全文获取类型
收费全文 | 10066篇 |
免费 | 622篇 |
国内免费 | 462篇 |
专业分类
电工技术 | 221篇 |
综合类 | 516篇 |
化学工业 | 3514篇 |
金属工艺 | 1428篇 |
机械仪表 | 309篇 |
建筑科学 | 69篇 |
矿业工程 | 234篇 |
能源动力 | 133篇 |
轻工业 | 41篇 |
水利工程 | 2篇 |
石油天然气 | 29篇 |
武器工业 | 58篇 |
无线电 | 495篇 |
一般工业技术 | 1437篇 |
冶金工业 | 2535篇 |
原子能技术 | 35篇 |
自动化技术 | 94篇 |
出版年
2024年 | 30篇 |
2023年 | 372篇 |
2022年 | 441篇 |
2021年 | 416篇 |
2020年 | 442篇 |
2019年 | 377篇 |
2018年 | 373篇 |
2017年 | 449篇 |
2016年 | 338篇 |
2015年 | 283篇 |
2014年 | 454篇 |
2013年 | 395篇 |
2012年 | 542篇 |
2011年 | 621篇 |
2010年 | 443篇 |
2009年 | 538篇 |
2008年 | 352篇 |
2007年 | 609篇 |
2006年 | 518篇 |
2005年 | 485篇 |
2004年 | 432篇 |
2003年 | 404篇 |
2002年 | 338篇 |
2001年 | 286篇 |
2000年 | 255篇 |
1999年 | 207篇 |
1998年 | 133篇 |
1997年 | 109篇 |
1996年 | 87篇 |
1995年 | 88篇 |
1994年 | 55篇 |
1993年 | 36篇 |
1992年 | 48篇 |
1991年 | 47篇 |
1990年 | 62篇 |
1989年 | 64篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
研制的陶瓷材料可在超低温度(1 030 ℃±15 ℃)下烧结,获得瓷料的相对介电常数高于2 100,介质损耗不高于1.5%,温度特性满足X7R特性要求标准.与传统的X7R特性材料比较,本材料烧结温度更低,同时材料中不添加Pb、Hg、Cd、Cr等有害元素,符合绿色环保要求及欧盟RoHS指令要求. 相似文献
152.
利用高温真空烧结炉对凝胶注模(Gel-casting)成型的SiC素坯进行反应烧结(RB-SiC),可制备得到光学级别的碳化硅反射镜镜体.测试结果表明,镜体内部结构均匀致密,机械性能优异,烧结线收缩率<0.23%,直接抛光后的表面粗糙度RMS值优于3 nm,适用于空间大尺寸碳化硅反射镜的制备. 相似文献
153.
154.
采用X-射线衍射(XRD)、扫描电镜(SEM)等手段研究了CeO2在堇青石基玻璃烧结中的作用及其添加量对微晶玻璃的烧结和性能的影响。结果表明,CeO2的加入可有效促进微晶玻璃的烧结致密化;随着CeO2加入量的增加,烧结样品的介电常数呈现先增加后降低的趋势,且与密度变化曲线相似;当CeO2添加量达4%(质量分数)时样品的介质损耗因子最低(≈0.2%)。 相似文献
155.
采用激光烧结技术,制备出相对密度为97.5%的Sr1.86Ca0.14NaNb5O15(SCNN)无Pb压电陶瓷。最佳烧结条件为:激光烧结功率密度为1.99W/mm2;激光烧结时间为60s;激光功率密度升降速率为0.50W/mm2.min。与传统炉烧SCNN陶瓷相比,激光烧结SCNN陶瓷室温下1MHz的介电常数κ从1312增长到1419,机电耦合系数k33从17%增长到了27%,压电常数d33从60pC/N提高到93pC/N。扫描电镜(SEM)观测发现:与传统炉烧陶瓷相比,激光烧结SCNN陶瓷的晶粒尺寸较小,气孔较少,Na挥发较少;陶瓷片的X射线衍射(XRD)分析表明,激光烧结陶瓷的晶粒具有一定程度的取向生长。 相似文献
156.
对激光直接快速成形金属零件过程中多道搭接进行了理论及实验研究,包括搭接率的确定,多道搭接的工艺研究以及搭接烧结层的组织形貌分析等. 相似文献
157.
Yanhao Dong Hongbing Yang Lin Zhang Xingyu Li Dong Ding Xiaohui Wang Ju Li Jiangong Li I-Wei Chen 《Advanced functional materials》2021,31(1):2007750
Nanocrystalline materials with superior properties are of great interest. Much is discussed about obtaining nanograins, but little is known about maintaining grain-size uniformity that is critical for reliability. An especially intriguing question is whether it is possible to achieve a size distribution narrower than what Hillert theoretically predicted for normal grain growth, a possibility suggested—for growth with a higher growth exponent—by the generalized mean-field theory of Lifshitz, Slyozov, Wagner (LSW), and Hillert but never realized in practice. Following a rationally designed two-step sintering route, it has been made possible in bulk materials by taking advantage of the large growth exponent in the intermediate sintering stage to form a uniform microstructure despite residual porosity, and freezing the grain growth thereafter while continuing densification to reach full density. The bulk dense Al2O3 ceramic thus obtained has an average grain size of 34 nm and a size distribution much narrower than Hillert's prediction. Bulk Al2O3 with a grain-size distribution narrower than the particle-size distribution of starting powders is also demonstrated, as are highly uniform bulk engineering metals (refractory Mo and W-Re alloy) and complex functional ceramics (BaTiO3-based alloys with superior dielectric strength and energy capacity). 相似文献
158.
PLZT ceramics with the composition of 9/62/38 (La/Zr/Ti) were fabricated from spraydried aqueous solution. Complete crystallization
of the spray-dried powder is achieved after 1 hr calcination at 650‡ C as compared to 800‡ C, 1 hr for conventional mixedoxide
method. Sintering environment plays an important role in the densification of PLZT ceramics. Densities of the atmosphere sintered
samples are much higher than those of normal sintered ones. PLZT ceramics derived from spray-dried powders have properties
comparable to those derived from sol-gel ones. The spray-dried method presents a less expensive and more effective approach
in the synthesis of PLZT ceramics. 相似文献
159.
Fanbo Meng Mingchang Zhang Jin Huang Wen Feng Lu Jun Min Xue Hao Wang 《Advanced functional materials》2021,31(9):2008280
The development of the Internet of things has prompted an exponential increase in the demand for flexible, wearable devices, thereby posing new challenges to their integration and conformalization. Additive manufacturing facilitates the fabrication of complex parts via a single integrated process. Herein, the development of a multinozzle, multimaterial printing device is reported. This device accommodates the various characteristics of printing materials, ensures high-capacity printing, and can accommodate a wide range of material viscosities from 0 to 1000 Cp. Complete capacitors, inclusive of the current collector, electrode, and electrolyte, can be printed without repeated clamping to complete the preheating, printing, and sintering processes. This method addresses the poor stability issue associated with printed electrode materials. Furthermore, after the intercalation of LiFePO4 with Na ions, X-ray photoelectron spectroscopy and X-ray diffraction results reveal that the Na ions permeate the interlayer structure of LiFePO4, enhancing the ion migration channels by increasing the ion transmission rate. A current rate of 2.5 mAh ensures >2000 charge/discharge cycles, while retaining a charge/discharge efficiency of 96% and a discharge capacity of 91.3 mAh g−1. This manufacturing process can provide conformal power modules for a diverse range of portable devices with various shapes, improving space utilization. 相似文献
160.
采用传统固相反应法合成ZnNb2O6陶瓷粉体。系统研究了添加不同含量V2O5对ZnNb2O6陶瓷的烧结特性及介电性能的影响。结果表明:其烧结温度降低到1 050℃,且当V2O5质量分数大于1.0%时有第二相ZnV2O6生成。添加V2O5后ZnNb2O6陶瓷的谐振频率温度系数向0方向偏移。当V2O5质量分数为1.0%的ZnNb2O6陶瓷在1 050℃烧结3h时,其介电性能为εr=28,tanδ=0.000 6,τf=-42.5×10-6/℃(在1 MHz下)。 相似文献