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671.
Angelika Preetz Wolfgang Baumann Hans‐Joachim Drexler Christian Fischer Jiangtao Sun Anke Spannenberg Oswald Zimmer Wolfgang Hell Detlef Heller 《化学:亚洲杂志》2008,3(11):1979-1982
Various trinuclear rhodium complexes of the type [Rh3(PP)3(μ3‐OH)x(μ3‐OMe)2?x]BF4 (where PP=Me‐DuPhos, dipamp, dppp, dppe; different ligands and μ‐bridging anions) are presented, which are formed upon addition of bases such as NEt3 to solvate complexes [Rh(PP)(solvent)2]BF4. They were extensively characterized by X‐ray diffraction and NMR spectroscopy (103Rh, 31P, 13C, 1H). Their in situ formation resulting from basic additives (NEt3) or basic prochiral olefins (without addition of another base) can cause deactivation of the asymmetric hydrogenation. This effect can be reversed by means of acidic additives. 相似文献
672.
C Fischer R Thede HJ Drexler A König W Baumann D Heller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(38):11920-11928
Rhodium-η(6) -arene complexes can be generated in the presence of arenes following the hydrogenation of the diolefin in rhodium catalyst precursors of the type [Rh(PP*)(diolefin)]X (PP*=chelating diphosphane, X=noncoordinating anion). In this paper we report the characterization of such arene complexes with the ligands DuPhos, dipamp, dppe, Tangphos, dppf, and diop by means of NMR spectroscopy ((31) P, (103) Rh) and X-ray analysis. A procedure that follows the approach to equilibrium as a function of time monitored by using an UV/Vis diode array was used to determine 20 stability constants. Analyses were accomplished directly from the spectra by either a numeric and/or a new analytic solution of the underlying system of differential equations. Additionally thermodynamic parameters were determined in the temperature range between 278 and 318?K. 相似文献
673.
Dr. Christian Fischer Dr. Richard Thede Dr. Hans‐Joachim Drexler Anja König Dr. Wolfgang Baumann Prof. Dr. Detlef Heller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(38):11920-11928
Rhodium–η6‐arene complexes can be generated in the presence of arenes following the hydrogenation of the diolefin in rhodium catalyst precursors of the type [Rh(PP*)(diolefin)]X (PP*=chelating diphosphane, X=noncoordinating anion). In this paper we report the characterization of such arene complexes with the ligands DuPhos, dipamp, dppe, Tangphos, dppf, and diop by means of NMR spectroscopy (31P, 103Rh) and X‐ray analysis. A procedure that follows the approach to equilibrium as a function of time monitored by using an UV/Vis diode array was used to determine 20 stability constants. Analyses were accomplished directly from the spectra by either a numeric and/or a new analytic solution of the underlying system of differential equations. Additionally thermodynamic parameters were determined in the temperature range between 278 and 318 K. 相似文献
674.
Kohrt C Hansen S Drexler HJ Rosenthal U Schulz A Heller D 《Inorganic chemistry》2012,51(13):7377-7383
Novel trinuclear rhodium-hydride complexes with diphosphine ligands Tangphos, t-Bu-BisP*, and Me-DuPHOS which contain bridging μ(2)- and μ(3)-hydrides as well as terminal hydrides in one molecule have been reported recently. In this work, these different rhodium-hydride bonds are characterized by Raman spectroscopy and the results are compared with those obtained by means of the more commonly applied IR spectroscopy. Density functional theory (DFT) calculations have been carried out to support the experimental findings. The structure of the Rh(3)H(7) core is described in the context of their vibrational stretching modes. 相似文献
675.
Ueki M Galonić DP Vaillancourt FH Garneau-Tsodikova S Yeh E Vosburg DA Schroeder FC Osada H Walsh CT 《Chemistry & biology》2006,13(11):1183-1191
Four adjacent open reading frames, cytC1-C4, were cloned from a cytotrienin-producing strain of a Streptomyces sp. by using primers derived from the conserved region of a gene encoding a nonheme iron halogenase, CmaB, in coronamic acid biosynthesis. CytC1-3 were active after expression in Escherichia coli, and CytC4 was active after expression in Pseudomonas putida. CytC1, a relatively promiscuous adenylation enzyme, installs the aminoacyl moieties on the phosphopantetheinyl arm of the holo carrier protein CytC2. CytC3 is a nonheme iron halogenase that will generate both gamma-chloro- and gamma,gamma-dichloroaminobutyryl-S-CytC2 from aminobutyryl-S-CytC2. CytC4, a thioesterase, hydrolytically releases the dichloroaminobutyrate, a known streptomycete antibiotic. Thus, this short four-protein pathway is likely the biosynthetic source of this amino acid antimetabolite. This four-enzyme system analogously converts the proS-methyl group of valine to the dichloromethyl product regio- and stereospecifically. 相似文献
676.
677.
Roy B. Lefkowitz Jennifer Y. Marciniak Che‐Ming Hu Geert W. Schmid‐Schönbein Michael J. Heller 《Electrophoresis》2010,31(2):403-410
In biomedical research and clinical diagnostics, it is a major challenge to measure disease‐related degradative enzyme activity directly in whole blood. Present techniques for assaying degradative enzyme activity require sample preparation, which makes the assays time‐consuming and costly. This study now describes a simple and rapid electrophoretic method that allows detection of degradative enzyme activity directly in whole blood using charge‐changing fluorescent peptide substrates. Charge‐changing substrates eliminate the need for sample preparation by producing positively charged cleavage fragments that can be readily separated from the oppositely charged fluorescent substrate and blood components by electrophoresis. Two peptide substrates have been developed for pancreatic α‐chymotrypsin and trypsin. For the first substrate, a detection limit of 3 ng for both α‐chymotrypsin and trypsin was achieved in whole rat blood using a 4% agarose gel. This substrate had minimal cross‐reactivity with the trypsin‐like proteases thrombin, plasmin, and kallikrein. For the second substrate (trypsin‐specific), a detection limit of about 10–20 pg was achieved using thinner higher resolution 20 and 25% polyacrylamide gels. Thus, the new charge changing peptide substrates enable a simple electrophoretic assay format for the measurement of degradative enzyme activity, which is an important step toward the development of novel point‐of‐care diagnostics. 相似文献
678.
679.
Bis(5,5″-bis(bromomethyl)-2,2′:6′,2″-terpyridine), bis-4′-(4-bromomethylphenyl)-2,2′:6′,2″-terpyridine and 4-hydroxymethyl-5′,5″-dimethyl-2,2′:6′,2″-terpyridine metal complexes have been used as initiators for the living polymerization of 2-oxazolines and L-lactides. In both cases polymers with controlled molecular weights and narrow molecular weight distributions have been obtained. In-line diode array GPC measurements of iron(II) complexed poly(ethyloxazoline)s showed an unexpected absence of fragmentation. Viscosity experiments demonstrated the differences of the complexed and uncomplexed systems. 相似文献