全文获取类型
收费全文 | 250381篇 |
免费 | 23128篇 |
国内免费 | 13455篇 |
专业分类
电工技术 | 17780篇 |
技术理论 | 15篇 |
综合类 | 18289篇 |
化学工业 | 38505篇 |
金属工艺 | 14237篇 |
机械仪表 | 16411篇 |
建筑科学 | 20226篇 |
矿业工程 | 7638篇 |
能源动力 | 7452篇 |
轻工业 | 18472篇 |
水利工程 | 5196篇 |
石油天然气 | 13690篇 |
武器工业 | 2317篇 |
无线电 | 29868篇 |
一般工业技术 | 27821篇 |
冶金工业 | 11334篇 |
原子能技术 | 2843篇 |
自动化技术 | 34870篇 |
出版年
2024年 | 1242篇 |
2023年 | 4407篇 |
2022年 | 8459篇 |
2021年 | 11246篇 |
2020年 | 8531篇 |
2019年 | 6669篇 |
2018年 | 7616篇 |
2017年 | 8533篇 |
2016年 | 7659篇 |
2015年 | 10470篇 |
2014年 | 13236篇 |
2013年 | 15462篇 |
2012年 | 17389篇 |
2011年 | 18199篇 |
2010年 | 16100篇 |
2009年 | 15378篇 |
2008年 | 15023篇 |
2007年 | 13800篇 |
2006年 | 13851篇 |
2005年 | 11599篇 |
2004年 | 8259篇 |
2003年 | 7296篇 |
2002年 | 7547篇 |
2001年 | 6576篇 |
2000年 | 5290篇 |
1999年 | 5287篇 |
1998年 | 4061篇 |
1997年 | 3420篇 |
1996年 | 3153篇 |
1995年 | 2563篇 |
1994年 | 2090篇 |
1993年 | 1492篇 |
1992年 | 1201篇 |
1991年 | 910篇 |
1990年 | 650篇 |
1989年 | 543篇 |
1988年 | 410篇 |
1987年 | 290篇 |
1986年 | 238篇 |
1985年 | 136篇 |
1984年 | 128篇 |
1983年 | 90篇 |
1982年 | 98篇 |
1981年 | 83篇 |
1980年 | 74篇 |
1979年 | 42篇 |
1978年 | 27篇 |
1977年 | 24篇 |
1976年 | 26篇 |
1951年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 25 毫秒
61.
In this study, 16 cases of unilateral alveolar cleft with cleft lip and palate were repaired with autografts of cancellous bone (13 cases) or hydroxyapatite (3 cases). The grafts were covered by reflected mucoperiosteal flaps and a mucosal flap from the upper lip. Twelve of the thirteen cases were followed up for 1-5 years. Nine of whom using cancellous bone had bony continuity of the maxilla and 7 cases erupted permanent maxillary canines within the area of autografts. None of the 3 cases using hydroxyapatite erupted a canine tooth. The results showed that autograft was better than hydroxyapatite in terms of maxillary canine eruption. 相似文献
62.
The coal filter cake is a product of fine coal after floatation which has an ash content of 7-13%, water content of 30±2%, and a particle size of less than 1 mm. The ash content was measured by the intensity of the single backscattered gamma-ray, and its accuracy is mainly dependent on the energy of the gamma-ray. The 238Pu low energy photon source is selected in this work. The energy of its gamma-ray is 15 keV, which can result not only in the best sensitivity, but also in the lowest contribution to the environment radiation. The root mean square deviation of the ash measurement is±0.33% (±1σ). 相似文献
63.
Yung-Chung Chang Wei-Tzen Yang Chun-Chang Liu 《Power Systems, IEEE Transactions on》1994,9(3):1665-1671
A method is proposed which avoids many limitations associated with traditional B-coefficient loss coefficient calculation. The proposed method, unlike the traditional B-coefficient method, is very fast and can handle line outages. The method utilizes network sensitivity factors which are established from DC load flow solutions, Line outage distribution factors (ODFs) are formulated using changes in network power generations to simulate the outaged line from the network. The method avoids the use of complicated reference frame transformations based upon Kron's tenser analysis. The necessity of data normalization used in least squares and the evaluation of the slope of &thetas;j versus PGn is not necessary with the proposed method. Using IEEE standard 14-bus and 30-bus systems, the method's results are compared against results obtained from an AC load flow program (LFED). The method's solution speed is compared to that of the LFED method, the base case database method and the conventional B-coefficient method based on Ajn-factor. The proposed method is easy to implement and, when compared to other methods, has exhibited good accuracy and rapid execution times. The method is well suited to online dispatch applications 相似文献
64.
Jian Ma 《Education, IEEE Transactions on》1996,39(3):388-393
Assessment is an important task in problem-based learning (PBL). It has a strong influence on students' approaches to learning and their outcomes. In order to provide an open and fair method of PBL assessment, a group decision support system (GDSS) has been developed. The system uses mathematical decision methods for collecting assessment criteria and their appropriate weights, and databases for storing students' details and data on the assessment criteria. It integrates databases with model bases in a cooperative decision-making environment and is implemented on a client-server platform using a relational database management system. The GDSS has been developed and used to improve the efficiency and quality of assessing students' PBL outcomes 相似文献
65.
Yufei Tao Xiaokui Xiao Jian Pei 《Knowledge and Data Engineering, IEEE Transactions on》2007,19(8):1072-1088
Skyline and top-k queries are two popular operations for preference retrieval. In practice, applications that require these operations usually provide numerous candidate attributes, whereas, depending on their interests, users may issue queries regarding different subsets of the dimensions. The existing algorithms are inadequate for subspace skyline/top-k search because they have at least one of the following defects: 1) they require scanning the entire database at least once, 2) they are optimized for one subspace but incur significant overhead for other subspaces, or 3) they demand expensive maintenance cost or space consumption. In this paper, we propose a technique SUBSKY, which settles both types of queries by using purely relational technologies. The core of SUBSKY is a transformation that converts multidimensional data to one-dimensional (1D) values. These values are indexed by a simple B-tree, which allows us to answer subspace queries by accessing a fraction of the database. SUBSKY entails low maintenance overhead, which equals the cost of updating a traditional B-tree. Extensive experiments with real data confirm that our technique outperforms alternative solutions significantly in both efficiency and scalability. 相似文献
66.
67.
68.
69.
本文提出采用高分子有机材料配合,生产石膏制品防水防潮剂的生产方法和工艺。该剂还可以应用到氧化镁系列板材,同时提出开发珠光或彩色防水防潮剂,能达到满足的装饰效果,值提开发推广。 相似文献
70.
��Consulting the relevant documents at home and abroad,the author finisheid the derivation of quations about critical flow quantity,critical flow rate,contrast flow quantity,contrast flow rate which are necessary to the continuous water withdrawal through the flow string with different diameters and the rational flow string formula that should be selected when the contrust parameter1.The author also works out the solving programme for TI-59 computer and designs and draws up the nomograrn of mathematical mode.The evident economical results have been obtained from practice of optimizing the flow string for water withdrawal in gas production in Southern Sichuan and from studying the gas-water two-phase flow characteristics through vertical pipe. 相似文献