全文获取类型
收费全文 | 63357篇 |
免费 | 8301篇 |
国内免费 | 3970篇 |
专业分类
电工技术 | 5969篇 |
技术理论 | 1篇 |
综合类 | 5994篇 |
化学工业 | 12058篇 |
金属工艺 | 4924篇 |
机械仪表 | 2844篇 |
建筑科学 | 3318篇 |
矿业工程 | 1486篇 |
能源动力 | 2264篇 |
轻工业 | 3166篇 |
水利工程 | 1208篇 |
石油天然气 | 2564篇 |
武器工业 | 686篇 |
无线电 | 8997篇 |
一般工业技术 | 7778篇 |
冶金工业 | 3841篇 |
原子能技术 | 625篇 |
自动化技术 | 7905篇 |
出版年
2024年 | 99篇 |
2023年 | 981篇 |
2022年 | 1376篇 |
2021年 | 1878篇 |
2020年 | 2102篇 |
2019年 | 2019篇 |
2018年 | 1913篇 |
2017年 | 2349篇 |
2016年 | 2562篇 |
2015年 | 2546篇 |
2014年 | 3557篇 |
2013年 | 3733篇 |
2012年 | 4199篇 |
2011年 | 4409篇 |
2010年 | 3211篇 |
2009年 | 3615篇 |
2008年 | 3407篇 |
2007年 | 4048篇 |
2006年 | 3834篇 |
2005年 | 3145篇 |
2004年 | 2671篇 |
2003年 | 2651篇 |
2002年 | 2235篇 |
2001年 | 2010篇 |
2000年 | 1640篇 |
1999年 | 1272篇 |
1998年 | 1091篇 |
1997年 | 969篇 |
1996年 | 784篇 |
1995年 | 743篇 |
1994年 | 659篇 |
1993年 | 448篇 |
1992年 | 432篇 |
1991年 | 318篇 |
1990年 | 317篇 |
1989年 | 256篇 |
1988年 | 152篇 |
1987年 | 104篇 |
1986年 | 90篇 |
1985年 | 188篇 |
1984年 | 291篇 |
1983年 | 312篇 |
1982年 | 243篇 |
1981年 | 346篇 |
1980年 | 146篇 |
1979年 | 48篇 |
1978年 | 51篇 |
1977年 | 21篇 |
1975年 | 26篇 |
1974年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
101.
102.
《Ceramics International》2022,48(9):12048-12055
Samples with inversion parameter values (δ) ranging from 0.27 to 0.14 while maintaining the crystallite size value have been successfully fabricated from commercially available powders by mechanical grinding and thermal annealing treatments at temperatures ranging between 400 and 600 °C. Detailed characterization studies of these samples using X-ray, neutron diffraction and magnetic measurements have confirmed for the first time the simultaneous coexistence at 2 K of short range antiferromagnetic and ferrimagnetic ordering for a wide range of the inversion parameter. The magnetic phase diagram obtained is different from the one previously reported, which shows at 2 K the coexistence of long range antiferromagnetic order and short range order for values of inversion parameters less than 0.1 and the presence of a ferrimagnetic order only for values of δ > 0.2. At room temperature, the Rietveld analysis of NPD patterns and the magnetization curves showed a paramagnetic behavior in the samples with δ ≤ 0.1. For the samples with higher cationic inversion, typical hysteresis curves of ferrimagnetic materials were observed and the saturation magnetization values obtained agree quite well with the net magnetic moment obtained from the Rietveld refinement of the neutron diffraction patterns. 相似文献
103.
《International Journal of Hydrogen Energy》2021,46(64):32358-32363
South Korea is pushing for the waste-to-hydrogen (W2H) project to reduce greenhouse gases and utilize plastic and vinyl waste (PVW) while reducing environmental pollution from PVW. This research seeks to estimate additional willingness to pay (WTP) for electricity produced using W2H over that produced using traditional power sources, such as coal and nuclear. For the purpose of the estimation, a contingent valuation survey of 1000 people was performed employing the closed-ended one-and-one-half-bound question during November 2020. A spike model is utilized to reflect zero WTP values that a number of interviewees reported in the survey. Several factors affecting the additional WTP were also analyzed to derive implications. The average WTP was computed as KRW 27.7 (USD 0.025) per kWh with statistical significance, which reaches 26.4% of the electricity price. One more point to note is that 54.3% of the respondents stated a zero WTP as they thought that W2H is of no value to them or were worried that the W2H project could increase electricity bills. 相似文献
104.
Qi Jing Jinxiang Huang Qingming Liu Dan wang Xu Chen Zhisong Wang Changqi Liu 《International Journal of Hydrogen Energy》2021,46(36):19158-19170
As a carbon-free fuel and a hydrogen-energy carrier, ammonia is a potential candidate for future energy utilization. Therefore, in order to promote the application of ammonia in detonation engines and to evaluate the safety of ammonia related industrial process, DDT experiments for ammonia/oxygen mixtures with different ERs were carried out in a large-scale horizontal tube. Moreover, pressure transducers and self-developed temperature sensors were applied to record the overpressure and the instantaneous flame temperature during DDT process. The results show that the DDT process in ammonia/oxygen mixtures contains four stages: Slow propagation stage, Flame and pressure wave acceleration stage, Fast propagation and detonation wave formation stage, Detonation wave self-sustained propagation stage. For stoichiometric ammonia/oxygen mixtures, flame front and the leading shock wave propagate one after another with different velocity, until they closely coupled and propagated together with one steady velocity. At the same time, it is found that an interesting retonation wave propagates backward. The peak overpressure, detonation velocity, and flame temperature of the self-sustained detonation are 2 MPa, 2000 m/s and 3500 K, respectively. With the ER increased from 0.6 to 1.6, the detonation velocities and peak overpressures ranged from 2310 m/s to 2480 m/s and 25.6 bar–28.7 bar, respectively. In addition, the detonation parameters of ammonia were compared with those of methane and hydrogen to evaluate the detonation performance and destructiveness of ammonia. 相似文献
105.
Yuzhi Zhou Linxia Zhang Lixia Qin Shi-Zhao Kang Xiangqing Li 《International Journal of Hydrogen Energy》2021,46(54):27495-27505
A mixed phase LaVO4 with high dispersion was in situ induced and implanted in graphene oxide-graphite carbon nitride composite. The obtained nanocomposite (GO–C3N4–LaVO4) showed high and stable photocatalytic activity for hydrogen evolution, which significantly benefited from the improved charge separation and light absorption in the special composite photocatalyst as evidenced by UV–vis spectra, fluorescence spectrum, photocurrent response and electrochemical impedance. The fabrication strategy of mixed phase LaVO4 in the GO-C3N4 provides a new idea for constructing cheap and active organic-inorganic semiconductor photocatalysts for hydrogen generation. 相似文献
106.
为详细了解高氯酸铵(AP)对5,5'-联四唑-1,1'-二氧二羟铵(HATO)热分解影响的机制,采用热重-质谱-傅里叶红外光谱(TG-MS-FTIR)联用技术、差示扫描量热法(DSC)、傅里叶红外光谱(FTIR)方法,对HATO和HATO/AP共混物的热分解特性、气体产物以及凝聚相变化进行了研究。结果表明,HATO具有两个连续热分解阶段,HATO/AP共混物则有3个热分解阶段;HATO、AP共混后,HATO使得AP熔融峰消失,AP可使HATO的热分解初始温度提前,热分解时间延长且不影响分解完全性;HATO热分解气体产物有CO_2、N_2O、HCN、NH_3、NO、N_2、H_2O,而HATO/AP共混物热分解产生气体主要有N_2、CO_2、N_2O、HCN、NH_3、H_2O、HCN、NO、HCl、NOCl;另外,采用等转化率法计算HATO和HATO/AP共混物四唑环基团的活化能分别为53.38 kJ·mol~(-1)和60.69 kJ·mol~(-1);通过对比HATO和HATO/AP共混物热分解特性以及凝聚相特征基团的变化,阐释了AP使HATO热分解温度提前的机理很可能是:AP的铵根离子与HATO之间发生了质子转移;推测AP导致HATO热分解时间延长的原因为:HATO/AP共混物产生的NH_3与热分解中间体1,1'-二羟基-5,5-联四唑(BTO)反应生成5,5'-联四唑-1,1'-二氧铵盐(ABTOX)。 相似文献
107.
Muntasir Hashim Farnoosh Farhad David Smyth‐Boyle Robert Akid Xiang Zhang Philip J. Withers 《工业材料与腐蚀》2019,70(11):2009-2019
The environmental performance of 316L grade stainless steel, in the form of tensile specimens containing a single corrosion pit with various aspect ratios, under cyclic loading in aerated chloride solutions is investigated in this study. Results from environmental tests were compared and contrasted with those obtained using finite element analysis (FEA). Fractography of the failed specimens obtained from experiments revealed that fatigue crack initiation took place at the base of the shallow pit. The crack initiation shifted towards the shoulder and the mouth of the pit for pits of increasing depth. This process is well predicted by FEA, as the strain contour maps show that strain is the highest around the centric strip of the pit. However, for shallow pits, local strain is uniformly distributed around that strip but begins to concentrate more towards the shoulder and the mouth region for increasingly deep pits. 相似文献
108.
Christian Berggren 《International Journal of Project Management》2019,37(3):461-472
In innovation and project management studies incremental development projects are perceived as theoreticlly and organisationally uninteresting. By means of a longitudinal study of product improvement projects at an automobile firm, this paper challenges such views and shows how the cumulative impact of the studied sequence resulted in a competitive repositioning of the company's product portfolio during a financially difficult period. Project managers achieved this by transcending the separation between exploration and exploitation projects; they not only adhered to time, cost and quality goals but also tried out new ways of testing and experimenting with controversial technical ideas. The paper analyzes the intensive inter project learning that generated these ambidextrous capabilities and emphasizes that practices at the project-level need to be buttressed by expanded management learning and capability development also at the sequence level. 相似文献
109.
Effect of element Ru on microstructure and creep behaviour of single crystal nickel-based superalloy
By means of creep property measurement and microstructure observation, the influence of element Ru on the microstructure and creep behaviour of single crystal nickel-based superalloy is investigated. The results show that the plate-like μ phase is precipitated along {111} plane of the Ru-free alloy during thermal exposure at 1080°C and creep at 980°C. And the precipitation of μ phase in the alloy with 6(wt)%Mo and 6(wt)%W may be restrained by adding 2% Ru element. Compared to Ru-free alloy, the creep life of the 2% Ru single crystal alloy at 980°C200 MPa increases form 123 h to 333h. Compared to the 2% Ru alloy, the precipitated plate-like μ phase in the Ru-free alloy may promote the initiation and propagation of cracks along the γ matrix up to fracture, which is thought to be the main reason of the alloy having a lower creep resistances and shorter lifetime. 相似文献
110.