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51.
The successive reaction of (CO)6M with Na[NCR21] and [Et3O]BF4 yields (CO)5M[C(NCR21)OEt] (II: M = Cr; III: M = W; CR21 = C(C6H4Br-p)2 (a), CPh2 (b), C(C6H4OMe-p)2 (c), C(C6H4)2O (d), CBu2tt (e)). Hexacarbonyltungsten, (CO)6W, reacts with Na[NCPh2] and MeOSO2F to give (CO)5W[C(NCPh2) OMe] (IV). X-Ray analysis of IIe shows that: (1) the CNC fragment is almost linear (171.7°); (2) the two NC bond lengths are equal within experimental error; and (3) the O,C,Cr,N plane is perpendicular to the C(Me3),C,N,C(Me3) plane (90.0°). Therefore compounds II–IV are best described as 1-alkoxy-2-azaallenyl complexes. 相似文献
52.
O-GlcNAcylation of serine and threonine residues is a dynamic and essential post-translational modification involved in signaling pathways in eukaryotes. Studies of O-GlcNAcylation would be aided by small-molecule inhibitors of O-GlcNAc transferase (OGT), the sole enzyme know to mediate this modification, but discovery of such molecules has been hampered by poor expression of cloned OGT and lack of suitable high-throughput screens. This Communication describes the development an expression system to access large amounts of the catalytic domain of OGT and the implementation of a fluorescence-based substrate analogue displacement assay that has led to the discovery of a set of OGT inhibitors. This work lays the foundation for both structural and functional analysis of the catalytic domain of OGT. 相似文献
53.
Zhou S Xu C Wang J Gao W Akhverdiyeva R Shah V Gross R 《Langmuir : the ACS journal of surfaces and colloids》2004,20(19):7926-7932
Acidic sophorolipid (SL) molecules derived from yeasts represent a novel type of asymmetrical bolaamphiphiles due to their unique structural features that include an asymmetrical polar head size (disaccharide vs COOH), a kinked hydrophobic core (cis-9-octadecenoic chain), and a non-amide polar-nonpolar linkage. Light microscopy, small- and wide-angle X-ray scattering, FT-IR spectroscopy, and dynamic laser light scattering were used to investigate the supramolecular structures of the self-assembled aggregates of SL molecules at different pH values. In acidic conditions (pH < 5.5), giant twisted and helical ribbons of 5-11 microm width and several hundreds of micrometers length were observed for the first time. Increase in solution pH values slowed ribbon formation, decreased ribbon yield, and increased the helicity and entanglements of the giant ribbons. An interdigitated lamellar packing model of acidic SL-COOH molecules with a long period of 2.78 nm, stabilized by both the strong hydrophobic association between the cis-9-octadecenoic chains and strong disaccharide-disaccharide hydrogen bonding, is proposed. The neutralization of SL-COOH in water to SL-COONa produced clear solutions with the formation of short-range ordered aggregates. At concentrations below 1.0 mg/mL, the size of self-assembled aggregates increased as the concentration increased. At concentrations above 1.0 mg/mL, narrowly distributed micellar aggregates with a constant hydrodynamic radius (R(h)) of about 100 nm are formed. The large micelles show strong angular dependence with the fast mode appearing at scattering angle theta >/= 60 degrees. 相似文献
54.
James J. Gallagher Edward K. Chess Saleh M. Arghestani Michael L. Gross 《Journal of mass spectrometry : JMS》1983,18(3):118-126
Mechanisms for decomposition of 1- and 2-phenyltetralins were investigated using low resolution mass spectrometry and metastable ion techniques. Four primary decompositions were observed for 1-phenyltetralin radical cations: (1) the loss of C6H6 via a 1,4-elimination; (2) the elimination of ethene via competing losses from carbons 3 + 4 and carbons 2 + 3; (3) the loss of C8H8, probably through a stepwise Diels-Alder cycloreversion to expel styrene; and (4) the loss of methyl radical involving carbon 2 and possibly carbon 4. Three major decompositions were observed for 2-phenyltetralin radical cations: (1) the loss of C8H8, possibly through a Diels-Alder cycloreversion to expel styrene; (2) the loss of C6H6 via a 1,3 elimination; and (3) the loss of methyl radical from carbon 1. Various exchange reactions occur prior to these losses, but they proved to be incomplete even for metastable ions. 相似文献
55.
Silvia Gross Andrea Zattin Vito Di Noto Sandra Lavina 《Monatshefte für Chemie / Chemical Monthly》2006,60(3):583-593
Silica-based inorganic–organic hybrid thin films embedding the organically modified oxohafnium clusters (Hf4O2(OMc)12, OMc=OC(O)–C(CH3)=CH2) were obtained by photo-activated free radical copolymerisation of the methacrylate groups of the cluster with those of the
pre-hydrolysed (methacryloxypropyl)trimethoxysilane (MAPTMS, (CH2=C(CH3)C(O)O)(CH2)3Si(OCH3)3). By this route, a covalent anchoring of the cluster to the forming silica network was achieved. Samples characterized by
two different Si/Hf compositions (18:1, 5:1) were prepared. The surface and in-depth composition of the thin films were investigated
through Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). XPS depth profiles performed on the thin
layers evidenced a homogenous in depth distribution of the hafnium guest species within the whole silica films and sharp film-substrate
interfaces.
Broad band dielectric spectroscopy (BDS) measurements permitted to investigate the electric response of the obtained films
in the frequency and temperature range of 40 Hz – 1 MHz and 0–160°C. 相似文献
56.
Urška L. Štangar Urh Černigoj Polonca Trebše Ksenija Maver Silvia Gross 《Monatshefte für Chemie / Chemical Monthly》2006,137(5):647-655
Summary. Transparent TiO2 films with a high photodegradation activity towards an azo dye in aqueous solution were prepared by sol–gel processing. Films
on soda–lime glass supports protected with a thin silica barrier layer exhibited better crystallization and monodisperse nanoparticles,
higher absorption of light below 370 nm, and higher photocatalytic activity than those films deposited on bare glass supports
proving the detrimental effect of interdiffused sodium ions on the development of the anatase nanostructure. The effect of
substrate was more pronounced in thinner films (300 nm) than in thicker ones (1200 nm), which were achieved by adding a template
(i.e. Pluronic F127) to the sol. 相似文献
57.
Friedrich Scholl 《Fresenius' Journal of Analytical Chemistry》1969,245(1-2):49-54
Zusammenfassung Für das zur Herstellung von Bleibatterien verwendete Grauoxid (bestehend aus einem feinteiligen Gemisch von ca. 60 bis 90% Bleioxid, PbO, und einem Rest metallischem Blei) wurde ein Verfahren zur kontinuierlichen bzw. quasikontinuierlichen, automatischen Bestimmung des PbO-Gehaltes an den Fertigungsanlagen benötigt. Eine schnelle Analyse mit vergleichsweise geringem Aufwand war durch Messung der Lösungswärme bei Behandlung einer abgewogenen Menge Grauoxid mit verd. Essigsäure möglich. Unter technisch bequem realisierbaren Bedingungen wurden Temperaturerhöhungen von einigen Grad erhalten. Der Einfluß verschiedener Arbeitsbedingungen, der verschiedenen PbO-Modifikationen und der Teilchengröße und -form wurde untersucht. Zur Zeit wird eine für die Fertigung bestimmte, automatische Apparatur aufgebaut, die bei einer Analysenfolge von 1 min die Bestimmung mit einer Standardabweichung unter ±1% durchzuführen gestattet.
Automatic procedure for the determination of the lead oxide content of gray oxides by measurement of the heat of solution
A continuous or semicontinuous automatic method for the determination of the lead oxide content was needed in the manufacturing process of gray oxides (a fine particle mixture of about 60 to 90% lead oxide, PbO, and metallic lead, used in manufacturing lead batteries).A rapid determination with comparatively small effort was possible by measuring the heat of solution of a weighed amount of gray oxides treated with acetic acid. Temperature rise of a few degrees could be reached under technically realisable conditions. The influence of different working conditions, of the particle size and shape and of the PbO modifications were investigated. An automatic apparatus for the determination is at present being built and will give one determination per minute with a standard deviation of less than ±1%.相似文献
58.
Viroids: a class of subviral pathogens 总被引:13,自引:0,他引:13
59.
Ronald L. Cerny Kenneth B. Tomer Michael L. Gross 《Journal of mass spectrometry : JMS》1986,21(10):655-660
Combining desorption ionization with tandem mass spectrometry overcomes the disadvantage of limited fragmentation accompanying desorption and permits mixtures of closely related substances to be investigated directly. These features of the combination are illustrated by completing the structure-proof of a minor component of an ornithine-containing lipid mixture isolated from Thiobacillus thiooxidans. The minor component is a homolog of the major constituent and differs from the principal component owing to the presence of a double bond in lieu of a cyclopropyl ring in one of the constituent fatty acids. Another feature of the combined method is the potentially complementary nature of collision-activated dissociation spectra of protonated and cationized biomolecules. This is illustrated by the differences in the collision-activated dissociations of the [M + Na]+ of sucrose, desorbed by field desorption, and [M + H]+, desorbed by fast atom bombardment. A third illustration is the application of field desorption and tandem mass spectrometry to an organometallic compound. The combined approach allows the ligands to be identified and the relative ligand binding energies to be approximated. 相似文献
60.
M. Friedrich K. Hiller M. Wiemer T. Geßner D. R. T. Zahn 《Analytical and bioanalytical chemistry》1998,361(6-7):558-559
Basic investigations have been carried out on the characterization of different processing steps in bond preparation using
etched <111> faces of silicon wafers for the incidence of the infrared beam to a multiple internal reflection geometry. The
method is very sensitive to the surface coverage and interface. Surface activation by RCA cleaning yields an increase of water
coverage and a decrease of SiH and CH groups. The detection limit for an oxide layer between silicon wafers has been found
to be about 3 nm.
Received: 18 July 1997 / Revised: 15 August 1997 / Accepted: 19 August 1997 相似文献