全文获取类型
收费全文 | 9931篇 |
免费 | 777篇 |
国内免费 | 344篇 |
专业分类
电工技术 | 382篇 |
综合类 | 413篇 |
化学工业 | 1625篇 |
金属工艺 | 538篇 |
机械仪表 | 632篇 |
建筑科学 | 544篇 |
矿业工程 | 189篇 |
能源动力 | 336篇 |
轻工业 | 471篇 |
水利工程 | 157篇 |
石油天然气 | 310篇 |
武器工业 | 35篇 |
无线电 | 1464篇 |
一般工业技术 | 1628篇 |
冶金工业 | 899篇 |
原子能技术 | 100篇 |
自动化技术 | 1329篇 |
出版年
2024年 | 43篇 |
2023年 | 142篇 |
2022年 | 264篇 |
2021年 | 349篇 |
2020年 | 276篇 |
2019年 | 282篇 |
2018年 | 274篇 |
2017年 | 281篇 |
2016年 | 265篇 |
2015年 | 364篇 |
2014年 | 422篇 |
2013年 | 609篇 |
2012年 | 565篇 |
2011年 | 613篇 |
2010年 | 509篇 |
2009年 | 542篇 |
2008年 | 483篇 |
2007年 | 479篇 |
2006年 | 432篇 |
2005年 | 410篇 |
2004年 | 285篇 |
2003年 | 277篇 |
2002年 | 267篇 |
2001年 | 255篇 |
2000年 | 218篇 |
1999年 | 273篇 |
1998年 | 274篇 |
1997年 | 224篇 |
1996年 | 190篇 |
1995年 | 165篇 |
1994年 | 141篇 |
1993年 | 109篇 |
1992年 | 95篇 |
1991年 | 82篇 |
1990年 | 64篇 |
1989年 | 68篇 |
1988年 | 59篇 |
1987年 | 51篇 |
1986年 | 38篇 |
1985年 | 43篇 |
1984年 | 33篇 |
1983年 | 22篇 |
1982年 | 35篇 |
1981年 | 26篇 |
1980年 | 17篇 |
1979年 | 15篇 |
1977年 | 20篇 |
1976年 | 19篇 |
1974年 | 19篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
用傅里叶变换红外扫描光致发光方法研究了Hg1-xCdxTe体单晶样品,该方法可直接得到HgCdTe晶片组分的二维平面分布,并可得到辐射复合在复合机制中所占比重的平面分布,以及晶体中非平衡载流子寿命的分布 相似文献
72.
本试验研究了ZrO2与40Cr钢在加入缓冲层前后的钎焊连接,结果表明:插入缓冲层Cu和Ti可以提高接头强度。对每一种缓冲层,存在一最佳厚度,对应的钎焊强度最大。此最佳厚度对Cu为0.4mm左右,对Ti为1mm左右。作者认为这是由缓冲层的力学性能和热膨胀系数对残余应力释放产生的两种相反影响而造成的。钎焊时,缓冲层Cu和Ti向钎料中均有程度不同的溶解,但不影响钎料对ZrO2的浸润和反应结合。ZrO2-40Cr钢连接的所有接头均断在陶瓷的近缝区,其断裂方式有三种。 相似文献
73.
Microring resonator channel dropping filters 总被引:17,自引:0,他引:17
Little B.E. Chu S.T. Haus H.A. Foresi J. Laine J.-P. 《Lightwave Technology, Journal of》1997,15(6):998-1005
Microring resonators side coupled to signal waveguides provide compact, narrow band, and large free spectral range optical channel dropping filters. Higher order filters with improved passband characteristics and larger out-of-band signal rejection are realized through the coupling of multiple rings. The analysis of these devices is approached by the novel method of coupling of modes in time. The response of filters comprised of an arbitrarily large dumber of resonators may be written down by inspection, as a continued fraction. This approach simplifies both the analysis and filter synthesis aspects of these devices 相似文献
74.
75.
76.
77.
D.C. Villeneuve I. Chu V.E. Secours M.G. Coté G.L. Plaa V.E. Valli 《The Science of the total environment》1985
Trichloropropanes have been identified as environmental contaminants in sediments of the Great Lakes region of North America. Since these chemicals had the potential to find their way into drinking water, a 90-day feeding study was carried out in order to determine their subchronic toxicity. Groups of 10 male and 10 female weanling Sprague-Dawley rats were supplied drinking water ad libitum, containing 1,2,3- or 1,1,2-trichloropropane at concentrations of 1, 10, 100 or 1000 mg/L for 13 weeks. Emulphor (0.5%) was used to solubilize the chemicals. At the end of the study, the animals were killed and examined for gross and microscopic changes. Heart, liver, brain, kidney and spleen were excised and weighed. Blood was collected and subjected to a comprehensive hematological analysis. Serum was collected and profiled for changes in 12 biochemical parameters and a portion of liver was used to determine mixed function oxidase activity. Although three animals died during the study, their deaths could not be related to treatment. Decreased growth rate was observed in both sexes of the group receiving 1000 mg/L 1,2,3-trichloropropane. There was an increase in liver, kidney and brain weights (relative to body weight) in rats of both sexes fed 1000 mg/L 1,2,3-trichloropropane. Fatty livers were observed in some of the treated animals but a clear dose-relationship was not evident. An elevation in serum cholesterol was observed in female rats fed the highest dose of 1,2,3-trichloropropane. This chemical also induced hepatic aminopyrine demethylase and aniline hydroxylase activities in male rats at the highest dose. Administration of both isomers produced only mild histological changes in the liver, thyroid and kidney of rats at the highest dose. The changes in the liver consisted of an increase in cytoplasmic eosinophilia in the periportal area together with vesiculation of biliary epithelial nuclei. Morphological changes were characterized by increased anisokaryosis in the proximal epithelium and occasional pyknosis associated with the accumulation of large eosinophilic inclusions. Changes in the thyroid consisted of a mild reduction in follicular size associated with an increased epithelial height. In general, these changes were more severe in the males than females, but were still mild overall. It was concluded that the no-effect level for both chemicals was 100 mg/L (15–20 mg/kg bw/day) and based on effects on growth rate and other changes, the 1,2,3- isomer was judged to be slightly more toxic than the 1,1,2- isomer. 相似文献
78.
The substrate growth temperature dependence of electrical properties for a low-noise MESFET fabricated on MBE-grown material has been demonstrated. The optimum noise figure and its associated gain were attributed to the higher epilayer quality and mobility at a growth temperature of 650°C between temperatures of 550°C and 700°C. 相似文献
79.
广义Foster定理 总被引:3,自引:0,他引:3
利用Maxwell方程组导出了适用于有耗网络的广义Foster定理,得到了一些有关电抗斜率以及Q值的有用公式及结论。 相似文献
80.
Low cardiac output after open heart operations in neonates and infants carries a high mortality. Delayed sternal closure may be life-saving but may prolong hospital stay and increase costs. To circumvent these issues, we shaped homograft bone and interposed it between the sternal edges to allow primary wound closure in 2 pediatric patients. Midterm results are satisfactory. 相似文献