全文获取类型
收费全文 | 25544篇 |
免费 | 1328篇 |
国内免费 | 397篇 |
专业分类
电工技术 | 406篇 |
综合类 | 257篇 |
化学工业 | 2672篇 |
金属工艺 | 888篇 |
机械仪表 | 913篇 |
建筑科学 | 2615篇 |
矿业工程 | 131篇 |
能源动力 | 1535篇 |
轻工业 | 731篇 |
水利工程 | 195篇 |
石油天然气 | 51篇 |
武器工业 | 2篇 |
无线电 | 2683篇 |
一般工业技术 | 4892篇 |
冶金工业 | 855篇 |
原子能技术 | 97篇 |
自动化技术 | 8346篇 |
出版年
2024年 | 79篇 |
2023年 | 589篇 |
2022年 | 446篇 |
2021年 | 728篇 |
2020年 | 662篇 |
2019年 | 577篇 |
2018年 | 739篇 |
2017年 | 1047篇 |
2016年 | 1208篇 |
2015年 | 1118篇 |
2014年 | 1601篇 |
2013年 | 2063篇 |
2012年 | 1392篇 |
2011年 | 1570篇 |
2010年 | 1361篇 |
2009年 | 1422篇 |
2008年 | 1086篇 |
2007年 | 1307篇 |
2006年 | 1123篇 |
2005年 | 790篇 |
2004年 | 694篇 |
2003年 | 727篇 |
2002年 | 737篇 |
2001年 | 561篇 |
2000年 | 413篇 |
1999年 | 446篇 |
1998年 | 531篇 |
1997年 | 375篇 |
1996年 | 279篇 |
1995年 | 170篇 |
1994年 | 140篇 |
1993年 | 105篇 |
1992年 | 72篇 |
1991年 | 88篇 |
1990年 | 70篇 |
1989年 | 74篇 |
1988年 | 129篇 |
1987年 | 211篇 |
1986年 | 172篇 |
1985年 | 74篇 |
1984年 | 54篇 |
1983年 | 26篇 |
1982年 | 33篇 |
1981年 | 46篇 |
1980年 | 34篇 |
1979年 | 33篇 |
1978年 | 17篇 |
1977年 | 15篇 |
1976年 | 19篇 |
1975年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Heterogeneous object modeling: A review 总被引:2,自引:0,他引:2
X.Y. Kou 《Computer aided design》2007,39(4):284-301
A review on the recent development in heterogeneous object modeling is provided in this paper. General problems and prevalent solutions to the modeling of heterogeneous objects are investigated. Vigorous heterogeneous object representations are roughly classified into three major categories: evaluated models, unevaluated models and composite models. We reveal their similarities and study their strengths and weaknesses in terms of the representational capacities, intuitiveness, exactness, compactness, efficiency and other criteria. Different design paradigms are briefly reviewed to provide an overview of the state-of-the-art in heterogeneous object design. Finally, open problems and possible future directions are discussed. 相似文献
73.
1. A case of poisoning due to the raw root tuber of a Chinese medicinal plant, Alocasia macrorrhiza is presented. 2. The patient developed neurological (severe pain and numbness in the perioral area and throat) and gastrointestinal (nausea, vomiting, abdominal pain) symptoms immediately after eating the root tuber. 3. A macrorrhiza has properties and morphology very similar to another medical plant. A. odora. The root tuber of the latter is known to contain a neurotoxin sapotoxin. 相似文献
74.
《Journal of Visual Languages and Computing》2007,18(1):48-70
Visualization is one of the most effective methods for analyzing how high-dimensional data are distributed. Dimensionality reduction techniques, such as PCA, can be used to map high dimensional data to a two- or three-dimensional space. In this paper, we propose an algorithm called HyperMap that can be effectively applied to visualization. Our algorithm can be seen as a generalization of FastMap. It preserves its linear computation complexity, and overcomes several main shortcomings, especially in visualization. Since there are more than two pivot objects in each axis of a target space, more distance information needs to be preserved in each dimension. Then in visualization, the number of pivot objects can go beyond the limitation of six (2-pivot objects × 3-dimensions). Our HyperMap algorithm also gives more flexibility to the target space, such that the data distribution can be observed from various viewpoints. Its effectiveness is confirmed by empirical evaluations on both real and synthetic datasets. 相似文献
75.
We report a new application of Wang-Landau sampling to numerical integration that is straightforward to implement. It is applicable to a wide variety of integrals without restrictions and is readily generalized to higher-dimensional problems. The feasibility of the method results from a reinterpretation of the density of states in statistical physics to an appropriate measure for numerical integration. The properties of this algorithm as a new kind of Monte Carlo integration scheme are investigated with some simple integrals, and a potential application of the method is illustrated by the evaluation of integrals arising in perturbation theory of quantum many-body systems. 相似文献
76.
K.N. Yu H.H.W. Lee A.W.T. Wong Y.L. Law S.F.L. Cheung D. Nikezic F.M.F. Ng 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2007,263(1):271-278
A ray tracing method based on geometrical optics was used to study the tracks from alpha particles with different energies and with an incident angle of 50°. The transmission operation mode of the microscope is simulated. Considering the distribution of light intensities from the tracks, the mean and the 80% percentile gray levels from real experiments are proposed as quantitative variables to differentiate among tracks. The gray level properties for the same track for different exposures can vary to large extents. We introduce three variables, κ, λ and ε, to make empirical corrections. It is interesting to see that these coefficients are very consistent for the same alpha particle track despite the very different gray level properties. Gray level results have been obtained for tracks from alpha particles with 50° incident angle and different incident energies. However, the track depths cannot be predicted by any one of the coefficients κ, λ and ε. Multivariate analyses can help separate the tracks corresponding to different alpha energies. By using discriminant analysis with κ, λ and ε as independents, effectively all alpha energies can be determined with an accuracy of ±0.5 MeV. 相似文献
77.
Stochastic analysis of file-swarming systems 总被引:1,自引:0,他引:1
File swarming (or file sharing) is one of the most important applications in P2P networks. In this paper, we propose a stochastic framework to analyze a file-swarming system under realistic setting: constraints in upload/download capacity, collaboration among peers and incentive for chunk exchange. We first extend the results in the coupon system [L. Massoulie, M. Vojnovic, Coupon replication systems, in: Proc. ACM SIGMETRICS, Banff, Alberta, Canada, 2005] by providing a tighter performance bound. Then we generalize the coupon system by considering peers with limited upload and download capacity. We illustrate the last-piece problem and show the effectiveness of using forward error-correction (FEC) code and/or multiple requests to improve the performance. Lastly, we propose a framework to analyze an incentive-based file-swarming system. The stochastic framework we propose can serve as a basis for other researchers to analyze and design more advanced features of file-swarming systems. 相似文献
78.
It is stated in the above-mentioned comment that the main result of the paper Xiong, Zhang, et al. [(2006). Performance evaluation of UKF-based nonlinear filtering. Automatica 42(2), 261-270] can be extended to a class of filters, such as the extended Kalman filter (EKF). As we show here, this belief can be justified in a rigorous way, even for the nonlinear stochastic system with a nonlinear measurement equation. 相似文献
79.
Duan Li Fucai Qian Peilin Fu 《Automatic Control, IEEE Transactions on》2002,47(12):2010-2020
80.
Abstract The key research question for this study was to ask whether or not innovative teaching practices would lead to the development of learning outcomes essential for preparing the younger generation for the challenges of life in the knowledge society of the 21st century, and if so, how are the pedagogical features related to the different learning outcomes. Preliminary analyses of the case study data collected from the SITES M2 Study in Hong Kong reveal that where the development of more significant learning gains were observed, the cases possess characteristics additional to the criteria defined in the Study for selection of innovation. More importantly, it was found that the impact of the pedagogical practices was not determined simply by the aggregation of characteristics of the practices per se , nor on the technologies used, but on whether 'empowerment' permeates the curriculum goal and process. Further, this paper claims that these affective and socio-cognitive learning outcomes are more important as preparation for lifelong learning in the 21st century than 'knowledge management competencies'. 相似文献