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91.
Armin Uhlmann 《Reports on Mathematical Physics》1980,18(2):177-182
Using an inequality of Lieb one can compute a probability distribution which is less mixed than any (z|ωz)dz, where z labels the points of phase space, w is a density matrix, and (z| the appropriate coherent state. 相似文献
92.
DEBELJKOVIC D. LJ.; BRASIC V. S.; MILINKOVIC S. A.; JOVANOVIC M.B. 《IMA Journal of Mathematical Control and Information》1996,13(1):13-17
A method is presented whereby the absolute and relative stabilityof linear control systems containing transport lag can be determined.As a result feedback systems with variable time delay and loopgain, may be investigated in straightforward manner. 相似文献
93.
Tumorigenesis is characterized by alterations of methylation profiles including loss and gain of 5-methylcytosine. Recently, we identified a single CpG, which seemed to be consistently hypomethylated in pilocytic astrocytomas but not in other gliomas. To evaluate its applicability as a biomarker, we examined its methylation status in a large panel of gliomas (n = 97). Methylation-dependent DNA sequence variation may be considered a kind of single nucleotide polymorphism (methylSNP). MethylSNPs can be easily converted into common SNPs of the C/T type by sodium bisulfite treatment of the DNA and afterwards subjected to conventional SNP typing. We adapted SnaPshot trade mark and Pyrosequencing trade mark to determine the methylation of our test CpG in a quantitative manner. The adapted methods, called SNaPmeth and PyroMeth, respectively, gave nearly identical results, however data obtained with PyroMeth showed less scattering. Furthermore, the integrated software for allele frequency determination from Pyrosequencing could be used directly for data analysis while SnaPmeth data had to be exported and processed manually. Although data did not confirm our previous result of a preferential hypomethylation of the tested CpG in pilocytic astrocytomas, we consider quantitative methylSNP analysis by SNaPmeth or PyroMeth a favorable alternative to existing high-throughput methylation assays. It combines single CpG analysis with accurate quantitation and is amenable to high throughput. 相似文献
94.
Preparation, Structures, and Properties of Tris-hexamethyl-trisila-tetraphospha-nortricyclene-bis-chromiumtricarbonyl [P4(Sime2)3]3[Cr(CO)3]2 Hexamethyl-trisila-tetraphospha-nortricyclene P4(Sime2)3 1 reacts with C6H6Cr(CO)3 or (CHT)Cr(CO)3 (CHT ? Cycloheptatriene) under formation of [P4(Sime2)3]3[Cr(CO)3]2 3 (red crystals), in which each of the Cr atoms is attached to one P atom of a P3 ring of the three molecules 1 . 3 can also be prepared by heating a solution of P4(Sime2)3Cr(CO)5 in benzene or THF up to 120–1307deg;C. The compound 3 crystallizes in an orthorhombic and a hexagonal form, the latter being stabilized by one mole toluene. As revealed by single crystal investigations, the symmetry ¯6, distances and angles are nearly unchanged. The o-form corresponds to a face centered cubic packing of the molecules, whereas the h-form is hexagonal close packed. 相似文献
95.
Acid-base and surface energy characterization of grafted polyethylene using inverse gas chromatography 总被引:3,自引:0,他引:3
For a specific design of interfaces, i.e. in composites and blends, it is essential to know the surface thermodynamics of the components. Polyethylene grafted with maleic anhydride and maleic anhydride-styrene mixtures, respectively, was the component of interest of our investigations. Inverse gas chromatography (IGC) at infinite dilution was shown to be an appropriate method to evaluate the dispersive and acid-base surface characteristics although there is an influence of bulk absorption and morphology when performing IGC above the glass transition temperature of the polymer. 相似文献
96.
K. Uhlmann W. Triftshäuser G. Kögel P. Sperr D. T. Britton A. Zecca R. S. Brusa G. Karwasz 《Fresenius' Journal of Analytical Chemistry》1995,353(5-8):594-597
The concept of a scanning positron microscope which is under construction in München and Trento will be shown. A beam with a variable energy from 1 to 30 keV and a spot diameter of 1 m, which can be scanned over an area of (0.6×0.6) mm2, is formed after a double stage stochastic cooling of the positrons emitted from a radioactive source. Additionally, the beam will be pulsed to have a well-defined time base for positron lifetime measurements. The design of the microscope is dominated by special demands of positron physics. Therefore, the microscope contains electron optical elements which are well known but rarely used. These are the through the lens reflection remoderator and the optical column with a magnetic side gap lens as probe forming lens. 相似文献
97.
The kinetics of photophysical processes has been measured in stilbene solutions in the temperature range between ?40°C and 20°C. The population of the S1 level excited by two-photon absorption (TPA) and of secondary populated levels has been investigated using a probe beam method. It was found an energy barrier ΔE = 5 × 102 cm?1 of the thermically activated transition S1 → 1′. The rate parameter of this transition is determined to be k?111′, ≈ 2 ps at very high temperatures. 相似文献
98.
Hexamethyl-trisila-tetraphospha-nortricyclene, P4 Sime23 Reaction of white phosphorus with Na/K alloy and subsequent treatment with me2SiCl2 (me = CH3) yields crystalline P4(Sime2)3 (m. p. 159–160°C) along with polymeric silylphosphanes. The structure is derived from 31P-n.m.r.and mass spectra and turns out to be analogous to P4S3. 相似文献
99.
Andrea Vasella Christian Witzig Christian Waldraff Peter Uhlmann Karin Briner Bruno Bernet Luigi Panza Ren Husi 《Helvetica chimica acta》1993,76(8):2847-2875
In the context of the hypothesis postlating a heterolytic cleavage of a C? N bond during thermolysis of alkoxydiazirines (Scheme 1), we report the preparation of the diazirines 4 , 5 , 7 , and 8 , the kinetic parameters for the thermolysis in MeOH of the diazirines 1 and 4–9 , and the products of their thermolysis in an aprotic environment. The diazirines 4 , 57 , and 8 (Scheme 2–5) were prepared from the known hemiacetals 10 , 19 , 34 (prepared from 31 in an improved way), and 42 according to an established method. The oximes 11 , 20 , 35 , and 43 were obtained from the corresponding hemiacetals as (E/Z)-mixtures; 43 was formed together with the cyclic hydroxylamine 44 . Oxidation of 11 , 35 , and 43 (N-chlorosuccinimide/1,8-diazabicyclo[5.4.0]undec-7-ene (NCS/DBU) or NaIO4) gave good yields of the (Z)-hydroximolactones 12 , 36 , and 45 , while the oxime 20 led to a mixture of the (E)- and (Z)-hydroximolactones 21 and 22 , which adopt different conformations. Their configuration was assigned, inter alia, by a comparison with the enol ethers 28 and 29 , which were obtained, together with 30 , from the reaction of the diazirine 5 with benzaldehyde and PBu3. Treatment of the hydroximolactone O-sulfonates 13 , 23 , 37 , and 46 with NH3/MeOH afforded the diaziridines 15 , 25 , 38 , and 47 in good yields, while the (E)-sulfonate 24 decomposed readily. Oxidation of the diaziridines gave 4 , 5 , 7 , and 8 , respectively. Thermolysis of the diazirines 1 and 4–9 in MeOH yielded the anomeric methyl glycosides 50/51 , 16/17 , 26/27 , 52/53 , 39/40 , 48/49 , and 54/55 , respectively. A comparison of the kinetic data of the thermolysis at four different temperatures shows the importance of conformational and electronic factors and is compatible with the hypothesis of a heterolytic cleavage of a C? N bond. An early transition state is evidenced by the absence of torsional strain by an annulated 1,3-dioxane ring. Thermolysis of 1 in MeCN at 23° led mostly to the diasteroisomeric (Z,Z)-, (E,E)-, and (E,Z)-lactone azines 56 , 57 , and 58 (Scheme 6), which convert to 56 under mild conditions, and to 59 (3%). The benzyloxyglucal 59 was obtained in higher yields (18%), together with 44% of 56–58 , by thermolysis of solid 1 . Similarly, thermolysis at higher temperatures of 4 in toluene, THF, or dioxane and of 9 in CH2Cl2 or THF yielded the (Z,Z)-lactone azines 60 and 61 , respectively, the latter being accompanied by the dihydro-oxazole 62 . 相似文献
100.
Uhlmann P Skorupa S Werner C Grundke K 《Langmuir : the ACS journal of surfaces and colloids》2005,21(14):6302-6307
Thin films of alternating maleic acid/anhydride copolymers (poly(octadecene-alt-maleic acid/anhydride), POMA; poly(propene-alt-maleic acid/anhydride), PPMA; poly(styrene-alt-maleic acid/anhydride), PSMA) were studied to unravel the influence of the comonomer characteristics in the backbone on the surface-energetic properties of the copolymer films in the dry state and in contact with aqueous solutions. Water contact angle measurements revealed a graduation of the wettability of the dry hydrolyzed and annealed copolymer films that was dependent on the comonomer unit. It ranged from moderately hydrophilic (PPMA, annealed gamma(sv) = 39.9 mJ/m2) to very hydrophobic (POMA, annealed, gamma(sv) = 18.4 mJ/m2) surfaces. Liquid-fluid contact angle measurements using captive air bubbles were performed in different aqueous media (pure water, phosphate-buffered saline, and 10(-)(3) M KCl of two different pH values (pH = 3 and pH = 10) to study the copolymer films in their hydrated states relevant for biointerfacial phenomena. It was found that the graduation of the wettability of the copolymer films in the dry state is overall maintained upon immersion in aqueous solutions. The dependence of the wettability on the pH value of the aqueous medium could be related to the (de)protonation of the carboxylic groups. 相似文献