全文获取类型
收费全文 | 129140篇 |
免费 | 12859篇 |
国内免费 | 8450篇 |
专业分类
电工技术 | 8348篇 |
技术理论 | 5篇 |
综合类 | 13864篇 |
化学工业 | 15585篇 |
金属工艺 | 9434篇 |
机械仪表 | 8176篇 |
建筑科学 | 21495篇 |
矿业工程 | 5310篇 |
能源动力 | 4290篇 |
轻工业 | 6151篇 |
水利工程 | 3627篇 |
石油天然气 | 9543篇 |
武器工业 | 1460篇 |
无线电 | 10463篇 |
一般工业技术 | 14458篇 |
冶金工业 | 5032篇 |
原子能技术 | 1257篇 |
自动化技术 | 11951篇 |
出版年
2024年 | 570篇 |
2023年 | 1937篇 |
2022年 | 3547篇 |
2021年 | 3957篇 |
2020年 | 3986篇 |
2019年 | 3314篇 |
2018年 | 3087篇 |
2017年 | 4073篇 |
2016年 | 4281篇 |
2015年 | 4602篇 |
2014年 | 7702篇 |
2013年 | 6872篇 |
2012年 | 8952篇 |
2011年 | 9879篇 |
2010年 | 7577篇 |
2009年 | 8045篇 |
2008年 | 7282篇 |
2007年 | 8811篇 |
2006年 | 8152篇 |
2005年 | 6987篇 |
2004年 | 5829篇 |
2003年 | 5257篇 |
2002年 | 4417篇 |
2001年 | 3664篇 |
2000年 | 3263篇 |
1999年 | 2737篇 |
1998年 | 2153篇 |
1997年 | 1857篇 |
1996年 | 1478篇 |
1995年 | 1234篇 |
1994年 | 1141篇 |
1993年 | 743篇 |
1992年 | 654篇 |
1991年 | 526篇 |
1990年 | 443篇 |
1989年 | 361篇 |
1988年 | 249篇 |
1987年 | 123篇 |
1986年 | 93篇 |
1985年 | 94篇 |
1984年 | 82篇 |
1983年 | 66篇 |
1982年 | 80篇 |
1981年 | 31篇 |
1980年 | 74篇 |
1979年 | 22篇 |
1978年 | 14篇 |
1975年 | 14篇 |
1959年 | 19篇 |
1951年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 24 毫秒
91.
We present a numerical study of the packing of uniform spheres under three-dimensional vibration using the discrete element method (DEM), focusing on the effects of vibration condition (amplitude and frequency) and inter-particle frictions (sliding and rolling frictions). The results are analysed in terms of packing density, coordination number (CN), radial distribution function (RDF) and pore structure. It is shown that increasing either the vibration amplitude or frequency causes packing density to increase initially to a maximum and then decrease. Both vibration frequency and amplitude should be considered to characterize the effect of vibration process on packing structure. The sliding and rolling frictions between particles can decrease packing density since they dissipate energy, although the effect of rolling friction is less significant. In line with the change of packing density, microstructural properties such as CN, RDF and pore distribution also change: a looser packing often corresponds to smaller CN, less peaked RDF and larger but more widely distributed pores. 相似文献
92.
S. K. Chen A. Serquis G. Serrano K. A. Yates M. G. Blamire D. Guthrie J. Cooper H. Wang S. Margadonna J. L. MacManus‐Driscoll 《Advanced functional materials》2008,18(1):113-120
By applying a combination of characterisation tools, changes in structural and superconducting properties with nominal Mg non‐stoichiometry in MgxB2 are found. The non‐stoichiometry produces enhanced in‐field critical current densities (Jc's) and upper critical field / irreversibility field (Hc2/Hirr(T)) values. Upper critical fields of ~ 21 T (4.2 K) were obtained in nominal Mg‐deficient samples compared to ~ 17 T (4.2 K) for near‐stoichiometric samples. 相似文献
93.
94.
Non-pinched, minimum energy solutions are important class of distillation designs that offer the potential advantage of a better trade-off between capital investment and operating costs. In this paper, two important tasks associated with non-pinched distillation designs are studied. Thus the novel contributions of this work to the literature are
- (1) A comprehensive methodology for finding non-pinched minimum energy designs.
- (2) Understanding of the reasons for the existence of non-pinched distillation designs.
95.
Jennifer Spenader 《Journal of Logic, Language and Information》2003,12(3):351-368
There are three ways to refer to a fact from the complement of afactive verb: (1) Via abstract object anaphoric reference, or, witha full sentential complement that will be interpreted either (2) asa bound presupposition or (3) as triggering a presupposition of afact that will have to be accommodated. Spoken corpus examplesreveal that these three possibilities differ in relation to thetype of information they tend to contribute, and this has twoeffects. First, the information status of the fact and its role inthe discourse seem to affect the preference for one constructionover another in a particular context. Second, presupposed factivecomplements that need to be accommodated tend to be hearer-new andthe focus of the utterance, meaning that information structureseems to contribute to the felicity of accommodation ofpresupposed facts. 相似文献
96.
沸石孔结构对1-己烯异构化性能的影响 总被引:1,自引:0,他引:1
采用1-己烯为原料,对硅铝比相近、不同孔结构的沸石在脉冲微反装置上进行了评价试验,考察了FCC条件下沸石孔结构对烯烃异构化性能的影响。结果表明,大孔径的Y型沸石具有良好的异构化性能,异构化能力由强到弱的排列顺序为Y>β>ZRP>丝光沸石>镁碱沸石。 相似文献
97.
98.
Anumberoflanthanideternarycomplexescon tainingheterocyclicamineshavebeenreportedsince1960 [1] .Inrecentyearsmuchattentionhasbeenpaidtoquaternarycomplexesoflanthanidesbecauseofin terestingstructure ,coordinationmode ,competitionre actionandproperty[2~ 9] .ESRcane… 相似文献
99.
The changes in surface composition of metallic alloys caused by segregation can be very efficiently studied by low-energy ion scattering (LEIS) due to the specific surface sensitivity of this technique. Investigations of single-crystal surfaces of ordered alloys are of particular interest because they provide the possibility to investigate the interplay between segregation effects and the order-disorder phase transition when passing through the transition temperature. Exemplifying these effects for bimetallic alloys we consider in particular the CuAu-system.For the quantitative interpretation of energy and angle resolved LEIS intensity distributions we compare experimental results with those from numerical simulations using the MARLOWE code which we extended with a detailed trajectory analysis. This allows us to apply various discrimination criteria, such as number of collisions, distance of closest approach, identification of the scattering crystal layer, total path length, etc. On this basis structural effects, ion survival probabilities and the influence of thermal vibrations can be studied.We demonstrate this potential by using CuAu(1 0 0) as a special example. The scattering potential parameters were calibrated with elemental single crystals of known structures and the anisotropic Debye temperatures taken from the literature showed good agreement, neutralization was of minor importance in this case. Our procedure could be successfully used for the quantitative analysis of the composition of the first and second layer as a function of temperature. These results are in good agreement with theoretical predictions. 相似文献
100.