全文获取类型
收费全文 | 125082篇 |
免费 | 11668篇 |
国内免费 | 5609篇 |
专业分类
电工技术 | 5629篇 |
技术理论 | 8篇 |
综合类 | 11590篇 |
化学工业 | 22162篇 |
金属工艺 | 3245篇 |
机械仪表 | 4092篇 |
建筑科学 | 18356篇 |
矿业工程 | 6337篇 |
能源动力 | 7235篇 |
轻工业 | 7923篇 |
水利工程 | 19535篇 |
石油天然气 | 9893篇 |
武器工业 | 538篇 |
无线电 | 5410篇 |
一般工业技术 | 8609篇 |
冶金工业 | 5522篇 |
原子能技术 | 1872篇 |
自动化技术 | 4403篇 |
出版年
2024年 | 187篇 |
2023年 | 1535篇 |
2022年 | 2793篇 |
2021年 | 3448篇 |
2020年 | 3786篇 |
2019年 | 3252篇 |
2018年 | 3120篇 |
2017年 | 3851篇 |
2016年 | 4330篇 |
2015年 | 4421篇 |
2014年 | 7552篇 |
2013年 | 7816篇 |
2012年 | 9554篇 |
2011年 | 9618篇 |
2010年 | 7117篇 |
2009年 | 7348篇 |
2008年 | 6535篇 |
2007年 | 8569篇 |
2006年 | 7886篇 |
2005年 | 6923篇 |
2004年 | 5548篇 |
2003年 | 5074篇 |
2002年 | 4349篇 |
2001年 | 3516篇 |
2000年 | 2832篇 |
1999年 | 2241篇 |
1998年 | 1639篇 |
1997年 | 1405篇 |
1996年 | 1121篇 |
1995年 | 1026篇 |
1994年 | 823篇 |
1993年 | 607篇 |
1992年 | 517篇 |
1991年 | 402篇 |
1990年 | 285篇 |
1989年 | 296篇 |
1988年 | 184篇 |
1987年 | 186篇 |
1986年 | 134篇 |
1985年 | 140篇 |
1984年 | 112篇 |
1983年 | 74篇 |
1982年 | 46篇 |
1981年 | 36篇 |
1980年 | 29篇 |
1979年 | 30篇 |
1977年 | 10篇 |
1976年 | 9篇 |
1975年 | 7篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
21.
22.
《International Journal of Hydrogen Energy》2022,47(39):17214-17223
The photocatalytic evolution of H2 over La2O3 decorated TiO2 catalyst was examined under solar light. It was observed that during the course of the reaction, the transformation of La2O3/TiO2 into La2O3–TiO2–La2O2CO3 occurred and these species effectively suppressed electron-hole pair recombination by forming electron trapping centres on the surface, resulting in an increased visible light absorption and improved H2 yield. The 2 wt%La2O3/TiO2 nanocomposite demonstrated better H2 yield (~8.76 mmol (gcat)?1) than the bare TiO2 (~1.1 mmol (gcat)?1). The catalyst was stable even after several consecutive recycles with no substantial loss of hydrogen production rate. The H2 rates were correlated with the physicochemical characteristics of the catalysts examined by BET–SA, H2-TPR, XRD, UV-DRS, Raman spectroscopy, FTIR, HRTEM, EPR and PL spectroscopy. 相似文献
23.
《International Journal of Hydrogen Energy》2022,47(64):27481-27492
Photocatalytic water splitting has become a promising technology to solve environmental pollution and energy shortage. Exploring stable and efficient photocatalysts are highly desired. Herein, we propose novel low-dimensional InSbS3 semiconductors with good stability based on density functional theory. Such InSbS3 structures could be obtained from their bulk crystal by suitable exfoliation methods. Our calculations indicate that two-dimensional (2D) and one-dimensional (1D) InSbS3 nanostructures have moderate band gaps (2.54 and 1.97 eV, respectively) and suitable band edge alignments, which represents sufficient redox capacity for photocatalytic water splitting. 2D InSbS3 monolayer possesses oxygen evolution reaction (OER) activity and 1D InSbS3 single-nanochain possesses hydrogen evolution reaction (HER) activity under acidic conditions. Interestingly, two edge electron states can be introduced when the dimension of InSbS3 is reduced from 2D to 1D and the new electron states can exist in arbitrary-width nanoribbons, which can effectively promote the process of HER. Moreover, InSbS3 monolayer and single-nanochain also exhibit large solar-to-hydrogen efficiency, high carrier mobility, and excellent optical absorption properties, which can facilitate the process of photocatalytic reactions. Our findings can stimulate the synthesis and applications of low-dimensional InSbS3 semiconductors for overall water splitting. 相似文献
24.
《International Journal of Hydrogen Energy》2022,47(61):25511-25521
Metal/carbon composite materials are highly promising electrocatalysts for water electrolysis. In this work, three composites of metal cobalt nanoparticles highly dispersed in N-doped carbon materials were facilely constructed by pyrolysis of different phenylenediamine based Schiff base-Co complexes (PDBs). Interestingly, the composites derived from PDBs based on different phenylenediamine exhibited different morphologies. The superior case is that rodlike composite catalyst was derived from o-phenylenediamine based PDBs. The obtained catalyst exhibited remarkable performances for both cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER), as well as overall water electrolysis. Only 172 and 289 mV of overpotentials and 1.57 V of cell voltage were exhibited at 10 mA cm?2 for HER, OER and water splitting in 1.0 M KOH, respectively. The catalyst also displayed robust stability and high Faraday efficiency, and thus are potential high-performance catalyst for commercial water electrolysis. 相似文献
25.
26.
《Soils and Foundations》2022,62(1):101089
In recent years, the mechanical properties of frozen soils under complex stress states have attracted significant attention; however, limited by the test apparatus, true triaxial tests on frozen soils have rarely been conducted. To study the strength and deformation properties of frozen sand under a true triaxial stress state, a novel frozen soil testing system, i.e., a true triaxial apparatus, was developed. The apparatus is mainly composed of a temperature control system, a servo host system, a hydraulic servo loading system, and a digital control system. Several true triaxial tests were conducted at a constant minor principal stress (σ3) and constant intermediate principal stress ratio (b) to study the effect of intermediate principal stress (σ2) on the mechanical properties of frozen sand. The test results showed that the stress–strain curve can be mainly divided into three stages, with evidence of strain hardening characteristics. The strength, elastic modulus, and friction angle increased with the increase in b from 0 to 0.6, but decreased when increasing b from 0.6 to 1, whereas the cohesion varied little with the variation in b. The deformation in the direction of σ2 changed from dilative to compressive and that in the direction of σ3 remained dilative throughout. 相似文献
27.
《Soils and Foundations》2022,62(6):101224
Internal erosion is a major threat to hydraulic earth structures, such as river levees and dams. This paper focuses on suffusion and suffosion phenomena which are caused by the movement of fine particles in the granular skeleton due to seepage flow. The present study investigates the impact of internal erosion on the dynamic response under cyclic torsional shear and monotonic responses under triaxial compression and torsional simple shear. A series of experiments, using a gap-graded silica mixture with a fines content of 20%, is performed under loose, medium, and dense conditions using a novel erosion hollow cylindrical torsional shear apparatus. The erosion test results indicate that the critical hydraulic gradient and the rate of erosion are density-dependent, where a transition from suffosion to suffusion is observed as the seepage continues. Regardless of the sample density, variations in the radial strain and particle size distribution, along the specimen height after erosion, are no longer uniform. Furthermore, the dynamic shearing results show that the small-strain shear modulus increases, but the initial damping ratio decreases after internal erosion, probably due to the removal of free fines. In addition, the elastic threshold strain and reference shear strain values are found to be higher for the eroded and non-eroded specimens, respectively. Finally, based on drained monotonic loading, the post-erosion peak stress ratio increases remarkably under triaxial compression, while that under torsional simple shear depends on the relative density where the direction of loading is normal to the direction of seepage. These observations indicate that the horizontal bedding plane becomes weaker, while the vertical one becomes stronger after downward erosion. 相似文献
28.
《Geotextiles and Geomembranes》2022,50(4):779-793
As a new type of material for civil engineering projects, the rubber and sand mixture is widely used in roadbed fillers, offering environmental benefits over traditional tyre disposal methods. This study uses a large-scale direct shear apparatus to examine the interface shear properties of the geogrid-reinforced rubber and sand mixture, considering different particle size ratios (r), rubber contents, and normal stresses. Based on indoor tests, direct shear models of the mixture with different values of r are established in PFC3D, revealing the meso-mechanical mechanism of the mixture in the direct shear process. The results show that when r is greater than 1, incorporating a certain amount of rubber particles can increase the shear strength of the mixture. The r values of 15.78, 7.63, and 3.98 correspond to an optimal rubber content of 30%, 10%, and 20%, respectively. When r is less than 1, mixing rubber particles can only reduce the shear strength of the mixture. When the rubber content is low, the smaller the value of r, the greater is the thickness of the shear band. Furthermore, the normal and tangential contact forces are greater. The fabric anisotropy evolution law of the mixture is consistent with the change in the contact force distribution. 相似文献
29.
为了解汉江上游干支流沉积物细菌多样性以及确定性过程和随机性过程在沉积物细菌群落构建过程中的相对重要性,基于Illumina高通量测序技术,分析了环境因子对细菌群落组成的影响,采用非度量多维尺度(NMDS)排序探究了季节之间沉积物细菌群落的差异,并结合中性群落模型和标准化随机率量化了确定性过程和随机过程对群落构建的影响。结果表明:汉江上游及其支流细菌群落主要由变形菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)、蓝藻门(Cyanophyta)、浮霉菌门(Planctomycetes)和酸杆菌门(Acidobacteria)等组成;细菌群落在不同季节有显著差异;地理距离和环境因子对细菌群落结构影响较小,确定性过程并未在细菌群落组成中起到主导作用;随机过程很大程度上影响了群落在秋季和春季的组成,是沉积物细菌群落构建的主导因素。 相似文献
30.