全文获取类型
收费全文 | 502776篇 |
免费 | 7000篇 |
国内免费 | 1811篇 |
专业分类
电工技术 | 8555篇 |
综合类 | 2660篇 |
化学工业 | 74681篇 |
金属工艺 | 18903篇 |
机械仪表 | 15040篇 |
建筑科学 | 14241篇 |
矿业工程 | 1486篇 |
能源动力 | 12494篇 |
轻工业 | 47965篇 |
水利工程 | 4616篇 |
石油天然气 | 2330篇 |
武器工业 | 14篇 |
无线电 | 64899篇 |
一般工业技术 | 93377篇 |
冶金工业 | 80160篇 |
原子能技术 | 5919篇 |
自动化技术 | 64247篇 |
出版年
2021年 | 2815篇 |
2019年 | 2553篇 |
2018年 | 17834篇 |
2017年 | 16868篇 |
2016年 | 13859篇 |
2015年 | 4116篇 |
2014年 | 6092篇 |
2013年 | 20115篇 |
2012年 | 13472篇 |
2011年 | 23990篇 |
2010年 | 19382篇 |
2009年 | 18436篇 |
2008年 | 20690篇 |
2007年 | 21962篇 |
2006年 | 13307篇 |
2005年 | 13398篇 |
2004年 | 12860篇 |
2003年 | 12614篇 |
2002年 | 11688篇 |
2001年 | 11409篇 |
2000年 | 10615篇 |
1999年 | 11022篇 |
1998年 | 24269篇 |
1997年 | 17815篇 |
1996年 | 14136篇 |
1995年 | 11185篇 |
1994年 | 9994篇 |
1993年 | 9594篇 |
1992年 | 7348篇 |
1991年 | 6959篇 |
1990年 | 6557篇 |
1989年 | 6283篇 |
1988年 | 6001篇 |
1987年 | 5060篇 |
1986年 | 4998篇 |
1985年 | 6185篇 |
1984年 | 5786篇 |
1983年 | 5003篇 |
1982年 | 4645篇 |
1981年 | 4606篇 |
1980年 | 4350篇 |
1979年 | 4231篇 |
1978年 | 3916篇 |
1977年 | 4670篇 |
1976年 | 6220篇 |
1975年 | 3263篇 |
1974年 | 3121篇 |
1973年 | 3001篇 |
1972年 | 2384篇 |
1971年 | 2064篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
111.
Douay M. Xie W.X. Taunay T. Bernage P. Niay P. Cordier P. Poumellec B. Dong L. Bayon J.F. Poignant H. Delevaque E. 《Lightwave Technology, Journal of》1997,15(8):1329-1342
A comprehensive survey of photosensitivity in silica glasses and optical fiber is reviewed. Recent work on understanding the mechanisms contributing to germanium or aluminum doped fiber photosensitivity is discussed within the framework of photoelastic densification models 相似文献
112.
Watanabe H. Komori J. Higashitani K. Sekine M. Koyama H. 《Semiconductor Manufacturing, IEEE Transactions on》1997,10(2):228-232
A novel monitoring method for plasma-charging damage is proposed. This method performs a quick and accurate evaluation using antenna PMOSFET. It was found that not only hot-carrier (HC) lifetime but transistor parameters such as initial gate current and substrate current were changed according to the degree of plasma-charging damage. However, the present work suggests that monitoring the shift of drain current after a few seconds of HC stress is a more accurate method to indicate plasma-charging damage. The monitoring method using the present test structure is demonstrated to be useful for realizing highly reliable devices 相似文献
113.
A simple phenomenological model for giant magnetoresistance (GMR) is employed for current and field parallel (CIP) to the magnetic multilayer planes in ordinary and discontinuous multilayer films. To our knowledge, it is the first model to include hysteresis in the field (H) dependence of the GMR. The computed GMR versus H curves qualitatively reproduce the GMR hysteresis seen experimentally. In particular, two GMR peaks are found to be symmetrically placed about H=0, and the GMR hysteresis curve itself is found to have an inverted butterfly shape. Also seen in the computed results is the general increase in GMR magnitude found for annealed discontinuous multilayer films. Various parameter variations are examined in the computed results. While the model reproduces GMR hysteresis quite well and the general increase in GMR for discontinuous multilayer films, it does not, in its present form, account for the oscillations seen in the GMR when the nonmagnetic layer thicknesses are varied, which is expected as a strictly quantum mechanical result 相似文献
114.
The water sorption behaviour of several cross-linked gelatin-based systems were investigated and compared. The systems were
gelatin, gelatin/ethyleneglycol, gelatin/polyoxypropylenediamine, and gelatin/polyethylene oxide. For all the systems, an
increased water gain was obtained by raising the concentration of the second component, while the swelling was reduced by
an increase of the cross-linking density.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
115.
J Havick 《The Journal of communication》1997,47(2):97-111
This study employed two perspectives to investigate media attention given women congressional candidates. The first perspective is that media attention may be explained by typical and normal media processes, such as focusing on incumbents. The second perspective considers a partisan explanation in which media attention is weighted more to Democratic candidates than Republican candidates. This study employs two established sources, Vanderbilt's Television News Index and Abstract and Information Access's National Newspaper Index , to examine the national media attention of Democratic and Republican women congressional candidates in 1990 and 1992. The investigation determined that media attention is related to whether the candidates are running for the Senate or House, incumbency, and state population. The results also reveal that party is a statistically significant factor associated with media attention. The investigation also determined that ethnic candidates tend to receive slightly less attention from the print media than nonethnic candidates. 相似文献
116.
Wavelength selection for low-saturation pulse oximetry 总被引:1,自引:0,他引:1
Mannheimer P.D. Cascini J.R. Fein M.E. Nierlich S.L. 《IEEE transactions on bio-medical engineering》1997,44(3):148-158
Conventional pulse oximeters are accurate at high oxygen saturation under a variety of physiological conditions but show worsening accuracy at lower saturation (below 70%). Numerical modeling suggests that sensors fabricated with 735 and 890 nm emitters should read more accurately at low saturation under a variety of conditions than sensors made with conventionally used 660 and 900 nm band emitters. Recent animal testing confirms this expectation. It is postulated that the most repeatable and stable accuracy of the pulse oximeter occurs when the fractional change in photon path lengths due to perturbations in the tissue (relative to the conditions present during system calibration) is equivalent at the two wavelengths. Additionally, the penetration depth (and/or breadth) of the probing light needs to be well matched at the two wavelengths in order to minimize the effects of tissue heterogeneity. At high saturation these conditions are optimally met with 660 and 900 nm band emitters, while at low saturation 735 and 890 nm provide better performance 相似文献
117.
The sudden onset of hypertension mandates investigation for secondary causes. We report the case of a young man with a very rare systemic fungal disease that included massive unilateral perirenal adenopathy. Treatment was associated with the abrupt onset of severe hypertension. Imaging studies suggested progressive constriction of one kidney with treatment, presumably as a result of healing adenopathy. We suggest that this case is a new example of hypertension secondary to constrictive perinephritis (Page kidney). 相似文献
118.
119.
Nitrous oxide (N2O) effects were evaluated, as a behavioural model of inert gas narcosis, in rats performing a vigilance task in which they were required to respond to a slight luminous increment of the house-light. A dose-related decrease of correct responses was produced by the tested range of concentrations of N2O (from 30 to 70% N2O), with a parallel increase of anticipatory responses up to 60% N2O and a dramatic increase of omissions at 70% N2O. The influence of preparatory period duration on hits delays suggested a 'conditional probability effect' conserved under N2O. Pretreatment of animals with flumazenil (a central benzodiazepine receptor antagonist) did not improve performance under 40% N2O. Naltrexone, an opiate receptor antagonist, however, increased the N2O-induced deficits. These results suggest that benzodiazepine receptors are not involved in N2O-induced impairments in this attentional task, but opiate mechanisms may be implicated. 相似文献
120.
An automatic tuning algorithm for decentralized PID control in multiple-input multiple-output (MIMO) plants is presented. This algorithm generalizes the authors' recent auto-tuner for two-input two-output systems to any number of inputs and outputs. The algorithm consists of two stages. In the first, the desired critical point, which consists of the critical gains of all the loops and a critical frequency, is identified. The auto-tuner identifies the desired critical point with almost no a priori information about the process. During the identification phase all controllers are replaced by relays, thus generating limit cycles with the same period in all loops. It is shown that each limit cycle corresponds to a single critical point of the process. By varying the relays parameters different points can be determined. The auto-tuner contains a procedure which converges rapidly to the desired critical point while maintaining the amplitudes of the process variables as well as of the manipulated variables within prespecified ranges. In the second stage, the data of the desired critical point is used to tune the PID controllers by the Ziegler-Nichols rules or their modifications. This paper focuses on the first stage. The steady-state process gains, which are required for the appropriate choice of the desired critical point, are determined by the auto-tuner in closed-loop fashion simultaneously with the identification of the critical point. The identification of the process gains is achieved at no extra plant time. Based upon a large number of simulated cases, the proposed auto-tuner seems to be efficient and robust. The paper discusses the underlying principles of the auto-tuner and its properties and capabilities are demonstrated via examples. 相似文献