全文获取类型
收费全文 | 1572篇 |
免费 | 44篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 36篇 |
综合类 | 2篇 |
化学工业 | 453篇 |
金属工艺 | 33篇 |
机械仪表 | 15篇 |
建筑科学 | 88篇 |
矿业工程 | 8篇 |
能源动力 | 28篇 |
轻工业 | 254篇 |
水利工程 | 10篇 |
石油天然气 | 1篇 |
无线电 | 69篇 |
一般工业技术 | 223篇 |
冶金工业 | 242篇 |
原子能技术 | 7篇 |
自动化技术 | 149篇 |
出版年
2022年 | 23篇 |
2021年 | 32篇 |
2020年 | 22篇 |
2019年 | 28篇 |
2018年 | 21篇 |
2017年 | 14篇 |
2016年 | 30篇 |
2015年 | 29篇 |
2014年 | 35篇 |
2013年 | 52篇 |
2012年 | 49篇 |
2011年 | 65篇 |
2010年 | 57篇 |
2009年 | 44篇 |
2008年 | 47篇 |
2007年 | 57篇 |
2006年 | 45篇 |
2005年 | 35篇 |
2004年 | 38篇 |
2003年 | 35篇 |
2002年 | 33篇 |
2001年 | 14篇 |
2000年 | 28篇 |
1998年 | 33篇 |
1997年 | 36篇 |
1996年 | 26篇 |
1995年 | 23篇 |
1994年 | 29篇 |
1993年 | 26篇 |
1992年 | 39篇 |
1991年 | 19篇 |
1990年 | 31篇 |
1989年 | 21篇 |
1988年 | 14篇 |
1987年 | 24篇 |
1986年 | 14篇 |
1985年 | 29篇 |
1984年 | 24篇 |
1983年 | 24篇 |
1982年 | 16篇 |
1981年 | 25篇 |
1980年 | 14篇 |
1979年 | 13篇 |
1978年 | 24篇 |
1977年 | 16篇 |
1976年 | 18篇 |
1974年 | 13篇 |
1972年 | 15篇 |
1970年 | 14篇 |
1963年 | 13篇 |
排序方式: 共有1618条查询结果,搜索用时 15 毫秒
141.
On-road emissions of light-duty vehicles in europe 总被引:1,自引:0,他引:1
Weiss M Bonnel P Hummel R Provenza A Manfredi U 《Environmental science & technology》2011,45(19):8575-8581
For obtaining type approval in the European Union, light-duty vehicles have to comply with emission limits during standardized laboratory emissions testing. Although emission limits have become more stringent in past decades, light-duty vehicles remain an important source of nitrogen oxides and carbon monoxide emissions in Europe. Furthermore, persisting air quality problems in many urban areas suggest that laboratory emissions testing may not accurately capture the on-road emissions of light-duty vehicles. To address this issue, we conduct the first comprehensive on-road emissions test of light-duty vehicles with state-of-the-art Portable Emission Measurement Systems. We find that nitrogen oxides emissions of gasoline vehicles as well as carbon monoxide and total hydrocarbon emissions of both diesel and gasoline vehicles generally remain below the respective emission limits. By contrast, nitrogen oxides emissions of diesel vehicles (0.93 ± 0.39 grams per kilometer [g/km]), including modern Euro 5 diesel vehicles (0.62 ± 0.19 g/km), exceed emission limits by 320 ± 90%. On-road carbon dioxide emissions surpass laboratory emission levels by 21 ± 9%, suggesting that the current laboratory emissions testing fails to accurately capture the on-road emissions of light-duty vehicles. Our findings provide the empirical foundation for the European Commission to establish a complementary emissions test procedure for light-duty vehicles. This procedure could be implemented together with more stringent Euro 6 emission limits in 2014. The envisaged measures should improve urban air quality and provide incentive for innovation in the automotive industry. 相似文献
142.
The structure of polytetrafluoroethylene and polyethylene bonded tungsten carbide electrodes was varied by changing the ratio of the bonding agent to the catalyst, and by adding various amounts of fillers of a different type. Of the series of fillers used, good results were obtained with oxalic acid, ammonium chloride and ammonium nitrate. The effect of the filler was ascribed to its influence on the surface properties of the pore wall rather than to the rise in the porosity of the electrode. 相似文献
143.
FRP-strengthened RC slabs anchored with FRP anchors 总被引:1,自引:0,他引:1
An abundance of tests over the last two decades has shown the bending capacity of flexural members such as reinforced concrete (RC) beams and slabs to be enhanced by the bonding of fibre-reinforced polymer (FRP) composites to their tension face. The propensity of the FRP to debond, however, limits its effectiveness. Different types of anchorages have therefore been investigated in order to delay or even prevent debonding. The so-called FRP anchor, which is made from rolled fibre sheets or bundles of lose fibres, is particularly suitable for anchoring FRP composites to a variety of structural element shapes. Studies that assess the effectiveness of FRP anchors in anchoring FRP strengthening in flexural members is, however, limited. This paper in turn reports a series of tests on one-way spanning simply supported RC slabs which have been strengthened in flexure with tension face bonded FRP composites and anchored with different arrangements of FRP anchors. The load-deflection responses of all slab tests are plotted, in addition to selected strain results. The behaviours of the specimens including the failure modes are also discussed. The greatest enhancement in load and deflection experienced by the six slabs strengthened with FRP plates and anchored with FRP anchors was 30% and 110%, respectively, over the unanchored FRP-strengthened control slab. The paper also discusses the strategic placement of FRP anchors for optimal strength and deflection enhancement in FRP-strengthened RC slabs. 相似文献
144.
Effects of dietary supplementation of vitamins D(3) and E on quality characteristics of pigs and longissimus muscle antioxidative capacity 总被引:1,自引:0,他引:1
Lahucky R Bahelka I Kuechenmeister U Vasickova K Nuernberg K Ender K Nuernberg G 《Meat science》2007,77(2):264-268
The effects of addition of vitamin D3 and vitamin E to pig diets on blood plasma calcium concentration, meat quality (longissimus muscle) and antioxidative capacity were investigated. Two treatments consisted of supplementation with vitamin D3 (500,000 IU/d) for 5 days separately (group D) and a combination of vitamin E (500 mg α-tocopheryl acetate/kg diet) for 30 days and vitamin D3 (500,000 IU/d) for 5 days (group D + E) to growing-finishing pigs before slaughter. Pigs fed with vitamin D3 had higher (P < 0.01) plasma calcium concentration compared with control pigs. Dietary supplementation of vitamin E significantly (P < 0.05) increased the concentration of α-tocopherol in meat (longissimus muscle). Vitamin D3 supplementation resulted in higher (P = 0.07) a∗ values of loin chops at 5 days of storage. Vitamin D3 and vitamin E supplementation did not affect other meat quality characteristics or tenderness (quantified by Warner–Bratzler shear force). Antioxidative capacity (measured as MDA production after incubation of longissimus muscle homogenates with Fe2+/ascorbate) was improved by vitamin E and partly by vitamin D3 supplementation. 相似文献
145.
真菌毒素是某些真菌菌种在特定条件下产生的有毒次级代谢产物。研究发现多种真菌毒素的联合暴露可引起胎儿发育迟缓、胚胎停育甚至流产等胚胎发育毒性。目前,尚没有关于孕期真菌毒素暴露对宫内胎儿胚胎发育毒性的影响和生物监测情况的系统报道。因此,为预防和降低孕期真菌毒素暴露带来的危害,本文梳理了孕期传统真菌毒素如黄曲霉毒素、脱氧雪腐镰刀菌烯醇、玉米赤霉烯酮和新兴真菌毒素如交链孢毒素、白僵菌素和恩镰孢菌素等暴露引起的胚胎发育毒性,以及以生物标志物如暴露标志物和效应标志物为基础的生物监测技术的研究现状。 相似文献
146.
Nadine Kretschmer Christin Durchschein Antje Hufner Beate Rinner Birgit Lohberger Rudolf Bauer 《International journal of molecular sciences》2022,23(10)
Melanoma is a complex and heterogenous disease, displays the deadliest form of skin cancer, and accounts for approx. 80% of all skin cancer deaths. In this study, we reported on the synthesis and pharmacological effects of a novel shikonin derivative (SK119), which is active in a nano-molar range and exhibits several promising in vitro effects in different human melanoma cells. SK119 was synthesized from shikonin as part of our search for novel, promising shikonin derivatives. It was screened against a panel of melanoma and non-tumorigenic cell lines using XTT viability assays. Moreover, we studied its pharmacological effects using apoptosis and Western blot experiments. Finally, it was combined with current clinically used melanoma therapeutics. SK119 exhibited IC50 values in a nano-molar range, induced apoptosis and led to a dose-dependent increase in the expression and protein phosphorylation of HSP27 and HSP90 in WM9 and MUG-Mel 2 cells. Combinatorial treatment, which is highly recommended in melanoma, revealed the synergistic effects of SK119 with vemurafenib and cobimetinib. SK119 treatment changed the expression levels of apoptosis genes and death receptor expression and exhibited synergistic effects with vemurafenib and cobimetinib in human melanoma cells. Further research indicates a promising potential in melanoma therapy. 相似文献
147.
Jacek Slowik Günter Borchardt Christian Khler Rudolf Jeschar Reinhard Scholz 《国际钢铁研究》1990,61(7):302-311
In order to model heat transfer from the slab to the cooling agent in the continuous casting process the thermophysical properties of the surface layer must be taken into account. For this purpose thermal conductivities and thermal diffusivities of wustite as well as of two carbon steels were measured. The oxide scale growth for six steels was measured as a function of time and at temperatures between 900 and 1200°C in air and in steam. Complex heterogeneous oxide scales were examined by optical and scanning electron microscopy, by SIMS, as well as by Mössbauer spectroscopy. Segregation of alloying elements in the metal-oxide contact zone was found. Cracks due to thermal stresses result in spalling of the scale. Therefore, a straightforward use of the data for process modelling can principally not be recommended without restrictions. 相似文献
148.
Recent practice with electric arc furnaces has been the injection of oxygen through nozzle positioned on the bottom of the furnace. This type of furnace places certain requirements on bottom injection. To enable a constant coupling of the energy over the electrodes, a calm bath surface must be guaranteed. On the other hand, a good mixing of the bath is required to avoid any thermal lamination in the bath. The latter condition in particular is prerequisite for a maximum melting capacity. When judging the effect of the jet on the bath, it must be taken into account that the oxygen disintegrates directly after entering the bath and merely transfers its impulse to the liquid melt. This jet effect is described by the calculation method introduced below which is adjusted to the actual behaviour using simulation tests. In this connection, changes in the jet consistency caused by the formation of carbon monoxide have not yet been considered. Parallel to this, the mixing of the bath was determined by conductivity measurements. In these experiments, the bath level xf, the vessel diameter D and the blown-in water mass-flux mw were changed. A comparison of the results for fountain height and mixing time formed the basis for the development of an optimization concept for bottom-blowing nozzles in electric arc furnaces. 相似文献
149.
By extending earlier stress-resistance research with a 1-yr time lag, findings with 254 adults show that adaptive personality characteristics and positive family support operate prospectively over 4 yrs in predicting reduced depression even when prior depression is controlled. By strengthening knowledge about the determinants and mediational role of coping, the results demonstrate in a 2-group LISREL analysis that the pattern of predictive relations differs under high and low stressors. Under high stressors, personal and social resources relate to future psychological health indirectly, through more adaptive coping strategies. Under low stressors, these resources relate directly to psychological health. The results support the idea that such resources play a causal role in maintaining psychological health, and they suggest the potential for a general, adaptively oriented framework applicable to adjustment under both high and low stressors. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
150.
Stefan Filipp Yuji Hasegawa Rudolf Loidl Helmut Rauch 《Journal of research of the National Institute of Standards and Technology》2005,110(3):251-257
We present a split-beam neutron interferometric experiment to test the non-cyclic geometric phase tied to the spatial evolution of the system: the subjacent two-dimensional Hilbert space is spanned by the two possible paths in the interferometer and the evolution of the state is controlled by phase shifters and absorbers. A related experiment was reported previously by some of the authors to verify the cyclic spatial geometric phase. The interpretation of this experiment, namely to ascribe a geometric phase to this particular state evolution, has met severe criticism. The extension to non-cyclic evolution manifests the correctness of the interpretation of the previous experiment by means of an explicit calculation of the non-cyclic geometric phase in terms of paths on the Bloch-sphere. The theoretical treatment comprises the cyclic geometric phase as a special case, which is confirmed by experiment. 相似文献