全文获取类型
收费全文 | 7641篇 |
免费 | 148篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 75篇 |
综合类 | 4篇 |
化学工业 | 1109篇 |
金属工艺 | 118篇 |
机械仪表 | 210篇 |
建筑科学 | 246篇 |
矿业工程 | 36篇 |
能源动力 | 194篇 |
轻工业 | 529篇 |
水利工程 | 50篇 |
石油天然气 | 14篇 |
武器工业 | 2篇 |
无线电 | 654篇 |
一般工业技术 | 1217篇 |
冶金工业 | 2562篇 |
原子能技术 | 119篇 |
自动化技术 | 657篇 |
出版年
2021年 | 66篇 |
2020年 | 52篇 |
2019年 | 61篇 |
2018年 | 66篇 |
2017年 | 74篇 |
2016年 | 78篇 |
2015年 | 67篇 |
2014年 | 110篇 |
2013年 | 256篇 |
2012年 | 172篇 |
2011年 | 272篇 |
2010年 | 201篇 |
2009年 | 199篇 |
2008年 | 224篇 |
2007年 | 227篇 |
2006年 | 220篇 |
2005年 | 157篇 |
2004年 | 168篇 |
2003年 | 157篇 |
2002年 | 145篇 |
2001年 | 144篇 |
2000年 | 135篇 |
1999年 | 177篇 |
1998年 | 732篇 |
1997年 | 403篇 |
1996年 | 339篇 |
1995年 | 199篇 |
1994年 | 189篇 |
1993年 | 217篇 |
1992年 | 114篇 |
1991年 | 112篇 |
1990年 | 107篇 |
1989年 | 112篇 |
1988年 | 88篇 |
1987年 | 95篇 |
1986年 | 101篇 |
1985年 | 103篇 |
1984年 | 104篇 |
1983年 | 85篇 |
1982年 | 82篇 |
1981年 | 114篇 |
1980年 | 101篇 |
1979年 | 93篇 |
1978年 | 82篇 |
1977年 | 110篇 |
1976年 | 183篇 |
1975年 | 77篇 |
1974年 | 47篇 |
1973年 | 68篇 |
1972年 | 46篇 |
排序方式: 共有7796条查询结果,搜索用时 689 毫秒
991.
An Approach to Handling Incomplete Information in Databases 总被引:1,自引:0,他引:1
992.
We have studied the characteristics of the stimulation of adenyl cyclase (AC) activity in human thyroid plasma membranes by thyroid-stimulating hormone (TSH) and by immunoglobulin G (IgG) from the sera of patients with Graves' disease. AC activity was measured as adenosine 3',5'-cyclic monophosphate (cAMP) generated by membranes in a 10 minute incubation. IgG from two patients with Graves' disease possessed particularly potent human thyroid AC-stimulating activity; the dose-response curves with these IgGs were essentially parallel to those obtained with TSH. As little as 30 mug of the IgG of one patient with Graves' disease or 8 muU of TSH caused significant AC stimulation. A Lineweaver-Burk plot of the data suggested similarity in the site of action of both TSH and human thyroid adenyl cyclase stimulator (HTACS) in Graves' IgG. Submaximal doses of HTACS and TSH had additive effects on AC stimulation, but a large dose of a Graves' IgG with potent AC stimulating activity did not enhance AC stimulation by a maximal dose of TSH. The effect of HTACS on AC was slower in onset and longer in duration than an equipotent dose of TSH. HTACS was detectable in IgGs of 9 of 15 untreated hyperthyroid Graves' disease patients; its concentration, however, did not correlate significantly with tests of thyroid function, nor with long-acting thyroid stimulator (LATS) activity. In another 11 treated patients with Graves' disease, selected for the presence of LATS, HTACS and LATS were significantly correlated. We observed no inhibition of LATS activity in a Graves' IgG chosen for such testing because of its high titer of HTACS and no detectable LATS. However, an inhibitor of HTACS was detected in 2 of 4 IgGs; one of these two IgGs also inhibited AC stimulation by TSH. Conclusions: 1) Some Graves' disease IgGs contain a human thyroid AC stimulator (HTACS), probably different from LATS. 2) HTACS may act via a common pathway with TSH; it differs from TSH, however, in having a slower onset and a greater effect during more prolonged incubation with plasma membranes. 3) There is also an inhibitor of HTACS activity in some Graves' disease IgGs. 相似文献
993.
J.R. Williams 《Solar Energy》1984,33(2):231-236
Thermodynamic and physical property data equations are presented for the NH3?LiNO3 and NH3?NaSCN absorption refrigeration systems. These equations are presented in a form readily adaptable to a computer program for use by other investigators when thermodynamic and economic cycle calculations for NH3?LiNO3 and NH3?NaSCN absorption systems are to be performed. 相似文献
994.
BA Williams 《Canadian Metallurgical Quarterly》1992,58(2):287-302
Procedures used to study anticipatory contrast are conceptually similar to those used to study autoshaping, in that two target stimuli signal either higher or lower rates of reinforcement in the following components of the schedule. Despite this signal contingency, anticipatory contrast entails response rates that are higher to the target stimulus followed by the lower rate of reinforcement. To determine the relation between such effects and autoshaping, different variations of the procedure were used in which the signal contingency was presented in the absence of reinforcement in the target components themselves and in which the reinforcement schedules in the different following components were signaled by the same stimulus. Autoshaping effects of this signal contingency were demonstrated when no reinforcement was available during the target-component signals themselves. Intermediate patterns of behavior occurred when reinforcement was available during the target-component signals and when their different following schedules were correlated with the same stimulus. Attempts to isolate these signal and contrast effects functionally by using the signal-key procedure were unsuccessful. The results demonstrate that Pavlovian stimulus contingencies are in competition with the dynamics of anticipatory contrast, thus reducing its occurrence under some circumstances. 相似文献
995.
On-Line Unsupervised Outlier Detection Using Finite Mixtures with Discounting Learning Algorithms 总被引:3,自引:0,他引:3
Kenji Yamanishi Jun-ichi Takeuchi Graham Williams Peter Milne 《Data mining and knowledge discovery》2004,8(3):275-300
Outlier detection is a fundamental issue in data mining, specifically in fraud detection, network intrusion detection, network monitoring, etc. SmartSifter is an outlier detection engine addressing this problem from the viewpoint of statistical learning theory. This paper provides a theoretical basis for SmartSifter and empirically demonstrates its effectiveness. SmartSifter detects outliers in an on-line process through the on-line unsupervised learning of a probabilistic model (using a finite mixture model) of the information source. Each time a datum is input SmartSifter employs an on-line discounting learning algorithm to learn the probabilistic model. A score is given to the datum based on the learned model with a high score indicating a high possibility of being a statistical outlier. The novel features of SmartSifter are: (1) it is adaptive to non-stationary sources of data; (2) a score has a clear statistical/information-theoretic meaning; (3) it is computationally inexpensive; and (4) it can handle both categorical and continuous variables. An experimental application to network intrusion detection shows that SmartSifter was able to identify data with high scores that corresponded to attacks, with low computational costs. Further experimental application has identified a number of meaningful rare cases in actual health insurance pathology data from Australia's Health Insurance Commission. 相似文献
996.
A crucial parameter in the design of compact dielectric waveguide integrated circuits is the minimum bend radius below which radiation losses become prohibitive. It is shown that, for waveguides with a relative permittivity of 10, values of bend radii down to four guide wavelengths are acceptable. 相似文献
997.
998.
A key-exchange system based on imaginary quadratic fields 总被引:2,自引:0,他引:2
We describe another key-exchange system which, while based on the general idea of the well-known scheme of Diffie and Hellman,
seems to be more secure than that technique. The new system is based on the arithmetic of an imaginary quadratic field, and
makes use, specifically, of the properties of the class group of such a field. 相似文献
999.
K. B. Reuter D. B. Williams J. I. Goldstein 《Metallurgical and Materials Transactions A》1989,20(4):711-718
The disorder-order transformation was generated in a range of Fe−Ni alloys using 1 MeV electrons in a high voltage electron
microscope. The experimental factors that influence the occurrence of the transformation were determined, and the critical
disordering temperature,T
c, was determined as a function of composition. It was demonstrated that the irradiation enhanced the ordering reaction kinetics.
A metastable, ordered phase transformation was not induced. From the results, it is possible to deduce new information about
the Fe−Ni phase diagram below 350°C. 相似文献
1000.
Stutius W. Gavrilovic P. Williams J.E. Meehan K. Zarrabi J.H. 《Electronics letters》1988,24(24):1493-1494
Separate confinement single-quantum-well lasers with 100-120 Å-thick strained Ga1-xInxAs/GaAs active layers have been grown on (100) GaAs substrates by metalorganic chemical vapour deposition. Ten-stripe proton-implanted arrays with 90 μm-wide aperture and 250 μm cavity length emit 200 mW CW optical power at wavelengths 0.87⩽λ⩽0.95 μm. Lifetest data on an uncoated device emitting 90 mW/facet at 50°C and λ=0.95 μm suggest a mean-time-to-failure in excess of 2500 h at room temperature. The performance of lasers with strained Ga1-xInxAs quantum wells is comparable to that of unstrained AlxGa1-xAs/GaAs quantum-well lasers without facet coating 相似文献