation and modification of conducting polymer/noble metal catalyst systems consisting of polypyrrole (PPy) and platinum (Pt) are described for the anodic oxidation of methanol. The first method consists of the electrochemical deposition of a thin PPy film on glassy carbon substrate, which is modified with Pt either by electroreduction of hexachloroplatinate, codeposition from a nanodispersed Pt solution, or incorporation of tetrachloroplatinate as counterion followed by cathodic reduction. A second method is based on the preparation of nanoscale PPy(PSS) particles by chemical polymerization with polystyrenesulfonate PSS– as the counterion. This material is a favorable catalyst support for nanodispersed Pt due to its mixed electronic and cationic conductivity. To study the electrochemical properties, the particulate system PPy(PSS)/Pt is fixed in a carbon fiber electrode. A third method was developed which brings the polypyrrole in close contact to a proton exchanger membrane (Nafion) using a special chemical deposition procedure. This method is useful for preparing a membrane electrode assembly (MEA) consisting of Nafion/PPy/Pt. The structural, morphological, and electrocatalytic properties for methanol oxidation were studied depending on the preparation method applied using surface analytical techniques (TEM, SEM, and EDX) and electrochemical measurements (cyclic voltammetry and transient techniques). 相似文献
77.
Lattice Vibration Spectra. LXIII. Be(IO3)2 · 4 H2O, a Hydrate with Unusual Bonding and Lattice Dynamics The IR and Raman spectra (4000–50 cm?1) of Be(IO3)2 · 4 H2O and of deuterated specimens are recorded at 90 and 300 K and discussed in terms of the unusual relations of the masses of the atoms involved and the large polarization power of the beryllium ions. Thus, the translatory modes of the Be2+ ions (BeO4 skeleton vibrations), the librations of the H2O molecules, and the internal vibrations of the IO3? ions in the spectral regions of 300–400 and 600–1000 cm?1 couple and coincide producing unusual vH/vD isotopic ratios of partly < 1. The H-bond donor strengths of the water molecules is so much increased (due to the very large ionic potential of Be2+ ions, viz. 49 e nm?1) (synergetic effect) that the H-bonds formed are similar in strength as those in hydrates of hydroxides with the very strong H-bond acceptor group OH? (vOD of matrix isolated HDO molecules 2 074 and 2 244 (H2O I) and 2 206 and 2 349 cm?1 (H2O II)) 相似文献
78.
The well-known method for the determination of selenium(IV), which is based on the cathodic stripping voltammetry of copper(I)
selenide, has been adapted for application at the thin-film mercury electrode on glassy carbon (TFME). Insufficient reproducibility
and sensitivity have been overcome by using a 0.1 mol/L HClO4 electrolyte solution containing 0.02 mol/L thiocyanate ions. Thiocyanate ions have been found to increase the peak height
of the selenium response and shift it to more positive potentials. This behaviour is explained by an adsorption of SCN– at the interface glassy carbon/Cu2Se and its action as an electron transfer catalyst between glassy carbon and copper(I) selenide. A 3σ-detection limit of 75
ng/L Se(IV) has been achieved. The relative standard deviation is 5.2% at 5 μg/L selenium(IV). The influence of cadmium(II), arsenic(III),
zinc(II), iron(III) and lead(II) ions on the selenium response has been studied. In case of lead ions, a new signal occurred
at more negative potentials than the reduction of Cu2Se. This signal, which is probably due to the reduction of PbSe, can also be used for the determination of selenium(IV).
Received: 13 November 1996 / Revised: 19 December 1996 / Accepted: 24 December 1996 相似文献
79.
T. P. Martin T. Bergmann H. Göhlich T. Lange 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1991,19(4):25-29
Intensity anomalies (magic numbers) have been observed in the mass spectra of sodium clusters containing up to 22 000 atoms. For small clusters (Na n ,n≤1500) the anomalies appear to be due to the filling of electronic shells (groups of subshells having the same energy). The shells can be characterized rather well by a pseudoquantum-number, indicating the possible existence of a symmetry higher than spherical. The mass spectra of larger clusters (1500≤n≤22 000) are well explained by the completion of icosahedral or cuboctahedral shells of atoms. The fact that the two types of shells (electron and atom) occur in distinct and non-overlapping size intervals might indicate the existence of a “liquid” to “solid” transition in going from small to large clusters. 相似文献
80.
Cooperative effects in binuclear zirconocenes: Their synthesis and use as catalyst in propene polymerization 总被引:3,自引:0,他引:3
Stephan Jüngling Rolf MüllhauptHerbert Plenio 《Journal of organometallic chemistry》1993,460(2):191-195
The mono- and bis-cyclopentadienyl compounds 1-(Cp″)-4-(CH3)C6H4 (1) and 1, 4-(Cp″)2C6H4 (2) (Cp″ = 3,4-dimethylcyclopenta-1,3-diene-1-yl) have been synthesized. The reactions of the lithium salts of 1 and 2 with CpZrCl3 · dme (dme = dimethoxyethane) and Cp*ZrCl3(CP* = C5(CH3)5) yielded the mono- and bi-nuclear bridged zirconocenes 1-(Cp″ZrCpCl2)-4-(CH3)C6H4 (3), 1,4-(Cp″ZrCpCl2)2C6H4 (4) and 1,4-(Cp″ZrCp*Cl2)2C6H4 (5). When activated with methylaluminoxane (MAO), the mono- and bi-nuclear zirconocenes 3 and 4 catalyse the polymerization of propene. The influence of the catalyst composition on the polymerization kinetics and molecular weight is discussed. 相似文献