全文获取类型
收费全文 | 130428篇 |
免费 | 15751篇 |
国内免费 | 6350篇 |
专业分类
电工技术 | 58313篇 |
技术理论 | 5篇 |
综合类 | 9869篇 |
化学工业 | 4164篇 |
金属工艺 | 2803篇 |
机械仪表 | 6586篇 |
建筑科学 | 6828篇 |
矿业工程 | 4696篇 |
能源动力 | 8913篇 |
轻工业 | 1828篇 |
水利工程 | 5543篇 |
石油天然气 | 1673篇 |
武器工业 | 784篇 |
无线电 | 15972篇 |
一般工业技术 | 4899篇 |
冶金工业 | 2562篇 |
原子能技术 | 2584篇 |
自动化技术 | 14507篇 |
出版年
2024年 | 417篇 |
2023年 | 1652篇 |
2022年 | 3274篇 |
2021年 | 3989篇 |
2020年 | 4441篇 |
2019年 | 3443篇 |
2018年 | 3170篇 |
2017年 | 4532篇 |
2016年 | 4980篇 |
2015年 | 5751篇 |
2014年 | 9717篇 |
2013年 | 7991篇 |
2012年 | 11304篇 |
2011年 | 11842篇 |
2010年 | 8418篇 |
2009年 | 8338篇 |
2008年 | 8124篇 |
2007年 | 9370篇 |
2006年 | 8343篇 |
2005年 | 6840篇 |
2004年 | 5575篇 |
2003年 | 4493篇 |
2002年 | 3445篇 |
2001年 | 2894篇 |
2000年 | 2393篇 |
1999年 | 1749篇 |
1998年 | 1211篇 |
1997年 | 966篇 |
1996年 | 887篇 |
1995年 | 677篇 |
1994年 | 579篇 |
1993年 | 349篇 |
1992年 | 290篇 |
1991年 | 196篇 |
1990年 | 153篇 |
1989年 | 141篇 |
1988年 | 98篇 |
1987年 | 66篇 |
1986年 | 53篇 |
1985年 | 47篇 |
1984年 | 66篇 |
1983年 | 61篇 |
1982年 | 62篇 |
1981年 | 33篇 |
1980年 | 17篇 |
1979年 | 17篇 |
1978年 | 14篇 |
1977年 | 9篇 |
1959年 | 13篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
大坝运行监测易受自然环境和监测条件影响,存在时间和空间上的变异性,监测数据具有不确定性。以云理论的随机性和不确定性分析方法为基础,并与空间数据辐射思想相结合,建立了云滴概率密度分布估计模型,然后导出云概率密度分布函数,依据样本监测数据推求母体空间数据的分布特征,并设计了基于逆向云算法云变换的计算程序。分析陆浑水库1979~1999年测压管监测数据和位移变形数据的云概率密度分布特征和云数字特征,得出了20 a来大坝的数据分布特征和运行状态。监测数据分析结果表明,云概率密度分布估计不仅能有效合理地分析大坝的运行状态,而且能够依据云数字特征来判断监测状态和监测环境的异常变化。
相似文献
52.
ABSTRACTSocial licence to operate (SLO) is a term that is finding increasing acceptance in a number of industries. Like all new terms, its precise meaning and implications are still being investigated. Using data from previous studies, this paper offers an analysis of the SLO of two case studies with each study being viewed separately through the grid of a distinct theoretical framework. Case study 1 looks at the development of differential social licence negotiated in the Hamlet of Cambridge Bay, Nunavut, as a result of an impact and benefit agreement negotiated between Tahera Diamond Corp. and the Kitikmeot Inuit Organisation in 2004. The study demonstrates that general acceptance of resource development can be uneven and reflect an unequal distribution of decision-making power. In case study 2, stakeholders of a failed mineral development project were queried across time about the specifics of the proposed mine development and were queried about resource development across different levels of consciousness. Perhaps, SLO is variable across different levels of consciousness. The paper concludes with observations about the variable nature of SLO acceptance across populations and across levels of consciousness within individuals. Perhaps, the concept of SLO is, in fact, complex, difficult to define and measure and, at this point, of limited utility as a measure of resource development acceptance. 相似文献
53.
《Microelectronics Journal》2015,46(11):1012-1019
This paper presents a voltage reference generator architecture and two different realizations of it that have been fabricated within a standard 0.18 μm CMOS technology. The architecture takes the advantage of utilizing a sampled-data amplifier (SDA) to optimize the power consumption. The circuits achieve output voltages on the order of 190 mV with temperature coefficients of 43 ppm/°C and 52.5 ppm/°C over the temperature range of 0 to 120°C without any trimming with a 0.8 V single supply. The power consumptions of the circuits are less then 500 nW while occupying an area of 0.2 mm2 and 0.08 mm2, respectively. 相似文献
54.
《The Electricity Journal》2020,33(5):106763
While wind and solar generation has increased dramatically over the past decade, there has been a much larger increase in gas generation (eia, 2019). This is driven in part by low gas prices but also in part by how electricity markets are organized. The intermittent nature of wind and solar generation increases the need for more flexible and reliable generation; a role gas plants fill well. However, current market structures and rules unfairly tip the balance in their favor compared to energy storage systems. They have created market barriers restrictive enough to prevent market participation of a technology key to a 100 % renewable grid: supercapacitors. Adjusting markets to remove the market barriers to supercapacitor and other energy storage systems will allow for increased renewable penetration while simultaneously improving grid performance and reducing costs. 相似文献
55.
ABSTRACTThe RF output power dissipated per unit area is calculated using Runge-Kutta method for the high-moderate-moderate-high (n+-n-p-p+) doping profile of double drift region (DDR)-based impact avalanche transit time (IMPATT) diode by taking different substrate at Ka band. Those substrates are silicon, gallium arsenide, germanium, wurtzite gallium nitride, indium phosphide and 4H-silicon carbide. A comparative study regarding power dissipation ability by the IMPATT using different material is being presented thereby modelling the DDR IMPATT diode in a one-dimensional structure. The IMPATT based on 4H-SiC element has highest power density in the order of 1010 Wm?2 and the Si-based counterpart has lowest power density of order 106 Wm?2 throughout the Ka band. So, 4H-SiC-based IMPATT should be preferable over others for the power density preference based application. This result will be helpful to estimate the power density of the IMPATT for any doping profile and to select the proper element for the optimum design of the IMPATT as far as power density is concerned in the Ka band. Also, we have focused on variation of power density with different junction temperatures and modelled the heat sink with analysis of thermal resistances. 相似文献
56.
简要介绍了在二滩拱坝1998年5月初次蓄水期,通过拱坝垂线和监测网系统,用统计模型和确定性模型理论分析方法,建立了施加于坝体各作用量与坝体受作用后的效应量(变位)间的数学关系;并根据预先计算分析成果,提出了在初次蓄水运行中拱坝变位的参考预报值,实时对二滩拱坝实际工作状态作出安全评判。 相似文献
57.
Smith J. David; Beran Michael J.; Redford Joshua S.; Washburn David A. 《Canadian Metallurgical Quarterly》2006,135(2):282
Although researchers are exploring animals' capacity for monitoring their states of uncertainty, the use of some paradigms allows the criticism that animals map avoidance responses to error-causing stimuli not because of uncertainty monitored but because of feedback signals and stimulus aversion. The authors addressed this criticism with an uncertainty-monitoring task in which participants completed blocks of trials with feedback deferred so that they could not associate reinforcement signals to particular stimuli or stimulus-response pairs. Humans and 1 of 2 monkeys were able to make cognitive, decisional uncertainty responses that were independent of feedback or reinforcement history within a task. This finding unifies the comparative literature on uncertainty monitoring. The dissociation of performance from reinforcement has theoretical implications, and the deferred-feedback technique has many applications. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
58.
多带OFDM-UWB系统峰均功率比降低方法研究 总被引:1,自引:0,他引:1
针对多带OFDM—UWB信号存在高峰均功率比的问题,提出了利用扩展与交织降低系统信号峰均功率比的方法。该方法通过对传输数据进行正交扩展与交织,使得进入多载波调制的数据趋于高斯分布,减小了传输数据自相关函数的旁瓣峰值,降低了OFDM-UWB信号的峰均功率比。由于采用正交矩阵进行扩展,扩展前后的数据传输速率保持不变。仿真结果表明,扩展与交织可以有效地降低信号峰均功率比2-5dB左右。同时该方法还具有抗窄带干扰的鲁棒性。 相似文献
59.
简述了电动助力转向系统的研究现状及其基本结构、工作原理和主要特点。分析了该系统的主要元件,论述了亥系统的发展趋势。 相似文献
60.