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141.
Couturier M Tucker JL Proulx C Boucher G Dubé P Andresen BM Ghosh A 《The Journal of organic chemistry》2002,67(14):4833-4838
5,5-Dimethyl-1,4,2-dioxazoles are readily installed by transketalization of 2,2-diethoxypropane, where both the NH and OH moieties are protected in a nonprotic form. The dioxazoles are stable to a wide variety of reaction conditions and readily revert back to the hydroxamic acid by treatment with Nafion-H in 2-propanol. The method is applicable to primary, secondary, tertiary, and aromatic hydroxamic acids, and the acidity of the protons adjacent to the dioxazole allows alpha-functionalization. 相似文献
142.
Sorption of mannans onto bleached kraft pulp (BKP) was investigated withreference to other interactions of mannans in mechanical pulping andpapermaking. O-Acetyl galactoglucomannans (GGM) isolated from thermomechanicalpulp (TMP), as well as enzymatically modified guar gum galactomannans (GM) wereused in the study. The results showed that deacetylation of TMP GGMs, alsooccurring during peroxide bleaching of TMP, dramatically increased thesorption.A higher sorption was also achieved after salt addition, while temperature hadno effect. Sorption of guar gum GMs onto BKP fibres was, on the other hand,quite unaffected by external conditions such as temperature, pH and saltaddition. The degree to which the pulp was beaten did not notablyinfluence the sorption either – only unbeaten pulp gave a clearly lower mannansorption. A lower number of galactose side groups, however, strongly affectedsorption – the lower the number of side groups, the higher the sorption.The molar mass did not seem to affect the rate of sorption to any higher extentat ambient temperature. At higher temperatures the rate of sorption of smallerGM polymers was, nevertheless, slightly increased. Low-molar-mass GMs alsosorbed at a higher rate onto unbeaten pulp compared to high-molar-mass mannans.GM sorption appeared to be virtually irreversible. 相似文献
143.
P. M. Grant R. E. Whipple F. Bazan J. L. Brunk K. M. Wong R. E. Russo B. D. Andresen 《Journal of Radioanalytical and Nuclear Chemistry》1995,193(1):165-169
Forensic analyses of debris from the fatal explosion of an electrochemical cold fusion cell at SRI International were conducted at LLNL at the request of Cal-OSHA. One investigation focused on the possibility of conventional nuclear reaction mechanisms contributing to the total energy inventory of the incident. Selected metal components of the electrolysis apparatus were subjected to nondestructive -ray spectrometry with high-sensitivity, low-background Ge detector systems. The anticipated analytes in these studies were radioactivation products potentially induced in the explosion residue by either fast or thermal neutrons. The results of this investigation were negative within the temporal constraints of the incident and the analytical sensitivities of the instrumentation. 相似文献
144.
Can nonspecifically bound divalent counterions induce attraction between DNA strands? Here, we present experimental evidence demonstrating attraction between short DNA strands mediated by Mg2+ ions. Solution small angle x-ray scattering data collected as a function of DNA concentration enable model independent extraction of the second virial coefficient. As the [Mg2+] increases, this coefficient turns from positive to negative reflecting the transition from repulsive to attractive inter-DNA interaction. This surprising observation is corroborated by independent light scattering experiments. The dependence of the observed attraction on experimental parameters including DNA length provides valuable clues to its origin. 相似文献
145.
Pingping Su Kim Granholm Andrey Pranovich Leo Harju Bjarne Holmbom Ari Ivaska 《Cellulose (London, England)》2010,17(5):1033-1044
Knowledge about how different metal ions are bound to pulp fibers is very important for optimal metal management in pulping
processes. A column chromatographic method was used to assess the differences in affinity of 14 metal ions to untreated, alkali-treated
and peroxide-bleached thermomechanical pulp (TMP). A method of competition between cations in the column chromatographic experiments
was used in the sorption experiments, with an excess of each metal ion compared to the total capacity of the pulp studied.
The method is very sensitive and even small differences in affinities can be detected. By combining the results from sorption
experiments with four different metal ion mixtures the following order of affinity was obtained: Pb2+ ≫ Cu2+ ≫ Cd2+ > Zn2+ > Ni2+ > Ba2+ > Ca2+ > Mn2+ > Sr2+ > Mg2+ ≫ Rb+ ≈ K+ > Na+ > Li+. All three types of pulps showed the same affinity order. Lead and copper ions were clearly most strongly bound to the pulp
fibers. Within the alkali and alkaline earth metal groups the differences in affinity were quite small. The sorption of metal
ions to pulp fibers takes place mainly by complexation, where the divalent metal ions are coordinated to functional groups
(acid groups) in the fiber phase. Protonation constants and concentrations of acid groups were determined by potentiometric
titration. A model with two carboxyl groups and two phenolic hydroxyl groups satisfied best the experimental data. By treatment
with alkali and peroxide new acid groups were created and the total binding capacity of hydrogen ions increased from 137 μeq/g
for untreated pulp to 187 and 228 μeq/g for alkali-treated and peroxide-treated pulp, respectively. 相似文献
146.
P. A. Léon Bouyou Johan J. Weisser Bjarne W. Strobel 《Analytical and bioanalytical chemistry》2014,406(20):5019-5030
Trace levels of the veterinary antibiotic compound sulfadiazine (SDZ) can be determined in agricultural drainage water samples with this new method. Optimized sample pretreatment and solid-phase extraction was combined with liquid chromatography coupled to tandem mass spectrometry (SPE LC-MS/MS) using positive electrospray ionization. The linear dynamic range for the LC-MS/MS was assessed from 5 μg/L to 25 mg/L with a 15-point calibration curve displaying a coefficient of correlation r 2?=?0.9915. Agricultural drainage water spiked at a concentration of 25 ng/L gave recoveries between 63 and 98 % (relative standard deviation 15 %), while at 10 ng/L, it showed a lower recovery of 32 % (relative standard deviation 47 %). The final SPE LC-MS/MS method had a limit of detection (LOD)Method and a limit of quantification (LOQ)Method of 7.5 and 23 ng/L agricultural drainage water, respectively. Determination of SDZ, spiked at a realistic concentration of 50 μg/L, in artificial drainage water (ADW) containing common and high levels of phosphate (0.05, 0.5, and 5 mg/L) gave recoveries between 70 and 92 % (relative standard deviation 7.4–12.9 %). Analysis of the same realistic concentration of SDZ in ADW, spiked with common and high levels of dissolved organic carbon (2, 6, and 15 mg/L) confirmed the possible adaptation of a tandem solid-phase extraction (strong anion exchange (SAX)-hydrophilic-lipophilic balance (HLB)) followed by liquid chromatography-tandem mass spectrometry methodology. Recoveries obtained ranged from 104 to 109 % (relative standard deviation 2.8–5.2 %). The new methods enable determination of the veterinary antibiotic compound SDZ in agricultural drainage water from field experiments and monitoring schemes for phosphate- and dissolved organic carbon (DOC)-rich water samples in intensive farming areas. Figure
Clean-up and up-concentration of sulfadiazine from agricultural drainage water 相似文献
147.
Blends of poly(ethylene terephthalate) (PET) and poly(ethylene-2,6-naphthalene dicarboxylate) (PEN) were obtained by coprecipitation from solution followed by melt-pressing for different timest
mand quenching in iced water. When the melt-pressing time was 0.2 and 0.5 min, two glass transition temperaturesT
gwere observed by means of dynamic mechanical analysis (DMA), indicating that there are two phases present, a PEN-rich phase and a PET-rich phase. The differential scanning calorimetry (DSC) curves show two crystallization peaks and two melting peaks which, according to wide-angle x-ray scattering (WAXS) measurements, can be attributed to PET and PEN, respectively. In the case oft
m=2 min or longer, a single value ofT
gand thus a single phase is found to exist. Fort
m=10 min and 45 min no crystallization and melting at all is observed during heating with 10°C/min, indicating that a copolyester of PET and PEN has been formed by transesterfication during melt-pressing.Time-resolved WAXS measurements during isothermal crystallization show that, in the blend, the half-time of crystallization of PET is different from that of PEN, and not the same as that which is found in the pure polymer.Dedicated with best wishes to Prof. Dr. E.W. Fischer on the occasion of his 65th birthday 相似文献
148.
A new concept, compulsory multi-disciplinary courses, was introduced in upper secondary school curriculum as a central part of a recent reform. This paper reports from a case study of such a triple/four-disciplinary project in mathematics, physics, chemistry and ‘general study preparation’ performed under the reform by a team of experienced teachers. The aim of the case study was to inquire how the teachers met the demands of the introduction of this new concept and, to look for signs of new relations established by the students between mathematics and other subjects, as a result of the multi-disciplinary teaching. The study revealed examples of good practice in planning and teaching. In addition, it served to illuminate interesting aspects of how students perceived the school subject mathematics and its relations to other subjects and to common sense. 相似文献
149.
C. Amole M. D. Ashkezari G. B. Andresen M. Baquero-Ruiz W. Bertsche P. D. Bowe E. Butler C. L. Cesar S. Chapman M. Charlton A. Deller S. Eriksson J. Fajans T. Friesen M. C. Fujiwara D. R. Gill A. Gutierrez J. S. Hangst W. N. Hardy R. S. Hayano M. E. Hayden A. J. Humphries R. Hydomako S. Jonsell L. Kurchaninov N. Madsen S. Menary P. Nolan K. Olchanski A. Olin A. Povilus P. Pusa F. Robicheaux E. Sarid D. M. Silveira C. So J. W. Storey R. I. Thompson D. P. van der Werf J. S. Wurtele Y. Yamazaki 《Hyperfine Interactions》2012,212(1-3):101-107
The ALPHA experiment, located at CERN, aims to compare the properties of antihydrogen atoms with those of hydrogen atoms. The neutral antihydrogen atoms are trapped using an octupole magnetic trap. The trap region is surrounded by a three layered silicon detector used to reconstruct the antiproton annihilation vertices. This paper describes a method we have devised that can be used for reconstructing annihilation vertices with a good resolution and is more efficient than the standard method currently used for the same purpose. 相似文献
150.
A comparison of relative populations of ZnI and ZnII levels excited in equilibrium plasma, sputtering, gas-phase single collision, and beam foil sources is presented, and includes data on the first reported excitation studies under single collision conditions for a (transition metal atom)-(transition metal ion) interaction. A search for continuum emission from atomic chromium, like that seen during sputtering of chromium metal, produced a negative result. 相似文献