全文获取类型
收费全文 | 474篇 |
免费 | 41篇 |
专业分类
电工技术 | 5篇 |
化学工业 | 125篇 |
金属工艺 | 4篇 |
机械仪表 | 7篇 |
建筑科学 | 18篇 |
矿业工程 | 1篇 |
能源动力 | 20篇 |
轻工业 | 56篇 |
水利工程 | 2篇 |
无线电 | 32篇 |
一般工业技术 | 91篇 |
冶金工业 | 82篇 |
原子能技术 | 5篇 |
自动化技术 | 67篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 12篇 |
2021年 | 19篇 |
2020年 | 11篇 |
2019年 | 23篇 |
2018年 | 20篇 |
2017年 | 13篇 |
2016年 | 21篇 |
2015年 | 10篇 |
2014年 | 24篇 |
2013年 | 27篇 |
2012年 | 30篇 |
2011年 | 31篇 |
2010年 | 16篇 |
2009年 | 19篇 |
2008年 | 15篇 |
2007年 | 16篇 |
2006年 | 23篇 |
2005年 | 10篇 |
2004年 | 8篇 |
2003年 | 11篇 |
2002年 | 13篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1999年 | 11篇 |
1998年 | 31篇 |
1997年 | 14篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 7篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有515条查询结果,搜索用时 343 毫秒
81.
The release of tritium from Li2TiO3 and Li2ZrO3 pebbles, in batch experiments, is studied by means of temperature programmed desorption. Data reduction focuses on the analysis of the non-oxidized and oxidized tritium components in terms of release limited by diffusion from the bulk of ceramic grains, or by first or second order surface desorption. By analytical and numerical methods the in-furnace tritium release is deconvoluted from the ionization chamber transfer functions, for which a semi-empirical form is established. The release from Li2TiO3 follows second order desorption kinetics, requiring a temperature for a residence time of 1 day (T1dRes) of 620 K, and 603 K, of the non-oxidized, and the oxidized components, respectively. The release from Li2ZrO3 appears as limited by either diffusion from the bulk of the ceramic grains, or by first order surface desorption, the first possibility being the more probable. The respective values of T1dRes for the non-oxidized component are 661 K, according to the first order surface desorption model, and 735 K within the bulk diffusion limited model. 相似文献
82.
83.
C. I. L. de Araujo M. A. Tumelero J. I. Avila A. D. C. Viegas N. Garcia A. A. Pasa 《Journal of Superconductivity and Novel Magnetism》2013,26(12):3449-3454
We present results on the magnetoresistance of the system Ni/Al2O3/Si/Al2O3/Ni fabricated in lateral nanostructures. The substrate n-type Si is a nondegenerated semiconductor with a doping level of 1015 cm?3. The results are presented between 11 and 30 K, where the electrical resistivity of the semiconductor varies about 4 orders of magnitude. The reduction of magnetoresistance at 30 K is consistent with the standard theory for spin injection between a metal and a semiconductor. By fitting the data with $e^{ - t_{N} / L_{\mathrm{SD}}}$ , the diffusion condition, as a function of the channel length t N , where the magnetoresistance takes place, we deduced the values of spin diffusion length L SD and spin lifetime τ s . 相似文献
84.
Oxygen-impurity boron-doped hydrogenated microcrystalline silicon (p-μc-Si:Ox:H) films have been deposited using catalytic chemical vapor deposition (Cat-CVD). Pure silane (SiH4), hydrogen (H2), oxygen (O2), and diluted diborane (B2H6) gases were used. The tungsten catalyst temperature (Tfil) was varied from 1900 to 2100 °C and films were deposited on glass substrates at temperatures of 100 to 300 °C. Different catalyst-to-substrate distances were employed and single- or double-coiled filaments were used. In addition to p-μc-Si:Ox:H deposition, we have also deposited conventional p-type microcrystalline silicon (p-μc-Si:H) in order to compare their electrical and optical properties to p-μc-Si:Ox:H. 相似文献
85.
86.
Dahlberg M Eklöf M Fredriksson P Jofre-Monseny J 《Urban studies (Edinburgh, Scotland)》2012,49(2):319-336
Using Swedish micro data, the paper examines the impact of local public services on community choice. The choice of community is modelled as a choice between a discrete set of alternatives. It is found that, given taxes, high spending on child care attracts migrants. Less conclusive results are obtained with respect to the role of spending on education and elderly care. High local taxes deter migrants. Relaxing the independence of the irrelevant alternatives assumption, by estimating a mixed logit model, has a significant impact on the results. 相似文献
87.
Søren Lindbæk Broman Samuel Lara‐Avila Christine Lindbjerg Thisted Andrew D. Bond Sergey Kubatkin Andrey Danilov Mogens Brøndsted Nielsen 《Advanced functional materials》2012,22(20):4249-4258
Molecular switches play a central role for the development of molecular electronics. In this work it is demonstrated that the reproducibility and robustness of a single‐molecule dihydroazulene (DHA)/vinylheptafulvene (VHF) switch can be remarkably enhanced if the switching kernel is weakly coupled to electrodes so that the electron transport goes by sequential tunneling. To assure weak coupling, the DHA switching kernel is modified by incorporating p‐MeSC6H4 end‐groups. Molecules are prepared by Suzuki cross‐couplings on suitable halogenated derivatives of DHA. The synthesis presents an expansion of our previously reported bromination–elimination–cross‐coupling protocol for functionalization of the DHA core. For all new derivatives the kinetics of DHA/VHF transition has been thoroughly studied in solution. The kinetics reveals the effect of sulfur end‐groups on the thermal ring‐closure of VHF. One derivative, incorporating a p‐MeSC6H4 anchoring group in one end, has been placed in a silver nanogap. Conductance measurements justify that transport through both DHA (high resistivity) and VHF (low resistivity) forms goes by sequential tunneling. The switching is fairly reversible and reenterable; after more than 20 “ON‐OFF” switchings, both DHA and VHF forms are still recognizable, albeit noticeably different from the original states. 相似文献
88.
Garde S Avila M Arias R Gaya P Nuñez M 《International journal of food microbiology》2011,150(1):59-65
In the manufacture of model cheeses, ovine milk was deliberately contaminated with spores of Clostridium beijerinckii INIA 63, a wild isolate from Manchego cheese with late blowing defect, and inoculated with nisin- and lacticin 481-producing Lactococcus lactis subsp. lactis INIA 415 as starter, to test its potential to prevent the late blowing defect, or with L. lactis subsp. lactis INIA 415-2, a spontaneous mutant not producing bacteriocins. Cheeses made individually with the lactococcal strains, without clostridial spores, served as controls. Cheese made with clostridial spores and L. lactis subsp. lactis INIA 415-2 showed late blowing defect after 120 days of ripening. Spoilt cheese also showed lower concentrations of lactic acid, and higher levels of acetic, propionic and butyric acids, and of other volatile compounds such as 2-propanol and 1-butanol, than control cheese. In addition, cheese made with the bacteriocin producer did not show any late blowing symptoms, despite its spore counts similar to those of blown cheese, pointing to outgrowth inhibition of C. beijerinckii spores by bacteriocins. Besides, cheese made with the bacteriocin producer showed similar concentrations of lactic acid and volatile compounds than control cheese. Inclusion of L. lactis subsp. lactis INIA 415 in starter cultures seems a feasible method to prevent late blowing defect in cheese without altering its sensory characteristics. 相似文献
89.
Ana Teresa SerraAna A. Matias Ana P.C. AlmeidaM.R. Bronze Paula M. Alves Hermínio C. de SousaCatarina M.M. Duarte 《The Journal of Supercritical Fluids》2011,55(3):1007-1013
In the last years, there has been a growing interest in the recovery of bioactive compounds from natural sources for the development of novel functional foods.In this study, natural extracts, previously obtained by fractioned high pressure extraction from “Saco” cherry culls, were characterized in terms of anticancer activity. The product derived from CO2:EtOH (90:10, v/v) extraction after a pre-treatment of raw material with supercritical CO2 during 1 h, exhibited the highest antiproliferative activity in human HT29 colon cancer cells. In addition, when compared with doxorubicin, cherry extracts induced cell cycle arrest in a different cell cycle checkpoint.In order to obtain extracts with enhanced antiproliferative activity, the extraction process was further explored. Using highly pure CO2 and EtOH 96% the inhibition of cancer cell growth was significantly enhanced by 16-fold. In addition, the incorporation of a conventional extraction step with MetOH or EtOH:H2O (50:50, v/v) prior to fractioned process allowed to obtain cherry extracts more concentrated in antiproliferative compounds. Perillyl alcohol present in cherry extracts was pointed to be one of the major responsible for anticancer properties of cherry extracts. 相似文献
90.
Urdampilleta M Nguyen NV Cleuziou JP Klyatskaya S Ruben M Wernsdorfer W 《International journal of molecular sciences》2011,12(10):6656-6667
We built new hybrid devices consisting of chemical vapor deposition (CVD) grown carbon nanotube (CNT) transistors, decorated with TbPc(2) (Pc = phthalocyanine) rare-earth based single-molecule magnets (SMMs). The drafting was achieved by tailoring supramolecular π-π interactions between CNTs and SMMs. The magnetoresistance hysteresis loop measurements revealed steep steps, which we can relate to the magnetization reversal of individual SMMs. Indeed, we established that the electronic transport properties of these devices depend strongly on the relative magnetization orientations of the grafted SMMs. The SMMs are playing the role of localized spin polarizer and analyzer on the CNT electronic conducting channel. As a result, we measured magneto-resistance ratios up to several hundred percent. We used this spin valve effect to confirm the strong uniaxial anisotropy and the superparamagnetic blocking temperature (T(B) ~ 1 K) of isolated TbPc(2) SMMs. For the first time, the strength of exchange interaction between the different SMMs of the molecular spin valve geometry could be determined. Our results introduce a new design for operable molecular spintronic devices using the quantum effects of individual SMMs. 相似文献