全文获取类型
收费全文 | 88307篇 |
免费 | 8185篇 |
国内免费 | 6154篇 |
专业分类
电工技术 | 3351篇 |
技术理论 | 1篇 |
综合类 | 5506篇 |
化学工业 | 23168篇 |
金属工艺 | 7917篇 |
机械仪表 | 4483篇 |
建筑科学 | 3480篇 |
矿业工程 | 2243篇 |
能源动力 | 2058篇 |
轻工业 | 5662篇 |
水利工程 | 1168篇 |
石油天然气 | 3132篇 |
武器工业 | 678篇 |
无线电 | 10373篇 |
一般工业技术 | 12427篇 |
冶金工业 | 3480篇 |
原子能技术 | 1203篇 |
自动化技术 | 12316篇 |
出版年
2024年 | 226篇 |
2023年 | 1526篇 |
2022年 | 1932篇 |
2021年 | 3468篇 |
2020年 | 2785篇 |
2019年 | 2526篇 |
2018年 | 2238篇 |
2017年 | 2758篇 |
2016年 | 3118篇 |
2015年 | 3168篇 |
2014年 | 4611篇 |
2013年 | 5092篇 |
2012年 | 5791篇 |
2011年 | 7348篇 |
2010年 | 5501篇 |
2009年 | 6125篇 |
2008年 | 5389篇 |
2007年 | 6243篇 |
2006年 | 5661篇 |
2005年 | 4702篇 |
2004年 | 3668篇 |
2003年 | 3239篇 |
2002年 | 2632篇 |
2001年 | 2012篇 |
2000年 | 1916篇 |
1999年 | 1540篇 |
1998年 | 1226篇 |
1997年 | 967篇 |
1996年 | 906篇 |
1995年 | 696篇 |
1994年 | 648篇 |
1993年 | 529篇 |
1992年 | 419篇 |
1991年 | 352篇 |
1990年 | 268篇 |
1989年 | 229篇 |
1988年 | 151篇 |
1987年 | 124篇 |
1986年 | 154篇 |
1985年 | 103篇 |
1984年 | 80篇 |
1983年 | 73篇 |
1982年 | 76篇 |
1981年 | 55篇 |
1980年 | 66篇 |
1979年 | 48篇 |
1977年 | 50篇 |
1976年 | 52篇 |
1975年 | 53篇 |
1974年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
91.
Anton Polotai Julie Voak Jim Henry David Thoss Yi Yang Sanjay Chitale 《International Journal of Applied Ceramic Technology》2020,17(2):728-733
The need for electronics to operate at temperatures of 200°C and above continues to grow. These applications include avionics, aerospace, automotive, downhole drilling, mining, and many others. To satisfy this demand, a significant amount of research and development has been conducted. Despite the efforts, the number of new electronic components designed specifically for high-temperature operation is still relatively limited. In Low Temperature Co-fired Ceramic (LTCC) packages, LTCC materials are generally used as the host media for a number of pre-fabricated semiconductor components. As a result, reliability of the entire LTCC package largely depends on the performance of the least robust component. Ferro A6M-E and Ferro L8 are the two well-established and recognized LTCC dielectrics widely used for mid and high frequency LTCC applications, including several high reliability aerospace and defense applications that require demanding Mil-Spec qualifications. This study is our first attempt to characterize and understand basic high-temperature dielectric properties of these two commercial LTCC materials. The secondary objective is to initiate a dialogue in attempt to establish reliability requirements for LTCC packages dedicated for high-temperature operation. 相似文献
92.
93.
Peng Jiang Jiafeng Lu Kun Li Xiquan Chen Ruiqi Dan 《Fullerenes, Nanotubes and Carbon Nanostructures》2020,28(5):381-386
AbstractPreparation condition can affect the structure and the properties of nanofiber membrane. In order to explore suitable conditions to prepare the Fe3O4/PVDF nanofiber membrane with good hydrophobicity, the hydrophobicity of Fe3O4/PVDF nanofiber membranes obtained by electrospinning was investigated by changing preparation conditions like weight percentage of Fe3O4 nanoparticles, blending quality concentration of poly (vinylidene fluoride) (PVDF) and Fe3O4 nanoparticles, and positive voltage. And the variations of hydrophobicity of Fe3O4/PVDF nanofiber membranes modified by 1H, 1H, 2H, 2H-perfluorodecyl trimethoxysilane were studied. The results show that the hydrophobicity of Fe3O4/PVDF nanofiber membranes has changed under different preparation conditions. The contact angles of samples increased after a modification by 1H, 1H, 2H, 2H-perfluorodecyl trimethoxysilane, which indicates that the hydrophobicity of Fe3O4/PVDF nanofiber membranes has been enhanced. 相似文献
94.
95.
Eicosapentaenoic acid (EPA) production by an oleaginous fungus Mortierella alpina expressing heterologous the Δ17‐desaturase gene under ordinary temperature 下载免费PDF全文
96.
《Ceramics International》2020,46(10):16465-16471
Pore size and connectivity of artificial bone scaffolds play key role in regulating cell ingrowth and vascularization during healing. The objective of this study was to develop a novel process for preparing 3D pore-interconnected open-cell bone substitutes with varying pore sizes. This was achieved by thermal-induced expansion, drying, then sintering the mixture of biphasic calcium phosphate (BCP) and a thermal responsive porogen comprising chitosan (CS) and hydroxypropyl methyl cellulose (HPMC). The interpolymer complexes (IPCs) of CS/HPMC were prepared and investigated by FT-IR. The mixtures of IPCs/BCP were heated up to 100 °C for analyzing their thermal expansion properties. This resulted in ~13% and ~42% volume increment for IPC-1/BCP and IPC-2/BCP, respectively, while ~230% volume increased in the case of IPC-3/BCP (therefore chosen for sintering bone blocks). Heating rate-dependent (0.20–0.25 °C/min range) sintering profiles for IPC-3/BCP were utilized to produce BCP bone blocks. Gasification of IPC during sintering resulted in the formation of interconnected porous structures, and the morphology was investigated by SEM, revealing varying sizes ranging from 106 ± 13 μm to 1123 ± 75 μm. The pore size range of bone blocks from 235 ± 46 μm to 459 ± 76 μm portrayed significantly high MC3T3-E1 cell viability with prominent filopodial extensions, and elongated cells, depicting efficient biocompatibility. Therefore, the process for preparing porous interconnected 3D bone blocks were feasible, thereby serving as an alternative for potential bone tissue engineering applications. 相似文献
97.
F. Schröder R. M. Ward A. R. Walpole R. P. Turner M. M. Attallah J.-C. Gebelin 《Materials Science & Technology》2015,31(3):372-384
Linear friction welding of the Ti6Al4V alloy is studied. A new definition of the energy input rate is proposed, based on an integration over time of the in-plane force and velocity; a strong correlation with the upset rate is then found. The effective friction coefficient is estimated to be 0·5±0·1 for varying frequencies and amplitudes, with only a weak dependence on the processing conditions displayed. A model is proposed that accounts for both the conditioning and equilibrium stages of the process, which is shown to be in good agreement with the experimental data. The model is used to study the mechanism by which the flash is formed. A criterion is proposed by which the rippled nature of its morphology can be predicted. 相似文献
98.
在Fe-As(Ⅲ)-Cu(Ⅱ)-H2O体系中, 研究了酸性废水中As(Ⅲ)、Cu(Ⅱ)与金属铁粉的反应行为, 考察了反应过程中As在气、液、固三相中的分配比。结果表明, As(Ⅲ)和Cu(Ⅱ)离子被Fe还原为单质As和Cu后, As、Cu进一步结合成Cu5As2等金属间化合物, 从而促进As(Ⅲ)沉淀反应的发生, 且无AsH3生成。在反应时间40min、铁粉过量系数1.2、溶液初始pH=0.0、温度40 ℃、Cu/As摩尔比1.0条件下, As在气、液、固三相中的分配比分别为0、20.7%和79.3%, 沉砷率为79.3%。 相似文献
99.
100.
Tomasz Wasiewicz Paulina Szyszka Miroslawa Cichorek Zorica Janjetovic Robert C. Tuckey Andrzej T. Slominski Michal A. Zmijewski 《International journal of molecular sciences》2015,16(4):6645-6667
Deregulated melanogenesis is involved in melanomagenesis and melanoma progression and resistance to therapy. Vitamin D analogs have anti-melanoma activity. While the hypercalcaemic effect of the active form of Vitamin D (1,25(OH)2D3) limits its therapeutic use, novel Vitamin D analogs with a modified side chain demonstrate low calcaemic activity. We therefore examined the effect of secosteroidal analogs, both classic (1,25(OH)2D3 and 25(OH)D3), and novel relatively non-calcemic ones (20(OH)D3, calcipotriol, 21(OH)pD, pD and 20(OH)pL), on proliferation, colony formation in monolayer and soft-agar, and mRNA and protein expression by melanoma cells. Murine B16-F10 and hamster Bomirski Ab cell lines were shown to be effective models to study how melanogenesis affects anti-melanoma treatment. Novel Vitamin D analogs with a short side-chain and lumisterol-like 20(OH)pL efficiently inhibited rodent melanoma growth. Moderate pigmentation sensitized rodent melanoma cells towards Vitamin D analogs, and altered expression of key genes involved in Vitamin D signaling, which was opposite to the effect on heavily pigmented cells. Interestingly, melanogenesis inhibited ligand-induced Vitamin D receptor translocation and ligand-induced expression of VDR and CYP24A1 genes. These findings indicate that melanogenesis can affect the anti-melanoma activity of Vitamin D analogs in a complex manner. 相似文献