全文获取类型
收费全文 | 2259篇 |
免费 | 74篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 8篇 |
综合类 | 8篇 |
化学工业 | 499篇 |
金属工艺 | 22篇 |
机械仪表 | 26篇 |
建筑科学 | 173篇 |
矿业工程 | 16篇 |
能源动力 | 65篇 |
轻工业 | 260篇 |
水利工程 | 30篇 |
石油天然气 | 8篇 |
无线电 | 129篇 |
一般工业技术 | 391篇 |
冶金工业 | 281篇 |
原子能技术 | 9篇 |
自动化技术 | 412篇 |
出版年
2023年 | 10篇 |
2022年 | 17篇 |
2021年 | 44篇 |
2020年 | 34篇 |
2019年 | 33篇 |
2018年 | 40篇 |
2017年 | 36篇 |
2016年 | 35篇 |
2015年 | 51篇 |
2014年 | 64篇 |
2013年 | 155篇 |
2012年 | 84篇 |
2011年 | 158篇 |
2010年 | 98篇 |
2009年 | 97篇 |
2008年 | 124篇 |
2007年 | 118篇 |
2006年 | 99篇 |
2005年 | 81篇 |
2004年 | 65篇 |
2003年 | 65篇 |
2002年 | 53篇 |
2001年 | 38篇 |
2000年 | 39篇 |
1999年 | 39篇 |
1998年 | 57篇 |
1997年 | 42篇 |
1996年 | 37篇 |
1995年 | 33篇 |
1994年 | 44篇 |
1993年 | 32篇 |
1992年 | 29篇 |
1991年 | 15篇 |
1990年 | 25篇 |
1989年 | 20篇 |
1988年 | 27篇 |
1987年 | 17篇 |
1986年 | 17篇 |
1985年 | 35篇 |
1984年 | 24篇 |
1983年 | 20篇 |
1982年 | 22篇 |
1981年 | 14篇 |
1980年 | 15篇 |
1979年 | 24篇 |
1978年 | 14篇 |
1977年 | 18篇 |
1976年 | 24篇 |
1975年 | 17篇 |
1973年 | 10篇 |
排序方式: 共有2337条查询结果,搜索用时 15 毫秒
131.
Cells of six strains of Cronobacter were subjected to dry stress and stored for 2.5 months at ambient temperature. The individual cell lag time distributions of recovered cells were characterized at 25 °C and 37 °C in non-selective broth. The individual cell lag times were deduced from the times taken by cultures from individual cells to reach an optical density threshold. In parallel, growth curves for each strain at high contamination levels were determined in the same growth conditions. In general, the extreme value type II distribution with a shape parameter fixed to 5 (EVIIb) was the most effective at describing the 12 observed distributions of individual cell lag times. Recently, a model for characterizing individual cell lag time distribution from population growth parameters was developed for other food-borne pathogenic bacteria such as Listeria monocytogenes. We confirmed this model’s applicability to Cronobacter by comparing the mean and the standard deviation of individual cell lag times to populational lag times observed with high initial concentration experiments. We also validated the model in realistic conditions by studying growth in powdered infant formula decimally diluted in Buffered Peptone Water, which represents the first enrichment step of the standard detection method for Cronobacter. Individual lag times and the pooling of samples significantly affect detection performances. 相似文献
132.
Abstract: It remains important to establish the stability of anthocyanins throughout commercial processing in order to maintain the bioactivity of the processed food/s. The present study aimed to assess the recovery and formation of anthocyanins and their free phenolic acid degradation products during the commercial processing of blackcurrant juice concentrate. A bench‐scale processing model was also established to allow for alteration of predefined parameters to identify where commercial processes could be modified to influence anthocyanin yield. No significant loss in anthocyanins was observed throughout the commercial processing of blackcurrants, from whole berry through milling, to pectin hydrolysis and sodium bisulphite addition (P ≥ 0.7). No significant loss in anthocyanins was observed following the subsequent processing of pressed juice, through pasteurization, decantation, filtration, and concentration (P ≥ 0.9). Similarly, the bench‐scale model showed no significant losses in anthocyanin content except during pasteurization (22%± 0.7%, P < 0.001). In the full‐factorial Design of Experiment model analysis, only sodium bisulphite concentration had an impact on anthocyanin recovery, which resulted in an increase (23% to 27%; P < 0.001) in final anthocyanin concentration. No phenolic degradation products (free protocatechuic acid or gallic acid derived from cyanidin and delphinin species, respectively) were identified in any processed sample when compared to authentic analytical standards, analyzed by ultra‐performance liquid chromatography DAD. Practical Application: This article provides crucial data directly applicable to commercial juice processing, such as improving anthocyanin yield and practical considerations for anthocyanin stability and degradation. This aspect is particularly pertinent considering the current commercial interest in anthocyanin‐derived phenolic acids and their health‐related benefits. Further research and development targets in the area of commercial juice product development are identified. 相似文献
133.
Geotrichum candidum is a ubiquitous yeast and an essential component in the production of many soft cheeses. We developed a multilocus sequence typing (MLST) scheme with five retained loci (NUP116, URA1, URA3, SAPT4 and PLB3) which were sufficiently divergent to distinguish 40 sequence types (STs) among the 67 G. candidum strains tested. Phylogenetic analyses defined five main clades; one clade was restricted to environmental isolates, three other clades included distinct environmental isolates and dairy strains, while the fifth clade comprised 34 strains (13 STs), among which all but two were isolated from milk, cheese or the dairy environment. These findings suggest an adaptation to the dairy ecosystems by a group of specialized European G. candidum strains. In addition, we developed a polymerase chain reaction inter‐long terminal repeat scheme, a fast and reproducible random amplification of polymorphic DNA‐like method for G. candidum, to type the closely related dairy strains, which could not be distinguished by MLST. Overall, our findings distinguished two types of dairy strains, one forming a homogeneous group with little genetic diversity, and the other more closely related to environmental isolates. Neither regional nor cheese specificity was observed in the dairy G. candidum strains analysed. This present study sheds light on the genetic diversity of both dairy and environmental strains of G. candidum and thus extends previous characterizations that have focused on the cheese isolates of this species. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
134.
135.
E. Siranidi D. Lampakis D. Palles E. Liarokapis C. Colin T. T. M. Palstra 《Journal of Superconductivity and Novel Magnetism》2009,22(2):185-188
The spin and orbital ordering have been examined for high-quality SmVO3 polycrystalline compound using Raman spectroscopy. Measurements were obtained on individual microcrystallites in the approximate
y(zz)y and y(xx)y scattering configurations at low temperatures (down to 20 K) and high pressures (up to 2.75 GPa). At room temperature and
ambient pressure only the Ag phonons have been observed in both polarizations examined. The decrease of temperature leads to the appearance of extra peaks
in the Raman spectra related to the magnetic and structural transitions that occur in the system. We present evidence of a
coexistence of the monoclinic and orthorhombic phases accompanied with the coexistence of the G- and C-type OO phases for
temperatures below 100 K. However, no sign of any structural transition has been observed in the high pressure Raman spectra
(1.87<P<2.75 GPa) at low temperatures T≥80 K, indicating that SmVO3 remains orthorhombic, at least down to 80 K. 相似文献
136.
137.
A rigorous and comparative evaluation of two biomass‐to‐gases (BtG) conversion routes was performed and, according to this outcome, it is suggested which of the options evaluated is most desirable. These options, the hydrogen and synthetic natural gas (SNG) production, were designed in Aspen Plus process simulation software. Sugar cane bagasse was considered as feedstock. Mass and energy balance data were extracted from the simulations, and consequently thermodynamic (exergy analysis), economic (financial and uncertainty analysis), and environmental (CO2 emissions) evaluations were carried out. Exergy and environmental analysis favor the SNG production while the hydrogen route provides higher profits. 相似文献
138.
The investigation summarised in this paper applied a sustainability assessment methodology on a renewable energy technological system in a rural village project that was commissioned by the South African Department of Minerals and Energy. The project comprised of wind, solar and lead-acid battery energy storage technologies that were implemented as a mini-hybrid off-grid electrification system for the village. The sustainability assessment methodology predicts the outcomes of such interventions by way of a learning model using discipline experts in the fields of economics, sociology, ecosystem sustainability, institutional governance, and the physics and chemistry of energy conversion processes. The comparison of the project's outcomes with a South African sustainable development framework shows that the specific village renewable off-grid electrification system is not viable. The main reason is that charges for electricity supply costs in village grids are too high for available subsidies; the economies of scale for renewable energy supply technologies favour national grids. The failure of the integrated system may also be attributable to the complexity of the social-institutional sub-system, which resulted in uncertainty for project planners and system designers, and the lack of resilience of the technological system to demands from the socio-economic and institutional sub-systems. Policy-related recommendations are made accordingly. 相似文献
139.
Creativity is commonly defined as the novel and useful combination of concepts previously thought to be unrelated. Fundamentally, this process rests on the ability to judge relatedness between concepts. The authors conducted an experiment to test the connection between divergent thinking ability and the speed of judging relatedness. Our results demonstrated that people with higher divergent thinking ability are faster in judging whether two concepts are related or unrelated. In real life, this can lead to a substantial advantage in the number of potentially useful relationships that could be assessed per unit of time. Equally important, there was no link between IQ and speed of judging relatedness. These results are interpreted in relation to a recently proposed model of creative cognition suggesting that creative people are faster in information processing under conditions of low ambiguity. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
140.
The thermal oxidation of poly(bismaleimide) of the F655‐2 type, supplied by Hexcel‐Genin, was studied by isothermal gravimetry at 180, 210, and 240°C and various oxygen pressures ranging from 0 to 1.2 bar. Comparison of various sample thicknesses and visible microscopy observations on bulk aged samples shows that the whole oxidized layer has a depth of about 75 μm at 240°C, 138 μm at 210°C, and 229 μm at 180°C. An attempt was made to build a kinetic model to predict this depth. It is based on a differential equation in which O2 diffusion and its consumption rate, r(C), are coupled, C being the O2 concentration. Its resolution needs two sets of experiments: the first one to determine the O2 diffusivity and solubility in the polymer, and the second one to determine r(C). The mathematical form of r(C) is derived from a mechanistic scheme of radical chain oxidation in which initiation is mainly due to POOH decomposition. This expression contains two kinetic parameters, α and β, the values of which are determined from the experimental curves of mass loss rate against O2 pressure (in the stationary state). The theoretical predictions, at each temperature under consideration, are in excellent agreement with experimental results. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3418–3430, 2001 相似文献