全文获取类型
收费全文 | 13168篇 |
免费 | 1427篇 |
国内免费 | 599篇 |
专业分类
电工技术 | 116篇 |
综合类 | 900篇 |
化学工业 | 4770篇 |
金属工艺 | 3666篇 |
机械仪表 | 275篇 |
建筑科学 | 454篇 |
矿业工程 | 509篇 |
能源动力 | 103篇 |
轻工业 | 835篇 |
水利工程 | 64篇 |
石油天然气 | 396篇 |
武器工业 | 109篇 |
无线电 | 152篇 |
一般工业技术 | 1637篇 |
冶金工业 | 1148篇 |
原子能技术 | 40篇 |
自动化技术 | 20篇 |
出版年
2024年 | 23篇 |
2023年 | 196篇 |
2022年 | 325篇 |
2021年 | 407篇 |
2020年 | 402篇 |
2019年 | 360篇 |
2018年 | 389篇 |
2017年 | 478篇 |
2016年 | 456篇 |
2015年 | 509篇 |
2014年 | 769篇 |
2013年 | 759篇 |
2012年 | 996篇 |
2011年 | 1099篇 |
2010年 | 853篇 |
2009年 | 835篇 |
2008年 | 663篇 |
2007年 | 938篇 |
2006年 | 1015篇 |
2005年 | 737篇 |
2004年 | 634篇 |
2003年 | 469篇 |
2002年 | 394篇 |
2001年 | 300篇 |
2000年 | 254篇 |
1999年 | 198篇 |
1998年 | 135篇 |
1997年 | 104篇 |
1996年 | 98篇 |
1995年 | 73篇 |
1994年 | 70篇 |
1993年 | 50篇 |
1992年 | 38篇 |
1991年 | 39篇 |
1990年 | 29篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 14篇 |
1986年 | 9篇 |
1985年 | 8篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1962年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Alessio Zandona Bernd Rüdinger Joachim Deubener 《Journal of the American Ceramic Society》2021,104(2):1146-1155
Glass powder samples of cordierite composition (doped with 8 mol% TiO2) were heat-treated to produce a series of increasingly SiO2-enriched Mg-bearing quartz solid solutions (Qss). The obtained materials were then analyzed by X-ray diffraction: Rietveld structural refinements revealed that Mg-bearing Qss phases possess trigonal symmetry and a compositionally dependent intermediate structural arrangement between those of low and high quartz. High-temperature diffraction measurements were performed up to 700°C to characterize the thermal expansion behavior of the crystals. At SiO2-rich compositions, a reversible high-to-intermediate inversion of the quartz structure is observed, which shifts with increasing stuffing to lower temperatures than the conventional 573°C for pure quartz. Similarities and differences to the better-established Li-bearing Qss are discussed in the text. 相似文献
2.
3.
A superhydrophobic ceria-based composite coating is developed to improve anticorrosion properties of AZ61 magnesium alloy, fabricating via chemical conversion method followed by hydrothermal treatment. The cerium conversion coating has a block structure with microcracks. After the hydrothermal treatment, a dense CeO2 layer, porous CeO2 nanorods, and stearic absorbing layers are grown stepwise on the conversion coating. And the composite coating is hydrophobic or even superhydrophobic and has almost no microcracks. As the hydrothermal reaction time increases, the water contact angle of the composite coating first increases and then decreases, and it reaches the maximum value of 152° after hydrothermal treatment for 4 h. Both the dense CeO2 layer and the superhydrophobic stearic absorbing layer can effectively prevent the electrolyte from contacting the substrate; the corrosion current density of the superhydrophobic composite coating is lower than that of the hydrophilic composite coating and the cerium conversion coating, and has the best corrosion resistance. 相似文献
4.
《International Journal of Hydrogen Energy》2022,47(42):18566-18575
In this study, a sulfidogenic reactor fed with microalgal biomass of Chlorella pyrenoidosa as an electron donor was operated in a continuous mode. This study evaluated the influence of various initial sulfate concentration from 1.0 to 2.5 g/L on anaerobic sulfate reduction kinetics by a sulfidogenic enrichment culture predominantly Desulfovibrio sp. VSV2. It was observed that volumetric sulfate reduction rate (VSRR) was consistently increasing with an increase in volumetric sulfate loading rate (VSLR) across the retention time of 7–10 days. For a retention time of 7 days, the maximum VSRR was noted as 0.0050 g/(L.h) with a corresponding VSLR of 0.0089 g/(L.h). When retention time was maintained for 10 days, a maximum sulfate reduction of 65% and a maximum bacterial concentration of 1.632 g/L were achieved for an initial sulfate concentration of 1.5 g/L. It was concluded that VSLR facilitated through both dilution rate and initial sulfate concentration had a significant influence over sulfate reduction kinetics. The results of the study suggested that the microalgal-fed sulfidogenic system could be effectively employed for reduction of sulfate from sulfate-rich wastewater. 相似文献
5.
Giulia Andreani Enea Ferlizza Riccardo Cabbri Micaela Fabbri Elisa Bellei Gloria Isani 《International journal of molecular sciences》2021,22(1)
The recent introduction of the Asian yellow-legged hornet, Vespa velutina, into Europe has raised concern regarding the threat to honeybees and the competition with the European hornet, Vespa crabro. The aim of this study was to investigated essential (Mg, Fe, Zn, Cu) and non-essential (Cd and Pb) elements in these two species. Element concentrations were determined in the whole body and separately in the head, thorax and abdomen using atomic absorption spectrometry (AAS). The changes in essential element concentration and speciation during metamorphosis were also studied using size exclusion chromatography followed by AAS and proteomic analysis. In both species, the essential elements were more concentrated in the abdomen due to the presence of fat bodies. Magnesium, Fe and Zn concentrations were significantly higher in V. crabro than in V. velutina and could have been related to the higher aerobic energy demand of the former species required to sustain foraging flight. Low concentrations of Cd and Pb were indicative of low environmental exposure. The concentration and speciation of essential elements, particularly Fe, varied among the developmental stages, indicating a modification of ligand preferences during metamorphosis. Overall, the results in the present study provide a better understanding of the hornet metal metabolism and a foundation for additional studies. 相似文献
6.
Cell surface proteoglycans are known to be important regulators of many aspects of cell behavior. The principal family of transmembrane proteoglycans is the syndecans, of which there are four in mammals. Syndecan-1 is mostly restricted to epithelia, and bears heparan sulfate chains that are capable of interacting with a large array of polypeptides, including extracellular matrix components and potent mediators of proliferation, adhesion and migration. For this reason, it has been studied extensively with respect to carcinomas and tumor progression. Frequently, but not always, syndecan-1 levels decrease as tumor grade, stage and invasiveness and dedifferentiation increase. This parallels experiments that show depletion of syndecan-1 can be accompanied by loss of cadherin-mediated adhesion. However, in some tumors, levels of syndecan-1 increase, but the characterization of its distribution is relevant. There can be loss of membrane staining, but acquisition of cytoplasmic and/or nuclear staining that is abnormal. Moreover, the appearance of syndecan-1 in the tumor stroma, either associated with its cellular component or the collagenous matrix, is nearly always a sign of poor prognosis. Given its relevance to myeloma progression, syndecan-1-directed antibody—toxin conjugates are being tested in clinical and preclinical trials, and may have future relevance to some carcinomas. 相似文献
7.
Ivan Kushkevych Blanka Hýov Monika Vítzov Simon K.-M. R. Rittmann 《International journal of molecular sciences》2021,22(8)
This paper is devoted to microscopic methods for the identification of sulfate-reducing bacteria (SRB). In this context, it describes various habitats, morphology and techniques used for the detection and identification of this very heterogeneous group of anaerobic microorganisms. SRB are present in almost every habitat on Earth, including freshwater and marine water, soils, sediments or animals. In the oil, water and gas industries, they can cause considerable economic losses due to their hydrogen sulfide production; in periodontal lesions and the colon of humans, they can cause health complications. Although the role of these bacteria in inflammatory bowel diseases is not entirely known yet, their presence is increased in patients and produced hydrogen sulfide has a cytotoxic effect. For these reasons, methods for the detection of these microorganisms were described. Apart from selected molecular techniques, including metagenomics, fluorescence microscopy was one of the applied methods. Especially fluorescence in situ hybridization (FISH) in various modifications was described. This method enables visual identification of SRB, determining their abundance and spatial distribution in environmental biofilms and gut samples. 相似文献
8.
Andreea-Mariana Negrescu Madalina-Georgiana Necula Adi Gebaur Florentina Golgovici Cristina Nica Filis Curti Horia Iovu Marieta Costache Anisoara Cimpean 《International journal of molecular sciences》2021,22(2)
Due to its excellent bone-like mechanical properties and non-toxicity, magnesium (Mg) and its alloys have attracted great interest as biomaterials for orthopaedic applications. However, their fast degradation rate in physiological environments leads to an acute inflammatory response, restricting their use as biodegradable metallic implants. Endowing Mg-based biomaterials with immunomodulatory properties can help trigger a desired immune response capable of supporting a favorable healing process. In this study, electrospun poly(ε-caprolactone) (PCL) fibers loaded with coumarin (CM) and/or zinc oxide nanoparticles (ZnO) were used to coat the commercial AZ31 Mg alloy as single and combined formulas, and their effects on the macrophage inflammatory response and osteoclastogenic process were investigated by indirect contact studies. Likewise, the capacity of the analyzed samples to generate reactive oxygen species (ROS) has been investigated. The data obtained by attenuated total reflection Fourier-transform infrared (FTIR-ATR) and X-ray photoelectron spectroscopy (XPS) analyses indicate that AZ31 alloy was perfectly coated with the PCL fibers loaded with CM and ZnO, which had an important influence on tuning the release of the active ingredient. Furthermore, in terms of degradation in phosphate-buffered saline (PBS) solution, the PCL-ZnO- and secondary PCL-CM-ZnO-coated samples exhibited the best corrosion behaviour. The in vitro results showed the PCL-CM-ZnO and, to a lower extent, PCL-ZnO coated sample exhibited the best behaviour in terms of inflammatory response and receptor activator of nuclear factor kappa-B ligand (RANKL)-mediated differentiation of RAW 264.7 macrophages into osteoclasts. Altogether, the results obtained suggest that the coating of Mg alloys with fibrous PCL containing CM and/or ZnO can constitute a feasible strategy for biomedical applications. 相似文献
9.
Recently, thermosensitive chitosan systems have attracted the interest of many researchers due to their growing application potential. Nevertheless, the mechanism of the sol-gel phase transition is still being discussed, and the glycerophosphate salt role is ambiguous. The aim of the work is to analyze the possibility of the exclusive use of a non-sodium glycerophosphate salt and to determine its impact on the gelation conditions determined by rheological and turbidimetric measurements as well as the stability of the systems by measuring changes in the Zeta potential value. It was found that ensuring the same proportions of glycerophosphate ions differing in cation to amino groups present in chitosan chains, leads to obtaining systems significantly different in viscoelastic properties and phase transition conditions. It was clearly shown that the systems with the calcium glycerophosphate, the insoluble form of which may constitute additional aggregation nuclei, undergo the gelation the fastest. The use of magnesium glycerophosphate salt delays the gelation due to the heat-induced dissolution of the salt. Thus, it was unequivocally demonstrated that the formulation of the gelation mechanism of thermosensitive chitosan systems based solely on the concentration of glycerophosphate without discussing its type is incorrect. 相似文献