全文获取类型
收费全文 | 342033篇 |
免费 | 26148篇 |
国内免费 | 15817篇 |
专业分类
电工技术 | 23881篇 |
技术理论 | 52篇 |
综合类 | 43427篇 |
化学工业 | 35302篇 |
金属工艺 | 11911篇 |
机械仪表 | 17635篇 |
建筑科学 | 51987篇 |
矿业工程 | 17360篇 |
能源动力 | 10401篇 |
轻工业 | 28695篇 |
水利工程 | 20108篇 |
石油天然气 | 14653篇 |
武器工业 | 2939篇 |
无线电 | 21249篇 |
一般工业技术 | 22393篇 |
冶金工业 | 19149篇 |
原子能技术 | 3203篇 |
自动化技术 | 39653篇 |
出版年
2024年 | 1197篇 |
2023年 | 3570篇 |
2022年 | 6678篇 |
2021年 | 8194篇 |
2020年 | 8576篇 |
2019年 | 7102篇 |
2018年 | 6651篇 |
2017年 | 8087篇 |
2016年 | 9406篇 |
2015年 | 10459篇 |
2014年 | 20187篇 |
2013年 | 17640篇 |
2012年 | 23078篇 |
2011年 | 24520篇 |
2010年 | 19380篇 |
2009年 | 20189篇 |
2008年 | 18742篇 |
2007年 | 24051篇 |
2006年 | 22496篇 |
2005年 | 19431篇 |
2004年 | 16740篇 |
2003年 | 15054篇 |
2002年 | 12502篇 |
2001年 | 10389篇 |
2000年 | 8775篇 |
1999年 | 7155篇 |
1998年 | 5369篇 |
1997年 | 4603篇 |
1996年 | 4190篇 |
1995年 | 3579篇 |
1994年 | 3105篇 |
1993年 | 2332篇 |
1992年 | 2058篇 |
1991年 | 1529篇 |
1990年 | 1289篇 |
1989年 | 1158篇 |
1988年 | 917篇 |
1987年 | 640篇 |
1986年 | 475篇 |
1985年 | 394篇 |
1984年 | 366篇 |
1983年 | 262篇 |
1982年 | 237篇 |
1981年 | 175篇 |
1980年 | 153篇 |
1979年 | 119篇 |
1978年 | 71篇 |
1977年 | 81篇 |
1976年 | 58篇 |
1975年 | 61篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
本介绍了锡矿山前闪星锑业有限责任公司如何加强对关键耗水工序的管理及提高重复水利用率的措施,并对所取得的效果进行了阐述,可供用水大户如何节水以借鉴。 相似文献
112.
This paper presents the development of an optimization and a computer-simulation model to evaluate the process plans of a manufacturing center by analyzing the effect of tool failure on system performance. The GPSS/PC simulation program that is used in this study has been built with variables, functions and matrices so that many experiments could be conducted with the model. Sensitivity analysis is presented and the developed model has proven to be useful in determining optimum sequencing of parts for various operating policies. 相似文献
113.
114.
115.
本文主要从土壤 pH ,重碳酸盐 ,和氮素形态等几方面综述了各种土壤因子对土壤缺铁失绿的影响 ,并提出了进一步加强研究的方向 相似文献
116.
Jennifer G. Winter M. Catherine Eimers Peter J. Dillon Lem D. Scott Wolfgang A. Scheider Campbell C. Willox 《Journal of Great Lakes research》2007,33(2):381-396
Total phosphorus (TP) inputs to Lake Simcoe have led to hypolimnetic dissolved oxygen (DO) depletion and loss of cold water fish habitat. Since 1990, efforts have been made to reduce the total TP input to the lake below a defined target of 75 t/year, which was predicted to lead to reductions in spring TP concentration and improvements in end-of-summer hypolimnetic DO concentrations. The total TP load to the lake during the most recent period of record (1998/99-2003/04) ranged from 53 to 76 t/yr and averaged 67 t/yr, compared to an average of 114 t/yr estimated between 1990/91 and 1997/98 (range 85-157 t/yr). Reductions in TP loads from the catchment via tributary discharge (∼26 t) accounted for the majority of the decrease in total load between the two time periods. Total P concentrations decreased significantly in four out of six long-term monitored tributaries; however, concentrations in all six tributaries remain above the level recommended to avoid nuisance plant growth (30 μg/L). Although TP loads to the lake are currently below the target 75 t/yr, excessive growths of filamentous algae and macrophytes continue to be a problem in the nearshore zone. End-of-summer minimum hypolimnetic DO concentrations (average 4.3 mg/L, 1998/99-2003/04) remain substantially below the level (7 mg/L) that is considered protective of lake trout. Efforts to reduce TP loads to the lake therefore need to continue. 相似文献
117.
Using the Internet, “public” computing grids can be assembled using “volunteered” PCs. To achieve this, volunteers download and install a software application capable of sensing periods of low local processor activity. During such times, this program on the local PC downloads and processes a subset of the project's data. At the completion of processing, the results are uploaded to the project and the cycle repeats. 相似文献
118.
Many real-world problems are multi-objective optimization problems and evolutionary algorithms are quite successful on such problems. Since the task is to compute or approximate the Pareto front, multi-objective optimization problems are considered as more difficult than single-objective problems. One should not forget that the fitness vector with respect to more than one objective contains more information that in principle can direct the search of evolutionary algorithms. Therefore, it is possible that a single-objective problem can be solved more efficiently via a generalized multi-objective model of the problem. That this is indeed the case is proved by investigating the computation of minimum spanning trees.This work was supported by the Deutsche Forschungsgemeinschaft (DFG) as part of the Collaborative Research Center Computational Intelligence (SFB 531) and by the German-Israeli Foundation (GIF) in the project Robustness Aspects of Algorithms. 相似文献
119.
U. Reimer
H. -J. Schek
《Data & Knowledge Engineering》1989,4(4):321-352The first part of this paper introduces the basic constructs of a frame representation model and gives a formal definition for them. Subsequently the nested relational model (NF2) is described as an extension of the classical relational model to support relation-valued attributes. In the second part of this paper both models are compared with each other and a mapping of frame representation structures to NF2 structures is specified. The structural similarities between frames and NF2 relations are made clear and it is shown that their main difference is due to the type polymorphism introduced by the concept hierarchy of the frame model. This causes type collisions to occur in the strictly typed NF2 model when frames are directly mapped to NF2 structures. Two solutions to this problem are suggested and compared. The paper concludes with a reformulation of query operations of the frame model in terms of NF2 algebra operations. 相似文献
120.
[Correction Notice: An erratum for this article was reported in Vol 20(2) of Canadian Journal of Behavioural Science Revue canadienne des Sciences du comportement (see record 2007-09831-001). The abstract accompanying the original article was incorrect; the correct abstract (in French) is presented in the erratum.] We know little about individuals who are declared unfit to stand trial and/or not guilty by reason of insanity. The few existing studies are characterized by methodological weaknesses, notably by short follow-up periods and a lack of external validity. The present investigation, which aims to evaluate and explain readmissions that occurred during a seven- to nine-year period, corrects only some of these weaknesses. Sixty-one per cent of the subjects were rehospitalized during the period of study. It proved difficult to identify the factors associated with readmission. However, males with a diagnosis of schizophrenia and who had committed violent crimes were found the most likely to be readmitted. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献