全文获取类型
收费全文 | 3464篇 |
免费 | 38篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 62篇 |
综合类 | 5篇 |
化学工业 | 216篇 |
金属工艺 | 10篇 |
机械仪表 | 40篇 |
建筑科学 | 107篇 |
矿业工程 | 1篇 |
能源动力 | 77篇 |
轻工业 | 52篇 |
水利工程 | 11篇 |
无线电 | 374篇 |
一般工业技术 | 263篇 |
冶金工业 | 2045篇 |
原子能技术 | 5篇 |
自动化技术 | 239篇 |
出版年
2022年 | 18篇 |
2021年 | 19篇 |
2020年 | 15篇 |
2019年 | 17篇 |
2018年 | 9篇 |
2017年 | 19篇 |
2016年 | 25篇 |
2015年 | 21篇 |
2014年 | 32篇 |
2013年 | 94篇 |
2012年 | 43篇 |
2011年 | 70篇 |
2010年 | 60篇 |
2009年 | 74篇 |
2008年 | 49篇 |
2007年 | 70篇 |
2006年 | 67篇 |
2005年 | 64篇 |
2004年 | 49篇 |
2003年 | 45篇 |
2002年 | 55篇 |
2001年 | 59篇 |
2000年 | 40篇 |
1999年 | 98篇 |
1998年 | 710篇 |
1997年 | 393篇 |
1996年 | 269篇 |
1995年 | 173篇 |
1994年 | 116篇 |
1993年 | 140篇 |
1992年 | 44篇 |
1991年 | 48篇 |
1990年 | 43篇 |
1989年 | 33篇 |
1988年 | 27篇 |
1987年 | 23篇 |
1986年 | 24篇 |
1985年 | 35篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 18篇 |
1981年 | 13篇 |
1980年 | 29篇 |
1979年 | 13篇 |
1978年 | 17篇 |
1977年 | 52篇 |
1976年 | 103篇 |
1974年 | 5篇 |
1973年 | 9篇 |
1972年 | 6篇 |
排序方式: 共有3507条查询结果,搜索用时 15 毫秒
1.
Development of a recurrent Sigma-Pi neural network rainfall forecasting system in Hong Kong 总被引:1,自引:1,他引:0
At the moment, weather forecasting is still an art — the experience and intuition of forecasters play a significant role in determining the quality of forecasting. This paper describes the development of a new approach to rainfall forecasting using neural networks. It deals with the extraction of information from radar images and an evaluation of past rain gauge records to provide shortterm rainfall forecasting. All of the meteorological data were provided by the Royal Observatory of Hong Kong (ROHK). Preprocessing procedures were essential for this neural network rainfall forecasting. The forecast of the rainfall was performed every half an hour so that a storm warning signal can be delivered to the public in advance. The network architecture is based on a recurrent Sigma-Pi network. The results are very promising, and this neural-based rainfall forecasting system is capable of providing a rain storm warning signal to the Hong Kong public one hour ahead. 相似文献
2.
SF Zakharov SH Kwok H Sokoloff HT Chang SP Radko A Chrambach 《Canadian Metallurgical Quarterly》1998,19(10):1625-1630
An automated gel electrophoresis apparatus, recently available commercially, allows one to follow the band during electrophoresis in real time, and lends itself therefore to an evaluation of bandwidth as a function of migration time (the dispersion coefficient), resolution and band shape. These determinations assume the constancy of band area with migration time and at various gel concentrations. The purpose of the present study was to verify these assumptions. Representative proteins and sodium dodecyl sulfate (SDS)-proteins, either natively fluorescent or fluorescein carboxylate labeled, were found to exhibit band areas which approach constancy as a function of migration time in both agarose and polyacrylamide gel electrophoresis, provided that (i) the protein concentration under the band was low enough to obviate self-quenching of fluorescence; (ii) the separation of the protein of interest from contaminants had progressed sufficiently during the time at which band areas were measured; (iii) the baseline under the peak was sufficiently well defined. However, band areas decrease with increasing gel concentration. Protein peaks exhibited leading and trailing tails. The ratio of the combined tail area to total area appeared to be near-constant at varying migration times. However, that ratio increases with increasing gel concentration. The tail area does not appear to be an artifact of fluorometric detection since it is reproduced upon fluorimetric analysis of the protein eluted from gel slices after electrophoresis. However, it may be due to photochemical destruction under the conditions of repetitive fluorometric peak detection. 相似文献
3.
Power distribution systems have been significantly affected by many outage-causing events. Good fault cause identification can help expedite the restoration procedure and improve the system reliability. However, the data imbalance issue in many real-world data sets often degrades the fault cause identification performance. In this paper, the E-algorithm, which is extended from the fuzzy classification algorithm by Ishibuchi to alleviate the effect of imbalanced data constitution, is applied to Duke Energy outage data for distribution fault cause identification. Three major outage causes (tree, animal, and lightning) are used as prototypes. The performance of E-algorithm on real-world imbalanced data is compared with artificial neural network. The results show that the E-algorithm can greatly improve the performance when the data are imbalanced 相似文献
4.
KW Sax SM Strakowski PE Keck SL McElroy SA West SP Stanton 《Canadian Metallurgical Quarterly》1998,44(8):784-786
BACKGROUND: This study examined patients with a first-episode of affective psychosis during acute and compensated states in order to determine whether changes in attentional functioning over time were accompanied by changes in the severity of psychotic or affective symptoms. METHODS: Attentional performance was measured in patients (n = 27) using the degraded-stimulus continuous Performance Test (CPT) and symptoms were assessed at the time of index hospitalization, and 2 months after discharge. A comparison group of normal volunteers (n = 31) also performed the CPT two months apart. RESULTS: Patients performed significantly worse than controls at the initial testing but not at follow-up. The improvement in attentional performance significantly correlated with decreased severity of manic symptoms. CONCLUSIONS: Results suggest attentional dysfunction is a state-dependent characteristic of mania, and may provide an additional measure of clinical improvement following treatment. 相似文献
5.
This paper studies a particular single-stage power-factor-correction (PFC) switching regulator employing a discontinuous-conduction-mode (DCM) boost-input cell and a continuous-current-mode (CCM) forward output cell. Although this single-stage PFC regulator can provide a reasonably high power factor when its PFC stage is operating in discontinuous mode, substantial reduction in line-current harmonics is possible by applying a suitable frequency-modulation scheme. This paper derives a frequency-modulation scheme and proposes a practical implementation using a simple translinear analog circuit. A quantitative analysis on the total harmonic distortion (THD) of the line current when the circuit is subject to a limited range of frequency variations is presented along with some considerations for practical design. Experimental data obtained from a prototype confirms the effectiveness of the proposed frequency-modulation scheme. The proposed analog translinear circuit allows custom integrated circuit implementation, making it a viable low-cost solution to the elimination of line-current harmonics in switching regulators 相似文献
6.
7.
8.
On smoke control for tunnels by longitudinal ventilation 总被引:2,自引:0,他引:2
W. K. Chow 《Tunnelling and Underground Space Technology incorporating Trenchless Technology Research》1998,13(3):336
Two aspects of smoke control by longitudinal ventilation systems in tunnels is analysed. The first is the increase in air entrainment rate of the plume after operating the system, and the second is the increase in heat release rate as a consequence of increase in air supply rate for combustion. Computational fluid dynamics (CFD) was applied for verifying the study. Keypoints to consider in the design of longitudinal ventilation systems are noted. 相似文献
9.
Antisera towards neurotensin (NT) and the structurally related peptide, LANT6, were used to characterize immunoreactive peptides and proteins in extracts of chicken tissues. A 17 kDa protein was identified by Western blotting as a potential precursor to NT and LANT6. However, the posttranslational processing of this common precursor appeared to be tissue specific, giving rise to disproportionate amounts of NT and LANT6, along with varying expression of a large molecular LANT6 (M(r), 15 kDa). The intestinal cells containing immunoreactive NT, LANT6, and large molecular LANT6 behaved similarly during fractionation by size and density. These activities also banded together in particles resembling vesicles during centrifugation of isotonic homogenates of tissue. These results suggest that chicken NT and LANT6 are biosynthesized as parts of the same precursor, the processing of which can give rise to a variety of products stored within secretory vesicles. 相似文献
10.
Haemangiopericytoma of nose and paranasal sinuses is relatively uncommon tumour. It occurs in adults in sixth and seventh decades of life. In view of paucity of intranasal haemangiopericytoma old in Indian literature and young age of patient, we are reporting one case in 28-year-old female who presented with recurrent, profuse epistaxis. 相似文献