全文获取类型
收费全文 | 37921篇 |
免费 | 4845篇 |
国内免费 | 2792篇 |
专业分类
电工技术 | 4493篇 |
技术理论 | 1篇 |
综合类 | 4695篇 |
化学工业 | 3350篇 |
金属工艺 | 1848篇 |
机械仪表 | 3382篇 |
建筑科学 | 2906篇 |
矿业工程 | 1270篇 |
能源动力 | 885篇 |
轻工业 | 1460篇 |
水利工程 | 708篇 |
石油天然气 | 1998篇 |
武器工业 | 548篇 |
无线电 | 5335篇 |
一般工业技术 | 3918篇 |
冶金工业 | 1038篇 |
原子能技术 | 375篇 |
自动化技术 | 7348篇 |
出版年
2024年 | 76篇 |
2023年 | 545篇 |
2022年 | 998篇 |
2021年 | 1268篇 |
2020年 | 1376篇 |
2019年 | 1088篇 |
2018年 | 1055篇 |
2017年 | 1350篇 |
2016年 | 1480篇 |
2015年 | 1673篇 |
2014年 | 2513篇 |
2013年 | 2411篇 |
2012年 | 2983篇 |
2011年 | 2948篇 |
2010年 | 2197篇 |
2009年 | 2204篇 |
2008年 | 2125篇 |
2007年 | 2566篇 |
2006年 | 2306篇 |
2005年 | 1951篇 |
2004年 | 1635篇 |
2003年 | 1498篇 |
2002年 | 1246篇 |
2001年 | 1131篇 |
2000年 | 927篇 |
1999年 | 665篇 |
1998年 | 571篇 |
1997年 | 501篇 |
1996年 | 422篇 |
1995年 | 368篇 |
1994年 | 336篇 |
1993年 | 241篇 |
1992年 | 217篇 |
1991年 | 148篇 |
1990年 | 121篇 |
1989年 | 115篇 |
1988年 | 79篇 |
1987年 | 44篇 |
1986年 | 24篇 |
1985年 | 33篇 |
1984年 | 26篇 |
1983年 | 21篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1976年 | 6篇 |
1959年 | 3篇 |
1957年 | 3篇 |
1956年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
5G系统将移动通信服务从移动电话、移动宽带和大规模机器通信扩展到新的应用领域,即所谓对通信服务有特殊要求的垂直领域。对使能未来工厂的5G能力进行了全面的分析总结,包括弹性网络架构、灵活频谱、超可靠低时延通信、时间敏感网络、安全和定位,而弹性网络架构又包括对网络切片、非公共网络、5G局域网和边缘计算的支持。希望从广度到深度,对相关的理论及技术应用做透彻、全面的梳理,对其挑战做清晰的总结,从而为相关研究和工程技术人员提供借鉴。 相似文献
2.
针对现有基于视频监控的人流量统计方案成本高、算法复杂且不利于个人隐私保护的局限性,利用毫米波雷达体积小、成本低、分辨率高的特点,提出了一种基于双时间点检测的人流量监测方法。该方法先获取人体目标散射点位置和多普勒频移信息来构成点云数据,然后根据多普勒频移正负来判断人体的运动方向,并筛选具有高多普勒频移值的点云数据以降低干扰点对聚类结果的影响;在双时间点对特定区域内人员数量进行统计,并根据双时间点之间所获取的点云数据聚类结果对所统计人员数据进行修正。实验结果表明,该方法能够用匿名的方式以较高的正确率统计人员进出。 相似文献
3.
配电网停电会造成电力系统供配电可靠性以及服务质量下降,研究基于地理信息系统(GIS)单线图的配网停电单模拟操作应用。利用网格长度作为基本单位建立坐标系,以选取起始点与终止点为基础,通过四参数法将GIS坐标映射至图纸网格内,实现配网内设备初步布局,将杆塔、站房和整体均匀分布作为优化目标,设置多目标优化目标函数实现GIS单线图最终优化。选取某电力公司配网作为单模拟操作应用对象,模拟结果表明,单模拟操作配网停电后,该配网各负荷点年故障率、次平均停电时间以及年停电时间均有所减少,可有效提升配网的供配电可靠性。 相似文献
4.
《Journal of the European Ceramic Society》2021,41(14):6983-6990
Ternary 0.552Pb(Ni1/3Nb2/3)O3-xPbZrO3-(0.448-x)PbTiO3 (PNN-PZ-PT) ceramics near the triple point compositions were fabricated by an improved two-step sintering method. The triple point composition 0.552PNN-0.135PZ-0.313PT ceramic has outstanding piezoelectric performance with piezoelectric coefficient d33 = 1200 pC/N. Its easy fabrication and low cost make this piezoelectric material an excellent candidate for high sensitivity sensors and ultrasonic transducers. The evolution of domain structures for ceramics with composition near the triple point provides deeper insight into the mechanism of ultrahigh piezoelectric properties of PNN-PZ-PT ceramics. 相似文献
5.
6.
7.
Jun Zhang Patrick Byers Amelie Erben Christine Frank Levin Schulte-Spechtel Michael Heymann Denitsa Docheva Heinz P. Huber Stefanie Sudhop Hauke Clausen-Schaumann 《Advanced functional materials》2021,31(19):2100066
Tissue engineering requires the precise positioning of mammalian cells and biomaterials on substrate surfaces or in preprocessed scaffolds. Although the development of 2D and 3D bioprinting technologies has made substantial progress in recent years, precise, cell-friendly, easy to use, and fast technologies for selecting and positioning mammalian cells with single cell precision are still in need. A new laser-based bioprinting approach is therefore presented, which allows the selection of individual cells from complex cell mixtures based on morphology or fluorescence and their transfer onto a 2D target substrate or a preprocessed 3D scaffold with single cell precision and high cell viability (93–99% cell survival, depending on cell type and substrate). In addition to precise cell positioning, this approach can also be used for the generation of 3D structures by transferring and depositing multiple hydrogel droplets. By further automating and combining this approach with other 3D printing technologies, such as two-photon stereolithography, it has a high potential of becoming a fast and versatile technology for the 2D and 3D bioprinting of mammalian cells with single cell resolution. 相似文献
8.
Xiaoqin Yang Huy Q. Ta Huimin Hu Shuyuan Liu Yu Liu Alicja Bachmatiuk Jinping Luo Lijun Liu Jin-Ho Choi Mark H. Rummeli 《Advanced functional materials》2021,31(38):2104340
In this study, in situ transmission electron microscopy is performed to study the interaction between single (monomer) and paired (dimer) Sn atoms at graphene edges. The results reveal that a single Sn atom can catalyze both the growth and etching of graphene by the addition and removal of C atoms respectively. Additionally, the frequencies of the energetically favorable configurations of an Sn atom at a graphene edge, calculated using density functional theory calculations, are compared with experimental observations and are found to be in good agreement. The remarkable dynamic processes of binary atoms (dimers) are also investigated and is the first such study to the best of the knowledge. Dimer diffusion along the graphene edges depends on the graphene edge termination. Atom pairs (dimers) involving an armchair configuration tend to diffuse with a synchronized shuffling (step-wise shift) action, while dimer diffusion at zigzag edge terminations show a strong propensity to collapse the dimer with each atom diffusing in opposite directions (monomer formation). Moreover, the data reveals the role of C feedstock availability on the choice a single Sn atom makes in terms of graphene growth or etching. This study advances the understanding single atom catalytic activity at graphene edges. 相似文献
9.
Siyao Li Shoulei Xu Xiangyu Wang Daini Wang Bernard A. Goodman Xing Hong Wen Deng 《Ceramics International》2021,47(3):3346-3353
Cubic zirconia single crystals stabilized with yttria and doped with Gd2O3 (0.10–5.00 mol%) were prepared by the optical floating zone method, and characterized by a combination of X-ray diffraction (XRD), and Raman, electron paramagnetic resonance (EPR), ultraviolet–visible (UV–Vis), photoluminescence excitation (PLE) and photoluminescence (PL) spectroscopic techniques. XRD and Raman spectroscopy showed that the crystal samples were all in the cubic phase, whereas the ceramic sample consisted of a mixture of monoclinic and cubic phases. The absorption spectrum showed four peaks at 245, 273, 308, and 314 nm in the ultraviolet region, and the optical band gap differed between samples with ≤3.00 mol% and those with >3.00 mol% Gd2O3. The emission spectrum showed a weak peak at 308 nm and a strong peak at 314 nm, which are attributed to the 6P5/2 → 8S7/2 and 6P7/2 → 8S7/2 transitions of Gd3+, respectively. The intensities of the peaks in the excitation and emission spectra increased with Gd3+ concentration, reached a maximum at 2.00 mol%, then decreased with higher concentrations. This quenching is considered to be the result of the electric dipole-dipole interactions, and this interpretation is supported by the Gd3+ EPR spectra, which showed progressive broadening with increasing Gd3+ concentration throughout the concentration range investigated. 相似文献
10.
《Ceramics International》2022,48(21):31811-31817
As one of the outstanding piezoelectric materials, relaxor-PbTiO3 single crystal also exhibits promising electro-optic and nonlinear-optic properties. Therefore, it is vital to understand the domain switching kinetics not only for optimizing strain-mediated devices performance but also for fabricating optical waveguides and periodic domain structures in optical applications. In this work, domain switching kinetics in annealed and pre-poled PMN-0.38PT single crystal under different external electric field were studied. Polarization reversal can be accomplished only by c-domain nucleation and growth in the annealed sample where the formation of the ferroelastic domains is hindered. In pre-poled sample, 90° domain switching happened by 90° domain wall reorientation under low electric field while 180° domain switching is accomplished by two-step 90° domain switching and c-domain growth under high electric field. The results are important for modulating domain structure for strain mediated and optical devices. 相似文献