全文获取类型
收费全文 | 742182篇 |
免费 | 9658篇 |
国内免费 | 2006篇 |
专业分类
电工技术 | 13867篇 |
综合类 | 1036篇 |
化学工业 | 111766篇 |
金属工艺 | 27084篇 |
机械仪表 | 21116篇 |
建筑科学 | 18432篇 |
矿业工程 | 2944篇 |
能源动力 | 20354篇 |
轻工业 | 67070篇 |
水利工程 | 6917篇 |
石油天然气 | 11572篇 |
武器工业 | 44篇 |
无线电 | 87188篇 |
一般工业技术 | 141457篇 |
冶金工业 | 145357篇 |
原子能技术 | 14034篇 |
自动化技术 | 63608篇 |
出版年
2021年 | 6345篇 |
2020年 | 4633篇 |
2019年 | 5943篇 |
2018年 | 10073篇 |
2017年 | 9791篇 |
2016年 | 10285篇 |
2015年 | 7214篇 |
2014年 | 12039篇 |
2013年 | 34141篇 |
2012年 | 19086篇 |
2011年 | 26626篇 |
2010年 | 20911篇 |
2009年 | 23669篇 |
2008年 | 24337篇 |
2007年 | 24031篇 |
2006年 | 21127篇 |
2005年 | 19436篇 |
2004年 | 18753篇 |
2003年 | 18424篇 |
2002年 | 17603篇 |
2001年 | 17743篇 |
2000年 | 16642篇 |
1999年 | 17681篇 |
1998年 | 44969篇 |
1997年 | 31747篇 |
1996年 | 24522篇 |
1995年 | 18545篇 |
1994年 | 16457篇 |
1993年 | 16012篇 |
1992年 | 11669篇 |
1991年 | 10978篇 |
1990年 | 10792篇 |
1989年 | 10486篇 |
1988年 | 9940篇 |
1987年 | 8658篇 |
1986年 | 8647篇 |
1985年 | 9871篇 |
1984年 | 9088篇 |
1983年 | 8248篇 |
1982年 | 7665篇 |
1981年 | 7853篇 |
1980年 | 7392篇 |
1979年 | 7238篇 |
1978年 | 6843篇 |
1977年 | 8346篇 |
1976年 | 10897篇 |
1975年 | 5986篇 |
1974年 | 5706篇 |
1973年 | 5790篇 |
1972年 | 4766篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
We propose and evaluate a medium-access control (MAC) protocol for synchronous cellular packet direct-sequence code-division multiple-access (DS/CDMA). The protocol is designed for handling a variety of multimedia traffic types in an integrated wireless-access network (IWAN). For instance, the protocol is suited for carrying multiple traffic types of different priorities. An analytical model for the equilibrium state has been developed for the proposed protocol. A comparative evaluation of the protocol is done for three different radio frequency bandwidths currently under consideration for personal communication services (PCS), i.e., 1.25 MHz, 5 MHz, and 10 MHz. Our results demonstrate that the proposed protocol is both robust and flexible for the intended IWAN applications. It offers a significant multiplexing gain as the bandwidth increases 相似文献
82.
In a prospective study we found good results concerning postoperative complications (21%), perioperative lethality (3.2%) and lethality during hospital stay (6.5%) after implantation of dynamic hip screws (DHS) in patients with per- and subtrochanteric fractures of the femur. The ability to walk, as well as housing and social care postoperatively and follow-up for at least six months after dismissal demonstrates the importance of these fractures for the elderly. One of three patients needs professional care, 21% at home, 13% in nursing homes. Six months after operation the lethality is nearly 20%, i.e. three times higher than in hospital. These are the essential data for all techniques of osteosynthesis used in patients with these fractures, which could only be documented in prospective studies. 相似文献
83.
84.
M.E.W. Eggenkamp V. A. Shvarts R. Blaauwgeers A. Storm R. Jochemsen G. Frossati 《Journal of Low Temperature Physics》1998,110(1-2):299-304
This paper focuses on the hydrodynamics of third sound on a superfluid
3
He film. We solve the hydrodynamical equations in the limit of thick films with weak interaction with the substrate. The surface tension at the free interface is shown to have a large effect on the third sound velocity and on the attenuation for frequencies larger than 1Hz. In the case of a diffusely scattering substrate a ripplon-like dispersion relation is found for this frequency range. 相似文献
85.
The Frizzled genes encode receptors for WNTs, secreted glycoproteins implicated in development as well as in carcinogenesis. In this paper, we report molecular cloning of Hfz6, the human homologue of Mfz6. Nucleotide sequence analysis showed that the Hfz6 gene encodes the 706 amino-acid protein with seven transmembrane domains, a cystein-rich domain in the N-terminal extracellular region, two N-linked glycosylation sites, and two cystein residues in the second and third extracellular loops. Hfz6 mRNA 4.4-kb in size was detected in various normal adult and fetal tissues, and a larger amount of Hfz6 mRNA was detected in both fetal lung and fetal kidney. The Hfz6 gene has been mapped to human chromosome 8q22.3-q23.1. In conclusion, we have cloned Hfz6, which encodes a seven-transmembrane receptor with the cystein-rich domain in the N-terminal extracellular region, but without the Ser/Thr-X-Val motif in the C-terminus. 相似文献
86.
87.
The objective of this study is to determine the economic and operational impact on energy cost of incorporating large photovoltaic (PV) and wind energy conversion systems (WECS) into the electric utility generation mix. In most cases, PV and WECS power outputs are subtracted from the utility load with the expectation that conventional generation would meet the residual load. This approach is valid for small penetration levels and/or for PV and WECS facilities connected near load centers, However, several constraints such as thermal generation characteristics, fuel supply and delivery, spinning reserve requirements, and hydro availability are not adequately represented in this process. To determine the optimal value of large-scale PV and WECS applications, a new methodology that would take into account the aforementioned constraints as well as a more global penetration is developed. Results indicate that while high hydro availability increases PV penetration levels, high ramping rates can also significantly increase penetration levels 相似文献
88.
89.
K Alanko L Kanerva B Mohell-Talolahti R Jolanki T Estlander 《Canadian Metallurgical Quarterly》1996,35(4):647-648
The biotransformation of oxazepam by Bifidobacterium bifidum was studied. The major metabolite was purified by chromatographic methods and found to be desmethyldiazepam using NMR, IR and other physicochemical data. 相似文献
90.