全文获取类型
收费全文 | 24430篇 |
免费 | 3204篇 |
国内免费 | 1458篇 |
学科分类
工业技术 | 29092篇 |
出版年
2024年 | 192篇 |
2023年 | 558篇 |
2022年 | 929篇 |
2021年 | 1129篇 |
2020年 | 1120篇 |
2019年 | 902篇 |
2018年 | 876篇 |
2017年 | 1009篇 |
2016年 | 1045篇 |
2015年 | 1175篇 |
2014年 | 1445篇 |
2013年 | 1514篇 |
2012年 | 1737篇 |
2011年 | 1867篇 |
2010年 | 1340篇 |
2009年 | 1339篇 |
2008年 | 1331篇 |
2007年 | 1627篇 |
2006年 | 1378篇 |
2005年 | 1125篇 |
2004年 | 984篇 |
2003年 | 849篇 |
2002年 | 688篇 |
2001年 | 551篇 |
2000年 | 492篇 |
1999年 | 382篇 |
1998年 | 296篇 |
1997年 | 227篇 |
1996年 | 182篇 |
1995年 | 139篇 |
1994年 | 121篇 |
1993年 | 104篇 |
1992年 | 85篇 |
1991年 | 52篇 |
1990年 | 54篇 |
1989年 | 50篇 |
1988年 | 20篇 |
1987年 | 30篇 |
1986年 | 17篇 |
1985年 | 27篇 |
1984年 | 19篇 |
1983年 | 16篇 |
1982年 | 23篇 |
1981年 | 4篇 |
1980年 | 10篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
稠油微生物开采技术现状及进展 总被引:2,自引:0,他引:2
综述了用微生物方法开采稠油的技术现状与进展,论题如下。①概述。②基本方法:异源微生物采油,包括微生物吞吐和微生物驱;本源微生物采油压大港孔店油田的实例。③主要机理,包括产表面活性剂,降解稠油中重质组分及其他。④技术研究,包括机理性、可行性及经济效益研究,列举了国内外6个实例。⑤现场应用,包括国外1个、国内6个实例。⑥该技术的优势及问题。参22。 相似文献
2.
3.
We report on picosecond time resolved spectroscopy of photogenerated infrared active vibrations in thin films of 2,5-dioctyloxy poly(phenylene vinylene). We excited the films by ?4 ps long pulses of 565 nm laser light with 2×1013 photons/cm2 per pulse and repetition rate of 76 MHz. We then followed the temporal evolution of the infrared active vibrational (IRAV) spectrum using a subsequent, variably delayed, weak tunable IR probe pulses of similar temporal duration. Under these conditions, we show clear spectroscopic evidence for photogenerated infrared active vibrations at times which are shorter than our temporal resolution (<4 ps). We suggest that the transient IRAV absorption is due to secondary polarons formation following exciton dissociation. 相似文献
4.
5.
The main difficulty with EM algorithm for mixture model concerns the number of components, say g. This is the question of model selection, and the EM algorithm itself could not estimate g. On the contrary, the algorithm requires g to be specified before the remaining parameters can be estimated. To solve this problem, a new algorithm, which is called stepwise split-and-merge EM (SSMEM) algorithm, is proposed. The SSMEM algorithm alternately splits and merges components, estimating g and other parameters of components simultaneously. Also, two novel criteria are introduced to efficiently select the components for split or merge. Experimental results on simulated and real data demonstrate the effectivity of the proposed algorithm. 相似文献
6.
A. F. Kurbatskii 《High Temperature》2004,42(1):79-87
The difference in the turbulent diffusion between the active (heat) and passive (mass) scalars in a thermally stably stratified medium is investigated. The axisymmetric problem is treated on the formation of a turbulent circulation flow above a heated disk and on the turbulent diffusion of a passive scalar (impurity) from a continuous surface source in a stably stratified medium. The results indicate that the thermal stratification causes appreciable differences in the coefficients of turbulent transfer between the active (heat) and passive (mass) scalars. This means that the assumption of the identity of the coefficient of turbulent diffusion of heat and mass, employed in conventional models of turbulence, produces significant errors in estimating the heat and mass transfer in a thermally stably stratified medium. 相似文献
7.
Christos Bouras Agisilaos Konidaris 《International Journal of Communication Systems》2005,18(2):119-142
Redundant data transfers over the Web, can be mainly attributed to the repeated transfers of unchanged data. Web caches and Web proxies are some of the solutions that have been proposed, to deal with the issue of redundant data transfers. In this paper we focus on the efficient estimation and reduction of redundant data transfers over the Web. We first prove that a vast amount of redundant data is transferred in Web pages that are considered to carry fresh data. We show this by following an approach based on Web page fragmentation and manipulation. Web pages are broken down to fragments, based on specific criteria. We then deal with these fragments as independent constructors of the Web page and study their change patterns independently and in the context of the whole Web page. After the fragmentation process, we propose solutions for dealing with redundant data transfers. This paper has been based on our previous work on ‘Web Components’ but also on related work by other researchers. It utilises a proxy based, client/server architecture, and imposes changes to the algorithms executed on the Proxy server and on clients. We show that our proposed solution can considerably reduce the amount of redundant data transferred on the Web. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
8.
9.
Amanda LaCoste Karen M. Schaich David Zumbrunnen Kit L. Yam 《Packaging Technology and Science》2005,18(2):77-87
Researchers from Rutgers University and Clemson University have collaborated to develop a concept of using smart blending to generate functional packaging films for the controlled release of active compounds such as antimicrobials, antioxidants and flavour compounds to extend the shelf‐life of food. In this paper, literature results are reviewed to justify the significance of controlled release packaging (CRP) and the research gaps for further development are identified. A major research gap is the lack of packaging materials that can provide the release of active compounds at rates suitable for a wide range of food packaging applications. Smart blending is a promising technology for bridging this research gap. To fully realize the potentials of smart blending, a systematic approach for developing CRP using smart blending is also presented. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
10.