全文获取类型
收费全文 | 10964篇 |
免费 | 1864篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 682篇 |
综合类 | 650篇 |
化学工业 | 7251篇 |
金属工艺 | 161篇 |
机械仪表 | 83篇 |
建筑科学 | 373篇 |
矿业工程 | 37篇 |
能源动力 | 83篇 |
轻工业 | 501篇 |
水利工程 | 22篇 |
石油天然气 | 5篇 |
武器工业 | 1篇 |
无线电 | 124篇 |
一般工业技术 | 1808篇 |
冶金工业 | 46篇 |
原子能技术 | 43篇 |
自动化技术 | 968篇 |
出版年
2023年 | 543篇 |
2022年 | 291篇 |
2021年 | 570篇 |
2020年 | 589篇 |
2019年 | 470篇 |
2018年 | 473篇 |
2017年 | 330篇 |
2016年 | 493篇 |
2015年 | 589篇 |
2014年 | 640篇 |
2013年 | 851篇 |
2012年 | 423篇 |
2011年 | 340篇 |
2010年 | 638篇 |
2009年 | 753篇 |
2008年 | 320篇 |
2007年 | 245篇 |
2006年 | 168篇 |
2005年 | 176篇 |
2004年 | 235篇 |
2003年 | 195篇 |
2002年 | 211篇 |
2001年 | 100篇 |
1999年 | 83篇 |
1998年 | 82篇 |
1997年 | 62篇 |
1996年 | 87篇 |
1995年 | 110篇 |
1994年 | 83篇 |
1993年 | 141篇 |
1992年 | 97篇 |
1991年 | 91篇 |
1990年 | 96篇 |
1989年 | 108篇 |
1988年 | 81篇 |
1987年 | 100篇 |
1986年 | 110篇 |
1985年 | 98篇 |
1984年 | 90篇 |
1983年 | 116篇 |
1982年 | 87篇 |
1981年 | 108篇 |
1980年 | 86篇 |
1979年 | 84篇 |
1977年 | 63篇 |
1976年 | 55篇 |
1975年 | 69篇 |
1974年 | 70篇 |
1973年 | 135篇 |
1972年 | 79篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
In photo-induced graft copolymerization of methyl methacrylate onto cellulose, the effect of metallic ions as sensitizer was investigated. Some metallic ions were effective in their adsorbed states and accelerated the formation of grafts in the order Fe2+ > Ag+ > Fe3+. However, Cu2+ acted negatively, and little effect was observed for Co2+, Ni2+, Mn2+, Zn2+, and Cr3+. In the systems in which aqueous metallic salt solutions were added, the formation of grafts was generally depressed, but Fe3+ was an exception. The effect of metallic ions on the scission reaction of cellulose main chains did not necessarily agree with the effect on the formation of grafts. This is attributed to the varied interaction between cellulose and the different active species produced by irradiation, depending on the type of metallic ions used. 相似文献
82.
Prof. Dr.-Ing. M. R. Krakowski 《Electrical Engineering (Archiv fur Elektrotechnik)》1991,74(5):329-334
Contents In the paper, theorems for the electric vector potentialT and magnetic scalar potentialU are discussed, which occur in the boundary-value problems for eddy currents induced in a conducting block by an external magnetic field. Uniqueness of the solution is examined. An integral representation of the scalar potentialU is derived for a nonmagnetic conductor. It is shown that for a thin metallic shell the integrodifferential equation results from general formulas related to the block.
List of principal symbols e coordinate unit vector - H magnetic intensity - J current density - T electric vector potential - U magnetic scalar potential - permeability - conductivity - V boundary of regionV 相似文献
Einige Theoreme der Wirbelstromtheorie
Übersicht In der Arbeit werden drei Theoreme für das elektrische VektorpotentialT und das magnetische SkalarpotentialU beschrieben, die in den Randwertaufgaben für in einem metallischen Block durch das äußere magnetische Feld induzierte Wirbelströme auftreten. Es wird bewiesen, daß eine solche Randwertaufgabe eine eindeutige Lösung hat, wenn das Vektorpotential auf dem Rand gleich Null ist. Eine Integralrepräsentation des Skalarpotentials wird abgeleitet. Es wird gezeigt, daß die Integrodifferentialgleichung für eine dünne metallische Hülle aus allgemeinen, den Block betreffenden Formeln hervorgeht.
List of principal symbols e coordinate unit vector - H magnetic intensity - J current density - T electric vector potential - U magnetic scalar potential - permeability - conductivity - V boundary of regionV 相似文献
83.
Prof. Dr. phil. nat. W. Gerlach Dr.-Ing. N. Qu 《Electrical Engineering (Archiv fur Elektrotechnik)》1991,74(6):433-444
Contents A fine structured GTO thyristor, abbreviated FGTO, has been developed to improve the switching characteristics. The new device has a cathode finger width of only 20 m and can be turned off without a negative gate bias at an anode current level of more than 200 A/cm2. The turn-off time can be shortened down tot
off
500 ns by increasing the negative gate current. A snubber circuit is not necessary to turn off the FGTO's. The maximum rate of rise of anode voltage du/dl reaches more than 10 kV/s. Analytical models are developed to describe the turn-off transients of the FGTO's. Good agreement between the theoretical and experimental results could be achieved.
FGTO — Ein feinstrukturierter GTO-Thyristor mit verbessertem Schaltverhalten
Übersicht Zur Verbesserung des Schaltverhaltens ist ein feinstrukturierter GTO-Thyristor, abgekürzt FGTO, entwickelt worden. Dieses neue Bauelement hat eine Kathoden-streifenbreite von nur 20 m und kann ohne negative Gatevorspannung bei einer Anodenstromdichte von mehr als 200 A/cm2 abgeschaltet werden. Die Abschaltzeit läßt sich durch Erhöhung des negativen Gatestroms bis zut off 500 ns verkürzen. Beim Abschalten von FGTOs ist keine RC-Beschaltung erforderlich. Der maximale du/dl-Wert erreicht mehr als 10 kV/s. Zur Beschreibung des Abschalt-verhaltens von FGTOs werden analytische Modelle entwickelt, die eine gute Übereinstimmung mit den Meßergebnissen liefern.相似文献
84.
Summary A robust kinematic hardening rule is proposed which appropriately blends the deviatoric stress rate rule and the Tseng-Lee rule in order to satisfy both the experimental observations made by Phillips et al. [1]–[5] and the nesting of the yield surface to the limit surface. The work presented in Part I is confined to the theoretical formulation of kinematic hardening rule with limited correlation to experimental results. A more general expression for the plastic modulus is proposed. The expressions proposed by McDowell and by Dafalias can be obtained as a special case of the proposed expression. An additional parameter is introduced that reflects the dependence of the plastic modulus on the angle between the deviatoric stress rate tensor and the direction of the limit backstress relative to the yield backstress. 相似文献
85.
Summary A class of self-propagating linear and nonlinear travelling wave solutions for compressible rotating fluid is studied using both numerical and analytical techiques. It is shown that, in general, a three dimensional linear wave is not periodic. However, for some range of wave numbers depending on rotation, horizontally propagating waves are periodic. When the rotation is equal to
, all horizontal waves are periodic. Here, is the ratio of specific heats. The analytical study is based on phase space analysis. It reveals that the quasi-simple waves are periodic only in some plane, even when the propagation is horizontal, in contrast to the case of non-rotating flows for which there is a single parameter family of periodic solutions provided the waves propagate horizontally. A classification of the singular points of the governing differential equations for quasi-simple waves is also appended. 相似文献
86.
Cecilia Laschi Gioel Asuni Eugenio Guglielmelli Giancarlo Teti Roland Johansson Hitoshi Konosu Zbigniew Wasik Maria Chiara Carrozza Paolo Dario 《Autonomous Robots》2008,25(1-2):85-101
This paper presents a sensory-motor coordination scheme for a robot hand-arm-head system that provides the robot with the capability to reach an object while pre-shaping the fingers to the required grasp configuration and while predicting the tactile image that will be perceived after grasping. A model for sensory-motor coordination derived from studies in humans inspired the development of this scheme. A peculiar feature of this model is the prediction of the tactile image. The implementation of the proposed scheme is based on a neuro-fuzzy module that, after a learning phase, starting from visual data, calculates the position and orientation of the hand for reaching, selects the best-suited hand configuration, and predicts the tactile feedback. The implementation of the scheme on a humanoid robot allowed experimental validation of its effectiveness in robotics and provided perspectives on applications of sensory predictions in robot motor control. 相似文献
87.
On finite dynamic equations for fluid-saturated porous media 总被引:2,自引:0,他引:2
Summary The paper concerns the relations between two principally different approaches to the formulation of momentum balance equations in porous media theories, namely, the dynamic approach similar to Biot's theory and the modern approach as a result of mixture theories extended by the concept of volume fractions. In particular, it is shown that both approaches necessarily lead to the same type of momentum balance equations and furthermore contain, in a certain sense, within the geometrically linear case, the well-known classical equations of Biot's theory. 相似文献
88.
We present a method depending on matrix continued fractions and Sturm's comparison theorem to obtain verified inclusions for eigenvalues of the underlying boundary value problem of the first-order phase locked loop equation $pu'' + (\lambda + \tilde g)u = 0$ ,p = 1/SNR with general phase detector characteristic $\tilde g(\phi )$ . 相似文献
89.
Prof. Dr. rer. nat. G. Lehner 《Electrical Engineering (Archiv fur Elektrotechnik)》1995,78(4):209-217
Contents We discuss some initial and boundary value problems of one-dimensional electromagnetic field diffusion. The solutions can be given by infinite series in two essentially different (however equivalent) forms, one being the usual Fourier-expansion and the other one being an infinite series of Gaussian exponentials or related functions (as for instance error-functions). The second form can be obtained by using infinitely many images to fulfill initial and boundary conditions. Finally the mathematical relations between the two equivalent types of solutions are discussed in terms of -functions and their transformation properties. The existence of the solutions in these two different forms is very interesting from a numerical point of view also.
Die Diffusion elektromagnetischer Felder, -Funktionen und Spiegelungsmethoden
Übersicht Es werden einige Anfangs- und Randwertprobleme eindimensionaler elektromagnetischer Felddiffusion erörtert. Die Lösungen können in zwei wesentlich verschiedenen (jedoch gleichwertigen) Formen angegeben werden, erstens in Form üblicher Fourier-Reihen und zweitens in Form unendlicher Reihen von Gaußschen Exponentialfunktionen oder damit verwandter Funktionen (z.B. Fehlerfunktionen). Diese zweite Form der Lösungen läßt sich durch die Anwendung unendlich oft wiederholter Spiegelung zur Erfüllung der Rand- und Anfangsbedingung anschaulich interpretieren. Abschließend werden die beiden Lösungstypen mit Hilfe von -Funktionen und deren Transformationseigenschaften erläutert. Die Verfügbarkeit der Lösungen in beiden Formen ist auch numerisch sehr interessant.相似文献
90.
A multi‐tip scanning tunneling microscope (STM) specifically designed for charge transport measurements at the nanoscale is described. Complementing the instrument with a versatile measurement electronics creates a powerful tool to give insight into fundamental transport properties at the nanoscale. We demonstrate the capabilities of the instrument by measuring resistance profiles along freestanding GaAs nanowires, by the acquisition of nanoscale potential maps, and by the identification of an anisotropy in the surface conductivity at a silicon surface. 相似文献