全文获取类型
收费全文 | 8122篇 |
免费 | 1158篇 |
国内免费 | 443篇 |
专业分类
电工技术 | 1515篇 |
综合类 | 591篇 |
化学工业 | 1181篇 |
金属工艺 | 172篇 |
机械仪表 | 607篇 |
建筑科学 | 190篇 |
矿业工程 | 105篇 |
能源动力 | 186篇 |
轻工业 | 701篇 |
水利工程 | 67篇 |
石油天然气 | 379篇 |
武器工业 | 47篇 |
无线电 | 1196篇 |
一般工业技术 | 1595篇 |
冶金工业 | 128篇 |
原子能技术 | 287篇 |
自动化技术 | 776篇 |
出版年
2024年 | 18篇 |
2023年 | 170篇 |
2022年 | 236篇 |
2021年 | 300篇 |
2020年 | 325篇 |
2019年 | 292篇 |
2018年 | 296篇 |
2017年 | 357篇 |
2016年 | 423篇 |
2015年 | 390篇 |
2014年 | 543篇 |
2013年 | 621篇 |
2012年 | 574篇 |
2011年 | 655篇 |
2010年 | 406篇 |
2009年 | 450篇 |
2008年 | 441篇 |
2007年 | 467篇 |
2006年 | 410篇 |
2005年 | 316篇 |
2004年 | 321篇 |
2003年 | 276篇 |
2002年 | 187篇 |
2001年 | 155篇 |
2000年 | 167篇 |
1999年 | 124篇 |
1998年 | 101篇 |
1997年 | 112篇 |
1996年 | 102篇 |
1995年 | 74篇 |
1994年 | 65篇 |
1993年 | 51篇 |
1992年 | 42篇 |
1991年 | 58篇 |
1990年 | 32篇 |
1989年 | 22篇 |
1988年 | 17篇 |
1987年 | 16篇 |
1986年 | 13篇 |
1985年 | 22篇 |
1984年 | 20篇 |
1983年 | 14篇 |
1982年 | 27篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1959年 | 2篇 |
排序方式: 共有9723条查询结果,搜索用时 15 毫秒
21.
Natsuko Goda Kana Shimizu Yohta Kuwahara Takeshi Tenno Tamotsu Noguchi Takahisa Ikegami Motonori Ota Hidekazu Hiroaki 《International journal of molecular sciences》2015,16(7):15743-15760
Intrinsically disordered proteins (IDPs) that lack stable conformations and are highly flexible have attracted the attention of biologists. Therefore, the development of a systematic method to identify polypeptide regions that are unstructured in solution is important. We have designed an “indirect/reflected” detection system for evaluating the physicochemical properties of IDPs using nuclear magnetic resonance (NMR). This approach employs a “chimeric membrane protein”-based method using the thermostable membrane protein PH0471. This protein contains two domains, a transmembrane helical region and a C-terminal OB (oligonucleotide/oligosaccharide binding)-fold domain (named NfeDC domain), connected by a flexible linker. NMR signals of the OB-fold domain of detergent-solubilized PH0471 are observed because of the flexibility of the linker region. In this study, the linker region was substituted with target IDPs. Fifty-three candidates were selected using the prediction tool POODLE and 35 expression vectors were constructed. Subsequently, we obtained 15N-labeled chimeric PH0471 proteins with 25 IDPs as linkers. The NMR spectra allowed us to classify IDPs into three categories: flexible, moderately flexible, and inflexible. The inflexible IDPs contain membrane-associating or aggregation-prone sequences. This is the first attempt to use an indirect/reflected NMR method to evaluate IDPs and can verify the predictions derived from our computational tools. 相似文献
22.
Protective coatings from diethylphosphatoethyltriethoxysilane (DEPETS) have been deposited on different polymer substrates in a plasma discharge operated at atmospheric pressure. Plasma polymer chemistry and structure were characterized by means of Fourier transform infrared spectroscopy (FTIR), laser desorption ionization-mass spectrometry (LDI-MS), nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). A chemical structure of the plasma polymer has been proposed based on the coating molecular characterization. Coatings were deposited on polycarbonate (PC) and polyamide 6 (PA6) substrates. The flame retardant properties of coated substrate samples were assessed using cone calorimetry and compared to those of bare substrates. A significant increase in the time to ignition (TTI), up to +143%, was recorded after coating deposition due to the formation of a high-performance barrier layer at the surface of both polymer substrates. 相似文献
23.
AbstractThe knowledge of moisture content (MC) and drying stress are crucial parameters to control the drying process and maintain the quality of dried wood. Herein, we investigated the pattern of moisture transfer and stress development in Chinese fir during the high-temperature drying process. The MC in each layer of lumber was separated into bound water and free water via nuclear magnetic resonance (NMR), and the drying and residual stress were measured using prong test method. There was different MC in each layer along the thickness, resulting in an MC gradient that initially increased and then decreased, which is consistent with the trend of drying stress. The T21 peak indicating bound water shifted to the left especially when MC was below the fiber saturation point, signifying that the discharge of moisture became difficult with prolonged drying time. The ratio of bound water to free water was different in each layer, indicating that the moisture transfer was different along the thickness. Furthermore, the residual stress was greater than the corresponding drying stress though the disparity reduced gradually, which suggests that the MC gradient was the largest affecting factor for drying stress at high MC stages but decreased to some extent as the drying process continued. 相似文献
24.
《International Journal of Hydrogen Energy》2022,47(12):8155-8163
Interfaces of ferromagnetic transition metals such as Iron, Cobalt, and Nickel with non-magnetic palladium are of interest due to their unique magnetic and spintronic properties. These interfaces enable ferromagnetic resonance (FMR) based sensing of hydrogen gas. In the present work, we synthesized Fe3O4–Pd core-shell nanospheres via a one-pot synthesis method using the thermal decomposition of Fe3+ acetylacetonate in the presence of a reducing agent to produce the Fe3O4 core, followed by the reduction of a Pd2+ precursor to form the pure Pd shell. We found that our in-situ synthesized core-shell nanostructure is magnetically active and shows excellent H2 gas sensing properties. The effect of reversible hydrogen gas absorption on the magnetism of Fe3O4–Pd core-shell nanospheres was investigated. The hydrogen-induced ferromagnetic-resonance (FMR) peak shift amounted to 30% of the peak linewidth for the virgin state of the sample. In addition, in the presence of hydrogen gas, we observed a fully reversible decrease in the FMR peak linewidth by about two times. This was accompanied by a nearly doubling of the FMR peak height. Response and recovery times of about 2 and 50 s, respectively, were extracted from the measurements. All the data was collected using a mix of just 3% hydrogen in a nitrogen carrier gas. 相似文献
25.
光降解乙醛(CH3CHO)是一种新型高效的乙醛去除方法,通常采用TiO2作为光催化剂。然而TiO2对乙醛吸附能力较弱,对产物的选择性较低,电子-空穴对重组率较高,严重限制了对乙醛的降解性能。本研究通过在TiO2上负载CuAg纳米粒子(CuAg/TiO2),成功构建了高效稳定的光催化降解乙醛催化剂,有效解决了TiO2的固有缺陷。在自然光照射下,CuAg/TiO2对乙醛的降解率高达42.49%。连续4轮全光谱光催化降解乙醛,CuAg/TiO2活性均保持在98.89%以上。进一步的机理研究表明,CuAg/TiO2中的CuAg纳米粒子在光照下产生热电子,随后热电子转移到TiO2和吸附在Ag位点上的氧中。CuAg/TiO2上生成的超氧自由基能有效地降解乙醛,从而在乙醛降解过程中表现出优异的性能。 相似文献
26.
Rémi Nguyen Mathilde Amouroux Alexis Duda Zéphirin Mouloungui 《Journal of the American Oil Chemists' Society》2020,97(7):679-689
The aim of this study was to develop an improved general method for detecting and quantifying mixtures of hydroxy acids and other products of glycerol oxidation in aqueous media, to prevent the confusions that can occur due to similarities and interactions between these compounds depending on media conditions. Standard potential products of glycerol oxidation—glycerol, glyceraldehyde, dihydroxyacetone, glyceric acid, lactic acid, glycolic acid, glyoxylic acid, oxalic acid, tartronic acid, and mesoxalic acid—were analyzed by high-performance liquid chromatography (HPLC) and quantitative 13C nuclear magnetic resonance (NMR), in mixtures of known composition. The results obtained were concordant with the known compositions tested. HPLC was more accurate than quantitative 13C NMR for simple mixtures, but 13C NMR was required for complex mixtures containing dihydroxyacetone and glycerol, oxalic acid and mesoxalic acid, or glyoxylic acid and tartronic acid, pairs of compounds not well separated or detected by HPLC. As proof-of-concept, an unknown mixture generated by glycerol oxidation was analyzed by HPLC and quantitative 13C NMR. The results obtained were concordant and allowed accurate determination of the composition of the sample, which contained mesoxalic acid as the major product, with oxalic acid, tartronic acid, and glyceric acid as by-products. 相似文献
27.
Martin G. Bakker Benjamin Fowler Michael K. Bowman Gregory S. Patience 《加拿大化工杂志》2020,98(8):1668-1681
Electron paramagnetic resonance (EPR) spectroscopy, also known as electron spin resonance spectroscopy (ESR), utilizes absorption of microwave radiation by unpaired electrons in a magnetic field. The interaction between the unpaired electron(s) and nearby magnetic nuclei helps identify paramagnetic species and can provide information about the motion of the molecule and the local polarity, pH, viscosity, concentration, and accessibility to other paramagnetic species. This mini-review discusses the fundamental underpinnings of EPR needed to correctly interpret EPR spectra. We describe various types of EPR spectra encountered by chemical engineers, and use application examples drawn from the chemical engineering literature to illustrate the information available from the technique. Few chemical engineering departments or even chemistry departments have EPR instruments, which contributes to the significant barrier that prevents this being adopted as a routine measurement technique. However, in 2016 and 2017, Web of Science indexed 7000 articles that applied EPR spectroscopy. A bibliometric map categorized the keywords in four categories based on co-occurrences: magnetic properties, films, and luminescence; crystal structure, complexes, and ligands; nanoparticles, oxidation, and degradation; and, systems, radicals, and H2 O2 . 相似文献
28.
《International Journal of Hydrogen Energy》2020,45(13):7779-7787
We report the application of plasmonic Bi nanoparticles supported rGO/BiVO4 anode for photoelectrochemical (PEC) water splitting. Nearly, 2.5 times higher activity was observed for Bi-rGO/BiVO4 composite than pristine BiVO4. Typical results indicated that Bi-rGO/BiVO4 exhibits the highest current density of 6.05 mA/cm2 at 1.23 V, whereas Bi–BiVO4 showed the current density of only 3.56 mA/cm2. This enhancement in PEC activity on introduction of Bi-rGO is due to the surface plasmonic behavior of BiNPs, which improves the absorption of radiation thereby reduces the charge recombination. Further, the composite electrode showed good solar to hydrogen conversion efficiency, appreciable incident photon-to-current efficiency and low charge transfer resistance. Hence, Bi-rGO/BiVO4 provides an opportunity to realize PEC water splitting. 相似文献
29.
《International Journal of Hydrogen Energy》2020,45(56):31963-31975
Three dimensional TiO2–Au cross-nanoporous structure (3D TiO2–Au CNS) as an efficient photoelectrocatalytic system was fabricated using superaligned carbon nanotube films as etching masks and electron-beam evaporation. The 3D TiO2–Au CNS exhibited a broad absorption band in the visible region, and the incident photon-to-current conversion efficiency of 3D TiO2–Au CNS/Ti electrode was 3–4 times higher than that of pure TiO2 electrode. The photocurrent density of the 3D TiO2–Au CNS device was 0.079 mA cm−2 at 0 V vs. Ag/AgCl with a solar irradiance of 100 mW cm−2. This developed preparation method was simple, of high flexibility and can be adopted for mass production due to its low cost and good compatibility with other processing technologies. The 3D TiO2–Au CNS and its preparation method have important value in design of photoelectrocatalytic system for research and practical applications, which may have a potential utility in photocatalytic and other photoelectrocatalytic reactions. 相似文献
30.
With an increase in awareness about the need for green chemistry, there is a shift in focus towards identifying eco-compatible technologies that can improve product yield and eliminate the use or generation of hazardous compounds. An immediate practical example of such an approach is the development of sustainable methods for alcohol oxidation as alternatives to the current processes that are energy intensive and rely on ecotoxic chemicals. In this regard, heterogeneous photocatalysis has been identified as a robust technique to catalyze reactions under benign conditions, which would otherwise require harsh synthesis routes. With the advent of materials sciences and nanotechnology, there has been a tremendous increase in the scope of applicability of photocatalysis in fine chemicals synthesis. Though an attractive choice, much of the fundamental information pertaining to catalyst activity, selectivity and reaction conditions for optimum conversion are still to be investigated for most of these systems. To this end, this review will encompass recent achievements in the selective photocatalytic oxidation of alcohols by harnessing solar radiation as a viable source of energy. The discussion will be arranged based on common types of photocatalysts reported in literature, namely metal oxides (eg, TiO2 and ZnO, Nb2O5), sulphides (eg, CdS, CuS, and Bi2S3), and carbonaceous photocatalysts (eg, g-C3N4). Several such candidates for photocatalysts will be discussed critically with the aim of providing useful insight into developing selective photocatalysts that can oxidize alcohols via eco-friendly pathways along with high yields. 相似文献