全文获取类型
收费全文 | 139584篇 |
免费 | 12568篇 |
国内免费 | 5629篇 |
专业分类
电工技术 | 6761篇 |
技术理论 | 27篇 |
综合类 | 9361篇 |
化学工业 | 22794篇 |
金属工艺 | 6218篇 |
机械仪表 | 7110篇 |
建筑科学 | 14441篇 |
矿业工程 | 6597篇 |
能源动力 | 2936篇 |
轻工业 | 14158篇 |
水利工程 | 2902篇 |
石油天然气 | 5236篇 |
武器工业 | 2622篇 |
无线电 | 16126篇 |
一般工业技术 | 10385篇 |
冶金工业 | 6364篇 |
原子能技术 | 936篇 |
自动化技术 | 22807篇 |
出版年
2024年 | 305篇 |
2023年 | 1821篇 |
2022年 | 3889篇 |
2021年 | 6188篇 |
2020年 | 4060篇 |
2019年 | 3117篇 |
2018年 | 3143篇 |
2017年 | 4452篇 |
2016年 | 5914篇 |
2015年 | 6649篇 |
2014年 | 10958篇 |
2013年 | 8878篇 |
2012年 | 9625篇 |
2011年 | 9574篇 |
2010年 | 7499篇 |
2009年 | 7691篇 |
2008年 | 7211篇 |
2007年 | 9429篇 |
2006年 | 8860篇 |
2005年 | 7800篇 |
2004年 | 6057篇 |
2003年 | 5524篇 |
2002年 | 4353篇 |
2001年 | 3338篇 |
2000年 | 2639篇 |
1999年 | 1922篇 |
1998年 | 1280篇 |
1997年 | 975篇 |
1996年 | 857篇 |
1995年 | 684篇 |
1994年 | 554篇 |
1993年 | 394篇 |
1992年 | 335篇 |
1991年 | 261篇 |
1990年 | 245篇 |
1989年 | 184篇 |
1988年 | 139篇 |
1987年 | 100篇 |
1986年 | 94篇 |
1985年 | 100篇 |
1984年 | 90篇 |
1983年 | 58篇 |
1982年 | 49篇 |
1981年 | 51篇 |
1980年 | 59篇 |
1979年 | 23篇 |
1966年 | 25篇 |
1964年 | 35篇 |
1962年 | 65篇 |
1959年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 352 毫秒
41.
华治国 《混凝土与水泥制品》2020,(6):70-72
选择了几份典型的外墙外保温系统标准,通过对这几份标准中胶粘剂和抹面胶浆的成型和检测方法的比较,分析了现有检测技术的优劣,并结合工作实践提出了建议。 相似文献
42.
构建工程咨询机构BIM技术应用能力评价的指标体系,提出改进的熵权TOPSIS评价模型,以4个典型的工程咨询单位为例,进行BIM技术运用能力评价。研究表明,BIM行业的整体水平已经有了明显的提升,但是区域间的发展还存在一定差距。 相似文献
43.
One specific class of non-linear evolution equations, known as the Tzitzéica-type equations, has received great attention from a group of researchers involved in non-linear science. In this article, new exact solutions of the Tzitzéica-type equations arising in non-linear optics, including the Tzitzéica, Dodd–Bullough–Mikhailov and Tzitzéica–Dodd–Bullough equations, are obtained using the expa function method. The integration technique actually suggests a useful and reliable method to extract new exact solutions of a wide range of non-linear evolution equations. 相似文献
44.
45.
通过河南省渑池地区含锂铝土矿(岩)层工艺矿物学分析,查明铝土矿的物质组成、嵌布特征、伴生锂分布特征和赋存状态,为矿产综合利用提供理论依据。结果显示:该铝土矿Al2O3含量为54.8%,铝硅比值(A/S)为2.6,铝土矿层和粘土岩层中Li2O含量均高于伴生锂边界品位,粘土岩中锂更为富集;矿物组成除一水硬铝石之外,主要是以集合体形态产出的粘土矿物。采用稀酸解析、选矿测试和电子探针分析锂的赋存状态,查明矿石中锂主要是以类质同象置换形式赋存在伊利石和高岭石等粘土矿物中;选矿富锂尾矿中Li2O可富集到0.57%左右,是锂综合回收利用的重点研究对象。 相似文献
46.
通过对紫金山东南矿段铜钼(金)矿床地质矿化特征分析,指出铜钼矿化带主要赋存于花岗闪长斑岩的内外接触带,处于似斑状花岗闪长斑岩的上部,金矿化带赋存在表生氧化带的英安玢岩、隐爆角砾岩中。经过对矿石的组构特征、矿物生成顺序等特征分析,将矿床的成矿演化过程分为斑岩热液期、高硫化浅成低温热液期、表生氧化期三个主要矿化期次,进一步将斑岩热液期分为黑云母-钾长石化阶段、石英-绢云母化阶段、碳酸盐化阶段三个阶段;高硫化浅成低温热液期分为地开石化阶段、明矾石化阶段、硅化阶段三个阶段。研究结果为进一步研究矿床成因提供了依据。 相似文献
47.
《Contact lens & anterior eye》2020,43(5):493-496
PurposeAccommodative micro-fluctuations (AMF) are small dioptric changes during accommodation. The aim of this study was to evaluate and compare changes in AMF when wearing silicone hydrogel contact lenses of two different optical designs.MethodsA multi-centre, randomised, cross-over, non-dispensing study was conducted on 68 adapted contact lens wearers aged 25–35 years to compare AMF responses to a spherical and aspheric silicone hydrogel (comfilcon A) lens designs. A Righton Speedy “i” series Auto Refractometer in accommodation analyser mode was utilized before and after reading a standard text in font size 8 on an iPhone 5 for 20 min at a 25 cm viewing distance. Phone screen brightness was set by automatic adjustment mode and ambient illumination was controlled at all sites.ResultsMean ± SD AMF change from before to after the reading task was 2.25 ± 5.6 and 0.13 ± 5.7 (relative values) for the spherical and aspheric lens designs, respectively. The difference was statistically significant (P = 0.017, Paired t-test).ConclusionsThe smaller change in AMF when using an aspheric lens design suggests reduced ciliary muscle stress when reading print on a smart phone at a close distance for short periods (20 min). Contact lens wearers who frequently use digital devices and are experiencing eye strain may benefit from switching from a spherical design to one that incorporates aspheric optics. 相似文献
48.
Perfluorocarbon gas is widely used in the semiconductor industry. However, perfluorocarbon has a
negative effect on the global environment owing to its high global warming potential (GWP) value.
An alternative solution is essential. Therefore, we evaluated the possibility of replacing conventional
perfluorocarbon etching gases such as CHF3 with C6F12O, which has a low GWP and is in a liquid
state at room temperature. In this study, silicon oxynitride (SiON) films were plasma-etched using
inductively coupled CF4 +C6F12O+O2 mixed plasmas. Subsequently, the etching characteristics
of the film, such as etching rate, etching profile, selectivity over Si, and photoresist, were investigated.
A double Langmuir probe was used and optical emission spectroscopy was performed for plasma
diagnostics. In addition, a contact angle goniometer and x-ray photoelectron spectroscope were used
to confirm the change in the surface properties of the etched SiON film surface. Consequently, the
etching characteristics of the C6F12O mixed plasma exhibited a lower etching rate, higher SiON/Si
selectivity, lower plasma damage, and more vertical etched profiles than the conventional CHF3 mixed plasma. In addition, the C6F12O gas can be recovered in the liquid state, thereby decreasing
global warming. These results confirmed that the C6F12O precursor can sufficiently replace the
conventional etching gas. 相似文献
49.
50.
With the emergence of distributed ledger technology (DLT), numerous practitioners and researchers have proclaimed its beneficial impact on supply chain transactions in the future. However, the vast majority of DLT initiatives are discontinued after a short period. With the full potential of DLT laying far down the road, especially managers in supply chain management (SCM) seek for short-term cost-saving effects of DLT in order to achieve long-term benefits of DLT in the future. However, the extant research has bypassed grounding long-term as well as short-term effects of DLT on supply chain transaction with empirical data. We address this shortcoming, following an abductive research approach and combining empirical data from a multiple case study design with the corresponding literature. Our study reveals that the effects of DLT on supply chain transactions are two-sided. We found six effects of DLT solutions that have a cost-reducing or cost avoidance impact on supply chain transactions. In addition, we found two effects that change the power distribution between buyers and suppliers in transactions and a single effect that reduces the dependency of supply chain transactions on third parties. While cost-reducing and avoidance as well as dependency-reducing effects are positive effects, the change in power distribution might come with disadvantages. With these findings, the paper provides the first empirical evidence of the impact of DLT on supply chain transactions, which will enable managers to improve their assessment of DLT usage in supply chains. 相似文献