全文获取类型
收费全文 | 31759篇 |
免费 | 3081篇 |
国内免费 | 2925篇 |
专业分类
电工技术 | 917篇 |
技术理论 | 2篇 |
综合类 | 4240篇 |
化学工业 | 1620篇 |
金属工艺 | 312篇 |
机械仪表 | 313篇 |
建筑科学 | 19300篇 |
矿业工程 | 2000篇 |
能源动力 | 544篇 |
轻工业 | 704篇 |
水利工程 | 4756篇 |
石油天然气 | 453篇 |
武器工业 | 35篇 |
无线电 | 167篇 |
一般工业技术 | 956篇 |
冶金工业 | 544篇 |
原子能技术 | 134篇 |
自动化技术 | 768篇 |
出版年
2024年 | 44篇 |
2023年 | 284篇 |
2022年 | 648篇 |
2021年 | 811篇 |
2020年 | 761篇 |
2019年 | 693篇 |
2018年 | 690篇 |
2017年 | 830篇 |
2016年 | 906篇 |
2015年 | 997篇 |
2014年 | 2491篇 |
2013年 | 1478篇 |
2012年 | 2435篇 |
2011年 | 2533篇 |
2010年 | 2300篇 |
2009年 | 2342篇 |
2008年 | 2014篇 |
2007年 | 2593篇 |
2006年 | 2326篇 |
2005年 | 2110篇 |
2004年 | 1636篇 |
2003年 | 1314篇 |
2002年 | 1121篇 |
2001年 | 884篇 |
2000年 | 730篇 |
1999年 | 602篇 |
1998年 | 469篇 |
1997年 | 371篇 |
1996年 | 303篇 |
1995年 | 274篇 |
1994年 | 181篇 |
1993年 | 100篇 |
1992年 | 90篇 |
1991年 | 69篇 |
1990年 | 58篇 |
1989年 | 49篇 |
1988年 | 36篇 |
1987年 | 37篇 |
1986年 | 31篇 |
1985年 | 14篇 |
1984年 | 21篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1979年 | 44篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1959年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 24 毫秒
61.
62.
63.
《Geotextiles and Geomembranes》2020,48(2):157-169
A GeoBarrier system (GBS) is a combination system of reinforced soil walls to stabilize near-vertical cut slopes and capillary barrier principles to protect the wall from the effect of rainfall infiltration. Singapore requires construction materials that are cost-effective to support sustainable urban development. Therefore, recycled materials are utilized as GBS materials to avoid the use of high-cost materials, such as steel or concrete. GBS consists of planting geobags with unique geosynthetic pockets for sustainable plant growth as a facing layer of GBS. The negative pore-water pressure (suction) within the reinforced soil behind GBS was assured to be constant during rainfall since GBS is designed specially to minimize the rainfall infiltration into the reinforced soil. This paper presents the practical design and stability analysis of the GBS, considering the presence of suction within the reinforced soil body. The monitoring of GBS performance in the field was carried out via field instrumentation. Finite element analyses of the GBS under extreme rainfalls were also performed for evaluation of the GBS performance. The field instrumentations and numerical analysis results showed that GBS was able to protect the slope from rainfall infiltration; therefore, the stability of the slope retained by GBS was not affected by the rainfall. Results from the analytical calculation showed that the most critical mode of failure is sliding along the base, followed by the global and local slope stability. The GBS is not susceptible to local instability. 相似文献
64.
Nishant SHARMA Kaustubh DASGUPTA Arindam DEY 《Frontiers of Structural and Civil Engineering》2020,14(1):62
This article describes a novel approach for deciding optimal horizontal extent of soil domain to be used for finite element based numerical dynamic soil structure interaction (SSI) studies. SSI model for a 12 storied building frame, supported on pile foundation-soil system, is developed in the finite element based software framework, OpenSEES. Three different structure-foundation configurations are analyzed under different ground motion characteristics. Lateral extent of soil domain, along with the soil properties, were varied exhaustively for a particular structural configuration. Based on the reduction in the variation of acceleration response at different locations in the SSI system (quantified by normalized root mean square error, NRMSE), the optimum lateral extent of the soil domain is prescribed for various structural widths, soil types and peak ground acceleration levels of ground motion. Compared to the past studies, error estimation analysis shows that the relationships prescribed in the present study are credible and more inclusive of the various factors that influence SSI. These relationships can be readily applied for deciding upon the lateral extent of the soil domain for conducting precise SSI analysis with reduced computational time. 相似文献
65.
66.
Targeted delivery of nanoparticles has the potential to enhance remediation and characterization of sites contaminated with non-aqueous phase liquids (NAPLs) by ensuring delivery of treatment or contrast agents to the NAPL/water interface. For a targeted delivery technique to be successful, nanoparticles must be capable of transporting through porous media and binding to NAPLs under relevant geological conditions. In this study, successful targeted delivery of nanoparticles to sandy aquifer material mixed with crude oil was achieved using an active targeting technique based on an amphiphilic polymer coating. It was determined that the molecular structure and concentration of the nanoparticle coating greatly influenced the recovery of nanoparticles injected into saturated columns. Coatings with longer polymer molecules and lower polymer concentrations reduced recovery, and the nanoparticle coating formulation could be adjusted to improve transport while maintaining targeted binding behaviour. This study demonstrated that nanoparticle retention in oil-impacted sand exceeded that of clean sand in flow through experiments, indicating that a nanoparticle targeted delivery strategy for soil contaminated with LNAPLs such as crude oil is possible under the experimental conditions explored. 相似文献
67.
68.
《工程(英文)》2021,7(11):1631-1645
The construction of a lunar base and habitation on the Moon has always been on researchers’ minds. Building materials used in in situ lunar resources are of great significance for saving expensive space freight. In this study, a new type of lunar soil simulant named Beihang (BH)-1 was developed. The chemical mineral composition and microstructure of BH-1 closely resemble those of real lunar soil, as verified by X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), and reflectance spectra. This research also synthesized a geopolymer based on BH-1 cured at simulated lunar atmospheric conditions. We also investigated the effect of supplementing aluminum (Al) sources on the enhancement of geopolymer strength based on BH-1. The rheological behavior of alkali-activated BH-1 pastes was determined for workability. XRF, XRD, Fourier transform infrared spectroscopy, SEM coupled with energy dispersive spectroscopy, and 27Al magic angle spinning-nuclear magnetic resonance were used to characterize resulting geopolymers. Rheological test findings showed that the rheology of BH-1 pastes fits the Herschel–Bulkley model, and they behaved like a shear-thinning fluid. The results showed that the 28-day compressive strength of the BH-1 geopolymer was improved by up to 100.8%. Meanwhile, the weight of additives required to produce per unit strength decreased, significantly reducing the mass of materials transported from the Earth for the construction of lunar infrastructure and saving space transportation costs. Microscopic analyses showed that the mechanism to improve the mechanical properties of the BH-1 geopolymer by adding an additional Al source enhances the replacement of silicon atoms by Al atoms in the silicon–oxygen group and generates a more complete and dense amorphous gel structure. 相似文献
69.
Primrose J. Boynton Vienna Kowallik Doreen Landermann Eva H. Stukenbrock 《Yeast (Chichester, England)》2019,36(11):657-668
Saccharomyces yeasts are emerging as model organisms for ecology and evolution, and researchers need environmental Saccharomyces isolates to test ecological and evolutionary hypotheses. However, methods for isolating Saccharomyces from nature have not been standardized, and isolation methods may influence the genotypes and phenotypes of studied strains. We compared the effectiveness and potential biases of an established enrichment culturing method against a newly developed direct plating method for isolating forest floor Saccharomyces spp. In a European forest, enrichment culturing was both less successful at isolating Saccharomyces paradoxus per sample collected and less labour intensive per isolated S. paradoxus colony than direct isolation. The two methods sampled similar S. paradoxus diversity: The number of unique genotypes sampled (i.e., genotypic diversity) per S. paradoxus isolate and average growth rates of S. paradoxus isolates did not differ between the two methods, and growth rate variances (i.e., phenotypic diversity) only differed in one of three tested environments. However, enrichment culturing did detect rare Saccharomyces cerevisiae in the forest habitat and also found two S. paradoxus isolates with outlier phenotypes. Our results validate the historically common method of using enrichment culturing to isolate representative collections of environmental Saccharomyces. We recommend that researchers choose a Saccharomyces sampling method based on resources available for sampling and isolate screening. Researchers interested in discovering new Saccharomyces phenotypes or rare Saccharomyces species from natural environments may also have more success using enrichment culturing. We include step-by-step sampling protocols in the supplemental materials. 相似文献
70.
为了解决农村农药面源污染问题,利用小流量渗透法将毒死蜱降解菌负载在微孔渗水型混凝土上,研究不同降雨强度下不同孔隙率混凝土对毒死蜱的降解截留效果。结果表明:对于3种不同透水系数的微孔混凝土,微孔渗水型混凝土负载生物量和生物活性随孔隙率增大呈先升高后降低趋势;对于两种不同的降雨强度,毒死蜱降解率最优的都是孔隙率为48.1%的试样;降雨强度较大时,土壤中毒死蜱析出质量浓度较高,且降雨强度越大析出速度越快,试样对析出的毒死蜱降解效果越差。微孔渗水型混凝土对土壤中残留毒死蜱具有较好的去除效果,材料本身具有高强度、高寿命、低成本等特点,在土壤护坡、河流护岸等方面具有较好的应用前景。 相似文献