全文获取类型
收费全文 | 5123篇 |
免费 | 391篇 |
国内免费 | 158篇 |
专业分类
电工技术 | 96篇 |
综合类 | 302篇 |
化学工业 | 1630篇 |
金属工艺 | 196篇 |
机械仪表 | 91篇 |
建筑科学 | 256篇 |
矿业工程 | 118篇 |
能源动力 | 192篇 |
轻工业 | 1516篇 |
水利工程 | 71篇 |
石油天然气 | 162篇 |
武器工业 | 7篇 |
无线电 | 160篇 |
一般工业技术 | 457篇 |
冶金工业 | 141篇 |
原子能技术 | 86篇 |
自动化技术 | 191篇 |
出版年
2024年 | 17篇 |
2023年 | 56篇 |
2022年 | 106篇 |
2021年 | 125篇 |
2020年 | 142篇 |
2019年 | 161篇 |
2018年 | 142篇 |
2017年 | 187篇 |
2016年 | 147篇 |
2015年 | 192篇 |
2014年 | 246篇 |
2013年 | 378篇 |
2012年 | 348篇 |
2011年 | 413篇 |
2010年 | 325篇 |
2009年 | 324篇 |
2008年 | 272篇 |
2007年 | 340篇 |
2006年 | 261篇 |
2005年 | 224篇 |
2004年 | 197篇 |
2003年 | 190篇 |
2002年 | 161篇 |
2001年 | 83篇 |
2000年 | 94篇 |
1999年 | 82篇 |
1998年 | 68篇 |
1997年 | 50篇 |
1996年 | 47篇 |
1995年 | 47篇 |
1994年 | 31篇 |
1993年 | 33篇 |
1992年 | 36篇 |
1991年 | 26篇 |
1990年 | 21篇 |
1989年 | 16篇 |
1988年 | 18篇 |
1987年 | 16篇 |
1986年 | 5篇 |
1985年 | 15篇 |
1984年 | 13篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有5672条查询结果,搜索用时 296 毫秒
121.
Zhuangzhuang Chang Lianjie Zhu Jian Zhao Peiwen Chen Deyou Chen Hongjia Gao 《International Journal of Hydrogen Energy》2021,46(5):3493-3503
We designed and fabricated non-precious and highly efficient electrocatalysts of nickelmolybdenum/copper-nanosheets/nickel-foam composites (NiMo/Cu-NS/NF) by step electrodepositions, combining with chemical oxidation method. The catalysts were charaterized by means of SEM, XRD and XPS spectra. Their electrocatalytic activities were assessed by hydrogen evolution reactions (HER) over a wide pH range, where acidic, neutral and alkaline electrolytes were used, respectively. Benefiting from the unique midlayer Cu nanosheets (NS) architecture and optimum Mo–Ni composition at the surface layer which led to high electronic conductivity and large electrochemically active surface area (ECSA), the NiMo/Cu-NS/NF-2 catalyst displayed superior electrocatalytic activities with low overpotentials of η10 = 43, 86 and 89 mV in 0.5 M H2SO4, 1.0 M PBS and 1.0 M KOH electrolyte, respectively. Especially in the acidic condition, it exhibited the best electrocatalytic activity with smaller Tafel slope of 54 mV dec?1 and higher exchange current density of 1.93 mA cm?2. 相似文献
122.
Yi‐Shen Zhu Alan Connolly Anders Guyon Richard J. FitzGerald 《International Journal of Food Science & Technology》2014,49(6):1600-1606
Marine minerals are a potential source of calcium and magnesium for nutritional supplementation. This study analysed the solubilisation of calcium and magnesium from the skeletal remains of Lithothamnion calcareum. Scanning electron microscopy analysis demonstrated a nonporous microstructure. Spectrophotometric determination showed that the calcium and magnesium contents were 30.01 and 6.22% (w/w), respectively. Solubilisation of calcium and magnesium was highly pH dependent. The temperature‐dependent solubilisation of calcium fitted the shrinking core model. The apparent activation energy for calcium solubilisation was 28.6 kJ mol?1. Inclusion of caseinophosphopeptides (CPPs), casein‐derived mineral binding peptides, during the solubilisation of calcium and magnesium appeared to decrease the extent of calcium solubilisation at pH 6.0 and 8.0. The results herein have implications for the choice of optimal pH conditions for the sustained release of calcium and magnesium from marine mineral sources. 相似文献
123.
Zwitterion (Z) monomer 3‐[diallyl{3‐(diethoxyphosphoryl)propyl}ammonio]propane‐1‐sulfonate underwent cyclocopolymerization with sulfur dioxide to give a new alternating copolymer poly(Z‐alt‐SO2) in excellent yield (ca 90%). The polyzwitterion (±) (PZ) (i.e. poly(Z‐alt‐SO2), bearing a diethylphosphonate as well as a sulfonate functionality in each repeat unit, upon ester hydrolysis gave its corresponding pH‐responsive polyzwitterionic acid (±) (PZA). The pH‐induced equilibrations (+) cationic polyelectrolyte ? (±) PZA ? polyzwitterion/anion (± ?) (PZAN) ? polyzwitterion/dianion (± =) (PZDAN) permitted us to examine the effects of charge types and their densities on the interesting solubility and viscosity behaviours. The apparent protonation constants of the basic functionalities &tbond;N±PO32? in (± =) PZDAN and &tbond;N±PO3H1? in (± ?) PZAN in salt‐free water and 0.1 mol L?1 NaCl were determined using potentiometric titrations. (±) PZA at a meagre concentration of 20 ppm was found to be an effective antiscalant to inhibit the precipitation of CaSO4 from its supersaturated solution: after 500 and 800 min, the respective scale inhibitions of 86 and 98% indicated its potential use as an effective antiscalant in reverse osmosis plant. © 2014 Society of Chemical Industry 相似文献
124.
Cuicui Ding Min Zhang Miao Ma Jiaojiao Zheng Qili Yang Ren Feng 《Polymer International》2019,68(8):1468-1477
Hydrogels with environment‐sensitive properties have great potential applications in the controlled drug release field. In this paper, hybrid hydrogels with semi‐interpenetrating polymer networks (semi‐IPNs), composed of poly(N‐isopropylacrylamide) (PNIPAM) as the thermo‐sensitive component by in situ polymerization and self‐assembled collagen nanofibrils as the pH‐sensitive framework, were prepared for controlled release of methyl violet as a model drug. From Fourier transform infrared spectroscopy and scanning electron microscopy, it was indicated that the crosslinking of PNIPAM in the presence of collagen nanofibrils led to the formation of semi‐IPNs with homogeneous porous structure, and the semi‐IPNs showed improved thermal stability and elastic properties compared with the native collagen as determined using differential scanning calorimetry and rheologic measurements. Furthermore, the semi‐IPNs possessed swelling behaviors quite different from those of neat collagen or PNIPAM hydrogel under various pH values and temperatures. Correspondingly, as expected, the drug release behavior in vitro for semi‐IPNs performed variously compared with that for single‐component semi‐IPNs, which revealed the tunable performance of semi‐IPNs for release ability. Finally the thermo‐ and pH‐responsive mechanism of the semi‐IPNs was illuminated to provide guidance for the application of the thermo‐ and pH‐sensitive collagen‐based hybrid hydrogels in controlled drug delivery systems. © 2019 Society of Chemical Industry 相似文献
125.
Yunyan Bai Zhe Zhang Mingxiao Deng Li Chen Chaoliang He Xiuli Zhuang Xuesi Chen 《Polymer International》2012,61(7):1151-1157
Microgel particles were prepared, made of hydroxypropylcellulose‐graft‐(acrylic acid) (HPC‐g‐AA) and acrylic acid(AA). The particles undergo reversible volume phase transitions in response to both pH and temperature changes while keeping the inherent properties of PAA and HPC‐g‐AA. Dynamic light scattering measurements reveal that the average hydrodynamic radius and hydrodynamic radius distributions of the microgel particles depend on temperature and pH. The microgels exhibit excellent pH sensitivity and a higher swelling ratio at higher pH in aqueous solution. In vitro release study shows that the amount of insulin released from the microgels is less at pH = 1.2 than at pH = 6.8. The results indicate that the resultant microgels seem to be of great potential for intelligent oral drug delivery. Copyright © 2012 Society of Chemical Industry 相似文献
126.
Cheng Cheng Hu Apostolos Giannis Chia-Lung Chen Jing-Yuan Wang 《International Journal of Hydrogen Energy》2014
In order to enhance bio-hydrogen production from food waste, pretreatment methods are widely used. The influence of the initial pH and autoclaving were investigated in batch experiments. Fermentative studies showed that pure cultures like Clostridium beijerinckii could directly utilize raw food waste to produce hydrogen, while other cultures (Clostridium butyricum and Clostridium pasteurianum) could produce hydrogen only after pH adjustment. In this case, the optimal starting pH of the culture was found to be 7. Autoclaving could further enhance hydrogen yields due to increased hydrolysis of food waste. The maximum hydrogen yield was achieved by C. butyricum (38.9 mL-H2/g-VSadded) after autoclaving food waste with pH adjustment at 7. In addition, the ratio acetic to butyric acid was decreased by autoclaving pretreatment, because butyrate metabolic pathway was favored in the fermentation process. However, suitable pH for bacteria growth and the low ammonia production could be achieved from autoclaving food waste. 相似文献
127.
《分离科学与技术》2012,47(11):2491-2509
Abstract Exchanged clays and cross-linked algae were compared based on their properties for the removal of phenol from aqueous solutions. Algae Lessonia nigrescens Bory (A1) and Macrocystis integrifolia Bory (A2) were cross-linked with CaCl2 to enhance their physical and mechanical properties. The natural clays were chemically-exchanged with salts of tetramethyl ammonium (B1), hexadecyltrimethyl ammonium (B2), and bencyltriethyl ammonium (B3) ions to increase their affinity towards organic substrates. The effects of pH and adsorbent dose were evaluated. pH exhibited a strong effect mainly on the phenol aqueous chemistry. Sorption isotherm results were modelled on the Langmuir and Freundlich equations and complemented with EDX analysis, indicating that adsorption of phenol from water was mostly driven by hydrophobic forces, with the exchanged bentonites being the adsorbents that reported the maximum adsorption capacities. Conversely, a polar surface adsorption is suggested for algae mostly by means of hydrogen bonding formation. These results provide further insight into the adsorption mechanism of phenol and analogues and their use as powerful and cheap adsorbent for the treatment of phenol-containing real wastewater. 相似文献
128.
《International Journal of Hydrogen Energy》2022,47(95):40264-40274
Hydrogen (H2) metabolism in Escherichia coli occurs via reversible membrane-associated hydrogenase enzymes (Hyd). Hyd-3 and Hyd-4 with formate dehydrogenase H (FDH-H) form formate hydrogen lyase complexes. The changes of metabolic pathways and ΔpH (pHin-pHex) regulation during fermentation of glucose, glycerol and formate in non H2-producing hypF (lack of all Hyds) and fdhF (lack of FDH-H) mutants at pH 7.5 were investigated. It was shown that specific growth rate was higher by ~23% in hypF and fdhF, compared to wild type (wt), suggesting the negative effect of H2 on bacterial growth. Moreover, it was shown that H2 generation did not have a vital role in glucose and glycerol utilization rate at 0–72 h. The utilization of external formate was detected in wt (~2.6 mM) and hypF (~0.68 mM), but not in fdhF, due to the absence of enzyme responsible for formate metabolism. Nevertheless, the changes in ΔpH were not evident at 3 h. The ratio of generated end-products and regulation of ΔpH at late log (6 h) and exponential phase (24, 72 h) were various in hypF and fdhF due to formate disproportionation in hypF and proton generation, therewith absence of H2 generation. Taken together it can be concluded that bacteria regulate generation of fermentation end-products via balancing the concentration of acids and ethanol to maintain ΔpH and redox potential values. The results obtained are important for development and regulation of H2 production technology when applying mixed carbon sources. 相似文献
129.
《Advanced Powder Technology》2022,33(11):103816
Carbon quantum dots (CQD)-based nanosponges have been widely designed for tumor theranostic application recently. However, the drug content is usually lower with the shorter dynamic covalent linkers while the longer hydrophilic dynamic covalent linkers led to a significant premature drug leakage. Here, a hydrophobic linear reducible-responsive linker with two terminal aldehyde group was designed to crosslink the hydrazine-functionalized PEGylated CQDs (Hy-CQD-PEG), resulting in Hy-CQDss-PEG nanosponges. After doxorubicin (DOX) conjugation, the DOX-Hy-CQDss-PEG prodrug nanosponges were obtained with DOX content of 18.76 % and hydrodynamic diameter of 140 nm, respectively. The DOX-Hy-CQDss-PEG nanosponges were stable in the normal physiological medium with very low drug leakage and fluorescence, while they could disintegrate in the tumor intracellular microenvironment, releasing DOX and the hydrazine-functionalized CQDs for theranostic application. 相似文献
130.
《International Journal of Hydrogen Energy》2022,47(11):7214-7227
In this work, vertically aligned β-Bi2O3 nanosheet arrays are deposited on FTO using a simple, cost-effective, low-temperature, and easy-tunable technique called chemical bath deposition. Coatings were deposited through selective correlation of varying bismuth ion concentrations at fixed pH and, also, a fixed bismuth ion concentration at different pH values to optimize their structure, morphology, and optical properties. With an increase in bismuth precursor concentration from 0.008 M to 0.5 M, a more crystallized and compact coating with finer nanosheets was formed. Low pH values tended to result in either no coating or a coating composed of discrete particles. As the pH increased to the optimal level, a thicker and more compact coating with a morphology made of thicker and wider nanosheets was formed. Further increase in pH led to a non-uniform coating composed of small and large nanosheets that could not cover the entire surface of the substrate. The optimized photoelectrode exhibited a maximum photocurrent density of 470 μA/cm2 at 1.23 VRHE under 100 mW/cm2 simulated sunlight, which is among the top recorded values of Bi2O3 photoelectrodes. 相似文献