全文获取类型
收费全文 | 402903篇 |
免费 | 4186篇 |
国内免费 | 995篇 |
专业分类
电工技术 | 7261篇 |
综合类 | 445篇 |
化学工业 | 59913篇 |
金属工艺 | 18409篇 |
机械仪表 | 13047篇 |
建筑科学 | 8716篇 |
矿业工程 | 2787篇 |
能源动力 | 8711篇 |
轻工业 | 30199篇 |
水利工程 | 5006篇 |
石油天然气 | 11380篇 |
武器工业 | 78篇 |
无线电 | 46108篇 |
一般工业技术 | 82641篇 |
冶金工业 | 70463篇 |
原子能技术 | 11111篇 |
自动化技术 | 31809篇 |
出版年
2021年 | 3255篇 |
2019年 | 3234篇 |
2018年 | 5814篇 |
2017年 | 5986篇 |
2016年 | 6358篇 |
2015年 | 3689篇 |
2014年 | 6430篇 |
2013年 | 16599篇 |
2012年 | 10094篇 |
2011年 | 13390篇 |
2010年 | 10665篇 |
2009年 | 11929篇 |
2008年 | 12712篇 |
2007年 | 12693篇 |
2006年 | 11236篇 |
2005年 | 10303篇 |
2004年 | 9893篇 |
2003年 | 9696篇 |
2002年 | 9292篇 |
2001年 | 9351篇 |
2000年 | 8996篇 |
1999年 | 8974篇 |
1998年 | 20348篇 |
1997年 | 14730篇 |
1996年 | 11425篇 |
1995年 | 8948篇 |
1994年 | 7964篇 |
1993年 | 7965篇 |
1992年 | 6490篇 |
1991年 | 6198篇 |
1990年 | 6140篇 |
1989年 | 5806篇 |
1988年 | 5627篇 |
1987年 | 5093篇 |
1986年 | 5030篇 |
1985年 | 5585篇 |
1984年 | 5283篇 |
1983年 | 4900篇 |
1982年 | 4558篇 |
1981年 | 4835篇 |
1980年 | 4549篇 |
1979年 | 4643篇 |
1978年 | 4603篇 |
1977年 | 5068篇 |
1976年 | 6276篇 |
1975年 | 4261篇 |
1974年 | 4289篇 |
1973年 | 4341篇 |
1972年 | 3722篇 |
1971年 | 3366篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
33.
V. N. Tsygankov V. V. Safonov A. I. Kozlov V. P. Gavrilov 《Inorganic Materials》2003,39(10):1076-1078
The GeO2–NiO system is studied in the stability range of Ni2GeO4 by temperature-dependent resistivity measurements, in combination with x-ray diffraction, differential thermal analysis, and thermogravimetry. The resistivity of the starting mixtures and heat-treated samples is measured in the composition range 55–90 mol % NiO. The effect of air humidity on the resistivity of the samples is examined. 相似文献
34.
The catalytic activities of alumina prepared from an Al alkoxide-amine adduct monomer for the reaction of cyclopentene oxide with piperidine was determined after various pretreatments, including calcination and exposure to moisture. They were compared with the activity of alumina prepared by the conventional hydrolysis method. It was found that the as-prepared sample from the alkoxide-amine monomer preparation was five times more active than a conventional preparation, suggesting that it has a higher density of surface Lewis acid sites. However, its activity was much more severely suppressed by exposure to moisture. 相似文献
35.
A decision support system for interactive decision making - Part II: analysis and output interpretation 总被引:2,自引:0,他引:2
Liping Fang K.W. Hipel D.M. Kilgour Xiaoyong Peng 《IEEE transactions on systems, man and cybernetics. Part C, Applications and reviews》2003,33(1):56-66
For pt.I see ibid., p.42-55 (2003). The development of a comprehensive decision support system, GMCR II, for the systematic study of real-world interactive decision problems is presented. The companion paper (Part I), discusses how GMCR II elicits, stores, and manages conflict models; here (Part II), the focus is on GMCR IIs analysis and output interpretation subsystems. Specifically, this paper describes the powerful and efficient analysis engine contained in GMCR II, its informative output presentation and interpretation facilities, and a number of follow-up analyses. Furthermore, an illustrative case study is used to demonstrate how GMCR II can be conveniently applied in practice. 相似文献
36.
37.
Gas/liquid mass transfer has been investigated using a stirred vessel gas/liquid contactor using non‐Newtonian media and carbon dioxide as absorbent and gas phase, respectively. The volumetric mass transfer coefficients at different operational variables have been determined. Non‐Newtonian media (liquid phase) were prepared as aqueous solutions of sodium carboxymethyl cellulose salt. The influence of the rheological properties, polymer concentration, stirring rate, and gas flow rate on mass transfer was studied for these liquid phases. Kinematic viscosity and density experimental data were used to calculate the average molecular weight corresponding to the polymer employed. The Ostwald model has been used to fit the rheological behavior of aqueous solutions of the polymer employed as absorbent phase. Reasonably good agreement was found between the predictions of the proposed models and the experimental data of mass transfer coefficients. 相似文献
38.
Rankin D.M. Gulliver T.A. Taylor D.P. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(9):2230-2235
This article investigates the asymptotic performance of single parity-check (SPC) product codes (PCs) from a decoding point of view. Specifically, the probability of bit error is bounded before and after the decoding of each dimension, similar to the analysis of "iterated codes" by Elias (1954). It is shown that the asymptotic probability of bit error can be driven to zero as the number of dimensions, and hence the block length, increases at signal-to-noise ratios (SNRs) within 2 dB of capacity over the additive white Gaussian noise (AWGN) channel. 相似文献
39.
High-efficiency LEDs of 1.6–2.4 µm spectral range for medical diagnostics and environment monitoring
N. D. Stoyanov B. E. Zhurtanov A. P. Astakhova A. N. Imenkov Yu. P. Yakovlev 《Semiconductors》2003,37(8):971-984
High efficient LED structures covering the spectral range of 1.6–2.4 μm have been developed on the basis of GaSb and its solid
solutions. The electroluminescent characteristics and their temperature and current dependences have been studied. The radiative
and nonradiative recombination mechanisms and their effect on the quantum efficiency have been investigated. A quantum efficiency
of 40–60% has been obtained in the quasi-steady mode at room temperature. A short-pulse optical power of 170 mW was reached.
__________
Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 8, 2003, pp. 996–1009.
Original Russian Text Copyright ? 2003 by Stoyanov, Zhurtanov, Astakhova, Imenkov, Yakovlev. 相似文献
40.
A fuzzy logic based-method for prognostic decision making in breast and prostate cancers 总被引:1,自引:0,他引:1
Seker H. Odetayo M.O. Petrovic D. Naguib R.N.G. 《IEEE transactions on information technology in biomedicine》2003,7(2):114-122
Accurate and reliable decision making in oncological prognosis can help in the planning of suitable surgery and therapy, and generally, improve patient management through the different stages of the disease. In recent years, several prognostic markers have been used as indicators of disease progression in oncology. However, the rapid increase in the discovery of novel prognostic markers resulting from the development in medical technology, has dictated the need for developing reliable methods for extracting clinically significant markers where complex and nonlinear interactions between these markers naturally exist. The aim of this paper is to investigate the fuzzy k-nearest neighbor (FK-NN) classifier as a fuzzy logic method that provides a certainty degree for prognostic decision and assessment of the markers, and to compare it with: 1) logistic regression as a statistical method and 2) multilayer feedforward backpropagation neural networks an artificial neural-network tool, the latter two techniques having been widely used for oncological prognosis. In order to achieve this aim, breast and prostate cancer data sets are considered as benchmarks for this analysis. The overall results obtained indicate that the FK-NN-based method yields the highest predictive accuracy, and that it has produced a more reliable prognostic marker model than both the statistical and artificial neural-network-based methods. 相似文献