全文获取类型
收费全文 | 1919篇 |
免费 | 43篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 3篇 |
化学工业 | 317篇 |
金属工艺 | 35篇 |
机械仪表 | 20篇 |
建筑科学 | 110篇 |
矿业工程 | 13篇 |
能源动力 | 29篇 |
轻工业 | 279篇 |
水利工程 | 24篇 |
石油天然气 | 4篇 |
无线电 | 73篇 |
一般工业技术 | 184篇 |
冶金工业 | 677篇 |
原子能技术 | 4篇 |
自动化技术 | 195篇 |
出版年
2023年 | 13篇 |
2022年 | 22篇 |
2021年 | 32篇 |
2020年 | 23篇 |
2019年 | 31篇 |
2018年 | 29篇 |
2017年 | 32篇 |
2016年 | 45篇 |
2015年 | 25篇 |
2014年 | 27篇 |
2013年 | 118篇 |
2012年 | 67篇 |
2011年 | 96篇 |
2010年 | 77篇 |
2009年 | 55篇 |
2008年 | 71篇 |
2007年 | 70篇 |
2006年 | 81篇 |
2005年 | 64篇 |
2004年 | 66篇 |
2003年 | 64篇 |
2002年 | 53篇 |
2001年 | 38篇 |
2000年 | 42篇 |
1999年 | 47篇 |
1998年 | 37篇 |
1997年 | 47篇 |
1996年 | 37篇 |
1995年 | 39篇 |
1994年 | 35篇 |
1993年 | 41篇 |
1992年 | 34篇 |
1991年 | 17篇 |
1990年 | 33篇 |
1989年 | 24篇 |
1988年 | 22篇 |
1987年 | 24篇 |
1986年 | 25篇 |
1985年 | 23篇 |
1984年 | 26篇 |
1983年 | 21篇 |
1982年 | 19篇 |
1981年 | 15篇 |
1980年 | 16篇 |
1978年 | 11篇 |
1977年 | 14篇 |
1976年 | 15篇 |
1975年 | 17篇 |
1974年 | 9篇 |
1973年 | 9篇 |
排序方式: 共有1967条查询结果,搜索用时 0 毫秒
1.
Vivien Walsh Robin Roy Margaret Bruce Stephen Potter 《Creativity & Innovation Management》1993,2(2):78-86
A series of studies of top European and other firms has revealed patterns of design management associated with commercial success. Firms that invest resources and professional expertise in product and industrial design in traditional and new industries have been commercially more successful than firms that pay less attention to these aspects of design. As an industry matures there is a shift in emphasis from design associated with technological innovation, to designs supporting technical improvements, and then to supporting user needs, fashion and product variants. These issues are illustrated through the history of the evolution of the bicycle. 相似文献
2.
Autologous or glutaraldehyde treated bovine pericardial valved patch was utilized for widening of the right ventricular outflow tract in 20 patients with tetralogy of Fallot (autologous pericardium group in 10 patients and bovine pericardium group in 10). Pericardial valve function of the both materials was evaluated by postoperative cardiac catheterization performed 1 year after the operation. There were no significant differences in pulmonary arterial and right ventricular pressures, and right ventricular ejection fraction and end-diastolic volume between the 2 groups. Pulmonary angiogram in the autologous pericardium group patients demonstrated the pulmonary regurgitation (PR) of grade 1 in 5 patients, grade 2 in 4 and grade 3 in 1. On the other hand, 1, 3 and 6 patients in the bovine pericardium group demonstrated no-PR, grade 1 PR and grade 2 PR, respectively. It was concluded that there were no significant differences between autologous and glutaraldehyde treated bovine pericardium as a material of valved patch for widening of the right ventricular outflow tract of tetralogy of Fallot. 相似文献
3.
A Saccharomyces cerevisiae sequence cloned by serendipity was found to encode a protein that is a new member of the Ypt/Rab monomeric G-protein family. This sequence shows high homology to the yeast genes SEC4 and YPT1 and, like SEC4 and YPT1, is essential for viability. The sequence was localized to chromosome V based upon hybridization to pulse-field gel-separated yeast chromosomes. The sequence has been deposited in the GenBank data library under Accession Number L17070. 相似文献
4.
Ten areas of health knowledge were investigated in 2 studies, 1 of college students (N=169) and 1 of adults from the community (ages 19-70; N=176). Measures assessed knowledge of aging, orthopedic/ dermatological concerns, common illnesses, childhood/early life, serious illnesses, mental health, nutrition, reproduction, safety, and treatment of illness/disease. Significant gender differences favoring women were found for most areas of health knowledge, especially reproduction and early life. Results showed that cognitive ability accounted for the most variance in health knowledge with nonability (personality and interest traits) and demographic variables accounting for smaller but significant amounts of variance across most knowledge domains. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
5.
The role of environmental context in mapping invasive plants with hyperspectral image data 总被引:1,自引:0,他引:1
Lepidium latifolium (perennial pepperweed) is a noxious Eurasian weed invading riparian and wetland areas of the western US. Effective management of Lepidium requires detailed, accurate maps of its distribution, as may be provided by remote sensing, to contain existing infestations and eradicate incipient populations. We mapped Lepidium with 3 m spatial resolution, 128-band HyMap image data in three sites of California's San Francisco Bay/Sacramento–San Joaquin Delta Estuary (Rush Ranch in Suisun Marsh and the Greater Jepson Prairie Ecosystem and the Cosumnes River Preserve in the Delta). These sites are markedly different in terms of hydrology, salinity, species composition, and structural and landscape diversity. Aggregated classification and regression tree models (CART), incorporating the results of mixture tuned matched filter (MTMF) analyses and spectral physiological indexes, were used to map Lepidium at the three sites. This approach was sufficiently flexible and robust to detect Lepidium with similar accuracies (~ 90%) at both Rush Ranch and Jepson Prairie, but was unsuccessful at Cosumnes River Preserve. Comparisons of the behavior of the MTMFs and the CARTs between sites reveal the importance of environmental context in species mapping. Rush Ranch presents the simplest conditions for mapping Lepidium: it is the wettest and least diverse site and Lepidium is spectrally distinct from co-occurring species. At Jepson Prairie, several co-occurring species closely resemble Lepidium spectrally. Nevertheless, hyperspectral data provide sufficient spectral detail to resolve Lepidium even at this challenging site, which is facilitated by phenological separation from the matrix of annual grasses. At Cosumnes River Preserve, however, Lepidium is neither spectrally nor phenologically distinct, and consequently could not be mapped successfully. Evidence suggests that the success of a remote sensing analysis declines as site complexity increases (species, structural, and landscape diversity; spectral variability; etc.), although this relationship is complex, indirect, and may be phenology-dependent. 相似文献
6.
7.
Karen A. Lee Margaret A. Frerking 《Journal of Infrared, Millimeter and Terahertz Waves》1989,10(7):789-802
A quasi-optical reflection cavity intended to be used as the resonant load of a submillimeter wavelength oscillator has been designed, constructed, and tested. The resonator consists of three elements in cascade: a high Q, high finesse folded Fabry-Perot resonator, a lower Q, low finesse Fabry-Perot resonator, and a Littrow mounted diffraction grating. The resonator exhibits a Q of 6600 and 2.5 dB of loss at 63 GHz. The design can be scaled to 1 THz, where waveguide structures become impractical, to serve as the resonator for high frequency quantum well resonant tunneling device oscillators. 相似文献
8.
Mobil Zeolite Catalysts for Monomers 总被引:1,自引:0,他引:1
It has been about 20 years since Plank, Rosinski, and Hawthorne reported their spectacular results with metal-modified zeolite cracking catalysts for more efficient production of gasoline [1]. This discovery has saved an estimated 200 million barrels of crude oil each year in the United States alone [2]. In 1972, a patent by Argauer and Landolt described the preparation of a member of a generation of new synthetic zeolites, called ZSM- 5. It was unique because of its high silica/alumina ratio and greatly reduced coking rates for reactions with hydrocarbons by comparison with known low silica zeolites [3]. This material was an early member of a series of over 50 synthetic zeolitic substances prepared in Mobil laboratories. 相似文献
9.
During germination of seeds of the gymnosperm,Pinus pinea, radioactivity from [2-14C]-mevalonate proceeded principally through the anaerobic reactions leading to squalene in the first 24 hr in both the haploid
endosperm and the diploid embryo, and only with succeeding time (3–9 days) in both cases was label transferred to sterols
in oxygen-requiring steps. The rates of turnover must be real and independent in the two tissues, since no consequential interchange
of labelled lipids occurred between the endosperm and the embryo. Similar delayed conversion of squalene to sterols has been
observed previously during germination of seeds of the angiosperm,Pisum sativum. 相似文献
10.
Friedman Richard; Sobel David; Myers Patricia; Caudill Margaret; Benson Herbert 《Canadian Metallurgical Quarterly》1995,14(6):509
The use of medical services is a function of several interacting psychological and social variables as well as a function of physical malfunction. The clinical significance of addressing patients' psychosocial issues has only occasionally been considered. However, the shift in health care economics toward health care maintenance is responsible for the increased interest in interventions in the domain of behavioral medicine and health psychology. Evidence is reviewed for 6 mechanistic pathways by which behavioral interventions can maximize clinical care and result in significant economic benefits. The rationale for further integration of behavioral and biomedicine interventions is also reviewed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献