全文获取类型
收费全文 | 434203篇 |
免费 | 7715篇 |
国内免费 | 1501篇 |
专业分类
电工技术 | 8065篇 |
综合类 | 566篇 |
化学工业 | 65702篇 |
金属工艺 | 14901篇 |
机械仪表 | 12399篇 |
建筑科学 | 12269篇 |
矿业工程 | 981篇 |
能源动力 | 11536篇 |
轻工业 | 46844篇 |
水利工程 | 3484篇 |
石油天然气 | 1964篇 |
武器工业 | 21篇 |
无线电 | 56559篇 |
一般工业技术 | 80518篇 |
冶金工业 | 80540篇 |
原子能技术 | 5698篇 |
自动化技术 | 41372篇 |
出版年
2021年 | 3195篇 |
2020年 | 2237篇 |
2019年 | 2786篇 |
2018年 | 4568篇 |
2017年 | 4550篇 |
2016年 | 4878篇 |
2015年 | 4048篇 |
2014年 | 6420篇 |
2013年 | 20701篇 |
2012年 | 11220篇 |
2011年 | 15691篇 |
2010年 | 12147篇 |
2009年 | 13696篇 |
2008年 | 14858篇 |
2007年 | 15160篇 |
2006年 | 13406篇 |
2005年 | 12468篇 |
2004年 | 11943篇 |
2003年 | 11613篇 |
2002年 | 11227篇 |
2001年 | 11376篇 |
2000年 | 10505篇 |
1999年 | 11095篇 |
1998年 | 25723篇 |
1997年 | 18611篇 |
1996年 | 14598篇 |
1995年 | 11404篇 |
1994年 | 10121篇 |
1993年 | 9682篇 |
1992年 | 7247篇 |
1991年 | 6909篇 |
1990年 | 6514篇 |
1989年 | 6226篇 |
1988年 | 5974篇 |
1987年 | 5010篇 |
1986年 | 4929篇 |
1985年 | 6139篇 |
1984年 | 5723篇 |
1983年 | 4954篇 |
1982年 | 4588篇 |
1981年 | 4571篇 |
1980年 | 4348篇 |
1979年 | 4177篇 |
1978年 | 3845篇 |
1977年 | 4722篇 |
1976年 | 6480篇 |
1975年 | 3175篇 |
1974年 | 3074篇 |
1973年 | 2981篇 |
1972年 | 2351篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
R.A. Cunningham N.E. Sanderson W.N.J. Snodgrass D.W. Banes S.D. Hoath J.N. Mo 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1985,234(1):67-80
The design, construction and performance of a modular, two pressure focal plane detector, 550 mm long, 1000 mm deep and with an active height of 60 mm are described. The detector has been operated with ions ranging from 50 MeV 1H to 200 MeV 36S. Typical results achieved are 0.5 mm and 0.3° for the spatial and angular resolutions, and 0.7% and 3% for the total energy and energy loss measurements. A height signal is also provided. 相似文献
992.
Alinur Büyükaksoy 《电信纪事》1985,40(7-8):402-410
An asymptotic solution to the problem of the diffraction of high-frequency waves by the edge of a cylindrically curved surface whose convex and concave faces present soft and hard boundary conditions is obtained. The results permit us to define new diffraction coefficients related to this kind of mixed boundary conditions. When the radius of the curvature becomes infinitely large, the edgediffraction coefficient reduces to this known for the softhard half-plane. 相似文献
993.
The electrochemical faceting of polycrystalline (pc) platinum yielding a (100)-preferred oriented electrode surface was accomplished in HF solutions by applying to the pc platinum electrode a square wave potential perturbation at 1 kHz in the 0.2 to 1.3 V range (vs rhe). SEM patterns of the resulting surfaces were also obtained. For HF concentrations up to 2 M no appreciable influence of the electrolyte concentration on the electrochemical faceting was noticed. Otherwise, the voltammetric response of the (100)-type preferred oriented platinum surface in the H-adatom potential range when compared to previously reported data resulted remarkably sensitive to the electrolyte composition. The discussion of results was based on the non-equilibrium adsorption conditions for anions under the periodic perturbation. 相似文献
994.
Examined whether location errors in tachistoscopic visual probe tasks reflect (1) uncertainty about the actual position of items, (2) inappropriate guesses, encouraged by a requirement to respond, or (3) confusion about the position being tested. 46 undergraduates completed probe tasks in which they provided confidence ratings on each trial and tasks that substituted a color cue for a visual pointer or used a double bar probe. Results suggest that location errors on visual probe tasks reflect confusion about the spatial position of target items. Findings are consistent with data questioning the concept of iconic memory and imply that the bar-probe task cannot be used to study precategorical visual memory. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
995.
A W-band divide-by-3 frequency divider with wide bandwidth and low power dissipation is presented using harmonic injection-locking technique. A cascode FET is employed for a self-oscillating second-harmonic mixer which is injection-locked by third-harmonic input to obtain the division order of three. The fabricated frequency divider using 0.1 /spl mu/m GaAs metamorphic HEMT technology shows superior performance such as large bandwidth of 6.1 GHz around 83.1 GHz (7.3%) under small DC power consumption of 12 mW. 相似文献
996.
O. Gauthier-Lafaye D. Mulin S. Bonnefont X. Checoury J.-M. Lourtioz A. Talneau F. Lozes-Dupuy 《Photonics Technology Letters, IEEE》2005,17(8):1587-1589
Lasing of W1 square lattice-based photonic crystal lasers on the substrate approach is analyzed. A second-order distributed feedback highly monomode behavior is observed. A comprehensive two-dimensional and three-dimensional finite-difference time-domain computation analysis shows that this characteristic arises from the lattice geometry. Single-mode lasers can be obtained using this geometry, opening the way to the realization of monomode laser arrays. 相似文献
997.
J Byrne S Kienzle D Johnson G Duke V Gannon B Selinger J Thomas 《Water science and technology》2006,53(10):327-334
Long-term trends in alpine and prairie snow pack accumulation and melt are affecting streamflow within the Oldman River Basin in southern Alberta, Canada. Unchecked rural and urban development also has contributed to changes in water quality, including enhanced microbial populations and increased waterborne pathogen occurrence. In this study we look at changing environment within the Oldman River Basin and its impact on water quality and quantity. The cumulative effects include a decline in net water supplies, and declining quality resulting in increased risk of disease. Our data indicates that decreases in the rate of flow of water can result in sedimentation of bacterial contaminants within the water column. Water for ecosystems, urban consumption, recreation and distribution through irrigation is often drawn from waterholding facilities such as dams and weirs, and concern must be expressed over the potential for contaminate build-up and disproportionate potential of these structures to pose a risk to human and animal health. With disruption of natural flow rates for water resulting from environmental change such as global warming and/or human intervention, increased attention needs to be paid to use of best management practices to protect source water supplies. 相似文献
998.
999.
Gesellschaft für Informatik 《Informatik-Spektrum》2008,31(6):526-526
Ohne Zusammenfassung 相似文献
1000.
Physically based simulation of human hair is a well studied and well known problem. But the “pure” physically based representation of hair (and other animation elements) is not the only concern of the animators, who want to “control” the creation and animation phases of the content. This paper describes a sketch-based tool, with which a user can both create hair models with different styling parameters and produce animations of these created hair models using physically and key frame-based techniques. The model creation and animation production tasks are all performed with direct manipulation techniques in real-time. 相似文献