全文获取类型
收费全文 | 298074篇 |
免费 | 23756篇 |
国内免费 | 14621篇 |
专业分类
电工技术 | 19614篇 |
技术理论 | 58篇 |
综合类 | 40130篇 |
化学工业 | 32076篇 |
金属工艺 | 10375篇 |
机械仪表 | 15543篇 |
建筑科学 | 42359篇 |
矿业工程 | 16831篇 |
能源动力 | 9382篇 |
轻工业 | 17541篇 |
水利工程 | 16086篇 |
石油天然气 | 12290篇 |
武器工业 | 2970篇 |
无线电 | 18305篇 |
一般工业技术 | 22031篇 |
冶金工业 | 17584篇 |
原子能技术 | 3040篇 |
自动化技术 | 40236篇 |
出版年
2024年 | 780篇 |
2023年 | 2847篇 |
2022年 | 5479篇 |
2021年 | 6925篇 |
2020年 | 7152篇 |
2019年 | 6063篇 |
2018年 | 5697篇 |
2017年 | 6811篇 |
2016年 | 8346篇 |
2015年 | 9218篇 |
2014年 | 17069篇 |
2013年 | 15748篇 |
2012年 | 20182篇 |
2011年 | 21692篇 |
2010年 | 17109篇 |
2009年 | 17597篇 |
2008年 | 16300篇 |
2007年 | 21119篇 |
2006年 | 19933篇 |
2005年 | 17296篇 |
2004年 | 14664篇 |
2003年 | 13179篇 |
2002年 | 10852篇 |
2001年 | 9088篇 |
2000年 | 7676篇 |
1999年 | 6271篇 |
1998年 | 4781篇 |
1997年 | 4142篇 |
1996年 | 3823篇 |
1995年 | 3266篇 |
1994年 | 2871篇 |
1993年 | 2160篇 |
1992年 | 1881篇 |
1991年 | 1408篇 |
1990年 | 1237篇 |
1989年 | 1115篇 |
1988年 | 907篇 |
1987年 | 614篇 |
1986年 | 465篇 |
1985年 | 399篇 |
1984年 | 376篇 |
1983年 | 283篇 |
1982年 | 253篇 |
1981年 | 199篇 |
1980年 | 165篇 |
1979年 | 134篇 |
1978年 | 77篇 |
1977年 | 87篇 |
1976年 | 60篇 |
1975年 | 59篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Naoki Yokokawa Yutaro Masuda Eri Amasawa Hirokazu Sugiyama Masahiko Hirao 《Packaging Technology and Science》2020,33(11):445-459
This study presents systematic packaging design tools integrating functional and environmental consequences on product life cycle. To design packaging for sustainability, the trade-offs between functional and environmental aspects of packaging throughout the product life cycle should be considered. However, it is difficult for packaging designers to understand the overall trade-offs because the extent of the design consequences on the entire life cycle of packaging and its contents is unclear. We developed two tools for packaging design: the Life Cycle Association Matrix (LCAM) and the Function Network Diagram (FND). The following three steps, based on literature reviews and interviews with industrial experts, were applied. Firstly, we listed the product functions and design variables related to the functions as the attributes allocated to the product life cycle. Secondly, the attributes were connected appropriately based on causal relationships. Lastly, we identified the factors to support decision making in the packaging design procedure. As a result, the LCAM depicts the design consequences on the life cycle, and the FND determines the stakeholders affected by the design consequences. Two case studies were demonstrated to analyze the trade-offs by using our tools. In the case studies, a liquid laundry detergent bottle and a milk carton were redesigned. The tools identified the design consequences and stakeholders affected by the redesign of the usability and protective function for the detergent and milk cases, respectively. The results showed the significance of understanding the design consequences on the product life cycle by integrating the functional and environmental aspects. 相似文献
72.
Reliability based criteria are quite popular for optimal sensor network design. We present a modified definition of system reliability for sensor network design for two applications: reliable estimation of variables in a steady state linear flow process, and reliable fault detection and diagnosis for any process. Unlike the weakest-link based definition of system reliability in the literature, the proposed definition considers the entire system and is consistent with the reliability concept used in classical reliability literature. For each application, dual approaches for defining system reliability are proposed, and their analogy with the reliability problem in the classical reliability literature is established. Using examples and stochastic simulations, the advantage of using the proposed system reliability in contrast to the existing definition is illustrated. Part II of this series of articles presents methods for efficient generation of the system reliability function and its use in optimization-based approaches for designing optimal sensor networks. 相似文献
73.
针对互联网中恶意域名攻击事件频发,现有域名检测方法实时性不强的问题,提出一种基于词法特征的恶意域名快速检测算法。该算法根据恶意域名的特点,首先将所有待测域名按照长度进行正则化处理后赋予权值;然后利用聚类算法将待测域名划分成多个小组,并利用改进的堆排序算法按照组内权值总和计算各域名小组优先级,根据优先级降序依次计算各域名小组中每一域名与黑名单上域名之间的编辑距离;最后依据编辑距离值快速判定恶意域名。算法运行结果表明,基于词法特征的恶意域名快速检测算法与单一使用域名语义和单一使用域名词法的恶意域名检测算法相比,准确率分别提高1.7%与2.5%,检测速率分别提高13.9%与6.8%,具有更高的准确率和实时性。 相似文献
74.
与传统比例-积分-微分(PID)控制方法相比,滑模控制(SMC)方法可以比较容易地将不确定性纳入控制器设计中,从而增强系统的鲁棒性。探索了SMC技术在运载器主动段姿态控制中的工程应用,首先通过分析基于趋近律的SMC系统,提出了降低不连续切换项系数的需求,然后研究了基于干扰上界的SMC方法。三通道小偏差仿真结果验证了两种方法的控制效果,表明第2种控制器的鲁棒性更好,稳态误差小,同时发动机喷管摆角需求较小。 相似文献
75.
Ali Maghami Dominik Schillinger 《International journal for numerical methods in engineering》2020,121(5):967-989
We explore a truncation error criterion to steer adaptive step length refinement and coarsening in incremental-iterative path following procedures, applied to problems in large-deformation structural mechanics. Elaborating on ideas proposed by Bergan and collaborators in the 1970s, we first describe an easily computable scalar stiffness parameter whose sign and rate of change provide reliable information on the local behavior and complexity of the equilibrium path. We then derive a simple scaling law that adaptively adjusts the length of the next step based on the rate of change of the stiffness parameter at previous points on the path. We show that this scaling is equivalent to keeping a local truncation error constant in each step. We demonstrate with numerical examples that our adaptive method follows a path with a significantly reduced number of points compared to an analysis with uniform step length of the same fidelity level. A comparison with Abaqus illustrates that the truncation error criterion effectively concentrates points around the smallest-scale features of the path, which is generally not possible with automatic incrementation solely based on local convergence properties. 相似文献
76.
泛在电力物联网是物联网在电力领域的具体体现,建设泛在电力物联网是推进"三型两网"建设的关键环节,也是实现能源转型的必要手段。阐述了泛在电力物联网的定义,从供电公司角度出发,根据北京经济技术开发区实际情况,讨论了依托地区特点的泛在电力物联网实施策略和实际应用场景,分析了可能遇到的问题。得出结论:随着泛在电力物联网的深入建设,供电公司能够为电力客户提供多元化服务,提高客户满意度;地市供电公司能够依托泛在电力物联网开展更多电力相关业务;泛在电力物联网的安全性、实用性、有效性是发展面临的首要问题。 相似文献
77.
78.
《Calphad》2020
This publication contains the thermodynamic results received by the drop calorimetry method. The experiments were conducted for four different cross sections, at the temperature of 1080 K. The investigated alloys were as follows: (Ga0.75Li0.25)1-xGex, (Ge0.50Li0.50)1-xGax, (Ga0.50Li0.50)1-xGex, (Ga0.25Li0.75)1-xGex. The mixing enthalpy changes measured for all four cross sections of the Ga-Ge-Li system are characterized by negative deviations from the ideal solutions. The Muggianu model with the ternary interaction parameters was applied to elaborate the experimental data of the mixing enthalpy change with the use of the optimized thermodynamic parameters of the binary systems available in the literature. 相似文献
79.
自工业革命以来人类社会的发展和经济的建设就离不开对矿产资源的使用。我国自改革开放以来,经济得到了前所未有的飞速发展,人民的生活水平日益提高,但经济高速发展的背后,存在着对矿产资源过度开采和使用的问题。矿产资源的不合理开采和使用对原有的自然环境造成了严重的破坏,为了改善此现状,对矿山地质环境的恢复治理技术的研究就至关重要。本文就矿山地质恢复治理的意义进行阐述,进一步对其方法进行探究,最终提出有关的措施和方法。 相似文献
80.
通过分析A公司在研发项目范围管理中所存在问题,提出研发项目范围管理的方法及其在C产品的应用实例,通过运用研发项目范围管理的工具和方法,改善产品开发流程,从而缩短新产品开发周期,提高响应市场的速度,并提高企业研发项目的管理能力。 相似文献