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81.
82.
Saul Arlosoroff Gerhard Tschannerl David Grey William Journey Andrew Karp Otto Langenegger 《国际水》2013,38(2):106-111
An estimated 1,800 million people need improved water supplies in the fifteen years to the end of the century, if developing countries are to reach the target of full coverage. The first half of the International Drinking Water Supply and Sanitation Decade (1981–1990) has seen increases in the percentages of the rural population with access to safe water supplies, but only in Asia has the pace been quick enough to envisage a target of essentiahy full coverage by the end of the century (ten years later than the original Decade goals). In Africa, present progress rates would leave half of the rural population still without safe water in the year 2000, while in Latin America, it may be ten years into the next century before full coverage is achieved unless progress improves dramatically. Accelerated progress is hampered by financial and technical resource constraints faced by many developing countries, and the problem is aggravated by the growing number of completed projects which are broken down and abandoned, or functioning much below capacity. Attempts to increase the pace of providing improved community water supplies have often been frustrated because the technology used has proved impossible to sustain in village conditions. To make a lasting impact on the urgent needs, community water supply (CWS) strategies must be based on sustainable and replicable programs, and must take account of the pace at which resource constraints can be overcome. Human resource development programs take time to produce results, and institutional changes can only be accomplished gradually. 相似文献
83.
Acoustic critical angle measurements usually involve broad beam or global isonification of a water-solid interface. In order to obtain local interface data, it is convenient to use a focused acoustic source with lens axis at incident angle and point-receiver at specular reflection angle . By scanning this combination at various critical angles (=crit), interface waves are generated locally near the lens focus. These waves penetrate the solid to a depth of approximately one shear wavelength
T
and are modulated by discontinuities such as flaws, inclusions, and debonds that may be present there. A radiated longitudinal wave in water accompanies these modulated interface waves and carries information on subsurface flaws to the point-detector along the direction of a specularly reflected wave. By scanning the focus-receiver combination along the interface, the receiver output may be used to form images of local subsurface detail. We show that in anisotropic materials, such as crystals, there are generally two different crit where a radiating interface wave provides subsurface information. We also discuss special problems associated with the use of a focused acoustic source including nonlinear effects (generation of harmonics) in the water. 相似文献
84.
The initiation and growth of porous oxide on Ta was investigated in mixed H2SO4/HF electrolytes. Under selected potentiodynamic anodic oxidation conditions the formation of nearly uniform porous Ta2O5 layer was observed. The porous Ta2O5 layers consist of self-organized pore arrays with single pore diameters ranging from 2 to 10 nm. The morphology and the thickness
of the layer depend strongly on the applied potential, the scan rate and on HF presence. The composition of the porous oxide
layer is Ta2O5. 相似文献
85.
Gerhard Klimeck 《Journal of Computational Electronics》2003,2(2-4):177-182
The coupling of the fundamentally quantum mechanical nanoelectronic transport simulation through resonant tunneling diodes to semi-classical drift diffusion in the contacts is demonstrated. The coupling between the non-equilibrium Green function formalism used in NEMO to the drift diffusion equation is established by the use of spatially dependent quasi Fermi levels in the reservoirs. The charge distributions are computed quantum mechanically throughout the whole device using the full bandstructure sp3s* tight binding model that includes band non-parabolicity and band warping. The formalism is applied to the simulation of high current density resonant tunneling diodes. Low mobility contacts are shown to introduce a bi-stability in the negative differential resistance region. 相似文献
86.
Gadolinium-enhanced magnetic resonance angiography of the pelvis in patients with erectile impotence
Michael K. Stehling Libin Liu Gerhard Laub Kurt Fleischmann Ulrike Rohde 《Magma (New York, N.Y.)》1997,5(3):247-254
This study evaluted the potential of contrast-enhanced digital-subtraction magnetic resonance angiography (CE-DS-MRA) for
noninvasive angiographic delineation of the arterial supply of the penis in patients with erectile dysfunction. After induction
of an erection with prostaglandin E, a three-dimensional fast imaging with steady-state precision (FISP) sequence with TE
of 1.8–2 milliseconds, TR of 4.4–5 milliseconds, and flip angle of 40°–60° was used to obtain high-resolution angiograms of
the pelvis and penis during the injection of gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) 0.3 mmol/kg body weight,
within 30–50 seconds. DS maximum intensity projections (MIPs) and multiplanar reconstructions (MPRs) were compared with clinical
work-up and directional Doppler ultrasound in 11 patients. In all 11 patients (100%), the arterial supply of the penis could
be delineated from the aortic bifurcation via the iliac and internal pudendal arteries to the dorsal and deep penile arteries.
Of the 22 internal pudendal arteries, 6 (27%) were occluded on CE-DS-MRA and 5 (23%) had stenoses, of which 4 (18%) were greater
than 50%. In 7 patients (64%) good correlation between CE-DS-MRA and clinical findings and/or Doppler ultrasound was found;
in 2 patients (18%), the correlation was moderate, and in 2 patients (18%) results were discrepant. In 6 patients (55%), MRA
provided additional information to the clinical and Doppler ultrasound work-up. CE-DS-MRA can delineate small sessels such
as the internal pudendal and penile arteries and thus has the potential to become a noninvasive angiography method in the
work-up of erectile impotence.
Supported by Siemens Medical Systems, Erlangen; Schering AG, Berlin; and Agfa-Gevaert AG, Leverkusen. 相似文献
87.
Data partitioning and load balancing in parallel disk systems 总被引:13,自引:0,他引:13
Peter Scheuermann Gerhard Weikum Peter Zabback 《The VLDB Journal The International Journal on Very Large Data Bases》1998,7(1):48-66
Parallel disk systems provide opportunities for exploiting I/O parallelism in two possible ways, namely via inter-request
and intra-request parallelism. In this paper, we discuss the main issues in performance tuning of such systems, namely striping
and load balancing, and show their relationship to response time and throughput. We outline the main components of an intelligent,
self-reliant file system that aims to optimize striping by taking into account the requirements of the applications, and performs
load balancing by judicious file allocation and dynamic redistributions of the data when access patterns change. Our system
uses simple but effective heuristics that incur only little overhead. We present performance experiments based on synthetic
workloads and real-life traces.
Received May 17, 1994 / Accepted June 9, 1997 相似文献
88.
The hardness and yield stress at room temperature and the brittle‐to‐ductile transition temperature of Fe‐Al alloys with 16 at.% Al, which is in the range of the so‐called K‐state with possible short‐range ordering reactions, and ternary additions of 0.5 and 4 at.% of the transition metals Cr, Mo, Mn, V, Ti and Ni were studied with respect to possible hardening effects of the ternary additions. The addition of Cr, Mo and Mn to the Fe‐Al alloys produce solid‐solution hardening which corresponds to the hardening effect of Al. Only Ti, V and Ni produce extra hardening effects which cannot be related to solid‐solution hardening. This extra hardening is attributed to possible fine NiAl precipitates in the Fe‐Al‐Ni case and to possible enhanced short‐range ordering and/or fine carbide precipitates in the cases of Fe‐Al‐V and Fe‐Al‐Ti. 相似文献
89.
Production Rate‐Dependent Key Performance Indicators for a Systematic Design of Biochemical Downstream Processes
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Key performance indicators have become a common tool in bioprocess development, as they allow an objective and independent rating and ranking of process alternatives screened. A disadvantage of all key performance indicators developed so far is their strong focus on costs, which makes them neglect the influence of the production rate on the profit of the process. But, since both production costs and production rate have an equally strong impact, both should be considered when decisions have to be made. Therefore, two new key performance indicators are introduced in this work, one for batch and one for continuous processing. They combine product yield, purity performance, variable manufacturing costs, and production rate to one objective. Thereby, misguided trade‐offs between these four individual measures can be replaced by one key performance indicator. This ensures a systematic development of biochemical downstream processes. 相似文献
90.