全文获取类型
收费全文 | 99261篇 |
免费 | 9327篇 |
国内免费 | 5927篇 |
专业分类
电工技术 | 4175篇 |
技术理论 | 4篇 |
综合类 | 10764篇 |
化学工业 | 13101篇 |
金属工艺 | 7968篇 |
机械仪表 | 6480篇 |
建筑科学 | 21597篇 |
矿业工程 | 3756篇 |
能源动力 | 2443篇 |
轻工业 | 4850篇 |
水利工程 | 2997篇 |
石油天然气 | 4780篇 |
武器工业 | 1004篇 |
无线电 | 6290篇 |
一般工业技术 | 10631篇 |
冶金工业 | 3710篇 |
原子能技术 | 562篇 |
自动化技术 | 9403篇 |
出版年
2024年 | 350篇 |
2023年 | 1364篇 |
2022年 | 2630篇 |
2021年 | 3046篇 |
2020年 | 2922篇 |
2019年 | 2467篇 |
2018年 | 2300篇 |
2017年 | 2910篇 |
2016年 | 3074篇 |
2015年 | 3383篇 |
2014年 | 6098篇 |
2013年 | 5268篇 |
2012年 | 6864篇 |
2011年 | 7652篇 |
2010年 | 5877篇 |
2009年 | 6330篇 |
2008年 | 5729篇 |
2007年 | 6839篇 |
2006年 | 6275篇 |
2005年 | 5465篇 |
2004年 | 4486篇 |
2003年 | 4042篇 |
2002年 | 3379篇 |
2001年 | 2832篇 |
2000年 | 2444篇 |
1999年 | 2031篇 |
1998年 | 1610篇 |
1997年 | 1352篇 |
1996年 | 1012篇 |
1995年 | 875篇 |
1994年 | 819篇 |
1993年 | 540篇 |
1992年 | 483篇 |
1991年 | 390篇 |
1990年 | 327篇 |
1989年 | 226篇 |
1988年 | 171篇 |
1987年 | 88篇 |
1986年 | 71篇 |
1985年 | 75篇 |
1984年 | 58篇 |
1983年 | 55篇 |
1982年 | 67篇 |
1981年 | 22篇 |
1980年 | 69篇 |
1979年 | 18篇 |
1978年 | 11篇 |
1975年 | 11篇 |
1959年 | 10篇 |
1955年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
51.
52.
基于深度学习的人体姿态估计方法旨在通过构建合适的神经网络,直接从二维的图像特征中回归出人体姿态信息。主要按照2D人体姿态估计到3D人体姿态估计的顺序,并从单人检测与多人检测、稀疏的关节点检测与密集的模型构建等方面,对近年来基于深度学习的人体姿态估计方法进行系统介绍,从而初步了解如何通过深度学习的方法得到人体姿态的各个要素,包括肢体部件的相对朝向和比例尺度、骨骼关节点的位置坐标和连接关系,甚至更为复杂的人体蒙皮模型信息。最后,对当前研究面临的挑战以及未来的热点动向进行概述,清晰地呈现出该领域的发展脉络。 相似文献
53.
针对传统的小区内开环功率控制算法通常以提升本小区的吞吐量性能为目标,忽略了当前小区用户对邻小区用户同频干扰的问题,为提升边缘用户性能的同时兼顾系统整体性能,提出了一种LTE系统小区间上行联合功率控制(UJPC)算法。该算法采用单基站三扇区为系统模型,以最优化系统吞吐量比例公平函数为目标,首先根据最小信干噪比(SINR)约束值和用户最大发射功率这两个约束条件得到相应的数学优化模型,然后采用连续凸近似的方法求解优化问题得出各个基站所管辖的小区内所有用户的最优发射功率。仿真结果表明,与基准的开环功控方案相比,联合功控方案在保证系统平均频谱利用率的情况下能够较大幅度地提高小区边缘频谱利用率,其最佳性能增益能达到50%。 相似文献
54.
Han Yan Gu Yi Chen Lei Li Bing Liu Xiang Ming Chen 《International Journal of Applied Ceramic Technology》2020,17(2):790-796
SrLa[Ga1−x(R0.5Ti0.5)x]O4 (R = Mg, Zn) ceramics were prepared by a standard solid state sintering method. The single-phase ceramics with K2NiF4-type layered perovskite structure and I4/mmm space group were obtained, indicating that SrLa(R0.5Ti0.5) and SrLaGaO4 can form the unlimited solid solutions. With increasing x for R = Mg and Zn, εr increases monotonously, the Qf value first increases and then decreases, while τf increases from a negative to a positive value. The optimized microwave dielectric properties were obtained as following: εr = 23.3, Qf = 89 400 GHz, τf = −0.8 ppm/°C for SrLa[Ga0.6(Mg0.5Ti0.5)0.4]O4 and εr = 23.3, Qf = 76 200 GHz, τf = 0.2 ppm/°C for SrLa[Ga0.7(Zn0.5Ti0.5)0.3]O4, indicating that the present solid solution ceramics are the promising candidates as microwave resonator materials for the telecommunication applications. 相似文献
55.
56.
The perpetual energy production of a wind farm could be accomplished (under proper weather conditions) if no failures occurred. But even the best possible design, manufacturing, and maintenance of a system cannot eliminate the failure possibility. In order to understand and minimize the system failures, the most crucial components of the wind turbines, which are prone to failures, should be identified. Moreover, it is essential to determine and classify the criticality of the system failures according to the impact of these failure events on wind turbine safety. The present study is processing the failure data from a wind farm and uses the Fault Tree Analysis as a baseline for applying the Design Structure Matrix technique to reveal the failure and risk interactions between wind turbine subsystems. Based on the analysis performed and by introducing new importance measures, the “readiness to fail” of a subsystem in conjunction with the “failure riskiness” can determine the “failure criticality.” The value of the failure criticality can define the frame within which interventions could be done. The arising interventions could be applied either to the whole system or could be focused in specified pairs of wind turbine subsystems. In conclusion, the method analyzed in the present research can be effectively applied by the wind turbine manufacturers and the wind farm operators as an operation framework, which can lead to a limited (as possible) design‐out maintenance cost, failures' minimization, and safety maximization for the whole wind turbine system. 相似文献
57.
58.
《International Journal of Hydrogen Energy》2020,45(29):14964-14971
Sr3Fe2O7-δ (SFO) with two-layer Ruddlesden-Popper (R–P) structure has recently been proved to be a promising material for the single phase cathode in proton conducting solid oxide fuel cells (P–SOFCs). To investigate the hydration reactions and proton conducting mechanisms of SFO and cobalt doped SFO (SFCO), both bulk and surface properties were calculated. We conclude that R–P structures have advantages in P–SOFCs. The unique Sr–O–M layer can facilitate the hydration process. Although in Sr–O–F and Sr–O–N layers, it is difficult for the formation and migration of oxygen vacancies, protons are most stable. Furthermore, cobalt doping can not only improve the electronic conductivity but also enhance surface properties of SFCO. The easily exposed Co–Fe–O surface can also facilitate the hydration reactions on the surface. Our work could give an informative insight into the relationships among the doped elements, the R–P structures, the hydration process and the proton conducting properties. 相似文献
59.
无源光网络(Passive Optical Network,PON)作为当今接入网的主要技术解决方案,具有带宽使用效率高、传输距离远、抗干扰能力强等特点.通过研究PON技术的发展动态,本文首先归纳了各种PON技术的产生背景和应用特点,整理出各技术间的连接关系及主要标准;其次介绍了PON技术的帧结构,并对带宽、波长、传输模式等PON技术的主要参数进行了汇总;然后将国内外研究热点进行划分,围绕媒体访问控制协议、帧结构、动态带宽分配算法、节能机制等关键技术,阐述了其研究现状及在PON中的重要作用;最后对PON技术的发展趋势进行了展望. 相似文献
60.
The molecular design of short peptides to achieve a tailor-made functional architecture has attracted attention during the past decade but remains challenging as a result of insufficient understanding of the relationship between peptide sequence and assembled supramolecular structures. We report a hybrid-resolution model to computationally explore the sequence–structure relationship of self-assembly for tripeptides containing only phenylalanine and isoleucine. We found that all these tripeptides have a tendency to assemble into nanofibers composed of laterally associated filaments. Molecular arrangements within the assemblies are diverse and vary depending on the sequences. This structural diversity originates from (1) distinct conformations of peptide building blocks that lead to different surface geometries of the filaments and (2) unique sidechain arrangements at the filament interfaces for each sequence. Many conformations are available for tripeptides in solution, but only an extended β-strand and another resembling a right-handed turn are observed in assemblies. It was found that the sequence dependence of these conformations and the packing of resulting filaments are determined by multiple competing noncovalent forces, with hydrophobic interactions involving Phe being particularly important. The sequence pattern for each type of assembly conformation and packing has been identified. These results highlight the importance of the interplay between conformation, molecular packing, and sequences for determining detailed nanostructures of peptides and provide a detailed insight to support a more precise design of peptide-based nanomaterials. 相似文献