全文获取类型
收费全文 | 258407篇 |
免费 | 3895篇 |
国内免费 | 1253篇 |
专业分类
电工技术 | 5109篇 |
综合类 | 316篇 |
化学工业 | 38952篇 |
金属工艺 | 11286篇 |
机械仪表 | 7414篇 |
建筑科学 | 6968篇 |
矿业工程 | 572篇 |
能源动力 | 6538篇 |
轻工业 | 26164篇 |
水利工程 | 1941篇 |
石油天然气 | 1357篇 |
武器工业 | 3篇 |
无线电 | 31935篇 |
一般工业技术 | 48860篇 |
冶金工业 | 50490篇 |
原子能技术 | 3967篇 |
自动化技术 | 21683篇 |
出版年
2021年 | 1933篇 |
2020年 | 1388篇 |
2019年 | 1718篇 |
2018年 | 2886篇 |
2017年 | 2825篇 |
2016年 | 3080篇 |
2015年 | 2458篇 |
2014年 | 3825篇 |
2013年 | 12104篇 |
2012年 | 6206篇 |
2011年 | 8692篇 |
2010年 | 7072篇 |
2009年 | 7652篇 |
2008年 | 8359篇 |
2007年 | 8428篇 |
2006年 | 7576篇 |
2005年 | 6933篇 |
2004年 | 6610篇 |
2003年 | 6615篇 |
2002年 | 6611篇 |
2001年 | 6634篇 |
2000年 | 6041篇 |
1999年 | 6592篇 |
1998年 | 16693篇 |
1997年 | 11745篇 |
1996年 | 9089篇 |
1995年 | 6830篇 |
1994年 | 6018篇 |
1993年 | 5819篇 |
1992年 | 4141篇 |
1991年 | 4064篇 |
1990年 | 3643篇 |
1989年 | 3559篇 |
1988年 | 3499篇 |
1987年 | 2967篇 |
1986年 | 2882篇 |
1985年 | 3526篇 |
1984年 | 3180篇 |
1983年 | 2817篇 |
1982年 | 2617篇 |
1981年 | 2661篇 |
1980年 | 2499篇 |
1979年 | 2331篇 |
1978年 | 2300篇 |
1977年 | 2851篇 |
1976年 | 4217篇 |
1975年 | 1954篇 |
1974年 | 1836篇 |
1973年 | 1831篇 |
1972年 | 1480篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Colour is the most widely used attribute in image retrieval and object recognition. A technique known as histogram intersection has been widely studied and is considered to be effective for color‐image indexing. The key issue of this algorithm is the selection of an appropriate color space and optimal quantization of the selected color space. The goal of this article is to measure the model performance in predicting human judgment in similarity measurement for various images, to explore the capability of the model with a wide set of color spaces, and to find the optimal quantization of the selected color spaces. Six color spaces and twelve quantization levels are involved in evaluating the performance of histogram intersection. The categorical judgment and rank order experiments were conducted to measure image similarity. The CIELAB color space was found to perform at least as good as or better than the other color spaces tested, and the ability to predict image similarity increased with the number of bins used in the histograms, for up to 512 bins (8 per channel). With more than 512 bins, further improvement was negligible for the image datasets used in this study. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 265–274, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20122 相似文献
82.
W. L. Siew F. C. H. Oh A. S. H. Ong 《Journal of the American Oil Chemists' Society》1985,62(6):1036-1039
Some of the factors affecting cloud point determination of palm oleins are described. These are the type of container used, method of stirring, rate of stirring and bath temperature. The repeatability and reproducibility standard deviations of the method are determined from collaborative trials. Recommendations for the test are made to reduce the large variations among laboratories. 相似文献
83.
84.
The biological decolorization of two industrial, spent textile reactive dyebaths was investigated using a suspended-growth, halophilic mixed culture fed with glucose. Dyebath I contained mainly Reactive Blue 19 (RB19), an anthraquinone dye, whereas dyebath II contained mainly Reactive Blue 21 (RB21), a phthalocyanine dye. Batch assays under anaerobic conditions with the two neutralized dyebaths resulted in 87 and 37% extent of decolorization for dyebaths I and II, respectively. The rate of glucose utilization and the extent of acetate production were impacted in the presence of each dyebath as compared to the control culture. However, dyebath decolorization occurred despite moderate culture inhibition. Reuse of a biologically renovated RB19-containing dyebath in the dyeing process resulted in reproducible but not identical cotton fabric shades as compared to a standard dyeing (i.e., control) using fresh water. This difference is attributed to a variable degree of RB19 aggregation during the dyeing process and is not related to the efficiency of the biodecolorization process. Further improvement of the redyeing efficiency will lead to the development of an in-plant, closed-loop decolorization system resulting in significant water conservation and minimization of textile pollutants such as salt and dyes. 相似文献
85.
Sure System 2000, a fault-tolerant computer that couples multiprocessors to offer low-priced, high-performance systems that deal effectively with faults and failures, is presented. The architecture is based on the local redundancy technique, ensuring that no hardware or software fault can cause a system crash. Software errors can be fixed, and hardware can be replaced, upgraded, or added dynamically. Existing fault-tolerant computers are briefly reviewed, and the logic hardware system configuration of the Sure System 2000 is described. The multiprocessor and I/O architecture are examined. The SXO Sure System 2000 expandable operating system is described 相似文献
86.
The new Editor in Chief of IEEE Micro introduces himself and the first issue of 2007. He thanks outgoing Editor in Chief Pradip Bose for his outstanding work on Micro during his tenure. He assesses the current state of the microarchitecture field, speculates on the future, and asks readers for their suggestions on topics the magazine should cover in coming issues. 相似文献
87.
A. Alt Dr.‐Ing. H. Mertens U. Arz L. Blessing C. Berger 《Materialwissenschaft und Werkstofftechnik》2007,38(5):402-409
High cycle fatigue of bolted connections Extensive tests regarding the influences on the fatigue of bolt‐nut‐connections of preloading with torsion, of preloading with yielding, of loading with superimposed bending and of the tested lot are processed. These influences are not yet known according to VDI 2230. New testing devices were designed for these tests, which allow a far less expensive operation and may easily be used for bolts of diameters up to M100 and testing frequencies up to 1000 Hz. The validity of fatigue resistance according to VDI 2230 is specified with respect to the test results. The determined influence of the tested lots is unexpectedly high. The manufacturing process of bolts should be improved to minimize this influence. 相似文献
88.
89.
Assessments of sewer performance are usually based on a single computation of CSO (combined sewer overflow) volumes using a time series of rainfall as system loads. A shortcoming of this method is that uncertainties in knowledge of sewer system dimensions are not taken into account. Moreover, sewer models are rarely calibrated. This paper presents the impacts of database errors and model calibration on return periods of calculated CSO volumes. The impact of uncertainties is illustrated with two examples. Variability of calculated CSO volumes is estimated using Monte Carlo simulations. The results show that calculated CSO volumes vary considerably due to database errors, especially uncertain dimensions of the catchment area. Furthermore, event-based calibration of a sewer model does not result in more reliable predictions because the calibrated parameters have low portability. However, it enables removal of database errors harmonising model predictions and 'reality'. 相似文献
90.
Phylogenetic scanning: a computer-assisted algorithm for mapping gene conversions and other recombinational events 总被引:1,自引:0,他引:1
An algorithm, 'phylogenetic scanning', is described for mapping gene conversion events where comparative DNA sequence data are available from different species. In this algorithm, sets of hypothetical phylogenetic trees are constructed that describe possible sequence relationships due to gene conversions in different species lineages; these trees are then evaluated by the principle of parsimony at intervals in the sequence alignment. When used to map gene conversion events that occurred between the pair of gamma-globin genes of higher primates, the algorithm gives results nearly identical to those obtained using a tedious manual approach. Suggestions are also provided for adaptation of this procedure to the analysis of other recombination events. 相似文献