全文获取类型
收费全文 | 1909篇 |
免费 | 94篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 24篇 |
综合类 | 2篇 |
化学工业 | 465篇 |
金属工艺 | 53篇 |
机械仪表 | 37篇 |
建筑科学 | 55篇 |
矿业工程 | 9篇 |
能源动力 | 58篇 |
轻工业 | 167篇 |
水利工程 | 10篇 |
石油天然气 | 2篇 |
无线电 | 139篇 |
一般工业技术 | 352篇 |
冶金工业 | 290篇 |
原子能技术 | 17篇 |
自动化技术 | 326篇 |
出版年
2023年 | 13篇 |
2022年 | 13篇 |
2021年 | 34篇 |
2020年 | 28篇 |
2019年 | 44篇 |
2018年 | 63篇 |
2017年 | 61篇 |
2016年 | 64篇 |
2015年 | 57篇 |
2014年 | 73篇 |
2013年 | 127篇 |
2012年 | 103篇 |
2011年 | 143篇 |
2010年 | 101篇 |
2009年 | 109篇 |
2008年 | 107篇 |
2007年 | 82篇 |
2006年 | 55篇 |
2005年 | 70篇 |
2004年 | 42篇 |
2003年 | 50篇 |
2002年 | 41篇 |
2001年 | 23篇 |
2000年 | 31篇 |
1999年 | 22篇 |
1998年 | 62篇 |
1997年 | 45篇 |
1996年 | 60篇 |
1995年 | 18篇 |
1994年 | 27篇 |
1993年 | 31篇 |
1992年 | 14篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 8篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1982年 | 19篇 |
1981年 | 9篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1977年 | 16篇 |
1976年 | 24篇 |
1975年 | 6篇 |
1974年 | 4篇 |
1973年 | 8篇 |
排序方式: 共有2006条查询结果,搜索用时 156 毫秒
91.
Maikel León Lusine Mkrtchyan Benoît Depaire Da Ruan Koen Vanhoof 《Knowledge and Information Systems》2014,39(2):435-462
In modern society, more and more attention is given to the increase in public transportation or bike use. In this regard, one of the most important issues is to find and analyse the factors influencing car dependency and the attitudes of people in terms of preferred transport mode. Although the individuals’ transport behavioural modelling is a complex task, it has a notable social and economic impact. Thus, in this paper, fuzzy cognitive maps are explored to represent the behaviour and operation of such complex systems. This soft-computing technique allows modelling how the travellers make decisions based on their knowledge of different transport modes properties at different levels of abstraction. These levels correspond to the hierarchy perception including different scenarios of travelling, different benefits of choosing a specific travel mode, and different situations and attributes related to those benefits. We use learning and clustering of fuzzy cognitive maps to describe travellers’ behaviour and change trends in different abstraction levels. Cluster estimations are done before and after the learning of the maps, in order to compare people’s way of thinking if only considering an initial view of a transport mode decision for a daily activity, and when they really have a deeper reasoning process in view of benefits and consequences. The results of this study will help transportation policy decision makers in better understanding of people’s needs and consequently will help them actualizing different policy formulations and implementations. 相似文献
92.
M. Corgneau J. Scher L. Ritie-Pertusa D. t. l. Le J. Petit Y. Nikolova 《Critical reviews in food science and nutrition》2017,57(15):3344-3356
The genetically programmed reduction in lactase activity during adulthood affects 70% of the world adult population and can cause severe digestive disorders, which are the sign of lactose intolerance. Lactose intolerance symptoms vary depending on the residual lactase activity, the small bowel transit time, and especially the amount of ingested lactose. To formulate dairy products suitable for the vast majority of lactose intolerants, it is essential to define lactose intolerance threshold. A recent meta-analysis permitted to show that almost all lactose intolerants tolerate 12 g of lactose in one intake and approximately 18 g of lactose spread over the day. The prevalence and severity of lactose intolerance are probably overestimated by the general public. This misconception usually leads to an unnecessary reduction of dairy foodstuff consumption. Nevertheless, dairy products are essential for health mainly due to their calcium content and the positive influence of probiotic bacteria. The formulation of dairy products suitable for most intolerant and suspicious subjects seems necessary. The use of exogenous enzyme preparations, as well as the consumption of lactose-free products or products rich in probiotic bacteria are proposed as symptom-reducing strategies. 相似文献
93.
A protective layers were prepared on a magnesium electrode by treatment in different solutions and times after modification
in 0.15 M HCl for 20 seconds. The corrosion of magnesium coated protective layer with different compounds was studied by using
potential-time, current-potential curves and AC impedance spectra. The coatings morphology depends on the treating bath compositions
and immersion times. The protective efficiencies of the surface layers were calculated by using corrosion rates obtained by
extrapolation of Tafel zones of current-potential curves to the corrosion potential and by using Stern-Geary equation with
polarization resistance from impedance spectra. 相似文献
94.
Ş. Aydoğan M. Sağlam A. Türüt Y. Onganer 《Materials science & engineering. C, Materials for biological applications》2009,29(4):1486-1490
The current–voltage (I–V) characteristics of Polypyrrole(PPy)/p-Si/Al structure have been investigated as a function of temperature. A modified Norde function combined with conventional forward I–V method has been used to extract the junction parameters including the ideality factor, barrier height and series resistance. Norde function has been compared with the Cheung functions and it has been seen that there is a good agreement with both method for the barrier height values. However, the values of series resistance have very different especially towards to the lower temperatures. This is attributed to non-ideal I–V characteristics of the Au/PPy/p-Si/Al structure and non-pure Thermionic emission theory due to the low temperature effects. 相似文献
95.
Data mining is sometimes treating data consisting of items representing measurements of a single property taken in different
time points. In this case data can be understood as a time series of one feature. It is no exception when the clue for evaluation
of such data is related to their development trends as observed in several successive time points. From the qualitative point
of view one can distinguish three basic types of behaviour between two neighbouring time points: the value of the feature
is stable (remains the same), it grows or it falls. This paper is concerned with identification of typical qualitative development
patterns as they appear in the windows of given length in the considered time-stamped data and their utilization for specification
of interesting subgroups. 相似文献
96.
97.
A series of novel photocrosslinked biobased shape‐stabilized phase change materials (PCMs) based on octadecanol, eicosanol and docosanol have been prepared by UV technique for the purpose of thermal energy storage applications. Epoxidized soybean oil was reacted with acrylic acid to form acrylated soybean oil (ASO). The structure and composition, cross‐section morphology, thermal stability performances and phase change behaviors of ASO and UV‐cured PCMs were examined by using Attenuated total reflection fourier transform infrared spectroscopy, thermogravimetric analysis system (TGA), scanning electron microscopy, and differential scanning calorimetry. The results indicate that the UV‐cured biobased PCMs possess perfect phase change properties and a suitable working temperature range. The heating process phase change enthalpy is measured between 30 and 68 J/g, and the freezing process phase change enthalpy is found between 18 and 70 J/g. The decomposition of UV‐cured PCMs started at 260 °C and reached a maximum of 430 °C. All the biobased UV‐cured PCMs improved latent heat storage capacity in comparison with the pristine ASO sample. With the obtained results we conclude that, these materials promise a great potential in thermal energy storage applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43757. 相似文献
98.
Multivalent Interactions between an Aromatic Helical Foldamer and a DNA G‐Quadruplex in the Solid State 下载免费PDF全文
Dr. Pradeep K. Mandal Dr. Benoît Baptiste Dr. Béatrice Langlois d'Estaintot Dr. Brice Kauffmann Dr. Ivan Huc 《Chembiochem : a European journal of chemical biology》2016,17(20):1911-1914
Quinoline‐based oligoamide foldamers have been identified as a potent class of ligands for G‐quadruplex DNA. Their helical structure is thought to target G‐quadruplex loops or grooves and not G‐tetrads. We report a co‐crystal structure of the antiparallel hairpin dimeric DNA G‐quadruplex (G4T4G4)2 with tetramer 1 —a helically folded oligo‐quinolinecarboxamide bearing cationic side chains—that is consistent with this hypothesis. Multivalent foldamer–DNA interactions that modify the packing of (G4T4G4)2 in the solid state are observed. 相似文献
99.
Phase Transfer Catalysis with Quaternary Ammonium Type Gemini Surfactants: <Emphasis Type="Italic">O</Emphasis>-Alkylation of Isovanillin 下载免费PDF全文
In this paper, O-alkylation of isovanillin with unusual phase transfer catalysts alkandiyl-α,ω-bis(dimethylalkylammonium bromide) dimeric surfactants (also known as gemini surfactants) is described. Some dimeric surfactants with simple hydrophobic alkyl chains and others with hydrophobic alkyl chains containing ester functionalities with different lengths were synthesized and characterized in our laboratory. The alkylation of isovanillin with alkyl halide was successively carried out in the presence of potassium carbonate and a phase transfer catalyst in tetrahydrofuran. The same reactions were also performed with both the traditional phase transfer catalyst tetrabutylammonium bromide and without any catalyst. The results were compared with those of dimeric surfactants. Consequently, it was expressed that alkandiyl-α,ω-bis(dimethylalkylammonium bromide) dimeric surfactants successively exhibit the character of phase transfer catalysts through environmentally friendly procedures under mild conditions. The most significant feature of this work is that dimeric surfactants have been determined to act as phase transfer agents. 相似文献
100.
A theory describing the behavior of chemically non-reacting binary mixtures can be based on a detailed formulation of the governing equations for the individual components of the mixture or on treating the mixture as a single homogenized continuous medium. We argue that if we accept that both approaches can be used to describe the behavior of the given mixture, then the requirement on the equivalence of these approaches places restrictions on the possible structure of the internal energy, entropy, Helmholtz potential, and also of the diffusive, energy, and entropy fluxes. (The equivalence of the approaches is understood in the sense that the quantities used in one approach can be interpreted in terms of the quantities used in the other approach and vice versa. Further, both approaches must lead to the same predictions concerning the evolution of the physical system under consideration). In the case of a general chemically non-reacting binary mixture of components at the same temperature, we show that these restrictions can indeed be obtained by purely algebraic manipulations. An important outcome of this analysis is, for example, a general form of the evolution equation for the diffusive flux. The restrictions can be further exploited in the specification of thermodynamically consistent constitutive relations for quantities such as the interaction (drag) force or the Cauchy stress tensor. As an example of the application of the current framework, we derive, among others, a generalization of Fick’s law and we recover several non-trivial results obtained by other techniques. The qualitative features of the derived generalization of Fick’s law are demonstrated by a numerical experiment. 相似文献