全文获取类型
收费全文 | 65758篇 |
免费 | 5112篇 |
国内免费 | 2259篇 |
专业分类
电工技术 | 825篇 |
技术理论 | 1篇 |
综合类 | 8525篇 |
化学工业 | 4190篇 |
金属工艺 | 2248篇 |
机械仪表 | 1825篇 |
建筑科学 | 31834篇 |
矿业工程 | 1435篇 |
能源动力 | 777篇 |
轻工业 | 482篇 |
水利工程 | 5385篇 |
石油天然气 | 565篇 |
武器工业 | 324篇 |
无线电 | 4099篇 |
一般工业技术 | 6383篇 |
冶金工业 | 1922篇 |
原子能技术 | 1180篇 |
自动化技术 | 1129篇 |
出版年
2024年 | 80篇 |
2023年 | 484篇 |
2022年 | 1133篇 |
2021年 | 1359篇 |
2020年 | 1456篇 |
2019年 | 1112篇 |
2018年 | 1211篇 |
2017年 | 1594篇 |
2016年 | 1707篇 |
2015年 | 2113篇 |
2014年 | 4060篇 |
2013年 | 3019篇 |
2012年 | 4497篇 |
2011年 | 5058篇 |
2010年 | 3934篇 |
2009年 | 4701篇 |
2008年 | 4507篇 |
2007年 | 5348篇 |
2006年 | 4506篇 |
2005年 | 3877篇 |
2004年 | 3049篇 |
2003年 | 2705篇 |
2002年 | 2342篇 |
2001年 | 1874篇 |
2000年 | 1560篇 |
1999年 | 1236篇 |
1998年 | 913篇 |
1997年 | 742篇 |
1996年 | 621篇 |
1995年 | 506篇 |
1994年 | 446篇 |
1993年 | 302篇 |
1992年 | 241篇 |
1991年 | 174篇 |
1990年 | 142篇 |
1989年 | 120篇 |
1988年 | 98篇 |
1987年 | 74篇 |
1986年 | 50篇 |
1985年 | 22篇 |
1984年 | 30篇 |
1983年 | 24篇 |
1982年 | 32篇 |
1981年 | 5篇 |
1980年 | 33篇 |
1979年 | 7篇 |
1975年 | 2篇 |
1964年 | 4篇 |
1959年 | 13篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
通过试验得出了C105混凝土100 mm×100 mm×100 mm立方体非标准试件抗压强度换算系数以及C105混凝土的标准方差和强度变异系数。采用理论计算,得到了棱柱体抗压强度与立方体抗压强度的比值αc1,并与试验实测平均值进行了比较,验证了理论计算方法的可行性。此外,通过对比分析,探讨了直接外延法和引用公式法两种C105混凝土设计参数计算方法的正确性,研究结果可为C105管桩混凝土的设计和应用提供参考。 相似文献
4.
《Soils and Foundations》2022,62(5):101206
Coral sand is one kind of the important building materials in coral reef engineering practice. The use of cement as a stabilizing agent can significantly improve the mechanical properties of coral sands and is widely applied in the subbase engineering construction in coral reef islands. Cement-stabilized coral sand structures may contain high contents of fine coral particles and salinity because of the high crushability of coral sands and the existence of seawater surrounding them. In this study, the effects of coral sand powders and seawater salinity on the dynamic mechanical properties of cemented coral sand (CCS) were investigated through the split Hopkinson pressure bar (SHPB) tests and Scanning Electron Microscope (SEM) analysis. It was found that the strength (i.e., the peak stress) of CCS specimens increased firstly and then decreased with the increase of powder content. The specimens reached the maximum peak stress when 3% powder content was included. The initial improvement of CCS strength was attributed to the pore-filling effect of coral powders, namely, the micro pores of the CCS specimens could be more effectively filled with higher percentages of coral powders being used in the experiments. However, excessive coral powders resulted in the reduction of specimen strength because these powders could easily be cemented into agglomerates by absorbing water from the specimens. These agglomerates could reduce the cementation strength between the coarse coral particles and the cement. Meanwhile, the peak stress of CCS specimens was found to be negatively correlated with the average strain rate and the ultimate strain. The degree of specimen fracture was found to be correlated with the amount of specific energy absorption during the tests. Furthermore, the “sulfate attack” caused by the inclusion of salinity of water had different influences on the CCS specimens with different coral powder contents. The ettringite and gypsum produced in “sulfate attack” could fill the pores and lead to cracking of the specimens, significantly affecting the specimen strength. 相似文献
5.
《Geotextiles and Geomembranes》2022,50(3):371-382
Internal stability assessment of geosynthetic-reinforced soil structures (GRSSs) has been commonly carried out assuming plane-strain conditions and dry backfills. However, failures of GRSSs usually show three-dimensional (3D) features and occur under unsaturated conditions. A procedure based on the kinematic limit-analysis method is proposed herein to assess 3D effects and the role of steady unsaturated infiltration on the required geosynthetic strength for GRSSs. A suction stress-based framework is used to describe the soil stress behavior under steady unsaturated infiltration. Based on the principle of energy-work balance, the required geosynthetic strength is determined. A comparison analysis with the prior research is conducted to verify the developed method. Two kinds of backfills, i.e., high-quality backfill and marginal backfill, are considered for comparison in this work. It is shown that accounting for 3D effects and the role of unsaturated infiltration considerably reduces the required geosynthetic strength. The 3D effects are primarily affected by the width-to-height ratio of GRSSs, and the contribution of unsaturated infiltration is mainly influenced by the soil type, flow rate, GRSS's height, and location of the water table. 相似文献
6.
《Geotextiles and Geomembranes》2022,50(4):632-643
This paper presents an experimental study on reduced-scale model tests of geosynthetic reinforced soil (GRS) bridge abutments with modular block facing, full-height panel facing, and geosynthetic wrapped facing to investigate the influence of facing conditions on the load bearing behavior. The GRS abutment models were constructed using sand backfill and geogrid reinforcement. Test results indicate that footing settlements and facing displacements under the same applied vertical stress generally increase from full-height panel facing abutment, to modular block facing abutment, to geosynthetic wrapped facing abutment. Measured incremental vertical and lateral soil stresses for the two GRS abutments with flexible facing are generally similar, while the GRS abutment with rigid facing has larger stresses. For the GRS abutments with flexible facing, maximum reinforcement tensile strain in each layer typically occurs under the footing for the upper reinforcement layers and near the facing connections for the lower layers. For the full-height panel facing abutment, maximum reinforcement tensile strains generally occur near the facing connections. 相似文献
7.
《Geotextiles and Geomembranes》2022,50(5):910-921
This paper presents a field-scale experimental track over a poor subgrade with an unreinforced section and a geocell-reinforced section subjected to in-situ performance tests. Plate load tests and Benkelman beam tests were carried out distributed in several unreinforced and reinforced layers. The objective was to: (1) examine the variability of the elastic modulus of unbound granular material (UGM) due the influence of its thickness and the presence of poor subgrade in its base, (2) evaluate the modulus improvement factor (MIF) generated by the geocell reinforcement in the UGM and (3) verify the most appropriate condition to apply the MIF to transport infrastructure design. The results showed that there is a significant influence of the thickness of the UGM layer on its elastic modulus when the layer is supported directly over a soft subgrade. The MIF values obtained in field suggest that its determination is mostly related to the UGM maximum elastic modulus rather than its decreased values (by virtue of poor subgrade or reduced thicknesses), and that the analytical formulation presented for MIF calculation has good predictive capability to be applied to pavement design. 相似文献
8.
9.
Tao TIAN Chao-lan ZHANG Feng ZHU Shan-xin YUAN Ying GUO Sheng-guo XUE 《中国有色金属学会会刊》2021,31(5):1484-1495
A column experiment was conducted to investigate the effect of phosphogypsum (PG) on the saline- alkalinity, and aggregate stability of bauxite residue. Results showed that: with increasing leaching time, the concentrations of saline-alkali ions decreased while the concentration increased in bauxite residue leachate; compared with CK (control group) treatment, pH, electric conductivity (EC), exchangeable sodium percentage (ESP), sodium absorption ratio (SAR), and exchangeable Na+ content of bauxite residue were reduced following PG treatment; average particle sizes in aggregates following CK and PG treatments were determined to be 155 and 193 nm, respectively. SR-μCT test results also confirmed that bauxite residue following PG treatment acquired larger aggregates and larger pore diameter. These results indicate that the PG treatment could significantly modulate the saline-alkalinity, and simultaneously enhance aggregate stability of bauxite residue, which provides a facile approach to reclaim bauxite residue disposal areas. 相似文献
10.
地铁混凝土处于地下空间,容易受到地下水的碳酸性侵蚀;碱集料反应 (AAR)是一种严重的混凝土耐久性问题,既难以发现又难以修补,由两者共同作用引起的混凝土耐久性降低严重影响地铁隧道的正常使用.为研究纳米材料对地铁混凝土在碳酸性侵蚀和AAR共同作用下耐久性的影响,在普通混凝土中掺入适量纳米SiO2和纳米Fe2O3,利用自行研制的碳酸性侵蚀试验箱进行试验,采用碳酸性侵蚀深度、膨胀率和声速作为测试指标来评价纳米混凝土在碳酸性侵蚀和AAR共同作用下的耐久性.试验结果表明:掺入纳米颗粒后,混凝土的膨胀率和侵蚀深度有了明显降低,而声速有了明显提升,说明纳米混凝土的耐久性优于普通混凝土;在182 d龄期时,掺量为2%的纳米SiO2混凝土耐久性改善最明显,侵蚀深度和膨胀率最小,声速最大且声速下降幅度最小;其次是掺量为1%的纳米Fe2O3混凝土.由于纳米颗粒特殊的物理化学性质,改善了混凝土内部的微观结构和孔溶液的化学组成,使碳酸性侵蚀和碱集料反应共同作用下混凝土的耐久性得到了提高. 相似文献