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101.
Singleton MJ Woods KN Conrad ME Depaolo DJ Dresel PE 《Environmental science & technology》2005,39(10):3563-3570
The nitrogen and oxygen isotopic compositions of nitrate in pore water extracts from unsaturated zone (UZ) core samples and groundwater samples indicate at least four potential sources of nitrate in groundwaters at the U.S. DOE Hanford Site in south-central Washington. Natural sources of nitrate identified include microbially produced nitrate from the soil column (delta15N of 4 - 8 per thousand, delta18O of -9 to 2 per thousand) and nitrate in buried caliche layers (delta15N of 0-8 per thousand, delta 18O of -6to 42 per thousand). Isotopically distinctindustrial sources of nitrate include nitric acid in low-level disposal waters (delta15N approximately per thousand, delta 18O approximately 23%o) per thousandnd co-contaminant nitrate in high-level radioactive waste from plutonium processing (6'5delta1of 8-33 % o, per thousand18delta oO -9 to 7%0). per thousandThe isotopic compositions of nitrate from 97 groundwater wells with concentrations up to 1290 mg/L NO3- have been analyzed. Stable isotope analyses from this study site, which has natural and industrial nitrate sources, provide a tool to distinguish nitrate sources in an unconfined aquiferwhere concentrations alone do not. These data indicate that the most common sources of high nitrate concentrations in groundwater at Hanford are nitric acid and natural nitrate flushed out of the UZ during disposal of low-level wastewater. Nitrate associated with high-level radioactive UZ contamination does not appear to be a major source of groundwater nitrate at this time. 相似文献
102.
The demonstration of monitored natural attenuation (MNA) of chlorinated hydrocarbons in groundwater is typically conducted through the evaluation of concentration trends and parent-daughter product relationships along prevailing groundwater flow paths. Unfortunately, at sites contaminated by mixtures of chlorinated ethenes, ethanes, and methanes, the evaluation of MNA by using solely concentration data and parent-daughter relationships can result in erroneous conclusions regarding the degradation mechanisms that are truly active at the site, since many of the daughter products can be derived from multiple parent compounds. Stable carbon isotope analysis was used, in conjunction with concentration data, to clarify and confirm the active degradation pathways at a former waste solvent disposal site where at least 14 different chlorinated hydrocarbons have been detected in the groundwater. The isotope data indicate that TCE, initially believed to be present as a disposed product and/or a PCE dechlorination intermediate, is attributable to dehydrochlorination of 1,1,2,2-PCA. The isotope data further support that vinyl chloride and ethene in the site groundwater result from dichloroelimination of 1,1,2-trichlorethane and 1,2-dichloroethane, respectively, rather than from reductive dechlorination of the chlorinated ethenes PCE, TCE, or 1,2-DCE. The isotope data confirm that the chlorinated ethanes and chlorinated methanes are undergoing significant intrinsic degradation, whereas degradation of the chlorinated ethenes may be limited. In addition to the classical trend of enriched isotope values of the parent compounds with increasing distance associated to biodegradation, shifts of isotope ratios of degradation byproduct in the opposite direction due to mixing of isotopically light byproducts of biodegradation with compounds from the source are shown to be of high diagnostic value. These data underline the value of stable isotope analysis in confirming transformation processes at sites with complex mixtures of chlorinated compounds. 相似文献
103.
Xiao Gong Vahid Vahdat Scott Frankert Evan Anderson Shaun Chen Yiao-Tee Hsia 《摩擦学汇刊》2013,56(4):679-685
Particle contamination at the head–disk interface (HDI) is a major concern for the long-term reliability of hard disk drives. In the current study, it is shown that, surprisingly, soft and lubricious talc particles have a significant damaging effect on the friction performance of media lubricants, nanometer-thick perfluoropolyethers. Thermogravimetric analysis (TGA) and the adsorption studies indicate that two mechanisms, Lewis acid–catalyzed decomposition and surface adsorption, are responsible for the observed tribological degradation. The potential impacts of the findings here on the design of next-generation media lubricant have been discussed. 相似文献
104.
Rong Zhang Jie Pan Evan P. Briggs Marvin Thrash Lei L. Kerr 《Solar Energy Materials & Solar Cells》2008,92(4):425-431
The interface between the ZnO and dye directly impacts the dye-sensitized solar cell (DSSC) performance. Nanostructured porous ZnO film was developed by a simple chemical solution process. Scanning electron microscope (SEM) images demonstrated the uniform ZnO films with sheet-like nanostructure. Adsorption studies indicated that the maximum adsorption capacity of RuN3 dye on the surface of ZnO films was approximately 0.016 mmol RuN3/g ZnO films. Adsorption studies were conducted at 25 and 40 °C. The results showed that the dye adsorption was significantly influenced by temperatures. Moreover, the problem of the dye aggregation on the ZnO surface was reduced at higher adsorption temperatures. The adsorption chemistry was studied with Raman spectroscopy. 相似文献
105.
In an effort to assess models of inductive reasoning and deductive reasoning, the authors, in 3 experiments, examined the effects of argument length and logical validity on evaluation of arguments. In Experiments 1a and 1b, participants were given either induction or deduction instructions for a common set of stimuli. Two distinct effects were observed: Induction judgments were more affected by argument length, and deduction judgments were more affected by validity. In Experiment 2, fluency was manipulated by displaying the materials in a low-contrast font, leading to increased sensitivity to logical validity. Several variants of 1-process and 2-process models of reasoning were assessed against the results. A 1-process model that assumed the same scale of argument strength underlies induction and deduction was not successful. A 2-process model that assumed separate, continuous informational dimensions of apparent deductive validity and associative strength gave the more successful account. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
106.
Evan J. Reed Marin Solja
i Mihai Ibanescu J. D. Joannopoulos 《Journal of Computer-Aided Materials Design》2005,12(1):1-15
We predict that reversed and anomalous non-relativistic Doppler shifts can be observed under some circumstances when light reflects from a shock wave front propagating through a photonic crystal, or material with a periodic modulation of the dielectric. This theoretical prediction is generalizable and applies to wave-like excitations in a variety of periodic media. An experimental observation of this effect has recently been made (Seddon, N. and Bearpark, T. Science, 302 (2003) 1537) and we provide a brief discussion of this experiment. 相似文献
107.
In industry and labs, predictive models describing processing-structure relationships are inherently valuable, yet few exist for cation ordering in perovskites. In this work, 15 compositions in the [(NayLi1−y)(1−3x)/2La(1+x)/2]TiO3 (NLLT) system (y = 0.25, 0.5, and 0.75; x = 0, 0.0533, 0.1, 0.1733, and 0.225) were synthesized using a conventional solid-state mixed-oxide method. X-ray diffraction data show that some degree of long-range ordering of A-site cations exists for x ≥ 0.1, although electron-diffraction data indicate that short-range ordering exists even for x < 0.1, with the degree of ordering decreasing as the value of x increases. Empirical models have been derived for the A-site ordering parameter (η) as well as the resultant expansion (ΔrA) for each y series in the NLLT system, from which two general models were derived for perovskites with any arbitrary degree of 1:1 layered A-site ordering. These general models allow for the prediction of the order parameter and resulting expansion using only published ionic radii data. 相似文献
108.
Anthony R. de Souza Michael R. Greenberg Ben-chieh Liu Karol J. Krotki Sallie A. Marston Ashok K. Dutt Yuk Lee David F. Batten Timothy J. Finan J. H. Holmes Brenton M. Barr Ryszard Domanski Victoria A. Lawson Dean M. Hanink Clarence G. Ray Saleem Mohammad Clyde Weaver Richard E. Caves Luis Suarez-Villa Dean Forbes Brenda J. Moscove Leland R. Pederson Nolin Masih Thomas A. Reiner Noel D. Uri Sidney R. Jumper Charles G. Schmidt James J. Parsons James T. Peach W. Donald McTaggart Daniel J. Fairbanks Peggy Evans Rutherford H. Platt 《The Annals of Regional Science》1987,21(3):126-187
109.
十多年来,通过对环境、工程、地下水以及浅度地层学的研究,验证并提高了探地雷达(6PR)在岩化松散沉积物中的有效性(例如,见Neal,2004及本文相关参考资料)。尽管如此,在探地雷达于任意设置情况下反射和衍射的实际外观和特性的控制因素方面,仍然存在一些较大的问题。 相似文献
110.
Chemical vapor infiltration is now being used to produce advanced materials for aerospace applications. It is also applicable to carbons to enhance the resistance against oxidation. In the present study, methane pyrolysis was conducted for several kinds of carbons such as electrode-grade graphite, electrode-grade carbon, coke and activated charcoal. The structural change of micropores (radius < 10 nm) accompanying infiltration and oxidation was investigated because oxidation is considered mainly to occur in such small pores due to their large specific surface area. The change of macropores measured by mercury porosimeter is also shown for comparison with that of fine pores. Pore-size distribution measured by the BET method have shown that the filling mode depends on the pore structure of carbons. 相似文献