全文获取类型
收费全文 | 767篇 |
免费 | 19篇 |
专业分类
电工技术 | 14篇 |
综合类 | 1篇 |
化学工业 | 153篇 |
金属工艺 | 22篇 |
机械仪表 | 25篇 |
建筑科学 | 45篇 |
矿业工程 | 6篇 |
能源动力 | 32篇 |
轻工业 | 84篇 |
水利工程 | 8篇 |
无线电 | 88篇 |
一般工业技术 | 117篇 |
冶金工业 | 117篇 |
原子能技术 | 9篇 |
自动化技术 | 65篇 |
出版年
2022年 | 10篇 |
2021年 | 12篇 |
2020年 | 5篇 |
2019年 | 12篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 18篇 |
2015年 | 12篇 |
2014年 | 21篇 |
2013年 | 41篇 |
2012年 | 23篇 |
2011年 | 37篇 |
2010年 | 36篇 |
2009年 | 29篇 |
2008年 | 28篇 |
2007年 | 22篇 |
2006年 | 37篇 |
2005年 | 29篇 |
2004年 | 26篇 |
2003年 | 27篇 |
2002年 | 16篇 |
2001年 | 28篇 |
2000年 | 18篇 |
1999年 | 16篇 |
1998年 | 23篇 |
1997年 | 24篇 |
1996年 | 11篇 |
1995年 | 12篇 |
1994年 | 18篇 |
1993年 | 9篇 |
1992年 | 5篇 |
1991年 | 12篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 6篇 |
1984年 | 11篇 |
1983年 | 4篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1972年 | 5篇 |
1971年 | 6篇 |
1966年 | 3篇 |
排序方式: 共有786条查询结果,搜索用时 15 毫秒
141.
Nowadays, food industry is facing challenges connected with the preservation of the highest possible quality of fruit products obtained after processing. Attention has been drawn to Aronia fruits due to numerous health promoting properties of their products. However, processing of Aronia, like other berries, leads to difficulties that stem from the preparation process, as well as changes in the composition of bioactive compounds. Consequently, in this study, Aronia commercial juice was subjected to different drying techniques: spray drying, freeze drying and vacuum drying with the temperature range of 40–80 °C. All powders obtained had a high content of total polyphenols. Powders gained by spray drying had the highest values which corresponded to a high content of total flavonoids, total monomeric anthocyanins, cyaniding-3-glucoside and total proanthocyanidins. Analysis of the results exhibited a correlation between selected bioactive compounds and their antioxidant capacity. In conclusion, drying techniques have an impact on selected quality parameters, and different drying techniques cause changes in the content of bioactives analysed. Spray drying can be recommended for preservation of bioactives in Aronia products. Powder quality depends mainly on the process applied and parameters chosen. Therefore, Aronia powders production should be adapted to the requirements and design of the final product. 相似文献
142.
Interference estimation with applications to blind multiple-accesscommunication over fading channels
McCloud M.L. Scharf L.L. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2000,46(3):947-961
We consider the detection of nonorthogonal multipulse signals on multiple-access fading channels. The generalized maximum-likelihood rule is employed to decode users whose complex fading gains are unknown. We develop geometrical interpretations for the resulting detectors and their corresponding asymptotic efficiencies. The generalized maximum-likelihood detection rule is then applied to find a matched subspace detector for the frequency-selective fading channel, under the assumption of a short coherence time (or long coherence time without the computational power to track the fading parameters). We propose blind implementations of these detectors for nonorthogonal multipulse signaling on both frequency-nonselective and frequency-selective multiple-access fading channels. These blind detectors extend the results of Wang and Poor (see ibid., vol.44, p.677-89, 1998) to multipulse modulation and fast frequency selective fading. For comparison, the minimum mean-squared error decision rules for these channels are derived and blind implementations of their corresponding detectors are developed 相似文献
143.
In 1897 physicists took the first e/m measurements at electrons, the consequence was a revival of the atomistic ideas in physics.
The researches in geophysics also contributed to the construction of the modern physics. Four examples are dealt with this
essay. 1) In 1899 J. J. Thomson was able to carry out the first direct determination of elementary electric charge with the
help of the conformity with the natural laws at the formation of fog, found by C. T. R. Wilson. 2) The cloud-chamber, called
after C. T. R. Wilson, was the result of various constructions of for- or cloud-chambers, in it there were shown for the first
time the tracks of α- and β-particles. 3) At the exploration of the photoelectric effect of the sunlight (especially of the
ultraviolet share) Elster and Geitel made essential preliminary studies for the lightquanta-hypothesis of Einstein. 4) Elster
and Geitel detected radioactive substances in the atmosphere and in the soil to be the main source of the atmospheric electricity.
相似文献
144.
145.
146.
There is increasing interest in distinguishing the effects of physical and psychosocial workplace stressors on the aetiology of work-related musculoskeletal disorders (MSD). Modest associations have been found between psychosocial stressors and MSD, such as intensive load, monotonous work and low job control. Interpretation of these results has been limited by likely covariation between physical and psychosocial stressors. This investigation examined exposure covariation among blue- and white-collar workers employed in a mass production manufacturing environment (N = 410). Physical stressors were assessed from questionnaire and accelerometry. Psychosocial stressors were assessed from questionnaire. Pearson and Spearman correlation coefficients were computed. An exploratory factor analysis procedure identified possible common factors linking specific physical and psychosocial stressors. Moderate to high correlations between some physical and psychosocial stressors showed evidence of covariation both across and within groups. Covariation was strongest among blue-collar production and low-status office workers. Factor analysis results showed considerable shared variance between some physical and psychosocial stressors, such as repetition and job control, suggesting that these disparate stressors manifest from common work organization factors that govern the structure of work. While recognizing the conceptual differences between physical and psychosocial stressors, these results call attention to the strong empirical relationships that can exist between some stressors in the workplace setting. To guard against ambiguous study findings that can occur when exposures are mixed, it is critical that future epidemiologic studies include information about the degree of association between task-level stressors. Future research on work organization determinants of task-level stressors, and their coincident occurrence in jobs with greater specialization, may provide promising new insights into the nature of risk for MSD and effective prevention strategies. 相似文献
147.
用伪并行遗传/模拟退火算法进行多流股换热器网络综合的研究 总被引:4,自引:0,他引:4
The multi-stream heat exchanger network synthesis (HENS) problem can be formulated as a mixed integer nonlinear programming model according to Yee et al. Its nonconvexity nature leads to existence of more than one optimum and computational difficulty for traditional algorithms to find the global optimum. Compared with deterministic algorithms, evolutionary computation provides a promising approach to tackle this problem. In this paper, a mathematical model of multi-stream heat exchangers network synthesis problem is setup. Different from the assumption of isothermal mixing of stream splits and thus linearity constraints of Yee et al., non-isothermal mixing is supported. As a consequence, nonlinear constraints are resulted and nonconvexity of the objective function is added. To solve the mathematical model, an algorithm named GA/SA (parallel genetic/simulated annealing algorithm) is detailed for application to the multi-stream heat exchanger network synthesis problem. The performance of the proposed approach is demonstrated with three examples and the obtained solutions indicate the presented approach is effective for multi-stream HENS. 相似文献
148.
149.
Daniel H. Scharf Pranatchareeya Chankhamjon Dr. Kirstin Scherlach Jan Dworschak Thorsten Heinekamp Martin Roth Prof. Axel A. Brakhage Prof. Dr. Christian Hertweck 《Chembiochem : a European journal of chemical biology》2021,22(2):336-339
Gliotoxin and related epidithiodiketopiperazines (ETP) from diverse fungi feature highly functionalized hydroindole scaffolds with an array of medicinally and ecologically relevant activities. Mutation analysis, heterologous reconstitution, and biotransformation experiments revealed that a cytochrome P450 monooxygenase (GliF) from the human-pathogenic fungus Aspergillus fumigatus plays a key role in the formation of the complex heterocycle. In vitro assays using a biosynthetic precursor from a blocked mutant showed that GliF is specific to ETPs and catalyzes an unprecedented heterocyclization reaction that cannot be emulated with current synthetic methods. In silico analyses indicate that this rare biotransformation takes place in related ETP biosynthetic pathways. 相似文献
150.
W.S. Rubink V. Ageh H. Lide N.A. Ley M.L. Young D.T. Casem E.J. Faierson T.W. Scharf 《Journal of the European Ceramic Society》2021,41(6):3321-3332
Spark plasma sintering (SPS) was employed to consolidate powder specimens consisting of B4C and various B4C-TiB2 compositions. SPS allowed for consolidation of pure B4C, B4C-13 vol.%TiB2, and B4C-23 vol.%TiB2 composites achieving ≥99 % theoretical density without sintering additives, residual phases (e.g., graphite), and excessive grain growth due to long sintering times. Electron and x-ray microscopies determined homogeneous microstructures along with excellent distribution of TiB2 phase in both small and larger-scaled composites. An optimized B4C-23 vol.%TiB2 composite with a targeted low density of ~3.0 g/cm3 exhibited 30–35 % increased hardness, fracture toughness, and flexural bend strength compared to several commercial armor-grade ceramics, with the flexural strength being strain rate insensitive under quasistatic and dynamic loading. Mechanistic studies determined that the improvements are a result of a) no residual graphitic carbon in the composites, b) interfacial microcrack toughening due to thermal expansion coefficient differences placing the B4C matrix in compression and TiB2 phase in tension, and c) TiB2 phase aids in crack deflection thereby increasing the amount of intergranular fracture. Collectively, the addition of TiB2 serves as a toughening and strengthening phase, and scaling of SPS samples show promise for the manufacture of ceramic composites for body armor. 相似文献