全文获取类型
收费全文 | 13913篇 |
免费 | 379篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 193篇 |
综合类 | 12篇 |
化学工业 | 3065篇 |
金属工艺 | 227篇 |
机械仪表 | 289篇 |
建筑科学 | 658篇 |
矿业工程 | 99篇 |
能源动力 | 381篇 |
轻工业 | 982篇 |
水利工程 | 130篇 |
石油天然气 | 162篇 |
武器工业 | 1篇 |
无线电 | 855篇 |
一般工业技术 | 2040篇 |
冶金工业 | 3381篇 |
原子能技术 | 141篇 |
自动化技术 | 1697篇 |
出版年
2022年 | 117篇 |
2021年 | 171篇 |
2020年 | 144篇 |
2019年 | 163篇 |
2018年 | 183篇 |
2017年 | 179篇 |
2016年 | 204篇 |
2015年 | 165篇 |
2014年 | 229篇 |
2013年 | 817篇 |
2012年 | 446篇 |
2011年 | 630篇 |
2010年 | 414篇 |
2009年 | 452篇 |
2008年 | 569篇 |
2007年 | 550篇 |
2006年 | 545篇 |
2005年 | 451篇 |
2004年 | 371篇 |
2003年 | 363篇 |
2002年 | 382篇 |
2001年 | 244篇 |
2000年 | 235篇 |
1999年 | 258篇 |
1998年 | 228篇 |
1997年 | 239篇 |
1996年 | 249篇 |
1995年 | 248篇 |
1994年 | 252篇 |
1993年 | 293篇 |
1992年 | 249篇 |
1991年 | 189篇 |
1990年 | 203篇 |
1989年 | 220篇 |
1988年 | 171篇 |
1987年 | 216篇 |
1986年 | 206篇 |
1985年 | 251篇 |
1984年 | 225篇 |
1983年 | 205篇 |
1982年 | 180篇 |
1981年 | 190篇 |
1980年 | 163篇 |
1979年 | 181篇 |
1978年 | 181篇 |
1977年 | 139篇 |
1976年 | 147篇 |
1975年 | 172篇 |
1974年 | 135篇 |
1973年 | 132篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
31.
Krenz William Robin Michael Barez Shirin Stark Lawrence 《IEEE transactions on bio-medical engineering》1985,(10):817-825
A model of the pathways controlling the size of the human pupil is presented. Computer simulation of this model demonstrates the role played by each of the elements in the pupil pathways. Simulations of the effects of drugs and a few common abnormalities in the system also help to illustrate the workings of the internal processes. Computer models of this type can be used as teaching aids or as tools for testing of hypotheses regarding the system. 相似文献
32.
The technique of analytical pyrolysis has been used to characterize 40 similar mid-rank western Kentucky coals of widely differing ASTM Gieseler plasticity. Certain pyrolysis/g.c. variables were shown to correlate well with both ASTM Gieseler and isothermal plasticity. Highly plastic coals were shown to exhibit certain characteristic peaks in the 450 °C pyrogram which were absent in the pyrogram of the non-plastic coals. Two coals, representing the two extremes in plasticity, were selected for further study. After extraction with solvents such as DMF the characteristic peaks were absent in the 450 °C pyrogram of the extraction residue of the highly plastic coal. These peaks were also shown to decrease with increasing severity of air oxidation of the plastic coal. This technique appears to be a useful tool for the analysis of mid-rank plastic coals and supports the view that the substances contained in the bitumen fraction of these coals are involved in the development of the plastic state. 相似文献
33.
Studies of elemental distributions within discrete coal macerals: Use of secondary ion mass spectrometry and X-ray photoelectron spectroscopy 总被引:3,自引:0,他引:3
N.Stewart Mclntyre Ronald R. Martin William J. Chauvin C.Gordon Winder James R. Brown J.Anthony MacPhee 《Fuel》1985,64(12):1705-1712
Secondary ion mass spectrometry has been used to measure qualitatively the distributions of many trace and minor elements within some well-characterized coal macerals: vitrinite, fusinite and exinite. Complementary information was obtained by using X-ray photoelectron spectroscopy. Within the vitrinite specimens studied, a widely-dispersed largely inorganic aluminosilicate phase was identified, which contained a number of other trace elements. By contrast, within the organic-rich phase of this macerai, titanium was detected in a very even distribution; this suggests that some titanium may be bonded in an organic complex. The fusinite was shown to contain elevated concentrations of calcium, magnesium and fluorine, dispersed over a large portion of the maceral. The high fluorine content could be identified as an organo-fluoro compound using XPS. Exinite was found to contain lower concentrations of most elements, compared to other macerals. The organic composition of this maceral was significantly different from that of surrounding macerals; this could be seen from the enhanced emission of the C2H2-secondary ion and images of this ion thus clearly outlined the position of such macerals. 相似文献
34.
The oxidation of chloro-5-10,15,20-tetramesitylporphyrinotoiron(III) with peroxyacids affords a reactive oxoiron(IV)-porphyrin cation radical species 2. The characterization of 2 and its oxochromium analogs 3, 4 and 5 are reviewed. The nature of reactive oxochromium species derived from chromyl reagents is also reviewed. The oxidation of triphenylphosphine by CrOTPP (11), CrOTTP (13) and CrOTMP (14) is described. Variations in the rate constants indicate that steric factors affect the rate of oxygen atom transfer. Activation parameters for the oxidation of triphenylphosphine by 14 are ΔH≠ = 6.96 kcal/mol and ΔS≠ = −39 eu. The oxidation of t-butylphenylcarbinol (18) by CrOTPP gave predominantly benzaldehyde via carbon—carbon bond cleavage while the chromium(III) porphyrin-catalyzed oxidation of 18 by iodosylbenzene afforded t-butylphenylketone. 相似文献
35.
Presents a strategy for analyzing social interactive behaviors occurring simultaneously in parallel streams. The standard strategy for representing such data has been interval coding. Interval coding converts the behavioral stream into a sequence of codes representing the behaviors observed in equal length intervals. This strategy is problematic because statistics calculated from interval coded data depend on the arbitrary choice of interval length. An alternative strategy is to represent the behavioral stream in a continuous-time format, using both the sequence of behaviors and their durations. A continuous-time model for social interactive data was applied to observations of mutual gaze between a husband and wife. The analysis uncovered different distributions of event durations in the two partners: The wife looked primarily at the husband and responded sensitively to his gaze behavior, whereas the husband looked primarily away, unresponsive to the wife. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
36.
van Baaren Rick B.; Maddux William W.; Chartrand Tanya L.; de Bouter Cris; van Knippenberg Ad 《Canadian Metallurgical Quarterly》2003,84(5):1093
The present studies demonstrated the moderation of self-construal orientation on mimicry. Recent research has indicated that an interdependent self-construal is associated with assimilation of the other to the self whereas an independent self-construal is associated with minimizing the influence of others on the self (H. R. Markus & S. Kitayama, 1991; D. Stapel & W. Koomen, 2001). Therefore, the authors hypothesized that an interdependent self-construal would be associated with more mimicry than an independent self-construal. When self-construal orientations were experimentally primed. as in Studies 1 and 2, independent self-construals produced less nonconscious mimicry than interdependent self-construals. When self-construals were examined as cultural differences with either a chronically dominant independent (Americans) or interdependent (Japanese) construal of the self, these results were replicated. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
37.
William F. Maloney 《Canadian Metallurgical Quarterly》2003,129(2):165-172
The satisfaction that a customer has with the construction product and construction services provided by a contractor has a direct influence on the customer’s willingness to select that contractor for future work. Labor and management working together have the opportunity to influence customer satisfaction. Activities at the contractor/craft worker level, the contractor/local union level, and the contractor association/local union level have the greatest potential to influence customer satisfaction. A precisely defined plan incorporating labor-management activities targeted at specific satisfaction factors will have the greatest likelihood of creating high customer satisfaction. 相似文献
38.
MRI fuzzy segmentation of brain tissue using neighborhood attraction with neural-network optimization. 总被引:11,自引:0,他引:11
Shan Shen William Sandham Malcolm Granat Annette Sterr 《IEEE transactions on information technology in biomedicine》2005,9(3):459-467
Image segmentation is an indispensable process in the visualization of human tissues, particularly during clinical analysis of magnetic resonance (MR) images. Unfortunately, MR images always contain a significant amount of noise caused by operator performance, equipment, and the environment, which can lead to serious inaccuracies with segmentation. A robust segmentation technique based on an extension to the traditional fuzzy c-means (FCM) clustering algorithm is proposed in this paper. A neighborhood attraction, which is dependent on the relative location and features of neighboring pixels, is shown to improve the segmentation performance dramatically. The degree of attraction is optimized by a neural-network model. Simulated and real brain MR images with different noise levels are segmented to demonstrate the superiority of the proposed technique compared to other FCM-based methods. This segmentation method is a key component of an MR image-based classification system for brain tumors, currently being developed. Index Terms-Improved fuzzy c-means clustering (IFCM), magnetic resonance imaging (MRI), neighborhood attraction, segmentation. 相似文献
39.
40.
Presents an obituary for Douglas W. Bray, the inventor of the modern-day assessment center, a method used by thousands of organizations around the world to identify the best people for critical roles and to guide individuals in optimizing their talents. Bray's death in Englewood, New Jersey, on May 9, 2006, ended the extraordinary career of a pioneer in industrial/organizational (I/O) psychology who optimized the interplay of research and application. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献