全文获取类型
收费全文 | 37787篇 |
免费 | 317篇 |
国内免费 | 989篇 |
专业分类
电工技术 | 380篇 |
综合类 | 203篇 |
化学工业 | 3904篇 |
金属工艺 | 944篇 |
机械仪表 | 1969篇 |
建筑科学 | 2132篇 |
矿业工程 | 708篇 |
能源动力 | 167篇 |
轻工业 | 8405篇 |
水利工程 | 583篇 |
石油天然气 | 619篇 |
武器工业 | 89篇 |
无线电 | 2101篇 |
一般工业技术 | 13927篇 |
冶金工业 | 531篇 |
原子能技术 | 335篇 |
自动化技术 | 2096篇 |
出版年
2023年 | 52篇 |
2022年 | 85篇 |
2021年 | 116篇 |
2020年 | 61篇 |
2019年 | 63篇 |
2018年 | 71篇 |
2017年 | 55篇 |
2016年 | 74篇 |
2015年 | 108篇 |
2014年 | 185篇 |
2013年 | 196篇 |
2012年 | 4305篇 |
2011年 | 5617篇 |
2010年 | 1107篇 |
2009年 | 523篇 |
2008年 | 3507篇 |
2007年 | 3447篇 |
2006年 | 2814篇 |
2005年 | 2434篇 |
2004年 | 2027篇 |
2003年 | 1729篇 |
2002年 | 1533篇 |
2001年 | 1228篇 |
2000年 | 1243篇 |
1999年 | 741篇 |
1998年 | 432篇 |
1997年 | 431篇 |
1996年 | 374篇 |
1995年 | 378篇 |
1994年 | 336篇 |
1993年 | 236篇 |
1992年 | 281篇 |
1991年 | 288篇 |
1990年 | 307篇 |
1989年 | 311篇 |
1988年 | 206篇 |
1987年 | 243篇 |
1986年 | 236篇 |
1985年 | 297篇 |
1984年 | 266篇 |
1983年 | 213篇 |
1982年 | 201篇 |
1981年 | 166篇 |
1980年 | 116篇 |
1979年 | 107篇 |
1978年 | 70篇 |
1976年 | 33篇 |
1975年 | 36篇 |
1973年 | 32篇 |
1965年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
151.
Pons MN Potier O Pontvianne S Laurent N France X Battaglia P 《Water science and technology》2011,64(3):602-609
In order to characterize the pollution discharged into the Moselle River and some of its tributaries, spectroscopic techniques, namely UV-vis spectroscopy and synchronous fluorescence spectroscopy, have been combined. UV-visible spectra were analysed using the maximum of the second derivative at 225 nm (related to nitrates), the SUVA254 and E2/E3 indices (related to the nature of organic matter). Synchronous fluorescence spectra (delta lambda = 50 nm) presented different shapes depending upon the type of pollution. The pollution results from anthropogenic activities: untreated domestic sewage due to misconnections in a periurban river, effluent from urban WWTPS, agricultural runoff (nitrates) in several streams, discharge from a paper mill (humic-like substances due to wood processing) and from steel mills (PAHs). 相似文献
152.
153.
农业是一项传统的产业,它为全球人口提供粮食,这一点从来没有被怀疑过。随着人类对食物需求量的增长,上游农业的持续发展对河流下游和流域的河口地区构成了威胁。在南亚,沿岸居住的人们依靠河流下游为其提供生活来源,例如农业和水产业。很多时候,河流下游会遭受到河流上游农业活动的影响。下游沿岸地区所遇到的问题包括河流干旱、地下水量枯竭、水污染和泥沙问题、盐碱化和海水入侵、土壤侵蚀和营养物质耗尽,以及滨河湿地系统的动态变化等。对当前农业实践和存在的问题及其对下游的影响进行评估,以便在南亚地区采取以流域为基础的方法进行水资源管理。 相似文献
154.
155.
The operation of machines typically requires attention to instruments that signal the state of the machine. One safeguard against primary instrument malfunction is to provide backup instruments, but this works only if the operators react to malfunction by switching attention to the backups. Little is known about the effect of negative outcomes or feedback on allocation of attention to backup instruments. Four experiments demonstrated that prior practice causes operators of a simulated machine to adapt to instrument malfunction by changing to a suboptimal decision rule rather than by reallocating attention to a different set of instruments. This fallacy appears linked to the operators' failures to notice feedback that they should switch during the simulations and operators' failures to correctly interpret outcome feedback following the simulations. The results raise theoretical questions and warn interface designers not to overrate backup instruments. 相似文献
156.
The purpose of the study was to investigate sex-related differences in foot morphology. In total, 847 subjects were scanned using a 3-D-footscanner. Three different analysis methods were used: (1) comparisons were made for absolute foot measures within 250-270 mm foot length (FL); (2) and for averaged measures (% FL) across all sizes; (3) the feet were then classified using a cluster analysis. Within 250-270 mm FL, male feet were wider and higher (mean differences (MD) 1.3-5.9 mm). No relevant sex-related differences could be found in the comparison of averaged measures (MD 0.3-0.6% FL). Foot types were categorised into voluminous, flat-pointed and slender. Shorter feet were more often voluminous, longer feet were more likely to be narrow and flat. However, the definition of 'short' and 'long' was sex-related; thus, allometry of foot measures was different. For shoe design, measures should be derived for each size and sex separately. Different foot types should be considered to account for the variety in foot shape. Improper footwear can cause foot pain and deformity. Therefore, knowledge of sex-related differences in foot measures is important to assist proper shoe fit in both men and women. The present study supplements the field of knowledge within this context with recommendations for the manufacturing of shoes. 相似文献
157.
Richmond VL Rayson MP Wilkinson DM Carter JM Blacker SD Nevill A Ross JD Moore S 《Ergonomics》2008,51(6):935-946
Since 2002, the Royal Air Force (RAF) has been working towards developing role-related physical tests for use as an operational fitness test (OFT). The purpose of this study was to establish reliability of the OFT (comprising four tests), investigate gym-based tests as predictors of performance and establish performance standards. Fifty-eight RAF personnel performed the OFT on three occasions. A separate cohort carried out fitness and anthropometric tests before performing the OFT, by way of establishing performance predictors. Documented evidence and views of an expert panel were used to determine OFT standards. Reliability ranged from moderate to good for three tests, with one test (Dig) showing poor reliability. The 95% limits of agreement for the prediction models ranged from good to poor (6.7-34.2%). The prediction models were not sufficiently accurate to estimate confidently OFT performance, but could be used as a guide to quantify likely outcome and training needs. 相似文献
158.
Liu S Kang K Tarel JP Cooper DB 《IEEE transactions on pattern analysis and machine intelligence》2008,30(1):131-146
In this paper, the duality in differential form is developed between a 3D primal surface and its dual manifold formed by the surface's tangent planes, i.e., each tangent plane of the primal surface is represented as a four-dimensional vector which constitutes a point on the dual manifold. The iterated dual theorem shows that each tangent plane of the dual manifold corresponds to a point on the original 3D surface, i.e., the dual of the dual goes back to the primal. This theorem can be directly used to reconstruct 3D surface from image edges by estimating the dual manifold from these edges. In this paper we further develop the work in our original conference papers resulting in the robust differential dual operator. We argue that the operator makes good use of the information available in the image data, by using both points of intensity discontinuity and their edge directions; we provide a simple physical interpretation of what the abstract algorithm is actually estimating and why it makes sense in terms of estimation accuracy; our algorithm operates on all edges in the images, including silhouette edges, self occlusion edges, and texture edges, without distinguishing their types (thus resulting in improved accuracy and handling locally concave surface estimation if texture edges are present); the algorithm automatically handles various degeneracies; and the algorithm incorporates new methodologies for implementing the required operations such as appropriately relating edges in pairs of images, evaluating and using the algorithm's sensitivity to noise to determine the accuracy of an estimated 3D point. Experiments with both synthetic and real images demonstrate that the operator is accurate, robust to degeneracies and noise, and general for reconstructing free-form objects from occluding edges and texture edges detected in calibrated images or video sequences. 相似文献
159.
Lefèvre J Baillet S 《IEEE transactions on pattern analysis and machine intelligence》2008,30(6):1081-1092
Dynamic pattern analysis and motion extraction can be efficiently addressed using optical flow techniques. This article presents a generalization of these questions to non-flat surfaces, where optical flow is tackled through the problem of evolution processes on non-Euclidian domains. The classical equations of optical flow in the Euclidian case are transposed to the theoretical framework of differential geometry. We adopt this formulation for the regularized optical flow problem, prove its mathematical well-posedness and combine it with the advection equation. The optical flow and advection problems are dual: a motion field may be retrieved from some scalar evolution using optical flow; conversely, a scalar field may be deduced from a velocity field using advection. These principles are illustrated with qualitative and quantitative evaluations from numerical simulations bridging both approaches. The proof-of-concept is further demonstrated with preliminary results from time-resolved functional brain imaging data, where organized propagations of cortical activation patterns are evidenced using our approach. 相似文献
160.
Favaro P Soatto S Burger M Osher SJ 《IEEE transactions on pattern analysis and machine intelligence》2008,30(3):518-531
Defocus can be modeled as a diffusion process and represented mathematically using the heat equation, where image blur corresponds to the diffusion of heat. This analogy can be extended to non-planar scenes by allowing a space-varying diffusion coefficient. The inverse problem of reconstructing 3-D structure from blurred images corresponds to an "inverse diffusion" that is notoriously ill-posed. We show how to bypass this problem by using the notion of relative blur. Given two images, within each neighborhood, the amount of diffusion necessary to transform the sharper image into the blurrier one depends on the depth of the scene. This can be used to devise a global algorithm to estimate the depth profile of the scene without recovering the deblurred image, using only forward diffusion. 相似文献