全文获取类型
收费全文 | 5760篇 |
免费 | 168篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 56篇 |
综合类 | 4篇 |
化学工业 | 1040篇 |
金属工艺 | 71篇 |
机械仪表 | 127篇 |
建筑科学 | 242篇 |
矿业工程 | 16篇 |
能源动力 | 181篇 |
轻工业 | 391篇 |
水利工程 | 54篇 |
石油天然气 | 35篇 |
武器工业 | 1篇 |
无线电 | 508篇 |
一般工业技术 | 912篇 |
冶金工业 | 1516篇 |
原子能技术 | 54篇 |
自动化技术 | 729篇 |
出版年
2021年 | 63篇 |
2020年 | 57篇 |
2019年 | 73篇 |
2018年 | 82篇 |
2017年 | 91篇 |
2016年 | 93篇 |
2015年 | 83篇 |
2014年 | 100篇 |
2013年 | 327篇 |
2012年 | 215篇 |
2011年 | 284篇 |
2010年 | 188篇 |
2009年 | 213篇 |
2008年 | 260篇 |
2007年 | 246篇 |
2006年 | 261篇 |
2005年 | 214篇 |
2004年 | 178篇 |
2003年 | 173篇 |
2002年 | 166篇 |
2001年 | 97篇 |
2000年 | 111篇 |
1999年 | 114篇 |
1998年 | 133篇 |
1997年 | 116篇 |
1996年 | 89篇 |
1995年 | 103篇 |
1994年 | 91篇 |
1993年 | 105篇 |
1992年 | 95篇 |
1991年 | 65篇 |
1990年 | 73篇 |
1989年 | 70篇 |
1988年 | 65篇 |
1987年 | 86篇 |
1986年 | 86篇 |
1985年 | 89篇 |
1984年 | 74篇 |
1983年 | 75篇 |
1982年 | 77篇 |
1981年 | 69篇 |
1980年 | 52篇 |
1979年 | 56篇 |
1978年 | 65篇 |
1977年 | 57篇 |
1976年 | 54篇 |
1975年 | 58篇 |
1974年 | 38篇 |
1973年 | 51篇 |
1972年 | 35篇 |
排序方式: 共有5937条查询结果,搜索用时 31 毫秒
1.
AbstractRecently, a literature has emerged using empirical techniques to study the evolution of international cities over many centuries; however, few studies examine long-run change within cities. Conventional models and concepts are not always appropriate and data issues make long-run neighbourhood analysis particularly problematic. This paper addresses some of these points. First, it discusses why the analysis of long-run urban change is important for modern urban policy and considers the most important concepts. Second, it constructs a novel data set at the micro level, which allows consistent comparisons of London neighbourhoods in 1881 and 2001. Third, the paper models some of the key factors that affected long-run change, including the role of housing. There is evidence that the relative social positions of local urban areas persist over time but, nevertheless, at fine spatial scales, local areas still exhibit change, arising from aggregate population dynamics, from advances in technology, and also from the effects of shocks, such as wars. In general, where small areas are considered, long-run changes are likely to be greater, because individuals are more mobile over short than long distances. Finally, the paper considers the implications for policy. 相似文献
2.
Lai-Ying Leong Teck-Soon Hew Keng-Boon Ooi Alain Yee Loong Chong Voon-Hsien Lee 《Information & Management》2021,58(2):103416
This paper examines what influences trust in mobile social commerce environment. Drawing on trust-based acceptance model (i.e. cognitive and emotional trust) and online review features (i.e. profile photo, linguistic style, and reported experience), we examine how these factors affect trust in mobile social commerce. Hypotheses were tested using survey data. The results of our model showed that there are significant influences of profile photo, reported experience, cognitive, and emotional trust towards trust in ms-commerce. This work contributes to existing literature by examining the roles of previous trust in mobile payments and online reviews on trust in mobile social commerce. 相似文献
3.
Timothy Zurrer Kenneth Wong Jonathan Horlyck Emma C. Lovell Joshua Wright Nicholas M. Bedford Zhaojun Han Kang Liang Jason Scott Rose Amal 《Advanced functional materials》2021,31(9):2007624
The vast chemical and structural tunability of metal–organic frameworks (MOFs) are beginning to be harnessed as functional supports for catalytic nanoparticles spanning a range of applications. However, a lack of straightforward methods for producing nanoparticle-encapsulated MOFs as efficient heterogeneous catalysts limits their usage. Herein, a mixed-metal MOF, NiMg-MOF-74, is utilized as a template to disperse small Ni nanoclusters throughout the parent MOF. By exploiting the difference in Ni O and Mg O coordination bond strength, Ni2+ is selectively reduced to form highly dispersed Ni nanoclusters constrained by the parent MOF pore diameter, while Mg2+ remains coordinated in the framework. By varying the ratio of Ni to Mg in the parent MOF, accessible surface area and crystallinity can be tuned upon thermal treatment, influencing CO2 adsorption capacity and hydrogenation selectivity. The resulting Ni nanoclusters prove to be an active catalyst for CO2 methanation and are examined using extended X-ray absorption fine structure and X-ray photoelectron spectroscopy. By preserving a segment of the Mg2+-containing MOF framework, the composite system retains a portion of its CO2 adsorption capacity while continuing to deliver catalytic activity. The approach is thus critical for designing materials that can bridge the gap between carbon capture and CO2 utilization. 相似文献
4.
The reported point centromeres of Scheffersomyces stipitis are retrotransposon long terminal repeats
Point centromeres, found in some ascomycete yeasts such Saccharomyces cerevisiae, are very different in structure from the centromeres of other eukaryotes. They are tiny and nonrepetitive and contain only two short conserved sequence motifs. Until recently, point centromeres were thought to have a single evolutionary origin, in the budding yeast family Saccharomycetaceae. Most yeasts outside this family have centromeres that are many kilobases in size. Some have centromeres consisting of a large inverted repeat sequence, others have centromeric clusters of retrotransposons, and a third group including Candida albicans has centromeres with no conserved sequence features. It was recently reported that Scheffersomyces stipitis has point centromeres with a strongly conserved 125-bp core sequence, which is unexpected because S. stipitis is only distantly related to the known point-centromere species. We show here that the 125-bp core sequence is actually part of the long terminal repeat (LTR) of the Ty5-like retrotransposon Tps5, which forms a cluster in the centromeric region of each S. stipitis chromosome. Thus, the LTR of a centromere-associated retrotransposon confers centromere-like mitotic stability when cloned into a plasmid. The centromeric regions of S. stipitis contain three types of Tps5 element (Tps5a, Tps5b, and Tps5c) and a noncoding nonautonomous large retrotransposon derivative. 相似文献
5.
This work examines the correlation between the 1H‐NMR T2 relaxation constant and the mechanical properties of aged crosslinked polyolefin cable insulation. T2 experiments on unswollen samples could not differentiate between unaged and highly aged materials; all exhibited 1H T2 constants of approximately 0.5 ms. To accentuate the effects of aging, samples were swollen in various solvents. Unaged samples had T2 values of approximately 15 ms in good solvents. With thermal aging, T2 values decreased as the ultimate tensile elongation decreased. However, the correlation between T2 and elongation differed for samples irradiated with high‐energy radiation and for materials aged above versus below the crystalline melting temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2578–2582, 2003 相似文献
6.
Boon Tiong Tan Siou Teck Chew Mook Seng Leong Ban Leong Ooi 《Microwave Theory and Techniques》2003,51(8):1906-1910
A dual-mode ring bandpass filter with two pairs of capacitors has been designed. The capacitors are used to control the location of the even- and odd-mode frequencies independently, allowing weak coupling for narrow-band filter design with realizable capacitance values. Theoretical expressions have been derived for these frequencies. A 4% bandwidth bandpass filter centered at 1.9 GHz was designed and tested with good agreement between theoretical and measured results. 相似文献
7.
A failed effort to implement new technology is always a failure to understand and adequately manage the change process. IS professionals are now in the change business and must become experts in managing organizational and human change. 相似文献
8.
The authors present two-year statistics on the rainfall attenuation of 21.225 GHz vertically polarized CW microwave signals in Singapore. The CCIR recommendation is found to underestimate the microwave specific attenuation (dB/km) per path average rain rate (mm/h) as well as the accumulated time of attenuation exceeding preset levels. A negative exponential raindrop size distribution based on spherical droplets is constructed from the measured data 相似文献
9.
Wen-Yan Yin Le-Wei Li Tat-Soon Yeo Mook-Seng Leong Pang-Shyan Kooi 《Electromagnetic Compatibility, IEEE Transactions on》2002,44(2):329-337
The direct integral equation is formulated for describing the current on the multiple perfectly conducting strips in cylindrical geometries for an E-polarization plane wave of normal incidence. By using the Galerkin's method, the surface currents on the conducting strips are expanded in the form of a series of Chebyshev polynomials of the first kind, while the unknown expanding coefficients are solved by a set of matrix equations of finite order with a fast convergence rate and a high accuracy. Furthermore, numerical results are presented to demonstrate the variation of the penetrated near-zone field in the presence of one, two, three, four and six cylindrical apertures, and the hybrid effects of both aperture number and aperture angular widths on the penetrated fields are investigated in detail 相似文献
10.