全文获取类型
收费全文 | 1167篇 |
免费 | 72篇 |
专业分类
电工技术 | 18篇 |
化学工业 | 309篇 |
金属工艺 | 7篇 |
机械仪表 | 17篇 |
建筑科学 | 45篇 |
能源动力 | 41篇 |
轻工业 | 139篇 |
水利工程 | 18篇 |
无线电 | 113篇 |
一般工业技术 | 184篇 |
冶金工业 | 180篇 |
原子能技术 | 16篇 |
自动化技术 | 152篇 |
出版年
2024年 | 3篇 |
2023年 | 8篇 |
2022年 | 66篇 |
2021年 | 62篇 |
2020年 | 30篇 |
2019年 | 26篇 |
2018年 | 36篇 |
2017年 | 31篇 |
2016年 | 32篇 |
2015年 | 35篇 |
2014年 | 58篇 |
2013年 | 69篇 |
2012年 | 65篇 |
2011年 | 52篇 |
2010年 | 49篇 |
2009年 | 52篇 |
2008年 | 52篇 |
2007年 | 35篇 |
2006年 | 37篇 |
2005年 | 29篇 |
2004年 | 33篇 |
2003年 | 33篇 |
2002年 | 27篇 |
2001年 | 19篇 |
2000年 | 10篇 |
1999年 | 28篇 |
1998年 | 57篇 |
1997年 | 36篇 |
1996年 | 31篇 |
1995年 | 17篇 |
1994年 | 17篇 |
1993年 | 11篇 |
1992年 | 12篇 |
1991年 | 4篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 8篇 |
1974年 | 2篇 |
排序方式: 共有1239条查询结果,搜索用时 31 毫秒
101.
Enrico Maccallini Theodoros Tsoufis Salvatore La Rosa Gennaro Chiarello Vincenzo Formoso Raffaele G. Agostino 《Carbon》2010,48(12):3434-3445
Fe-Co bimetallic catalysts supported on MgO were studied for the catalytic chemical vapor deposition growth of carbon nanotubes (CNTs). Different wt.% metal loadings were investigated at various deposition temperatures and times. Characterization of the products involved thermal analysis (DTA-TGA), X-ray diffraction, spectroscopy (Raman, UPS, EELS and STS) and microscopy (SEM, TEM and STM) techniques. It was found that the metal content is critical, not only to the yield and the structural quality of the synthesized carbon nanotubes, but it can be also used to tune the desired type of synthesized nanotubes. Lower (2 wt.%) loadings of Fe-Co catalysts favor the formation of single- and/or double-wall CNTs for deposition time and temperature 30 min and 800 °C, respectively. Thermal analysis and Raman measurements showed that these thin CNTs were synthesized at high amounts (CNT-per-catalyst wt.% of more than 100%), exhibiting high graphitization degree with only traces of by-products (mainly amorphous carbon) among them. Microscopy results revealed the formation of CNTs bundles, consisting of individual nanotubes with less than 2 nm outer diameter, while additional energy loss measurements pointed out that the deposited CNTs are mainly single wall. Higher (10 wt.%) Fe-Co loadings resulted to the formation of multi-wall CNTs. 相似文献
102.
Yi‐Kai Fang Cheng‐Liang Liu Chaoxu Li Chih‐Jung Lin Raffaele Mezzenga Wen‐Chang Chen 《Advanced functional materials》2010,20(18):3012-3024
Novel donor–acceptor rod–coil diblock copolymers of regioregular poly(3‐hexylthiophene) ( P3HT )‐block‐poly(2‐phenyl‐5‐(4‐vinylphenyl)‐1,3,4‐oxadiaz‐ole) ( POXD ) are successfully synthesized by the combination of a modified Grignard metathesis reaction ( GRIM ) and atom transfer radical polymerization ( ATRP ). The effects of the block ratios of the P3HT donor and POXD pendant acceptor blocks on the morphology, field effect transistor mobility, and memory device characteristics are explored. The TEM, SAXS, WAXS, and AFM results suggest that the coil block fraction significantly affects the chain packing of the P3HT block and depresses its crystallinity. The optical absorption spectra indicate that the intramolecular charge transfer between the main chain P3HT donor and the side chain POXD acceptor is relatively weak and the level of order of P3HT chains is reduced by the incorporation of the POXD acceptor. The field effect transistor (FET) hole mobility of the system exhibits a similar trend on the optical properties, which are also decreased with the reduced ordered P3HT crystallinity. The low‐lying highest occupied molecular orbital (HOMO) energy level (–6.08 eV) of POXD is employed as charge trap for the electrical switching memory devices. P3HT‐ b ‐POXD exhibits a non‐volatile bistable memory or insulator behavior depending on the P3HT / POXD block ratio and the resulting morphology. The ITO/ P3HT44 ‐b‐ POXD18 /Al memory device shows a non‐volatile switching characteristic with negative differential resistance (NDR) effect due to the charge trapped POXD block. These experimental results provide the new strategies for the design of donor‐acceptor rod‐coil block copolymers for controlling morphology and physical properties as well as advanced memory device applications. 相似文献
103.
104.
Structure-activity relationship study of 16 a-thiocamptothecins: an integrated in vitro and in silico approach 总被引:1,自引:0,他引:1
Samorì C Beretta GL Varchi G Guerrini A Di Micco S Basili S Bifulco G Riccio R Moro S Bombardelli E Zunino F Fontana G 《ChemMedChem》2010,5(12):2006-2015
The instability of the hydroxylactone E ring represents a critical drawback of camptothecins, because the lactone ring is recognized to be essential for stabilization of topoisomerase I‐mediated DNA cleavage. In an attempt to investigate the effect of the thiopyridone pharmacophofore on the molecular and pharmacological features of the drug, we prepared a series of novel 16 a‐thiocamptothecin analogues. Due to the sulfur atom, a destabilization of the hydrogen bond between the hydroxy group in position 17 of the opened E ring and the carbonyl of the pyridone moiety is predicted, thus shifting the equilibrium toward the closed lactone form and increasing the lipophilic properties of the compounds. This feature was associated with superior antiproliferative potency, with reduced interaction with the human serum albumin and with substantial increase of the persistence of the topoisomerase I–DNA cleavable complex. These effects were prominent for thio‐SN38, the most active compound of the series. The favorable interactions at the molecular and cellular level of the reported thiocamptothecins confer promising features, and these compounds warrant preclinical development. 相似文献
105.
Arturo Di Fraia Edoardo Miliotti Andrea Maria Rizzo Giulia Zoppi Giuseppe Pipitone Raffaele Pirone Luca Rosi David Chiaramonti Samir Bensaid 《American Institute of Chemical Engineers》2023,69(1):e17652
Lignin-rich stream from lignocellulosic ethanol production was converted into biocrude by continuous hydrothermal liquefaction (HTL) while hydrogen was produced by aqueous phase reforming (APR) of the HTL aqueous by-product. The effects of Na2CO3 and NaOH were investigated both in terms of processability of the feedstock as well as yield and composition of the obtained products. A maximum biocrude yield of 27 wt% was reached in the NaOH-catalyzed runs. A relevant amount of dissolved phenolics were detected in the co-produced aqueous phase (AP), and removed by liquid–liquid extraction using butyl acetate or diethyl ether, preserving the APR catalyst stability and reaching an hydrogen yield up to 146 mmol H2 L−1 AP. Preliminary mass balances integrating HTL and APR showed that the hydrogen provided by APR may account for up to 46% of the hydrogen amount theoretically required for upgrading the HTL biocrude, thus significantly improving the process performance and sustainability. 相似文献
106.
Juliana Mendes de Oliveira Iara Alves Anes Jorge Luís Coleti Denise Crocce Romano Espinosa Marcelo Siqueira de Carvalho Jorge Alberto Soares Tenório 《加拿大化工杂志》2023,101(4):1743-1761
Niobium (Nb) and Tantalum (Ta) are used to increase materials' mechanical resistance and produce lighter alloys. Worldwide Nb production reached 78 000 t in 2020. The reduced ore offer justifies the recycling of these metals from tin slag, contributing to the circular economy. Nb2O5 and Ta2O5 extraction either from the primary source or the tin slag is an industrial challenge. Nb and Ta dissolution processes already implemented are fluoride leaching, sulphuric leaching, alkaline leaching, and alkaline roasting. The fluoride process raises environmental concerns about waste control. The sulphuric method can be managed to have higher Nb and Ta extraction in a less aggressive process, if some changes are implemented, such as increasing the number of extraction steps, decreasing the pulp density, or increasing the temperature; however, the efficiency of this methodology must be tested for tin slag. The alkaline method seems to be more selective to Nb and Ta by reactants and temperature control. Despite those well-established Nb and Ta treatments, they must be adapted to recover Nb and Ta from slag. The slag has low Nb and Ta content, while high Si and Ca concentrations exist in the matrix. This paper brings the main methods used to extract the Nb and Ta from the primary resources and an overview of Nb and Ta recovery from the slag. This investigation comes as a tool to guide the development of new methods to recover Nb and Ta from low-grade sources such as tin slag. 相似文献
107.
Dr. Erik Strandberg Dr. Parvesh Wadhwani Dr. Jochen Bürck Dr. Patrick Anders Dr. Christian Mink Dr. Jonas van den Berg Raffaele A. M. Ciriello Dr. Manuel N. Melo Prof. Dr. Miguel A. R. B. Castanho Prof. Dr. Eduard Bardají Prof. Dr. Jakob P. Ulmschneider Prof. Dr. Anne S. Ulrich 《Chembiochem : a European journal of chemical biology》2023,24(4):e202200602
BP100 is a cationic undecamer peptide with antimicrobial and cell-penetrating activities. The orientation of this amphiphilic α-helix in lipid bilayers was examined under numerous conditions using solid-state 19F, 15N and 2H NMR. At high temperatures in saturated phosphatidylcholine lipids, BP100 lies flat on the membrane surface, as expected. Upon lowering the temperature towards the lipid phase transition, the helix is found to flip into an upright transmembrane orientation. In thin bilayers, this inserted state was stable at low peptide concentration, but thicker membranes required higher peptide concentrations. In the presence of lysolipids, the inserted state prevailed even at high temperature. Molecular dynamics simulations suggest that BP100 monomer insertion can be stabilized by snorkeling lysine side chains. These results demonstrate that even a very short helix like BP100 can span (and thereby penetrate through) a cellular membrane under suitable conditions. 相似文献
108.
Isabel Medina M. Jesús González Manuel Pazos Dorotea Della Medaglia Raffaele Sacchi José Manuel Gallardo 《European Food Research and Technology》2003,217(4):301-307
The ability of antioxidants obtained from natural sources to stabilise foodstuffs containing long n-3 fatty acids of marine origin has been determined. Food systems enriched in polyunsaturated fatty acids (PUFA) were: emulsified horse mackerel (Trauchurus trauchurus) muscle, fish oil-in-water emulsions (4% of n-3 PUFA) and fish oils (40% of n-3 PUFA). Rosemary leaves and extra virgin olive oil (EVO) were employed as sources of natural phenolic antioxidants. Both vegetable extracts were able to retard lipid oxidation in the different lipid systems. Rosemary extracts with a high content of carnosoic acid showed a significant synergism with fish proteins, by reinforcing their antioxidative effectiveness. Fish proteins and EVO-phenolics showed minor cooperative effects for inhibiting oxidation. The antioxidative partition into the different phases in the emulsified systems showed minor amounts of phenolics in the aqueous phases, except hydroxytyrosol and tyrosol, and a high adsorption on fish muscle.An erratum to this article can be found at 相似文献
109.
Ownership, Investment Policies and Funding Choices of Italian Water Utilities: An Empirical Analysis 总被引:2,自引:2,他引:0
Nowadays, the efficient management of water has become the focus of vast debate, both in the academic literature and in the practical and regulatory field. Due to the growing importance and scarcity of water resources, it has become crucial to better understand how to improve the organizational efficiency of water utilities. By adopting an accounting perspective and using statistical methods, this paper analyzes whether and to what extent investment and financial strategies differ among clusters of water utilities with different ownership structures. The paper focuses on the Italian water industry, a context considered particularly appropriate due to the coexistence of utilities with different ownership structures. The main results of the paper show that ownership affects the level of investment as well as the financial structure and costs of water utilities. The evidence provided by this study should encourage national governments and regulatory authorities to select water utilities with the greatest investment potential measured in terms of financial efficiency and effectiveness. 相似文献
110.
The study investigated the effect of wearing chipper knives on machine productivity, fuel consumption and particles size distribution. The test included two different tree species (poplar and pine), two tree parts (branches and logs) and two screen types (large and medium). Chip quality was defined by CEN international technical standards. Knife wear causes a significant reduction of chipping productivity and a remarkable increase of fuel consumption. The replacement of the standard wide mesh screen with a narrower screen has a similar effect, further decreasing productivity and increasing fuel consumption. For the same screen type and knife wear level, productivity and fuel consumption are the same for poplar and pine. Knife, tree species and tree part also have a significant impact on chip size distribution. Chips produced from logs always contain a smaller proportion of oversize particles and a higher proportion of accepts. For the same large mesh screen, poplar chips tend to be larger than pine chips and to contain a higher proportion of oversize particles. On the contrary, pine chips tend to be smaller and to contain a higher proportion of fines. The use of a narrower mesh screen on pine material does not seem to offer any significant reduction of oversize particles, whose presence is already very limited. Therefore, a standard large mesh screen should be used when chipping pine material. 相似文献