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91.
Metallcarbonyl-Synthesen,XIV. Neuartige Vanadium-, Niob- und Tantal-Komplexe mit Wasserstoff-Brücken
Wolfgang A. Herrmann Helmut Biersack Barbara Balbach Peter Wülknitz Manfred L. Ziegler 《欧洲无机化学杂志》1984,117(1):79-94
Syntheses of Metal Carbonyls, XIV. Novel Vanadium, Niobium, and Tantalum Complexes Having Hydrido Bridges The novel homo- and heterodinuclear organometallic μ-hydrido compounds 3a – c of vanadium, niobium, and tantalum have been synthesized by light-induced reactions of the hydridoniobium complex (η5-C5H5)2NbH3 ( 1 ) with the half-sandwich complexes (η5-C5H5)M(CO)4 ( 2a : M = V; 2b : M = Nb; 2c : M = Ta). These compounds have the general composition LxM – H – Nb(CO)(η5-C5H5)2. The formation of the M – H – Nb moieties is a dark-reaction preceded by two photoreactions that are independent from each other elimination of CO from 2a – c and elimination of H2 from 1 , with the extruded carbon monoxide being transfered to the (η5-C5H5)2NbH fragment; subsequent fixation of the species (η5-C5H5)2Nb(CO)H thus generated to the photogragments (η5-C5H5)M(CO)3 results in donor stabilization of these latter groups. The structural architecture of the derivatives 3a und b was established by X-Ray diffraction. The hydrogen bridges are to be considered as three-center two-electron functions that are responsible for a serious lengthening of the otherwise by at least 40 pm shorter metal-to-metal distances amounting to 371.3 pm in 3a and 373.3 pm in 3b (mean values). 相似文献
92.
Helmut Thomann 《Fresenius' Journal of Analytical Chemistry》1961,184(4):241-247
Zusammenfassung Zur photometrischen Auswertung komplexometrischer Titrationen von Metallspuren in sehr verdünnten Lösungen mit Hilfe von Metallindicatoren wird aus mathematischen Überlegungen ein Verfahren abgeleitet, das auf der Messung von Extinktionsänderungen während der Titration beruht. Im Vergleich zu herkömmlichen photometrischen Methoden wird die Empfindlichkeit etwa um den Faktor 30 verbessert.Auszug aus der von der Fakultät für Allgemeine Wissenschaften der Technischen Hochschule München genehmigten Dissertation.Herrn Prof. Dr. F. Hegemann möchte der Verfasser für die Anregung und Förderung der vorliegenden Arbeit sehr danken. Der Deutschen Forschungsgemeinschaft, Bad. Godesberg, und der Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e. V., München, sei für die gewährte Unterstützung auch an dieser Stelle verbindlichst gedankt. 相似文献
93.
Kurt Hiebl Engelbert Tuscher Helmut Bittner 《Monatshefte für Chemie / Chemical Monthly》1979,110(4):869-877
The hydrogen absorption of the phase Ti64Co32–x
Fe
x
(x=0...16) and its influence on the magnetic properties have been investigated. Measurements of the vapour-pressure, wide-line NMR and magnetic susceptibility have been performed. Substitution of Co by Fe does not change the amount of absorbed hydrogen. However the reaction rate of hydriding process, the activation energy of diffusion and the magnetic quantities change upon this substitution. 相似文献
94.
Petrovic AG Polavarapu PL Drabowicz J Zhang Y McConnell OJ Duddeck H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(14):4257-4262
The enantiomers of 3,3,3',3'-tetramethyl-1,1'-spirobi[3 H,2,1]benzoxaselenole have been separated on a chiral preparative chromatographic column. The experimental vibrational circular dichroism (VCD) spectra have been obtained for both enantiomers in CH(2)Cl(2). The theoretical VCD spectra have been obtained by means of density functional theoretical calculations with the B3 LYP density functional. From a comparison of experimental and theoretical VCD spectra, the absolute configuration of an enantiomer with positive specific rotation in CH(2)Cl(2) at 589 nm is determined to be R. This conclusion has been verified by comparing results of experimental optical rotatory dispersion (ORD) and electronic circular dichroism (ECD) to predictions of the same properties using the B3 LYP functional for the title compound. 相似文献
95.
Denise Bohrer Uwe Heitmann Mao-dong Huang Helmut Becker-Ross Stefan Florek Bernhard Welz Denise Bertagnolli 《Spectrochimica Acta Part B: Atomic Spectroscopy》2007
High-resolution continuum source atomic absorption spectrometry (HR-CS AAS) has been used to investigate spectral and non-spectral interferences found with a conventional line source atomic absorption spectrometer in the determination of aluminum in pharmaceutical products containing elevated iron and sugar concentrations. A transversely heated graphite furnace was used as the atomizer in both spectrometers. The two most sensitive aluminum lines at 309.3 nm and 396.2 nm were investigated and it was found that an iron absorption line at 309.278 nm, in the vicinity of the aluminum line at 309.271 nm, could be responsible for some spectral interference. The simultaneous presence of iron and the organic components of the matrix were responsible for radiation scattering, causing high continuous and also structured background absorption at both wavelengths. The aluminum and iron absorption could not be separated in time, i.e., the iron interference could not be eliminated by optimizing the graphite furnace temperature program. However, an interference-free determination of aluminum was possible carrying out the measurements with HR-CS AAS at 396.152 nm after applying least squares background correction for the elimination of the structured background. Analytical working range and other figures of merit were determined and are presented for both wavelengths using peak volume registration (center pixel ± 1) and the center pixel only. Limits of detection and characteristic masses ranged from 1.1 to 2.5 pg and 13 to 43 pg, respectively. The method was used for the determination of the aluminum contamination in pharmaceutical formulations for iron deficiency treatment, which present iron concentrations from 10 to 50 g l− 1. Spike recoveries from 89% to 105% show that the proposed method can be satisfactorily used for the quality control of these formulations. 相似文献
96.
Gundula Voss Michael Gradzielski Jürgen Heinze Helmut Reinke Carlo Unverzagt 《Helvetica chimica acta》2003,86(6):1982-2004
Two new types of 4,4′,7,7′‐tetraalkoxyindigotins, 1a – f and 2a – f along with the new N‐substituted indigotins 4e – f , were synthesized from dinitrobenzaldehydes 5a – f , which were prepared from 2‐hydroxy‐5‐methoxybenzaldehyde ( 7 ) via dialkoxybenzaldehydes 6a – f (Scheme). The new dialkoxyindigotin 3g was obtained from dialkoxybenzaldehyde 6g via nitrobenzaldehyde 8g . The 1,4‐dialkoxy‐2,3‐dinitrobenzenes 9 were isolated as by‐products. The 4,4′,7,7′‐tetraalkoxy‐5,5′‐diaminoindigotins 1 are soluble in organic solvents, and their solutions are green, which is highly uncommon for indigotins and is primarily caused by electronic effects of substituents, steric effects playing a minor role. The indigotins 1 produce a strong red shift of the longest‐wavelength absorption and negative solvatochromism indicating the predominance of polar resonance structures in the ground state. Tautomeric structures were excluded. These indigotins are valuable compounds for technical applications, for synthetic purposes, and for analytical studies. SANS (Small‐angle neutron scattering) experiments showed that certain 4,4′,7,7′‐tetraalkoxy‐5,5′‐diaminoindigotins 1 form rod‐like aggregates in solution. The similarly substituted 4,4′,7,7′‐tetraalkoxy‐5,5′‐dinitroindigotins 2 are far less soluble. They produce red monoanions (preferably dimers) and bluish‐purple dianions in organic solvents. 相似文献
97.
Heller B Sundermann B Buschmann H Drexler HJ You J Holzgrabe U Heller E Oehme G 《The Journal of organic chemistry》2002,67(13):4414-4422
The photocatalyzed [2 + 2 + 2]-cycloaddition of nitriles with 2 equiv of acetylene to 2-pyridines can be carried out under mild conditions and represents a valuable extension to common synthetical methods. For the ideal wavelength range (350-500 nm), lamps as well as sunlight can be used. Working at room temperature and in organic solvents such as toluene or hexane as well as in water gives satisfying results in many cases. However, it is also possible to vary the solvent and the reaction temperature of the photocatalyzed synthesis and to choose, with respect to the specific substrate, specific requirements for this particular reaction and general requirements of the method. This simple and selective method derives its potential mainly from the large variety of applicable nitriles. Suitable substrates include (functionalized) aliphatic and aromatic nitriles as well as cyanamides derived from secondary amines. 相似文献
98.
99.
Helmut Endres 《无机化学与普通化学杂志》1984,513(6):78-88
Formation of Octahedral Complexes via cis-Addition to Square Planar Bis (oxamideoximato)nickel(II): Three Structure Examples In the reaction of orange square planar bis(oxamide oximato)nickel(II) with acids, blue to blue-green octahedral complexes are formed with neutral oxamide oximide ligands and two acid anions in cis-positions. Three compounds are described: cis-dichlorobis(oxamide oxime)nickel(II) ( 1 ), NiCl2(C2H6N4O2)2, Mr = 365.81, monoclinic P21/n, a = 6.641(2), b = 14.086(4), c = 13.473(3) Å, β = 96.26(2)°, V = 1 252.8 Å3, Z = 4, dc = 1.94 gcm?3, final Rw = 0.031 for 4090 reflections. In cis-di(sulfanilato)bis(oxamide oxime)nickel(II) dihydrate ( 2 ) one sulfanilic anion coordinates via the sulfonic acid group, the other one via the amino group; Ni(C6H6NO3S)2(C2H6N4O2)2 · 2 H2O, Mr = 675.30, monoclinic P21, a = 6.879(3), b = 14.305(5), c = 13.930(5) Å, β = 103.62(4)°, V = 1332 Å, Z = 2, dc = 1.68 gcm?3, R = 0.067 for 2693 reflections. In catena-μ-(phthalato)bis(oxamide oxime)nickel(II) tetrahydrate ( 3 ) bidentate bridging phthalate anions lead to chain formation; Ni(C8H4O4)(C2H6N4O2)2 · 4H2O, Mr = 531.09, monoclinic P21/c, a = 10.633(8), b = 11.324(5), c = 17.680(14) Å, β = 98.25(7)°, V = 2107 Å3, Z = 4, dc = 1.67 gcm?3. Final R = 0.110 for 3290 reflections. 相似文献
100.