全文获取类型
收费全文 | 102650篇 |
免费 | 9354篇 |
国内免费 | 6919篇 |
专业分类
电工技术 | 3469篇 |
技术理论 | 2篇 |
综合类 | 6397篇 |
化学工业 | 27669篇 |
金属工艺 | 9452篇 |
机械仪表 | 4709篇 |
建筑科学 | 5236篇 |
矿业工程 | 2484篇 |
能源动力 | 2863篇 |
轻工业 | 6155篇 |
水利工程 | 1198篇 |
石油天然气 | 3726篇 |
武器工业 | 801篇 |
无线电 | 11874篇 |
一般工业技术 | 14640篇 |
冶金工业 | 4061篇 |
原子能技术 | 1628篇 |
自动化技术 | 12559篇 |
出版年
2024年 | 259篇 |
2023年 | 1791篇 |
2022年 | 2234篇 |
2021年 | 3961篇 |
2020年 | 3167篇 |
2019年 | 2922篇 |
2018年 | 2574篇 |
2017年 | 3237篇 |
2016年 | 3746篇 |
2015年 | 3720篇 |
2014年 | 5362篇 |
2013年 | 5816篇 |
2012年 | 6575篇 |
2011年 | 8374篇 |
2010年 | 6268篇 |
2009年 | 7114篇 |
2008年 | 6071篇 |
2007年 | 7136篇 |
2006年 | 6419篇 |
2005年 | 5392篇 |
2004年 | 4250篇 |
2003年 | 3948篇 |
2002年 | 3151篇 |
2001年 | 2407篇 |
2000年 | 2314篇 |
1999年 | 1857篇 |
1998年 | 1459篇 |
1997年 | 1107篇 |
1996年 | 1025篇 |
1995年 | 815篇 |
1994年 | 769篇 |
1993年 | 604篇 |
1992年 | 510篇 |
1991年 | 422篇 |
1990年 | 346篇 |
1989年 | 260篇 |
1988年 | 172篇 |
1987年 | 156篇 |
1986年 | 189篇 |
1985年 | 136篇 |
1984年 | 104篇 |
1983年 | 95篇 |
1982年 | 92篇 |
1981年 | 77篇 |
1980年 | 78篇 |
1979年 | 72篇 |
1977年 | 68篇 |
1976年 | 68篇 |
1975年 | 75篇 |
1974年 | 78篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
与传统的涂覆、沉积等加工手段相比,使用3D打印技术可制造复杂立体功能结构的传感器,将3D打印与柔性传感技术结合可以促进未来生物医疗、人工智能等领域的发展。本文介绍了国内外基于3D打印技术制造柔性传感器的最新进展,其中包括聚酰亚胺等多种基底材料、纳米金属等多种打印传感材料;按照熔融沉积、黏弹性墨水沉积、粉末烧结熔化、还原光聚合和材料喷射的制造原理分别阐述了多种传感器的材料选择、成型特点,并对制造方法进行总结分析。虽然3D打印制造柔性传感器件存在着缺乏行业标准及多种类打印材料等问题,但经过不断创新与发展,3D打印将成为柔性传感领域极佳的制造手段。 相似文献
62.
63.
64.
Wan‐Xia Wu 《Polymer International》2019,68(11):1848-1855
A series of novel aliphatic poly(β‐thioether ester)s with various methylene group contents were prepared by direct lipase‐catalyzed polycondensation of the monomer with an acid‐labile β‐thiopropionate group. The polycondensation reaction using immobilized lipase B from Candida antarctica was carried out in diphenyl ether at 90 °C. Poly(β‐thioether ester)s with high molecular weights of 20 500–57 000 Da and narrow polydispersities in the range 1.40–1.48 were obtained. Thermogravimetric analysis, differential scanning calorimetry and wide‐angle X‐ray diffraction were used to investigate the thermal properties and crystal structures of these polyesters. All the poly(β‐thioether ester)s were semicrystalline polymers and thermally stable up to at least 200 °C. In vitro degradation studies showed that they can rapidly degrade under acidic conditions by the hydrolysis of the β‐thiopropionate groups, suggesting their potential as acid‐degradable polymeric materials. © 2019 Society of Chemical Industry 相似文献
65.
Potential mGAT4 inhibitors derived from the lead substance (S)-SNAP-5114 have been synthesized and characterized for their inhibitory potency. Variations from the parent compound included the substitution of one of its aromatic 4-methoxy and 4-methoxyphenyl groups, respectively, with a more polar moiety, including a carboxylic acid, alcohol, nitrile, carboxamide, sulfonamide, aldehyde or ketone function, or amino acid partial structures. Furthermore, it was investigated how the substitution of more than one of the aromatic 4-methoxy groups affects the potency and selectivity of the resulting compounds. Among the synthesized test substances (S)-1-{2-[(4-formylphenyl)bis(4-methoxyphenyl)-methoxy]ethyl}piperidine-3-carboxylic acid, that features a carbaldehyde function in place of one of the aromatic 4-methoxy moieties of (S)-SNAP-5114, was found to have a pIC50 value of 5.89±0.07, hence constituting a slightly more potent mGAT4 inhibitor than the parent substance while showing comparable subtype selectivity. 相似文献
66.
《Ceramics International》2019,45(15):18972-18979
Kaolin/graphene oxide composite has been widely utilized in aero-space and architectural engineering applications due to its excellent mechanical property. Direct ink writing (DIW) is a freeform rapid prototyping technology that could be used to accurately fabricate the resulting size with complex shapes. In this study, we reported the DIW of kaolin/graphene oxide (GO) composite suspensions (KGCS) to assemble 3D structures at ambient temperature for the first time. The effects of GO on the chemical constitution and microstructure of kaolin suspensions were investigated. Rheology was characterized to ensure printability of KGCS. The addition of GO in kaolin suspensions quickened a flocculation structure, which dramatically changed their rheology properties. The DIW of 3D structures from the optimal KGCS sample maintained their initial shape without spreading. The flexural and compressive strengths of the dried optimal KGCS samples were obviously enhanced due to the improvement and reduction of the micro-defects compared from cured kaolin matrix. 相似文献
67.
在伯克氏菌Bth264野生株产新型抗癌药物Thailandepsin A以及调节基因tdp R正向调控Thailandepsin A生物合成的基础上,利用基因工程菌Bth264/p BMTL3-tdp R发酵生产Thailandepsin A,以提高产量。以0.5%乳糖为诱导剂,确定最佳诱导条件:发酵15 h添加乳糖,诱导时间6 h;通过单因素实验,确定葡萄糖和胰蛋白胨作为碳氮源、装液量65/250 m L以及接种量1%;同时结合优化发酵培养基进行发酵,Thailandepsin A产量达到252.14 mg·L-1,比优化前的产量提高56%;另外在发酵过程中,添加大孔树脂HP-20原位吸附产物,Thailandepsin A产量可达283.75 mg·L-1,比不加树脂提高13.8%;最后,基于RT-PCR和比较Ct值法,基因工程菌和野生菌相比,Thailandepsin A生物合成基因tdp B、tdp C1的转录水平分别提高11.4倍和6.0倍,对应的产量增加4.6倍,从而在很大程度上说明调节基因tdp R的过表达促进生物合成基因转录水平的提高以及产量的增加。 相似文献
68.
The effect of Li2O on the crystallization properties of CaO-Al2O3-SiO2-Li2O-Ce2O3 slags was investigated. With increasing the Li2O content, LiAlO2 and CaCeAlO4 were the main crystalline phases. LiAlO2 formed for the charge compensating of Li+ ions to [AlO45?]-tetrahedrons, and CaCeAlO4 formed as a result of the charge balance of Ce3+ ions, Ca2+ ions, and [AlO69?]-octahedrons. Increasing the content of Li2O to 10%, the crystallization temperature was the highest, and the incubation time was the shortest. The crystallization ability was strong due to the three factors of strengthening the interaction between ions and ion groups, decreasing the polymerization degree, and increasing the melting temperature. Further increasing the content of Li2O, the crystallization performance was obviously suppressed, because the melting temperature and the force between the cations and the anion groups decreased. 相似文献
69.
本研究分别利用水冷铜坩埚真空感应熔炼气雾化(VIGA-CC)和等离子旋转电极(PREP)两种技术制备出球形Ti-6Al-4V合金粉末,作者利用SEM、同步辐射CT扫描-三维重建和氩气含量测试等分析手段对不同粒径的Ti-6Al-4V合金粉末的孔洞缺陷和氩气含量、硬度值进行了表征。实验结果表明, VIGA-CC粉末粒度分布宽,细粉收得率较多,粉末粒度分布在40~180 μm之间, PREP粉末的粒度分布较窄,主要集中在110~180 μm之间;金属粉末内部的孔隙率、气体含量和孔尺寸随着粉末粒度的增大而增大,且同一粒径范围内VIGA-CC粉末的气孔概率多于PREP粉末;随着粉末粒径减小,粉末截面组织逐渐细化,其硬度值逐渐升高,整体上VIGA-CC粉末硬度值高于PREP粉末。 相似文献
70.