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991.
992.
Sung Hyup Lee 《Journal of power sources》2010,195(15):5049-7024
Thermal reactions of charged LixCoO2 and electrolyte are investigated by means of temperature-programmed decomposition-mass spectrometry (TPD-MS), DSC, TGA, and XRD. The electrolyte is composed of ethylene carbonate, propylene carbonate, and dimethyl carbonate. Direct observation of gas species resulting from the reactions is beneficial in understanding the reaction mechanisms. From O2 peaks in the TPD-MS spectra with weight loss in TGA and XRD results, it is obvious that the reduction of LixCoO2 to LiCoO2 and Co3O4 is triggered at 190 °C and completed at 400 °C. The initial stages of electrolyte combustion and decomposition are confirmed by H2O and CO2 peaks in the TPD-MS spectra along with exothermic peaks in DSC plots. The reaction of electrolyte with O2 released from the reduction of LixCoO2 begins at 240 °C; the decomposition starts at 290 °C. 相似文献
993.
The distribution of 15 aroma constituents, including the (R)- and (S)-enantiomers of ethyl 2-methylbutanoate, in 30 commercially available and laboratory prepared apple juices was evaluated
by multivariate statistical methods. Principal component analysis and cluster analysis revealed ethyl 3-methylbutanoate, 3-methylbutyl
acetate and (R)-ethyl 2-methylbutanoate as key components for the differentiation of apple juices. In freshly pressed and some commercial
juices ethyl 3-methylbutanoate and 3-methylbutyl acetate were not present, and the (S):(R) ratio of ethyl 2-methylbutanoate was found to be >99 : 1%. Another group of commercial products was separated in which the
amounts of ethyl 3-methylbutanoate and 3-methylbutyl acetate exceeded 1 μg/l and 180 μg/l, respectively, and in which the
(S):(R) ratio of ethyl 2-methylbutanoate was <97 : 3%. The statistical data confirmed the high selectivity of apple fruit tissue
in biosynthesizing 2-methylbutyl and 2-methylbutanoate esters, and could also be used to extend the results of enantio-multidimensional
gas chromatography and other authenticity analyses.
Received: 20 April 1998 / Revised version: 23 June 1998 相似文献
994.
Stefania Vichi Montserrat Riu-Aumatell Mercé Mora-Pons Josep M. Guadayol Susana Buxaderas Elvira López-Tamames 《Food chemistry》2007,105(4):1748-1754
HS-SPME coupled to GC/MS was applied to the analysis of the volatile fraction of Juniperus communis L. berries, which are the principal ingredient used for gin aromatization. Seventy seven compounds were identified by comparison with reference compounds or tentatively identified by comparing their mass spectra and retention index with those reported in mass spectra libraries and literature, respectively. Seventy four were detected by SPME and sixty eight were detected by solvent distillation extraction (SDE). These were mainly mono- and sesquiterpenic compounds that represented more than the 80% of the gin’s volatile composition. A high percent content was due to monoterpenoids, whose analysis could be important for the assessment of sensory quality control of juniper due to their impact on gin aroma. The main monoterpenoids detected in the headspace of the juniper berries from two periods of collection were terpinen-4-ol, p-cymene, β-myrcene, γ-terpinene, α-pinene and limonene. These represented more than the 70% of the sample’s volatile fraction. The proposed SPME method required short times and the low cost of analysis and enabled to detect a number of compounds comparable with SDE or much higher than the number of compounds reported by other extraction techniques. The results suggested the suitability of this technique for the assessment of the volatile composition of juniper berries intended for gin flavouring. 相似文献
995.
J. C. J. Da Silva S. Cadore J. A. Nobrega N. Baccan 《Food Additives & Contaminants》2007,24(2):130-139
Samples of commercial wine vinegar were introduced in an axially viewed inductively coupled plasma optical emission spectrometry instrument (AX-ICP OES) equipped with different sample introduction systems: a cross-flow nebulizer combined with a double-path spray chamber (CF-DP) and cone spray associated with a cyclone spray chamber (CS-CC). Samples of white and red wine vinegar were diluted with water before analysis. Higher magnesium Mg II/Mg I ratios (11 and 10 for CS-CC and CF-DP, respectively) were obtained using a nebulization gas flow rate of 0.6 l min-1 and an applied power of 1.3 kW. The background equivalent concentrations (BEC) and signal-to-background ratio (SBR) of analytes were improved using scandium (Sc) as the internal standard. The limits of detection (LOD) and limits of quantification (LOQ) for mineral constituents were similar for both introduction systems. Best recoveries values were obtained using a plasma under robust conditions, CS-CC system and Sc as the internal standard. The concentration determined in 13 commercial samples of wine vinegars varied between 0.2 and 3.0, between 0.02 and 0.4, between 8.5 and 100.0, between 0.01 and 0.05, between 27.0 and 540.0, between 4.0 and 79.0, between 0.4 and 10.0, and between 0.01 and 2.0 for aluminium (Al), barium (Ba), calcium (Ca), copper (Cu), potassium (K), magnesium (Mg), manganese (Mn), and zinc (Zn), respectively. 相似文献
996.
A model for the global dynamics of a sorption heat pump is presented in this work. It involves a model of a reactor where gas-solid reaction takes place coupled with a model of a two-phase closed thermosyphon cooling exchanger. Simulations of the whole discontinuous cold production process have been performed. The good agreement between experimental and simulation data shows the ability of the present model to accurately represent the dynamics of such systems. An analysis of the physical mechanisms governing the dynamics of each process stage is made. It was shown that mass limitation strongly slowed down the synthesis when the other phases of the process are mainly dependent on the thermal behavior of the transformer. This model can be used as a powerful tool for the optimization of sorption systems and for the intensification of such processes. 相似文献
997.
Prashanth K. Vijalapura Sanjay Govindjee 《International journal for numerical methods in engineering》2005,64(6):819-848
This paper deals with the design and implementation of an adaptive hybrid scheme for the solution of highly non‐linear, strongly coupled problems. The term ‘hybrid’ refers to a composite time stepping scheme where a controller decides whether a monolithic scheme or a fractional step (splitting) scheme is appropriate for a given time step. The criteria are based on accuracy and efficiency. The key contribution of this paper is the development of a framework for incorporating error criteria for stepsize selection and a mechanism for choosing from splitting or monolithic possibilities. The resulting framework is applied to silylation, a highly non‐linear, strongly coupled problem of solvent diffusion and reaction in deforming polymers. Numerical examples show the efficacy of our new hybrid scheme on both two‐ and three‐dimensional silylation simulations in the context of microlithography. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
998.
For the analysis of polymers soft ionization mass spectrometry, in which only molecular ions are observed, can provide the complete distribution of chains (length, composition, end-groups) in under ten minutes on microgram quantities of material. Moreover, molecular ion information of neat organic pigments or those present in crosslinked networks can also be furnished. No other analytical technique can supply these data in such a short time. The application of mass spectrometry to the characterization of materials used in today's high performance automotive coatings is presented. These include functional monomers, several acrylic copolymers, organic pigments and an epoxide prepolymer. While there are a variety of mass spectrometric techniques, in this paper we will highlight the techniques that we have found useful for the characterization of organic coating components. The selection of the mass spectrometric technique is dictated by the molecular weight of the material and to a lesser extent the chemical composition. We used potassium ionization of desorbed species (K+IDS) performed on a quadrupole mass spectrometer for materials under 1000 Daltons (Da). However, many of the ingredients used in current automotive finishes fall between 1000 and 10 000 Da. For these materials we used a Fourier transform mass spectrometer (FTMS) which is well suited for this mass range and boasts the highest resolution and mass accuracy available. Direct desorption/ionization using a carbon dioxide laser is our standard method of sample introduction. Recently, we coupled a gel permeation chromatograph to our FTMS using an electrospray ionization interface. This hyphenated technique offers one of the most powerful characterization methods for the coatings chemist. 相似文献
999.
1000.