全文获取类型
收费全文 | 127159篇 |
免费 | 14201篇 |
国内免费 | 8280篇 |
专业分类
电工技术 | 10693篇 |
技术理论 | 6篇 |
综合类 | 10993篇 |
化学工业 | 18073篇 |
金属工艺 | 7336篇 |
机械仪表 | 8690篇 |
建筑科学 | 10481篇 |
矿业工程 | 4334篇 |
能源动力 | 3429篇 |
轻工业 | 11178篇 |
水利工程 | 3266篇 |
石油天然气 | 5546篇 |
武器工业 | 1748篇 |
无线电 | 14855篇 |
一般工业技术 | 12288篇 |
冶金工业 | 5236篇 |
原子能技术 | 1803篇 |
自动化技术 | 19685篇 |
出版年
2024年 | 779篇 |
2023年 | 2330篇 |
2022年 | 4899篇 |
2021年 | 6510篇 |
2020年 | 4815篇 |
2019年 | 3632篇 |
2018年 | 4059篇 |
2017年 | 4644篇 |
2016年 | 4031篇 |
2015年 | 6012篇 |
2014年 | 7574篇 |
2013年 | 8776篇 |
2012年 | 10375篇 |
2011年 | 10657篇 |
2010年 | 9855篇 |
2009年 | 9209篇 |
2008年 | 8961篇 |
2007年 | 8306篇 |
2006年 | 7416篇 |
2005年 | 6140篇 |
2004年 | 4217篇 |
2003年 | 2908篇 |
2002年 | 2703篇 |
2001年 | 2232篇 |
2000年 | 2056篇 |
1999年 | 1593篇 |
1998年 | 877篇 |
1997年 | 799篇 |
1996年 | 734篇 |
1995年 | 615篇 |
1994年 | 430篇 |
1993年 | 340篇 |
1992年 | 284篇 |
1991年 | 191篇 |
1990年 | 144篇 |
1989年 | 123篇 |
1988年 | 101篇 |
1987年 | 56篇 |
1986年 | 53篇 |
1985年 | 21篇 |
1984年 | 28篇 |
1983年 | 14篇 |
1982年 | 17篇 |
1981年 | 26篇 |
1980年 | 35篇 |
1979年 | 12篇 |
1978年 | 4篇 |
1976年 | 4篇 |
1959年 | 16篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
以钛酸四丁酯为原料,利用溶胶凝胶法制备了Cr/Ag共掺杂的TiO2纳米材料.采用XRD、SEM、EDS等测试分析技术对掺杂纳米TiO2粉体进行了表征;以甲基橙为降解物,在太阳光照射条件下研究了掺杂对光催化活性的影响.研究结果表明:掺杂后的纳米TiO2的光催化性能明显提高,优于纯TiO2.当共掺杂的比例为Cr 1.0%/Ag 0.5%时,样品的效果最佳,对甲基橙的3h降解率达到97.63%. 相似文献
992.
改良型腰果酚醛树脂应用到铸件等浸渍、粘合、烘干等过程中会产生恶臭,排放前需要降解处理。研究采用低温等离子体技术结合吸收方法处理改良型腰果酚醛树脂废气,考察了处理工程中峰值电压、停留时间、吸收液pH值对废气去除率的影响。实验室小试改良型腰果酚醛树脂废气进口浓度85 ppm,停留时间1.2 s时,去除率可达92%;工业扩大示范工程去除率最高可达80%,排气口出气平均恶臭浓度1 239.5(无量纲),满足《恶臭污染物排放标准》(GB14554-93)中相关规定。 相似文献
993.
介绍一种基于六边形人工磁导体结构采用标准CMOS工艺的60 GHz片上天线的设计。标准CMOS工艺以金属硅为衬底,但衬底硅的低电阻率(10Ω·cm)和低的电子迁移率特性对天线辐射有较大影响。AMC结构通过合理的设计具有类似于理想磁壁的同相位反射特性。通过在天线与硅衬底之间周期加载AMC结构,可以有效地提高天线的增益、辐射效率等。重点讨论了采用人工磁导体结构的天线优化设计,并基于三维电磁仿真软件Ansoft HFSS仿真比较了不同排列的人工磁导体结构对天线性能的影响。 相似文献
994.
防凌期河道流量演进受复杂凌情影响,研究成果少.在分析防凌期流量演进特点的基础上,考虑封开河日期、槽蓄水增量、气温等凌情影响因子,提出了分期分河段的混合算法以改进传统演进方法.以宁蒙河段为例,考虑流量传播时间,分为稳定封冻河段、不稳定封冻河段,分畅流期、封河期、封冻期、开河期,采用混合演进算法对宁蒙河段各断面的流量进行计算.结果显示,采用分期分河段的混合算法演进流量的精度大大提高,验证了混合算法的合理性、可靠性. 相似文献
995.
分析了高压变频器的工作原理与泵类负载的节能原理,介绍了国产HARSVERT高压变频调速系统在包钢供水泵站的应用情况及效果,着重阐述了高压同步电动机变频调速装置在包钢供水泵站中的应用. 相似文献
996.
Zeolite NaA was successfully prepared from nickel laterite residue for the first time via a fusion-hydrothermal procedure. The structure and morphology of the as-synthesized zeolite NaA were characterized with a range of experimental techniques, such as X-ray diffraction, scanning electronic microscopy, and infrared spectroscopy. It was revealed that the structures of the produced zeolites were dependent on the molar ratios of the reactants and hydrothermal reaction conditions, so the synthesis conditions were optimized to obtain pure zeolite NaA. Adsorption of nitrogen and carbon dioxide on the prepared zeolite NaA was also measured and analyzed. The results showed that zeolite NaA could be prepared with reasonable purity, it had physicochemical properties comparable with zeolite NaA made from other methods, and it had excellent gas adsorption properties, thus demonstrating that zeolite NaA could be prepared from nickel laterite residue. 相似文献
997.
As the spring equation is limited to the accuracy of mill stiffness and the linearity of the mill spring curve, the traditional gaugemeter automatic gauge control (GM-AGC) system based on spring equation cannot meet the requirements of practical production. In allusion to this problem, a kind of novel GM-AGC system based on mill stretch characteristic curve was proposed. The error existing in calculating strip thickness by spring equation were analyzed first. And then the mill stretch characteristic curve which could effectively eliminate the influence of mill stiffness was described. The novel GM-AGC system has been applied successfully in a hot strip mill, the application results show that the thickness control precision is improved significantly, with the novel GM-AGC system, over 98.6% of the strip thickness deviation of 3.0 mm class can be controlled within the target tolerances of ±20 μm. 相似文献
998.
The cracking behavior of lightweight aggregate concrete(LWAC) was investigated by mechanical analysis, SEM and cracking-resistant test where a shrinkage-restrained ring with a clapboard was used. The relationship between the ceramsite type and the cracking resistance of LWAC was built up and compared with that of normal-weight coarse aggregate concrete(NWAC). A new method was proposed to evaluate the cracking resistance of concrete, where the concepts of cracking coefficient ζt(t) and the evaluation index Acr(t) were proposed, and the development of micro-cracks and damage accumulation were recognized. For the concrete with an ascending cracking coefficient curve, the larger Acr(t) is, the lower cracking resistance of concrete is. For the concrete with a descending cracking coefficient curve, the larger Acr(t) is, the stronger the cracking resistance of concrete is. The evaluation results show that in the case of that all the three types of coarse aggregates in concrete are pre-soaked for 24 h, NWAC has the lowest cracking resistance, followed by the LWAC with lower water absorption capacity ceramsite and the LWAC with higher water absorption capacity ceramsite has the strongest cracking resistance. The proposed method has obvious advantages over the cracking age method, because it can evaluate the cracking behavior of concrete even if the concrete has not an observable crack. 相似文献
999.
Contrastive research was carried out to study the thermal properties of open-celled aluminum foams prepared by counter-gravity infiltration casting system and the traditional process respectively.The experimental results show that the thermal conductivity coefficients of aluminum foams prepared by two different infiltration methods have similar increasing trend with the increase of particle size; along with the reducing porosity,the thermal conductivity coefficients will be enhanced oppositely.However,with the same particle size,the open-celled aluminum foam prepared by the former method has a higher thermal conductivity coefficient obviously.It is largely because that the sample prepared by counter-gravity infiltration casting has a lower void content and better dense crystallization of metal-matrix after the constant pressure process. 相似文献
1000.