全文获取类型
收费全文 | 28084篇 |
免费 | 2413篇 |
国内免费 | 1122篇 |
专业分类
电工技术 | 1564篇 |
技术理论 | 1篇 |
综合类 | 1731篇 |
化学工业 | 4736篇 |
金属工艺 | 1624篇 |
机械仪表 | 1663篇 |
建筑科学 | 2273篇 |
矿业工程 | 859篇 |
能源动力 | 858篇 |
轻工业 | 2033篇 |
水利工程 | 543篇 |
石油天然气 | 1320篇 |
武器工业 | 219篇 |
无线电 | 3140篇 |
一般工业技术 | 3533篇 |
冶金工业 | 1248篇 |
原子能技术 | 380篇 |
自动化技术 | 3894篇 |
出版年
2024年 | 139篇 |
2023年 | 530篇 |
2022年 | 892篇 |
2021年 | 1247篇 |
2020年 | 996篇 |
2019年 | 779篇 |
2018年 | 828篇 |
2017年 | 1026篇 |
2016年 | 874篇 |
2015年 | 1137篇 |
2014年 | 1382篇 |
2013年 | 1717篇 |
2012年 | 1807篇 |
2011年 | 1970篇 |
2010年 | 1681篇 |
2009年 | 1566篇 |
2008年 | 1518篇 |
2007年 | 1435篇 |
2006年 | 1372篇 |
2005年 | 1324篇 |
2004年 | 838篇 |
2003年 | 700篇 |
2002年 | 610篇 |
2001年 | 512篇 |
2000年 | 547篇 |
1999年 | 638篇 |
1998年 | 590篇 |
1997年 | 469篇 |
1996年 | 508篇 |
1995年 | 414篇 |
1994年 | 347篇 |
1993年 | 265篇 |
1992年 | 205篇 |
1991年 | 173篇 |
1990年 | 124篇 |
1989年 | 102篇 |
1988年 | 99篇 |
1987年 | 66篇 |
1986年 | 45篇 |
1985年 | 33篇 |
1984年 | 31篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1976年 | 5篇 |
1972年 | 3篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
Changwei HU Yu YANG Jia LUO Pan PAN Dongmei TONG Guiying LI 《Frontiers of Chemical Science and Engineering》2011,5(2):188
Biomass is considered as a renewable and alternative resource for the production of fuels and chemicals, since it is the only carbon and hydrogen containing resource that we can find in the world except for fossil resources, capable of being converted to hydrocarbons. The pyrolytic liquefaction of biomass is a promising way to convert biomass to useful products. This paper briefly surveys the present status of the direct catalytic pyrolysis for the liquefaction of biomass. The direct use of catalysts could decrease the pyrolysis temperature, increase the conversion of biomass and the yield of bio-oil, and change the distribution of the pyrolytic liquid products then improve the quality of the bio-oil obtained. The fact that biomass is in solid state present great challenges for its conversion and for the effective use of catalysts due to the bad heat transfer characteristics and bad mass transfer properties. These barriers appeal for the development of a new catalyst and new catalytic process as well as the integration of both. Process design and process intensification are of significant importance in the catalytic conversion of biomass. 相似文献
972.
Heng‐Lei Su Jung‐Mu Hsu Jing‐Pin Pan Tsung‐Hsiung Wang Fu‐En Yu Chorng‐Shyan Chern 《Polymer Engineering and Science》2011,51(6):1188-1197
Both the isothermal and non‐isothermal polymerizations of N,N′‐bismaleimide‐4,4′‐diphenylmethane (BMI) with barbituric acid (BTA) were investigated by the differential scanning calorimeter. The experimental results showed that the polymerizations of BMI with BTA were governed by the competitive Michael addition reaction and free radical polymerization mechanisms. Furthermore, the contribution of free radical polymerization becomes more important when the mole fraction of BTA decreases. 1H NMR and 13C NMR measurements further support the coexistence of the Michael addition reaction and free radical polymerization mechanisms. A preliminary kinetic model that took into account the competitive Michael addition reaction and free radical polymerization mechanisms was developed. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers 相似文献
973.
水库(群)实时调度能结合有效的水文预报信息对水库在实时运行层面权衡防洪与兴利效益具有指导意义。然而,水文预报信息的利用面临着不可规避的不确定性问题,故水库(群)实时调度运行需要考虑风险控制方法的研究。针对耦合水文预报的水库群汛期运行水位动态控制问题,提出了可考虑各水库不同预见期长度、不同预报精度的两阶段风险率计算方法,并将其应用于构建水库群汛期运行水位动态控制模型。首先,两阶段风险率思想是将未来调度时段按预见期节点分为预见期以内和预见期以外两个阶段,预见期以内考虑径流预报不确定性带来的风险,采用集合预报思想统计多组预报径流情景在预见期以内的失事概率,预见期以外考虑因预见期末水位过高难于应对后续洪水的潜在风险,根据历史设计洪水的调洪演算试算风险率。其次,基于所提出的两阶段风险率方法构建以发电量最大为目标函数的水库群汛期运行水位动态控制模型。研究结果表明:提出的两阶段风险率计算方法可兼顾考虑实时调度阶段由径流不确定性引起的预见期以内、预见期以外的潜在风险;基于两阶段风险分析构建的水库群优化调度模型,可求解得出的水库群系统库容动态最优决策过程,且该优化调度模型可在不增加汛期防洪风险的基础上提高水库群系统的发电效益,即2010年汉江流域五库系统在夏汛期可提高总发电量2.30亿kWh。 相似文献
974.
975.
在催化剂存在下,以N-乙基-N-苄基苯胺磺化物与对-(N,N-二乙基)氨基苯甲醛在酸性条件下于95℃-100℃进行缩合。在pH=5-6时,用30%过氧化氢氧化,合成了C.I.酸性紫17,氧化收率86.5%。成品中铬含量为10.8mg/kg。 相似文献
976.
977.
干-喷湿纺聚丙烯腈纤维拉伸工艺研究 总被引:1,自引:0,他引:1
研究了干 -喷湿纺聚丙烯腈 (PAN)初生纤维的喷丝头拉伸比和三级拉伸 (空气拉伸、DMF浴拉伸、热水和沸水拉伸、干热拉伸 )工艺中各拉伸比对纤维性能的影响。结果表明 :提高喷丝头拉伸比可明显地降低初生纤维的线密度 ,提高强度 ;三级拉伸工艺中各拉伸比的提高均有利于PAN纤维线密度的减小及其强度、声速取向度和抗张模量的提高 ;合理调配三级拉伸中各拉伸比可制得强度超过 7.0cN/dtex的PAN纤维 相似文献
978.
979.
980.
Modern industrial systems are usually in large scale, consisting of massive components and variables that form a complex system topology. Owing to the interconnections among devices, a fault may occur and propagate to exert widespread influences and lead to a variety of alarms. Obtaining the root causes of alarms is beneficial to the decision supports in making corrective alarm responses. Existing data-driven methods for alarm root cause analysis detect causal relations among alarms mainly based on historical alarm event data. To improve the accuracy, this paper proposes a causal fusion inference method for industrial alarm root cause analysis based on process topology and alarm events. A Granger causality inference method considering process topology is exploited to find out the causal relations among alarms. The topological nodes are used as the inputs of the model, and the alarm causal adjacency matrix between alarm variables is obtained by calculating the likelihood of the topological Hawkes process. The root cause is then obtained from the directed acyclic graph (DAG) among alarm variables. The effectiveness of the proposed method is verified by simulations based on both a numerical example and the Tennessee Eastman process (TEP) model. 相似文献