全文获取类型
收费全文 | 103320篇 |
免费 | 1768篇 |
国内免费 | 442篇 |
专业分类
电工技术 | 1066篇 |
综合类 | 2340篇 |
化学工业 | 16104篇 |
金属工艺 | 5231篇 |
机械仪表 | 3487篇 |
建筑科学 | 2905篇 |
矿业工程 | 657篇 |
能源动力 | 1619篇 |
轻工业 | 4629篇 |
水利工程 | 1440篇 |
石油天然气 | 549篇 |
无线电 | 10636篇 |
一般工业技术 | 20608篇 |
冶金工业 | 5547篇 |
原子能技术 | 531篇 |
自动化技术 | 28181篇 |
出版年
2023年 | 213篇 |
2022年 | 493篇 |
2021年 | 580篇 |
2020年 | 426篇 |
2019年 | 395篇 |
2018年 | 14837篇 |
2017年 | 13715篇 |
2016年 | 10456篇 |
2015年 | 1088篇 |
2014年 | 936篇 |
2013年 | 1524篇 |
2012年 | 4058篇 |
2011年 | 10445篇 |
2010年 | 9029篇 |
2009年 | 6322篇 |
2008年 | 7617篇 |
2007年 | 8527篇 |
2006年 | 851篇 |
2005年 | 1800篇 |
2004年 | 1666篇 |
2003年 | 1641篇 |
2002年 | 993篇 |
2001年 | 415篇 |
2000年 | 470篇 |
1999年 | 352篇 |
1998年 | 492篇 |
1997年 | 388篇 |
1996年 | 342篇 |
1995年 | 248篇 |
1994年 | 246篇 |
1993年 | 245篇 |
1992年 | 201篇 |
1991年 | 198篇 |
1990年 | 180篇 |
1989年 | 195篇 |
1988年 | 163篇 |
1987年 | 176篇 |
1986年 | 169篇 |
1985年 | 196篇 |
1984年 | 205篇 |
1983年 | 163篇 |
1982年 | 159篇 |
1981年 | 145篇 |
1980年 | 138篇 |
1979年 | 136篇 |
1978年 | 122篇 |
1977年 | 152篇 |
1976年 | 185篇 |
1975年 | 128篇 |
1974年 | 127篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
This paper presents a model of heterogenous diffusion in capillary porous materials during the process of drying. The governing heat and mass transfer equations have been established using the liquid as well as vapor flow. Two models have been presented. Model 1 does not consider the heat conduction while the model 2 has been established by considering the conduction. The developed models and the numerical solutions of the resulting differential equations can take into account the moisture and temperature dependent thermophysical properties of the product. All equations have been established in spherical coordinates but the programme written for the purpose of calculations can be used for other geometries also. Numerical calculations have been performed for gas concrete and tiles using model 1, while model 2 has been used for gas concrete only because of the lack of data for thermophysical properties of the tile. For gas concrete it was seen that conduction has only marginal effect on the drying process and the numerical predictions of the drying process were reasonably accurate. 相似文献
13.
14.
15.
J-M Choe 《欧洲信息系统杂志》2002,11(2):142-158
This study empirically examined the organisational learning effects of the nonfinancial performance information provided by management accounting information systems (MAISs) under advanced manufacturing technology (AMT). In this study, a target costing system and the frequent and quick reporting of information were considered the facilitators of learning. First, we examined the relationships between AMT level and the amount of nonfinancial performance information produced by MAISs. The empirical results showed that there are significant positive relationships between the level of AMT and nonfinancial performance information. With a systems approach, we also proved the impact of the relationships among AMT levels, nonfinancial performance information and learning facilitators on the organisational performance of a firm. The results of our research suggest that under a high level of AMT, for the provision of information to result in an increase of performance through organisational learning, a target costing system must be introduced and a large amount of information should be provided frequently and quickly. The results of this study also showed that although AMT level may be low, fairly well-arranged facilitators and a moderately large amount of information may be necessary for the improvement of performance. In conclusion, effective organisational learning depends on the provision of relevant information as well as efficient learning support mechanisms. 相似文献
16.
George L. Gaines 《Thin solid films》1980,68(1):vii-viii
17.
Yanqiu Shao Jiqing Han Ting Liu Yongzhen Zhao 《International Journal of Speech Technology》2007,10(1):45-55
In real speech, not like lexical words (LWs), prosodic words (PWs) are basic rhythmic units. The naturalness of a Text-to-Speech
(TTS) system is directly influenced by the segmentation of the PWs. Most of the PWs are the combination of several LWs. In
this paper, three Lexical Combination Models are proposed to combine LWs into PWs, including a Directed Acyclic Graph Model,
a Segmentation Model and a Markov Model (MM). To cope with the situation where some long LWs should be segmented into two
or more PWs, a Lexical Split Model (LSM) is applied to the long LWs. Experimental results prove that relatively constant results
with various training data can be obtained from a MM. The Transformation-Based Error Driven Learning (TBED) algorithm, for
its high performance of individual property, is applied in combination with the MM to improve the precision of PW segmentation.
Experiments show that among the three proposed models, the MM combined with TBED and LSM, leads to the best performance, in
which a precision of 93.00% and a recall of 93.23% are achieved. The perception test indicates that by using PWs as the lowest
prosodic units a speech sounds more natural and acceptable than by using LWs.
This paper is supported by NSFC Project (60503071); 973 Natural Basic Research Program of China (2004CB318102); Postdoctor
Science Foundation of P. R. China (20070420275). 相似文献
18.
In this paper we describe, from a theoretical point of view, critical configurations for the projective reconstruction of
a set of points, for a single view, i.e. for calibration of a camera, in the case of projections from ℙk to ℙ2 for k ≥ 4. We give first a general result describing these critical loci in ℙk, which, if irreducible, are algebraic varieties of dimension k−2 and degree 3. If k=4 they can be either a smooth ruled surface or a cone and if k = 5 they can be a smooth three dimensional variety, ruled in planes, or a cone. If k≥ 6, the variety is always a cone, the
vertex of which has dimension at least k − 6. The reducible cases are studied in Appendix A.
These results are then applied to determine explicitly the critical loci for the projections from ℙk which arise from the dynamic scenes in ℙ3 considered in [13].
Marina Bertolini is currently Associate Professor of Geometry at the Department of Mathematics at the Università degli Studi di Milano, Italy.
Her main field of research is Complex Projective Algebraic Geometry, with particular interest for the classification of projective
varieties and for the geometry of Grassmann varieties. On these topics M. Bertolini has published more than twenty reviewed
papers on national and international journals. She has been for some years now interested also in applications of Algebraic
Geometry to Computer Vision problems.
Cristina Turrini is Associate Professor of Geometry at the Department of Mathematics of Università degli Studi di Milano, Italy. Her main
research interest is Complex Projective Algebraic Geometry: subvarieties of Grassmannians, special varieties, automorphisms,
classification. In the last two years she has started to work on applications of Algebraic Geometry to problems of Computer
Vision. She is author or co-author of about thirty reviewed papers. She is also involved in popularization of Mathematics,
and on this subject she is co-editor of some books. 相似文献
19.
It is established that the capillary rise of a liquid has an oscillatory character, in contrast to the commonly accepted opinion that a vertical capillary is filled at a monotonically varying velocity. The value of the tangential shear stress arising in an ascending liquid is evaluated for ethyl alcohol and distilled water. 相似文献
20.
A. M. Kozodaev O. V. Shvedov V. N. Konev B. Yu. Sharkov V. V. Vasil'ev E. B. Volkov N. V. Lazarev A. M. Raskopin G. G. Shimchuk P. V. Bogdanov A. I. Kiryushin V. V. Petrunin E. I. Azhnin E. I. Tyurin I. I. Titaev Yu. P. Severgin A. Yu. Konstantinov 《Atomic Energy》2003,94(1):56-60
The purpose and current construction status, at the Institute of Theoretical and Experimental Physics, of an experimental electronuclear setup, combining a pulsed proton linear accelerator (36 MeV, 0.5 mA) and a subcritical blanket thermal-power assembly 100 kW, are discussed. The main equipment is already available or is being built in industry. The setup can be used to investigate the dynamics of the interaction of a linac–driver and a subcritical reactor and problems concerning the accelerator–driver and the target–blanket assembly. The proton beams and neutron fluxes will be used for applied purposes. In the future it will be possible to increase substantially the current and energy of the proton beam. 相似文献