全文获取类型
收费全文 | 38680篇 |
免费 | 3179篇 |
国内免费 | 1832篇 |
专业分类
电工技术 | 4585篇 |
技术理论 | 3篇 |
综合类 | 3738篇 |
化学工业 | 1649篇 |
金属工艺 | 601篇 |
机械仪表 | 1713篇 |
建筑科学 | 1312篇 |
矿业工程 | 705篇 |
能源动力 | 530篇 |
轻工业 | 949篇 |
水利工程 | 486篇 |
石油天然气 | 377篇 |
武器工业 | 390篇 |
无线电 | 11899篇 |
一般工业技术 | 2295篇 |
冶金工业 | 1944篇 |
原子能技术 | 545篇 |
自动化技术 | 9970篇 |
出版年
2024年 | 48篇 |
2023年 | 426篇 |
2022年 | 588篇 |
2021年 | 924篇 |
2020年 | 931篇 |
2019年 | 693篇 |
2018年 | 685篇 |
2017年 | 963篇 |
2016年 | 1090篇 |
2015年 | 1376篇 |
2014年 | 2330篇 |
2013年 | 2318篇 |
2012年 | 2791篇 |
2011年 | 3020篇 |
2010年 | 2298篇 |
2009年 | 2123篇 |
2008年 | 2380篇 |
2007年 | 2665篇 |
2006年 | 2488篇 |
2005年 | 2219篇 |
2004年 | 1950篇 |
2003年 | 1897篇 |
2002年 | 1400篇 |
2001年 | 1146篇 |
2000年 | 847篇 |
1999年 | 741篇 |
1998年 | 580篇 |
1997年 | 479篇 |
1996年 | 430篇 |
1995年 | 353篇 |
1994年 | 289篇 |
1993年 | 185篇 |
1992年 | 132篇 |
1991年 | 103篇 |
1990年 | 89篇 |
1989年 | 97篇 |
1988年 | 65篇 |
1987年 | 36篇 |
1986年 | 33篇 |
1985年 | 56篇 |
1984年 | 49篇 |
1983年 | 32篇 |
1982年 | 38篇 |
1981年 | 20篇 |
1979年 | 16篇 |
1977年 | 17篇 |
1964年 | 34篇 |
1959年 | 18篇 |
1956年 | 16篇 |
1955年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
31.
分析研究目前通信工程网络安全问题,提出几点解决问题的对策,旨在为提升通信工程网络安全性提供一定的帮助,以此来促使通信工程网络系统安全性的提升。 相似文献
32.
MIL-53(Fe)/polyaniline (PANI) composite was prepared by in situ depositing PANI on the surface of MIL-53(Fe) and their catalytic performances on the simultaneous removal of RhB and Cr(VI) were investigated. The elimination efficiency of both RhB and Cr(VI) reached more than 98% under pH=2 where hydrochloric acid and citric acid were used to adjust the pH. The results indicated that MIL-53(Fe)/PANI revealed an obvious pH response to the degradation of RhB, while citric acid promoted the Cr(VI) photoreduction. UV-Vis spectra, EIS, and photocurrent response experiments showed that MIL-53(Fe)/PANI had a better light response and carrier migration ability than MIL-53(Fe). The transient absorption spectra also exhibited that the lifetimes of photo-generated carriers were prolonged after the conductive polymer deposition on the MIL-53(Fe) surface. Scavenger experiments demonstrated that the main active species were ·O2- and OH. Combined with activity evaluation results, and the possible photocatalytic mechanism of MIL-53(Fe)/PANI on RhB oxidation and Cr(VI) reduction was proposed. The addition of conductive polymer can effectively improve the light response of the catalyst under acidic conditions, and meanwhile citric acid also provided a new mediation for the synergistic degradation of multiple pollutants. Good activity and stability of the catalysts made the scale-up purification of acid water feasible under UV-Vis light. 相似文献
33.
M. Radhika R. J. Punith Gowda R. Naveenkumar Siddabasappa B. C. Prasannakumara 《亚洲传热研究》2021,50(3):2150-2167
The melting effect with the magnetic field performs a significant role in various manufacturing and industrial applications, such as welding, casting, magma-solidification, nuclear engineering, and so forth. The present study focuses on the impact of the melting effect and magnetic field with inhomogeneous heat origination and sink. The formulation of the mathematical model is done by considering fluid with hybrid nanoparticles and dust particles in two different phases. We have considered Fe2SO4 and Cu as nanoparticles dispersed in the base fluid water along with suspended dust particles. The set of partial differential equations is reduced by using apt similarity variables and boundary conditions to obtain ordinary differential equations. The numerical solution is approximated using MATLAB-bvp4c adopting the shooting technique. The impact of numerous pertinent physical parameters on the velocity and thermal profiles is plotted and deliberated. Furthermore, the rate of heat flow and friction factor is also tabulated and visualized through the graphs. Streamlines are also drawn to know the behavior of the fluid flow. The rise in values of ME quickly increases the velocity of the fluid motion but declines the thermal gradient and thickness of its related boundary layer. Also, inclining values of Pr enhance the thermal profile due to the impact of melting. 相似文献
34.
Muttukuru Santhi Kavaturi Venkata Suryanarayana Rao Patakota Sudarsana Reddy Paluru Sreedevi 《亚洲传热研究》2021,50(3):2929-2949
Unsteady magnetohydrodynamic heat and mass transfer analysis of hybrid nanoliquid flow over a stretching surface with chemical reaction, suction, slip effects, and thermal radiation is analyzed in this study. A combination of alumina (Al2O3) and titanium oxide (TiO2) nanoparticles are taken as hybrid nanoparticles and water is considered as the basefluid. Using the similarity transformation method, the governing equations are changed into a system of ordinary differential equations. These equations together with boundary conditions are numerically evaluated by using the Finite element method. The influence of various pertinent parameters on the profiles of fluids concentration, temperature, and velocity is calculated and the outcomes are plotted through graphs. The values of nondimensional rates of heat transfer, mass transfer, and velocity are also analyzed and the results are depicted in tables. Temperature sketches of hybrid nanoliquid intensified in both the steady and unsteady cases as the volume fraction of both nanoparticles rises. 相似文献
35.
Occupants’ satisfaction had been researched independently related to thermal and visual stimuli for many decades showing among others the influence of self-perceived control. Few studies revealed interactions between thermal and visual stimuli affecting occupant satisfaction. In addition, studies including interactions between thermal and visual stimuli are lacking different control scenarios. This study focused on the effects of thermal and visual factors, their interaction, seasonal influences, and the degree of self-perceived control on overall, thermal, and visual satisfaction. A repeated-measures laboratory study with 61 participants running over two years and a total of 986 participant sessions was conducted. Mixed model analyses with overall satisfaction as outcome variable revealed that thermal satisfaction and visual satisfaction are the most important predictors for overall satisfaction with the indoor environment. Self-perceived thermal control served as moderator between thermal satisfaction and overall satisfaction. Season had slight influence on overall satisfaction. Random effects explained the highest amount of variance, indicating that intra- and interindividual differences in the ratings of satisfaction are more prevalent than study condition. Future building design and operation plans aiming at a high level of occupant satisfaction should consider personal control opportunities and take into account the moderating effect of control opportunities in multimodal interactions. 相似文献
36.
Andrew T. Miranda 《Theoretical Issues in Ergonomics Science》2019,20(1):73-83
AbstractLike many scientific topics, Human Factors, and Ergonomics concepts are susceptible to being misunderstood by people unfamiliar with the subject matter. Most of the time these misunderstandings are harmless, like when a safety poster within a work setting encourages employees to 'overcome complacency'. This misunderstanding of complacency suggests it is a motivational aspect of human behaviour correctable with encouragement, whereas the human factors approach to overcoming complacency would be to evaluate how task design could diminish the destructive consequences of unexpected changes within a routine setting. No harm comes from the message within the safety poster, other than some wasted ink and paper, but misconceptions among particular audiences can eventually result in dire consequences for the human operator. This paper presents recent evidence that the concepts are being misapplied by casual consumers of human factors, particularly in the aftermath of accidents within complex systems, in ways detrimental to the core mission of improving the well-being of the human operator. Later, because this special issue presents new ways to demonstrate value via return on investment, practical efforts we can take to overcome such misconceptions are suggested. 相似文献
37.
A broadband 8‐antenna multiple‐input and multiple‐output (MIMO) system working for 5G new radio N77 (3.3‐4.2 GHz) in mobile terminals is proposed. In particular, each antenna element/unit consists of a monopole‐type meandered branch and an inverted U‐shaped self‐isolated antenna branch; and the antenna unit is fed by the meandered branch. The antenna unit has two resonances generated separately by each branch of the antenna unit. Since the monopole couples strongly with the self‐isolated antenna element that has the inherent self‐isolation characteristics, quite good isolation for the broadband 8‐antenna MIMO system can be obtained. The results such as antenna efficiency, radiation patterns, envelope correlation coefficient, and channel capacity are also presented. 相似文献
38.
In this paper, we first re-examine the previous protocol of controlled quantum secure direct communication of Zhang et al.’s scheme, which was found insecure under two kinds of attacks, fake entangled particles attack and disentanglement attack. Then, by changing the party of the preparation of cluster states and using unitary operations, we present an improved protocol which can avoid these two kinds of attacks. Moreover, the protocol is proposed using the three-qubit partially entangled set of states. It is more efficient by only using three particles rather than four or even more to transmit one bit secret information. Given our using state is much easier to prepare for multiqubit states and our protocol needs less measurement resource, it makes this protocol more convenient from an applied point of view. 相似文献
39.
40.
Jia-Liang Chen Xiao Wang Yu-Hao Xiao Xun-Cheng Su 《Chembiochem : a European journal of chemical biology》2019,20(21):2738-2742
Unstable and low-abundance protein complexes represent a large family of transient protein complexes that are difficult to characterize, even by means of high-resolution NMR spectroscopy. A method to assign the NMR signals of these unstable complexes through a combination of selective isotope labeling of amino acids in a protein and site-specific labeling the protein with a paramagnetic tag is presented herein. By using this method, the resonances of unstable thioester intermediate complex (lifetime <5 h and highest concentration ≈20 μm ) generated by Staphylococcus aureus sortase A and its peptide substrate under a real-time reaction have been assigned. 相似文献