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71.
Ferrite formation from the ultra-fine dynamically recrystallized austenite (dγ < 5 μm) was investigated on a microalloyed steel with 0.11%C. Hot rolling conditions were simulated by the hot deformation simulator Wumsi. Due to accelerated cooling a corresponding fine homogeneous ferrite grain of dα < 2 μm was achieved with a pearlite free acicular microstructure after a cooling rate of more than 20 K/s. Excellent mechanical properties (2.0% proof stress of over 700 MPa and impact transition temperature of -180°C) were obtained, superior to those after thermomechanical processing of the same steel without dynamic recrystallization of the low-temperature austenite. 相似文献
72.
Summary Polyketones with indane structure elements were prepared by Friedel-Crafts polycondensation in three different reaction media.
Only oligomers or insoluble material could be obtained, probably due to a side reaction of the indane ring, which leads to
crosslinking at high conversion. The oligomers are soluble in common organic solvents such as THF and CHCl3. Melting points, glass transition temperatures, and thermal stability of the oligomers were determined. 相似文献
73.
Zur Erweiterung der Grundlagen des Warmwalzens wurde das Walzen auf geneigter Bahn experimentell und theoretisch analysiert. Den Schwerpunkt der Arbeit stellt eine Untersuchung des Breitungsverhaltens dar. Basierend auf den Versuchsdaten wird eine Breitungsformel angegeben, die für Walzbahnneigungswinkel bis 60° anwendbar ist und als Sonderfall auch das Flachwalzen beinhaltet. Ausgehend vom Satz der ?Oberen Schranke“ wurde ein Rechenmodell entwickelt, das die Berechnung der Breitung für beliebige Walzbahnneigungswinkel kleiner als 60° ermöglicht. Während die Anwendung der Breitungsformel aufgrund ihrer einfachen Handhabung eher für den praktischen Einsatz im Walzbetrieb sinnvoll erscheint, ist die mit wesentlich größerem Rechenaufwand verbundene Modellrechnung in rechnergestützten Systemen zur Stichplanoptimierung einsetzbar oder als Ansatz für die Entwicklung weiterer mathematischer Modelle zu werten. 相似文献
74.
Summary
A novel synthetic procedure for the preparation of block copolymers based on the combination of diphenylethene (DPE) mediated
controlled radical polymerization and radical promoted cationic polymerization is described. In the first step, the controlled
polymerization of styrene (St) and methyl methacrylate (MMA) in presence of DPE yields polymers with various structures of
diphenylethyl units in the main chain. Upon heating these prepolymers undergo scission to give polymeric radicals. Oxidation
of these radicals by onium salts such as diphenyliodonium heaxfluorophosphate (Ph2I+PF6
−) and N-ethoxy-2-methylpyridinium hexafluorophosphate (EMP+PF6
−) yields reactive cations capable of initiating cationic polymerization of cyclohexene oxide (CHO). Block copolymer structure
was confirmed by IR and NMR spectral measurements and GPC analysis.
Received: 13 December 2002/Revised version: 25 March 2003/ Accepted: 11 March 2003
Correspondence to Yusuf Yagci 相似文献
75.
Summary The cationic polymerization of various α- and β-substituted vinyl ethers, initiated by 1-iodo-1-(2-methylpropyloxy)ethane
1 and tetrabuty lammonium perchlorate (TBAP) was investigated. The polymerization of 2,3-dihydrofuran (DHF, 3a) in CH2Cl2 at -40°C proceeds via opening of the ethylenic double bond and yields polymers with narrow molar mass distributions and high
glass transitions. The number average of molar mass increased linearly with conversion. Under these conditions, a controlled
polymerization of two propenyl ethers (1-ethoxypropene 2a and 2-methoxypropene 2b) and two other cyclic unsaturated ethers (3,4-dihydro-2H-pyran 3b and 5-methyl-2,3-dihydrofuran 3c) could not be achieved. Either transfer reactions or the decomposition of 1 prevented the formation of high molar mass polymers of these vinyl ethers. 相似文献
76.
Claudia Böttcher Oskar Dressler 《Annals of Mathematics and Artificial Intelligence》1994,11(1-4):241-261
In recent years reasoning about structure and function of physical systems for the purpose of diagnosis has seen a dramatic increase in activities. New exciting results concerning modelling issues, diagnostic inference patterns and inferential power have emerged. A state of the art diagnosis agent now has a considerable toolset at hand. A main obstacle for building large diagnosis systems, however, remains. How can we controlwhen to usewhich inference pattern or representation? We argue that the actions available to a diagnosis agent can be understood in terms of change ofworking hypotheses. The control problem then becomes a belief revision problem: when to adopt or drop beliefs. Our approach proceeds in two steps. First, we adopt the principle of informational economy from Gärdenfors, Knowledge in Flux (MIT Press, 1988) as kind of a law of inertia for diagnostic processes, that helps us identify candidates for revised belief states. In a second step we employ specificdiagnostic knowledge to actually choose the next belief state. We demonstrate the use of our concepts on an example in the domain of ballast tank systems as e.g. used in offshore plants. 相似文献
77.
A path planning and path‐following control framework for a general 2‐trailer with a car‐like tractor
Oskar Ljungqvist Niclas Evestedt Daniel Axehill Marcello Cirillo Henrik Pettersson 《野外机器人技术杂志》2019,36(8):1345-1377
Maneuvering a general 2‐trailer with a car‐like tractor in backward motion is a task that requires a significant skill to master and is unarguably one of the most complicated tasks a truck driver has to perform. This paper presents a path planning and path‐following control solution that can be used to automatically plan and execute difficult parking and obstacle avoidance maneuvers by combining backward and forward motion. A lattice‐based path planning framework is developed in order to generate kinematically feasible and collision‐free paths and a path‐following controller is designed to stabilize the lateral and angular path‐following error states during path execution. To estimate the vehicle state needed for control, a nonlinear observer is developed, which only utilizes information from sensors that are mounted on the car‐like tractor, making the system independent of additional trailer sensors. The proposed path‐planning and path‐following control framework is implemented on a full‐scale test vehicle and results from simulations and real‐world experiments are presented. 相似文献
78.
The in-plane Young’s modulus and the shear modulus of carbon nanocrystallites were investigated during in-situ tension tests of single carbon fibers by X-ray diffraction using the shift of the 10 band in the meridional direction and the change in the azimuthal width of the 002 reflection. The limiting value for the Young’s modulus was found to be 1140 GPa, which is higher than the value for graphite obtained from macroscopic specimens, but coincides with recent measurements on nanotubes. Furthermore, the shear modulus was evaluated using a uniform stress approach and was found to increase with increasing misorientation of the crystallites. It turns out that both the in-plane Young’s modulus and the shear modulus are not constant, but dependent on the orientation parameter. 相似文献
79.
Oskar Mahrenholtz 《Forschung im Ingenieurwesen》1963,29(2):47-56
Zusammenfassung Mechanische Herzklappenfehler werden vom Blutkreislauf h?ufig kompensiert. Der Internist G. Liebau hat nach physikalischen
Erkl?rungen dieses Ph?nomens gesucht und dazu mehrere Modelle angegeben. An einem dieser die physiologischen Bedingungen sehr
vereinfachenden Modelle, das durch eine unsymmetrische Flüssigkeitsverteilung sowie durch Querschnittsunterschiede der (starren)
Leitungen und eine ventillose Kolbenpumpe mit unsymmetrischem Hubgesetz als Antrieb gekennzeichnet ist, wurde die F?rderwirkung
experimentell und rechnerisch untersucht. Es zeigte sich, da? eine lineare Gleichung das Problem nicht beschreiben kann. Vielmehr
führt der vollst?ndige Ansatz auf eine Riccatische Differentialgleichung. Sie wurde auf einem Analogrechner integriert. Die
Ergebnisse erm?glichten es, den physikalisch gut erkl?rbaren F?rdereffekt numerisch zu ermitteln und dimensionslos darzustellen.
Eine gesonderte Untersuchung betrifft das Verhalten einer inkompressiblen newtonschen Flüssigkeit bei laminarer, periodischer
Rohrstr?mung. Die am Modell gewonnenen Ergebnisse führen zu bestimmten Folgerungen für den Blutkreislauf.
Gekürzte Fassung der gleichnamigen Dissertation des Verfassers, Technische Hochschule Hannover 1962. Den Herren Prof. Dr.-Ing.E. Pestel und Doz. Dr. med. habil.G. Liebau dankt der Verfasser für die Anregung zu dieser Untersuchung und für ihr stetes Interesse, Herrn Doz. Dr. med. habil.G. Liebau insbesondere für seine ?medizinische Beratung?. 相似文献
80.
The paper presents an algorithm that solvestwo-point boundary-value problems that arise in economic control models incontinuous time with an infinite time horizon and several state variables.The algorithm can determine optimal trajectories that converge to anisolated equilibrium point. It therefore provides a numerical solution toa large class of problems for which no solvers were yet available. 相似文献