全文获取类型
收费全文 | 248114篇 |
免费 | 23688篇 |
国内免费 | 11385篇 |
专业分类
电工技术 | 18567篇 |
技术理论 | 33篇 |
综合类 | 24601篇 |
化学工业 | 27748篇 |
金属工艺 | 10081篇 |
机械仪表 | 13737篇 |
建筑科学 | 34021篇 |
矿业工程 | 14710篇 |
能源动力 | 8801篇 |
轻工业 | 16407篇 |
水利工程 | 13182篇 |
石油天然气 | 12479篇 |
武器工业 | 3337篇 |
无线电 | 18271篇 |
一般工业技术 | 17609篇 |
冶金工业 | 12000篇 |
原子能技术 | 2112篇 |
自动化技术 | 35491篇 |
出版年
2024年 | 464篇 |
2023年 | 3139篇 |
2022年 | 5878篇 |
2021年 | 8130篇 |
2020年 | 7874篇 |
2019年 | 5872篇 |
2018年 | 5550篇 |
2017年 | 7025篇 |
2016年 | 8834篇 |
2015年 | 9717篇 |
2014年 | 17466篇 |
2013年 | 15383篇 |
2012年 | 18863篇 |
2011年 | 20482篇 |
2010年 | 14928篇 |
2009年 | 15185篇 |
2008年 | 13912篇 |
2007年 | 16700篇 |
2006年 | 15186篇 |
2005年 | 13367篇 |
2004年 | 11085篇 |
2003年 | 9582篇 |
2002年 | 7704篇 |
2001年 | 6227篇 |
2000年 | 5238篇 |
1999年 | 4013篇 |
1998年 | 2829篇 |
1997年 | 2432篇 |
1996年 | 2015篇 |
1995年 | 1705篇 |
1994年 | 1429篇 |
1993年 | 1019篇 |
1992年 | 805篇 |
1991年 | 583篇 |
1990年 | 495篇 |
1989年 | 461篇 |
1988年 | 261篇 |
1987年 | 191篇 |
1986年 | 172篇 |
1985年 | 196篇 |
1984年 | 142篇 |
1983年 | 126篇 |
1982年 | 71篇 |
1981年 | 84篇 |
1980年 | 85篇 |
1979年 | 42篇 |
1978年 | 22篇 |
1977年 | 25篇 |
1964年 | 20篇 |
1959年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
为解决沧州市涉地税源管理手段单一等问题,文中提出以测绘地理信息技术为支撑,通过对多源数据组织管理,建立风险分析指标,采用多种GIS空间分析方法构建了涉地风险税源识别模式并在沧州进行应用。结果表明:该模式能有效识别多种涉地风险,为涉地税源管理提供了支撑。 相似文献
32.
Kazushi Shibutani Jun Nakai Ketkanok Aphichartsuphapkhajorn Yoshihito Kayaki Shigeki Kuwata Yoshihiko Arao Masatoshi Kubouchi 《应用聚合物科学杂志》2021,138(17):50311
The effect of oxygen and additional oxygen providers on furfuryl alcohol polymerization was investigated through chemical analyses and mechanical evaluation. NMR, UV–vis, Fourier transform infrared, and gas chromatography–mass spectrometry (GC–MS) results suggested that atmospheric oxygen and the further addition of an oxygen source functioned as an activator for the entire network polymerization. Interestingly, the construction of a conjugated structure on the furan linear chain, which is key to three-dimensional cross-linking, also appears to be accelerated in the presence of oxygen. Furthermore, the introduction of oxygen providers into the curing system successfully enhanced the mechanical properties of the cured furan resin. 相似文献
33.
为改善涂层在真空、高温等苛刻条件下的摩擦学性能,利用中频直流磁控溅射技术在硅片和316L不锈钢上沉积了CrN和CrN/Ag涂层,利用扫描电镜、透射电镜和X射线衍射仪对涂层的成分及相结构进行了表征,通过划痕测试仪、纳米压痕仪和摩擦磨损试验机测试了涂层的力学及摩擦学性能。结果表明:添加Ag元素以后,CrN/Ag涂层硬度及承载能力有所减小,但结合强度增加;真空高温环境下CrN与CrN/Ag涂层摩擦因数随温度升高呈下降趋势,其中CrN涂层通过软化镀层减小剪切强度和阻力,从而减小摩擦因数,CrN/Ag涂层主要通过高温产生的热驱动力诱导表面Ag润滑膜的形成来减小摩擦因数;CrN涂层依靠自身剪切特性参与摩擦,而CrN/Ag涂层在真空高温下具有自润滑和持续润滑性能,作为自润滑零部件具有潜在的应用价值。 相似文献
34.
文中提出了一种利用有限数量的相量测量单元(PMU)和相量数据集中器(PDC)设计最优监控结构的方法。通过在大量的设定值场景下,使电力系统可观测性曲线的期望值最大化,同时使通信基础设施成本最小化,最终确定PMU和PDC的最佳位置。提出了一种非线性动态扩展卡尔曼滤波(EFK)状态观测器。这种状态观测器可以将暂态行为转换为由代数微分方程描述的广域电力系统,而无需非线性反演技术。最后以IEEE-5电力系统为例,说明了该方法的有效性。 相似文献
35.
Navid Khaleghimoghaddam Havva Alkan Bala G zin zmen &Scedil erefnur zt rk 《建筑学研究前沿(英文版)》2022,11(5):877-890
Environment psychologically affects individuals. According to the base of cognitive psychology, there is a direct relationship between human behavior, environment, and emotional process. Assuming that pleasantness and unpleasantness are associated with peripheral nervous system activation, the current study aims to explore if the pleasant or unpleasant architectural places can stimulate the brain regions engaged in emotions or not. As the main contribution, we used functional magnetic resonance imaging (fMRI) measuring blood oxygenation level-dependent (BOLD) changes to effectively detect the brain's region that mainly responds to the emotional-perceptual processes. Based on the results of examining the emotional assessment model of “Pleasure-Arousal” applied to 140 students, 30 most-rated images representing 15 pleasant and 15 unpleasant places were shown to 32 participants in a 1.5-T MRI scanner. After applying standard preprocessing steps (re-alignment, slice-timing, co-registration, segmentation, normalization, and smoothing) to functional MR images, first-level analysis was applied to each subject. The results were evaluated using statistical corrections at different levels for female and male participants with the second-level analysis. In conclusion, it has been shown that there is a significant linkage between environmental experience and brain activation so that the architectural qualities can change blood flow in specific brain regions. 相似文献
36.
《International Journal of Hydrogen Energy》2022,47(9):6078-6088
The widespread use of fuel cell technology is hampered by the use of expensive and scarce platinum metal in electrodes which is required to facilitate the sluggish oxygen reduction reaction (ORR). In this work, a viable synthetic approach was developed to prepare iron-based sulfur and nitrogen dual doped porous carbon (Fe@SNDC) for use in ORR. Benzimidazole, a commercially available monomer, was used as a precursor for N doped carbon and calcined with potassium thiocyanate at different temperatures to tune the pore size, nitrogen content and different types of nitrogen functionality such as pyridinic, pyrrolic and graphitic. The Fe@SNDC–950 with high surface area, optimum N content of about 5 at% and high amount of pyridinic and graphitic N displayed an onset potential and half-wave potential of 0.98 and 0.83 V vs RHE, respectively, in 0.1 M KOH solution. The catalyst also exhibits similar oxygen reduction reaction performance compared to Pt/C (20 wt%) in acidic media. Furthermore, when compared to commercially available Pt/C (20 wt%), Fe@SNDC–950 showed enhanced durability over 6 h and poison tolerance in case of methanol crossover with the concentration up to 3.0 M in oxygen saturated alkaline electrolyte. Our study demonstrates that the presence of N and S along with Fe-N moieties synergistically served as ORR active sites while the high surface area with accessible pores allowed for efficient mass transfer and interaction of oxygen molecules to the active sites contributing to the ORR activity of the catalyst. 相似文献
37.
38.
39.
40.