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991.
Adherend surface effects on the amine cure of epoxy resins were investivated using finely divided aluminum oxide as high surface area models for aluminum. Calorimetric analysis of simplified crosslinking systems revealed significantly faster reactions which led to lower glass transition temperature materials for activated aluminum oxide filled samples. A monofunctional amine and epoxy were then utilized to obtain soluble reaction products amenable to molecular characterization. These studies similarly showed an increase in the rate of epoxy consumption in the presence of activated aluminum oxide which was attributed to both an increase in the rate of amine addition to epoxy as well as to epoxy homopolymerization. The latter was not observed in the unfilled mixtures. Such changes in reaction mechanism at the adherend surface have implications for the strength and durability of actual adhesive bonds. 相似文献
992.
993.
Maria Graças Andrade Korn Mauro Agildo Barbosa Guida José Tiago Pereira Barbosa Ednildo Andrade Torres Andréa Pires Fernandes Josué Carinhanha Caldas Santos Kelly das Graças Fernandes Dantas Joaquim Araújo Nóbrega 《Food Analytical Methods》2013,6(3):872-880
Propolis is a complex mixture of substances collected by honeybees from buds or exudates of plants, beeswax, and other constituents, as pollen and sugars. The main purpose of this study was to evaluate two digestion procedures for determination of major, minor, and trace elements (Ba, Ca, Cd, Cr, Co, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, and Zn) in natura propolis samples by inductively coupled plasma optical emission spectrometry (ICP OES). The first procedure studied was an open-vessel digestion using HNO3 + H2SO4 + H2O2 in a heating block and the second one was a microwave-assisted concentrated acid digestion using HNO3 + H2O2. Both digestion procedures led to similar results and quantitative recoveries. The residual carbon contents (RCCs) for propolis sample digests were 0.269?±?0.012 % when using the first procedure with conventional heating and 0.458?±?0.023 % by microwave-assisted closed vessel digestion, demonstrating high efficiency of both procedures. Accuracy of the results was demonstrated using a certified reference material and by comparison with a recommended official method. The t test (unpaired) at 95 % confidence level showed that there was no significant difference between determined and certified values of all analytes under investigation, except Ca concentration employing conventional procedure. The optimized microwave-assisted digestion procedure led to recoveries around 89–103 % and precision better than 5 % for most samples. The second procedure was faster, safer, and more accurate than the one based on conductive heating. Additionally, principal component analysis (PCA) was applied for checking if there was correlation between inorganic composition and source of propolis samples collected around Bahia State in the Northeast of Brazil. 相似文献
994.
ABSTRACT This paper presents the application of Kalman Filtering algorithm for tracking the power system voltage magnitude, the rate of change of the frequency, the frequency deviation as well as the voltage phase angle, when the the frequency of the voltage signal varies linearly with the time during the data window size. The proposed algorithm uses the digitized samples of the voltage signal at the relay location. Effects of sampling rate, data window size and the harmonics contaminating the voltage signal on the performance of the algorithm are studied. Furthermore, effects of the noise level are also investigated. A sample of the results obtained is reported in this paper. 相似文献
995.
ABSTRACT A microcomputer interface for the control of valve position using stepping motors is described. Designed to be used on Z-80 microcomputers employing the IEEE-696/S-100 bus, the interface is easy to program and has been used in the control of a laboratory-scale continuous stirred-tank reactor. 相似文献
996.
Lorenzo Berti Paola Serena D’Agostino Kelly Boeneman Igor L. Medintz 《Nano Research》2009,2(2):121-129
We demonstrate improved peptide linkers which allow both conjugation to biomolecules such as DNA and self-assembly with luminescent
semiconductor quantum dots. A hexahistidine peptidyl sequence was generated by standard solid phase peptide synthesis and
modified with the succinimidyl ester of iodoacetamide to yield a thiol-reactive iodoacetyl polyhistidine linker. The reactive
peptide was conjugated to dye-labeled thiolated DNA which was utilized as a model target biomolecule. Agarose gel electrophoresis
and fluorescence resonance energy transfer analysis confirmed that the linker allowed the DNA to self-assemble with quantum
dots via metal-affinity driven coordination. In contrast to previous peptidyl linkers that were based on disulfide exchange
and were thus labile to reduction, the reactive haloacetyl chemistry demonstrated here results in a more stable thioether
bond linking the DNA to the peptide which can withstand strongly reducing environments such as the intracellular cytoplasm.
As thiol groups occur naturally in proteins, can be engineered into cloned proteins, inserted into nascent peptides or added
to DNA during synthesis, the chemistry demonstrated here can provide a simple method for self-assembling a variety of stable
quantum dot bioconjugates.
相似文献
997.
Culbert Kristen M.; Burt S. Alexandra; McGue Matthew; Iacono William G.; Klump Kelly L. 《Canadian Metallurgical Quarterly》2009,118(4):788
Twin studies from the Minnesota Twin Family Study (MTFS) suggest negligible genetic effects on eating pathology before puberty but increased genetic effects during puberty. However, an independent study found no pubertal differences in genetic and environmental effects (R. Rowe, A. Pickles, E. Simonoff, C. M. Bulik, & J. L. Silberg, 2002). Discrepant results may be due to methodological differences. The MTFS studies divided twins at mid-puberty, whereas R. Rowe et al. (2002) divided twins based on menarche alone. In the present study, the authors aimed to reconcile discrepant findings by examining differences in etiologic effects for disordered eating attitudes and behaviors (i.e., levels of weight preoccupation, body dissatisfaction, binge eating, compensatory behaviors) using both classification methods in a new sample of 656 female twins. Using the MTFS method (i.e., K. L. Klump, M. McGue, & W. G. Iacono, 2003), the authors observed nominal genetic effects in prepubertal twins but significant genetic effects in pubertal and young adult twins. Conversely, genetic effects were moderate and equal in all groups using the R. Rowe et al. (2002) method. Findings highlight the potentially important role of puberty in the genetic diathesis of disordered eating attitudes and behaviors and the need to use early indicators of pubertal status in studies of developmental effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
998.
Accurate measurement of energy savings from industrial energy efficiency projects can reduce uncertainty about the efficacy of the projects, guide the selection of future projects, improve future estimates of expected savings, promote financing of energy efficiency projects through shared-savings agreements, and improve utilization of capital resources. Many efforts to measure industrial energy savings, or simply track progress toward efficiency goals, have had difficulty incorporating changing weather and production, which are frequently major drivers of plant energy use. This paper presents a general method for measuring plant-wide industrial energy savings that takes into account changing weather and production between the pre and post-retrofit periods. In addition, the method can disaggregate savings into components, which provides additional resolution for understanding the effectiveness of individual projects when several projects are implemented together. The method uses multivariable piece-wise regression models to characterize baseline energy use, and disaggregates savings by taking the total derivative of the energy use equation. Although the method incorporates search techniques, multi-variable least-squares regression and calculus, it is easily implemented using data analysis software, and can use readily available temperature, production and utility billing data. This is important, since more complicated methods may be too complex for widespread use. The method is demonstrated using case studies of actual energy assessments. The case studies demonstrate the importance of adjusting for weather and production between the pre- and post-retrofit periods, how plant-wide savings can be disaggregated to evaluate the effectiveness of individual retrofits, how the method can identify the time-dependence of savings, and limitations of engineering models when used to estimate future savings. 相似文献
999.
Hydrogen for fuel-cell electric vehicles (FCEVs) was produced using clean, renewable solar energy to electrolyze water. This report describes the design, construction, and initial performance testing of a solar hydrogen fueler at the GM Proving Ground in Milford, MI. The system used high-efficiency photovoltaic (PV) modules, a high-pressure (6500 psi, 44.8 MPa) electrolyzer, and an optimized direct connection between the PV and electrolyzer systems. This resulted in world-class solar to hydrogen efficiencies as high as 9.3% (based on H2 lower heating value, LHV). The system could potentially supply approximately 0.5 kg of hydrogen per day from solar power for the average solar insolation in Detroit; more hydrogen would be produced in locations with more abundant sunshine. This is sufficient hydrogen to operate an FCEV for an average daily urban commute. Thus, the solar hydrogen fueler testing served as a “proof of concept” for clean, renewable hydrogen with potential applications including convenient, clean, quiet, small-scale home fueling of FCEVs (that can contribute to the growth of a future FCEV fleet) and fueling in remote locations where grid electricity is not available. 相似文献
1000.
Pigeons were trained to search for hidden food in a rectangular environment designed to eliminate any external cues. Following training, the authors administered unreinforced test trials in which the geometric properties of the apparatus were manipulated. During tests that preserved the relative geometry but altered the absolute geometry of the environment, the pigeons continued to choose the geometrically correct corners, indicating that they encoded the relative geometry of the enclosure. When tested in a square enclosure, which distorted both the absolute and relative geometry, the pigeons randomly chose among the 4 corners, indicating that their choices were not based on cues external to the apparatus. This study provides new insight into how metric properties of an environment are encoded by pigeons. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献