全文获取类型
收费全文 | 4683篇 |
免费 | 314篇 |
国内免费 | 173篇 |
专业分类
电工技术 | 192篇 |
技术理论 | 3篇 |
综合类 | 328篇 |
化学工业 | 742篇 |
金属工艺 | 139篇 |
机械仪表 | 191篇 |
建筑科学 | 365篇 |
矿业工程 | 94篇 |
能源动力 | 69篇 |
轻工业 | 296篇 |
水利工程 | 68篇 |
石油天然气 | 190篇 |
武器工业 | 23篇 |
无线电 | 502篇 |
一般工业技术 | 441篇 |
冶金工业 | 852篇 |
原子能技术 | 20篇 |
自动化技术 | 655篇 |
出版年
2024年 | 7篇 |
2023年 | 50篇 |
2022年 | 109篇 |
2021年 | 98篇 |
2020年 | 104篇 |
2019年 | 85篇 |
2018年 | 96篇 |
2017年 | 136篇 |
2016年 | 126篇 |
2015年 | 146篇 |
2014年 | 165篇 |
2013年 | 253篇 |
2012年 | 256篇 |
2011年 | 278篇 |
2010年 | 252篇 |
2009年 | 232篇 |
2008年 | 240篇 |
2007年 | 231篇 |
2006年 | 266篇 |
2005年 | 217篇 |
2004年 | 134篇 |
2003年 | 118篇 |
2002年 | 119篇 |
2001年 | 78篇 |
2000年 | 97篇 |
1999年 | 134篇 |
1998年 | 311篇 |
1997年 | 181篇 |
1996年 | 146篇 |
1995年 | 81篇 |
1994年 | 79篇 |
1993年 | 83篇 |
1992年 | 26篇 |
1991年 | 39篇 |
1990年 | 23篇 |
1989年 | 29篇 |
1988年 | 29篇 |
1987年 | 24篇 |
1986年 | 16篇 |
1985年 | 13篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1978年 | 2篇 |
1977年 | 14篇 |
1976年 | 16篇 |
1975年 | 1篇 |
排序方式: 共有5170条查询结果,搜索用时 15 毫秒
71.
Abstract Owing to the lack of face-to-face interactions, students using a web-based learning system are likely to study alone and with relatively little classmate support and pressure. Teachers in a web-based learning system may apply a group-learning model to overcome this problem. Teachers first need to organise, manage and monitor the group learning and they must take appropriate actions based on teaching strategies to improve the learning achievements of the students. To perform these tasks effectively, teachers must obtain relevant information by analysing the huge volume of web-access logs or by monitoring web interactions. This paper presents novel methodologies for developing instruments to assist teachers in performing intervention and strategy analysis. The proposed methodologies apply data mining tools provided by existing database management systems. Database techniques, including the multi-dimensional cube, are then applied to make student web logs meaningful and helpful to teachers in managing group learning. The associate rule mining tool is finally employed to assist teachers in analysing their pedagogical strategies. These tools relieve teachers of tedious data collection and analysis, allowing them to focus on managing the groups to promote students' learning achievement. 相似文献
72.
In this paper, a model‐refining method is proposed to alleviate the complexity involved in specification interpretation of DES control problems. The legal constraint language is defined in terms of illegal states and events in contrast with constructing the automaton of the specification language. This method could provide a more intuitive view of the DES control problem and would be suitable for practical implementation. Two examples, which have commonly been used in the literature, are employed to show the efficiency of the proposed method. Further, under this framework, it is shown that the supremal controllable sublanguage can take a simpler form based on the concept of an illegal state set. A state‐based supervisor synthesis procedure is presented, and a simple example is provided. 相似文献
73.
Subei Ou Lianguo Wang Peipei Wang Zhansheng Wang Jihui Huang Donglei Zhou 《矿业科学技术学报(英文版)》2013,23(2):237-244
Based on the importance of fractured rock mass seepage research, in order to analyze seepage flow characteristics of collapse column under the influence of mining, a method by embedding fractured rock mass flow solid coupling relationship into FLAC3D internal flow models is presented according to fluid–solid coupling theory and strength criterion. A calculation model of numerical analysis was established, and the influences of mining pressure and plastic damage to pore water pressure and seepage vector change rule were studied. The results show that collapse column is the main channel of confined water seepage upward. The impact is not big when the workface is away from the collapse column. But when the workface is nearing a collapse column, there will be a seepage channel on a side near the workface, in which seepage vector and head are comparatively large. With workface pushing through collapse column, the seepage channel transfers to the other side of the column. In addition, when the plastic damage area within the collapse column breaks through, a “pipeline flow” will be formed within the column, and seepage field will change remarkably and the possibility of water bursting will be greater. 相似文献
74.
In this research we study the multi-product Economic Lot Scheduling Problem (ELSP) with manufacturing and remanufacturing opportunities. Manufacturing and remanufacturing operations are performed on the same production line. Both manufactured and remanufactured products have the same quality thus they fulfil the same demand stream. Tang and Teunter (2006) firstly studied this type of Economic Lot Scheduling Problem with Returns (ELSPR) and presented a complex algorithm for the optimal solution. More recently Teunter, Tang, and Kaparis (2009) proposed several heuristics to deal with the same problem using more computational efficient approaches. However, both studies have limited the attention to the common cycle policy with the assumption that a single (re)manufacturing lot is used for each item in each cycle. Relaxing the constraint of common cycle time and a single (re)manufacturing lot for each item in each cycle, we propose a simple, easy to implement algorithm, based on Segerstedt (1999), to solve the model using a basic period policy. Several numerical examples show the applicability of the algorithm and the cost savings. 相似文献
75.
Jiawei Ou Feng Xie Parashar Krishnamachari Fabio Pellacini 《Computer Graphics Forum》2012,31(4):1537-1545
We present an importance sampling method for the bidirectional scattering distribution function (bsdf) of hair. Our method is based on the multi‐lobe hair scattering model presented by Sadeghi et al. [ [SPJT10] ]. We reduce noise by drawing samples from a distribution that approximates the bsdf well. Our algorithm is efficient and easy to implement, since the sampling process requires only the evaluation of a few analytic functions, with no significant memory overhead or need for precomputation. We tested our method in a research raytracer and a production renderer based on micropolygon rasterization. We show significant improvements for rendering direct illumination using multiple importance sampling and for rendering indirect illumination using path tracing. 相似文献
76.
To investigate airflow pattern and its impact on particle deposition, finite-volume based computational fluid dynamics (CFD)
simulations were conducted in the diseased triple-bifurcation airways. Computations were carried out for twenty Reynolds numbers
ranging from 100 to 2 000 in the step of 100. Particles in the size range of 1–10 μm were conducted. Two particle deposition
mechanisms (gravitational sedimentation and inertial impaction) were considered. The results indicate that there are strong
relationship between airflow structures and particle deposition patterns. Deposition efficiency is different for different
particles in the whole range of the respiratory rates. Particles in different sizes can deposit at different sites. Smaller
particles can be uniformly deposited at the inside wall of the considered model. Larger particles can be mainly deposited
in the proximal bifurcations. Deposition fraction varies a lot for different inlet Reynolds numbers. For lower Reynolds numbers,
deposition fraction is relatively small and varies a little with varying the diameters. For higher Reynolds numbers, there
is a most efficient diameter for each Reynolds number to target the aerosols at the specific site. 相似文献
77.
研究有限域GF(28)上线性变换对应的正交矩阵具有最佳分支数的判定问题,得到若干相关结果,由此提出了筛选分支数最佳正交矩阵的算法,并使用c语言进行了编程实现。通过从4阶方阵空间内抽取一部分进行穷举搜索,搜索2×316个方阵并一一进行构造和筛选,最终找到4784479个具有最佳分支数5的4阶正交无零元方阵。 相似文献
78.
针对变压器损耗及容量离线检测方法的弊端,提出在线检测方法,构建变压器损耗和容量在线检测实验系统,完成数据采集系统和上位机分析软件的设计,搭建模拟实验平台.实验结果显示,在线测试误差较小. 相似文献
79.
安全性、可靠性是计算机软硬件系统达到用户满意度的重要指标,为了保证其安全,在系统投入使用之前必须要经过严格的安全性测试。提出一种基于FSM(Finate State Machine)和FTA(fault tree analysis)的模型检测的形式化安全性测试方法来验证被测系统的安全性。该方法具有较高的通用性,能详细地分析软件模型可能出现的故障。 相似文献
80.