全文获取类型
收费全文 | 4125篇 |
免费 | 463篇 |
国内免费 | 284篇 |
专业分类
电工技术 | 138篇 |
综合类 | 378篇 |
化学工业 | 486篇 |
金属工艺 | 513篇 |
机械仪表 | 337篇 |
建筑科学 | 344篇 |
矿业工程 | 544篇 |
能源动力 | 62篇 |
轻工业 | 160篇 |
水利工程 | 95篇 |
石油天然气 | 225篇 |
武器工业 | 34篇 |
无线电 | 381篇 |
一般工业技术 | 514篇 |
冶金工业 | 243篇 |
原子能技术 | 36篇 |
自动化技术 | 382篇 |
出版年
2024年 | 24篇 |
2023年 | 84篇 |
2022年 | 121篇 |
2021年 | 165篇 |
2020年 | 154篇 |
2019年 | 129篇 |
2018年 | 122篇 |
2017年 | 148篇 |
2016年 | 151篇 |
2015年 | 146篇 |
2014年 | 214篇 |
2013年 | 254篇 |
2012年 | 318篇 |
2011年 | 284篇 |
2010年 | 212篇 |
2009年 | 241篇 |
2008年 | 206篇 |
2007年 | 262篇 |
2006年 | 283篇 |
2005年 | 216篇 |
2004年 | 187篇 |
2003年 | 178篇 |
2002年 | 139篇 |
2001年 | 124篇 |
2000年 | 123篇 |
1999年 | 70篇 |
1998年 | 75篇 |
1997年 | 53篇 |
1996年 | 35篇 |
1995年 | 48篇 |
1994年 | 23篇 |
1993年 | 22篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1990年 | 12篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1982年 | 2篇 |
1979年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有4872条查询结果,搜索用时 15 毫秒
1.
Reliable joints of Ti3SiC2 ceramic and TC11 alloy were diffusion bonded with a 50 μm thick Cu interlayer. The typical interfacial structure of the diffusion boned joint, which was dependent on the interdiffusion and chemical reactions between Al, Si and Ti atoms from the base materials and Cu interlayer, was TC11/α-Ti + β-Ti + Ti2Cu + TiCu/Ti5Si4 + TiSiCu/Cu(s, s)/Ti3SiC2. The influence of bonding temperature and time on the interfacial structure and mechanical properties of Ti3SiC2/Cu/TC11 joint was analyzed. With the increase of bonding temperature and time, the joint shear strength was gradually increased due to enhanced atomic diffusion. However, the thickness of Ti5Si4 and TiSiCu layers with high microhardness increased for a long holding time, resulting in the reduction of bonding strength. The maximum shear strength of 251 ± 6 MPa was obtained for the joint diffusion bonded at 850 °C for 60 min, and fracture primarily occurred at the diffusion layer adjacent to the Ti3SiC2 substrate. This work provided an economical and convenient solution for broadening the engineering application of Ti3SiC2 ceramic. 相似文献
2.
Hasrul Abdi Hasibuan Azis Boing Sitanggang Nuri Andarwulan Purwiyatno Hariyadi 《International Journal of Food Science & Technology》2021,56(9):4549-4558
This research aimed to produce triacylglycerols fraction rich in palmitic acid (PA) at the sn-2 position from hard palm stearin (HPS) through acetone fractionation. Fractionations were done at HPS-to-acetone ratios of 1:3, 1:5 and 1:7 (w/v) and at temperatures of 25, 30 and 35 °C for 3 h. Triacylglycerols with PA at the sn-2 position, such as tripalmitoylglycerol (PPP) and dipalmitoyl-stearoyl-glycerol (PPS), were concentrated in the solid fraction, obtained after separation by filtration. The optimal fractionation conditions were at a HPS-to-acetone ratio of 1:5 (w/v) and 30 °C. The total PPP and PPS content was more than 91%, with a corresponding yield of more than 59%. Triacylglycerols obtained were composed of more than 91% PA in which 88% were at the sn-2 position. Conclusively, the solvent fractionation is a suited alternative method for the preparation of triacylglycerols used for the enzymatic synthesis of 1,3-dioleoyl-2-palmitoylglycerol which is the main triacylglycerol for human milk fat substitute. 相似文献
3.
Bo Wang Edison Huixiang Ang Yang Yang Yufei Zhang Hongbo Geng Minghui Ye Cheng Chao Li 《Advanced functional materials》2020,30(28)
Orthorhombic molybdenum trioxide (MoO3) is one of the most promising anode materials for sodium‐ion batteries because of its rich chemistry associated with multiple valence states and intriguing layered structure. However, MoO3 still suffers from the low rate capability and poor cycle induced by pulverization during de/sodiation. An ingenious two‐step synthesis strategy to fine tune the layer structure of MoO3 targeting stable and fast sodium ionic diffusion channels is reported here. By integrating partially reduction and organic molecule intercalation methodologies, the interlayer spacing of MoO3 is remarkably enlarged to 10.40 Å and the layer structural integration are reinforced by dimercapto groups of bismuththiol molecules. Comprehensive characterizations and density functional theory calculations prove that the intercalated bismuththiol (DMcT) molecules substantially enhanced electronic conductivity and effectively shield the electrostatic interaction between Na+ and the MoO3 host by conjugated double bond, resulting in improved Na+ insertion/extraction kinetics. Benefiting from these features, the newly devised layered MoO3 electrode achieves excellent long‐term cycling stability and outstanding rate performance. These achievements are of vital significance for the preparation of sodium‐ion battery anode materials with high‐rate capability and long cycling life using intercalation chemistry. 相似文献
4.
5.
Ratnabali Biswas Kaushik Chowdhury Dharma P. Agrawal 《International Journal of Wireless Information Networks》2006,13(4):303-315
Wireless sensor network is an emerging technology that enables remote monitoring of large geographical regions. In this paper, we address the problem of distributing attributes over such a large-scale sensor network so that the cost of data retrieval is minimized. The proposed scheme is a data-centric storage scheme where the attributes are distributed over the network depending on the correlations between them. The problem addressed here is similar to the Allocation Problem of distributed databases. In this paper, we have defined the Allocation Problem in the context of sensor networks and have proposed a scheme for finding a good distribution of attributes to the sensor network. We also propose an architecture for query processing given such a distribution of attributes. We analytically determine the conditions under which the proposed architecture is beneficial and present simulation results to demonstrate the same. To the best of our knowledge, this is the first attempt to determine an allocation of attributes over a sensor network based on the correlations between attributes. 相似文献
6.
7.
陆西凹陷包日温都断裂构造带岩性油藏研究 总被引:1,自引:1,他引:0
为寻找岩性油藏,应用波阻抗反演地震储层预测技术,对包日温都断裂构造带砂体展布情况进行了预测,发现并落实了2个岩性圈闭,由此认为,研究区北部是大型水下扇砂体与半深湖相暗色泥岩交汇之处,有利于形成岩性油藏,这一结论将对今后加强储层预测工作和寻找有利砂体提供借鉴。 相似文献
8.
Effects of storage period on hydroxymethylfurfural, pH and colour were studied in white hard grape pekmez (Zile pekmezi), a Turkish traditional product. Pekmez samples were stored at 20 °C for 8 months. Analysis of variance revealed significant differences in hydroxymethylfurfural, pH, L, a and b values (P<0.01) based on storage time. 相似文献
9.
We study the stressed state of an inhomogeneous welded joint containing an interlayer of a more high-strength material under the action of tensile loads. It is assumed that the contact boundary has a cracklike defect. We deduce analytic dependences of the fracture load on the mechanical inhomogeneity of the joint, thickness of the interlayer, and depth of the defect. The maximum depth of the defect to which the joint is insensitive is established. The proposed theoretical results are innovative and agree with the experimental data obtained for specimens cut out from a pipe of 14KhGS steel. 相似文献
10.
Sucrose crystallization in thin films (50–55 μm) was studied, using a videomicroscopy technique, at conditions encountered during hard panning processes. No nucleation occurred in unseeded films, while a linear increase in seeded crystals occurred during drying. Crystal growth rate increased with temperature (25–30°C) and with air velocity (2.4–12.5 m/sec), but did not change with varying sucrose concentrations (70–76% w/w) and relative humidities (0–66% at 30°C). FD & C Yellow No. 5 food coloring in the dye form (0.05–0.5 g/100 mL) showed no effects while similar concentrations in the lake form inhibited crystal growth rate. 相似文献