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131.
132.
Molecular structure of the oxidized, recombinant, heterocyst [2Fe-2S] ferredoxin from Anabaena 7120 determined to 1.7-A resolution 总被引:3,自引:0,他引:3
BL Jacobson YK Chae JL Markley I Rayment HM Holden 《Canadian Metallurgical Quarterly》1993,32(26):6788-6793
The [2Fe-2S] ferredoxin produced in the heterocyst cells of Anabaena 7120 plays a key role in nitrogen fixation, where it serves as an electron acceptor from various sources and an electron donor to nitrogenase. The three-dimensional structure of this ferredoxin has now been determined and refined to a crystallographic R value of 16.7%, with all measured X-ray data from 30.0 to 1.7 A. The molecular motif of this ferredoxin is similar to that of other plant-type ferredoxins with the iron-sulfur cluster located toward the outer edge of the molecule and the irons tetrahedrally coordinated by both inorganic sulfurs and sulfurs provided by protein cysteinyl residues. The overall secondary structure of the molecule consists of seven strands of beta-pleated sheet, two alpha-helices, and seven type I turns. It is of special interest that 4 of the 22 amino acid positions thought to be absolutely conserved in nonhalophilic ferredoxins are different in the heterocyst form of the protein. Three of these positions are located in the metal-cluster binding loop. 相似文献
133.
BACKGROUND: The death of a patient is a significant event that occurs often enough in general practice for it to have the potential to tell us much about the care we provide. There are few large series in the literature and we still know little about the collaborative use of this outcome measure. AIM: To determine the pattern of deaths and potentially preventable factors in our practices. METHOD: We completed a standard data collection form after each death in four general practices over a 40-month period. The results were discussed at quarterly meetings. RESULTS: A total of 1263 deaths occurred among our registered patients during the period of the audit. Preventable factors contributing to deaths were considered to be attributable to: patients (40%): mainly cigarette smoking, poor compliance, and alcohol problems; general practice teams (5%): mainly delayed referral, diagnosis and treatment, and failure to prescribe aspirin to patients with vascular disease; hospitals (6%): mainly delayed diagnosis and perceived treatment problems; the environment (3%): mainly falls, principally resulting in fractured neck of femur. CONCLUSION: A simple audit of deaths along the lines that we describe gives important information about the care provided by general practice teams and those in hospital practice. It has both educational value and is a source of ideas for service improvement and further study, particularly when carried out over several years. 相似文献
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135.
DJ Paustenbach SM Hays BA Brien DG Dodge BD Kerger 《Canadian Metallurgical Quarterly》1996,49(5):453-461
The uptake and elimination of Cr(VI) in a male volunteer who ingested 2 L/d of water containing 2 mg/L for 17 consecutive days was measured. Total chromium was measured in urine, plasma, and red blood cells (RBCs) for 4 d prior to and 2 wk after dosing (34 d total). The estimated bioavailability (2%) and the plasma elimination half-life (36 h) were consistent with our previous studies of Cr(VI) ingestion in humans. Steady-state chromium concentrations in urine and blood were achieved after 7 d of Cr(VI) ingestion. Both plasma and red blood cell (RBC) chromium concentrations returned rapidly to background levels within a few days after cessation of dosing. Since the concentration of chromium in the RBC should not decrease quickly if the chromium had entered the RBC as Cr(VI), these data support our prior work suggesting that concentrations of 10 mg Cr(VI)/L or less in drinking water of exposed humans appears to be completely reduced to Cr(III) prior to systemic distribution. Clinical chemistry data indicate that no toxicity occurred. 相似文献
136.
F. J. Zanner L. A. Bertram C. Adasczik T. O’Brien 《Metallurgical and Materials Transactions B》1984,15(1):117-125
Statistically designed experiments were conducted at two different production melt shops to evaluate the influence of arc
power, CO pressure, and electrode gap on melt rate. Approximately 11,000 kg of Inconel 718 alloy 0.4 m diameter electrodes
were vacuum consumable arc remelted into 0.5 m diameter ingots. Analysis of the experimental results revealed that melting
efficiency (melting rate/kW) was maximized when CO pressure and electrode gap were held at low levels. Under these conditions,
the heat distribution (created by the vacuum arc) on the electrode tip and the molten pool exhibited macro uniformity. Increased
CO pressure and/or electrode gap depressed the melt rate, and at 13.3 Pa (100 microns) and a 0.050 m electrode gap, this depression
exceeds 46 pct. Increasing these parameters also changed the arc behavior to that of a constricted arc with a highly localized
heat input. It is hypothesized that the change from the usual diffuse arc to this constricted arc results in intense Lorentz
pumping in a localized region of the molten pool atop the ingot causing fluid flow transients. These transients could, in
turn, create solidification defects. 相似文献
137.
A. J. Holden R. W. Allen K. Beasley D. R. Parker 《Quality and Reliability Engineering International》1988,4(3):247-254
A physical model describes device failure in terms of a series of n microscopic events (such as defect creation) which are describable in terms of an identifiable activation energy. The results show a ‘Weibull like’ time dependence, but the temperature dependence is not of the simple Arrhenius form. Application is made to the ‘dark’ leakage current in a PIN photodiode and to the deviation in threshold voltage in a MOSFET. In particular the threshold voltage is shown to depend on a series of activated processes, and the required number of such processes to cause failure increases with the width of the gate electrode. 相似文献
138.
Examined the ability of personnel test item response latencies to differentiate between individuals instructed to fake and those instructed to respond honestly with 64 undergraduates in Exp 1 and 100 unemployed Ss in Exp 2. Results supported a general model of lying derived from schema theory, demonstrating that fakers take relatively longer than honest respondents to admit to delinquent characteristics concerning themselves. Discriminant function analysis indicated that response latencies to items on standard personnel tests could significantly distinguish between fakers and honest test respondents in a personnel testing scenario. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
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140.