全文获取类型
收费全文 | 38964篇 |
免费 | 5836篇 |
国内免费 | 3833篇 |
专业分类
电工技术 | 3073篇 |
技术理论 | 1篇 |
综合类 | 3937篇 |
化学工业 | 3416篇 |
金属工艺 | 2714篇 |
机械仪表 | 2918篇 |
建筑科学 | 4205篇 |
矿业工程 | 691篇 |
能源动力 | 1842篇 |
轻工业 | 2935篇 |
水利工程 | 493篇 |
石油天然气 | 769篇 |
武器工业 | 241篇 |
无线电 | 5959篇 |
一般工业技术 | 4910篇 |
冶金工业 | 1090篇 |
原子能技术 | 203篇 |
自动化技术 | 9236篇 |
出版年
2024年 | 259篇 |
2023年 | 1204篇 |
2022年 | 1687篇 |
2021年 | 1920篇 |
2020年 | 1883篇 |
2019年 | 1613篇 |
2018年 | 1560篇 |
2017年 | 1769篇 |
2016年 | 1763篇 |
2015年 | 2109篇 |
2014年 | 2808篇 |
2013年 | 3389篇 |
2012年 | 4761篇 |
2011年 | 4610篇 |
2010年 | 3377篇 |
2009年 | 3355篇 |
2008年 | 1825篇 |
2007年 | 2531篇 |
2006年 | 2252篇 |
2005年 | 808篇 |
2004年 | 320篇 |
2003年 | 239篇 |
2002年 | 272篇 |
2001年 | 277篇 |
2000年 | 248篇 |
1999年 | 267篇 |
1998年 | 137篇 |
1997年 | 87篇 |
1996年 | 161篇 |
1995年 | 132篇 |
1994年 | 119篇 |
1993年 | 114篇 |
1992年 | 80篇 |
1991年 | 65篇 |
1990年 | 71篇 |
1989年 | 54篇 |
1988年 | 76篇 |
1987年 | 155篇 |
1986年 | 163篇 |
1985年 | 42篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1976年 | 4篇 |
1965年 | 1篇 |
1959年 | 7篇 |
1951年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
Energy bands, effective mass of carriers, absolute band edge positions and optical properties of tetragonal AgInS2 were calculated using a first-principles approach with the exchange correlation described by B3LYP hybrid functional. The results indicate that tetragonal AgInS2 has a direct band gap of 1.93 eV, which reproduce well experimental value. Calculated effective masses of electrons and holes are both small which are beneficial to separation and migration of electron and hole pairs. This implies that AgInS2 has good photocatalytic performance. The calculated optical characteristics indicate that AgInS2 has a slight anisotropy for both the real and imaginary parts of the dielectric function and exhibits large optical absorption in the visible light region. Furthermore, the calculated band edge positions in (100), (010) and (001) surfaces indicate that tetragonal AgInS2 is beneficial to the reduction and oxidation of water to hydrogen and oxygen under visible light irradiation. 相似文献
22.
23.
Wireless Personal Communications - The traditional simultaneous wireless information and power transfer (SWIPT) system uses a part of signals to decode information, and the other part is used for... 相似文献
24.
25.
26.
In this paper, the dynamic behaviors on the basis of simulation for high-purity heat integrated air separation column (HIASC) are studied. A nonlinear generic model control (GMC) scheme is proposed based on the nonlinear behavior analyses of a HIASC process, and an adaptive generic model control (AGMC) scheme is further presented to correct the model parameters online. Related internal model control (IMC) scheme and multi-loop PID (M-PID) scheme are also developed as the comparative base. The comparative researches are carried out among these linear and nonlinear control schemes in detail. The simulation research results show that the proposed AGMC schemes present advantages in both servo control and regulatory control for the high-purity HIASC. 相似文献
27.
《Carbon》2015
In the past decade, there have been great advances in the controllable growth of two-dimensional (2D) graphene sheets. However, the preparation of 3D structured graphene such as graphene coatings on arbitrary-shaped micro/nano materials still remains a formidable challenge. Herein, we have proposed a general strategy for the in situ growth of 3D graphene coatings on the micro/nano particles with arbitrary shapes. Inspired by the CVD growth mechanism of 2D graphene sheets on the bulk metal substrates, we have in situ constructed a nanometer-thick catalytic interface on the micro/nano particle surface by introducing a trace amount of transition metal salts and solid carbon sources with strictly-controlled content and ratio. Growth of 3D graphene coatings is accomplished through a solid-state reaction. Under the catalysis of the in situ formed catalytic interface consisting of highly-ordered metal nanoislands, the nano-thick amorphous carbon layer which arousing from the pyrolysis of carbon sources can be effectively transformed into a continuous and uniform graphene coating throughout the material surface based on a “dissolution–precipitation” mechanism. 3D graphene coatings have been successfully grown on lithium iron phosphate, silver, copper and silicon particles. The growth mechanism of the 3D graphene coatings has been studied in detail and a growth model is also proposed. 相似文献
28.
The grouping of pixels based on some similarity criteria is called image segmentation. In this paper the problem of color image segmentation is considered as a clustering problem and a fixed length genetic algorithm (GA) is used to handle it. The effectiveness of GA depends on the objective function (fitness function) and the initialization of the population. A new objective function is proposed to evaluate the quality of the segmentation and the fitness of a chromosome. In fixed length genetic algorithm the chromosomes have same length, which is normally set by the user. Here, a self organizing map (SOM) is used to determine the number of segments in order to set the length of a chromosome automatically. An opposition based strategy is adopted for the initialization of the population in order to diversify the search process. In some cases the proposed method makes the small regions of an image as separate segments, which leads to noisy segmentation. A simple ad hoc mechanism is devised to refine the noisy segmentation. The qualitative and quantitative results show that the proposed method performs better than the state-of-the-art methods. 相似文献
29.
We introduce a new architecture for the design of a tool for modeling and simulation of continuous and hybrid systems. The environment includes a compiler based on Modelica, a modular and a causal standard specification language for physical systems modeling (the tool supports models composed using certain component classes defined in the Modelica Standard Library, and the instantiation, parameterization and connection of these MSL components are described using a subset of Modelica). Models are defined in Modelica and are translated into DEVS models. DEVS theory (originally defined for modeling and simulation of discrete event systems) was extended in order to permit defining these of models. The different steps in the compiling process are show, including how to model these dynamic systems under the discrete event abstraction, including examples of model simulation with their execution results. 相似文献
30.
Meifang Luo Chaozhong Guo Xinyi Luo Zhaoxu Li Yuan Qin Weizhong Zhang 《International Journal of Hydrogen Energy》2021,46(2):2117-2127
It is of great urgency to design inexpensive and high-performance oxygen reduction reaction (ORR) electrocatalysts derived from biowastes as substitutes for Pt-based materials in electrochemical energy-conversion devices. Here we propose a strategy to synthesize three-dimensional (3D) porous nitrogen-doped network carbons to catalyze the ORR from two-step pyrolysis engineering of biowaste scale combined with the use of a ZnCl2 activator and a FeCl2 promotor. Electrochemical tests show that the synthesized network carbons have exhibited comparable ORR catalytic activity with a half-wave potential (~0.85 V vs. RHE) and outstanding cyclical stability in comparison to the Pt/C catalyst. Beyond that, a high electron transfer number (~3.8) and a low peroxide yield (<7.6%) can be obtained, indicating a four-electron reaction pathway. The maximum power density is ~68 mW cm?2, but continuous discharge curves (at a constant potential of ~1.30 V) for 12 h are not obviously declined in Zn-air battery tests using synthesized network carbons as the cathodic catalyst. The formation of 3D porous structures with high BET surface area can effectively expose the surface catalytic sites and promote mass transportation to boost the ORR activity. This work may open a new idea to prepare porous carbon-based catalysts for some important reactions in new energy devices. 相似文献