全文获取类型
收费全文 | 520篇 |
免费 | 10篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 3篇 |
综合类 | 2篇 |
化学工业 | 43篇 |
金属工艺 | 10篇 |
机械仪表 | 15篇 |
建筑科学 | 9篇 |
能源动力 | 4篇 |
轻工业 | 31篇 |
水利工程 | 2篇 |
石油天然气 | 1篇 |
武器工业 | 1篇 |
无线电 | 28篇 |
一般工业技术 | 60篇 |
冶金工业 | 304篇 |
原子能技术 | 4篇 |
自动化技术 | 19篇 |
出版年
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 7篇 |
2017年 | 7篇 |
2016年 | 7篇 |
2015年 | 4篇 |
2014年 | 11篇 |
2013年 | 22篇 |
2012年 | 5篇 |
2011年 | 6篇 |
2010年 | 7篇 |
2009年 | 10篇 |
2008年 | 14篇 |
2007年 | 15篇 |
2006年 | 6篇 |
2005年 | 5篇 |
2004年 | 7篇 |
2003年 | 9篇 |
2002年 | 4篇 |
2001年 | 3篇 |
2000年 | 6篇 |
1999年 | 20篇 |
1998年 | 85篇 |
1997年 | 47篇 |
1996年 | 33篇 |
1995年 | 26篇 |
1994年 | 22篇 |
1993年 | 20篇 |
1992年 | 9篇 |
1991年 | 8篇 |
1990年 | 10篇 |
1989年 | 5篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1978年 | 3篇 |
1977年 | 9篇 |
1976年 | 17篇 |
1969年 | 1篇 |
1966年 | 1篇 |
1956年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有536条查询结果,搜索用时 15 毫秒
1.
J.P.R. Lacey S.J. Madden M.A. Summerfield 《Photonics Technology Letters, IEEE》1997,9(10):1355-1357
Multichannel wavelength converters may be important components in the cross-connects in future wavelength-division multiplexed (WDM) transport networks. We demonstrate a multichannel, polarization-insensitive, optically transparent wavelength converter, based on four-wave mixing in two semiconductor optical amplifiers in a polarization-diversity arrangement. Bit-error-rate (BER) measurements with four input 2.5-Gb/s WDM channels, spaced by 2 nm, show penalties for wavelength conversion less than 2.6 dB at 10/sup -9/ BER. Changes in the state of polarization of the input signals cause the output power to change by less than 1.2 dB, and the corresponding power penalties change by less than 0.9 dB. 相似文献
2.
DL Lacey JM Erdmann SL Teitelbaum HL Tan J Ohara A Shioi 《Canadian Metallurgical Quarterly》1995,136(6):2367-2376
Interleukin 4 (IL-4) is an immune cytokine that inhibits bone resorption in mice and suppresses osteoclastic cell formation in vitro through an undefined mechanism. In this report, we have established the cellular identity of the IL-4 target cell using a variety of bone marrow/stromal cell coculture methods. Initially, we found that the majority of IL-4's inhibition of osteoclastic cell formation was due to its effect on bone marrow cells, not stromal cells. Consequently, bone marrow macrophages were used as osteoclastic cell progenitors after they had been transiently exposed to IL-4 (48 h), before the addition of stromal cells, 1,25-dihydroxyvitamin D3, and dexamethasone. In this circumstance, IL-4 impaired subsequent osteoclastic cell formation, suggesting that the macrophage may be potentially targeted by many factors known to influence osteoclast formation. Consequently, we discovered that interferon-gamma (IFN gamma), prostaglandin E (PGE), and cell-permeant cAMP analogs also impacted osteoclastic cell formation when used to selectively treat bone marrow macrophages. IFN gamma suppressed osteoclastic cell formation, whereas PGE and cAMP analog treatment led to the formation of significantly enlarged osteoclastic cells. Importantly, PGE antagonized the inhibitory effects of both IL-4 and IFN gamma on the osteoclastic cell-forming potential of bone marrow macrophages. Collectively, these findings establish bone marrow macrophages as osteoclastic cell precursors with the degree of their commitment to the osteoclast pathway sensitive to the effects of soluble mediators, including IL-4, IFN gamma, and PGE. 相似文献
3.
4.
5.
S Whitman L Lacey D Ansell EH Chen J Dell CW Phillips 《Canadian Metallurgical Quarterly》1993,22(3):393-397
Magnetic resonance imaging allows a noninvasive assessment of myelination during normal brain maturation as well as the detection of genetically determined and acquired diseases that affect the synthesis and maintenance of myelin. If this high sensitivity of magnetic resonance imaging for white matter changes is completed by adequate clinical and biochemical information, a unique diagnostic tool is available to gain new insights in the formation of myelin and pathogenesis of myelin disorders. 相似文献
6.
7.
PURPOSE: A new dietary zinc assessment tool (ZAT) was evaluated to determine its usefulness in estimating zinc intakes among college students. METHODS: A food frequency questionnaire specifically designed for calculating average zinc intakes was administered to university students who had also completed three-day food records. Zinc intakes from the two instruments were compared. RESULTS: Among 171 participants (38 male, 133 female) aged 20.2 +/- 1.6 years (mean +/- standard deviation), the two dietary assessment methods were positively correlated (r=0.33, p<0.001). The ZAT correctly identified 76% of the women who were obtaining less than the National Academy of Sciences Recommended Dietary Allowance for zinc (8 mg/day for females, 11 mg/day for males). CONCLUSIONS: This convenient tool may assist in the identification of problematic dietary patterns at an early stage. Further design modifications and expanded studies are warranted. 相似文献
8.
9.
KO Honikel 《Canadian Metallurgical Quarterly》1998,105(8):327-329
The production of organic (ecological) food of animal origin is done in many ways and uses many different breeds. Therefore a real comparison with conventionally produced food is difficult. From the limited number of published data it appears, that the characteristics of quality of the products, the nutritional, hygienic, sensorial and technological factors, are not very different in both systems of production. In some factors organic food gets better marks, in others the conventionally produced food. The differences are in the production system (process quality) during lifetime of the animals. 相似文献
10.
During studies to develop serum tests of small intestinal permeability, we detected an unidentified disaccharide in HPLC traces of sera from untreated celiacs. This present study aimed to identify the disaccharide and determine whether the presence of the disaccharide in the serum after an oral challenge had potential as a simple screening test for celiac disease. The disaccharide was identified as sucrose by incubation studies of sera with disaccharidases. Twenty untreated celiacs, 15 treated celiacs, and 20 normal or dyspeptic controls were studied for the presence of sucrose in their serum after an oral load (8 g). The results in celiacs were compared with the presence of serum IgA endomysial antibodies. The 10 normal controls were also given a larger sucrose challenge (50 g). Ten of the untreated celiacs and 10 controls had their brush border disaccharidase activities measured. Sucrose eluted in the same position as the unidentified disaccharide in the HPLC trace and the latter could be removed by incubation with sucrase. All untreated celiacs but none of the treated celiacs had sucrose in their serum after the 8-g oral challenge. None of the controls had sucrose in their serum after the 8-g or 50-g challenges. Three untreated celiacs were IgA endomysial antibody negative as were all the treated cases. Brush border sucrase activity was low in untreated celiac disease. The presence of sucrose in the serum after an oral load shows promise as a noninvasive test for celiac disease. 相似文献