全文获取类型
收费全文 | 52952篇 |
免费 | 3942篇 |
国内免费 | 2903篇 |
专业分类
电工技术 | 1759篇 |
综合类 | 2354篇 |
化学工业 | 15448篇 |
金属工艺 | 4928篇 |
机械仪表 | 2082篇 |
建筑科学 | 666篇 |
矿业工程 | 866篇 |
能源动力 | 4824篇 |
轻工业 | 2413篇 |
水利工程 | 120篇 |
石油天然气 | 1098篇 |
武器工业 | 171篇 |
无线电 | 6427篇 |
一般工业技术 | 12339篇 |
冶金工业 | 2466篇 |
原子能技术 | 685篇 |
自动化技术 | 1151篇 |
出版年
2024年 | 40篇 |
2023年 | 976篇 |
2022年 | 1254篇 |
2021年 | 1797篇 |
2020年 | 1778篇 |
2019年 | 1619篇 |
2018年 | 1525篇 |
2017年 | 1811篇 |
2016年 | 1570篇 |
2015年 | 1582篇 |
2014年 | 2427篇 |
2013年 | 2898篇 |
2012年 | 3300篇 |
2011年 | 4289篇 |
2010年 | 3152篇 |
2009年 | 3234篇 |
2008年 | 2818篇 |
2007年 | 3392篇 |
2006年 | 3080篇 |
2005年 | 2542篇 |
2004年 | 2270篇 |
2003年 | 1980篇 |
2002年 | 1661篇 |
2001年 | 1437篇 |
2000年 | 1291篇 |
1999年 | 1017篇 |
1998年 | 915篇 |
1997年 | 704篇 |
1996年 | 650篇 |
1995年 | 553篇 |
1994年 | 496篇 |
1993年 | 390篇 |
1992年 | 332篇 |
1991年 | 242篇 |
1990年 | 186篇 |
1989年 | 156篇 |
1988年 | 104篇 |
1987年 | 65篇 |
1986年 | 30篇 |
1985年 | 43篇 |
1984年 | 39篇 |
1983年 | 24篇 |
1982年 | 36篇 |
1981年 | 23篇 |
1980年 | 16篇 |
1979年 | 15篇 |
1978年 | 5篇 |
1976年 | 6篇 |
1974年 | 4篇 |
1959年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Because of its ability to change optical absorption dynamically by applied electric field, nickel oxide (NiO) is a promising anodic material in smart windows, which can improve energy conversion efficiency in construction buildings. Although many works have achieved high electrochromic performance with different method. The underlying mechanism is still not fully investigated. In this article, we prepared the NiO films with large specific surface area and high stability by electron beam evaporation. X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were employed to figure out the surface morphology and composition of as-deposited films. Afterwards, the electrochemical properties and optical performance of the prepared NiO films were investigated. On this basis, the origin of surface charge was fully analyzed by cyclic voltammetry and diffusion coefficient test. These experimental and theoretical results firmly confirm that both the surface reaction and capacitive effect bring about the excellent EC performance in NiO films. These results not only provide clear evidence about electrochemical kinetics in NiO films, but also offer some useful guidelines for the design of EC materials with higher performance and longer stability. 相似文献
2.
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
3.
Yana Y. Toporkova Elena O. Smirnova Natalia V. Lantsova Lucia S. Mukhtarova Alexander N. Grechkin 《International journal of molecular sciences》2021,22(9)
The CYP74 clan cytochromes (P450) are key enzymes of oxidative metabolism of polyunsaturated fatty acids in plants, some Proteobacteria, brown and green algae, and Metazoa. The CYP74 enzymes, including the allene oxide synthases (AOSs), hydroperoxide lyases, divinyl ether synthases, and epoxyalcohol synthases (EASs) transform the fatty acid hydroperoxides to bioactive oxylipins. A novel CYP74 clan enzyme CYP440A18 of the Asian (Belcher’s) lancelet (Branchiostoma belcheri, Chordata) was biochemically characterized in the present work. The recombinant CYP440A18 enzyme was active towards all substrates used: linoleate and α-linolenate 9- and 13-hydroperoxides, as well as with eicosatetraenoate and eicosapentaenoate 15-hydroperoxides. The enzyme specifically converted α-linolenate 13-hydroperoxide (13-HPOT) to the oxiranyl carbinol (9Z,11R,12R,13S,15Z)-11-hydroxy-12,13-epoxy-9,15-octadecadienoic acid (EAS product), α-ketol, 12-oxo-13-hydroxy-9,15-octadecadienoic acid (AOS product), and cis-12-oxo-10,15-phytodienoic acid (AOS product) at a ratio of around 35:5:1. Other hydroperoxides were converted by this enzyme to the analogous products. In contrast to other substrates, the 13-HPOT and 15-HPEPE yielded higher proportions of α-ketols, as well as the small amounts of cyclopentenones, cis-12-oxo-10,15-phytodienoic acid and its higher homologue, dihomo-cis-12-oxo-3,6,10,15-phytotetraenoic acid, respectively. Thus, the CYP440A18 enzyme exhibited dual EAS/AOS activity. The obtained results allowed us to ascribe a name “B. belcheri EAS/AOS” (BbEAS/AOS) to this enzyme. BbEAS/AOS is a first CYP74 clan enzyme of Chordata species possessing AOS activity. 相似文献
4.
《中国有色金属学会会刊》2021,31(7):2081-2101
In flotation, metal ions possess significant roles that are usually fulfilled by either selectively activating or depressing the target minerals. Despite that tremendous efforts have been made to address the roles of metal ions in flotation, it still lacks a comprehensive review, especially to compare various ions instead of focusing on a specific one. This review begins by elaborately categorizing the factors involved in affecting the roles of metal ions in flotation. After that, well-accepted mechanisms are updated and discussed from the ore type. Furthermore, typical approaches to explore the underlying mechanisms are emphasized, including traditional techniques such as micro-flotation, contact angle measurement, zeta potential measurement, and other recent prevailing methodologies, like computational method, solution chemistry calculation, and cyclic voltammetry. This work will pave the way to promote flotations via activities like selectively adding/reducing metal ions, choosing reagents, and regulating the slurry chemistry. 相似文献
5.
Yunhai Zhang Yongsheng Liu Yejie Cao Liyang Cao Jing Wang Yu Pan Ning Wang 《Journal of the American Ceramic Society》2021,104(1):645-653
C/SiC composites prepared by chemical vapor infiltration technique (CVI) have been regarded as thermal structural materials widely. However, these composites still suffer from poor functional properties like low thermal conductivity, especially in thickness direction of the composites, limiting their large-scale applications. Herein, mesophase pitch based carbon fiber (MPCF) and continuous wave laser machining were utilized to construct highly effective heat conductive micro-pipelines within CVI C/SiC composite. The effect of initial density on the final density and thermal conductivity of the as-obtained MPCF-C/SiC composites were investigated. The results revealed that higher initial density would directly enhance the thermal conductivity and reduce the negative impact of the bottle-neck effect. At temperatures between 100°C and 500°C, MPCF-C/SiC composites preserved more than threefold of the thermal conductivity (340%) when compared to reference C/SiC composites. This work provides a highly effective route for enhancing the thermal conductivity of C/SiC, which would broaden their future applications. 相似文献
6.
Kun Yang Yachun Wang Penghui Lei Tiankai Yao Dong Zhao Jie Lian 《Journal of the European Ceramic Society》2021,41(12):6018-6028
Chemical durability of lanthanide zirconates (A2Zr2O7) (A = La-Yb) under near-field environments is important for evaluating their application as potential nuclear waste forms. In this work, A2Zr2O7 (A = La-Yb) are synthesized by spark plasma sintering with controlled microstructure and their chemical durability are evaluated in a nitric acid solution (pH = 1). Scanning transmission electron microscopy analysis reveals an amorphous passivation film either enriched with Zr or lanthanide. The complex chemistry of the passivation films can be correlated with a transition in corrosion mechanisms from a preferential release of lanthanide in La2Zr2O7 to a preferential release of Zr in Er2Zr2O7 and Yb2Zr2O7. These results suggest a dominant mechanism of incongruent dissolution and surface reorganization for the formation of passivation films. Strong correlations are identified between the leaching rates and cation ionic size, ionic potential, electronegativity differences between A-site cation and Zr, and bonding valence sum of oxygen, suggesting important impacts of structural and bonding characteristics in controlling chemical durability of lanthanide zirconates. 相似文献
7.
8.
Sergey Tkachev Miguel Monteiro João Santos Ernesto Placidi Mohamed Ben Hassine Pedro Marques Paulo Ferreira Pedro Alpuim Andrea Capasso 《Advanced functional materials》2021,31(33):2103287
Graphene-based materials have attracted significant attention in many technological fields, but scaling up graphene-based technologies still faces substantial challenges. High-throughput top-down methods generally require hazardous, toxic, and high-boiling-point solvents. Here, an efficient and inexpensive strategy is proposed to produce graphene dispersions by liquid-phase exfoliation (LPE) through a combination of shear-mixing (SM) and tip sonication (TS) techniques, yielding highly concentrated graphene inks compatible with spray coating. The quality of graphene flakes (e.g., lateral size and thickness) and their concentration in the dispersions are compared using different spectroscopic and microscopy techniques. Several approaches (individual SM and TS, and their combination) are tested in three solvents (N-methyl-2-pyrrolidone, dimethylformamide, and cyrene). Interestingly, the combination of SM and TS in cyrene yields high-quality graphene dispersions, overcoming the environmental issues linked to the other two solvents. Starting from the cyrene dispersion, a graphene-based ink is prepared to spray-coat flexible electrodes and assemble a touch screen prototype. The electrodes feature a low sheet resistance (290 Ω □−1) and high optical transmittance (78%), which provide the prototype with a high signal-to-noise ratio (14 dB) and multi-touch functionality (up to four simultaneous touches). These results illustrate a potential pathway toward the integration of LPE-graphene in commercial flexible electronics. 相似文献
9.
10.
为研究氮气含量的变化对AlCrTaTiZrV高熵合金薄膜性能的影响,检验在最佳氮气含量下厚度为15 nm的(AlCrTaTiZrV)N扩散阻挡层的热稳定性。采用直流磁控溅射设备在N型Si(111)基底上溅射不同氮气含量的高熵合金氮化物;选取最佳氮气含量为制备条件,在硅基底上沉积15 nm厚的AlCrTaTiZrVN10高熵合金氮化物为扩散阻挡层,并在阻挡层顶部沉积50 nm厚度的Cu膜,最终形成Si/AlCrTaTiZrVN10/Cu三层堆叠结构。利用真空退火炉将Si/AlCrTaTiZrVN10/Cu薄膜体系在500 ℃下进行不同时间的退火处理,用以模拟恶劣的工作环境。利用场发射扫描电子显微镜(FESEM)、原子力显微镜(AFM)、X射线衍射仪(XRD)及四探针电阻测试仪(FPP)对试样的表面形貌、粗糙度、物相组成及方块电阻和进行表征。试验结果为:当氮气含量低于10%时,高熵合金氮化物薄膜为非晶结构。当氮气含量为20%时,高熵合金氮化物薄膜呈现FCC结构,并随着氮气含量的增加,薄膜的结晶性得到提高。薄膜表面的粗糙度在氮气含量为10%时最低,Ra仅为0.124 nm。三层堆叠结构500 ℃退火8 h后,Cu表面发生团聚,薄膜的方阻维持在较低的0.070 Ω/□,且并未发现Cu-Si化合物。厚度为15 nm的非晶结构AlCrTaTiZrVN10薄膜在500 ℃退火8 h后,依旧可以抑制Cu的扩散,表现出了优异的热稳定性及扩散阻挡性能。 相似文献