全文获取类型
收费全文 | 58227篇 |
免费 | 5511篇 |
国内免费 | 2965篇 |
专业分类
电工技术 | 4136篇 |
技术理论 | 5篇 |
综合类 | 4115篇 |
化学工业 | 8863篇 |
金属工艺 | 3488篇 |
机械仪表 | 3458篇 |
建筑科学 | 5136篇 |
矿业工程 | 1484篇 |
能源动力 | 1754篇 |
轻工业 | 3669篇 |
水利工程 | 1117篇 |
石油天然气 | 3081篇 |
武器工业 | 500篇 |
无线电 | 7174篇 |
一般工业技术 | 7181篇 |
冶金工业 | 2468篇 |
原子能技术 | 761篇 |
自动化技术 | 8313篇 |
出版年
2024年 | 125篇 |
2023年 | 1019篇 |
2022年 | 1507篇 |
2021年 | 2416篇 |
2020年 | 1775篇 |
2019年 | 1473篇 |
2018年 | 1677篇 |
2017年 | 1867篇 |
2016年 | 1652篇 |
2015年 | 2293篇 |
2014年 | 2791篇 |
2013年 | 3429篇 |
2012年 | 3738篇 |
2011年 | 3975篇 |
2010年 | 3595篇 |
2009年 | 3329篇 |
2008年 | 3455篇 |
2007年 | 3302篇 |
2006年 | 3319篇 |
2005年 | 2806篇 |
2004年 | 2006篇 |
2003年 | 1824篇 |
2002年 | 1888篇 |
2001年 | 1670篇 |
2000年 | 1447篇 |
1999年 | 1553篇 |
1998年 | 1166篇 |
1997年 | 1020篇 |
1996年 | 987篇 |
1995年 | 804篇 |
1994年 | 658篇 |
1993年 | 484篇 |
1992年 | 433篇 |
1991年 | 325篇 |
1990年 | 214篇 |
1989年 | 183篇 |
1988年 | 158篇 |
1987年 | 92篇 |
1986年 | 62篇 |
1985年 | 55篇 |
1984年 | 33篇 |
1983年 | 18篇 |
1982年 | 30篇 |
1981年 | 15篇 |
1980年 | 17篇 |
1979年 | 8篇 |
1978年 | 2篇 |
1959年 | 2篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
苯并噁嗪树脂作为一类新型的热固性树脂,具有分子设计性强、阻燃性能和耐腐蚀性能优异、固化时不需要强酸、无小分子放出等优点,在航空、建筑、电子等领域获得了广泛应用。本文主要介绍了苯并噁嗪单体的合成方法(溶剂法、无溶剂法和悬浮法)、降低苯并噁嗪开环聚合温度的方法(合成具有特殊基团的苯并噁嗪单体、添加催化剂)及苯并噁嗪树脂在形状记忆聚合物中的应用(与其他聚合物混合,纯苯并噁嗪化学改性),对苯并噁嗪形状记忆聚合物目前存在的问题进行了概述并对苯并噁嗪形状记忆聚合物的发展前景做出了展望。 相似文献
93.
针对含风电互联电网日前安全约束机组组合的规模大、约束复杂、求解困难等问题,提出基于目标级联分析技术的分散协调优化策略。将问题分解为负责区域间边界节点电压相角协调的上层优化问题和以并行方式独立优化各区域发电计划的下层优化问题。下层优化以弃风电量期望和电量不足期望,量化各区域内风电、负荷预测误差,以及常规机组强迫停运等系统运行不确定性所带来的风险,并以罚函数的形式引入目标函数,以综合优化系统可靠性与经济性。2区域12节点系统和IEEE RTS96三区域互联系统算例仿真验证所建模型和算法的有效性。 相似文献
94.
Digital light processing (DLP) has been studied and developed in the field of three-dimensional (3D) printing in recent years due to its fast curing rate and high resolution. To reduce the cost and viscosity of the resin system, the aromatic polyurethane acrylates (PUAs) were used as oligomer. The matrix resin called PUH2 consists of oligomers (PUA, bisphenol A polyoxyethylene ether dimethyl acrylate) and active diluents (hydroxyethyl acrylate, hydroxyethyl methacrylate). However, the photosensitive resin containing aromatic isocyanate groups was easily yellowed under ultraviolet light. In this article, we developed a resin for DLP 3D printing with yellowing resistance, excellent mechanical properties and high heat resistance. The optimal ratio of 3DP-PUH2 resin was PUH2/TPO/RYOJI-292/dye/nanosilica = 100/5/0.4/0.01/0.1, and its viscosity was 500 cp, which is suitable for DLP 3D printing. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48369. 相似文献
95.
96.
本文研究了砂类型、砂率、石粉含量和抗压强度对机制砂混凝土耐磨性的影响,建立了磨损量的多因素计算模型。结果表明:由于含石粉及具有更高的粗糙度和坚固性,石灰岩与辉绿岩机制砂制备的C30、C40混凝土耐磨性比河砂混凝土提高20%以上;在0.40~0.44范围内选取较低的砂率可获得较优的耐磨性;利用石粉含量为5%~11%(质量分数)的机制砂制备混凝土,石粉含量为9%时可获得最佳的混凝土耐磨性,微观分析表明此时混凝土密实度最佳;通过灰色系统理论确定了耐磨性影响因素的影响程度排序为:砂率R3>压碎值R2>粗糙度R1>抗压强度R5>石粉含量R4>0.6;对比验证表明提出的混凝土磨损量多因素计算模型具有较高的预测精度和良好的适用性。 相似文献
97.
Hao Shi Qiuyun Fu Geng Wang Lu Zhang Zhiping Zheng Wei Luo Fan Tian Chaohong Wang Tao Yang 《Ceramics International》2018,44(16):19165-19170
A series of (ZrTi)1-x(Mg1/3Sb2/3)2xO4 (0.04?≤?x?≤?0.36) ceramics were successfully synthesized through the conventional solid-state processing. Appropriate content of CuO was added as sintering aids to promote the density of ceramics. The XRD analysis revealed that the main crystalline phase of ceramics sintered at optimal temperature belonged to α-PbO2-type structure. Raman spectroscopy and far infrared reflectivity (FIR) spectra were employed to study the phonon modes of ceramics, which explained the relationship between microwave dielectric properties and structure. It is interesting that the τf are near-zero (+6.6 ~ ?4.6?ppm/°C) and meanwhile the Q×f are relatively high (29,000–41,800?GHz) for samples with x in a very wide range of 0.10–0.36. In this range, their dielectric constants (εr) can be adjustable from 35.4 to 24.4. The results demonstrated this ceramic system is a potential candidate for microwave dielectric applications requiring an adjustable dielectric constants and near zero τf. 相似文献
98.
Wei Zheng Peigen Zhang Li Yang Jian Chen Wubian Tian Yamei Zhang ZhengMing Sun 《Ceramics International》2018,44(18):22456-22461
We report herein a fast and scalable approach to the synthesis of MO/CNT/Fe (MCI) hybrid nanostructures via microwave irradiation of MXene under ambient condition. The effect of three arcing materials, CNT, graphite (C), and carbon fiber (Cf), on the growth of carbon nanotubes on MXene-derived metal oxides were investigated. The resulted MCI nanostructures were tested as anodes in LIBs, all exhibiting better electrochemical performance than that of pristine Ti3C2. Remarkably, MCI-Cf delivered reversible capacities of 430?mA?h?g?1 and 175?mA?h?g?1 at 1?A?g?1 and 10?A?g?1, respectively, which is much higher than that of commercial graphite at high rates. The findings in this work open new exciting opportunities to developing hybrid electrode materials with high specific capacity for energy conversion and storage. 相似文献
99.
WeiJia Luo LingXia Li Shihui Yu Qianyu Guo Bowen Zhang Zheng Sun 《Ceramics International》2018,44(11):12414-12419
Low-loss (Zn1-xNix)ZrNbTaO8 (0.02?≤?x?≤?0.10) ceramics possessing single wolframite structure are initiatively synthesized by solid-state route. Based on the results of Rietveld refinement, complex chemical bond theory is used to establish the correlation between structural characteristics and microwave performance in this ceramic system. A small amount of Ni2+ (x?=?0.06) in A-site with the fixed substitution of Ta5+ in B-site can effectually raise the Q?×?f value of ZnZrNb2O8 ceramic, embodying a dense microstructure and high lattice energy. The dielectric constant and τf are mainly affected by bond ionicity and the average octahedral distortion. The (Zn0.94Ni0.06)ZrNbTaO8 ceramic sample sintered at 1150?°C for 3?h exhibits an outstanding combination of microwave dielectric properties: εr =?27.88, Q?×?f?=?128,951?GHz, τf =?–39.9?ppm/°C. Thus, it is considered to be a candidate material for the communication device applications at high frequency. 相似文献
100.
Shihui Yu Rongchuang Liu Leijiao Ge Lingxia Li Chunmei Zhang Haoran Zheng Yongtao Sun 《Ceramics International》2018,44(3):3005-3008
Using a pulsed laser deposition method the BaZr0.2Ti0.8 O3 (BTZ) lead–free thin films with a thickness of ~250 nm were grown on FTO, ITO and Pt–Si substrates, respectively. The analysis results of microstructural, dielectric properties and leakage current reveal that the thin films deposited on Pt–Si substrates are oriented growth along the (1 1 0) direction and exhibit the optimal performance characteristics. Calculations of figure of merit (FoM) and dielectric tunability display a maximum value of ~42.8 and ~68.5% at E = 400 kV/cm at room temperature, respectively. The excellent tunable properties, high dielectric constant (~635@ 100 kHz) and low leakage current density of (9.3 × 10–8 A/cm2 at 400 kV/cm) make the (1 1 0)–oriented BaZr0.2Ti0.8 O3 thin film to be an attractive material for applications of tunable devices. 相似文献