全文获取类型
收费全文 | 80349篇 |
免费 | 3661篇 |
国内免费 | 1700篇 |
专业分类
电工技术 | 2372篇 |
技术理论 | 2篇 |
综合类 | 2869篇 |
化学工业 | 10903篇 |
金属工艺 | 2697篇 |
机械仪表 | 3116篇 |
建筑科学 | 3760篇 |
矿业工程 | 1309篇 |
能源动力 | 1275篇 |
轻工业 | 4305篇 |
水利工程 | 1125篇 |
石油天然气 | 2724篇 |
武器工业 | 206篇 |
无线电 | 6439篇 |
一般工业技术 | 8103篇 |
冶金工业 | 23464篇 |
原子能技术 | 585篇 |
自动化技术 | 10456篇 |
出版年
2024年 | 199篇 |
2023年 | 813篇 |
2022年 | 1050篇 |
2021年 | 1503篇 |
2020年 | 1071篇 |
2019年 | 939篇 |
2018年 | 1417篇 |
2017年 | 1818篇 |
2016年 | 2077篇 |
2015年 | 2130篇 |
2014年 | 2139篇 |
2013年 | 2605篇 |
2012年 | 4281篇 |
2011年 | 4870篇 |
2010年 | 2866篇 |
2009年 | 2779篇 |
2008年 | 2620篇 |
2007年 | 2635篇 |
2006年 | 2593篇 |
2005年 | 5105篇 |
2004年 | 3751篇 |
2003年 | 3083篇 |
2002年 | 1848篇 |
2001年 | 1600篇 |
2000年 | 1171篇 |
1999年 | 1707篇 |
1998年 | 7092篇 |
1997年 | 4626篇 |
1996年 | 3317篇 |
1995年 | 2078篇 |
1994年 | 1611篇 |
1993年 | 1477篇 |
1992年 | 582篇 |
1991年 | 557篇 |
1990年 | 496篇 |
1989年 | 441篇 |
1988年 | 426篇 |
1987年 | 322篇 |
1986年 | 274篇 |
1985年 | 224篇 |
1984年 | 125篇 |
1983年 | 110篇 |
1982年 | 164篇 |
1981年 | 199篇 |
1980年 | 208篇 |
1979年 | 70篇 |
1978年 | 100篇 |
1977年 | 615篇 |
1976年 | 1326篇 |
1975年 | 100篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
13.
Hao Li Pengcheng Zhang Shengquan Yu Hongyu Yang Bin Tang Fuhai Li Shuren Zhang 《Ceramics International》2019,45(9):11639-11647
Mg2(Ti1-xSnx)O4 (x?=?0–1) ceramics were prepared through conventional solid-state method. This paper focused on the dependence of microwave dielectric properties on crystal structural characteristics via crystal structure refinement, Raman spectra study and complex chemical bond theory. XRD spectrums delineated the phase information of a spinel structure, and structural characteristic of these compositions were achieved with the help of Rietveld refinements. Raman spectrums were used to depict the correlations between vibrational phonon modes and dielectric properties. The variation of permittivity is ascribed to the Mg2(Ti1-xSnx)O4 average bond covalency. The relationship among the B-site octahedral bond energy, tetrahedral bond energy and temperature coefficient are discussed by defining on the change rate of bond energy and the contribution rate of octahedral bond energy. The quality factor is affected by systematic total lattice energy, and the research of XPS patterns illustrated that oxygen vacancies can be effectively restrained in rich oxygen sintering process. Obviously, the microwave dielectric properties of Mg2(Ti1-xSnx)O4 compounds were obtained (= 12.18, ?=?170,130?GHz, ?=??53.1?ppm/°C, x?=?0.2). 相似文献
14.
A new constitutive equation of thermoelasticity for crystals is presented based on the interatomic potential and solid mechanics at finite temperature. Using the new constitutive equation, the calculations for crystal copper and graphene are carried out under different loading paths at different temperatures. The calculated results are in good agreement with those of the previous thermoelasticity constitutive equation based on quantum mechanics, which clearly indicates that our new constitutive equation of thermoelasticity is correct. A lot of comparisons also show that the present theory is more concise and efficient than the previous thermal stress theory in the practical application. 相似文献
15.
From an experimental and theoretical investigation of the continuity of influent inorganic suspended solids (ISS) along the links connecting the primary settling tank (PST), fully aerobic or N removal activated sludge (AS) and anaerobic and aerobic sludge digestion unit operations, it was found that the influent wastewater (fixed) ISS concentration is conserved through primary sludge anaerobic digestion, activated sludge and aerobic digestion unit operations. However, the measured ISS flux at different stages through a series of wastewater treatment plant (WWTP) unit operations is not equal to the influent ISS flux, because the ordinary heterotrophic organisms (OHO) biomass contributes to the ISS flux by differing amounts depending on the active fraction of the VSS solids at that stage. 相似文献
16.
Role stress has received a lot of research attention in psychological, sociological, and organizational studies over the last several decades. Based on a literature review of about 300 journal articles, this article examines prominent consequences of role stress. Specific focus is on researching differences in relationships between facets of role stress (i.e., role ambiguity, role conflict, and role overload) and frequently cited consequences using techniques of meta-analysis. Findings indicate that each role stress facet has a different relationship with the eight consequences studied. Role stress research can benefit from looking at each facet individually in addition to role stress generally. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
17.
四川盆地上三叠统划分对比研究 总被引:36,自引:6,他引:30
四川盆地上三叠统对比长期存在混乱,给盆地整体评价带来困难。通过岩石地层、地震地层、事件地层及高分辨率旋回地层等多种方法讨论了须家河组与香溪群各岩性段的对比关系,得出了全盆地上三叠统的对比关系;指出须四段底可近似看成等时界面;须家河组下部地层自西向东、向南逐层超覆在雷口坡组之上,上部地层在盆地西北部自东南向西北方向剥蚀层位渐次变老。文章建议四川盆地上三叠统废除“香溪群”,统一使用“须家河组”,以利于对全盆地上三叠统进行油气资源整体评价与深化研究。 相似文献
18.
19.
The objective of this study was to compare methane production and characteristics of digested material in anaerobic digestion concepts according to the Animal By-Products Regulation (ABP-Regulation) of the EC (hygienisation of biowaste for 1 hour at 70 degrees C, particle size < 12 mm) and Finnish national regulations (treatment temperature 55 degrees C, feeding interval 24 h, hydraulic retention time (HRT) 20 d, particle size < 40 mm) and with small variations in treatment methods for treating manure and biowaste. Moreover, the survival of three different salmonella bacteria in these processes was studied. Hygienisation of biowaste prior to digestion at 35 degrees C enhanced methane production by 14-18% compared to similar treatment without hygienisation. The differences in treatment temperature, HRT and hygienisation of biowaste prior to digestion did not significantly affect the characteristics of digested material. The concepts according to the ABP-Regulation and Finnish national regulations were effective in destroying salmonella bacteria to an undetectable level. 相似文献
20.
贴片机脱机编程的快捷方法 总被引:7,自引:4,他引:3
SMT生产线中的大多数加工设备均为数控设备。它们编程所需要的大多数特征数据均可从CAD设计系统中得到。文章介绍了如何从CAD设计系统中导出X、Y坐标数据,并转换成贴片数据的方法和思路,以期引起更多的同行加入到这方面的研究中。 相似文献