全文获取类型
收费全文 | 50777篇 |
免费 | 4221篇 |
国内免费 | 2517篇 |
专业分类
电工技术 | 2994篇 |
技术理论 | 2篇 |
综合类 | 3498篇 |
化学工业 | 8127篇 |
金属工艺 | 2956篇 |
机械仪表 | 3327篇 |
建筑科学 | 3996篇 |
矿业工程 | 1475篇 |
能源动力 | 1374篇 |
轻工业 | 3981篇 |
水利工程 | 993篇 |
石油天然气 | 2894篇 |
武器工业 | 456篇 |
无线电 | 5725篇 |
一般工业技术 | 5802篇 |
冶金工业 | 2529篇 |
原子能技术 | 670篇 |
自动化技术 | 6716篇 |
出版年
2024年 | 197篇 |
2023年 | 885篇 |
2022年 | 1476篇 |
2021年 | 1998篇 |
2020年 | 1650篇 |
2019年 | 1270篇 |
2018年 | 1466篇 |
2017年 | 1623篇 |
2016年 | 1472篇 |
2015年 | 1983篇 |
2014年 | 2610篇 |
2013年 | 3066篇 |
2012年 | 3362篇 |
2011年 | 3442篇 |
2010年 | 3236篇 |
2009年 | 3100篇 |
2008年 | 3017篇 |
2007年 | 2948篇 |
2006年 | 2901篇 |
2005年 | 2415篇 |
2004年 | 1703篇 |
2003年 | 1584篇 |
2002年 | 1538篇 |
2001年 | 1321篇 |
2000年 | 1162篇 |
1999年 | 1154篇 |
1998年 | 938篇 |
1997年 | 801篇 |
1996年 | 713篇 |
1995年 | 592篇 |
1994年 | 471篇 |
1993年 | 327篇 |
1992年 | 265篇 |
1991年 | 195篇 |
1990年 | 159篇 |
1989年 | 134篇 |
1988年 | 98篇 |
1987年 | 59篇 |
1986年 | 57篇 |
1985年 | 26篇 |
1984年 | 27篇 |
1983年 | 20篇 |
1982年 | 22篇 |
1981年 | 14篇 |
1980年 | 11篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1966年 | 1篇 |
1959年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Xi Shen Li-Peng Cao Jian-Fa Zhao Wei-Peng Wang Qing-Qing Liu Yuan Yao Jun-Jie Li Chang-Zhi Gu Ming-Wei Chen Chang-Qing Jin Ri-Cheng Yu 《Journal of the American Ceramic Society》2019,102(11):6469-6474
We propose the question of the modulated structures of copper oxide is caused by the [CuO2] in-plane oxygen vacancy or apical oxygen vacancy. Sr2CuO3+δ single-crystal samples were prepared using high-temperature and high-pressure methods. The major phase of Sr2CuO3+δ (δ = 0.4) single-crystal system is found to be constituted by the 5 a modulated structure with the Fmmm space group, which originates from the [CuO2] in-plane oxygen vacancy appearing in octahedral Cu-O. Besides, the presence of the [CuO2] in-plane oxygen vacancy may obliterate the superconductivity of the system. Experimental results deduce that the oxygen vacancy may appear in the apical oxygen sites in high-temperature copper oxide superconductors. 相似文献
43.
44.
Y S Cao C M Ang K S Raajeevan A K Kiran K C Lai S W Ng I Zulkifli Y L Wah 《Water science and technology》2006,54(8):237-246
This paper analyses the performance of the anaerobic selector (A/O process) in a full-scale activated sludge process receiving mostly industrial sewage discharge (> 60%) in Singapore. In addition to the sludge settleability, enhanced biological phosphorus removal (EBPR) was studied. The sludge volume index (SVI) reduced from 200 to 80 ml g(-1) and foaming was suppressed significantly, indicating the effectiveness of the anaerobic selector in improving sludge settleability. The phosphorus removal efficiency was 66%, and 7.5 mg HAc-COD was consumed per mg PO4(3-) -P removed. In the anaerobic compartment, 31% of the SCOD and 73% of the acetic acid in the settled sewage were removed with PO4(3-) -P release of 14.1 mg PO4(3-)-P l(-1). The linear correlation between PO4(3-) -P release in the anaerobic compartment and PO4(3-) -P uptake in the aerobic compartment indicates that there is about 0.8 mg PO4(3-) -P release in the anaerobic compartment per mg PO34(3-) -P uptake in the aerobic compartment. The fates of volatile fatty acids (VFAs) and its short chain acids (SCAs) in the process were studied and discussed. 相似文献
45.
宁东供水工程供水水泵共有卧式和立式离心泵2种方案可供选择,也是工程论证时争论的焦点,经综合比较及主机设备的国际招标,最终确定了奥地利安德里兹公司的卧式双吸中开式离心泵为宁东供水工程的供水水泵。 相似文献
46.
47.
48.
In this paper, we consider the problem of designing optimal asynchronous wake-up schedules to facilitate distributed power management and neighbor discovery in multihop wireless networks. We first formulate it as a block design problem and derive the fundamental trade-offs between wake-up latency and the average duty cycle of a node. After the theoretical foundation is laid, we then devise a neighbor discovery and schedule bookkeeping protocol that can operate on the optimal wake-up schedule derived. To demonstrate the usefulness of asynchronous wake-up, we investigate the efficiency of neighbor discovery and the application of on-demand power management, which overlays a desirable communication schedule over the wake-up schedule mandated by the asynchronous wake-up mechanism. Simulation studies demonstrate that the proposed asynchronous wake-up protocol has short discovery time which scales with the density of the network; it can accommodate various traffic characteristics and loads to achieve an energy savings that can be as high as 70 percent, while the packet delivery ratio is comparable to that without power management. 相似文献
49.
SO4^2-/ZrO2固体超强酸的制备及其催化合成ETBE的研究 总被引:5,自引:2,他引:3
采用沉淀一浸渍法制备了负载型SO4^2-/ZrO2固体超强酸催化剂,运用IR、XRD等方法表征所制备催化剂的物化性质。结果表明,所制备的催化剂具有固体超强酸催化剂的特征,酸性与焙烧温度有关,适当提高焙烧温度有利于样品酸强度的提高,但焙烧温度过高会导致脱硫;浸渍液H2SO4浓度高有利于提高催化剂的硫含量,但是浓度过高,会在催化剂上形成硫酸盐,从而降低催化剂的比表面积和酸性。采用制备的催化剂气相催化乙醇与叔丁醇合成乙基叔丁基醚反应,乙基叔丁基醚的选择性为54.71%。 相似文献
50.
The oxidation behavior of Hastelloy-XR alloy was investigated to obtain the optimum surface condition for corrosion-resistant glass-coatings. The surface morphology of oxide scales changed significantly with variation of temperatureand oxygen partial pressure (po2 ). The oxidation kinetics was mainly parabolic independent of oxidation conditions.The oxide scales were consisted of inner Cr2O3 and outer spinel layers. The phase component of spinel layers wereMn1.5Cr1.5O4 and (Mn,Ni)(Cr,Fe)2O4 for the oxygen partial pressures po2<10 kPa and po2>10 kPa, respectively.The optimum oxidation condition to obtain an oxide scale for well-adhered glass-coating to the substrate was 1248 Kand po2 =0.01 kPa for the oxidation time of 43 ks. 相似文献