全文获取类型
收费全文 | 570071篇 |
免费 | 67001篇 |
国内免费 | 46857篇 |
专业分类
电工技术 | 52118篇 |
技术理论 | 2篇 |
综合类 | 63141篇 |
化学工业 | 69531篇 |
金属工艺 | 39738篇 |
机械仪表 | 41632篇 |
建筑科学 | 45321篇 |
矿业工程 | 24622篇 |
能源动力 | 14939篇 |
轻工业 | 59914篇 |
水利工程 | 19681篇 |
石油天然气 | 20313篇 |
武器工业 | 9427篇 |
无线电 | 60178篇 |
一般工业技术 | 45891篇 |
冶金工业 | 21858篇 |
原子能技术 | 9183篇 |
自动化技术 | 86440篇 |
出版年
2024年 | 2097篇 |
2023年 | 8640篇 |
2022年 | 21689篇 |
2021年 | 27681篇 |
2020年 | 20067篇 |
2019年 | 13994篇 |
2018年 | 15063篇 |
2017年 | 17127篇 |
2016年 | 15421篇 |
2015年 | 25029篇 |
2014年 | 32104篇 |
2013年 | 37241篇 |
2012年 | 47834篇 |
2011年 | 49878篇 |
2010年 | 47862篇 |
2009年 | 45513篇 |
2008年 | 47245篇 |
2007年 | 46078篇 |
2006年 | 39627篇 |
2005年 | 32216篇 |
2004年 | 23388篇 |
2003年 | 15908篇 |
2002年 | 15490篇 |
2001年 | 13953篇 |
2000年 | 10478篇 |
1999年 | 4228篇 |
1998年 | 1439篇 |
1997年 | 1121篇 |
1996年 | 902篇 |
1995年 | 772篇 |
1994年 | 586篇 |
1993年 | 519篇 |
1992年 | 443篇 |
1991年 | 301篇 |
1990年 | 274篇 |
1989年 | 303篇 |
1988年 | 178篇 |
1987年 | 132篇 |
1986年 | 126篇 |
1985年 | 56篇 |
1984年 | 76篇 |
1983年 | 62篇 |
1982年 | 59篇 |
1981年 | 103篇 |
1980年 | 176篇 |
1979年 | 119篇 |
1965年 | 16篇 |
1964年 | 10篇 |
1959年 | 117篇 |
1951年 | 121篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
981.
The behaviour of hydrogen permeation and diffusion in amorphous alloy Ni68Cr7Si8B14Fe3 hasbeen investigated by an ultrahigh vacuum gas permeation technique. A comparison experimentwas carried out between the as-quenched and annealed States (400℃/2h) of the amorphousalloy. The results show that, for both states of the amorphous alloy in the temperature rangeof 200~350℃, the diffusivity and permeability of hydrogen are in agreement with Arrheniusrelationship, there does not exist H-trapping effect, and the activation energies of diffusion andpermeation almost keep the same. 相似文献
982.
An investigation has been carried out into the possibility of in situ formation of MoS2 within porous anodic films on aluminium, to improve subsequent tribological behaviour, by re-anodizing in thiomolybdate electrolyte. Acidification of thiomolybdate was employed to simulate the conditions for formation of the sulphide at the anodic film/electrolyte interface, followed by appropriate vacuum heat treatments to study possible temperature effects on the sulphide due to either friction or Joule heating during anodizing. The products of both acidification and heat treatment, characterized by X-ray powder diffraction and scanning electron microscopy, were compared with those formed by direct thermal decomposition of ammonium tetrathiomolybdate crystals. The precipitate formed by acidification was mainly amorphous molybdenum trisulphide (MoS3), which on heat treatment at 450 and 850°C yielded 3R-MoS2. 3R-MoS2 also formed by the thermal decomposition of thiomolybdate crystals. Thermogravimetric and differential thermal analyses showed that the decomposition of MoS3 to MoS2 occurred in the range 220–370°C and revealed the sequence of reaction steps. The findings suggest that mainly amorphous MoS3 is formed as a consequence of changes in the pH of the film/electrolyte interface during re-anodizing but the product is relatively easily transformed to crystalline MoS2 on moderate heating which may occur during wear processes. 相似文献
983.
984.
单分散六边形扁平溴碘化银微晶的结构与性能的研究 总被引:1,自引:1,他引:0
应用可控双注仪制备了一系列碘含量相同而碘在微晶中分布不同的单分散六边形扁平溴碘化银乳剂。用扫描电镜(STEM)与X-射线能谱仪(EDS)对单个微晶进行了微区分析,并用介电损耗,微波光导等方法研究了此类乳剂微晶的结构与性能的关系。结果表明:严格控制微晶成核、成熟、生长三个阶段的条件,可制得含六边形颗粒92%以上的扁平溴碘化银乳剂,颗粒大小变化系数小于12%。此外碘在微晶中的分布明显影响微晶的电性质和 相似文献
985.
本文报道 Nb,Ti 微合金钢的热变形动态模拟变形抗力模型。在试验中用热加工模拟试验机进行高温压缩试验,其变形温度为1123—1423K,变形速率为0.1—60s~(-1)。结果表明,在峰值以前该钢种的流变应力数学模型为:σ=5.99.ε~(0.167)·(?)~(6.47×10~(-5)·T)·exp(4064/T)。形变激活能(Q)为444 kJ/mol,β系数为0.080。峰值应力(σ_p),临界应变(ε_c)和温度补偿应变速率参数(Z)之间的关系分别为:σ_p=12.56·lnZ-391.8;lnε_c=0.157·lnZ-7.39。 相似文献
986.
987.
OBJECTIVE: To determine if a relationship exists between the extent of iron-catalyzed injury and the degree of tissue iron overload during reperfusion. METHODS: To selectively increase tissue iron only during early reperfusion, isolated, buffer perfused rabbit hearts were exposed to 20 microM Fe(2+)-100 microM ADP during the last 3 minutes of ischemia and the initial 4 minutes of reperfusion. Control groups were exposed to ADP and iron-ADP regimens that did not increase intracellular iron. All the hearts received 30 minutes of normothermic global ischemia and 30 minutes of reperfusion. Heart function was monitored continuously throughout each experiment. Tissue iron and biochemical markers were analyzed at the end of experiments. RESULTS: Hemodynamic recovery was decreased and tissue lipid peroxide levels were increased in the 20 microM Fe(2+)-100 microM ADP group compared to controls. The recoveries of developed pressure and positive/negative dP/dT at 30 minutes of reperfusion were negatively correlated with tissue iron levels, while cytosol and membrane lipid peroxide levels correlated positively with the iron levels during reperfusion. CONCLUSION: The extent of oxidative injury during reperfusion was directly related to the tissue iron burden present during reperfusion. Increased lipid peroxidation was the principal chemical marker of iron-catalyzed injury. 相似文献
988.
三峡库区湖北宜昌、秭归、兴山、巴东四县幅员面积11589.3平方公里,总人口数166.02万人,三峡水库形成后,淹没土面积74.47平方公里,涉及8.94万人,规划农业生产安置2.8万人。本文以四县土地资源利用现状主和环境容量的分析为基础,进行三峡库区移民安置对水土流失的影响评价,论证综合开发利用水土资源,水土保持与开发性移民相结合,是扩大库区人口环境容量的必由之路,研究制订出移民安置与水土资源的 相似文献
989.
990.
1 IntroductionInmanyapplications,suchasradar,sonar,geophysics,radiocommunicationandmedicalimag ing ,theproblemoftwo dimensionalfrequencyesti mationhasreceivedalotofattentioninrecentyears.InthecaseofadditivewhiteGaussiannoise,numerousmethodssuchasMEMP[1 ] ,MUS… 相似文献