全文获取类型
收费全文 | 45049篇 |
免费 | 5004篇 |
国内免费 | 2323篇 |
专业分类
电工技术 | 3081篇 |
技术理论 | 3篇 |
综合类 | 5476篇 |
化学工业 | 2373篇 |
金属工艺 | 780篇 |
机械仪表 | 2027篇 |
建筑科学 | 5722篇 |
矿业工程 | 1960篇 |
能源动力 | 1176篇 |
轻工业 | 5949篇 |
水利工程 | 2916篇 |
石油天然气 | 4330篇 |
武器工业 | 875篇 |
无线电 | 2614篇 |
一般工业技术 | 2952篇 |
冶金工业 | 2637篇 |
原子能技术 | 320篇 |
自动化技术 | 7185篇 |
出版年
2024年 | 240篇 |
2023年 | 769篇 |
2022年 | 1430篇 |
2021年 | 1757篇 |
2020年 | 1757篇 |
2019年 | 1457篇 |
2018年 | 1342篇 |
2017年 | 1511篇 |
2016年 | 1796篇 |
2015年 | 1834篇 |
2014年 | 3015篇 |
2013年 | 2791篇 |
2012年 | 3467篇 |
2011年 | 3659篇 |
2010年 | 2669篇 |
2009年 | 2725篇 |
2008年 | 2502篇 |
2007年 | 2952篇 |
2006年 | 2671篇 |
2005年 | 2353篇 |
2004年 | 1853篇 |
2003年 | 1564篇 |
2002年 | 1146篇 |
2001年 | 977篇 |
2000年 | 720篇 |
1999年 | 610篇 |
1998年 | 435篇 |
1997年 | 412篇 |
1996年 | 339篇 |
1995年 | 280篇 |
1994年 | 215篇 |
1993年 | 173篇 |
1992年 | 109篇 |
1991年 | 103篇 |
1990年 | 79篇 |
1989年 | 96篇 |
1988年 | 52篇 |
1987年 | 46篇 |
1986年 | 45篇 |
1985年 | 41篇 |
1984年 | 46篇 |
1983年 | 47篇 |
1982年 | 37篇 |
1981年 | 20篇 |
1980年 | 16篇 |
1979年 | 17篇 |
1966年 | 14篇 |
1963年 | 17篇 |
1961年 | 13篇 |
1958年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
文章通过对五口井的现场应用介绍,阐述了快速色谱分析技术在油气层识别和解释方面的准确性,探讨了该技术在薄油气层的发现和评价、快速钻进条件下油气层的发现、对油气层全烃组份变化的统一、水平井的地质导向以及排除钻井液添加荆对油气显示的影响五个方面的优势,从而论证了快速色谱分析技术在油气勘探中的应用价值。 相似文献
83.
Conceptual damage-sensitive features for structural health monitoring: Laboratory and field demonstrations 总被引:2,自引:0,他引:2
F. Necati Catbas Mustafa Gul Jason L. Burkett 《Mechanical Systems and Signal Processing》2008,22(7):1650-1669
The use of damage-sensitive features to evaluate structural condition or health is a very critical aspect of structural health monitoring. The purpose of this paper is to investigate the potential of two different damage-sensitive features for detecting damage. Different damage scenarios are simulated on a large-scale laboratory structure and a three-span highway bridge for demonstration. The features presented in this paper are the modal flexibility-based deflection and curvature both of which are obtained directly from dynamic properties. In the literature, flexibility associated with mode shapes and mode shapes curvatures have been mostly explored. In this study, multi-input–multi-output dynamic data are used to obtain modal flexibility, which is a close approximation to the actual flexibility. A main novelty is that the curvature is calculated from the deflected shapes using the modal flexibility as opposed to using modal vectors. In this paper, the theory of the methodology is explained and then experimental studies and results are presented. For the experimental studies, the laboratory specimen and the three-span bridge were gradually damaged. It is shown that both deflection and curvature are conceptual and physically meaningful features for damage detection and localization. The issues and the requirements for these features to perform successfully are also presented. 相似文献
84.
保健食品行业GMP的实施有利HACCP的应用推广。本文应用HACCP于传统保健食品西洋参口服液生产过程中,将生产及加工过程中危害因素降最低限度,以确保产品的质量与安全。 相似文献
85.
There is widespread application of indicators to the assessment of environmental condition of streams. These indicators are intended for use by managers in making various comparative and absolute assessments and often have a role in resource allocation and performance assessment. Therefore, the problem of formally defining confidence in the results is important but difficult because the sampling strategies used are commonly based on a compromise between the requirements of statistical rigour and the pragmatic issues of access and resources. It is rare to see this compromise explicitly considered and consequently there is seldom quantification of the uncertainty that could affect the confidence a manager has in an indicator. In this paper, we present a method for quantitatively assessing the tradeoffs between sampling density and uncertainty in meeting various monitoring objectives. Assessments using judgement‐based representative reaches are shown to be unreliable; instead a sampling approach is recommended based on the random selection of measuring sites. A detailed dataset was collected along two streams in Victoria, Australia, and the effect of sampling density was assessed by subsampling from this dataset with precision related to the number of sites assessed per reach length and the intensity of the sampling at each site. The sampling scheme to achieve a given precision is shown to depend on the monitoring objective. In particular, three objectives were considered: (1) making a baseline assessment of current condition; (2) change detection; and (3) detection of a critical threshold in condition. Change detection is shown to be more demanding than assessing baseline condition with additional sampling effort required to achieve the same precision. Sampling to detect a critical threshold depends on nominating acceptable values of Type I and II error and the size of the effect to be detected. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
86.
�����������������������������ܿ��������о� 总被引:5,自引:1,他引:4
白马庙气田蓬莱镇气藏储层致密 ,孔隙结构复杂 ,非均质性强 ,单井产能低 ,研究储层特征和受控因素 ,加强储层改造方是气藏效益开发的出路。储层精细研究揭示 ,气井产能受沉积相和构造条件控制 ;高、中产井与大而厚、物性好的河口坝、河道砂坝沉积微相有关 ,纵向上具很强的层段性 ,主产层集中在Ⅳ~③、Ⅲ~③两套砂组 ,其钻探成功率分别达 82 %和 10 0 % ;平面上多分布于主体构造和东南鼻状突起 ,二者高、中产能井分别占 30 %和 70 %。在深入的地质研究和储层压裂评层选井的基础上 ,采用多层打开、分层压裂、多层合采的方法可提高气井产能 ,并形成了一套行之有效的压裂评层选井的综合配套技术。采用该技术优选出 19口井 ,已实施 5口井全获成功 ,气产量成倍或十几倍增加 ,其中白浅 4 5井气无阻流量高达 18× 10 4m3 /d ,白浅 38井投产 16 5d净增产值 10 0余万元 相似文献
87.
We have fabricated and tested a high-Tc dc-SQUID magnetometer patterned on a YBCO thin film deposited on a SrTiO3 bicrystal substrate. The measurement of noise spectrum at 77 K showed that the magnetometer has a white noise of 333 fT/Hz1/2 without superconducting shield, corresponding to a flux sensitivity of 14.5 μΦ0/Hz1/2. We constructed a test system for eddy current non-destructive evaluation of conducting aluminum plates by using the magnetometer. Flaws over 10 mm below the surface can be clearly identified. By mapping the magnetic field distribution, we can locate the flaw position. The signals caused by flaw were expanded due to the use of double-D type driving coil with a wider central slit. The experimental results confirmed that this test system could operate in a magnetic unshielded environment. 相似文献
88.
Rudolf Habison 《International Journal of Project Management》1985,3(3):178-181
Meeting time and cost objectives in complex projects involves specific problems and risks. An attempt is made to analyse the components of total cost increase of a project caused by time delay. An outline is given as to how these considerations can be used to estimate cost increases in investors' decision situations as well as to ascertain fair contractual penalties and claims for compensation and for the evaluation of justified project acceleration costs. 相似文献
89.
1 Introduction Acquiring knowledge is constantly encountered in the mechanical product evaluation process, such as during setting up evaluation index system and determining evaluation knowledge. The most useful expression form of knowledge is production rule whenever concerning the field knowledge or decision knowledge. How to effectively acquire and express the knowledge becomes the issue that the evaluation work must solve at first. One of an important application of the rough set theory is … 相似文献
90.
It is well recognized that performance changes over time. However, the effect of these changes on overall assessments of performance is largely unknown. In a laboratory experiment, we examined the influence of salient Gestalt characteristics of a dynamic performance profile on supervisory ratings. We manipulated performance trend (flat, linear-improving, linear-deteriorating, U-shaped, and ∩-shaped), performance variation (small, large), and performance mean (negative, zero, positive) within subjects and display format (graphic, tabular) between subjects. Participants received and evaluated information about the weekly performance of different employees over a simulated 26-week period. Results showed strong main effects on performance ratings of both performance mean and performance trend, as well as interactions with display format. Theoretical and practical implications of the results are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献