全文获取类型
收费全文 | 458401篇 |
免费 | 5246篇 |
国内免费 | 2018篇 |
专业分类
电工技术 | 8599篇 |
综合类 | 353篇 |
化学工业 | 67971篇 |
金属工艺 | 18781篇 |
机械仪表 | 15267篇 |
建筑科学 | 9681篇 |
矿业工程 | 2551篇 |
能源动力 | 12862篇 |
轻工业 | 33476篇 |
水利工程 | 4901篇 |
石油天然气 | 9467篇 |
武器工业 | 55篇 |
无线电 | 54324篇 |
一般工业技术 | 94623篇 |
冶金工业 | 84337篇 |
原子能技术 | 11042篇 |
自动化技术 | 37375篇 |
出版年
2022年 | 2936篇 |
2021年 | 4456篇 |
2020年 | 3380篇 |
2019年 | 4295篇 |
2018年 | 7449篇 |
2017年 | 7516篇 |
2016年 | 8075篇 |
2015年 | 4958篇 |
2014年 | 8196篇 |
2013年 | 22557篇 |
2012年 | 13050篇 |
2011年 | 17221篇 |
2010年 | 13830篇 |
2009年 | 15558篇 |
2008年 | 15890篇 |
2007年 | 15623篇 |
2006年 | 13935篇 |
2005年 | 12512篇 |
2004年 | 11840篇 |
2003年 | 11719篇 |
2002年 | 11077篇 |
2001年 | 10989篇 |
2000年 | 10371篇 |
1999年 | 10678篇 |
1998年 | 27092篇 |
1997年 | 18673篇 |
1996年 | 14299篇 |
1995年 | 10670篇 |
1994年 | 9401篇 |
1993年 | 9408篇 |
1992年 | 6807篇 |
1991年 | 6504篇 |
1990年 | 6477篇 |
1989年 | 6133篇 |
1988年 | 5760篇 |
1987年 | 5100篇 |
1986年 | 4982篇 |
1985年 | 5545篇 |
1984年 | 5010篇 |
1983年 | 4574篇 |
1982年 | 4192篇 |
1981年 | 4269篇 |
1980年 | 3959篇 |
1979年 | 3838篇 |
1978年 | 3821篇 |
1977年 | 4364篇 |
1976年 | 5595篇 |
1975年 | 3307篇 |
1974年 | 3101篇 |
1973年 | 3177篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
This paper presents a new self-routing packet network called the plane interconnected parallel network (PIPN). In the proposed design, the traffic arriving at the network is shaped and routed through two banyan network based interconnected planes. The interconnections between the planes distribute the incoming load more homogeneously over the network. The throughput of the network under uniform and heterogeneous traffic requirements is studied analytically and by simulation. The results are compared with the results of the baseline network and another banyan network based parallel interconnection network. It is shown that, for the proposed design, a higher degree of heterogeneity results in better performance 相似文献
52.
This paper presents the design criteria, procedure, and implementation of a soft-switched power-factor-correction (PFC) circuit based on the extended-period quasi-resonant (EPQR) principles. All power electronic devices including switches and diodes in the circuit are fully soft switched. The design method is demonstrated in a prototype circuit. The operating principles are confirmed with computer simulation and experimental results. A comparison of the EP-QR operation and zero-voltage-transition (ZVT) pulse-width modulation (PWM) method 相似文献
53.
Two novel configurations for digitally tunable optical filters based on arrayed-waveguide grating (AWG) multiplexers are described in detail with emphasis on the connection of the AWG multiplexer and optical switches. Performance comparisons show that conventional configurations are disadvantaged by the switch size required and loss imbalance among the optical frequency-division-multiplexed (FDM) channels; the proposed configurations require only O(√(N)) switch elements to select one of N FDM channels, and the loss imbalance is lower by up to 75% in decibel 相似文献
54.
55.
56.
Malignant bone pain: pathophysiology and treatment 总被引:1,自引:0,他引:1
S Mercadante 《Canadian Metallurgical Quarterly》1997,69(1-2):1-18
2-acetyl aminofluorene (AAF) reacts in acidic conditions with nitrous fume yielding N-nitroso-AAF (N-NO-AAF), as previously described, that exerts more toxic and mutagenic effects than its parental compound. In this study, the effect of sodium nitrite (NaNO2) on the tumorigenicity of AAF in rats fed with AAF and NaNO2 was observed. Wistar rats were divided into five groups: group I served as control; group II were treated with NaNO2 (0.3%); group III was given 0.02% AAF alone; groups IV and V received both AAF and NaNO2 (0.2 and 0.3% respectively) in their diet for 12 weeks. At the end of the experiment, all rats in groups III, IV and V developed early stage phenomena of hepatocellular carcinoma, including hepatomegaly with variable-sized foci and neoplastic nodules. Severe damage was observed in the rats treated with AAF and NaNO2. Feeding of AAF (0.02%) for 3 months elevated the levels of c-Fos, c-Jun and c-Myc proteins in the rat livers. The AAF-induced c-Jun, c-Fos and c-Myc expressions were significantly magnified (P < 0.001) by NaNO2. These data confirmed that the strengthening of AAF-induced hepatocarcinogenesis by NaNO2 should be associated with its enhancing effect on the AAF-induced increases in the expressions of c-Jun, c-Fos and c-Myc. 相似文献
57.
58.
59.
S. Otakulov 《Cybernetics and Systems Analysis》1994,30(3):458-462
Translated from Kibernetika i Sistemnyi Analiz, No. 3, pp. 172–176, May–June, 1994 相似文献
60.
An extended logistic model with a varying asymptotic upper bound for long-range peak demand forecasting is described. The model has been applied to a typical fast growing system, the Saudi Consolidated Electric Company. The forecasts are compared with actual demands and with those obtained from classical forecasting methods. The model gave relatively accurate peak demand forecasts compared with other classical methods. The model with a single load observation is capable of producing several peak demand forecasts corresponding to different levels of maximum temperature and various levels of social activity. The forecasts produced by the model were also stable irrespective of the length of the ex-post simulation period 相似文献