全文获取类型
收费全文 | 172683篇 |
免费 | 16369篇 |
国内免费 | 9229篇 |
专业分类
电工技术 | 13809篇 |
技术理论 | 8篇 |
综合类 | 17818篇 |
化学工业 | 16968篇 |
金属工艺 | 7133篇 |
机械仪表 | 15802篇 |
建筑科学 | 20313篇 |
矿业工程 | 6667篇 |
能源动力 | 7763篇 |
轻工业 | 12805篇 |
水利工程 | 7453篇 |
石油天然气 | 8252篇 |
武器工业 | 2001篇 |
无线电 | 9864篇 |
一般工业技术 | 16555篇 |
冶金工业 | 6663篇 |
原子能技术 | 2517篇 |
自动化技术 | 25890篇 |
出版年
2024年 | 432篇 |
2023年 | 1956篇 |
2022年 | 3891篇 |
2021年 | 5008篇 |
2020年 | 5123篇 |
2019年 | 4333篇 |
2018年 | 4198篇 |
2017年 | 5209篇 |
2016年 | 6349篇 |
2015年 | 6744篇 |
2014年 | 11074篇 |
2013年 | 11120篇 |
2012年 | 12985篇 |
2011年 | 14330篇 |
2010年 | 10298篇 |
2009年 | 10477篇 |
2008年 | 9829篇 |
2007年 | 11806篇 |
2006年 | 10251篇 |
2005年 | 8624篇 |
2004年 | 7290篇 |
2003年 | 6223篇 |
2002年 | 5034篇 |
2001年 | 4147篇 |
2000年 | 3536篇 |
1999年 | 2940篇 |
1998年 | 2522篇 |
1997年 | 2131篇 |
1996年 | 1751篇 |
1995年 | 1439篇 |
1994年 | 1294篇 |
1993年 | 964篇 |
1992年 | 888篇 |
1991年 | 650篇 |
1990年 | 541篇 |
1989年 | 467篇 |
1988年 | 389篇 |
1987年 | 264篇 |
1986年 | 228篇 |
1985年 | 214篇 |
1984年 | 252篇 |
1983年 | 239篇 |
1982年 | 196篇 |
1981年 | 96篇 |
1980年 | 94篇 |
1979年 | 65篇 |
1978年 | 53篇 |
1977年 | 47篇 |
1976年 | 43篇 |
1959年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
991.
992.
Prediction of the effects on dynamic response due to distributed structural modification with additional degrees of freedom 总被引:1,自引:0,他引:1
Huajiang Hang Krishna Shankar Joseph C.S. Lai 《Mechanical Systems and Signal Processing》2008,22(8):1809-1825
The aim of this study is to investigate means of efficiently assessing the effects of distributed structural modification on the dynamic properties of a complex structure. The dynamic properties of the modified structure can be determined by experimental testing or numerical simulation, both of which are complex, expensive and time-consuming. Assuming that the original dynamic characteristics are already established and that the modification is a relatively simple attachment, the modified dynamic properties may be determined numerically without solving the equations of motion of the full-modified structure. The frequency response functions (FRFs) of the modified structure can be computed by coupling the original FRFs and a delta dynamic stiffness matrix for the modification introduced. The validity of this approach is investigated by applying it to a cantilever beam to which a smaller beam is attached as modification. The original FRFs were obtained experimentally as well as numerically. The delta dynamic stiffness matrix was determined numerically by modeling the attachment and part of the original structure including the attachment points. The FRFs of the modified beam were then computed. Good agreement is obtained by comparing the results to the FRFs of the modified beam determined experimentally as well as by numerical modeling of the complete modified structure. 相似文献
993.
从劳务市场的现状入手,分析劳务合同存在的问题,寻找解决办法,有利于对建筑市场进行行政指导、行政监督和建筑业企业的健康发展。 相似文献
994.
Development of adolescent reading comprehension in language 1 and language 2: A longitudinal analysis of constituent components. 总被引:1,自引:0,他引:1
van Gelderen Amos; Schoonen Rob; Stoel Reinoud D.; de Glopper Kees; Hulstijn Jan 《Canadian Metallurgical Quarterly》2007,99(3):477
This study investigated the relationship between reading comprehension development of 389 adolescents in their dominant language (Language 1 [L1], Dutch) and a foreign language (Language 2 [L2], English). In each consecutive year from Grades 8 through 10, a number of measurements were taken. Students' reading comprehension, their linguistic knowledge (vocabulary and grammar knowledge) and processing efficiency (speed of word recognition and sentence comprehension) in both languages, and their metacognitive knowledge about reading were assessed. The relative strengths of the effects of these components of reading were analyzed to distinguish among 3 hypotheses about the relationship between L1 and L2 reading comprehension: the transfer hypothesis, the threshold hypothesis, and the processing efficiency hypothesis. The transfer hypothesis predicts a strong relationship between L1 and L2 reading comprehension and a strong effect of metacognitive knowledge on L2 reading comprehension, whereas the threshold and processing efficiency hypotheses predict a more important role of language-specific knowledge and processing skills. Results support the transfer hypothesis, although language-specific knowledge and fluency also contribute to L2 reading performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
995.
由于混流式水轮机整体结构的复杂性,因没有成熟的理论指导,在设计阶段对动力特性难加以考虑.通过有限元建立其动力学控制方程,以大型有限元软件为平台建立有限元计算模型,并使用先进的Lanczos法对结构整体与局部模态分析确定结构的固有频率和振型等动力特性.同时与其他振源频率进行了比较分析,研究其出现共振的可能性. 相似文献
996.
Consumers' beliefs, attitudes and intentions towards genetically modified foods, based on the 'perceived safety vs. benefits' perspective 总被引:1,自引:0,他引:1
Ioannis S. Arvanitoyannis & Athanasios Krystallis 《International Journal of Food Science & Technology》2005,40(4):343-360
It has been repeatedly claimed that the application of genetic engineering in the field of agricultural and food production is both beneficial and advantageous. However, biotechnology is developing in an environment where public concerns about food safety and environmental protection are steadily increasing. The present study aims at gaining an insight into Greek consumers’ beliefs, attitudes and intentions towards genetically modified (GM) food products. The objectives of this study are summarized as follows (i) to provide evidence that consumer beliefs are built around the ‘safety‐benefits’ axis, and (ii) to segment the Greek market in terms of consumer beliefs about GM food products and identify a number of clusters with clear‐cut behavioural profiles. Although the overall attitude of Greek consumers towards GM food is negative, the research very interestingly concludes that there exists a market segment of substantial size, whose beliefs about GM food appears to be positive. This finding suggests that there is not a ‘consensus’ regarding the rejection of GM foods in the Greek market as one might have expected thus ‘encouraging’ the implementation of adequate marketing strategies to target this segment of ‘early adopters’ in the first place. 相似文献
997.
An upper-bound analysis of the pressure-assisted injection forging (PAIF) of thick-walled tubular components with hollow flanges was conducted to predict the maximum forming-pressure requirements. The polymeric pressurizing material and the pure aluminium work material employed were assumed to obey the von-Mises’ yield criterion, the two materials being divided into three and six zones, respectively, and described using kinematically admissible velocity fields. An upper-bound solution was derived based on this model. Experiments were conducted to validate the solution. The results suggest that the upper-bound analysis has sufficient accuracy for the prediction of the forming-pressure requirements. Subsequently, a parametric analysis was conducted to study the effects of variation of the principal parameters of the process and the geometry, such as tube thicknesses, flange dimensions and friction, on the forming-force requirements, which showed other useful applications of the upper-bound solutions. 相似文献
998.
999.
Generalized null space uncorrelated Fisher discriminant analysis for linear dimensionality reduction
We propose a generalized null space uncorrelated Fisher discriminant analysis (GNUFDA) technique integrating the uncorrelated discriminant analysis and weighted pairwise Fisher criterion. The GNUFDA can effectively deal with the small sample-size problem and perform satisfactorily when the dimensionality of the null space decreases with increase in the number of training samples per class and/or classes, C. The proposed GNUFDA can extract at most C-1 optimal uncorrelated discriminative vectors without being influenced by the null-space dimensionality. 相似文献
1000.