全文获取类型
收费全文 | 54275篇 |
免费 | 4782篇 |
国内免费 | 2517篇 |
专业分类
电工技术 | 3271篇 |
技术理论 | 7篇 |
综合类 | 3471篇 |
化学工业 | 9185篇 |
金属工艺 | 3309篇 |
机械仪表 | 3481篇 |
建筑科学 | 3820篇 |
矿业工程 | 1722篇 |
能源动力 | 1641篇 |
轻工业 | 3442篇 |
水利工程 | 881篇 |
石油天然气 | 3462篇 |
武器工业 | 519篇 |
无线电 | 6285篇 |
一般工业技术 | 6916篇 |
冶金工业 | 2592篇 |
原子能技术 | 750篇 |
自动化技术 | 6820篇 |
出版年
2024年 | 294篇 |
2023年 | 1033篇 |
2022年 | 1752篇 |
2021年 | 2484篇 |
2020年 | 1832篇 |
2019年 | 1517篇 |
2018年 | 1684篇 |
2017年 | 1949篇 |
2016年 | 1719篇 |
2015年 | 2247篇 |
2014年 | 2851篇 |
2013年 | 3428篇 |
2012年 | 3598篇 |
2011年 | 3841篇 |
2010年 | 3208篇 |
2009年 | 3064篇 |
2008年 | 3083篇 |
2007年 | 2894篇 |
2006年 | 2801篇 |
2005年 | 2377篇 |
2004年 | 1678篇 |
2003年 | 1450篇 |
2002年 | 1436篇 |
2001年 | 1265篇 |
2000年 | 1254篇 |
1999年 | 1265篇 |
1998年 | 1031篇 |
1997年 | 877篇 |
1996年 | 843篇 |
1995年 | 655篇 |
1994年 | 539篇 |
1993年 | 362篇 |
1992年 | 304篇 |
1991年 | 217篇 |
1990年 | 184篇 |
1989年 | 150篇 |
1988年 | 114篇 |
1987年 | 65篇 |
1986年 | 66篇 |
1985年 | 34篇 |
1984年 | 30篇 |
1983年 | 29篇 |
1982年 | 24篇 |
1981年 | 14篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1976年 | 6篇 |
1973年 | 2篇 |
1970年 | 2篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
对抗航母——巡航导弹优于弹道导弹 总被引:1,自引:0,他引:1
分析比较了反航母战斗群主战装备的两种方案,对巡航/飞航导弹和精确制导弹道导弹的反航母作战能力进行了分析.通过分析,指出巡航/飞航导弹仍是反航母战斗群的主战装备,必须从新军事变革发展趋势和国情出发,紧紧把握重要战略机遇期,争取巡航/飞航导弹的跨越性发展;同时,反航母战斗群作战需要巡航/飞航导弹主战装备与精确制导弹道导弹等其它弹种的合理配置,共同构建反航母战斗群的多层次、优配置的立体进攻体系。 相似文献
992.
993.
994.
Hui Li Jianlu Zhang Khalid Fatih Zhenwei Wang Yanghua Tang Zheng Shi Shaohong Wu Datong Song Jiujun Zhang Nengyou Jia Silvia Wessel Rami Abouatallah Nathan Joos 《Journal of power sources》2008
The effects of toluene contamination on the performance of polymer electrolyte membrane (PEM) fuel cells were investigated, using various levels of toluene concentration in the air streams, under different operational conditions and with different catalyst loadings. Constant-current polarization and electrochemical impedance spectroscopy (EIS) were conducted to analyze the poisoning behaviour of toluene. The severity of the contamination effect increased with an increase in both the current density and the toluene concentration, but decreased with an increase in both the relative humidity (RH) and the cathode-side Pt loading. The toluene-poisoned fuel cell could not be fully recovered by replacing toluene-contaminated air with pure air. EIS measurements revealed that both kinetic resistance and mass transfer resistance increased as a result of toluene contamination, while membrane resistance remained unchanged. However, the increase in kinetic resistance was a major contributor to cell performance degradation. 相似文献
995.
目的评价急症经导管动脉栓塞术(TAE)治疗难治性产后出血的疗效及安全性。方法临床25例难治性产后出血患者,采用右股动脉Seldinger穿刺技术,选择性插管至双侧髂内动脉或子宫动脉,行DSA明确出血部位后以明胶海绵颗粒栓塞。结果插管成功率100%,手术时间25~60min,平均(42.5±4.6)min,术后止血时间3~15min。术后止血总有效率100%。比较术前术后患者血红蛋白及心率,差异具有显著性(t=29.49,P<0.01;t=16.51,P<0.01)。所有患者宫体按期复旧,转经后月经正常。结论TAE创伤小,疗效快速肯定,术后短期及长期随访无严重并发症,对危及生命的产后出血是一种有效治疗措施。 相似文献
996.
Nano-sized SnSbCux alloy anode materials are prepared by reductive co-precipitation method combining with the aging treatment in water bath at 80 °C. The microstructure, morphology and electrochemical properties of synthesized SnSbCux alloy powders are evaluated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and galvanostatical cycling tests. The results indicate that the average particle size is reduced and the Cu6Sn5, Cu2Sb phases appear successively along with the increase of Cu content in the SnSbCux alloy. The reduction of average particle size, the existence of inactive element Cu and the complex multi-step reaction mechanism in SnSbCux alloy anodes are propitious to improve the structure stability and thus improve the cycling performance. When cycled at a constant current density of 0.1 mA cm−2 between 0.02 and 1.50 V, the coulomb efficiency of first cycle exceeds 74% and the reversible capacity of 20th cycle attains to 490 mAh g−1 in SnSbCu0.5 alloy anode. 相似文献
997.
Yan-Bing He Zhi-Yuan Tang Quan-Sheng Song Hui Xie Quan-Hong Yang Yuan-Gang Liu Guo-Wei Ling 《Journal of power sources》2008
The commercial 18650 Li(Ni1/3Co1/3Mn1/3)O2/graphite high power batteries were prepared and their electrochemical performance at temperatures of 25 and 50 °C was extensively investigated. The results showed that the charge-transfer resistance (Rct) and solid electrolyte interface resistance (Rsei) of the high power batteries at 25 °C decreased as states of charge (SOC) increased from 0 to 60%, whereas Rct and Rsei increased as SOC increased from 60 to 100%. The discharge plateau voltage of batteries reduced greatly with the increase in discharge rate at both 25 and 50 °C. The high power batteries could be discharged at a very wide current range to deliver most of their capacity and also showed excellent power cycling performance with discharge rate of as high as 10 C at 25 °C. The elevated working temperature did not influence the battery discharge capacity and cycling performance at lower discharge rates (e.g. 0.5, 1, and 5 C), while it resulted in lower discharge capacity at higher discharge rates (e.g. 10 and 15 C) and bad cycling performance at discharge rate of 10 C. The batteries also exhibited excellent cycle performance at charge rate of as high as 8 C and discharge rate of 10 C. 相似文献
998.
Chaojie Song Chris Jensen Chua Yanghua Tang JianLu Zhang Jiujun Zhang Jing Li Keping Wang Scott McDermid Paul Kozak 《International Journal of Hydrogen Energy》2008
A PEM fuel cell with a Nafion 211 membrane-based membrane electrode assembly (MEA) was tested with an H2/air stoichiometry of 2/4 at 25%, 50%, 75%, and 100% relative humidities. A voltage jump on the polarization curve was observed when the cell was operated at a lower humidity. This phenomenon may be explained by the water back-diffusion from the cathode into the membrane resulting in both a non-uniform water distribution in the membrane and a liquid-equilibrated interface between the membrane and the anode catalyst layer. Experimental results obtained by AC impedance spectroscopy measuring the MEA resistance (membrane+catalyst ionomer layers) at different current densities as well as collected polarization data at high feed-gas flow rates (or at low backpressures) and high temperatures all confirmed the validity of the proposed water back-diffusion hypothesis. 相似文献
999.
1000.
川东地区中二叠统茅口组一段(茅一段)非常规泥质灰岩储层近期取得重大勘探发现。基于野外露头剖面及钻井岩心观察,通过薄片鉴定、物性分析、X射线衍射、氮气吸附、氩离子抛光扫描电镜、总有机碳含量(TOC)测定、CT扫描以及测井分析等手段,对茅一段泥质灰岩储层及其主控因素进行研究。结果表明,川东地区茅一段主要发育泥晶灰岩、泥晶生屑灰岩、生屑泥晶灰岩和(含)泥质生屑泥晶灰岩等4种岩石类型以及粒缘孔(缝)、有机质孔、溶孔(缝)、裂缝、滑石收缩孔(缝)等5类储集空间。其中,泥晶灰岩和泥晶生屑灰岩孔隙度低,有机质含量低,储集性能差;生屑泥晶灰岩和(含)泥质生屑泥晶灰岩孔隙度高,有机质含量高,储集性能好。茅一段储层受岩相、有机质丰度和成岩作用的综合控制,生屑泥晶灰岩微相和(含)泥质生屑泥晶灰岩微相中的原始孔隙发育好且富含粘土矿物;粘土矿物转化形成的粘土微孔和有机质孔为茅一段主要的储集空间;白云石化作用和溶蚀作用为茅一段提供了部分储集空间。基于此,提出茅一段优质储层发育模式:沉积期,由于原始组构差异,生屑泥晶灰岩和(含)泥质生屑泥晶灰岩中的原始孔隙发育;中-深埋藏期,海泡石发生成岩转化,形成粘土微孔和有机质孔,同时释放富镁成岩流体,发生白云石化;深埋藏期,酸性流体进一步改造储层,使生屑泥晶灰岩和(含)泥质生屑灰岩储层发育为优质储层。 相似文献