全文获取类型
收费全文 | 23294篇 |
免费 | 359篇 |
国内免费 | 122篇 |
专业分类
电工技术 | 500篇 |
综合类 | 64篇 |
化学工业 | 3198篇 |
金属工艺 | 940篇 |
机械仪表 | 658篇 |
建筑科学 | 550篇 |
矿业工程 | 67篇 |
能源动力 | 600篇 |
轻工业 | 1861篇 |
水利工程 | 212篇 |
石油天然气 | 181篇 |
武器工业 | 1篇 |
无线电 | 2594篇 |
一般工业技术 | 4097篇 |
冶金工业 | 6152篇 |
原子能技术 | 420篇 |
自动化技术 | 1680篇 |
出版年
2021年 | 153篇 |
2020年 | 118篇 |
2019年 | 159篇 |
2018年 | 231篇 |
2017年 | 229篇 |
2016年 | 260篇 |
2015年 | 180篇 |
2014年 | 298篇 |
2013年 | 824篇 |
2012年 | 512篇 |
2011年 | 785篇 |
2010年 | 562篇 |
2009年 | 624篇 |
2008年 | 720篇 |
2007年 | 750篇 |
2006年 | 631篇 |
2005年 | 722篇 |
2004年 | 589篇 |
2003年 | 639篇 |
2002年 | 681篇 |
2001年 | 674篇 |
2000年 | 599篇 |
1999年 | 619篇 |
1998年 | 2162篇 |
1997年 | 1409篇 |
1996年 | 1047篇 |
1995年 | 721篇 |
1994年 | 621篇 |
1993年 | 641篇 |
1992年 | 358篇 |
1991年 | 345篇 |
1990年 | 343篇 |
1989年 | 345篇 |
1988年 | 292篇 |
1987年 | 267篇 |
1986年 | 246篇 |
1985年 | 277篇 |
1984年 | 217篇 |
1983年 | 201篇 |
1982年 | 185篇 |
1981年 | 220篇 |
1980年 | 202篇 |
1979年 | 167篇 |
1978年 | 152篇 |
1977年 | 278篇 |
1976年 | 387篇 |
1975年 | 127篇 |
1974年 | 112篇 |
1973年 | 117篇 |
1972年 | 90篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Irradiated restructured pork loins treated with rosemary-tocopherol/double-packaging had lower TBARS values than vacuum-packaged control after 10 days of refrigerated storage. The rosemary-tocopherol combination, however, had no effect on the production of sulfur volatiles responsible for the irradiation off-odor, and color changes in irradiated pork. V7/A3 double-packaging was effective in reducing the sulfur volatiles significantly. Rosemary-tocopherol combination was highly effective in reducing the volatile hexanal in irradiated restructure pork. Irradiation was effective in reducing Listeria monocytogenes and Salmonella typhimurium inoculated on the surface of restructured pork loin in dose-dependent manner. The irradiation D(10) values for L. monocytogenes and S. typhimurium were 0.58 and 0.55kGy, respectively. During the 20 days of refrigerated storage, L. monocytogenes in both nonirradiated and irradiated samples grew gradually, but the number of S. typhimurium decreased. The added rosemary-tocopherol, however, showed little bacteriocidal effects to L. monocytogenes and S. typhimurium. 相似文献
992.
The modern fruit juice industry needs their products to be characterized by high-quality attributes to meet consumers’ expectation. In this view, the composition of 26 Italian commercial apricot juices obtained from organic, integrated and conventional agriculture was analysed for carbohydrates, organic acids, amino acids, phenolic compounds and furanic compounds by high-performance liquid chromatography (HPLC). The content of 5-hydroxymethylfurfural in apricot juices (range 0.1–18 mg/l) was within the regulatory limit of 20 mg/l. The lack of furanic compounds in apricot fresh fruits confirmed their importance as quality markers of heating condition during processing and storage of fruit juices. Univariate analysis disclosed some significant differences among the composition of the apricot juices in terms of glucose, fructose, malic acid, glycine, chlorogenic acid, rutin, and a∗-parameter (redness). Principal component analysis on chemical composition of apricot juices resulted in two principal components (PCs) that accounted for 66% of the total variance. Organic apricot juices showed some separation from the other juices, whereas a lack of distinction between integrated and conventional juices appeared. 相似文献
993.
994.
995.
U.M. Cowgill 《The Science of the total environment》1973,2(3):259-303
A hydrogeochemical study to determine the abundance of the chemical elements in the water of Linsley Pond, North Branford, Conn., U.S.A., was initiated in 1965. As the investigation progressed, it became clear that the aquatic macrophytes, associated sediments, and the soils and rocks of the basin had to be examined chemically in order to elucidate the biogeochemical cycle of the elements in the water. This aspect of the study concerns the elemental chemical composition of Nymphaea odorata Ait. and the aphid Rhopalosiphum nymphaeae (L.) feeding on its leaves. Thirty-five elements were detected in the water but fifty-four were found in this water-lily and its aphid. Those not encountered in lake water concentrated twenty-fold were Cs, Sc, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, Ge, Zr, Hf, Th, As, Nb and Se. The water-lily, the aphid, the lake sediment and the soils and rocks of the basin all contained detectable quantities of the rare earths, though beyond Sm only those of even atomic number were encountered. The aphids contained more Na, Li, Cs, Ba, Zn, Al, Ga, Si, Ge, Pb, Ti, Hf, P, Bi, S, Se, Cr, Mo, I, Fe, Co, Ni, Mn, Y, La, Ce, Pr and Sm than the leaves upon which they feed. The water-lily leaves contain more Ag, Ca, Mg, Cd, Hg, B, Sn, Zr, Th, Cl, Br, Nd and Sc than the aphids. The amount of Be, Gd, Dy, Er, Yb, K, Rb, Cu, Sr, As, V and F is essentially the same in the insects as in the leaves which support them. Pertinent comparative data from other sources are also presented. 相似文献
996.
997.
998.
999.
Recent developments in the design of bifunctional and activatable photosensitizers rejuvenate the aging field of photodynamic sensitization and photodynamic therapy. While systematic studies have uncovered new dyes that can serve as potential photosensitizers, the most promising results have come from studies aimed at gaining precise control over the location and rate of cytotoxic singlet oxygen generation. As a consequence, higher selectivities and efficiencies in photodynamic treatment protocols are now within reach. This feature article highlights the variety of approaches that have been pursued to improve photodynamic therapy and to transform simple photosensitizers into smarter theranostic agents. 相似文献
1000.
Calculations on a modulator based on quantum interference in AlGaAs/GaAs asymmetric double quantum wells (QWs) are performed. The modulation of the absorption is based on the anti-crossing behavior of the two lowest states in the coupled wells. At anti-crossing, the oscillator strengths of the transitions from these two lowest states to a higher state are changed in opposite directions. The width of the barrier between the wells should be thick enough to allow a large change in oscillator strength with applied field, yet thin enough so that the absorption peaks of the transitions are resolved. The QWs are designed so that one absorption peak has only a small energy shift for the transition used for modulation while the absorption varies rapidly with the applied voltage. A complete structure including a surface plasmon waveguide is proposed enabling calculations of modal absorption. Parameters important for the performance of the modulator are then determined. An extinction ratio of 10 dB at a wavelength of 8.4 μm is predicted for a device length of 18 μm and a peak-to-peak voltage of 0.9 V. The resistance-capacitance-limited 3-dB bandwidth is 130 GHz. The predicted performance compares very favorably with present interband modulators based on the quantum-confined Stark effect 相似文献