全文获取类型
收费全文 | 85936篇 |
免费 | 1191篇 |
国内免费 | 429篇 |
专业分类
电工技术 | 817篇 |
综合类 | 2328篇 |
化学工业 | 11933篇 |
金属工艺 | 4831篇 |
机械仪表 | 3110篇 |
建筑科学 | 2288篇 |
矿业工程 | 565篇 |
能源动力 | 1274篇 |
轻工业 | 3744篇 |
水利工程 | 1301篇 |
石油天然气 | 367篇 |
无线电 | 9455篇 |
一般工业技术 | 16649篇 |
冶金工业 | 2783篇 |
原子能技术 | 281篇 |
自动化技术 | 25830篇 |
出版年
2023年 | 51篇 |
2022年 | 99篇 |
2021年 | 172篇 |
2020年 | 155篇 |
2019年 | 185篇 |
2018年 | 14573篇 |
2017年 | 13496篇 |
2016年 | 10073篇 |
2015年 | 704篇 |
2014年 | 404篇 |
2013年 | 458篇 |
2012年 | 3312篇 |
2011年 | 9586篇 |
2010年 | 8384篇 |
2009年 | 5663篇 |
2008年 | 6842篇 |
2007年 | 7805篇 |
2006年 | 162篇 |
2005年 | 1242篇 |
2004年 | 1145篇 |
2003年 | 1193篇 |
2002年 | 558篇 |
2001年 | 109篇 |
2000年 | 188篇 |
1999年 | 68篇 |
1998年 | 72篇 |
1997年 | 40篇 |
1996年 | 55篇 |
1995年 | 20篇 |
1994年 | 17篇 |
1993年 | 18篇 |
1992年 | 11篇 |
1991年 | 27篇 |
1988年 | 9篇 |
1969年 | 25篇 |
1968年 | 43篇 |
1967年 | 33篇 |
1966年 | 42篇 |
1965年 | 45篇 |
1964年 | 11篇 |
1963年 | 28篇 |
1962年 | 22篇 |
1961年 | 18篇 |
1960年 | 30篇 |
1959年 | 35篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Wireless Networks - In this paper, we analyze the performance of wireless networks subject to random loss. In this regard, we revisit our TCP Congestion Control Enhancement for Random Loss (CERL)... 相似文献
2.
Wireless Networks - Orthogonal frequency-division multiplexing with random multiple access (OFDRMA) is discussed for down-link communications, whereby a single base-station transmits information... 相似文献
3.
Amini Amir Jafari Azin Vafaei Mostafa Mahmoodian Mehrnoosh 《Journal of Materials Science: Materials in Electronics》2022,33(3):1293-1306
Journal of Materials Science: Materials in Electronics - The main weakness of polymer gas sensors is its stability. Here, we report stability enhancement of a 100 nm polypyrrole (PPy) thin... 相似文献
4.
In this work, we designed a magnetically-separable Fe3O4-rGO-ZnO ternary catalyst, ZnO anchored on the surface of reduced graphene oxide (rGO)-wrapped Fe3O4 magnetic nanoparticles, where rGO, as an effective interlayer, can enhance the synergistic effect between ZnO and Fe3O4. The effects of three operational parameters, namely irradiation time, hydrogen peroxide dosage, and the catalyst dosage, on the photo-Fenton degradation of methylene blue and methyl orange were investigated. The results showed that the Fe3O4-rGO-ZnO had great potential for the destruction of organic compounds from wastewater using the Fenton chemical oxidation method at neutral pH. Repeatability of the photocatalytic activity after 5 cycles showed only a tiny drop in the catalytic efficiency. 相似文献
5.
Material encapsulation is a relatively new technique for coating a micro/nanosize particle or droplet with polymeric or inorganic shell. Encapsulation technology has many applications in various fields including drug delivery, cosmetic, agriculture, thermal energy storage, textile, and self-healing polymers. Poly(methyl methacrylate) (PMMA) is widely used as shell material in encapsulation due to its high chemical stability, biocompatibility, nontoxicity, and good mechanical properties. The main approach for micro/nanoencapsulation of materials using PMMA as shell comprises emulsion-based techniques such as emulsion polymerization and solvent evaporation from oil-in-water emulsion. In the present review, we first focus on the encapsulation techniques of liquid materials with PMMA shell by analyzing the effective processing parameters influencing the preparation of PMMA micro/nanocapsules. We then describe the morphology of PMMA capsules in emulsion systems according to thermodynamic relations. The techniques to investigation of mechanical properties of capsule shell and the release mechanisms of core material from PMMA capsules were also investigated. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48039. 相似文献
6.
Amir Abdolmaleki Mohammad Reza Molavian 《Polymer-Plastics Technology and Engineering》2015,54(12):1241-1250
2,6-Bis(5-amino-1H-benzimidazol-2-yl)pyridine was prepared and characterized by Fourier transform infrared spectroscopy, elemental analysis, 1H-NMR, and 13C-NMR spectroscopic methods. Then a new poly(benzimidazole-amide) was synthesized by polymerization of the corresponding diamine and isophthalic acid. The obtained poly(benzimidazole-amide) exhibited good yield and high thermal stability. Due to the existence of benzimidazole moieties in polymer’s structure, it has the tendency to form complexes with metal ions. So, a new poly(benzimidazole-amide)/Co nanocomposite was prepared. Morphological studies revealed that metal nanoparticles were dispersed in the polymer matrix without any aggregation. poly(benzimidazole-amide)/Co nanocomposite was used as a catalyst in the oxidation of ethyl benzene to acetophenone with tert-butyl hydroperoxide. 相似文献
7.
Reza Soleimani Amir Hossein Saeedi Dehaghani Ali Rezai-Yazdi Seyed Abolhassan Hosseini Seyedeh Pegah Hosseini Alireza Bahadori 《化学工程与技术》2020,43(3):514-522
Solubility is one of the most indispensable physicochemical properties determining the compatibility of components of a blending system. Research has been focused on the solubility of carbon dioxide in polymers as a significant application of green chemistry. To replace costly and time-consuming experiments, a novel solubility prediction model based on a decision tree, called the stochastic gradient boosting algorithm, was proposed to predict CO2 solubility in 13 different polymers, based on 515 published experimental data lines. The results indicate that the proposed ensemble model is an effective method for predicting the CO2 solubility in various polymers, with highly satisfactory performance and high efficiency. It produces more accurate outputs than other methods such as machine learning schemes and an equation of state approach. 相似文献
8.
Mirmohseni Seyedeh Maedeh Tang Chunming Javadpour Amir 《Wireless Personal Communications》2020,115(1):653-677
Wireless Personal Communications - The integration of the Internet of Things (IoT) and cloud environment has led to the creation of Cloud of Things, which has given rise to new challenges in IoT... 相似文献
9.
Mobile software applications have to cope with a particular environment that involves small size, limited resources, high autonomy requirements, competitive business models and many other challenges. To provide development guidelines that respond to these needs, several practices have been introduced; however, it is not clear how these guidelines may contribute to solve the issues present in the mobile domain. Furthermore, the rapid evolution of the mobile ecosystem challenges many of the premises upon which the proposed practices were designed. In this paper, we present a survey of the literature on software assurance practices for mobile applications, with the objective of describing them and assessing their contribution and success. We identified, organized and reviewed a body of research that spans in three levels: software development processes, software product assurance practices, and software implementation practices. By carrying out this literature survey, we reviewed the different approaches that researchers on Software Engineering have provided to address the needs that raise in the mobile software development arena. Moreover, we review the evolution of these practices, identifying how the constant changes and modernization of the mobile execution environment has impacted the methods proposed in the literature. Finally, we introduced discussion on the application of these practices in a real productive setting, opening an area for further research that may determine if practitioners have followed the proposed assurance paradigms. 相似文献
10.
Sahar Hashemi Daryan Jafar Javadpour Alireza Khavandi Mohammad Erfan 《Ceramics International》2018,44(16):19743-19750
Well-ordered and surface engineered hierarchical hydroxyapatite microspheres (HAM) were prepared via a template free hydrothermal process. Ethylene diamine tetra (methylene phosphonic acid) (EDTMP) was used as chelating or regulating agent for the first time in this study. The results indicated the formation of sheet-like particles in the absence of EDTMP. On the other hand, microspheres with radially grown nanorods (HAMNR) or nanosheets (HAMNS) on the surface were obtained (with average diameter of 5?µm) in the presence of EDTMP. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were used to characterize the crystalline phases in the synthesized samples. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that EDTMP concentration played an important part in regulating the morphology to form well organized microspheres with nanosheets or nanorods on the surface. Brunauer-Emmett-Teller (BET) revealed an increase in the specific surface area with the change in morphology from the HAMNS to HAMNR. Possible mechanisms are proposed to account for the formation of different morphologies based upon thermodynamic and kinetic theories. 相似文献