全文获取类型
收费全文 | 5242篇 |
免费 | 238篇 |
国内免费 | 113篇 |
专业分类
电工技术 | 263篇 |
综合类 | 60篇 |
化学工业 | 675篇 |
金属工艺 | 318篇 |
机械仪表 | 251篇 |
建筑科学 | 56篇 |
矿业工程 | 35篇 |
能源动力 | 606篇 |
轻工业 | 53篇 |
水利工程 | 5篇 |
石油天然气 | 17篇 |
武器工业 | 16篇 |
无线电 | 926篇 |
一般工业技术 | 705篇 |
冶金工业 | 108篇 |
原子能技术 | 28篇 |
自动化技术 | 1471篇 |
出版年
2024年 | 19篇 |
2023年 | 389篇 |
2022年 | 194篇 |
2021年 | 230篇 |
2020年 | 277篇 |
2019年 | 239篇 |
2018年 | 141篇 |
2017年 | 478篇 |
2016年 | 516篇 |
2015年 | 368篇 |
2014年 | 439篇 |
2013年 | 250篇 |
2012年 | 210篇 |
2011年 | 165篇 |
2010年 | 137篇 |
2009年 | 224篇 |
2008年 | 89篇 |
2007年 | 154篇 |
2006年 | 174篇 |
2005年 | 88篇 |
2004年 | 53篇 |
2003年 | 57篇 |
2002年 | 83篇 |
2001年 | 87篇 |
2000年 | 62篇 |
1999年 | 67篇 |
1998年 | 25篇 |
1997年 | 16篇 |
1996年 | 19篇 |
1995年 | 21篇 |
1994年 | 24篇 |
1993年 | 12篇 |
1992年 | 11篇 |
1991年 | 21篇 |
1990年 | 18篇 |
1989年 | 17篇 |
1988年 | 32篇 |
1987年 | 68篇 |
1986年 | 68篇 |
1985年 | 14篇 |
1984年 | 10篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 7篇 |
1980年 | 1篇 |
1979年 | 8篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 4篇 |
排序方式: 共有5593条查询结果,搜索用时 15 毫秒
151.
Organic thin-film transistors (OTFTs) based on bottom-gate bottom-contact configuration were fabricated by inserting two kinds of modifying layers at the interface of source/drain electrode and organic semiconductor, while nitrogen dioxide (NO2) sensing capability was also evaluated based on the obtained OTFTs. Compared to OTFT without interfacial layer, the field-effect mobility (μ) was enhanced from 0.018 cm2/Vs to 0.15 cm2/Vs by incorporating with MoOx interfacial layer. Moreover, when exposed to 30 ppm NO2, the saturation current and μ of OTFT with MoOx interfacial layer increase 22.7% and 26.7%, respectively, while in original OTFT, the values are only 3.0% and 3.7%, respectively. The mechanism of performance improvement of OTFT sensor was systematically studied by focusing on the interface of source/drain electrode and organic semiconductor. The reduced contact resistance leads to higher μ, meanwhile, pentacene morphology modulation on MoOx contributes to better diffusion of NO2 molecules. As a result, higher μ and more diffused gas molecules enhance the gas sensing property of the transistor. 相似文献
152.
Chaewoon Park Rui Wu Ping Lu Hui Zhao Jinbo Yang Bruce Zhang Weiwei Li Chao Yun Haiyan Wang Judith L. MacManus‐Driscoll Seungho Cho 《Advanced functional materials》2018,28(11)
Despite the advances in the methods for fabricating nanoscale materials, critical issues remain, such as the difficulties encountered in anchoring, and the deterioration in their stability after integration with other components. These issues need to be addressed to further increase the scope of their applicability. In this study, using epitaxial mesoscopic host matrices, materials are spatially confined at the nanoscale, and are supported, anchored, and stabilized. They also exhibit properties distinct from the bulk counterparts proving their high quality nanoscale nature. ZnFe2O4 and SrTiO3 are used as the model confined material and host matrix, respectively. The ZnFe2O4 phases are spatially confined by the SrTiO3 mesoscopic matrix and have strongly enhanced ferrimagnetic properties as compared to bulk and plain thin films of ZnFe2O4, with a Curie temperature of ≈500 K. The results of a series of control experiments and characterization measurements indicate that cationic inversion, which originates from the high interface‐to‐volume ratio of the ZnFe2O4 phase in the ZnFe2O4–SrTiO3 nanocomposite film, is responsible for the magnetization enhancement. An exchange bias is observed, owing to the coexistence of ferrimagnetic and antiferromagnetic regions in the confined ZnFe2O4 phase. The magnetic properties are dependent on the ZnFe2O4 crystallite size, which can be controlled by the growth conditions. 相似文献
153.
In recent years, numerous facial expression recognition related applications had been commercialized in the market. Many of them achieved promising and reliable performance results in real-world applications. In contrast, the automated micro-expression recognition system relevant research analysis is still greatly lacking. This is because of the nature of the micro-expression that is usually appeared with relatively lesser duration and lower intensity. However, due to its uncontrollable, subtlety, and spontaneity properties, it is capable to reveal one’s concealed genuine feelings. Therefore, this paper attempts to improve the performance of current micro-expression recognition systems by introducing an efficient and effective algorithm. Particularly, we employ genetic algorithms (GA) to discover an optimal solution in order to facilitate the computational process in producing better recognition results. Prior to the GA implementation, the benchmark preprocessing method and feature extractors are directly adopted herein. Succinctly, the complete proposed framework composes three main steps: the apex frame acquisition, optical flow approximation, and feature extraction with CNN architecture. Experiments are conducted on the composite dataset that is made up of three publicly available databases, viz, CASME II, SMIC, and SAMM. The recognition performance tends to prevail the state-of-the-art methods by attaining an accuracy of 85.9% and F1-score of 83.7%. 相似文献
154.
为减少球形Ni/Al填充量并提高Ni/Al填充导电硅橡胶屏蔽效能,选取Ni/C纤维加入到此种导电橡胶中,并从导电性、屏蔽性能方面对其进行评价。实验发现Ni/C纤维的掺杂可以提高导电橡胶的导电性及屏蔽性能。当总颗粒填充量为130 phr时,掺杂纤维使导电橡胶的体积电阻率从1010Ω·cm降至1.4Ω·cm;当总颗粒填充量为240 phr时,在1.0~2.5 GHz的频段内,其屏蔽效能在90 d B以上,而未经过掺杂的仅能超过60 d B。利用面心立方堆垛结构模型计算颗粒间最小距离,结果发现导电橡胶的渗流阈值与颗粒最小间距有较为明显的相关性。 相似文献
155.
《Optical Fiber Technology》2006,12(1):48-58
A ring launching scheme using a mode converter based on hollow optical fibre (HOF) is theoretically investigated for the purpose of increasing bandwidth for multimode Gigabit Ethernet communication. The mode converter based on HOF transforms the fundamental mode of a single-mode fibre (SMF) to a ring-shaped mode. It has the characteristic to improve the bandwidth by exciting higher-order modes of the multimode fibre (MMF) selectively. The HOF launch is studied under various aspects such as induced coupling efficiency, mode power distribution, and bandwidth-length product and is compared to centre and offset launching schemes. It is shown that the ring launching scheme is expected to support 10-Gb Ethernet applications using conventional multimode fibres. 相似文献
156.
Engineered Elastomer Substrates for Guided Assembly of Complex 3D Mesostructures by Spatially Nonuniform Compressive Buckling 下载免费PDF全文
Kewang Nan Haiwen Luan Zheng Yan Xin Ning Yiqi Wang Ao Wang Juntong Wang Mengdi Han Matthew Chang Kan Li Yutong Zhang Wen Huang Yeguang Xue Yonggang Huang Yihui Zhang John A. Rogers 《Advanced functional materials》2017,27(1)
Approaches capable of creating 3D mesostructures in advanced materials (device‐grade semiconductors, electroactive polymers, etc.) are of increasing interest in modern materials research. A versatile set of approaches exploits transformation of planar precursors into 3D architectures through the action of compressive forces associated with release of prestrain in a supporting elastomer substrate. Although a diverse set of 3D structures can be realized in nearly any class of material in this way, all previously reported demonstrations lack the ability to vary the degree of compression imparted to different regions of the 2D precursor, thus constraining the diversity of 3D geometries. This paper presents a set of ideas in materials and mechanics in which elastomeric substrates with engineered distributions of thickness yield desired strain distributions for targeted control over resultant 3D mesostructures geometries. This approach is compatible with a broad range of advanced functional materials from device‐grade semiconductors to commercially available thin films, over length scales from tens of micrometers to several millimeters. A wide range of 3D structures can be produced in this way, some of which have direct relevance to applications in tunable optics and stretchable electronics. 相似文献
157.
A study on the damage effect of a GaAs pseudomorphic high-electron-mobility transistor (pHEMT) low-noise amplifier (LNA) induced by a Ku-band microwave is presented in this paper based on an experiment and simulation study. The experimental results suggest that the burn-out in the first stage is responsible for the LNA damage. Scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS) were used to observe the damage situation and compare the element composition before and after the high power microwave (HPM) injection. It is found that the gate metal is melted as a result of heat generation. The location beneath the gate near the source side is badly burned and splashes out. A detail simulation is performed by establishing a two-dimensional electric-thermal model considering several physical models and thermal parameters using the simulator Sentaurus-TCAD. The results show that the burn-out location is consistent with the experiment findings. Meanwhile, a temperature elevation occurs in both the positive and negative half cycles. Moreover, the damage to pHEMT shows the working voltage dependence, and the burn-out time increases with the increase in drain voltage. 相似文献
158.
Spatially resolved extrinsic photoresponse experiments in pentacene two terminal devices without or under additional intrinsic bias-light excitation are employed. These experiments are used to investigate the microscopic mechanism of the recently observed phenomenon of the photoresponse enhancement under additional bias-light intrinsic excitation and to preclude that this phenomenon arises from contact-related artifacts. It is found that the extrinsic photogeneration near the contacts via electric field-assisted exciton splitting and/or light-induced depletion width-reduction have a negligible contribution to the extrinsic photoresponse. Under additional bias-light intrinsic excitation, a uniform increase of the photogenerated hole density is found to take place across the whole conduction channel, without changes in the electric field distribution and in the interfacial properties of the contacts. The photoresponse enhancement by the blue bias-light becomes stronger upon increasing the red-light intensity. A nearly square root dependence of the photoresponse enhancement on the blue bias-light intensity is found. It is shown that the observed dependence of the photoresponse enhancement on the light intensities of the extrinsic and intrinsic excitation can be explained with the extrinsic photogeneration mechanism based on hole detrapping by triplet exciton dissociation. 相似文献
159.
Yishuang Geng Jie He Kaveh Pahlavan 《International Journal of Wireless Information Networks》2013,20(4):306-317
In time-of-arrival (TOA) based indoor human tracking system, the human body mounted with the target sensor can cause non-line of sight (NLOS) scenario and result in significant ranging error. However, the previous studies on the behavior of indoor TOA ranging did not take the effects of human body into account. In this paper, measurement of TOA ranging error has been conducted in a typical indoor environment and sources of inaccuracy in TOA-based indoor localization have been analyzed. To quantitatively describe the TOA ranging error caused by human body, we introduce a statistical TOA ranging error model for body mounted sensors based on the measurement results. This model separates the ranging error into multipath error and NLOS error caused by the creeping wave phenomenon. Both multipath error and NLOS error are modeled as a Gaussian variable. The distribution of multipath error is only relative to the bandwidth of the system while the distribution of NLOS error is relative to the angle between human facing direction and the direction of transmitter–receiver, signal to noise ratio and bandwidth of the system, which clearly shows the effects of human body on TOA ranging. 相似文献
160.