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   673篇
  免费   41篇
  国内免费   1篇
电工技术   6篇
化学工业   140篇
金属工艺   2篇
机械仪表   3篇
建筑科学   35篇
矿业工程   1篇
能源动力   12篇
轻工业   103篇
水利工程   31篇
无线电   58篇
一般工业技术   109篇
冶金工业   143篇
原子能技术   3篇
自动化技术   69篇
  2024年   2篇
  2023年   11篇
  2022年   21篇
  2021年   29篇
  2020年   25篇
  2019年   22篇
  2018年   19篇
  2017年   15篇
  2016年   19篇
  2015年   15篇
  2014年   18篇
  2013年   37篇
  2012年   47篇
  2011年   61篇
  2010年   35篇
  2009年   30篇
  2008年   33篇
  2007年   33篇
  2006年   17篇
  2005年   22篇
  2004年   22篇
  2003年   12篇
  2002年   9篇
  2001年   6篇
  2000年   9篇
  1999年   10篇
  1998年   21篇
  1997年   17篇
  1996年   8篇
  1995年   7篇
  1994年   10篇
  1993年   7篇
  1992年   5篇
  1991年   2篇
  1990年   5篇
  1989年   3篇
  1988年   4篇
  1987年   6篇
  1986年   4篇
  1985年   2篇
  1984年   3篇
  1982年   4篇
  1980年   4篇
  1979年   5篇
  1977年   3篇
  1976年   2篇
  1974年   2篇
  1973年   3篇
  1970年   2篇
  1919年   1篇
排序方式: 共有715条查询结果,搜索用时 15 毫秒
1.
We present the results of an evaluation of the performance characteristics of a composite multivariate quality control (CMQC) system that incorporates quality control rules for univariate, multivariate, and correlation conditions. The CMQC system evaluated is designed to help analysts detect unacceptable trends and systematic error in one or more variables, unacceptable random error in one or more variables, and unacceptable changes in the correlation structure of any pair of variables. It is also designed to be tolerant of missing data, to allow analysts to reject as few as one or as many as all variables in a run, and to provide analysts with control statistics and graphics that logically relate to sources of analytical error. We show that the various components of the CMQC system have adequate statistical power to detect systematic errors, random errors, and correlation changes under the conditions likely to be encountered with multivariate analytical measurement systems: (1) a single variable with increased systematic or random error; (2) all variables or a subgroup of variables affected by a common problem that increases systematic or random error; and (3) missing data for one or more variables in a run. We also show that the power of the multivariate component of the CMQC system to detect systematic and random errors is higher than the power of an alternative multivariate test criterion.  相似文献   
2.
PURPOSE: Histology has been identified as an important prognostic factor in Hodgkin's disease (HD) in adults. Information regarding the impact of histology on outcome in childhood HD is scarce. This study determines the effect of histology on the overall survival (OS) or progression-free survival (PFS) in a national series of children treated in a standardized manner. PATIENTS AND METHODS: The results of treatment of 331 assessable patients, treated between January 1, 1982 and June 30, 1992, in the United Kingdom Children's Cancer Study Group (UKCCSG) Hodgkin's study I were reviewed to evaluate OS, PFS, and deaths according to stage and histology. Treatment was either involved-field radiation alone (stage IA) or chlorambucil, vinblastine, procarbazine, and prednisolone (ChlVPP) chemotherapy with or without mediastinal radiation. All were clinically staged at diagnosis. RESULTS: Nodular sclerosing (NS) HD was the most common histologic subtype (155 of 331 patients [47%]) and was uniformly distributed through all stages. Lymphocyte-depletion (LD) HD was extremely uncommon (< 1%). Mixed-cellularity (MC) HD had the highest relapse rate, but this was only significant (P < .05) in stage I patients who received local irradiation alone. There was no other statistically significant difference in OS and PFS between the various histologic subtypes. Multivariate analysis for PFS and OS confirmed that stage was the most important prognostic factor and that histology did not have an effect after stratification by stage. CONCLUSION: This study demonstrates that with effective multiagent chemotherapy, histologic subtype does not influence outcome. The high relapse rates in stage I MC subtype indicates that MC HD is biologically aggressive and systemic treatment with or without local irradiation may be indicated. The high relapse rate in stage IV patients appeared to be independent of histology.  相似文献   
3.
We propose a composite multivariate quality control (CMQC) system to control simultaneously measured variables. This system is designed to detect unacceptable trends and systematic error in one or more variables, unacceptable random error in one or more variables, and unacceptable changes in the correlation structure in any pair of variables. It is also designed to be tolerant of missing data, to be capable of rejecting as few as one or as many as all variables in a run, and to provide the analyst with control statistics and graphics that logically relate to sources of analytical error. Quality control rules for univariate, multivariate, and correlation conditions are incorporated in the system, as are plots displaying CMQC statistic values and control limits for univariate, multivariate, and correlation parameters. We also discuss advantages of the CMQC over the T2 and principal component multivariate quality control methods. We demonstrate the CMQC procedure using data from a laboratory process in which 40 variables were measured during 40 characterization runs and 23 runs analyzing unknowns.  相似文献   
4.
This paper introduces the concepts of state observability and condition observability for condition systems, a class of systems composed of discrete state components which interact via discrete binary signals called conditions. Given a set of externally observed conditions, state observability implies that the state of the system can be determined from the observations, and condition observability implies that all unobserved input and output conditions of the system can be determined from the observations. In this paper, we present a class of systems which is state observable and condition observable. We present a method to synthesize an observer system to provide state and condition signal estimates for a single component subsystem.  相似文献   
5.
The effects of kairomone pattern and preconditioning on parasitization rates of fall armyworm larvae,Spodoptera frugiperda (J.E. Smith) byCotesia (=Apanteles)marginiventris (Cresson) were investigated in the laboratory and greenhouse using a hexane extract of frass and actual fall armyworm frass. Parasitization rates increased 55 and 26% in Petri dishes and on corn seedlings, respectively, when the entire experimental area was sprayed with the frass extract. Applying the extract in spots resulted in a 20–30% reduction in parasitization compared to treating the entire area. However, spot application produced significantly better parasitization rates compared to the control treatment. Exposing the parasitoids to actual fall armyworm frass resulted in ca. 50% greater retention in the release area and an increase of ca. 60–75% in the number of parasitoids searching.C. marginiventris parasitized factitious hosts topically treated with an extract of fall armyworm frass.Mention of a commercial or proprietary product does not constitute an endorsement by the USDA.Submitted in partial fulfillment of the requirements for the degree Doctor of Philosophy, Department of Entomology and Nematology, University of Florida, Gainesville  相似文献   
6.
Electroless deposition has been used to prepare Cu–Pd/SiO2 bimetallic catalysts wherein initial Cu coverages are limited only to the pre-existing Pd surface. Cu loading on the Pd surface can be systematically varied by modification of deposition kinetic parameters. In this case deposition time was used as the kinetic variable for the preparation of a series of Cu–Pd catalysts. These materials have been characterized using atomic absorption, CO chemisorption, and FT-IR (adsorption of CO), and then evaluated for the hydrogenation of 3,4-epoxy-1-butene, a functionalized olefin having many potential reaction pathways. Catalyst performance and characterization results suggest that Cu is not distributed in a monodisperse manner on the Pd surface, indicating the existence of autocatalytic deposition of Cu on Cu sites. The FT-IR results suggest that although CO adsorption on all sites is suppressed by Cu addition, initial Cu deposition occurs more readily on certain sites. The bimetallic Cu–Pd sites that are formed exhibit unusually high activity for EpB conversion and formation of unsaturated alcohols and aldehydes. This bimetallic effect on catalyst activity and selectivity is best explained, not by the existence of either ligand or ensemble effects, but rather by the bifunctional nature of the Cu–Pd sites present on the surface of these catalysts.  相似文献   
7.
Artificial Life and Robotics - Honey bees (Apis mellifera L.) are social insects that makes frequent use of volatile pheromone signals to collectively navigate unpredictable and unknown...  相似文献   
8.

In this work we study, design, and evaluate computational methods to support interpretation of statutory terms. We propose a novel task of discovering sentences for argumentation about the meaning of statutory terms. The task models the analysis of past treatment of statutory terms, an exercise lawyers routinely perform using a combination of manual and computational approaches. We treat the discovery of sentences as a special case of ad hoc document retrieval. The specifics include retrieval of short texts (sentences), specialized document types (legal case texts), and, above all, the unique definition of document relevance provided in detailed annotation guidelines. To support our experiments we assembled a data set comprising 42 queries (26,959 sentences) which we plan to release to the public in the near future in order to support further research. Most importantly, we investigate the feasibility of developing a system that responds to a query with a list of sentences that mention the term in a way that is useful for understanding and elaborating its meaning. This is accomplished by a systematic assessment of different features that model the sentences’ usefulness for interpretation. We combine features into a compound measure that accounts for multiple aspects. The definition of the task, the assembly of the data set, and the detailed task analysis provide a solid foundation for employing a learning-to-rank approach.

  相似文献   
9.
Huang Q  Ashley PR 《Applied optics》1996,35(20):3899-3901
A new grating coupler that incorporates a hybrid grating-mirror is proposed. An analysis of the device indicates that it has a much larger achromatic range than that of conventional grating couplers, as well as a relaxed fabrication requirement for the grating.  相似文献   
10.
This paper reviews literature on information channel type and disasters, and presents results on hurricane evacuation information gathering. Results show that respondents reported they would use television and radio most frequently for gathering information about hurricane evacuation. Minority respondents reported more preference of the use of community or local government as information sources than white respondents, females gathered information from multiple channels more than males, and younger residents gathered information from multiple channels more than older respondents. Implications include areas for future research in how channel utilization occurs during slow onset hazards in predominantly black communities, how age and gender relate to channel preference, and how channel preferences affect length of time to make decisions and engage in protective actions.  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