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排序方式: 共有879条查询结果,搜索用时 15 毫秒
101.
This work describes the synthesis, hydration and durability behavior of β-Ca(2)SiO(4) doped with chromium. β-Ca(2)SiO(4) is a component of commercial cement. Rice hull is an agricultural residue containing about 10% of silica as inorganic constituent. The controlled burning of rice hull was used to obtain this biogenic silica, used as starting material. In many situations chromium is added during cement preparation in order to promote encapsulation, at temperatures around 1500°C. The synthesis presented here is completed at 800°C, causing a substantial reduction in energy consumption. Moreover, chromium is chemically bonded to cement crystal, which is safer than simple physical encapsulation. Results show that chromium can be inserted into the structure of β-Ca(2)SiO(4) up to 1% (molar ratio). Hydration degree and durability studies show that insertion of chromium causes no deleterious effects on physical and chemical properties of these doped materials when compared to β-pure Ca(2)SiO(4). 相似文献
102.
Roberto B. Pontes Erika E. Nishi Renato O. Crajoinas Maycon I. O. Milanez Adriana C. C. Girardi Ruy R Campos Cassia T Bergamaschi 《International journal of molecular sciences》2023,24(1)
We examined the effects of an acute increase in blood pressure (BP) and renal sympathetic nerve activity (rSNA) induced by bicuculline (Bic) injection in the paraventricular nucleus of hypothalamus (PVN) or the effects of a selective increase in rSNA induced by renal nerve stimulation (RNS) on the renal excretion of sodium and water and its effect on sodium-hydrogen exchanger 3 (NHE3) activity. Uninephrectomized anesthetized male Wistar rats were divided into three groups: (1) Sham; (2) Bic PVN: (3) RNS + Bic injection into the PVN. BP and rSNA were recorded, and urine was collected prior and after the interventions in all groups. RNS decreased sodium (58%) and water excretion (53%) independently of BP changes (p < 0.05). However, after Bic injection in the PVN during RNS stimulation, the BP and rSNA increased by 30% and 60% (p < 0.05), respectively, diuresis (5-fold) and natriuresis (2.3-fold) were increased (p < 0.05), and NHE3 activity was significantly reduced, independently of glomerular filtration rate changes. Thus, an acute increase in the BP overcomes RNS, leading to diuresis, natriuresis, and NHE3 activity inhibition. 相似文献
103.
Manuel Silva Jorge Júlvez Cristian Mahulea C. Renato Vázquez 《Discrete Event Dynamic Systems》2011,21(4):427-497
As a preliminary overview, this work provides first a broad tutorial on the fluidization of discrete event dynamic models,
an efficient technique for dealing with the classical state explosion problem. Even if named as continuous or fluid, the relaxed models obtained are frequently hybrid in a technical sense. Thus,
there is plenty of room for using discrete, hybrid and continuous model techniques for logical verification, performance evaluation
and control studies. Moreover, the possibilities for transferring concepts and techniques from one modeling paradigm to others
are very significant, so there is much space for synergy. As a central modeling paradigm for parallel and synchronized discrete
event systems, Petri nets (PNs) are then considered in much more detail. In this sense, this paper is somewhat complementary
to David and Alla (2010). Our presentation of fluid views or approximations of PNs has sometimes a flavor of a survey, but also introduces some new
ideas or techniques. Among the aspects that distinguish the adopted approach are: the focus on the relationships between discrete and continuous PN models, both for untimed, i.e., fully non-deterministic abstractions, and timed versions; the use of structure theory of (discrete) PNs, algebraic and graph based concepts and results; and the bridge to Automatic Control Theory. After discussing
observability and controllability issues, the most technical part in this work, the paper concludes with some remarks and
possible directions for future research. 相似文献
104.
In traditional networks special efforts are put to secure the perimeter with firewalls: particular routers that analyze and filter the traffic to separate zones with different levels of trust. In wireless multi-hop networks the perimeter is a concept extremely hard to identify, thus, it is much more effective to enforce control on the nodes that will route more traffic. But traffic filtering and traffic analysis are costly activities for the limited resources of mesh nodes, so a trade-off must be reached limiting the number of nodes that enforce them. This work shows how, using the OLSR protocol, the centrality of groups of nodes with reference to traffic can be estimated with high accuracy independently of the network topology or size. We also show how this approach greatly limits the impact of an attack to the network using a number of firewalls that is only a fraction of the available nodes. 相似文献
105.
In this paper we study lot-sizing and changeover decisions in production schedules that are implemented on a rolling-horizon basis. The study is carried out by comparing production schedules for the packaging operations of a pharmaceutical company that produces various products on several capacitated production lines. The schedules are obtained by solving a mixed-integer programming formulation by using a heuristic procedure. We examine the effects of the number of periods in the planning horizon, the starting inventory and the demand fluctuation on the schedules. We show empirically that the saving in annual production cost diminishes rapidly as more demand periods are added to the planning horizon. Computational results are reported. 相似文献
106.
Quantitative determination of physical and chemical measurands in honey by near-infrared spectrometry 总被引:1,自引:0,他引:1
Kaspar Ruoff Werner Luginbühl Stefan Bogdanov Jacques-Olivier Bosset Barbara Estermann Thomas Ziolko Sohrab Kheradmandan Renato Amadò 《European Food Research and Technology》2007,225(3-4):425-423
Fourier transform near-infrared spectroscopy (FT-NIR) was evaluated to quantitatively determine 24 different measurands in honey. The reference values of 421 honey samples of different botanical origins were determined by classical physical and chemical methods. Partial least squares regression was used to develop the calibration models for the measurands studied. These calibrations were then validated using independent samples and proved satisfying accuracies for the determination of water (standard error of prediction: 0.3 g/100 g), glucose (1.3 g/100 g), fructose (1.6 g/100 g), sucrose (0.4 g/100 g), total monosaccharide content (2.6 g/100 g) as well as fructose/glucose ratio (0.09) and glucose/water ratio (0.12). The prediction accuracy for hydroxymethylfurfural, proline, pH-value, electrical conductivity, free acidity and the minor sugars maltose, turanose, nigerose, erlose, trehalose, isomaltose, kojibiose, melezitose, raffinose, gentiobiose, melibiose, maltotriose was poor and unreliable. The results demonstrate that near-infrared spectrometry is a valuable, rapid and non-destructive tool for the quantitative analysis of some measurands related to the main components in honey. 相似文献
107.
Ignazio Renato Bellobono Bruno Marcandalli Elena Selli Alessandra Polissi Giorgio Leidi 《应用聚合物科学杂志》1984,29(10):3185-3195
A model has been applied to release of plasticizers from polymer films through vapor phase, for which the overall rate of release may be generally determined by evaporation of the plasticizer from the surface of the film, and/or by migration to the surface at below saturation in the polymer. The experimental system employed made use of n-butyl formate, diethyl-phthalate, di-n-butylphthalate, and N,n-butylbenzenesulfonamide as model molecules in polycaprolactam films, both with the aims of studying undesirable loss of plasticizers, and of simulating a model able to envisage releasing, at a constant rate, of any desired additive, with relatively high solubility and vapor pressure, to the content of packaging films. Experimental measurements were made (at 298–333 K) by investigating in a suitable cell the permeation of plasticizers both at concentrations below and above the saturation limit. Rate of evaporation of plasticizers from the membrane surface above the saturation limit, measured in this cell, were found to coincide satisfactorily with those calculated by application of the mass transfer theory to evaporation from a stationary liquid into a stirred gas, at a known velocity of gas flowing past the surface. From these latter rates and solubilities, the mass transfer coefficients H for evaporation could be obtained, as well as from experimental time lags the diffusivities Dp through the polymer membrane. In the light of the theoretical model a correlation was found between activation energies of H and evaporation enthalpies of the model molecules. 相似文献
108.
The potentialities for 1-aryl-5-methyl-3-hydroxypyrazoles as intermediates in the field of dyes have been analysed. Some azoic derivatives have been synthesized and both electronic spectra and tinctorial properties on various substrates (wool, nylon, polyester, plasticized PVC) examined. The effect of substituents on the position of the long wavelength absorption maxima is discussed in terms of Hammett σ constants and interesting relationships are obtained. For each application the most important technical properties are assessed and significant fastness to various agents is evaluated.Finally a comparison with properties of similar pyrazol-5-one derivatives is made. 相似文献
109.
Terry S. King Dorab N. Baria Renato G. Bautista 《Metallurgical and Materials Transactions B》1976,7(3):411-415
An apparatus for measuring the normal spectral emittance (λ = 0.645 μ.) of metals with very high vapor pressures has been
designed and used for erbium, dysprosium and samarium at temperatures above 1000 K. The samples are maintained in an argon
atmosphere at a pressure slightly above atmospheric pressure. The measured normal spectral emittances are: Erbium, (solid),
∈
nλ
= 0.372 ± 0.011; (liquid), ∈
nλ
= 0.372 ± 0.011; Dysprosium, (solid), ∈
nλ
= 0.631 – 1.889 × 10–4
T (deg K); (liquid), ∈
nλ
= 0.297 ± 0.088; Samarium, (solid), ∈
nλ
= 0.437 ± 0.030; (liquid, estimated), ∈
nλ
= 0.437 ± 0.03.
TERRY S. KING, formerly Undergraduate Research Helper.
DORAB N. BARIA, formerly NSF Presidential Intern and Post-Doctoral Fellow.
Prepared for the Energy Research and Development Administration under Contract No. W-7405-eng-82. 相似文献
110.
The normal spectral emittance of Ti and Zr was obtained in the temperature range 1100 to 1800 K and wavelength 0.645 μ for
electrochemically polished, mechanically polished and 60 grit ground surfaces at a pressure below 10-8 mm Hg. The emittance at the melting point of both metals was obtained by extrapolation of an empirical equation fitted to
the experimental data obtained for the electrochemically polished surface and was found to be in good agreement with reported
values. The considerable grain growth on the surface affected the emittance. The emittance was found to increase with temperature
up to 1300 K and then decreased with further increase in temperature.
Formarly a National Science Foundation Presidential Intern and an Ames Laboratory-USAEC Postdoctoral Fellow, Iowa State University,
Ames, Iowa. 相似文献