全文获取类型
收费全文 | 97801篇 |
免费 | 9088篇 |
国内免费 | 5926篇 |
专业分类
电工技术 | 5248篇 |
技术理论 | 4篇 |
综合类 | 10860篇 |
化学工业 | 12667篇 |
金属工艺 | 6733篇 |
机械仪表 | 6608篇 |
建筑科学 | 19433篇 |
矿业工程 | 3752篇 |
能源动力 | 2851篇 |
轻工业 | 4948篇 |
水利工程 | 2626篇 |
石油天然气 | 4616篇 |
武器工业 | 989篇 |
无线电 | 6277篇 |
一般工业技术 | 10615篇 |
冶金工业 | 3662篇 |
原子能技术 | 561篇 |
自动化技术 | 10365篇 |
出版年
2024年 | 280篇 |
2023年 | 1312篇 |
2022年 | 2459篇 |
2021年 | 2915篇 |
2020年 | 2896篇 |
2019年 | 2360篇 |
2018年 | 2229篇 |
2017年 | 2824篇 |
2016年 | 3038篇 |
2015年 | 3328篇 |
2014年 | 5954篇 |
2013年 | 5148篇 |
2012年 | 6807篇 |
2011年 | 7592篇 |
2010年 | 5824篇 |
2009年 | 6237篇 |
2008年 | 5729篇 |
2007年 | 6839篇 |
2006年 | 6181篇 |
2005年 | 5380篇 |
2004年 | 4404篇 |
2003年 | 3956篇 |
2002年 | 3368篇 |
2001年 | 2815篇 |
2000年 | 2434篇 |
1999年 | 2011篇 |
1998年 | 1592篇 |
1997年 | 1340篇 |
1996年 | 1009篇 |
1995年 | 881篇 |
1994年 | 830篇 |
1993年 | 541篇 |
1992年 | 506篇 |
1991年 | 408篇 |
1990年 | 318篇 |
1989年 | 220篇 |
1988年 | 181篇 |
1987年 | 88篇 |
1986年 | 65篇 |
1985年 | 76篇 |
1984年 | 56篇 |
1983年 | 59篇 |
1982年 | 72篇 |
1981年 | 21篇 |
1980年 | 67篇 |
1979年 | 18篇 |
1978年 | 12篇 |
1976年 | 9篇 |
1975年 | 14篇 |
1959年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
42.
Heat exchanger network synthesis (HENS) has progressed by using mathematical programming-based simultaneous methodology. Although various considerations such as non-isothermal mixing and bypass streams are applied to consider real world alternatives in modeling phase, many challenges are faced because of its properties within non-convex mixed-integer nonlinear programming (MINLP). We propose a modified superstructure, which contains a utility substage for use in considering multiple utilities in a simultaneous MINLP model. To improve model size and convergence, fixed utility locations according to temperature and series connections between utilities are suggested. The numbers of constraints, discrete, and continuous variables show that overall model size decreases compared with previous research. Thus, it is possible to expand the feasible search area for reaching the nearest global solution. The model's effectiveness and applications are exemplified by several literature problems, where it is used to deduce a network superior to that of any other reported methodology. 相似文献
43.
44.
A series of spray coating experiments were conducted on an UV-curable, polyurethane-modified, acrylate-based coating formulation with the aim to control defects, coating thickness, and thickness variation. Statistical approaches including design of experiment, residual examination, analysis of variance, and t-test were used in designing the experiments and analyzing data. Viscosity of formulation, atomizing pressure, liquid feeding pressure, distance between nozzle and substrate, and travel speed of substrate were the process variables studied. The ranges of process variables that gave defect-free coating were identified and used in the subsequent experiments to determine process variables and interactions that had significant contribution to the changes in coating thickness and thickness variation. All process variables studied were found to have contribution to the change in coating thickness, but they showed no significant contribution to the variation of coating thickness. No interaction displayed significant contribution. Confirmation tests performed on extra samples prepared with varying coating thicknesses indicated a good agreement with the experimental results. Additional samples were tested for total transmittance, transmission haze, adhesion, surface roughness, hardness, scratch hardness, abrasion resistance, and durability to attack of car wash chemicals. Spray coated samples showed slight improvement in the total transmittance over the uncoated samples, while maintaining the transmission haze and exhibiting rougher surfaces. Only samples with thin coatings were found to possess sufficient adhesion to the substrate. These thin coatings gave improved hardness, scratch hardness, and durability to car wash attack to the level comparable to commercial coated polycarbonate headlamp lenses, whilst giving better abrasion resistance. 相似文献
45.
Nitrile rubber (NBR) blends with excellent performance have always been a hot research topic in petroleum field. Due to the excellent performance and compatibility of polyamide 6 (PA6), it provides an opportunity for the preparation of high-performance NBR/PA6 blends. In this article, NBR/PA6 blends were prepared by the three-step molding process. Experimentally, it was found that PA6 has a prominent reinforcement effect in NBR matrix. The variation of this mechanical property was investigated from different aspects of the crystal structure, crystallinities, phase morphology, and so on. It can be cleared that the formation of fibrous structure of PA6 phase is the main factor for reinforcement of the polymer blends. Meanwhile, the formation mechanism of the special phase structure induced by the three-step process is deeply expounded and its structural evolution schematic is established. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47472. 相似文献
46.
不同含量低污染水对人工湿地中细菌的影响研究 总被引:1,自引:0,他引:1
探究水平流人工湿地(HFCW)系统处理低污染水过程中,相同COD/ρ(TN)下不同碳氮含量对细菌群落结构的影响。结果表明,进水为较高碳氮含量的HFCW(HF1)和进水为较低碳氮含量的HFCW(HF2)对COD和TN的去除效率具有一定的差异,HF1和HF2对COD的去除效率分别为48.26%和28.89%,对TN的去除率分别为79.06%和81.87%。HF1中细菌的丰富度和多样性均高于HF2,HF1中富集的优势细菌为Chloroflexaceae、Comamonadaceae和Rhodocyclaceae,均具有异养反硝化功能,HF2中富集的优势细菌为Xanthomonadaceae和Rhodocyclaceae,其中Xanthomonadaceae具有自养反硝化功能。COD、NH4^+-N和NO3^--N对HF1中细菌群落的影响大于对HF2中细菌群落的影响,HF1中COD对细菌群落的影响大于NH4^+-N和NO3^--N。 相似文献
47.
科学合理地确定矿山隔水护顶矿柱安全厚度是矿山安全生产的前提条件,为保障某铁矿地表民房、道路等建(构)筑物安全,防止矿山开采过程中产生的导水裂隙带贯通第四系含水层,采用荷载传递交汇线法、K.B.鲁别涅依他估算法和冒落带、导水裂隙带高度估算法3种理论分析方法对隔水护顶矿柱厚度进行计算,并利用数值模拟手段对留设隔水护顶矿柱后的开采过程安全影响进行了分析,对理论计算结果进行了验证。3种理论计算方法得出的隔水护顶矿柱厚度分别为14.3~17.3 m、17.5~31.4 m和41.8~57.4 m,推荐隔水护顶矿柱留设厚度为60 m。通过数值模拟分析得出,在留设60 m厚的隔水护顶矿柱的基础上,开采区域和隔水护顶矿柱位置产生的最大拉应力约0.47 MPa,矿山开采不会对隔水护顶矿柱造成破坏;地表产生的最大水平位移约5.8 cm,最大垂直位移约26.5 cm,最大倾斜为1.70 mm/m,最大曲率为0.20 mm/m2,最大水平变形值为0.70 mm/m,满足相关规范要求,预测矿山开采不会造成地表建(构)筑物破坏。 相似文献
48.
Textured surface is commonly used to enhance the efficiency of silicon solar cells by reducing the overall reflectance and improving the light scattering. In this study, a comparison between isotropic and anisotropic etching methods was investigated. The deep funnel shaped structures with high aspect ratio are proposed for better light trapping with low reflectance in crystalline silicon solar cells. The anisotropic metal assisted chemical etching (MACE) was used to form the funnel shaped structures with various aspect ratios. The funnel shaped structures showed an average reflectance of 14.75% while it was 15.77% for the pillar shaped structures. The average reflectance was further reduced to 9.49% using deep funnel shaped structures with an aspect ratio of 1:1.18. The deep funnel shaped structures with high aspect ratios can be employed for high performance of crystalline silicon solar cells. 相似文献
49.
Chaoxin Li Yi Zhou Yuming Tian Yuanyuan Zhao Kaiyue Wang Guomin Li Yuesheng Chai 《Ceramics International》2019,45(5):5613-5616
Ceramics with mullite whiskers were prepared from coal fly ash and Al2O3 raw materials, with AlF3 used as an additive. The phase structures and microstructures of the ceramics were identified via X-ray diffraction and scanning electron microscopy, respectively. The results show that pickling of coal fly ash is an effective method for enhancing the flexural strength of ceramics. Sintering temperature and AlF3 addition were also key factors influencing the creation of ideal ceramics. The ceramic made from pickled coal fly ash, 6?wt% AlF3, and sintered at 1200?°C, exhibited the highest flexural strength of 59.1?MPa, and had a bulk density of 1.32?g/cm3 and porosity of 26.8%. The results show that ceramic materials made under these conditions are ideal candidates for manufacturing ceramic proppants for the exploitation of unconventional oil and gas resources. 相似文献
50.