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991.
An approach for automated fast extraction of the fat content in bakery products based on focused microwave-assisted Soxhlet extraction (FMASE) and gravimetric determination is proposed. The main factors affecting the extraction efficiency—namely, power of irradiation, number of cycles and irradiation time—were optimized using experimental design methodology. The proposed method was applied to six samples, which were classified in two groups—namely, snacks and cookies. The results obtained agree with those provided by the AOAC 920.39 reference extraction method. No significant differences in the extraction efficiency of the fat content in bakery samples using FMASE versus the official method were found. Moreover, a drastic reduction in both the extraction time (60 and 35 min versus 16 and 8 h, respectively, for the two above commented groups) and sample handling are achieved with similar precision (expressed as repeatability and within-laboratory reproducibility standard deviation) to that provided by the AOAC 920.39 method. In addition, the proposed method is cleaner than the reference method as 75-80% of the extractant is recycled. 相似文献
992.
Eva E. Stüeken Maria de Castro Liliana Krotz Christopher Brodie Mattia Iammarino Guido Giazzi 《Rapid communications in mass spectrometry : RCM》2020,34(18):e8821
Rationale
Elemental abundances and isotopic ratios of carbon, nitrogen, sulfur and hydrogen have become important tools for reconstructing the evolution of Earth and life over geologic timescales, requiring accurate and precise analytical methods with high sample throughput. However, these measurements may require separate instruments for each task, such as an elemental analyzer (EA) with a thermal conductivity detector (TCD) for elemental abundances and an EA interfaced with a mass spectrometer for isotopic ratios.Methods
To improve sample throughput and laboratory up-time, we developed a switch that allows converting an EA IsoLink™ system from a standalone mode using only a TCD to a mode for isotope ratio mass spectrometry (IRMS) within minutes. This permits accurate measurements of elemental abundances and isotopic ratios with high throughput and lower cost. We validated this method with six shale standards from the US Geological Survey (USGS) and compared our abundance data with those from another laboratory.Results
Our results show that (a) abundance data agree well between the different laboratories and setups; (b) reproducible isotopic data can be obtained before and after the switch-over from EA standalone mode; and (c) the USGS rock standards cover a wide range in CHNS abundances and CNS isotopes, making them ideal reference materials for future geochemical studies.Conclusions
This ideal analytical setup has the advantage that abundance measurements can be performed to determine optimal sample amounts for later isotopic analyses, ensuring higher data quality. Our setup eliminates the need for a separate EA while freeing up the mass spectrometer for other tasks during abundance measurements.993.
M. J. Anjos R. T. Lopes E. F. O. de Jesus S. Moreira R. C. Barroso C. R. F. Castro 《Spectrochimica Acta Part B: Atomic Spectroscopy》2003,58(12):2227-2232
Several wines produced in different regions from south of Brazil and available in markets in Rio de Janeiro were analyzed for their contents of elements such as: P, S, Cl, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Rb and Sr. Multi-element analysis was possible with simple sample preparation and subsequent analysis by total-reflection X-ray fluorescence using synchrotron radiation. The measurement was carried at the X-ray fluorescence beamline in the Synchrotron Light Source Laboratory in Campinas, Brazil. The levels of the various elements obtained were lower in the Brazilian wines than the values generally found in the literature. The present study indicates the capability of multi-element analysis for determining the contents of various elements present in wines coming from Brazil vineyards by using a simple, sensitive and precise method. 相似文献
994.
Pervaporation has been coupled on-line to capillary electrophoresis (CE) by a simple interface consisting of a modified CE vial. The approach allows volatile analytes to be removed and injected into the capillary meanwhile the sample matrix remains in the pervaporator. By this approach volatile acidity and free sulfur dioxide have been simultaneously determined in wines. The detection limits (LODs) are 1.25 and 5.00 microg/mL, the quantification limits 4.12 and 16.50 microg/mL, and the linear dynamic ranges between LOD and 50 microg/mL and between 0.1 and 0.9 g/L for free sulfur dioxide and volatile acidity, respectively. The repeatability and within laboratory reproducibility, expressed as relative standard deviation (RSD), are 1.61% and 3.00% for free sulfur, and 3.35% and 4.58% for volatile acidity, respectively. The optimal pervaporation time and the time necessary for the individual separation-detection of the target analytes are 6 and 5 min, respectively. The analysis frequency is 7 h(-1) and the sample amount necessary is less than 7 mL. The proposed method and official methods for the analytes were applied to 32 wine samples. A two-tailed t-test was used to compare the methods, which yielded similar results. The errors, expressed as RSD for the two parameters, ranged between 1.3 and 4.1%. 相似文献
995.
Baldomero Bermúdez Fernando Lzaro M. Dolores Luque de Castro Miguel Valcrcel 《Microchemical Journal》1987,35(3)
A dual-channel flow injection configuration is proposed for individual and simultaneous determinations of glycine and cysteine (based on their reaction with phthaldialdehyde) in the range 1 × 10−7 – 1.5 × 10−5 M, with relative standard deviations of ± 1.7 and ± 1.3%, respectively, and a sampling frequency of 75–80 hr−1 for both analytes. The inclusion of a selecting valve in the configuration allows the simultaneous determination of these analytes in the concentration range achieved in their individual determinations. The resolution of mixtures is feasible with average errors of ± 2.2%. 相似文献
996.
Summary A mixed-phase capillary GC column has been designed for the separation of the compounds commonly present in the volatile fraction of cheeses. The design includes the calculation of the optimum phase concentration and the operating conditions. The evaluation of the resulting column indicates that its performance in the qualitative and quantitative analysis of cheese volatile compounds is better than those of other columns coated with a single stationary phase. 相似文献
997.
A gas chromatographic method for the identification and quantification of n-octyl esters (from n-octyl tetradecanoate to n-octyl hexa-cosanoate including dioctyl hexanedioate) and phthalates [dibutyl phthalate, benzyl butyl phthalate and di(2-ethylhexyl) phthalate] in sediments and biota from estuarine environments is described. Standards used for identification and quantification of some n-octyl esters were synthesized. The method has allowed the analysis of these compounds in polychaeta (Nereis diversicolor), oysters (Crassostea angulata), crabs (Carcinus maenas) and fish (Chelon labrosus, Platichtys flesus and Chondostroma polylepis) that were collected at different locations of the Urdaibai estuary (Bizkaia, Basque Country, Spain). Total phthalates and n-octyl esters ranged between 0.01 and 12 microg g(-1) and 0.05 and 9.4 microg g(-1), respectively, and were predominantly found in polychaeta and fish. Sediments did not contain these compounds in significant amount, only benzyl butyl phthalate, dioctyl hexanedioate and di(2-ethylhexyl) phthalate were found above limit of detection (0.01-0.05 microg g(-1)). 相似文献
998.
Dopico G MS González R MV Castro R JM González S E Pérez I J Rodrı́guez T M Calleja A Vilariño JM 《Talanta》2003,59(3):561-569
Triazine herbicides form a wide group of substances that belong among the most common agrochemicals applied for pre- and post-emergence weed control. So, they can be found in the environment at trace level. In order to determine their concentrations in water samples by the usual analytical techniques, a preconcentration step is commonly necessary. In this paper, a simple analytical method for the quantification of eight triazines (three chlorotriazines, four methylthiotriazines and one methoxytriazine) in water samples by solid phase extraction-reversed phase liquid chromatography (LC) has been developed. LC shows good analytical performance for simultaneous multiple triazine analysis (repeatability <2%, reproducibility <3%), except for prometon (repeatability 5.52%, reproducibility 16%). The results, obtained by using carbograph and polymeric sorbents for solid phase extraction (SPE), have been compared. The limits of quantification achieved permit the application of the proposed SPE-LC method for the determination of eight triazines in water samples (0.0065-0.028 μg l−1). 相似文献
999.
An electrochemical stripping procedure for ultra-trace measurements of adenine is described based on the adsorption of the adenine-copper complex on a static mercury drop electrode. Cyclic voltammetry was used to characterize the interfacial and redox behavior. Optimum experimental conditions were found when using a 0.005 M NaOH solution containing 0.4 ppm of copper, an accumulation potential of -0.30 V, a scan rate of 100 mV s(-1) and a linear scan mode. There is a linear response to adenine concentration in the range of 0.1-1.0 ppb and the detection limit for 6 min accumulation time was of 4.0 ppt (3.0x10(-11) M). Proper conditions for measuring the adenine in presence of guanine, thymine and cytosine were also investigated. The method was applied for the determination of adenine in a sample of single-stranded calf thymus DNA. 相似文献
1000.
Ligia Gomes John Nicolson Low Mrio A. D. C. Valente Cristina Freire Baltazar Castro 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(7):m293-m296
The title complex, [Cu(C12H9N2O)(C2H3O2)(C12H10N2O)], is a neutral CuII complex with a primary N3O2 coordination sphere. The Cu centre coordinates to both a deprotonated and a neutral molecule of N‐phenylpyridine‐2‐carboxamide and also to an acetate anion. The coordination around the metal centre is asymmetric, the deprotonated ligand providing two N donor atoms [Cu—N = 1.995 (2) and 2.013 (2) Å] and the neutral ligand providing one N and one O donor atom to the coordination environment [Cu—N = 2.042 (2) Å and Cu—O = 2.2557 (19) Å], the fifth donor being an O atom of the acetate ion [Cu—O = 1.9534 (19) Å]. The remaining O atom from the acetate ion can be considered as a weak donor atom [Cu—O = 2.789 (2) Å], conferring to the Cu complex an asymmetric octahedral geometry. The crystal structure is stabilized by intermolecular N—H...O, C—H...O and C—H...π interactions. 相似文献