全文获取类型
收费全文 | 1327篇 |
免费 | 106篇 |
国内免费 | 54篇 |
专业分类
电工技术 | 65篇 |
综合类 | 104篇 |
化学工业 | 226篇 |
金属工艺 | 59篇 |
机械仪表 | 75篇 |
建筑科学 | 63篇 |
矿业工程 | 25篇 |
能源动力 | 34篇 |
轻工业 | 72篇 |
水利工程 | 15篇 |
石油天然气 | 28篇 |
武器工业 | 3篇 |
无线电 | 158篇 |
一般工业技术 | 225篇 |
冶金工业 | 89篇 |
原子能技术 | 7篇 |
自动化技术 | 239篇 |
出版年
2023年 | 21篇 |
2022年 | 35篇 |
2021年 | 56篇 |
2020年 | 46篇 |
2019年 | 54篇 |
2018年 | 45篇 |
2017年 | 21篇 |
2016年 | 50篇 |
2015年 | 54篇 |
2014年 | 33篇 |
2013年 | 65篇 |
2012年 | 51篇 |
2011年 | 53篇 |
2010年 | 48篇 |
2009年 | 56篇 |
2008年 | 54篇 |
2007年 | 46篇 |
2006年 | 64篇 |
2005年 | 40篇 |
2004年 | 50篇 |
2003年 | 72篇 |
2002年 | 123篇 |
2001年 | 76篇 |
2000年 | 70篇 |
1999年 | 47篇 |
1998年 | 32篇 |
1997年 | 16篇 |
1996年 | 11篇 |
1995年 | 15篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有1487条查询结果,搜索用时 15 毫秒
1.
Upconversion phosphors are known as a material system that can convert near-infrared light into visible/ultraviolet emissions by sequentially absorbing multiple photons. The studies on upconversion materials often use two rare earth (RE) ions as a sensitizer-activator pair. We investigated the influences on luminescence intensity depending on Cr-doping content (x) of hexagonal NaLu0.98–xCrxF4Er0.02 (x = 0–0.9) upconversion material by substituting Lu3+ ions with Cr3+in the absence of Gd3+. The change in upconversion luminescence intensity appears with saddle-like shape. We suggest that Cr3+ ions play the dual role as a constituent in host lattice and a sensitizer in the upconversion process. Optimal conditions for gaining the strongest upconversion emission correspond to x = 0.3–0.5, where there are effective energy transfers between Cr3+ and Er3+ ions and CrEr dimers. Apart from these values, the emission intensity decreases rapidly which can be ascribed to the absence of multiple-photon absorption for the case of low Cr3+ contents, and to the coupling between Cr3+ and/or Er3+ ions for the case of high Cr3+ contents. Magnetization and electron-spin-resonant measurements were performed to understand the correlation between the optical and magnetic properties. 相似文献
2.
3.
Youngseok Lee Cheolmin Park Nagarajan Balaji Youn-Jung Lee Vinh Ai Dao 《Israel journal of chemistry》2015,55(10):1050-1063
Over the past few decades, crystalline silicon solar cells have been extensively studied due to their high efficiency, high reliability, and low cost. In addition, these types of cells lead the industry and account for more than half of the market. For the foreseeable future, Si will still be a critical material for photovoltaic devices in the solar cell industry. In this paper, we discuss key issues, cell concepts, and the status of recent high-efficiency crystalline silicon solar cells. 相似文献
4.
5.
In this paper, a two-dimensional (2-D) method describing the whispering gallery mode in a microgear resonator is presented. The microgear is a microdisk surrounded by a circular grating. The method, which is based on the Floquet-Bloch formalism, analytically describes the field within the disk and outside the grating. On the other hand, the field within the grating is calculated using a finite-difference scheme in polar coordinates. Matching the boundary conditions, it is possible to work in a forced oscillation regime or in a free oscillation regime (laser mode). The resonant wavelength and quality factor can then be deduced. Compared to the coupled mode theory and to 2-D finite-difference time-domain computations, the method is faster and more accurate. Moreover, a polarization effect of the microgear is demonstrated. The TE polarization experiences a Q-factor improvement contrary to TM polarization. Finally, microgear structures prove to be more efficient than micro flowers. 相似文献
6.
P Rajasekariah RS Warlow ME Campbell N Ozsarac PL Dao MK Swanton RS Walls 《Canadian Metallurgical Quarterly》1998,30(3):353-367
Bradykinin (BK) is a potent mediator with a broad spectrum of pharmacological and inflammatory actions which are exerted through cell surface receptors. We report here the affinity chromatographic purification of a novel 14 kDa BK binding protein from human blood neutrophils and also peripheral blood mononuclear cells (PBMC), 80% of which are lymphocytes. Radioreceptor crosslinking experiments using bifunctional crosslinkers and radiolabelled BK identified a 14 kDa protein in these cell types both on the cell surface, in glycerol purified plasma membranes and in detergent solubilized cell extracts. Purification by BK affinity chromatography from a variety of BK responsive human cell types i.e. CCD-16Lu lung fibroblasts, HL60 promyelocytes, U937 myelomonocytes and Jurkat T lymphocytes also demonstrated a 14 kDa protein. Purified material obtained from three different BK affinity columns all demonstrated three major proteins at 190, 50 and 14 kDa when eluted with either excess BK or mild acid. Neutrophil fractions from detergent solubilized cell extracts contained an additional 150 kDa protein when eluted with mild acid. Neutrophil and PBMC crude plasma membrane BK affinity column purifications yielded only a single 14 kDa protein. Radioreceptor dot assays of the purified neutrophil eluates containing the 14 kDa protein revealed specific binding to [125I]-BK with a 160 fold excess signal ratio over the original membrane extract. Our data indicates that we have successfully isolated a 14 kDa novel human BK specific binding protein expressed on the surface of inflammatory cells. 相似文献
7.
8.
9.
10.