全文获取类型
收费全文 | 2646篇 |
免费 | 85篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 57篇 |
综合类 | 1篇 |
化学工业 | 356篇 |
金属工艺 | 52篇 |
机械仪表 | 34篇 |
建筑科学 | 71篇 |
矿业工程 | 9篇 |
能源动力 | 51篇 |
轻工业 | 160篇 |
水利工程 | 16篇 |
石油天然气 | 7篇 |
无线电 | 232篇 |
一般工业技术 | 417篇 |
冶金工业 | 839篇 |
原子能技术 | 25篇 |
自动化技术 | 406篇 |
出版年
2023年 | 14篇 |
2022年 | 31篇 |
2021年 | 38篇 |
2020年 | 38篇 |
2019年 | 43篇 |
2018年 | 51篇 |
2017年 | 52篇 |
2016年 | 46篇 |
2015年 | 34篇 |
2014年 | 52篇 |
2013年 | 118篇 |
2012年 | 90篇 |
2011年 | 132篇 |
2010年 | 99篇 |
2009年 | 71篇 |
2008年 | 116篇 |
2007年 | 91篇 |
2006年 | 86篇 |
2005年 | 88篇 |
2004年 | 69篇 |
2003年 | 75篇 |
2002年 | 58篇 |
2001年 | 33篇 |
2000年 | 52篇 |
1999年 | 55篇 |
1998年 | 109篇 |
1997年 | 94篇 |
1996年 | 86篇 |
1995年 | 63篇 |
1994年 | 57篇 |
1993年 | 51篇 |
1992年 | 33篇 |
1991年 | 29篇 |
1990年 | 35篇 |
1989年 | 43篇 |
1988年 | 38篇 |
1987年 | 46篇 |
1986年 | 26篇 |
1985年 | 36篇 |
1984年 | 23篇 |
1983年 | 35篇 |
1982年 | 22篇 |
1981年 | 25篇 |
1980年 | 21篇 |
1979年 | 34篇 |
1978年 | 27篇 |
1977年 | 29篇 |
1976年 | 32篇 |
1973年 | 17篇 |
1972年 | 13篇 |
排序方式: 共有2733条查询结果,搜索用时 28 毫秒
51.
George Teodoro Eduardo Valle Nathan Mariano Ricardo Torres Wagner Meira Jr Joel H. Saltz 《The VLDB Journal The International Journal on Very Large Data Bases》2014,23(3):427-448
Similarity search in high-dimensional spaces is a pivotal operation for several database applications, including online content-based multimedia services. With the increasing popularity of multimedia applications, these services are facing new challenges regarding (1) the very large and growing volumes of data to be indexed/searched and (2) the necessity of reducing the response times as observed by end-users. In addition, the nature of the interactions between users and online services creates fluctuating query request rates throughout execution, which requires a similarity search engine to adapt to better use the computation platform and minimize response times. In this work, we address these challenges with Hypercurves, a flexible framework for answering approximate k-nearest neighbor (kNN) queries for very large multimedia databases. Hypercurves executes in hybrid CPU–GPU environments and is able to attain massive query-processing rates through the cooperative use of these devices. Hypercurves also changes its CPU–GPU task partitioning dynamically according to the observed load, aiming for optimal response times. In our empirical evaluation, dynamic task partitioning reduced query response times by approximately 50 % compared to the best static task partition. Due to a probabilistic proof of equivalence to the sequential kNN algorithm, the CPU–GPU execution of Hypercurves in distributed (multi-node) environments can be aggressively optimized, attaining superlinear scalability while still guaranteeing, with high probability, results at least as good as those from the sequential algorithm. 相似文献
52.
Charge transfer complexes possessing a … DADA … structure with both the donor, D, and acceptor, A, being S = 1/2 radicals may exhibit cooperative magnetic phenomena. The complex [Fe(C5Me5)2]+·[TCNQ]−· exhibits metamagnetic behavior. The similarly structured [TCNE]−· and [C4(CN)6]−· complexes are ferromagnets, whereas the [DDQ]−· salt is a paramagnet. The high temperature magnetic susceptibility obeys the Curie-Weiss expression with θ = + 30, + 30, and + 3 for the [TCNE]−·, [C4(CN)6]−·, and [TCNQ]−· salts, respectively. The ferromagnetic [TCNE]−· salt exhibits zero field Zeeman split 57Fe Mossbauer spectra with an internal field of 425.6 kOe at 4.23 K. After reviewing the current papers discussing ferromagnetism in molecular (organic) compounds, a qualitative model consistent with the necessary bulk spin alignment required for a ferromagnet is presented. 相似文献
53.
Aronsson Sanna Artman Henrik Brynielsson Joel Lindquist Sinna Ramberg Robert 《Cognition, Technology & Work》2021,23(1):117-130
Cognition, Technology & Work - Simulator training is becoming increasingly important for training of time-critical and dynamic situations. Hence, how simulator training in such domains is... 相似文献
54.
The effect of copper content (0.01 and 2.1%) and microstructure on the intrinsic hydrogen embrittlement susceptibility of unl nercially-processed AI---6Zn---2Mg---XCu alloys was investigated. (The alloy with 2.1 Cu corresponds to 7059). Hydrogen was introduced into the alloys using cathodic charging, both with and without concurrent plastic straining. The copper-free alloy in both the under-aged and peak-aged conditions was embrittled by hydrogen and the effect was enhanced by concurrent plastic strain. The copper-containing alloy (7050) was susceptible to hydrogen embrittlement when under-aged, but once the peak-strength microstructure had been developed, the alloy in the longitudinal direction showed no embrittlement even under severe hydrogen-entry conditions. Similar beneficial effects have been reported for copper additions in imparting resistance to humid air and stress-corrosion cracking for high strength AI-Zn-Mg alloys, and the results are discussed with emphasis on the parallel nature of the phenomena of stress-corrosion cracking and hydrogen embrittlement. 相似文献
55.
Grain coarsening tests were carried out on Al-4.5 pct Cu and Al-4.5 pct Si alloys. The effects of three variables, melt composition, pour temperature, and mold temperature, were determined. It was found that the macrostructure generally coarsened with increased pour and mold temperatures. Coarsening was extreme in the unrefined alloys but was retarded by the active grain refiners like titanium and columbium. The effect of boron was spectacular in suppressing coarsening tendencies. The results of the investigation support the carbide theory of nucleation as opposed to the peritectic theory. 相似文献
56.
Vydyanathan Naga Krishnamoorthy Sriram Sabin Gerald M. Catalyurek Umit V. Kurc Tahsin Sadayappan Ponnuswamy Saltz Joel H. 《Parallel and Distributed Systems, IEEE Transactions on》2009,20(8):1158-1172
Complex parallel applications can often be modeled as directed acyclic graphs of coarse-grained application tasks with dependences. These applications exhibit both task and data parallelism, and combining these two (also called mixed parallelism) has been shown to be an effective model for their execution. In this paper, we present an algorithm to compute the appropriate mix of task and data parallelism required to minimize the parallel completion time (makespan) of these applications. In other words, our algorithm determines the set of tasks that should be run concurrently and the number of processors to be allocated to each task. The processor allocation and scheduling decisions are made in an integrated manner and are based on several factors such as the structure of the task graph, the runtime estimates and scalability characteristics of the tasks, and the intertask data communication volumes. A locality-conscious scheduling strategy is used to improve intertask data reuse. Evaluation through simulations and actual executions of task graphs derived from real applications and synthetic graphs shows that our algorithm consistently generates schedules with a lower makespan as compared to Critical Path Reduction (CPR) and Critical Path and Allocation (CPA), two previously proposed scheduling algorithms. Our algorithm also produces schedules that have a lower makespan than pure task- and data-parallel schedules. For task graphs with known optimal schedules or lower bounds on the makespan, our algorithm generates schedules that are closer to the optima than other scheduling approaches. 相似文献
57.
This paper describes an advanced simulation environment which is used to examine, validate, and predict the performance of mobile wireless network systems. This simulation environment overcomes many of the limitations found with analytical models, experimentation, and other commercial network simulators available on the market today. We identify a set of components which make up mobile wireless systems and describe a set of flexible modules which can be used to model the various components and their integration. These models are developed using the Maisie simulation language. By modeling the various components and their integration, this simulation environment is able to accurately predict the performance bottlenecks of a multimedia wireless network system being developed at UCLA, determine the trade-off point between the various bottlenecks, and provide performance measurements and validation of algorithms which are not possible through experimentation and too complex for analysis.This work was supported in part by the Advanced Research Projects Agency, ARPA/CSTO, under Contract J-FBI-93-112 Computer Aided Design of High Performance Wireless Networked Systems, and by ARPA/CSTO under Contract DABT-63-94-C-0080 TransparentVirtual Mobile Environment.This paper was in part presented at the ACM Mobile Computing and Networking Conference (Mobicom '95), Berkeley, California, 14–15 November 1995. 相似文献
58.
Silvia G. Motti Manuel Kober-Czerny Marcello Righetto Philippe Holzhey Joel Smith Hans Kraus Henry J. Snaith Michael B. Johnston Laura M. Herz 《Advanced functional materials》2023,33(32):2300363
Metal halide perovskite (MHP) semiconductors have driven a revolution in optoelectronic technologies over the last decade, in particular for high-efficiency photovoltaic applications. Low-dimensional MHPs presenting electronic confinement have promising additional prospects in light emission and quantum technologies. However, the optimisation of such applications requires a comprehensive understanding of the nature of charge carriers and their transport mechanisms. This study employs a combination of ultrafast optical and terahertz spectroscopy to investigate phonon energies, charge-carrier mobilities, and exciton formation in 2D (PEA)2PbI4 and (BA)2PbI4 (where PEA is phenylethylammonium and BA is butylammonium). Temperature-dependent measurements of free charge-carrier mobilities reveal band transport in these strongly confined semiconductors, with surprisingly high in-plane mobilities. Enhanced charge-phonon coupling is shown to reduce charge-carrier mobilities in (BA)2PbI4 with respect to (PEA)2PbI4. Exciton and free charge-carrier dynamics are disentangled by simultaneous monitoring of transient absorption and THz photoconductivity. A sustained free charge-carrier population is observed, surpassing the Saha equation predictions even at low temperature. These findings provide new insights into the temperature-dependent interplay of exciton and free-carrier populations in 2D MHPs. Furthermore, such sustained free charge-carrier population and high mobilities demonstrate the potential of these semiconductors for applications such as solar cells, transistors, and electrically driven light sources. 相似文献
59.
Photoacoustic‐Guided Surgery with Indocyanine Green‐Coated Superparamagnetic Iron Oxide Nanoparticle Clusters
下载免费PDF全文
![点击此处可从《Small (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jayesh P. Thawani Ahmad Amirshaghaghi Lesan Yan Joel M. Stein Jessica Liu Andrew Tsourkas 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(37)
A common cause of local tumor recurrence in brain tumor surgery results from incomplete surgical resection. Adjunctive technologies meant to facilitate gross total resection have had limited efficacy to date. Contrast agents used to delineate tumors preoperatively cannot be easily or accurately used in the real‐time operative setting. Although multimodal imaging contrast agents are developed to help the surgeon discern tumor from normal tissue in the operating room, these contrast agents are not readily translatable. This study has developed a novel contrast agent comprised solely of two Food and Drug Administration approved components, indocyanine green (ICG) and superparamagnetic iron oxide (SPIO) nanoparticles—with no additional amphiphiles or carrier materials, to enable preoperative detection by magnetic resonance (MR) imaging and intraoperative photoacoustic (PA) imaging. The encapsulation efficiency of both ICG and SPIO within the formulated clusters is ≈100%, and the total ICG payload is 20–30% of the total weight (ICG + SPIO). The ICG–SPIO clusters are stable in physiologic conditions; can be taken up within tumors by enhanced permeability and retention; and are detectable by MR. In a preclinical surgical resection model in mice, following injection of ICG–SPIO clusters, animals undergoing PA‐guided surgery demonstrate increased progression‐free survival compared to animals undergoing microscopic surgery. 相似文献
60.
Provides an overview of the 1995 Consumer Reports survey of the effectiveness of psychotherapy. Specific issues addressed include the study's goals; the findings for mental health professionals, family doctors, and self-help groups; and methodological strengths and weaknesses related to external validity, sampling, controls, self-reports, and time frame. The data show that, free of the artificial constraints of controlled studies in the real world, a population of consumers can often benefit from psychological intervention services. Real relief can be found at the hands of professional mental health providers. M. Kotkin et al reaffirm their independence from M. E. P. Seligman (see record 1996-13324-001) regarding the interpretation of the data. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献