全文获取类型
收费全文 | 586201篇 |
免费 | 8513篇 |
国内免费 | 2070篇 |
专业分类
电工技术 | 10598篇 |
综合类 | 527篇 |
化学工业 | 87399篇 |
金属工艺 | 19595篇 |
机械仪表 | 16609篇 |
建筑科学 | 16284篇 |
矿业工程 | 1275篇 |
能源动力 | 16244篇 |
轻工业 | 62031篇 |
水利工程 | 4656篇 |
石油天然气 | 3384篇 |
武器工业 | 16篇 |
无线电 | 76634篇 |
一般工业技术 | 106305篇 |
冶金工业 | 111541篇 |
原子能技术 | 7684篇 |
自动化技术 | 56002篇 |
出版年
2021年 | 3968篇 |
2020年 | 2855篇 |
2019年 | 3622篇 |
2018年 | 5622篇 |
2017年 | 5708篇 |
2016年 | 6203篇 |
2015年 | 4928篇 |
2014年 | 8248篇 |
2013年 | 27695篇 |
2012年 | 14701篇 |
2011年 | 21223篇 |
2010年 | 16348篇 |
2009年 | 18615篇 |
2008年 | 19828篇 |
2007年 | 20153篇 |
2006年 | 18316篇 |
2005年 | 16864篇 |
2004年 | 16306篇 |
2003年 | 15982篇 |
2002年 | 15253篇 |
2001年 | 15589篇 |
2000年 | 14319篇 |
1999年 | 15325篇 |
1998年 | 36185篇 |
1997年 | 25906篇 |
1996年 | 20005篇 |
1995年 | 15499篇 |
1994年 | 13691篇 |
1993年 | 13314篇 |
1992年 | 9720篇 |
1991年 | 9258篇 |
1990年 | 8747篇 |
1989年 | 8378篇 |
1988年 | 8087篇 |
1987年 | 6708篇 |
1986年 | 6558篇 |
1985年 | 8081篇 |
1984年 | 7473篇 |
1983年 | 6626篇 |
1982年 | 6100篇 |
1981年 | 6164篇 |
1980年 | 5742篇 |
1979年 | 5455篇 |
1978年 | 5063篇 |
1977年 | 6151篇 |
1976年 | 8129篇 |
1975年 | 4267篇 |
1974年 | 4044篇 |
1973年 | 3969篇 |
1972年 | 3121篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Memory reallocation is used to construct a run-time data structure for fast/efficient storage of information during collection and analysis. The data structure presented uses dynamic memory but does not require the use of pointers to link nodes of information together. It allows for simple and efficient access to data via array indexing rather than through the use of lists or tree structures and it provides flexibility for competing storage requirements that are determined dynamically. The data structure is developed in the C programming language and a suite of ANSI standard C subroutines that make up a run-time data structure management system is provided. 相似文献
992.
For discrete systems, the set of all state covariances X which can be assigned to the closed-loop system via a dynamic controller is characterized explicitly. For any assignable state covariance X , the set of all controllers that assign this X to the closed-loop system is parameterized with an arbitrary orthonormal matrix U of proper dimension 相似文献
993.
The authors propose techniques for adaptive nonlinear cancellation of intersymbol interference (ISI) in the electrical signal at the receiver in Gb/s lightwave systems and describe several demonstrations of these techniques. Techniques for adjustable nonlinear cancellations are discussed and demonstrations of these techniques using commercially available integrated circuits (ICs) at data rates as high as 1.7 Gb/s are described. Techniques for automatic adjustment are discussed, and a demonstration of adaptive nonlinear cancellation at 450 Mb/s is described. The authors discuss how these techniques can be integrated onto the detector IC for operations at 2.5 Gb/s and higher data rates. These techniques allow a single IC detector with adaptive nonlinear cancellation to be used in long-haul and undersea lightwave systems to optimize the detector threshold and compensate for the ISI 相似文献
994.
A new 3-D graded TLM model for thin radiating wires is presented. The model differs from previous TLM models because the wire is modelled at the interfaces between cells, rather than through the centre of the node. The connection between the TLM symmetrical condensed-node link lines and the line forms a 'wire interface'. The scattering algorithm for the interface and simulation results are given.<> 相似文献
995.
996.
The author discusses the concept that data sampled beyond the Nyquist frequency is meaningless. A simple signal processing scheme to extend resolution to nearly twice the Nyquist without the problem of alias emerged. It starts by placing one-dimensional signals into a simulated sample-and-hold process in a Mathcad application 相似文献
997.
Based on data obtained in terms of the first International cooperative program on the effects of acidic precipitations on materials (ICP Materials) of the United Nations European Commission on Economics (UN ECE), the relations between the ozone O3 and nitrogen dioxide NO2 concentrations in combination with the sunshine effect (taken into account either as the solar radiation (Rad) or the sunshine duration (Sun)) are considered. Analysis based on monthly and annual averages led to a new equation recommended for predicting ozone levels over rural, urban, and industrial areas of Europe as a function of NO2 concentration and Sun parameter. Using Rad instead of Sun provides similar results, but, for practical usage, the equation involving a more easily available parameter Sun was recommended. The new equation corrects and improves the earlier proposed one, in which the concentration of ozone was given as a function of NO2 concentration solely, and is included in the UN ECE Manual on mapping critical loads / levels and geographical areas where they are exceeded. 相似文献
998.
This two-part paper presents a closed-form procedure for evaluation of estimates of local thermomechanical stress fields in two-phase fibrous composites and laminates. The first part is concerned with a unidirectional elastic laminate subjected to uniform mechanical loads and to uniform changes in temperature. Both phases are assumed to be elastic, with temperature-dependent moduli and expansion coefficients; the solution reflects the influence of thermomechanical interactions. Exact solutions are not possible for any real system, because the local geometry is not known in detail. Instead, estimates of the fields are found from a modified Mori-Tanaka approximation. Examples are presented for two SiC/Ti---Al---Nb composites. Local stresses of interest are found after cooling from fabrication to room temperature. The presence of local yielding, and the influence of coupling terms on the local stress magnitudes are examined. Extension of the results to laminated plates is presented in Part II (Dvorak, G.J., Chen, T. & Teply, J., Composites Science and Technology, 43 (1992) 359–368, this issue). 相似文献
999.
J. M. Criado M. J. Dianez F. Gotor C. Real M. Mundi S. Ramos J. DEL Cerro 《Ferroelectrics Letters Section》1992,14(3):79-84
The Constant Rate Thermal Analysis method has been used under different experimental conditions to obtain barium titanate powder of very small grain size. Both a crystallographic and a dielectric study ham been carried out on samples sintered at different temperatures. It is deduced that the formation of small coherently diffracting domains is improved by the generation of oxygen vacancies and the cubic phase stabilization depends on the coherently diffracting domain size rather than on the particle size. 相似文献
1000.
The interstitial assemblages of the River Rhine were studied in the Rhinau sector (France). The studied area is located in aVegulated channel of the river, controlled by a hydroelectric dam. Twenty stations were sampled in September 1988. Ten litres of interstitial water were pumped at 50 cm depth in each station using the Bou-Rouch technique. Interstitial waters were poorly oxygenated and the hyporheic fauna had three major characteristics: (1) microcrustaceans were dominant, (2) the insects were rare and (3) the stygofauna was absent. The richest stations were well oxygenated and did not correspond to any particular geomorphological features. These findings contrast with the situation observed on other large European rivers (Rhǒne, Danube) where the interstitial assemblages appear to be locally more diversified and rich in stygofauna. 相似文献