全文获取类型
收费全文 | 49979篇 |
免费 | 5730篇 |
国内免费 | 3488篇 |
专业分类
电工技术 | 4358篇 |
技术理论 | 4篇 |
综合类 | 4138篇 |
化学工业 | 6999篇 |
金属工艺 | 3052篇 |
机械仪表 | 3227篇 |
建筑科学 | 4338篇 |
矿业工程 | 1427篇 |
能源动力 | 1505篇 |
轻工业 | 3573篇 |
水利工程 | 1095篇 |
石油天然气 | 2229篇 |
武器工业 | 609篇 |
无线电 | 6272篇 |
一般工业技术 | 5694篇 |
冶金工业 | 2088篇 |
原子能技术 | 634篇 |
自动化技术 | 7955篇 |
出版年
2024年 | 312篇 |
2023年 | 1039篇 |
2022年 | 1858篇 |
2021年 | 2718篇 |
2020年 | 1948篇 |
2019年 | 1539篇 |
2018年 | 1716篇 |
2017年 | 1819篇 |
2016年 | 1569篇 |
2015年 | 2223篇 |
2014年 | 2739篇 |
2013年 | 3233篇 |
2012年 | 3649篇 |
2011年 | 3845篇 |
2010年 | 3566篇 |
2009年 | 3195篇 |
2008年 | 3126篇 |
2007年 | 3035篇 |
2006年 | 2710篇 |
2005年 | 2230篇 |
2004年 | 1675篇 |
2003年 | 1623篇 |
2002年 | 1829篇 |
2001年 | 1618篇 |
2000年 | 1093篇 |
1999年 | 810篇 |
1998年 | 488篇 |
1997年 | 424篇 |
1996年 | 335篇 |
1995年 | 286篇 |
1994年 | 204篇 |
1993年 | 184篇 |
1992年 | 139篇 |
1991年 | 75篇 |
1990年 | 77篇 |
1989年 | 55篇 |
1988年 | 52篇 |
1987年 | 26篇 |
1986年 | 25篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1976年 | 8篇 |
1973年 | 4篇 |
1959年 | 6篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
12.
Guoxiang
Zhang Junyu Xiang 《International journal for numerical methods in engineering》2020,121(15):3339-3361
A new eight-node conforming quadrilateral element with high-order completeness, denoted as QH8-C1, is proposed in this article. First, expressions for the interpolation displacement function satisfying the requirements for high-order completeness in the global coordinate system are constructed. Second, the displacement function expression in global coordinates is transformed into isoparametric coordinates, and the relationships between the two series of coefficients for the two kinds of displacement function expressions are found. Third, the displacement function expression is modified to satisfy the requirements of nodal freedom and interelement boundary continuity. The key to the new element construction is the derivation of the linear relationship expressions among 12 coefficients of element displacement interpolation polynomials in the global and isoparametric coordinate systems. As a result, the relationship between quadratic completeness and interelement continuity is explicitly given, and a proof of the completeness and the continuity was conducted to theoretically guarantee the validity of the derivation results. Furthermore, in order to verify the correctness of the theoretical work, nine numerical examples were performed. The computation results from these examples demonstrate that QH8-C1 exhibited excellent performance, including high simulation accuracy, fast convergence, insensitivity to mesh distortion, and monotonic convergence. 相似文献
13.
根据柴油机机体裂纹产生的原因,对机体裂纹缺陷进行分析,找到了机体裂纹产生的主要原因。其主要原因可概括为铸件结构、化学成分、铸件补缩条件及开箱温度等,针对裂纹的主要原因采取相应的措施后,裂纹缺陷得到了根本的控制。 相似文献
14.
Rui ZHAO Weikai LI Tian WANG Ke ZHAN Zheng YANG Ya YAN Bin ZHAO Junhe YANG 《材料科学前沿(英文版)》2020,14(2):188
Effective thermal management of electronic integrated devices with high powder density has become a serious issue, which requires materials with high thermal conductivity (TC). In order to solve the problem of weak bonding between graphite and Cu, a novel Cu/graphite film/Cu sandwich composite (Cu/GF/Cu composite) with ultrahigh TC was fabricated by electro-deposition. The micro-riveting structure was introduced to enhance the bonding strength between graphite film and deposited Cu layers by preparing a rectangular array of micro-holes on the graphite film before electro-deposition. TC and mechanical properties of the composites with different graphite volume fractions and current densities were investigated. The results showed that the TC enhancement generated by the micro-riveting structure for Cu/GF/Cu composites at low graphite content was more effective than that at high graphite content, and the strong texture orientation of deposited Cu resulted in high TC. Under the optimizing preparing condition, the highest in-plane TC reached 824.3 W·m−1·K−1, while the ultimate tensile strength of this composite was about four times higher than that of the graphite film. 相似文献
15.
16.
Muntasir Hashim Farnoosh Farhad David Smyth‐Boyle Robert Akid Xiang Zhang Philip J. Withers 《工业材料与腐蚀》2019,70(11):2009-2019
The environmental performance of 316L grade stainless steel, in the form of tensile specimens containing a single corrosion pit with various aspect ratios, under cyclic loading in aerated chloride solutions is investigated in this study. Results from environmental tests were compared and contrasted with those obtained using finite element analysis (FEA). Fractography of the failed specimens obtained from experiments revealed that fatigue crack initiation took place at the base of the shallow pit. The crack initiation shifted towards the shoulder and the mouth of the pit for pits of increasing depth. This process is well predicted by FEA, as the strain contour maps show that strain is the highest around the centric strip of the pit. However, for shallow pits, local strain is uniformly distributed around that strip but begins to concentrate more towards the shoulder and the mouth region for increasingly deep pits. 相似文献
17.
18.
19.
20.
Minli Yu Ke Wang Harrie Vredenburg 《International Journal of Hydrogen Energy》2021,46(41):21261-21273
The primary aim of this study is to provide insights into different low-carbon hydrogen production methods. Low-carbon hydrogen includes green hydrogen (hydrogen from renewable electricity), blue hydrogen (hydrogen from fossil fuels with CO2 emissions reduced by the use of Carbon Capture Use and Storage) and aqua hydrogen (hydrogen from fossil fuels via the new technology). Green hydrogen is an expensive strategy compared to fossil-based hydrogen. Blue hydrogen has some attractive features, but the CCUS technology is high cost and blue hydrogen is not inherently carbon free. Therefore, engineering scientists have been focusing on developing other low-cost and low-carbon hydrogen technology. A new economical technology to extract hydrogen from oil sands (natural bitumen) and oil fields with very low cost and without carbon emissions has been developed and commercialized in Western Canada. Aqua hydrogen is a term we have coined for production of hydrogen from this new hydrogen production technology. Aqua is a color halfway between green and blue and thus represents a form of hydrogen production that does not emit CO2, like green hydrogen, yet is produced from fossil fuel energy, like blue hydrogen. Unlike CCUS, blue hydrogen, which is clearly compensatory with respect to carbon emissions as it captures, uses and stores produced CO2, the new production method is transformative in that it does not emit CO2 in the first place. In order to promote the development of the low-carbon hydrogen economy, the current challenges, future directions and policy recommendations of low-carbon hydrogen production methods including green hydrogen, blue hydrogen, and aqua hydrogen are investigated in the paper. 相似文献