全文获取类型
收费全文 | 69580篇 |
免费 | 7496篇 |
国内免费 | 4963篇 |
专业分类
电工技术 | 2953篇 |
技术理论 | 2篇 |
综合类 | 5658篇 |
化学工业 | 7248篇 |
金属工艺 | 2829篇 |
机械仪表 | 4710篇 |
建筑科学 | 7075篇 |
矿业工程 | 13345篇 |
能源动力 | 3190篇 |
轻工业 | 3316篇 |
水利工程 | 2340篇 |
石油天然气 | 7176篇 |
武器工业 | 619篇 |
无线电 | 2299篇 |
一般工业技术 | 4648篇 |
冶金工业 | 3370篇 |
原子能技术 | 831篇 |
自动化技术 | 10430篇 |
出版年
2024年 | 201篇 |
2023年 | 703篇 |
2022年 | 1679篇 |
2021年 | 2218篇 |
2020年 | 2430篇 |
2019年 | 1821篇 |
2018年 | 1721篇 |
2017年 | 2093篇 |
2016年 | 2356篇 |
2015年 | 2496篇 |
2014年 | 4501篇 |
2013年 | 4265篇 |
2012年 | 5700篇 |
2011年 | 5800篇 |
2010年 | 4190篇 |
2009年 | 4254篇 |
2008年 | 4008篇 |
2007年 | 4782篇 |
2006年 | 4510篇 |
2005年 | 3835篇 |
2004年 | 3376篇 |
2003年 | 2912篇 |
2002年 | 2295篇 |
2001年 | 1897篇 |
2000年 | 1612篇 |
1999年 | 1245篇 |
1998年 | 1011篇 |
1997年 | 830篇 |
1996年 | 677篇 |
1995年 | 609篇 |
1994年 | 525篇 |
1993年 | 303篇 |
1992年 | 250篇 |
1991年 | 216篇 |
1990年 | 147篇 |
1989年 | 134篇 |
1988年 | 95篇 |
1987年 | 77篇 |
1986年 | 52篇 |
1985年 | 55篇 |
1984年 | 17篇 |
1983年 | 16篇 |
1982年 | 22篇 |
1981年 | 16篇 |
1980年 | 18篇 |
1979年 | 22篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1964年 | 5篇 |
1959年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
31.
通过对大直径平底负压容器平底板的设计计算,平底板计算厚度很厚。通过分析,提出了对平底板采取加强措施,从而减薄平底板计算厚度的方法。该容器在实际生产过程中性能可靠、稳定,对类似设备设计具有借鉴意义。 相似文献
32.
Petre Badica Dan Batalu Mihail Burdusel Mihai A. Grigoroscuta Gheorghe V. Aldica Monica Enculescu Raluca A. Gabor Zhiyong Wang Ruoxuan Huang Peifeng Li 《Ceramics International》2018,44(9):10181-10191
Pristine and (SiC+Te)-added MgB2 powders, green and spark plasma sintered (SPS) compacts were investigated from the viewpoint of quasi-static and dynamic (Split-Hopkinson Pressure Bar, SHPB) compressive mechanical properties The amount of the additive (SiC+Te) was selected to be the optimum one for maximization of the superconducting functional parameters. Pristine and added MgB2 show very similar compressive parameters (tan δ, fracture strength, Vickers hardness, others) and fragment size in the SHPB test. However, for the bulk SPSed samples the ratio of intergranular to transgranular fracturing changes, the first one being stronger in the added sample. This is reflected in the quasi-static KIC that is higher for the added sample. Despite this result, sintered samples are brittle and have roughly similar fragmentation behavior as for brittle engineering ceramics. In the fragmentation process, the composite nature of our samples should be considered with a special focus on MgB2 blocks (colonies) that show the major contribution to fracturing. The Glenn-Chudnovsky model of fracturing under dynamic load provides the closest values to our experimental fragment size data. 相似文献
33.
34.
如何在海量不确定数据集中提高频繁模式挖掘性能是目前研究的热点.传统算法大多是以期望、概率或者权重等单一指标为数据项集支持度,在大数据背景下,同时考虑概率和权重支持度的算法难以兼顾其执行效率.为此,本文提出一种基于Spark的不确定数据集频繁模式挖掘算法(UWEFP),首先,为了同时兼顾数据项的概率和权重,计算一项集的最大概率权重值并进行剪枝;然后,为了减少对数据集的多次扫描,结合Spark框架的优点,设计了一种具有FP-tree特征的新颖的UWEFP-tree结构进行模式树的构建及挖掘;最后在Spark环境下,以UCI数据集进行实验验证.实验结果表明本文的方法在保证挖掘结果的同时,提高了效率. 相似文献
35.
The titanium carbides are potential candidates to achieve both high hardness and refractory property. We carried out a structural search for titanium carbides at three pressures of 0 GPa, 30 GPa and 50 GPa. A phase diagram of the Ti-C system at 0 K was obtained by elucidating formation enthalpies as a function of compositions, and their mechanical and metallic properties of titanium carbides were investigated systematically. We also discussed the relation of titanium concentration to the both mechanical and metallic properties of titanium carbides. It has been found that the average valence electron density and tractility improved at higher concentrations of titanium, while the degree of covalent bonding directionality decreased. To this effect, the hardness of titanium carbide decreases as the content of titanium increases. Our results indicated that the titanium content significantly affected the metallic properties of the Ti-C system. 相似文献
36.
This paper presents two well-instrumented large-scale field tests of PVD-improved soft soil with vacuum and surcharge preloading, respectively. The two large-scale field tests were conducted adjacent to each other with the same preload. A comparative analysis was performed to investigate the performance of subsoil (i.e., the ground settlement, the layered settlement, the lateral displacement of subsoil and pore water pressure) under vacuum preloading and equivalent surcharge preloading. Some design methods were verified based on the field data. Cone Penetration Tests (CPT) and Vane Shear Tests (VST) were conducted to assess the improvement effects on subsoil after preloading. The results showed that as compared with surcharge preloading, vacuum preloading mitigated the differential settlement of the ground. The vacuum pressure transmitted into the soil with a minor loss through the PVD length. From a practical point of view, the improvement effects by vacuum preloading and surcharge preloading were similar in terms of influence depth and soil strength based on the in-situ tests. 相似文献
37.
38.
分析了乐滩灌区工程北干渠溯河隧洞段长约1.06 km穿合山煤矿采空区的地质情况.借鉴高速公路煤矿采空区的成功处理经验,通过科学分析,对采空区变形和区域内覆岩的稳定性做了评价,论述了输水线路穿采空区段采取全充填压力注浆法的工程处理方法. 相似文献
39.
40.
在油气井的试油测试资料中,压力恢复曲线有时会出现下滑现象,常被认为是施工失误所致。本文以实际资料为例,分析了“下滑恢复”的压力响应特征和影响因素,认为只在低渗透地层有可能产生“下滑恢复”现象,并提出了避免“下滑恢复”的施工建议。 相似文献