全文获取类型
收费全文 | 197861篇 |
免费 | 2116篇 |
国内免费 | 633篇 |
专业分类
电工技术 | 4063篇 |
综合类 | 123篇 |
化学工业 | 26709篇 |
金属工艺 | 7507篇 |
机械仪表 | 5461篇 |
建筑科学 | 4037篇 |
矿业工程 | 747篇 |
能源动力 | 4658篇 |
轻工业 | 14396篇 |
水利工程 | 1695篇 |
石油天然气 | 2842篇 |
武器工业 | 7篇 |
无线电 | 27293篇 |
一般工业技术 | 37406篇 |
冶金工业 | 45386篇 |
原子能技术 | 3560篇 |
自动化技术 | 14720篇 |
出版年
2021年 | 1246篇 |
2019年 | 1280篇 |
2018年 | 2128篇 |
2017年 | 2105篇 |
2016年 | 2171篇 |
2015年 | 1490篇 |
2014年 | 2618篇 |
2013年 | 7950篇 |
2012年 | 4463篇 |
2011年 | 6111篇 |
2010年 | 4932篇 |
2009年 | 5774篇 |
2008年 | 6148篇 |
2007年 | 6197篇 |
2006年 | 5640篇 |
2005年 | 5304篇 |
2004年 | 5253篇 |
2003年 | 5090篇 |
2002年 | 4901篇 |
2001年 | 5305篇 |
2000年 | 4916篇 |
1999年 | 5435篇 |
1998年 | 15618篇 |
1997年 | 10314篇 |
1996年 | 7933篇 |
1995年 | 5786篇 |
1994年 | 5017篇 |
1993年 | 5022篇 |
1992年 | 3385篇 |
1991年 | 3263篇 |
1990年 | 3218篇 |
1989年 | 3040篇 |
1988年 | 2785篇 |
1987年 | 2238篇 |
1986年 | 2302篇 |
1985年 | 2610篇 |
1984年 | 2312篇 |
1983年 | 2063篇 |
1982年 | 1903篇 |
1981年 | 2043篇 |
1980年 | 1790篇 |
1979年 | 1659篇 |
1978年 | 1656篇 |
1977年 | 2022篇 |
1976年 | 2703篇 |
1975年 | 1422篇 |
1974年 | 1369篇 |
1973年 | 1316篇 |
1972年 | 1124篇 |
1971年 | 956篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Microstructure and mechanical behaviour of 3Y-TZP/Mo nanocomposites possessing a novel interpenetrated intragranular microstructure 总被引:2,自引:0,他引:2
Yttria stabilized tetragonal zirconia polycrystal (Y-TZP)/0-100 vol % molybdenum (Mo) composites were fabricated by hot-pressing a mixture of Y-TZP powder containing 3 mol % yttria (Y2O3) and a fine Mo powder in vacuum. This composite system possessed a novel microstructural feature composed of an interpenetrated intragranular nanostructure, in which either nanometer sized Mo particles or equivalent sized zirconia (ZrO2) particles located within the ZrO2 grains or Mo grains, respectively. The strength and toughness were both greatly enhanced with increasing Mo content for the 3Y-TZP/Mo composites thus breaking through the strength-toughness tradeoff relation in transformation toughened ZrO2 and its composite materials. They exhibited a maximum strength of 2100 MPa and a toughness of 11.4 MPa·m1/2 for the composite containing 70 vol % Mo. These simultaneous improvements in strength and toughness were determined to be the result of a decrease in flaw size associated with the interpenetrated intragranular nanostructure, and a stress shielding effect created in the crack tip by the elongated Mo polycrystals bridging the crack tip in addition to the stress induced phase transformation. 相似文献
112.
Comparative analysis of the characteristics of amplitude-dependent internal friction (IF) was carried out to explain reasons leading to an increase of the creep limit of the butt welded joint in PT-3V titanium alloy (PT-2V filler material) after cyclic loading. IF was measured by the method of the direct torsional pendulum on cylindrical specimens representing the gage part of the specimens subjected to preliminary cyclic loading. The data were processed using the Granato-Lucke theory. The results show that the reduction of IF after cyclic loading took place as a result of an increase of the number and redistribution of pinning points of the dislocations. Consequently, the density of mobile dislocations decreases by 8% and the length of dislocation segments by 18%. These processes of stabilization of the structure were completed within 5·10
4
cycles of preliminary loading. Stabilization of the dislocation structure of the material of the welded joint increases its creep limit.Translated from Problemy Prochnosti, No. 4, pp. 35–40, April, 1996. 相似文献
113.
T Takikawa H Hayashi N Nishimura M Yano T Isomura N Sakamoto 《Canadian Metallurgical Quarterly》1994,29(5):593-597
Chronic hepatitis C has been demonstrated to be associated with hepatic iron overload, and the hypothesis that the disease activity of hepatitis C is associated with iron cytotoxicity was tested in male volunteer blood donors. Sera with either antibody to hepatitis C virus or hepatitis B surface antigen were selected for determination of ferritin concentration and alanine aminotransferase activity. A correlation between serum ferritin concentration (Y; microgram/l) and alanine aminotransferase activity (X; IU/l) was found in donors with antibody to hepatitis C (log Y = 0.65 x log X + 0.98, r = 0.53, and P < 0.01). The correlation was lower in donors with hepatitis B surface antigen (r = 0.37; P < 0.01). Hepatitis C virus infection probably induces time-dependent iron accumulation associated with the progression of disease activity, while hepatitis B virus infection results in a variety of iron loads with different clinical features. The high disease activity related to hyperferritinemia suggests the presence of iron-induced liver damage in donors with hepatitis C. 相似文献
114.
Ipratropium bromide is a synthetic derivative of atropine with little absorption when used in inhalation, and therefore little secondary effects. The authors review its pharmacological properties and therapeutic efficacy in the treatment of asthma in children. Combined nebulized inhalation of ipratropium bromide and beta 2 sympathomimetic results in a more efficient and more sustained bronchodilatation than beta 2 sympathicomimetic alone in the treatment of acute asthma in children. Ipratropium bromide should be usefully introduced in the therapeutic scheme of acute asthma in children. Further studies will be necessary in order to determine its efficacy and tolerance in infants. 相似文献
115.
116.
117.
The expression patterns of laminin A, B1, B2, and nidogen genes were identified by in situ hybridization in postimplantation mouse extraembryonic tissues and maternal decidua during the period when the chorioallantoic placenta is established. Laminin and nidogen genes were not coordinately expressed either in the decidua or in trophoblast cells, indicating that these genes are regulated independently in these cell types during the establishment of the placenta. Laminin A mRNA was absent from the decidua except in the outer layer of cells adjacent to the myometrium and in the central decidual zone adjacent to the remnant of the uterine epithelium on Day 9. At this stage laminin B1, B2, and nidogen genes were strongly expressed in these cells and also in other regions of the decidua. Laminin B1 mRNA was present at higher levels in the decidua capsularis than in the decidua basalis, while nidogen mRNA showed highest expression in the decidua basalis. Laminin B2 mRNA was produced uniformly throughout the decidua at very high levels, suggesting that laminin B2 chains may be an important component of the decidual matrix. By Day 11, the nidogen gene was expressed only in endothelial cells lining the maternal blood spaces within the decidua. Laminin B1 and nidogen mRNAs were found at high levels within trophoblast giant cells at all stages, while laminin A mRNA was detected in trophoblast giant cells at later stages and laminin B2 mRNA was not produced in high levels by these cells. The patterns of gene expression show a very high degree of regional specialization, suggesting that the extracellular matrices in different regions of the decidua and extraembryonic membranes are likely to be composed of quite different ratios of laminin and nidogen polypeptides.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
118.
119.
A. A. Konstantinov N. V. Kurenkov A. B. Malinin T. E. Sazonova S. V. Sepman 《Atomic Energy》1989,67(3):696-698
Translated from Atomnaya Énergiya, Vol. 67, No. 3, pp. 215–216, September, 1989. 相似文献
120.