全文获取类型
收费全文 | 85622篇 |
免费 | 1042篇 |
国内免费 | 414篇 |
专业分类
电工技术 | 793篇 |
综合类 | 2319篇 |
化学工业 | 11916篇 |
金属工艺 | 4806篇 |
机械仪表 | 3057篇 |
建筑科学 | 2230篇 |
矿业工程 | 566篇 |
能源动力 | 1191篇 |
轻工业 | 3808篇 |
水利工程 | 1301篇 |
石油天然气 | 351篇 |
无线电 | 9377篇 |
一般工业技术 | 16549篇 |
冶金工业 | 2850篇 |
原子能技术 | 267篇 |
自动化技术 | 25697篇 |
出版年
2023年 | 33篇 |
2022年 | 92篇 |
2021年 | 116篇 |
2020年 | 80篇 |
2019年 | 68篇 |
2018年 | 14492篇 |
2017年 | 13421篇 |
2016年 | 10016篇 |
2015年 | 673篇 |
2014年 | 284篇 |
2013年 | 331篇 |
2012年 | 3272篇 |
2011年 | 9524篇 |
2010年 | 8364篇 |
2009年 | 5632篇 |
2008年 | 6848篇 |
2007年 | 7854篇 |
2006年 | 198篇 |
2005年 | 1275篇 |
2004年 | 1182篇 |
2003年 | 1207篇 |
2002年 | 583篇 |
2001年 | 121篇 |
2000年 | 190篇 |
1999年 | 81篇 |
1998年 | 105篇 |
1997年 | 65篇 |
1996年 | 66篇 |
1995年 | 26篇 |
1994年 | 27篇 |
1993年 | 26篇 |
1992年 | 19篇 |
1991年 | 36篇 |
1989年 | 18篇 |
1988年 | 17篇 |
1969年 | 26篇 |
1968年 | 44篇 |
1967年 | 35篇 |
1966年 | 42篇 |
1965年 | 44篇 |
1963年 | 28篇 |
1962年 | 22篇 |
1961年 | 18篇 |
1960年 | 30篇 |
1959年 | 35篇 |
1958年 | 38篇 |
1957年 | 37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 15 毫秒
91.
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
92.
93.
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
94.
95.
We present some sufficient and necessary conditions for convergent splitting of a non-Hermitian indefinite matrix. Some sufficient
conditions to determinate a matrix with a (strongly) dominant symmetric part for a class of boundary value problem are also
obtained. These results are applicable to identify the convergence of iterative methods for solving large sparse systems of
linear equations. 相似文献
96.
P Hourdequin L Bednarczyk R Gabriel G Harika C Quereux P Wahl 《Canadian Metallurgical Quarterly》1996,25(5):528-532
We report three cases of pulmonary edema associated with prolonged intravenous tocolytic therapy with beta 2-adrenergic agonists among patients with multiple pregnancies. Although beta 2-adrenergic agonists may have direct myocardial side-effects, the underlying pathophysiologic mechanisms are mainly noncardiogenic. The most important one appears to be the fluid overload, related to amounts of fluids given intravenously and to direct result of beta-sympathomimetic therapy on renal excretion of sodium and water. Neonatal benefit of prolonged tocolytic therapy remains hypothetical. If this strategy is used, the prevention of cardiovascular adverse effects requires an intensive maternal supervision, especially in case of multiple pregnancy, the use of beta 2-adrenergic agonists in concentrated solution in order to reduce the amounts of fluids given intravenously, and the association with progesterone therapy which can reduce the infusion rate and the duration of tocolytic therapy. 相似文献
97.
Gabriel C.M.W. Heffels J.J.M. Hou X. Ouibrahim H. 《Electronics & Communication Engineering Journal》1993,5(2):103-112
Introduction of the broadband integrated services digital network (B-ISDN) will enable network users to make use of advanced multimedia, multiparty services. With this aim in view, RACE II project R2044, MAGIC, is investigating long-term signalling requirements, architecture and protocols for B-ISDN. New service concepts are being developed in MAGIC which will provide more flexibility when compared to narrowband ISDN (N-ISDN). The service requirements and other signalling requirements, such as the separation between call and associated connections at the network-node interface, are used to determine the distribution of functions over the network. The signalling protocols which are used to exchange the signalling information are subsequently developed. These signalling protocols are simulated to prove the performance and the feasibility of call handling concepts 相似文献
98.
Keng Siau 《Requirements Engineering》2007,12(4):199-201
99.
100.
Phase-change read-and-write memory (PRAM) is a promising memory that can solve the problems of conventional memory—scalability, read/write speed, and reliability. We will review the opportunities and technical challenges of PRAM. The most important challenge of PRAM is the reduction of the writing current. Various approaches to reduce the writing current will be reviewed and the prospects of PRAM are discussed. 相似文献