全文获取类型
收费全文 | 42445篇 |
免费 | 3949篇 |
国内免费 | 1986篇 |
专业分类
电工技术 | 5114篇 |
综合类 | 4754篇 |
化学工业 | 2267篇 |
金属工艺 | 1843篇 |
机械仪表 | 5792篇 |
建筑科学 | 6022篇 |
矿业工程 | 1896篇 |
能源动力 | 2288篇 |
轻工业 | 513篇 |
水利工程 | 2068篇 |
石油天然气 | 2037篇 |
武器工业 | 714篇 |
无线电 | 1617篇 |
一般工业技术 | 7066篇 |
冶金工业 | 1226篇 |
原子能技术 | 714篇 |
自动化技术 | 2449篇 |
出版年
2024年 | 141篇 |
2023年 | 465篇 |
2022年 | 1078篇 |
2021年 | 1093篇 |
2020年 | 1242篇 |
2019年 | 856篇 |
2018年 | 862篇 |
2017年 | 1195篇 |
2016年 | 1394篇 |
2015年 | 1485篇 |
2014年 | 2690篇 |
2013年 | 2167篇 |
2012年 | 3244篇 |
2011年 | 3348篇 |
2010年 | 2496篇 |
2009年 | 2535篇 |
2008年 | 2134篇 |
2007年 | 2846篇 |
2006年 | 2585篇 |
2005年 | 2234篇 |
2004年 | 1839篇 |
2003年 | 1635篇 |
2002年 | 1316篇 |
2001年 | 1315篇 |
2000年 | 1154篇 |
1999年 | 926篇 |
1998年 | 722篇 |
1997年 | 682篇 |
1996年 | 522篇 |
1995年 | 466篇 |
1994年 | 387篇 |
1993年 | 292篇 |
1992年 | 242篇 |
1991年 | 180篇 |
1990年 | 162篇 |
1989年 | 177篇 |
1988年 | 103篇 |
1987年 | 56篇 |
1986年 | 22篇 |
1985年 | 20篇 |
1984年 | 16篇 |
1983年 | 11篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1974年 | 3篇 |
1965年 | 2篇 |
1959年 | 14篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 867 毫秒
1.
《International Journal of Hydrogen Energy》2022,47(16):9566-9578
The construction of heterostructure is an effective strategy to synergetically couple wide-band-gap with the narrow-band-gap semiconductor with a mediate optical property and charge transfer capability. Herein, the Z-Scheme CdS/ZnSnO3 (CdS/ZSO) heterostructures were constructed by anchoring CdS nanoparticles on the surface of double-shell hollow cubic ZnSnO3 via the hydrothermal method. The direct recombination of excited electrons in the conduction band (CB) of ZSO and holes in the valence band (VB) of CdS via d-p conjugation at the interface greatly accelerated the internal electric field (IEF). The transfer mode follows the Z-Scheme mechanism, where CdS/ZSO synergistically facilitates the efficient charges transfer from CdS to ZnSnO3 through the intimate interface. Here, ZnSnO3 and CdS serve as an oxidation photocatalyst (OP) and reduction photocatalyst (RP), respectively. Thus, it can promote synergistically the oxidation half-reaction and reduction half-reaction of H2 evolution. The density-functional theory (DFT) calculation further confirms the charges transfer from CdS to ZnSnO3. The hydrogen evolution of 5% CdS/ZSO heterostructure reached 1167.3 μmol g?1, which was about 8 and 3 folds high compared to pristine ZSO (141.9 μmol g?1) and CdS (315.5 μmol g?1), during 3 h of reaction respectively. Furthermore, the CdS/ZSO heterostructures could suppress the photo corrosion of CdS, resulting in its high stability. This work is expected to enlighten the rational design of heterostructure for OP and RP to promote the hybrid heterostructures photocatalytic H2 evolution. 相似文献
2.
3.
4.
Borazine rings act as a pivotal part in siliconboroncarbonitride ceramics (SiBCN) for high-temperature stability and great resistance to crystallization. A detailed investigation of the ring formation mechanism will guide the design and synthesis of SiBCN to meet application requirements under extreme conditions. Boron trichloride (BCl3) and hexamethyldisilazane (HN(SiMe3)2) are common raw materials for the synthesis of precursors for SiBCN. In this paper, quantum chemical calculation was used to study the cyclization reaction mechanism between BCl3 and HN(SiMe3)2 to form trichloroborazine (TCBZ) at the MP2/6-31G (d,p) level of theory. We discussed the structure properties, reaction pathways, energy barriers, reaction rates, and other aspects in detail. The results show that BCl3 and HN(SiMe3)2 alternately participate in the reaction process, accompanied by the release of trimethylchlorosilane (TMCS), and that the entire reaction shows an absolute advantage in terms of energy. In the Step by step reaction, lower reaction barriers are formed due to the introduction of BCl3 with more heat released compared to that for the introduction of HN(SiMe3)2. The final single-molecule cyclization and TMCS elimination steps are found to be faster compared to all previous bimolecular reactions. 相似文献
5.
Amino acid modified polyaspartic acids were evaluated as calcium-scale inhibitors. Feasibility of scale inhibition experiments was analyzed by molecular dynamics simulation and Gaussian optimization, and the scale inhibition mechanism was theoretically analyzed. Scale inhibition performance was studied by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, static scale inhibition experiments, and electrochemical performance testing, which provided an experimental basis for the molecular dynamics simulation. The experimental results showed that Arg-SA-PASP has better scale inhibition and corrosion inhibition performance than His-SA-PASP. The scale inhibition effect increased with increasing concentration. Electrochemical tests indicated that Arg-SA-PASP is an excellent scale and corrosion inhibitor. 相似文献
6.
A small handful of recent studies have addressed a phenomenon known as “phantom vibration syndrome”. This refers to when phone users perceive their device to vibrate, indicating that a call or text is incoming, when in fact the phone did not vibrate at all. Though these studies show that most users do not find phantom vibration hallucinations to be very bothersome, they also find that a large majority of users experience this phenomenon. This paper explores what the striking prevalence of phantom vibration syndrome means for our contemporary relationships with technology. I begin with a review of the theories purporting to explain these data, which largely rely on particular understandings of the brain. Next I develop an alternative theory of phantom vibration syndrome based on insights from the philosophical tradition of phenomenology. This account considers the ways users develop bodily and perceptual habits regarding how the phone is understood and used. By critically contrasting these different theories, we can refine our questions about what the high prevalence of phantom vibration syndrome implies about our contemporary technological situation. 相似文献
7.
氢工质在新能源与动力、航天推进、化工材料等领域有着广泛应用。通过开展高温氢工质热力学与输运性质研究,建立了原子态氢、分子态氢、热解平衡态氢的热物理性质计算模型,开发了热物性计算程序Prop_H_H2,适用范围为温度100~3 500 K、压力104~5×107 Pa 。验证表明,Prop_H_H2在适用范围内计算氢工质的物性参数合理可靠,在温度200~3 000 K、压力104~107 Pa范围内,程序预测值更加准确,相对偏差在±5%左右。本研究可为氢工质相关的航天推进、应用物理学、能源动力等行业的科研和应用提供支持借鉴。 相似文献
8.
A method for estimating the sway angle using an observer has already been proposed. The state observer estimates the sway angle accurately and must use the detected sway angle value. However, the estimated sway angle has an error owing to rope length error, friction force, and wind. Moreover, the container mass cannot be determined, and therefore the observer parameter is not suitable. We already proposed robust antisway control for overcoming rope length error without adding a new sensor. Further, we designed a friction disturbance observer to cancel out the influence of the friction force. In this paper, we first propose a container mass estimation method when a crane system performs rolling up control. The observer parameter can be selected using the estimated mass value. Second, in crane parallel shift control, we propose a robust antisway control even when there is a wind disturbance. We design a wind disturbance observer and propose a wind disturbance estimator to separate the friction observer output from the wind disturbance observer output. We confirm through experiments that the proposed method can reduce vibration. 相似文献
9.
针对大型旋转机械通过临界转速时振动过大及运行中故障频发等问题,搭建转子试验台,模拟启停机过程和碰摩、不对中故障。不改变原有支撑形式,安装自主设计的磁流变阻尼器,在不停机的情况下,试验研究阻尼器抑制转子通过临界转速时振动过大及各类故障振动。试验结果表明,阻尼器可以有效抑制转子系统临界转速附近的振动,降幅在60%以上;转子发生碰摩或不对中故障时,阻尼器可以降低其高倍频振动。 相似文献
10.
NO2 fission is regarded to be the most important initial decomposition process of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20). In this study, four CL-20 conformers based on the ε-CL-20 were obtained after the optimization at m062x/cc-pvtz level, and the bond length, bond order and bond dissociation energy of the N-N bonds were examined to investigate the stability of these bonds. In addition, the rate constants and activation energy of the NO2 fission were evaluated using the microcanonical variational transition state theory (μVT). The calculation results have shown that N-N bonds in the case of pseudo-equatorial and axial of nitro groups are the most stable and the least stable, respectively, by evaluating the bond length, bond order and minimum energy path (MEP). The NO2 fission rate constants are affected by not only the stability of N-N bonds but also the repulsion forces from the other nitro groups, and the fission process for pseudo-equatorial positioning of nitro groups is easier to be accelerated due to the increase of the repulsion forces. The decomposition of CL-20 conformer may mainly originate from the fission of the pseudo-equatorial positioning of nitro groups, especially for CL-20 III conformer because of the significant low activation energy. 相似文献