全文获取类型
收费全文 | 17158篇 |
免费 | 1969篇 |
国内免费 | 1401篇 |
专业分类
电工技术 | 1291篇 |
综合类 | 1782篇 |
化学工业 | 2151篇 |
金属工艺 | 1233篇 |
机械仪表 | 1129篇 |
建筑科学 | 1406篇 |
矿业工程 | 604篇 |
能源动力 | 367篇 |
轻工业 | 1780篇 |
水利工程 | 576篇 |
石油天然气 | 885篇 |
武器工业 | 251篇 |
无线电 | 1909篇 |
一般工业技术 | 1554篇 |
冶金工业 | 760篇 |
原子能技术 | 359篇 |
自动化技术 | 2491篇 |
出版年
2024年 | 91篇 |
2023年 | 248篇 |
2022年 | 547篇 |
2021年 | 745篇 |
2020年 | 576篇 |
2019年 | 422篇 |
2018年 | 418篇 |
2017年 | 493篇 |
2016年 | 478篇 |
2015年 | 729篇 |
2014年 | 927篇 |
2013年 | 1142篇 |
2012年 | 1374篇 |
2011年 | 1378篇 |
2010年 | 1373篇 |
2009年 | 1325篇 |
2008年 | 1468篇 |
2007年 | 1326篇 |
2006年 | 1251篇 |
2005年 | 975篇 |
2004年 | 739篇 |
2003年 | 524篇 |
2002年 | 506篇 |
2001年 | 466篇 |
2000年 | 314篇 |
1999年 | 211篇 |
1998年 | 84篇 |
1997年 | 89篇 |
1996年 | 69篇 |
1995年 | 54篇 |
1994年 | 34篇 |
1993年 | 34篇 |
1992年 | 26篇 |
1991年 | 22篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1968年 | 2篇 |
1963年 | 1篇 |
1961年 | 1篇 |
1959年 | 2篇 |
1956年 | 1篇 |
1955年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
2.
Grain refinement is critical for fabricating high-quality Al-Si casting components in the application of automobile and aerospace industries,while the well-known Si-poisoning effect makes it difficult.Nbbased refiners offer an effective method to refine Al-Si casting alloys,but their anti Si-poisoning capability is far from being understood.In this work,the grain refining mechanism and the anti Si-poisoning effect in the Al-10 Si/Al-5 Nb-B system were systematically investigated by combining transmission electron microscope,first-principles calculations,and thermodynamic calculations.It is revealed that NbB2provides the main nucleation site in the Al-10 Si ingot inoculated by 0.1 wt.%Nb Al-5 Nb-B refiner.The exposed Nb atoms on the(0001)NbB2and(1-100)NbB2surface can be substituted by Al to form(Al,Nb)B2intermedia layers.In addition,a layer of NbAl3-like compound(NbAl3')can cover the surface of NbB2with the orientation relation of(1-100)[11-20]NbB2//(110)[110]NbAl3'.Both of the(Al,Nb)B2and NbAl3'intermedia layers contribute to enhancing the nucleation potency of NbB2particles.These discoveries provide fundamental insight to the grain refining mechanism of the Nb-B based refiners for Al-Si casting alloys and are expected to guide the future development of stronger refiners for Al-Si casting alloys. 相似文献
3.
4.
5.
以转基因水稻中最常用的CaMV35S启动子、NOS终止子、Cry1Ab/Ac基因、HPT基因及SPS水稻内标基因为研究对象,利用5 种不同的荧光信号(FAM、HEX、Taxas Red、Cy5、Cy5.5)进行多重实时聚合酶链式反应(real-time polymerase chain reaction,real-time PCR)检测方法的研究。通过引物组合筛选、反应体系优化、特异性测试、灵敏度测试、适用性测试等一系列实验,建立了5 重real-time PCR方法,灵敏度可达0.032%。此方法具有灵敏度高、结果准确、通量大等优点,可实现水稻中转基因成分的快速、高效检测。 相似文献
6.
Wen Cao Zhonghua Zhou Chenyu Li Qun Wang Yue Huang Shirley Shen 《Ceramics International》2021,47(2):1807-1818
Sodalime float (SF) glass is widely used in our societies and industries. Hydrothermal corrosion method is one of the effective ways to prepare a superhydrophobic glass, but there is still lack of knowledge about hydrothermal corrosion behavior and mechanism of SF glass. We have hydrothermally treated SF glass at 180 °C for different time, and tried to reveal the aqueous corrosion process of SF glass. We have characterized the morphologies and chemical compositions of samples, and found that (1) the two sides of SF glass have different corrosion resistances, and (2) a multilayer structural coating with a nanoflake layer (Mg-rich gel layer), a nanowire layer (Ca-rich gel layer), and a porous layer (etched layer) is formed on the air-side of SF glass. Based on the experimental results, we have proposed an aqueous corrosion mechanism of SF glass. The insights of the hydrothermal corrosion behaviors and mechanism provide helpful guidelines to glass surface structural control and functionalization. 相似文献
7.
Qun Ren Haijun Su Jun Zhang Haifang Liu Weidan Ma Guangrao Fan Di Zhao Min Guo Lin Liu Hengzhi Fu 《Ceramics International》2019,45(6):6632-6638
Directionally solidified microstructures of Al2O3-Er3Al5O12 eutectic and off-eutectic in situ composite ceramics were explored under abrupt-change pulling rate conditions. Corresponding temperature distributions and interface locations were studied. In eutectic composition, fluctuation of eutectic spacing occurred when the pulling rate increased abruptly. A gradually increase or abrupt increase in eutectic spacing was observed when the pulling rate decreased abruptly. In hypoeutectic and hypereutectic compositions, formation of the primary phases were suppressed when the pulling rate increased abruptly from 10?µm/s to 100?µm/s, while primary phases precipitated when the pulling rate decreased abruptly from 100?µm/s to 10?µm/s. The interface altitude decreased after the pulling rate increased abruptly, but increased after the pulling rate decreased abruptly. The liquid composition restriction (around the eutectic composition) at the eutectic interface plays an important role in the suppression of the primary dendrite and coupled eutectic oxides can be obtained in off-eutectic compositions even under higher solidification rate conditions. 相似文献
8.
2A12铝合金化学铣切加工工艺探讨 总被引:1,自引:0,他引:1
为了精确加工2Al2铝合金,探讨了化铣时间和温度对其化铣速率及表面粗糙度的影响,采用现代技术对化铣工件的力学性能进行了测试与分析.结果表明:延长非化铣部位保护胶固化时间并使保护部位向非加工面位移3~5 mm可很好地解决未化铣区域的腐蚀问题;随化铣时间的延长,化铣速率降低,且化铣温度与化铣速率呈现正相关性;化铣表面的粗糙度随化铣时间的延长而增加,随化铣温度的升高呈先减小后增加的趋势;化铣后材料的抗拉强度和屈服强度均有所提高. 相似文献
9.
Chemical processes are becoming increasingly complicated, leading to an increase in process variables and more complex relationships among them. The vine copula has a significant advantage in portraying the dependence of high-dimensional variables. However, as the dimensions increase, the vine copula model incurs a high computational load; such pressure greatly reduces model efficiency. Relationships among variables in the industrial process are complex. Different variables may be strongly or weakly associated or even independent. This paper proposes a process monitoring method based on correlation variable classification and vine copula. The weighted correlation measure is first used to divide variables into a correlated subspace and weakly correlated subspace. Then, two vine structures, C-vine and D-vine, are applied to the correlated and weakly correlated subspaces, respectively. This method takes advantage of C-vine for correlated variables and the flexibility of D-vine for weakly correlated variables. Finally, comprehensive statistics are established based on different subspaces. Monitoring results of the numerical system and the Tennessee Eastman process demonstrate the effectiveness and validity of the proposed method. 相似文献
10.
利用振冲碎石桩处理软土地基,对地基具有置换、排水、加筋等作用,与原土基构成复合地基,可提高地基承载力。结合台州市海堤工程实例,对振冲碎石桩的技术工艺、设计、施工和检测等方面进行介绍。 相似文献