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21.
F. Nava G. Wagner C. Lanzieri P. Vanni E. Vittone 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2003,510(3):273-280
The development of SiC minimum ionising particle (MIP) detectors imposes severe constrains in the electronic quality and the thickness of the material due to the relatively high value of the energy required to produce an electron–hole pair in this material by MIP against the value for Si. In this work, particle detectors were made using semiconductor epitaxial undoped n-type 4H-SiC as the detection medium. The thickness of the epilayer is on the order of 40 μm and the detectors are realised by the formation of a nickel silicide on the silicon surface of the epitaxial layer (Schottky contact) and of the ohmic contact on the back side of 4H-SiC substrate. The low doping concentration (6×1013 cm−3) of the epilayer allows the detector to be totally depleted at relatively low reverse voltages (100 V). We present experimental data on the charge collection properties by using 5.486 MeV -particles impinging on the Schottky contact. A 100% charge collection efficiency (CCE) is demonstrated for reverse voltages higher than the one needed to have a depletion region equal to the -particle extrapolated range in SiC. The diffusion contribution of the minority change carriers to CCE is pointed out. By comparing measured CCE values to the outcomes of drift–diffusion simulation, values are inferred for the hole lifetime within the neutral region of the charge carrier generation layer. 相似文献
22.
R. W. Simon C. E. Platt A. E. Lee K. P. Daly M. K. Wagner 《Journal of Superconductivity and Novel Magnetism》1988,1(3):313-326
High-quality superconducting films of erbium-barium-copper-oxide have been produced in a multisource sputtering system on a variety of substrates, including buffered sapphire and silicon wafers as well as various single-crystal materials. Fine-grained polycrystalline films with narrow (<4 K) resistive transitions have been grown on a number of different substrates. The use of erbium in the 12–3 compound leads to improved film morphology and to more forgiving conditions for establishing of the superconducting phase. Sputtered neutral mass spectroscopy (SNMS) yields useful information about the compositional profile of the films. 相似文献
23.
D. Bergmann U. KaiserS. Wagner 《Journal of Wind Engineering & Industrial Aerodynamics》2003,91(4):543-550
The determination of dynamic wind loads on buildings, i.e. pressure and deflection, has gained increasing interest (European Prestandard ENV 1991-2-4, Eurocode 1: basis of design and actions on structures—Part 2-4: actions on structures—wind actions, European Committe for Standardization, Brussels, 1995; DIN 1055 Teil 4 Lastannahmen für Bauten, Verkehrslasten, Windlasten bei nicht schwingungsanfälligen Bauwerken, 1991; N. Hölscher, M. Hortmanns, J. Sahlem, Praxisnahe Erfassung von Windwirkung an Industrie- und Hochbauten, Windwirkung im Bauwesen, Braunschweig, 7, Dreiländertagung D-A-CH 2001, Windtechnologische Gesselschaft, 2001 [1], [2] and [3]). Therefore, the spectral distributions of velocity and pressure fluctuations in wind tunnels are an important quality aspect. While velocity fluctuations can be manipulated by the obstacles used to create the turbulence, pressure fluctuations are influenced by acoustic noise as well. Especially, the first eigenfrequency of the longitudinal mode of the wind tunnel tends to disturb the pressure spectrum.In this paper, a solution for the reduction of low-frequency acoustic pressure fluctuation is presented and its application in the atmospheric boundary layer wind tunnel at the IAG is shown. 相似文献
24.
H. Wolf F. Wagner Th Wichert R. Grill E. Belas Isolde Collaboration 《Journal of Electronic Materials》2006,35(6):1350-1353
Anomalous diffusion profiles of Ag in single crystalline CdTe were observed using the radiotracer 111Ag. The diffusion anneals were performed at 800 K under Cd or Te vapor and in vacuum with low Ag concentrations. The measured
Ag profiles directly reflect the distribution of the self-interstitials and vacancies of the Cd sublattice and are the result
of chemical self-diffusion which describes the variation of the deviation from stoichiometry of the binary crystal as a function
of depth and time. It turned out that the spread of the Ag dopant essentially is determined by the drift of the charged defects
within the electric field caused by the distribution of the extrinsic and intrinsic defects. 相似文献
25.
Reviews the empirical literature available on the phenomenon of depression in Alzheimer's disease (AD). Although not extensively studied, there is accumulating evidence to suggest that depression affects a large number of patients with AD and can have profound effects on both the long-term functioning of these patients and the well-being of their caregivers. Thus far, the field is dominated by studies of prevalence. Considerably rarer are studies investigating etiology, association with other aspects of the disease, impact on patients and caregivers, assessment, and treatment. The conceptual issues, methodological differences, and implications of the studies that exist thus far are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
26.
BACKGROUND: Because the relative efficacy of antiarrhythmic agents on halothane-epinephrine arrhythmias has not been well characterized, this study was undertaken to comparatively evaluate the antiarrhythmic action of Na(+)-, K(+)- and Ca(2+)-channel blockers on epinephrine-induced ventricular arrhythmias during halothane anesthesia in rats. METHODS: Rats were anesthetized at random with either halothane (1.5%), isoflurane (2.0%), or pentobarbital (50 mg/kg intraperitoneally), and the lungs were mechanically ventilated with oxygen. The rats were studied in three consecutive protocols. Protocol I determined the arrhythmogenic thresholds of epinephrine during the three types of anesthesia in 33 rats. Protocol II determined the arrhythmogenic thresholds of epinephrine during halothane anesthesia in 64 rats receiving saline (control) or one of five antiarrhythmic agents. Protocol III measured the duration of epinephrine-induced arrhythmias during halothane anesthesia in 42 rats receiving saline (control) or one of five antiarrhythmic agents. RESULTS: In protocol I, the arrhythmogenic doses of epinephrine during halothane, isoflurane, or pentobarbital anesthesia were 1.7 +/- 3.2, 11.1 +/- 0.6, and 39.0 +/- 3.9 micrograms/kg, respectively, and the corresponding plasma concentrations were 4.3 +/- 0.8, 103.7 +/- 9.2, and 246.7 +/- 28.9 ng/ml, respectively. In protocol II, the arrhythmogenic doses were similar in rats receiving saline and in those receiving lidocaine. The arrhythmogenic doses in rats receiving verapamil, flecainide (Na(+)- and K(+)-channel blocker), E-4031 (K(+)-channel blocker), or amiodarone(K(+)-channel blocker with Na(+)-, Ca(2+)-, and beta-blocking activity) increased significantly, i.e., 4.2, 4.2, 5.5, and 31.7 times control (P < 0.01). In protocol III, lidocaine had no effect on the duration of arrhythmias. Flecainide, E-4031, and verapamil markedly reduced the duration of arrhythmias induced by epinephrine, 8 micrograms/kg intravenously (P < 0.01), whereas only amiodarone markedly reduced the duration of arrhythmias induced by epinephrine, 16 micrograms/kg intravenously (P < 0.01). CONCLUSIONS: It was concluded that agents with K(+)-channel blocking properties were the most effective in preventing halothane-epinephrine arrhythmias in rats. 相似文献
27.
N.J. Wagner 《Fuel》2008,87(8-9):1687-1697
With a finite amount of economically viable coal reserves in South Africa, it is becoming increasingly important to consider coal discards as vital energy resources. The energy content of discard coal is generally low and high in ash, but can be effectively utilised in power stations. However, coals weather during storage, and weathered coals behave differently to their fresh counterparts. During this investigation, discard coals from four stockpiles varying in age from 5 to 40 years were characterised chemically and petrographically, with a specific focus on the petrographic-based abnormal condition analysis to determine the degree of secondary weathering. Drop tube furnace tests were conducted to determine the combustibility of the weathered stockpiled or dumped coals relative to typical Eskom coals, and the resultant char forms were characterised. A direct correlation with the extent of weathering and combustion performance was determined, with the more weathered coals reporting enhanced combustion reactions at lower temperatures. 相似文献
28.
Coal-fired power generation facilities are the largest single anthropogenic source of mercury to the atmosphere. Global mapping of anthropogenic emissions has previously estimated the mercury emission from stationary combustion from South Africa at being 82.6 tonnes per annum, but preliminary in-house calculations have placed this at a significantly lower amount. A petrochemical facility in South Africa, utilising a significant amount of coal in its gasification and steam generation processes, undertook a project to determine a mercury mass balance across the complex, and to apportion the Hg emissions from the facility. 相似文献
29.
LC Myers MP Terranova AE Ferentz G Wagner GL Verdine 《Canadian Metallurgical Quarterly》1993,261(5125):1164-1167
The Escherichia coli Ada protein repairs methylphosphotriesters in DNA by direct, irreversible methyl transfer to one of its own cysteines. Upon methyl transfer, Ada acquires the ability to bind specific DNA sequences and thereby to induce genes that confer resistance to methylating agents. The amino-terminal domain of Ada, which comprises the methylphosphotriester repair and sequence-specific DNA binding elements, contains a tightly bound zinc ion. Analysis of the zinc binding site by cadmium-113 nuclear magnetic resonance and site-directed mutagenesis revealed that zinc participates in the autocatalytic activation of the active site cysteine and may also function as a conformational switch. 相似文献
30.
Solar cells based on hydrogenated amorphous silicon are now made from a variety of materials including alloys and microcrystalline
films. Research aimed at improving cell efficiency should emphasize studies of alloys and metastable defects. We discuss several
research topics related to the growth, structure, and electronic properties of these materials, which should lead to improved
photovoltaic devices. 相似文献