全文获取类型
收费全文 | 236155篇 |
免费 | 19968篇 |
国内免费 | 14092篇 |
专业分类
电工技术 | 35958篇 |
技术理论 | 27篇 |
综合类 | 26764篇 |
化学工业 | 10913篇 |
金属工艺 | 7538篇 |
机械仪表 | 18781篇 |
建筑科学 | 19554篇 |
矿业工程 | 9273篇 |
能源动力 | 8454篇 |
轻工业 | 4997篇 |
水利工程 | 6773篇 |
石油天然气 | 6698篇 |
武器工业 | 4088篇 |
无线电 | 25514篇 |
一般工业技术 | 11710篇 |
冶金工业 | 6881篇 |
原子能技术 | 2329篇 |
自动化技术 | 63963篇 |
出版年
2024年 | 510篇 |
2023年 | 2099篇 |
2022年 | 3997篇 |
2021年 | 5437篇 |
2020年 | 5784篇 |
2019年 | 4158篇 |
2018年 | 3833篇 |
2017年 | 5469篇 |
2016年 | 6549篇 |
2015年 | 7728篇 |
2014年 | 15321篇 |
2013年 | 12860篇 |
2012年 | 17825篇 |
2011年 | 19029篇 |
2010年 | 14343篇 |
2009年 | 14461篇 |
2008年 | 14791篇 |
2007年 | 18678篇 |
2006年 | 16731篇 |
2005年 | 14866篇 |
2004年 | 12158篇 |
2003年 | 10944篇 |
2002年 | 8219篇 |
2001年 | 6824篇 |
2000年 | 5616篇 |
1999年 | 4485篇 |
1998年 | 3339篇 |
1997年 | 2702篇 |
1996年 | 2359篇 |
1995年 | 2021篇 |
1994年 | 1677篇 |
1993年 | 1136篇 |
1992年 | 959篇 |
1991年 | 701篇 |
1990年 | 572篇 |
1989年 | 471篇 |
1988年 | 334篇 |
1987年 | 195篇 |
1986年 | 131篇 |
1985年 | 147篇 |
1984年 | 126篇 |
1983年 | 108篇 |
1982年 | 88篇 |
1981年 | 73篇 |
1980年 | 54篇 |
1979年 | 52篇 |
1978年 | 35篇 |
1977年 | 32篇 |
1976年 | 26篇 |
1959年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
As a symbol of sharing economy, ride-hailing services have spread to Asia, where various forms of services have been established according to the existing socio-technical regimes, including legal, policy, and environmental concerns. China, in particular, has accepted ride-hailing services by revising existing institutions. This study analyzes China’s acceptance of ride-hailing services in the socio-technical system context set up for legacy services. Simulation modeling, combined with transition theory and an agent-based model, is used to analyze the data. This study calculates consumer disutility based on mobility market share, reflecting consumer preference, and predicts the sustainability of ride-hailing services. The simulation results conclude that legalization and socio-technical context are of importance for sustainable mobility. 相似文献
63.
64.
针对区域地面沉降监测点数量有限、分布不均的情况,一般采用空间插值的手段建立表面拟合模型来解决。基于分形插值,采用随机选择迭代函数的思想对传统的趋势面拟合法作出改进,改进后拟合优度系数提高0.03,达到0.995,且改进前后的拟合结果符合显著性检验的要求。实验结果表明:改进前后趋势面拟合法拟合结果满足地面沉降监测的精度要求,改进后方法的拟合优度更高,对现实地面沉降量变化的描绘更加真实,可为沉降灾害评价工作提供更准确的依据。 相似文献
65.
王学鹏 《电子制作.电脑维护与应用》2015,(6)
CAN-BUS系统自问世以来,已将近30年,当代各品牌车辆纷纷采用,但大部分技术人员对CAN总线系统既熟悉又陌生。经常能听到,但具体操作又显得有些力不从心。本文通过对奇瑞A3品牌轿车CAN总线的巧妙应用,引导大家进一步理解和应用CAN总线。 相似文献
66.
分析了全球微波接入互存(WiMAX)的技术特点和算法复杂度,探讨了其在电源监控系统中的应用,提出了基于Inter WiMAX Connection 2250技术的远程电源监控系统。在讨论WiMAX物理层算法的基础上,确定了以正交频分多址(OFDMA)模式为主体的物理层通信协议,提高了信道的利用率,抑制了码间干扰,为构建电源监控系统打下了良好的基础。 相似文献
67.
The main purpose of this paper is to survey some recent progresses on control theory for stochastic distributed parameter systems, i.e., systems governed by stochastic differential equations in infinite dimensions, typically by stochastic partial differential equations. We will explain the new phenomenon and difficulties in the study of controllability and optimal control problems for one dimensional stochastic parabolic equations and stochastic hyperbolic equations. In particular, we shall see that both the formulation of corresponding stochastic control problems and the tools to solve them may differ considerably from their deterministic/finite-dimensional counterparts. More importantly, one has to develop new tools, say, the stochastic transposition method introduced in our previous works, to solve some problems in this field. 相似文献
68.
Phytoalexins are inducible secondary metabolites possessing antimicrobial activity against phytopathogens. Rice produces a wide array of phytoalexins in response to pathogen attacks and environmental stresses. With few exceptions, most phytoalexins identified in rice are diterpenoid compounds. Until very recently, flavonoid sakuranetin was the only known phenolic phytoalexin in rice. However, recent studies have shown that phenylamides are involved in defense against pathogen attacks in rice. Phenylamides are amine-conjugated phenolic acids that are induced by pathogen infections and abiotic stresses including ultra violet (UV) radiation in rice. Stress-induced phenylamides, such as N-trans-cinnamoyltryptamine, N-p-coumaroylserotonin and N-cinnamoyltyramine, have been reported to possess antimicrobial activities against rice bacterial and fungal pathogens, an indication of their direct inhibitory roles against invading pathogens. This finding suggests that phenylamides act as phytoalexins in rice and belong to phenolic phytoalexins along with sakuranetin. Phenylamides also have been implicated in cell wall reinforcement for disease resistance and allelopathy of rice. Synthesis of phenolic phytoalexins is stimulated by phytopathogen attacks and abiotic challenges including UV radiation. Accumulating evidence has demonstrated that biosynthetic pathways including the shikimate, phenylpropanoid and arylmonoamine pathways are coordinately activated for phenolic phytoalexin synthesis, and related genes are induced by biotic and abiotic stresses in rice. 相似文献
69.
《矿业科学技术学报(英文版)》2020,30(6):785-797
In this study, uniaxial compressive strength (UCS), unit weight (UW), Brazilian tensile strength (BTS), Schmidt hardness (SHH), Shore hardness (SSH), point load index (Is50) and P-wave velocity (Vp) properties were determined. To predict the UCS, simple regression (SRA), multiple regression (MRA), artificial neural network (ANN), adaptive neuro-fuzzy inference system (ANFIS) and genetic expression programming (GEP) have been utilized. The obtained UCS values were compared with the actual UCS values with the help of various graphs. Datasets were modeled using different methods and compared with each other. In the study where the performance indice PIat was used to determine the best performing method, MRA method is the most successful method with a small difference. It is concluded that the mean PIat equal to 2.46 for testing dataset suggests the superiority of the MRA, while these values are 2.44, 2.33, and 2.22 for GEP, ANFIS, and ANN techniques, respectively. The results pointed out that the MRA can be used for predicting UCS of rocks with higher capacity in comparison with others. According to the performance index assessment, the weakest model among the nine model is P7, while the most successful models are P2, P9, and P8, respectively. 相似文献
70.
Private information retrieval(PIR) is an important privacy protection issue of secure multi-party computation, but the PIR protocols based on classical cryptography are vulnerable because of new technologies,such as quantum computing and cloud computing. The quantum private queries(QPQ) protocols available, however, has a high complexity and is inefficient in the face of large database. This paper, based on the QKD technology which is mature now, proposes a novel QPQ protocol utilizing the key dilution and auxiliary parameter. Only N quits are required to be sent in the quantum channel to generate the raw key, then the straight k bits in the raw key are added bitwise to dilute the raw key, and a final key is consequently obtained to encrypt the database. By flexible adjusting of auxiliary parameters θ and k, privacy is secured and the query success ratio is improved. Feasibility and performance analyses indicate that the protocol has a high success ratio in first-trial query and is easy to implement, and that the communication complexity of O(N) is achieved. 相似文献