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   2370篇
  免费   115篇
  国内免费   7篇
电工技术   30篇
综合类   3篇
化学工业   628篇
金属工艺   32篇
机械仪表   77篇
建筑科学   74篇
矿业工程   4篇
能源动力   117篇
轻工业   266篇
水利工程   17篇
石油天然气   9篇
无线电   193篇
一般工业技术   394篇
冶金工业   86篇
原子能技术   15篇
自动化技术   547篇
  2024年   6篇
  2023年   36篇
  2022年   93篇
  2021年   83篇
  2020年   89篇
  2019年   82篇
  2018年   104篇
  2017年   90篇
  2016年   97篇
  2015年   77篇
  2014年   123篇
  2013年   181篇
  2012年   184篇
  2011年   184篇
  2010年   145篇
  2009年   114篇
  2008年   113篇
  2007年   96篇
  2006年   85篇
  2005年   50篇
  2004年   68篇
  2003年   56篇
  2002年   44篇
  2001年   27篇
  2000年   26篇
  1999年   15篇
  1998年   22篇
  1997年   30篇
  1996年   11篇
  1995年   11篇
  1994年   13篇
  1993年   12篇
  1992年   10篇
  1990年   6篇
  1989年   12篇
  1988年   3篇
  1987年   10篇
  1986年   11篇
  1985年   12篇
  1984年   11篇
  1983年   11篇
  1982年   5篇
  1981年   6篇
  1980年   4篇
  1979年   3篇
  1978年   4篇
  1977年   3篇
  1974年   3篇
  1973年   2篇
  1967年   2篇
排序方式: 共有2492条查询结果,搜索用时 15 毫秒
991.
We have recently demonstrated that a single injection of 4,900 IU of interleukin-12 (IL-12) on the day of bone marrow transplantation (BMT) markedly inhibits acute graft-versus-host disease (GVHD) in a fully major histocompatibility complex plus minor antigen-mismatched BMT model (A/J --> B10, H-2(a) --> H-2(b)), in which donor CD4(+) T cells are required for the induction of acute GVHD. We show here that donor CD8-dependent graft-versus-leukemia (GVL) effects against EL4 (H-2(b)) leukemia/lymphoma can be preserved while GVHD is inhibited by IL-12 in this model. In mice in which IL-12 mediated a significant protective effect against GVHD, marked GVL effects of allogeneic T cells against EL4 were observed. GVL effects against EL4 depended on CD8-mediated alloreactivity, protection was not observed in recipients of either syngeneic (B10) or CD8-depleted allogeneic spleen cells. Furthermore, we analyzed IL-12-treated recipients of EL4 and A/J spleen cells which survived for more than 100 days. No EL4 cells were detected in these mice by flow cytometry, tissue culture, adoptive transfer, necropsies, or histologic examination. Both GVL effects and the inhibitory effect of IL-12 on GVHD were diminished by neutralizing anti-interferon-gamma (IFN-gamma) monoclonal antibody. This study demonstrates that IL-12-induced IFN-gamma production plays a role in the protective effect of IL-12 against GVHD. Furthermore, IFN-gamma is involved in the GVL effect against EL4 leukemia, demonstrating that protection from CD4-mediated GVHD and CD8-dependent anti-leukemic activity can be provided by a single cytokine, IFN-gamma. These observations may provide the basis for a new approach to inhibiting GVHD while preserving GVL effects of alloreactivity.  相似文献   
992.
Tested the suggestion of R. B. Cialdini et al (see record 1987-21901-001) that the motivation to help associated with empathic emotion is directed toward the egoistic goal of negative-state relief, not toward the altruistic goal of relieving the victim's distress. To test this suggestion, we led empathically aroused Ss to anticipate an imminent mood-enhancing experience. We reasoned that if the motivation to help associated with empathy were directed toward the goal of negative-state relief, then empathically aroused individuals who anticipate mood-enhancement should help less than those who do not. Study 1 verified the effectiveness of our anticipated mood-enhancement manipulation; results indicated that this manipulation could serve as an effective source of negative-state relief. Results of Studies 2 and 3, in which empathy was either measured or manipulated, indicated that the rate of helping among high-empathy Ss was no lower when they anticipated mood enhancement than when they did not. Regardless of anticipated mood enhancement, high-empathy Ss helped more than low-empathy Ss. Results support the empathy–altruism hypothesis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
993.
On the use of pyrrole black in zinc-halogen batteries   总被引:1,自引:0,他引:1  
The storage of Br2/Br and I2/I couples in a conducting polymer matrix, polypyrrole coated on a reticulated vitreous carbon disc, is described and the application of these positive electrodes in zinc-halogen model batteries is discussed. The cell based on the polypyrrole bromine adduct shows the higher open circuit voltage which, however, depends on the state of charge. Such cells self discharge thus limiting their usefulness. In the case of the iodine cell the self discharge is due to loss of iodine from the polymer to the bulk solution, but with the bromine cell the cause is oxidative bromination and depolymerization of the polypyrrole.  相似文献   
994.
This research aims to analyse how drivers integrate the information provided by traffic signs with their general goals (i.e. where they want to go). Some previous studies have evaluated the comparative advantages of obligatory and prohibitory traffic signs using a judgement task. In this work, a new experimental task with greater similarity to driving situations is proposed. Participants imagine they are driving a vehicle and must make right or left turn manoeuvres according to a previously indicated objective and the information from obligatory and prohibitory traffic signs. Eighty-two participants took part in two different experiments. According to the results, an obligatory traffic sign is associated with faster and more accurate responses only when the participant's initial objective is allowed. When the initial objective was not allowed, an advantage in accuracy was observed with prohibitory traffic signs and there was no significant difference in reaction time between the two types of sign. These results suggest that having an obligatory traffic sign may facilitate a correct response when the driver's goal is effectively allowed, whereas a prohibitory traffic sign could be more effective in preventing error when the driver has a not-allowed goal in mind. However, processing a prohibitory sign requires an extra inference (i.e. deciding which is the allowed manoeuvre), and thus the potential advantage in reaction time of the prohibitory sign may disappear. A second experiment showed that the results could not be explained by a potential congruency effect between the location (left or right) of the road signs and the position of the key or the hand used to respond (such as the Simon effect or the spatial Stroop effect). Also, an increase in the difficulty of the task (using an incongruent hand to respond) affected performance more strongly in experimental conditions that required making inferences. This made the advantage of the obligatory sign over the prohibitory sign in this condition more noteworthy. The evidence gathered in the current study could be of particular interest in some applied research areas, such as the assessment of road traffic signalling strategies or the ergonomic design of GPS navigation systems.  相似文献   
995.
Sergio Cabello 《Algorithmica》2012,62(1-2):361-381
We show how to compute in O(n 4/3log?1/3 n+n 2/3 k 2/3log?n) time the distance between k given pairs of vertices of a planar graph G with n vertices. This improves previous results whenever (n/log?n)5/6kn 2/log?6 n. As an application, we speed up previous algorithms for computing the dilation of geometric planar graphs.  相似文献   
996.
997.
The possibility of accidental contamination of a suspect by gunshot residues (GSRs) is considered. If two hypotheses are taken into account ("the suspect has shot a firearm" and "the suspect has not shot a firearm"), the likelihood ratio of the conditional probabilities of finding a number n of GSRs is defined. Choosing two Poisson distributions, the parameter lambda of the first one coincides with the mean number of GSRs that can be found on a firearm shooter, while the parameter mu of the second one is the mean number of GSRs that can be found on a nonshooter. In this scenario, the likelihood ratio of the conditional probabilities of finding a number n of GSRs in the two hypotheses can be easily calculated. The evaluation of the two parameters lambda and mu and of the goodness of the two probability distributions is performed by using different sets of data: "exclusive" lead-antimony-barium GSRs have been detected in two populations of 31 and 28 police officers at diverse fixed times since firearm practice, and in a population of 81 police officers who stated that they had not handled firearms for almost 1 month. The results show that the Poisson distributions well fit the data for both shooters and nonshooters, and that the probability of detection of two or more GSRs is normally greater if the suspect has shot firearms.  相似文献   
998.
The condition-based approach studies restrictions on the inputs to a distributed problem, called conditions, that facilitate its solution. Previous work considered mostly the asynchronous model of computation. This paper studies conditions for consensus in a synchronous system where processes can fail by crashing. It describes a full classification of conditions for consensus, establishing a continuum between the asynchronous and synchronous models, with the following hierarchy where includes all conditions (and in particular the trivial one made up of all possible input vectors). For a condition , we have:
–  For values of consensus is solvable in an asynchronous system with t failures, and we obtain the known hierarchy of conditions that allows solving asynchronous consensus with more and more efficient protocols as we go from d = 0 to d = −t.
–  For values of consensus is solvable in an asynchronous system with t failures, and we obtain the known hierarchy of conditions that allows solving asynchronous consensus with more and more efficient protocols as we go from d = 0 to d = −t.
–  For values of d<0 consensus is known not solvable in an asynchronous system with t failures, but we obtain a hierarchy of conditions that allows solving synchronous consensus with protocols that can take more and more rounds, as we go from d = 0 to d = t.
–  d = 0 is the borderline case where consensus can be solved in an asynchronous system with t failures, and can be solved optimally in a synchronous system.
After having established the complete hierarchy, the paper concentrates on the two last items: . The main result is that the necessary and sufficient number of rounds needed to solve uniform consensus for a condition (such that ) is d +1. In more detail, the paper presents a generic synchronous early-deciding uniform consensus protocol that enjoys the following properties. Let f be the number of actual crashes, I the input vector and the condition the protocol is instantiated with. The protocol terminates in two rounds when and , and in at most d +1 rounds when and . (It also terminates in one round when and .) Moreover, whether I belongs or not to C, no process requires more than min rounds to decide. The paper then proves a corresponding lower bound stating that at least d +1 rounds are necessary to get a decision in the worst case when (for and ). This paper is based on the DISC’03 and DISC’04 conference versions MRR03,MRR04 A. Mostefaoui is currently Associate Professor at the Computer Science Department of the University of Rennes, France. He received his Engineer Degree in Computer Science in 1990 from the University of Algiers, and a Ph.D. in Computer Science in 1994 from the University of Rennes, France. His research interests include fault-tolerance and synchronization in distributed systems, group communication, data consistency and distributed checkpointing. Achour Mostefaoui has published more than 70 scientific publications and served as a reviewer for more than 20 major journals and conferences. Moreover, Achour Mostéfaoui is heading the software engineer degree of the University of Rennes S. Rajsbaum received a degree in Computer Engineering from the National Autonomous University of Mexico (UNAM) in 1985, and a PhD in the Computer Science from the Technion, Israel, in 1991. Since then he has been a member of the Institute of Mathematics at UNAM, where he is now a Full Professor with Tenure. He has been a regular visiting scientist at the Laboratory for Computer Science of MIT. Also, he was a member of the Cambridge Research Laboratory of HP from 2000 to 2002. He was chair of the program committee for Latin American Theoretical Informatics LATIN2002, and for ACM Principles of Distributed Computing PODC03, and member of the Program Committee of various international conferences such as ADHOC, DISC, ICDCS, IPDPS, LADC, PODC, and SIROCCO. His research interests are in the theory of distributed computing, especially issues related to coordination, complexity and computability, and fault-tolerance. He has also published in graph theory and algorithms. Overall, he has published over fifty papers in journals and international conferences. He runs the Distributed Computing Column of SIGACT News, the newsletter of the ACM Special Interest Group on Algorithms and Computation Theory. He has been editor of several special journal issues, such as the Special 20th PODC Anniversary Special Issue of Distributed Computing Journal (with H. Attiya) and of Computer Networks journal special issue on algorithms. M. Raynalhas been a professor of computer science since 1981. At IRISA (CNRS-INRIA-University joint computing research laboratory located in Rennes), he founded a research group on Distributed Algorithms in 1983. His research interests include distributed algorithms, distributed computing systems, networks and dependability. His main interest lies in the fundamental principles that underly the design and the construction of distributed computing systems. He has been Principal Investigator of a number of research grants in these areas, and has been invited by many universities all over the world to give lectures on distributed algorithms and distributed computing. He belongs to the editorial board of several international journals. Professor Michel Raynal has published more than 90 papers in journals (JACM, Acta Informatica, Distributed Computing, Comm. of the ACM, Information and Computation, Journal of Computer and System Sciences, JPDC, IEEE Transactions on Computers, IEEE Transactions on SE, IEEE Transactions on KDE, IEEE Transactions on TPDS, IEEE Computer, IEEE Software, IPL, PPL, Theoretical Computer Science, Real-Time Systems Journal, The Computer Journal, etc.); and more than 190 papers in conferences (ACM STOC, ACM PODC, ACM SPAA, IEEE ICDCS, IEEE DSN, DISC, IEEE IPDPS, Europar, FST&TCS, IEEE SRDS, etc.). He has also written seven books devoted to parallelism, distributed algorithms and systems (MIT Press and Wiley). Michel Raynal has served in program committees for more than 70 international conferences (including ACM PODC, DISC, ICDCS, IPDPS, DSN, LADC, SRDS, SIROCCO, etc.) and chaired the program committee of more than 15 international conferences (including DISC -twice-, ICDCS, SIROCCO and ISORC). He served as the chair of the steering committee leading the DISC symposium series in 2002-2004. Michel Raynal received the IEEE ICDCS best paper Award three times in a row: 1999, 2000 and 2001. He is a general co-chair of the IEEE ICDCS conference that will be held in Lisbon in 2006.  相似文献   
999.
Spatial Optimization Models for Water Supply Allocation   总被引:1,自引:0,他引:1  
Climate change is likely to result in increased aridity, lower runoff, and declining water supplies for the cities of the Southwestern United States, including Phoenix. The situation in Phoenix is particularly complicated by the large number of water providers, each with its own supply portfolio, demand conditions, and conservation strategies. This paper details spatial optimization models to support water supply allocation between service provider districts, where some districts experience deficits and others experience surpluses in certain years. The approach seeks to reconcile and integrate projections derived from a complex simulation model taking into account current and future climate conditions. The formulated and applied models are designed to help better understand the expected increasingly complex interactions of providers under conditions of climate change. Preliminary results show cooperative agreements would reduce spot shortages that would occur even without climate change. In addition, they would substantially reduce deficits if climate change were to moderately reduce river flows in Phoenix’s major source regions, but have little effect under the most pessimistic scenarios because there are few surpluses available for re-allocation.  相似文献   
1000.
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