全文获取类型
收费全文 | 5340篇 |
免费 | 955篇 |
国内免费 | 900篇 |
专业分类
电工技术 | 208篇 |
综合类 | 436篇 |
化学工业 | 846篇 |
金属工艺 | 56篇 |
机械仪表 | 150篇 |
建筑科学 | 163篇 |
矿业工程 | 43篇 |
能源动力 | 116篇 |
轻工业 | 3535篇 |
水利工程 | 27篇 |
石油天然气 | 28篇 |
武器工业 | 18篇 |
无线电 | 223篇 |
一般工业技术 | 736篇 |
冶金工业 | 71篇 |
原子能技术 | 32篇 |
自动化技术 | 507篇 |
出版年
2024年 | 42篇 |
2023年 | 134篇 |
2022年 | 143篇 |
2021年 | 195篇 |
2020年 | 175篇 |
2019年 | 187篇 |
2018年 | 125篇 |
2017年 | 158篇 |
2016年 | 163篇 |
2015年 | 173篇 |
2014年 | 337篇 |
2013年 | 351篇 |
2012年 | 465篇 |
2011年 | 498篇 |
2010年 | 364篇 |
2009年 | 383篇 |
2008年 | 282篇 |
2007年 | 447篇 |
2006年 | 395篇 |
2005年 | 359篇 |
2004年 | 306篇 |
2003年 | 306篇 |
2002年 | 259篇 |
2001年 | 222篇 |
2000年 | 163篇 |
1999年 | 119篇 |
1998年 | 84篇 |
1997年 | 64篇 |
1996年 | 64篇 |
1995年 | 53篇 |
1994年 | 30篇 |
1993年 | 31篇 |
1992年 | 24篇 |
1991年 | 7篇 |
1990年 | 14篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1968年 | 2篇 |
1955年 | 1篇 |
排序方式: 共有7195条查询结果,搜索用时 15 毫秒
51.
52.
以漂白桉木浆和废报纸为原料,利用2,2,6,6-四甲基哌啶-1-氧自由基(TEMPO)/NaBr/NaClO氧化体系对其进行处理制备氧化纳米纤维素,并探究两种氧化纳米纤维素添加量对纸张性能的影响。研究结果表明:桉木浆氧化纳米纤维素的平均纤维长度约为75~95 nm,长径比约为6.5~8.5,均高于废报纸氧化纳米纤维素(45~75 nm,4~6)。添加桉木浆氧化纳米纤维素和废报纸氧化纳米纤维素均可使纸张抗张指数、耐破指数和撕裂指数增加。添加6%桉木浆氧化纳米纤维素时,纸张抗张指数由21.16(N·m)/g增加至31.37(N·m)/g,耐破指数由1.32(kPa·m^(2))/g增加至1.84(kPa·m^(2))/g,撕裂指数由6.61(mN·m^(2))/g增加至8.03(mN·m^(2))/g;添加6%废报纸氧化纳米纤维素时,纸张抗张指数由21.16(N·m)/g增加至27.22(N·m)/g,耐破指数由1.32(kPa·m^(2))/g增加至1.79(kPa·m^(2))/g,添加4%废报纸氧化纳米纤维素,纸张撕裂指数由6.61(mN·m^(2))/g增加至8.12(mN·m^(2))/g,可见,添加桉木浆氧化纳米纤维素效果更佳。添加1%阳离子淀粉,有助于两种氧化纳米纤维素对纸张强度的提高,其中桉木浆氧化纳米纤维素可使抗张指数最大提高51.09%,耐破指数提高50.00%,撕裂指数提高27.62%。 相似文献
53.
54.
This paper considers the state‐dependent interference relay channel (SIRC) in which one of the two users may operate as a secondary user and the relay has a noncausal access to the signals from both users. For discrete memoryless SIRC, we first establish the achievable rate region by carefully merging Han‐Kobayashi rate splitting encoding technique, superposition encoding, and Gelfand‐Pinsker encoding technique. Then, based on the achievable rate region that we derive, the capacity of the SIRC is established in many different scenarios including (a) the weak interference regime, (b) the strong interference regime, and (c) the very strong interference regime. This means that our capacity results contain all available known results in the literature. Next, the achievable rate region and the associated capacity results are also evaluated in the case of additive Gaussian noise. Additionally, many numerical examples are investigated to show the value of our theoretical derivations. 相似文献
55.
Perovskite solar cells are one of the most promising photovoltaic technology, presenting the fastest power conversion efficiency (PCE) growth from 3.8 % to 24.2 % in just 10 years. However, there are still challenges hindering its commercialization such as the expensive back‐contact made of gold. Carbon‐based materials, mainly carbon pastes made of carbon black and graphite, have already proven to be good candidates as back‐contacts because of their features such as low cost, high conductivity, and high stability. In this work, the replacement of gold back‐contact by a carbon paper with a microporous layer coated with a PEDOT:PSS dispersion is reported. To the best of the author's knowledge, this material has never been reported for perovskite solar cells. A PCE of 9.22 % was obtained, representing 62 % of the PCE obtained for the same cell but with a gold back‐contact. 相似文献
56.
This paper studies the cognitive broadcast channel in which the primary user com- municates to the primary receiver, while the secondary user has noncausal knowledge of the primary radio's codeword and expects to communicate to two secondary receivers. Comparing with the existing cognitive radio channel which considers only one secondary receiver, cognitive broadcast channel studies the case that there are multiple secondary receivers. To this end, we investigate the fundamental limits of the performance of the Gaussian cognitive broadcast channel from the information theoretic perspective. Specifically, we derive the capacity region of the Gaussian cognitive degraded broadcast channel with weak interference. 相似文献
57.
《影响评估与项目评价》2013,31(3):163-174
Efforts have been made to mainstream the environment in European Commission (EC) development co-operation. In programming, the main tool is the Country Environmental Profile (CEP) which informs, from an environmental point of view, the preparation of Country Strategy Papers (CSPs). Recently CEPs have improved significantly; they have different entry points in CSPs and the results of environmental integration can be found in a series of ‘environmental integration outputs’. This paper describes the structure of CEPs, their place in the EC cycle of operations and how they can influence CSPs. It shows, through case studies, the impact CEPs are having on CSPs, resulting in CSPs that prepare the ground for more effective environmental integration throughout the cycle of operations. 相似文献
58.
醌类化合物是PM2.5中的一类有害物质。本研究建立了纸喷雾离子化衍生质谱法快速测定PM2.5中的醌类污染物。通过衍生化反应在醌化合物中引入氨基,提高醌在纸喷雾中的离子化效率。随后对衍生化试剂种类、电压、喷雾溶剂种类等反应条件进行优化。在最优实验条件下,采用内标法定量分析1,4-苯醌、甲基对苯醌、1,4-萘醌和1,4-蒽醌,4种化合物均呈现较好的线性关系,其检出限分别为4.49、20.89、0.13、0.17 ng。利用该方法分析PM2.5实际样品中的萘醌和蒽醌,均获得了较好的定性和定量结果。 相似文献
59.
60.
《Energy Policy》2015
Pulp and paper production, an energy-intensive process, is among the main light industries contributing to energy saving and pollution emission reduction in China. The improvement of energy efficiency is essential for energy consumption and sustainable development. This study analyzes the negative factors in the pulp and paper sector by calculating energy efficiency from the lengthways time and investigating the gap between China and foreign countries through a horizontal comparison. Accordingly, energy efficiency has increased in the Chinese pulp and paper industry with years of efforts, but its transformation remains unclear. Furthermore, the energy-saving potential, energy cost saving, and carbon dioxide emission reduction in the pulp and paper industry are evaluated according to the Twelfth Five-year Plan (2011–2015). The results show that the pulp and paper industry has further capabilities for energy-saving and carbon dioxide emission reduction by improving energy efficiency in China, resulting in great economic benefit. In brief, new technology and energy structure adjustment are long-term strategies for energy conversation, with changes in the scale of mills expected to provide huge opportunities to improve energy efficiency in China within a short period. 相似文献