全文获取类型
收费全文 | 178148篇 |
免费 | 10114篇 |
国内免费 | 5311篇 |
专业分类
电工技术 | 7228篇 |
技术理论 | 3篇 |
综合类 | 8890篇 |
化学工业 | 26355篇 |
金属工艺 | 10283篇 |
机械仪表 | 9451篇 |
建筑科学 | 9392篇 |
矿业工程 | 3904篇 |
能源动力 | 3661篇 |
轻工业 | 10314篇 |
水利工程 | 3111篇 |
石油天然气 | 5508篇 |
武器工业 | 921篇 |
无线电 | 20794篇 |
一般工业技术 | 26896篇 |
冶金工业 | 6835篇 |
原子能技术 | 1266篇 |
自动化技术 | 38761篇 |
出版年
2024年 | 546篇 |
2023年 | 1737篇 |
2022年 | 3149篇 |
2021年 | 4241篇 |
2020年 | 3287篇 |
2019年 | 2750篇 |
2018年 | 17089篇 |
2017年 | 16490篇 |
2016年 | 12825篇 |
2015年 | 4975篇 |
2014年 | 5485篇 |
2013年 | 6250篇 |
2012年 | 9880篇 |
2011年 | 16522篇 |
2010年 | 14301篇 |
2009年 | 11160篇 |
2008年 | 12151篇 |
2007年 | 12900篇 |
2006年 | 5535篇 |
2005年 | 5634篇 |
2004年 | 4241篇 |
2003年 | 3599篇 |
2002年 | 2683篇 |
2001年 | 1995篇 |
2000年 | 2126篇 |
1999年 | 2047篇 |
1998年 | 1750篇 |
1997年 | 1447篇 |
1996年 | 1340篇 |
1995年 | 1077篇 |
1994年 | 924篇 |
1993年 | 643篇 |
1992年 | 505篇 |
1991年 | 428篇 |
1990年 | 292篇 |
1989年 | 252篇 |
1988年 | 208篇 |
1987年 | 131篇 |
1986年 | 100篇 |
1985年 | 63篇 |
1980年 | 34篇 |
1968年 | 43篇 |
1966年 | 43篇 |
1965年 | 45篇 |
1959年 | 39篇 |
1958年 | 38篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
181.
Nonlinear dynamical method of projecting the transmission of an epidemic is accurate if the input parameters and initial value
variables are reliable. Here, such a model is proposed for predicting an epidemic. A method to supplement two variables and
two parameters for this proposed model is demonstrated through a robust statistical approach. The method described here worked
well in case of three continuous distributions. Model predictions could be lower estimates due to under-reporting of disease
cases. Anad hoc procedure with a technical note is provided in the appendix
An earlier version of this paper was presented at the annual conference of the Indian Society for Mathematical Modelling &
Computer Simulation, Bangalore, November 14–15, 2002 相似文献
182.
Jefferson Fabrício Cardoso Lins Hugo Ricardo Z. Sandim Hans-Jürgen Kestenbach 《Journal of Materials Science》2007,42(16):6572-6577
The present paper reports the experimental results on the microstructural and textural characterization of a hot-rolled IF
steel. The IF steel was hot-rolled in multiple passes in the austenitic field (1,070 °C) followed by air-cooling. SEM, TEM,
and LOM were used to image the microstructure of the material. The global texture was determined by X-ray diffraction (XRD)
technique. The mesotexture of selected regions was investigated by electron backscatter diffraction (EBSD). Results show the
presence of a diffuse (nearly random) and weak texture in the hot-band that consists of recrystallized polygonal grains and
subgrains. The fraction of boundaries with misorientations comprised in the interval 2° ≤ ψ < 15° was found to be lower than
5%. It can be concluded that these low angle boundaries and the presence of subgrains can be associated to the existence of
a few areas softened by recovery during or after hot rolling in austenitic field. 相似文献
183.
Effect of hydrogen charging on dislocation behavior in Ni-Cr and Ni<Subscript>2</Subscript>Cr alloys
Kaori Miyata 《Metallurgical and Materials Transactions A》2003,34(6):1249-1257
The effects of hydrogen charging on the dislocation behaviour in Ni-Cr binary alloys have been investigated by means of transmission
electron microscope (TEM) observations using single-crystalline specimens. The deformation mode of Ni-Cr alloys in the absence
of hydrogen is characterized by planar dislocations. However, hydrogen charging changed the dislocation configurations to
promote curved dislocations, such as dislocation loops and dipoles. The hydrogen-affected dislocation configurations are enhanced
with increasing Ni content and reducing Cr content. Weak-beam images show that the Shockley partials of the hydrogen-affected
dislocations frequently constrict to make kinks and cross-slip, as if the dislocations were generated by a thermally activated
process. The effect of hydrogen charging on superdislocations of a Ni2Cr superstructure has been also investigated using an aged 70Ni-30Cr alloy. While the deformation mode in the Ni2Cr superlattice is classified as five variants of superdislocation triplets and one variant of ordinary dislocations, the
hydrogen charging has preferred the ordinary dislocations to the superdislocation triplets. The results suggest that the charged
hydrogen changes the local plasticity to affect the deformation dynamics in Ni-Cr alloys, where the influence of hydrogen
on the plasticity is sensitive to the Ni/Cr concentration and the symmetry of atomic arrangement. 相似文献
184.
Bayesian and Dempster-Shafer fusion 总被引:3,自引:0,他引:3
The Kalman Filter is traditionally viewed as a prediction-correction filtering algorithm. In this work we show that it can
be viewed as a Bayesian fusion algorithm and derive it using Bayesian arguments. We begin with an outline of Bayes theory,
using it to discuss well-known quantities such as priors, likelihood and posteriors, and we provide the basic Bayesian fusion
equation. We derive the Kalman Filter from this equation using a novel method to evaluate the Chapman-Kolmogorov prediction
integral. We then use the theory to fuse data from multiple sensors. Vying with this approach is the Dempster-Shafer theory,
which deals with measures of “belief”, and is based on the nonclassical idea of “mass” as opposed to probability. Although
these two measures look very similar, there are some differences. We point them out through outlining the ideas of the Dempster-Shafer
theory and presenting the basic Dempster-Shafer fusion equation. Finally we compare the two methods, and discuss the relative
merits and demerits using an illustrative example. 相似文献
185.
186.
This paper reports the findings of a detailed study of Web-based systems design (WBSD) practices in Ireland based on data
collected over a 3-year period (2002–2005), the objectives of which were to (1) contribute towards a richer understanding
of the current “real-world” context of WBSD by characterising the profile of a typical project (team size, timeframe, nature
of requirements, etc.) and identifying the key challenges, constraints, and imperatives (i.e. “mediating factors”) faced by
Web-based system designers, and (2) understand how those contextual parameters and mediating factors influence the activity
of WBSD as regards the selection and enactment of whatever design practices are therefore engaged (i.e. the use of methods,
procedures, etc.). Data was gathered through a survey which yielded 165 usable responses, and later through a series of semi-structured
qualitative interviews. Using grounded theory, an explanatory conceptual framework is derived, based on an extension of the
“method-in-action” model, the application of which to WBSD has not been previously investigated in depth. It is proposed that
this framework of WBSD issues is valuable in a number of ways to educators, researchers, practitioners, and method engineers. 相似文献
187.
基于物质平衡方程、产能方程和递减方程的结合,提出了定容气田开发规划的概算法.该法可用于预测地层压力、井底流动压力、井口流动压力和稳产年限.实际应用表明,本文提供的方法是实用有效的. 相似文献
188.
189.
190.
采用二甲苯为溶剂,将不同乙烯含量(5% ̄15%质量)的抗冲聚丙烯用特定程序进行分级,将各样品分为室温下可溶于甲苯和不可溶于甲苯的两部分。使用^13C-NMR方法和FT-IR方法对各组分进行表征,明确了乙烯链段在聚丙烯链上的分布,并在此基础上提出了产生这种链结构的聚合工艺的特点。 相似文献