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951.
Interactions of Isonitriles with Metal–Boron Bonds: Insertions,Coupling, Ring Formation,and Liberation of Monovalent Boron
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Prof. Dr. Holger Braunschweig Dr. Mehmet Ali Celik Dr. Rian D. Dewhurst Dr. Katharina Ferkinghoff Alexander Hermann Dr. J. Oscar C. Jimenez‐Halla Dr. Thomas Kramer Dr. Krzysztof Radacki Dr. Rong Shang Dr. Eva Siedler Felix Weißenberger Christine Werner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(33):11736-11744
Boryl, borylene, and base‐stabilized borylene complexes of manganese and iron undergo a range of different reactions when treated with isonitriles including single, double, and partial isonitrile insertions into metal?boron bonds, ring formation, isonitrile coupling, and the liberation of new monovalent boron species. Two of the resulting cyclic species have also been found to react selectively with anhydrous HCl to form ring‐opened products. The diverse isonitrile‐promoted reactivity of transition‐metal–boron compounds has been explored computationally. 相似文献
952.
Benjamin F. Hartmeier Michael A. Brady Neil D. Treat Maxwell J. Robb Thomas E. Mates Alexander Hexemer Cheng Wang Craig J. Hawker Edward J. Kramer Michael L. Chabinyc 《Journal of polymer science. Part A, Polymer chemistry》2016,54(2):237-246
Ternary organic blends have potential in realizing efficient bulk heterojunction (BHJ) organic solar cells by harvesting a larger portion of the solar spectrum than binary blends. Several challenging requirements, based on the electronic structure of the components of the ternary blend and their nanoscale morphology, need to be met in order to achieve high power conversion efficiency in ternary BHJs. The properties of a model ternary system comprising two donor polymers, poly(3-hexylthiophene) (P3HT) and a furan-containing, diketopyrrolopyrrole-thiophene low-bandgap polymer (PDPP2FT), with a fullerene acceptor, PC61BM, were examined. The relative miscibility of PC61BM with P3HT and PDPP2FT was examined using diffusion with dynamic secondary ion mass spectrometry (dynamic SIMS) measurements. Grazing incidence small and wide angle X-ray scattering analysis (GISAXS and GIWAXS) were used to study the morphology of the ternary blends. These measurements, along with optoelectronic characterization of ternary blend solar cells, indicate that the miscibility of the fullerene acceptor and donor polymers is a critical factor in the performance in a ternary cell. A guideline that the miscibility of the fullerene in the two polymers should be matched is proposed and further substantiated by examination of known well-performing ternary blends. The ternary blending of semiconducting components can improve the power conversion efficiency of bulk heterojunction organic photovoltaics. The blending of P3HT and PDPP2FT with PC61BM leads to good absorptive coverage of the incident solar spectrum and cascading transport energy levels. The performance of this ternary blend reveals the impact of the miscibility of PC61BM in each polymer as a function of composition, highlighting an important factor for optimization of ternary BHJs. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 237–246 相似文献
953.
You L Ferdani R Li R Kramer JP Winter RE Gokel GW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(1):382-396
Six amphiphilic heptapeptides with the structure (C18H37)2NCOCH2OCH2CO-(Gly)3-Pro-(Gly)n-(Glx)-(Gly)m-O(CH2)6CH3, in which Glx represents glutamic acid or its benzyl ester and n+m=2, have been studied. In addition, the glutamate residue in the GGGPGGE sequence was esterified by fluorescent 1-pyrenemethanol. These compounds insert into phospholipid bilayers and form anion-conducting pores. Hill plots based on carboxyfluorescein release indicate that the pores are at least dimeric. Studies that involved ion-selective electrode techniques showed that transport of chloride varied with the position of glutamate within the peptide chain and whether glutamic acid was present as the free acid or its benzyl ester. Chloride transport activity was significantly higher for the glutamate esters than for free carboxylates irrespective of the glutamate position. Activity was highest when the glutamate residue in approximately (Gly)3-Pro-(Xxx)3 approximately was closest to the C terminus of the peptide. A fluorescent pyrene residue was introduced to probe the aggregation state of the amphiphile. The selectivity of the pore for Cl(-) over K+ was maintained even when the carboxylate anion was present within it. Complexation of Cl(-) by the ionophoric peptides was confirmed by negative ion mass spectrometry. Planar bilayer voltage clamp experiments confirmed that pores with more than one conductance state may form in these dynamic, self-assembled pores. 相似文献
954.
Noyori-type reductions of pairs of beta-ketoamides and beta-ketoesters with elemental hydrogen (4 bar) proceeded substrate by substrate. When Et(2)NH(2) (+)[{RuCl(S)-binap}(2)](mu-Cl)(3)(-) was employed as a catalyst in a methanol or ethanol solution, the substrates were reduced at room temperature in the order beta-ketopyrrolidide > or = beta-ketopiperidide > or = beta-keto(N,N-diethylamide) > beta-keto(alkyl esters) > beta-keto(oligofluoroalkyl esters). This is the first time that beta-ketoamides have been reduced asymmetrically (91 to >98 % ee) under such mild conditions. Monitoring the concentrations of these beta-ketocarboxyl acid derivatives and their respective hydrogenation products over the course of time showed that the most electron-rich substrate is captured by the catalyst preferentially and exothermically; whether this occurs reversibly or irreversibly remains to be determined. The hydrogenation product is subsequently formed. The last transformation includes the rate-determining step. The combination of these events explains why starting from appropriate mixtures of substrates a "first-choice substrate" reacted from early on while the "second-choice substrate" stayed virtually untouched over an extended period of time and reacted no earlier than after the "first-choice substrate" had disappeared. From then onward, however, the "second-choice substrate" also reacted relatively rapidly. 相似文献
955.
Mossoba MM Milosevic V Milosevic M Kramer JK Azizian H 《Analytical and bioanalytical chemistry》2007,389(1):87-92
The mandatory requirement in many countries to declare the amount of trans fat present in food products and dietary supplements has led to a need for sensitive and accurate methodologies for the rapid
quantitation of total trans fats and oils. Capillary gas chromatography (GC) and infrared spectroscopy (IR) are the two methods most commonly used to
identify and quantify trans fatty acids for food labeling purposes (see the article by Delmonte and Rader in this ABC issue for a detailed presentation of GC methodology). The present article provides a comprehensive review of the IR technique
and the current attenuated total reflection (ATR) Fourier-transform (FT) IR methodologies for the rapid determination of total
trans fats and oils. This review also addresses potential sources of interferences and inaccuracies in FTIR determinations, particularly
those done at low trans levels. Recent observations have shown that the presence of saturated fats caused interferences in the FTIR spectra observed
for trans triacylglycerols. The recognition and resolution of previously unresolved quantitative issues improved the accuracy and sensitivity
of the FTIR methodology. Once validated, it is anticipated that the new negative second-derivative ATR-FTIR procedure will
make IR spectroscopy more suitable than ever, and a rapid alternative and/or complementary method to GC, for the rapid determination
of total trans fats for regulatory compliance.
Figure Infrared light bouncing inside an internal reflection crystal 相似文献
956.
John W. Kramer 《Tetrahedron》2008,64(29):6973-6978
Efficient and mild reaction conditions were developed for the catalytic carbonylation of fluorinated epoxides to their corresponding β-lactones. Six new lactones with fluorinated side chains were prepared in high isolated yields. These lactones were polymerized to form a series of new poly(β-hydroxyalkanoate)s with fluorinated side chains, and their properties were examined with respect to their hydrocarbon analogs. Finally, copolymerizations were performed with fluorinated lactones and β-butyrolactone, which resulted in tapered copolymers rather than the expected random copolymers. 相似文献
957.
Edson JB Wang Z Kramer EJ Coates GW 《Journal of the American Chemical Society》2008,130(14):4968-4977
A series of bis(phenoxyketimine)titanium dichloride complexes were synthesized and evaluated as catalysts for living, isoselective propylene polymerization upon activation with methylaluminoxane (MAO). Catalysts bearing phenoxyketimine ligands with different substituents at the ortho and para positions of the phenolate ring and substituents at the ketimine carbon were investigated. The identity of the ketimine substituent had the largest effect on the activity and isoselectivity of propylene polymerization. Complex 12/MAO promoted the living, isoselective polymerization of propylene ([m4] = 0.73, alpha = 0.94). This catalyst system was used for the synthesis of a number of block copolymers featuring isotactic polypropylene semicrystalline blocks and poly(ethylene-co-propylene) amorphous blocks. Several triblock samples with varying block lengths, a pentablock, and a heptablock copolymer were synthesized. Mechanical testing has revealed that each is elastomeric with elongations at break between approximately 790-1000%. 相似文献
958.
959.
Heidbrink WW Gorelenkov NN Luo Y Van Zeeland MA White RB Austin ME Burrell KH Kramer GJ Makowski MA McKee GR Nazikian R;DIII-D team 《Physical review letters》2007,99(24):245002
Neutral-beam injection into plasmas with negative central shear produces a rich spectrum of toroidicity-induced and reversed-shear Alfvén eigenmodes in the DIII-D tokamak. The first application of fast-ion D_{alpha} (FIDA) spectroscopy to Alfvén-eigenmode physics shows that the central fast-ion profile is anomalously flat in the inner half of the discharge. Neutron and equilibrium measurements corroborate the FIDA data. The current density driven by fast ions is also strongly modified. Calculations based on the measured mode amplitudes do not explain the observed fast-ion transport. 相似文献
960.