首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   803篇
  免费   44篇
  国内免费   1篇
电工技术   10篇
化学工业   145篇
金属工艺   19篇
机械仪表   24篇
建筑科学   20篇
矿业工程   1篇
能源动力   19篇
轻工业   155篇
水利工程   1篇
石油天然气   1篇
无线电   39篇
一般工业技术   149篇
冶金工业   51篇
原子能技术   11篇
自动化技术   203篇
  2024年   3篇
  2023年   9篇
  2022年   26篇
  2021年   26篇
  2020年   22篇
  2019年   24篇
  2018年   25篇
  2017年   25篇
  2016年   25篇
  2015年   19篇
  2014年   34篇
  2013年   63篇
  2012年   68篇
  2011年   55篇
  2010年   52篇
  2009年   59篇
  2008年   39篇
  2007年   32篇
  2006年   30篇
  2005年   21篇
  2004年   24篇
  2003年   22篇
  2002年   17篇
  2001年   12篇
  2000年   3篇
  1999年   11篇
  1998年   12篇
  1997年   10篇
  1996年   10篇
  1995年   7篇
  1994年   3篇
  1993年   7篇
  1992年   3篇
  1991年   2篇
  1990年   3篇
  1989年   3篇
  1988年   2篇
  1987年   3篇
  1986年   4篇
  1985年   4篇
  1984年   6篇
  1983年   4篇
  1982年   2篇
  1979年   5篇
  1978年   2篇
  1977年   2篇
  1976年   2篇
  1974年   2篇
  1973年   1篇
  1972年   1篇
排序方式: 共有848条查询结果,搜索用时 15 毫秒
801.
A general class of approximate models for the transport equation is derived by the Weighted Residual Method using polynomial trial and test spaces. For two, particularly relevant, of such models a closed form of the approximate solution is given in the Laplace-transform domain. A strict connection is established between the approximate transfer function and the Padé approximants to exp(-sx). Furthermore it is shown that Galerkin model minimizes in the considered class a measure of the initial state approximation error. Finally an application to the solution of systems of first order hyperbolic equations is reported.  相似文献   
802.
Let (Xt) be the solution of a stochastic differential system. We consider the following situations: computation of Eƒ(Xt) by a Monte-Carlo method (for example, computation of moments of the solution); integration of ƒ(·) with respect to the invariant probability law of (Xt) (when this process is ergodic); or of the upper Lyapunov exponent, by simulating a single trajectory.

We propose to perform an extrapolation between approximate values due to first-order schemes; we show that this algorithm (simpler to implement than second-order schemes) provides a second-order accuracy, and we give results of numerical tests.  相似文献   

803.
We have built an intelligent controller for acquisition and pre-elaboration of data coming from the read-out electronics of streamer tube calorimeters. Its main features are very short acquisition time and low costs.  相似文献   
804.
The Accelerator-Driven System has the potential to safely fission Minor Actinides and transmute, on industrial scale, selected long-lived fission products into isotopes of lesser concern. European leading nuclear Industrial Companies and Research Centers,within the EURATOM 5th Framework Programme, have studied three solutions of eXperimental Accelerator Driven Systems (XADS), different for the power (80 and 50 MW) or the primary coolant (Lead Bismuth Eutectic and Gas). Two main concepts of Target Unit are envisaged: the Window Target Unit which features a thin metallic sheet as a barrier between the LBE target and the Proton Beam Pipe and the Windowless Target Unit in which the proton beam impinges directly on the free surface of the liquid LBE target. These designs are under study in order to assess and compare them on a common basis, and to outline the main R&D needs.  相似文献   
805.
Interferon-alpha (IFN-alpha) is an established treatment for chronic myelogenous leukemia (CML) in chronic phase, but the mechanism of its antileukemic activity is not clear. One possible mechanism of action might include the induction of apoptosis, and especially Fas-mediated cell killing may play an important role in the elimination of malignant cells. We investigated Fas receptor (Fas-R) expression and the consequences of Fas-R triggering in CML patients. Using two-color flow cytometry, we found a significantly higher number of Fas-R-expressing CD34+ cells in the bone marrow (BM) of CML patients compared with normal subjects. We have previously shown that IFN-gamma induces Fas-R expression on CD34+ cells; in this study, we investigated whether IFN-alpha induces Fas-R expression on CML progenitor cells. Dose-dependent induction of Fas-R expression was observed after IFN-alpha stimulation of CD34+ cells from CML BM. In methylcellulose culture, IFN-alpha alone at a therapeutic concentration showed only marginal antiproliferative effects on both normal and CML BM progenitors. In contrast, a Fas-R agonist, the anti-CD95 monoclonal antibody CH11, inhibited colony formation from normal progenitors, and the inhibition was even stronger on CML progenitors. When CML BM cells were cultured in the presence of IFN-alpha, Fas-R-mediated inhibition of colony growth was potentiated in a dose-dependent fashion, consistent with IFN-alpha induction of Fas-R expression. This functional effect did not require the presence of accessory cells, since similar results were obtained with purified CD34+ cells. In suspension cultures, we demonstrated that suppression of CML hematopoiesis by IFN-alpha and Fas-R agonist was exerted through Fas-R-mediated induction of apoptosis. Our findings suggest that the Fas-R/Fas-ligand system might be involved in the immunologic regulation of CML progenitor growth and that its effect can be amplified by IFN-alpha.  相似文献   
806.
807.
Three experiments examine how the type of language used to describe in-group and out-group behaviors contributes to the transmission and persistence of social stereotypes. Two experiments tested the hypothesis that people encode and communicate desirable in-group and undesirable out-group behaviors more abstractly than undesirable in-group and desirable out-group behaviors. Experiment 1 provided strong support for this hypothesis using a fixed-response scale format controlling for the level of abstractness developed from G. R. Semin and K. Fiedler's (see record 1988-20078-001) linguistic category model. Experiment 2 yielded the same results with a free-response format. Experiment 3 demonstrated the important role that abstract versus concrete communication plays in the perpetuation of stereotypes. The implications of these findings and the use of the linguistic category model are discussed for the examination of the self-perpetuating cycle of stereotypes in communication processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
808.
809.
The development of large software systems is a complex and error prone process. Faults might occur at any development stage and they must be identified and removed as early as possible to stop their propagation and reduce verification costs. Quality engineers must be involved in the development process since the very early phases to identify required qualities and estimate their impact on the development process. Their tasks span over the whole development cycle and go beyond the product deployment through maintenance and post mortem analysis. Developing and enacting an effective quality process is not a simple task, but it requires that we integrate many quality-related activities with product characteristics, process organization, available resources and skills, and budget constraints.This paper discusses the main characteristics of a good quality process, then surveys the key testing phases and presents modern functional and model-based testing approaches.  相似文献   
810.
This paper reports the development of a powerful andversatile laboratory for vision research, namely ynergos,which has been developed and implemented under Delphi/Windowsin a distributed systems of microcomputers. The main paradigmunderlying the whole approach consists in integrating severalconcepts and techniques into a single computing environment,i.e. ynergos, in such a way that the requisitesand possibilities of each of the constituent components complementone another and the thus obtained result becomes greater thanthe sum of its parts. The components of ynergosinclude distributed system capabilities and a number of librariescontaining algorithms for: computer vision, modeling and simulationof biological visual systems, data and classification analysis,software validation and comparative evaluation, Internet, off-the-shelfapplication, image databases, artificial intelligence, data mining,and visualization resources. In this paper special emphasis isplaced upon the Internet, distributed implementation and biologicalvision. After outlining the principal requisites and potentialsunderlying each of such components, some specific situationsof interest arising from the integration of two or more of suchelements are described and discussed. Details concerning theintegration with Internet and the implementation of the laboratoryas a distributed system are provided, and a complete case-exampleis presented. This applications regards the implementation ofa psychophysical experiment aimed at investigating human perceptionof pictorial complexity, including the derivation of a mathematic-computationalframework modeling such a perception as well as the use of theInternet as a source of stimuli and for reporting the obtainedresults. In addition, the mathematic-computational model is derivedby using a parallel version of the genetic algorithm runningon the distributed system of PCs. The obtained encouraging resultssubstantiate the potential of this vision laboratory for multidisciplinaryvision research.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号