全文获取类型
收费全文 | 325932篇 |
免费 | 37187篇 |
国内免费 | 31873篇 |
专业分类
电工技术 | 28925篇 |
技术理论 | 10篇 |
综合类 | 30282篇 |
化学工业 | 54566篇 |
金属工艺 | 13479篇 |
机械仪表 | 21528篇 |
建筑科学 | 26007篇 |
矿业工程 | 8541篇 |
能源动力 | 10441篇 |
轻工业 | 21782篇 |
水利工程 | 8624篇 |
石油天然气 | 10004篇 |
武器工业 | 3799篇 |
无线电 | 39255篇 |
一般工业技术 | 37874篇 |
冶金工业 | 9538篇 |
原子能技术 | 5379篇 |
自动化技术 | 64958篇 |
出版年
2024年 | 1602篇 |
2023年 | 5085篇 |
2022年 | 9311篇 |
2021年 | 10779篇 |
2020年 | 10904篇 |
2019年 | 9708篇 |
2018年 | 9194篇 |
2017年 | 12116篇 |
2016年 | 13289篇 |
2015年 | 14592篇 |
2014年 | 17633篇 |
2013年 | 20278篇 |
2012年 | 24601篇 |
2011年 | 26508篇 |
2010年 | 19729篇 |
2009年 | 19880篇 |
2008年 | 20374篇 |
2007年 | 23681篇 |
2006年 | 21799篇 |
2005年 | 18592篇 |
2004年 | 15614篇 |
2003年 | 12712篇 |
2002年 | 10105篇 |
2001年 | 7994篇 |
2000年 | 6865篇 |
1999年 | 5848篇 |
1998年 | 4707篇 |
1997年 | 3948篇 |
1996年 | 3244篇 |
1995年 | 2828篇 |
1994年 | 2408篇 |
1993年 | 1768篇 |
1992年 | 1513篇 |
1991年 | 1141篇 |
1990年 | 957篇 |
1989年 | 819篇 |
1988年 | 608篇 |
1987年 | 364篇 |
1986年 | 322篇 |
1985年 | 285篇 |
1984年 | 260篇 |
1983年 | 172篇 |
1982年 | 227篇 |
1981年 | 142篇 |
1980年 | 123篇 |
1979年 | 59篇 |
1978年 | 32篇 |
1977年 | 36篇 |
1975年 | 26篇 |
1959年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 25 毫秒
41.
42.
Digital technology becomes more powerful, intelligent, pervasive and ubiquitous. Ethical aspects of this development have not yet drawn the appropriate attention of researchers and engineers. This paper presents an instrument that aims at measuring the individual ethical position with regard to the design and development of computer software. The development of the Epos tool was based on two data collections. The data of the first survey (n1 = 147 participants) were used to select items and to determine the factorial structure of the questionnaire. Results show that the Epos instrument reliably assesses peoples’ ethical opinion with respect to five central components: (1) regulation, (2) data privacy, (3) domain specific knowledge, (4) societal responsibility and (5) company responsibility. In the second survey, we determined the stability of the instruments factor structure by assessing a sample of n2?=?196 participants. A confirmatory factor analysis (CFA) supported the initial factor structure. Next steps and further implications are discussed regarding the final version of the questionnaire. 相似文献
43.
现有毒品滥用流行病模型假设吸毒者康复后对毒品拥有永久"免疫"力,而忽视了其再次成为毒品易感者的可能性。针对这一问题,通过考虑社区治疗和隔离治疗两种措施,分析了毒品滥用人群的演化过程,提出了基于暂时"免疫"力的毒品滥用流行病模型,并计算了模型的基本再生数,讨论了模型平衡点的存在性和稳定性。当基本再生数小于1时,模型存在一个局部渐进稳定的无毒平衡点;当基本再生数大于1时,模型存在唯一的地方病平衡点,并利用几何方法证明了地方病平衡点的全局稳定性;当基本再生数等于1时,如果满足一定条件,模型出现后向分支现象。数值模拟验证了上述所有结果。研究结果表明提高隔离治疗率、改善社区治疗效果和降低接触传染率可以有效抑制毒品滥用的流行。 相似文献
44.
Efficient hydrogen production for industry and electricity storage via high-temperature electrolysis
《International Journal of Hydrogen Energy》2019,44(35):19089-19101
The paper describes the development status of Sunfire's reversible solid oxide cell (RSOC) technology. Here, Sunfire is a pioneer in the field of high-temperature electrolysers (HTE) for renewable hydrogen production which can be operated as a fuel cell for power generation in a reverse mode. The maturity of the technology is improved stepwise so that first applications in the field of hydrogen production for industry and electricity storage can be tackled. Three application examples where larger scale prototype has been installed will be discussed: 1) A power-to-power electricity storage based on hydrogen, 2) a RSOC unit that is installed in an iron and steel works, and 3) a pressurized SOEC prototype which will be integrated with a methanation unit. Results show the potentials of the technology in connection with fluctuating renewable energy sources. 相似文献
45.
The performance of surface ionic conduction single chamber fuel cell (SIC‐SCFC) prepared by the sol gel method was studied on electric characteristics due to the differences of the operating temperature and humidity, the electrode distance and electrolyte film depth, and multiple cells with the series and parallel connections. The SIC–SCFC was arranged the both anode of Pt and cathode of Au on the boehmite electrolyte. The open circuit voltage (OCV) of single cell achieved a maximum of 530mV in the dry gas mixtures of O2/H2=50% in room temperature operation, and but it became decrease as over 60%. The OCV was maintained the constant value between operating temperatures of 30°C to 80°C, and but it was decreased sharply at over 90°C because a humidity on the cell became lower as increasing operating temperature. Then, the cell property was improved to 120°C by adding to the humidity of 70% using a humidifier. The electrode distance and the electrolyte film depth of SIC‐SCFC found to be contributed to the reductions of the cell resistance and the surface roughness on the electrode, respectively. Moreover, the power property of SIC‐SCFC was significantly improved by cell stacks comprised of the series or parallel connection of a cell. 相似文献
46.
47.
Fatemeh Abdi 《Optimization methods & software》2019,34(1):25-36
In this paper, we propose a globally convergent BFGS method to solve Variational Inequality Problems (VIPs). In fact, a globalization technique on the basis of the hyperplane projection method is applied to the BFGS method. The technique, which is independent of any merit function, is applicable for pseudo-monotone problems. The proposed method applies the BFGS direction and tries to reduce the distance of iterates to the solution set. This property, called Fejer monotonicity of iterates with respect to the solution set, is the basis of the convergence analysis. The method applied to pseudo-monotone VIP is globally convergent in the sense that subproblems always have unique solutions, and the sequence of iterates converges to a solution to the problem without any regularity assumption. Finally, some numerical simulations are included to evaluate the efficiency of the proposed algorithm. 相似文献
48.
The rate of penetration (ROP) model is of great importance in achieving a high efficiency in the complex geological drilling process. In this paper, a novel two-level intelligent modeling method is proposed for the ROP considering the drilling characteristics of data incompleteness, couplings, and strong nonlinearities. Firstly, a piecewise cubic Hermite interpolation method is introduced to complete the lost drilling data. Then, a formation drillability (FD) fusion submodel is established by using Nadaboost extreme learning machine (Nadaboost-ELM) algorithm, and the mutual information method is used to obtain the parameters, strongly correlated with the ROP. Finally, a ROP submodel is established by a neural network with radial basis function optimized by the improved particle swarm optimization (RBFNN-IPSO). This two-level ROP model is applied to a real drilling process and the proposed method shows the best performance in ROP prediction as compared with conventional methods. The proposed ROP model provides the basis for intelligent optimization and control in the complex geological drilling process. 相似文献
49.
《工程(英文)》2019,5(4):637-645
The rapid development of information and communication technologies (ICTs) and cyber–physical systems (CPSs) has paved the way for the increasing popularity of smart products. Context-awareness is an important facet of product smartness. Unlike artifacts, various bio-systems are naturally characterized by their extraordinary context-awareness. Biologically inspired design (BID) is one of the most commonly employed design strategies. However, few studies have examined the BID of context-aware smart products to date. This paper presents a structured design framework to support the BID of context-aware smart products. The meaning of context-awareness is defined from the perspective of product design. The framework is developed based on the theoretical foundations of the situated function–behavior–structure ontology. A structured design process is prescribed to leverage various biological inspirations in order to support different conceptual design activities, such as problem formulation, structure reformulation, behavior reformulation, and function reformulation. Some existing design methods and emerging design tools are incorporated into the framework. A case study is presented to showcase how this framework can be followed to redesign a robot vacuum cleaner and make it more context-aware. 相似文献
50.
The Chinese Remainder Theorem (CRT) explains how to estimate an integer-valued number from the knowledge of the remainders obtained by dividing such unknown integer by co-prime integers. As an algebraic theorem, CRT is the basis for several techniques concerning data processing. For instance, considering a single-tone signal whose frequency value is above the sampling rate, the respective peak in the DFT informs the impinging frequency value modulo the sampling rate. CRT is nevertheless sensitive to errors in the remainders, and many efforts have been developed in order to improve its robustness. In this paper, we propose a technique to estimate real-valued numbers by means of CRT, employing for this goal a Kroenecker based M-Estimation (ME), specially suitable for CRT systems with low number of remainders. Since ME schemes are in general computationally expensive, we propose a mapping vector obtained via Kroenecker products which considerably reduces the computational complexity. Furthermore, our proposed technique enhances the probability of estimating an unknown number accurately even when the errors in the remainders surpass 1/4 of the greatest common divisor of all moduli. We also provide a version of the mapping vectors based on tensorial n-mode products, delivering in the end the same information of the original method. Our approach outperforms the state-of-the-art CRT methods not only in terms of percentage of successful estimations but also in terms of smaller average error. 相似文献