全文获取类型
收费全文 | 277546篇 |
免费 | 20763篇 |
国内免费 | 14174篇 |
专业分类
电工技术 | 17111篇 |
技术理论 | 51篇 |
综合类 | 37000篇 |
化学工业 | 29964篇 |
金属工艺 | 10798篇 |
机械仪表 | 16776篇 |
建筑科学 | 38337篇 |
矿业工程 | 15223篇 |
能源动力 | 8480篇 |
轻工业 | 14758篇 |
水利工程 | 14150篇 |
石油天然气 | 11757篇 |
武器工业 | 2592篇 |
无线电 | 17675篇 |
一般工业技术 | 19525篇 |
冶金工业 | 15782篇 |
原子能技术 | 2738篇 |
自动化技术 | 39766篇 |
出版年
2024年 | 828篇 |
2023年 | 2614篇 |
2022年 | 5004篇 |
2021年 | 6056篇 |
2020年 | 6347篇 |
2019年 | 5402篇 |
2018年 | 5114篇 |
2017年 | 6231篇 |
2016年 | 7416篇 |
2015年 | 8317篇 |
2014年 | 15340篇 |
2013年 | 14291篇 |
2012年 | 17984篇 |
2011年 | 19534篇 |
2010年 | 15433篇 |
2009年 | 16098篇 |
2008年 | 15166篇 |
2007年 | 19808篇 |
2006年 | 18805篇 |
2005年 | 16459篇 |
2004年 | 14054篇 |
2003年 | 12790篇 |
2002年 | 10463篇 |
2001年 | 8889篇 |
2000年 | 7446篇 |
1999年 | 6159篇 |
1998年 | 4698篇 |
1997年 | 4133篇 |
1996年 | 3780篇 |
1995年 | 3204篇 |
1994年 | 2812篇 |
1993年 | 2081篇 |
1992年 | 1871篇 |
1991年 | 1372篇 |
1990年 | 1207篇 |
1989年 | 1069篇 |
1988年 | 850篇 |
1987年 | 576篇 |
1986年 | 438篇 |
1985年 | 368篇 |
1984年 | 342篇 |
1983年 | 252篇 |
1982年 | 221篇 |
1981年 | 172篇 |
1980年 | 136篇 |
1979年 | 112篇 |
1978年 | 63篇 |
1977年 | 73篇 |
1976年 | 57篇 |
1975年 | 55篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
热镀锌板(卷)工程设计中的环境保护问题 总被引:1,自引:0,他引:1
对热镀锌板(卷)的生产工艺、主要生产设备进行了简要介绍,并就其污染源(工序)、生产过程中产生的污染物及其控制措施进行了评述,同时就设计和生产中宜注意的几个环保问题进行了分析。 相似文献
12.
13.
A method of measuring and identifying the static parameters of a bipolar transistor is considered. The characteristic of the transistor, from which the parameters of the model are determined, is chosen depending on what group the calculated parameters belong to. The characteristics are measured in such a way that the equations of the model describing them can be reduced to the simplest form. 相似文献
14.
This article, the first of three articles on the synthesis of rice processing plants, focuses on the development of simplified mathematical models necessary for use in optimizing rice processing plants. The second concentrates on the optimal synthesis of a rice plant and the third on the sensitivity of the optimization to uncertainty in model parameters. Existing models for rice processing unit operations are not suitable for flowsheet optimization and new models need to be developed to overcome numerical difficulties that occur in optimization applications, specifically in mixed integer nonlinear programming (MINLP) applications. Simplified models of the drying, cooling, and tempering units are developed. In addition head rice yield models, used as a quality indicator, energy consumption, and economic models were also developed. Naturally, the new models exhibit some mismatch with respect to the existing models from which they were developed. However, a sensitivity analysis, presented in Part III, has shown that the optimal flowsheet structure was not sensitive to a lack of fit between the simplified and complex models. The simplified models were found adequate to be appropriate for use at the synthesis stage. 相似文献
15.
The problem of operating freeze drying of pharmaceutical products in vials placed in trays of a freeze dryer to remove free water (in frozen state) at a minimum time was formulated as an optimal control problem. Two different types of freeze dryer designs were considered. In type I freeze dryer design, upper and lower plate temperatures were controlled together, while in type II freeze dryer design, upper and lower plate temperatures were controlled independently. The heat input to the material being dried and the drying chamber pressure were considered as control variables. Constraints were placed on the system state variables by the melting and scorch temperatures during primary drying stage. Necessary conditions of optimality for the primary drying stage of freeze drying process in vials are derived and presented. Furthermore, an approach for constructing the optimal control policies that would minimize the drying time for the primary drying stage was given. In order to analyze optimal control policy for the primary drying stage of the freeze-drying process in vials, a rigorous multi-dimensional unsteady state mathematical model was used. The theoretical approach presented in this work was applied in the freeze drying of skim milk. Significant reductions in the drying times of primary drying stage of freeze drying process in vials were obtained, as compared to the drying times obtained from conventional operational policies. 相似文献
16.
Introduces the current issue of the American Psychologist, which examines the ramifications of the Brown vs. Board of Education decision and its sequelae over the last 50 years, with a special focus on the mixed role of psychological research and practice. Despite the great strides toward a more just society since May 17, 1954, inequities remain in schooling, in social relations, and in economic opportunity. How will history judge American psychology 50 years from now vis-a-vis the possibilities it helped create via Brown? The articles in this special issue suggest several important directions of research and action our field will need to take if the verdict of history is to be a positive one. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
17.
从"天人合一"到"物我合一"——设计艺术中我国观念的转化 总被引:1,自引:1,他引:0
通过我国设计艺术中人与自然以及人与物古今观念的对比,试图分析这种观念的转化产生的深层社会背景和对设计的影响。 相似文献
18.
套保稠油油田火烧油层可行性分析 总被引:2,自引:1,他引:1
从火烧油层的筛选标准、实际地质条件及室内物理模拟实验入手,对该油田火烧可行性进行了分析。分析结果认为,套保油田进行火烧总体上是可行的,在实际火烧时应避开底水的影响,火烧区域应选在构造高部位或仅烧其主力层。 相似文献
19.
大型连杆流线简易试验方法 总被引:1,自引:1,他引:0
程里 《理化检验(物理分册)》2004,40(9):457-458
介绍了一种大型连杆流线的简易试验方法及其评价原则。该方法可清晰显示流线,并适合任何尺寸和形状的锻造连杆的流线试验。 相似文献
20.
The scale along the coordinate axes in the equations of motion hitherto used for an H-maser (in relative units) is shown to depend on Q as the quality factor for an H-maser. This hinders both analysis of the operation of the H-maser and optimization of its parameters. The modified equations of motion proposed here do not have that shortcoming. We determine the atomic flux into the bulb that gives the H-maser the best metrological characteristics. 相似文献