全文获取类型
收费全文 | 105107篇 |
免费 | 7435篇 |
国内免费 | 4306篇 |
专业分类
电工技术 | 5989篇 |
技术理论 | 3篇 |
综合类 | 5910篇 |
化学工业 | 13320篇 |
金属工艺 | 4321篇 |
机械仪表 | 5068篇 |
建筑科学 | 6150篇 |
矿业工程 | 2038篇 |
能源动力 | 2204篇 |
轻工业 | 6822篇 |
水利工程 | 2106篇 |
石油天然气 | 2738篇 |
武器工业 | 703篇 |
无线电 | 9566篇 |
一般工业技术 | 10219篇 |
冶金工业 | 23556篇 |
原子能技术 | 1009篇 |
自动化技术 | 15126篇 |
出版年
2024年 | 428篇 |
2023年 | 1280篇 |
2022年 | 2275篇 |
2021年 | 3088篇 |
2020年 | 2266篇 |
2019年 | 1769篇 |
2018年 | 2218篇 |
2017年 | 2736篇 |
2016年 | 2952篇 |
2015年 | 3457篇 |
2014年 | 3745篇 |
2013年 | 4326篇 |
2012年 | 6841篇 |
2011年 | 7296篇 |
2010年 | 5074篇 |
2009年 | 5092篇 |
2008年 | 4976篇 |
2007年 | 4547篇 |
2006年 | 4270篇 |
2005年 | 6279篇 |
2004年 | 4681篇 |
2003年 | 3887篇 |
2002年 | 2989篇 |
2001年 | 2626篇 |
2000年 | 1693篇 |
1999年 | 1625篇 |
1998年 | 6783篇 |
1997年 | 4336篇 |
1996年 | 2933篇 |
1995年 | 1796篇 |
1994年 | 1334篇 |
1993年 | 1289篇 |
1992年 | 413篇 |
1991年 | 425篇 |
1990年 | 386篇 |
1989年 | 352篇 |
1988年 | 347篇 |
1987年 | 262篇 |
1986年 | 219篇 |
1985年 | 189篇 |
1984年 | 83篇 |
1983年 | 88篇 |
1982年 | 142篇 |
1981年 | 185篇 |
1980年 | 204篇 |
1979年 | 65篇 |
1978年 | 97篇 |
1977年 | 608篇 |
1976年 | 1320篇 |
1975年 | 98篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
From an experimental and theoretical investigation of the continuity of influent inorganic suspended solids (ISS) along the links connecting the primary settling tank (PST), fully aerobic or N removal activated sludge (AS) and anaerobic and aerobic sludge digestion unit operations, it was found that the influent wastewater (fixed) ISS concentration is conserved through primary sludge anaerobic digestion, activated sludge and aerobic digestion unit operations. However, the measured ISS flux at different stages through a series of wastewater treatment plant (WWTP) unit operations is not equal to the influent ISS flux, because the ordinary heterotrophic organisms (OHO) biomass contributes to the ISS flux by differing amounts depending on the active fraction of the VSS solids at that stage. 相似文献
2.
Role stress has received a lot of research attention in psychological, sociological, and organizational studies over the last several decades. Based on a literature review of about 300 journal articles, this article examines prominent consequences of role stress. Specific focus is on researching differences in relationships between facets of role stress (i.e., role ambiguity, role conflict, and role overload) and frequently cited consequences using techniques of meta-analysis. Findings indicate that each role stress facet has a different relationship with the eight consequences studied. Role stress research can benefit from looking at each facet individually in addition to role stress generally. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
3.
易前 《水利水电工程设计》2006,25(4):12-13
镜面混凝土是水电工程建设中新兴的一门施工技术,在乌江索风营水电站地下厂房岩锚梁混凝土施工中采用了镜面混凝土,这在技术上是一次大胆的尝试和创新,既满足了功能上的要求,同时也达到了美观和装饰地下厂房的效果,为今后水电工程施工中广泛采用镜面混凝土技术提供了样本和宝贵经验。 相似文献
4.
5.
W. Shieh R. Hui X. Yi 《Photonics Technology Letters, IEEE》2006,18(10):1122-1124
We perform a systematic measurement of the degree-of-polarization (DOP) and eye-closure penalty for optical signals with orthogonal polarizations. We find that the symmetry of DOP is maintained for the orthogonal polarizations under both first and higher order polarization-mode dispersion (PMD), whereas the symmetry of eye-closure penalty is broken under second-order PMD. An orthogonal polarization pair can have large disparity of eye-closure penalty despite an identical DOP. We also demonstrate a novel approach to estimate the maximum eye-closure penalty asymmetry with three orthogonal polarizations on the Poincare/spl acute/ sphere. 相似文献
6.
The objective of this study was to compare methane production and characteristics of digested material in anaerobic digestion concepts according to the Animal By-Products Regulation (ABP-Regulation) of the EC (hygienisation of biowaste for 1 hour at 70 degrees C, particle size < 12 mm) and Finnish national regulations (treatment temperature 55 degrees C, feeding interval 24 h, hydraulic retention time (HRT) 20 d, particle size < 40 mm) and with small variations in treatment methods for treating manure and biowaste. Moreover, the survival of three different salmonella bacteria in these processes was studied. Hygienisation of biowaste prior to digestion at 35 degrees C enhanced methane production by 14-18% compared to similar treatment without hygienisation. The differences in treatment temperature, HRT and hygienisation of biowaste prior to digestion did not significantly affect the characteristics of digested material. The concepts according to the ABP-Regulation and Finnish national regulations were effective in destroying salmonella bacteria to an undetectable level. 相似文献
7.
8.
On the effect of spatial variances in historical rainfall time series to CSO performance evaluation.
Historical, high-resolution rain series are the backbone of modern combined sewer overflow (CSO) structure design. These rain series are the input to the computational estimation of the performance of the measures with respect to CSO pollution abatement. However, those historical precipitation measurements are available at only a few locations. Frequently rain series have to be used from gauging stations at a significant distance. In order to judge and to compensate for this influence an estimate between rain characteristics and combined sewer outflow (CSO) performance indicators would be useful. In this paper such correlations have been sought for a collection of 37 rain series covering large areas of Europe. It was found that the mean annual rain volume can explain most of the variances for the performance indicators Number of overflows and CSO volume. For explaining the spatial differences in the efficiency of the CSO structure another rain characteristic, i.e. the maximum event with a return period of one year, is to be used. 相似文献
9.
宽带DDS跳频源设计 总被引:1,自引:0,他引:1
直接数字合成(DDS)简单可靠、控制方便,具有很高的频率分辨率,高速转换,非常适合快速跳频的要求。在对DDS基本原理进行了简要介绍和分析后,提出宽带跳频源设计方案。 相似文献
10.
Data mining extracts implicit, previously unknown, and potentially useful information from databases. Many approaches have been proposed to extract information, and one of the most important ones is finding association rules. Although a large amount of research has been devoted to this subject, none of it finds association rules from directed acyclic graph (DAG) data. Without such a mining method, the hidden knowledge, if any, cannot be discovered from the databases storing DAG data such as family genealogy profiles, product structures, XML documents, task precedence relations, and course structures. In this article, we define a new kind of association rule in DAG databases called the predecessor–successor rule, where a node x is a predecessor of another node y if we can find a path in DAG where x appears before y. The predecessor–successor rules enable us to observe how the characteristics of the predecessors influence the successors. An approach containing four stages is proposed to discover the predecessor–successor rules. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 621–637, 2006. 相似文献