全文获取类型
收费全文 | 343篇 |
免费 | 20篇 |
国内免费 | 31篇 |
专业分类
系统科学 | 62篇 |
丛书文集 | 9篇 |
教育与普及 | 7篇 |
理论与方法论 | 7篇 |
现状及发展 | 6篇 |
研究方法 | 2篇 |
综合类 | 301篇 |
出版年
2023年 | 9篇 |
2022年 | 11篇 |
2021年 | 7篇 |
2020年 | 6篇 |
2019年 | 7篇 |
2018年 | 11篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 8篇 |
2014年 | 20篇 |
2013年 | 14篇 |
2012年 | 10篇 |
2011年 | 17篇 |
2010年 | 35篇 |
2009年 | 19篇 |
2008年 | 19篇 |
2007年 | 16篇 |
2006年 | 31篇 |
2005年 | 23篇 |
2004年 | 12篇 |
2003年 | 23篇 |
2002年 | 17篇 |
2001年 | 6篇 |
2000年 | 11篇 |
1999年 | 8篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 8篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有394条查询结果,搜索用时 31 毫秒
141.
Paleoproterozoic reworking of ancient crust in the Cathaysia Block, South China: Evidence from zircon trace elements, U-Pb and Lu-Hf isotopes 总被引:4,自引:0,他引:4
LIU Rui ZHOU HanWen ZHANG Li ZHONG ZengQiu ZENG Wen XIANG Hua JIN Song LU XinQian & LI ChunZhong State Key Laboratory of Geological Processes Mineral Resources Faculty of Earth Sciences China University of Geosciences Wuhan China State Key Laboratory of Continental Dynamics Northwest University Xi’an The th Geological Team of Zhejiang Province Lishui 《科学通报(英文版)》2009,54(9):1543-1554
A combined study of zircon LA-ICP-MS U-Pb dating, trace elements and Hf isotope was carried out for gneissic granite from
the Sanzhishu area in Jingning, SW Zhejiang Province. Nearly all the zircons separated from the granite exhibited oscillatory
zoning and high Th/U ratios (>0.1). The REE profile showed a pronounced positive Ce anomaly, negative Eu anomaly and an enrichment
of HREE, which are typical characteristics of magmatic zircon. Thirteen concordant or nearly concordant analytical data yielded
a weighted mean 207Pb/206Pb age of 1860±13 Ma (MSWD=0.084), representing the formation age of the granite. The magmatic zircons had negative εHf(t)
values of −15.6 to −10.0 and two-stage Hf model ages of 3.1 to 3.4 Ga, indicating that the granites were formed by reworking
of ancient crust. The major- and trace-element data indicate that the gneissic granites are metaluminous high-K calc-alkaline
rocks and exhibit the same geochemical characteristics as aluminous A-type granites, implying the emplacement of the granite
in a post-orogenic extensional tectonic setting. We conclude that the Paleoproterozoic crustal reworking event in the Cathaysia
Block of South China marked the transition from assembly to break-up of the Columbia supercontinent.
Supported by National Natural Science Foundation of China (Grant No. 40873004), Special Funds for National Scientific Research
of Commonweal Industries, the Ministry of Land and Resources of China (Grant No. 2008110015), Opening Foundation of State
Key Laboratory of Continental Dynamics, Northwest University (Grant No. 06LCD12) and the Project of Land and Resources Bureau
of Zhejiang Province (Grant No. 2004005) 相似文献
142.
The ZrO2 ceramic particles strengthened NiAl/Cr(Mo,Hf) composite was fabricated from the rapidly solidified NiAl/Cr(Mo,Hf) pre-alloyed powder and the ZrO2 powder by powder metallurgy technique.Microstr... 相似文献
143.
Macrostructure and properties of thin walled copper tubes prepared by the downward continuous unidirectional solidification method
下载免费PDF全文
![点击此处可从《矿物冶金与材料学报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The macrostructure and properties of the thin walled copper tube prepared by the downward continuous unidirectional solidification (DCUS) method were studied. The result shows that the macrostructure is closely related to the solid-liquid interface profile, which is influenced by the distance between the cooling water location and the solidification front. The mechanical properties of the thin walled copper tube prepared by the DCUS method are near those of the normal cast copper, and it has good relative density, electrical conductivity, and elongation, which are not greatly affected by casting speed. The thin walled copper tube prepared by the DCUS method also has good processing properties that can be taken to further drawing procedures directly without an intermediate process, and obtains good mechanical properties with the total processing rate of 89.8%. 相似文献
144.
ZHANG Ni DI YaGe HUANG ZuoHua & ZHANG ZhiYuan State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an China 《科学通报(英文版)》2010,55(3):314-320
Combustion characteristics of premixed diethyl ether-air mixtures were studied at different equivalence ratios and elevated initial pressures using schlieren photography and spherically propagating flame. Laminar burning velocities, Markstein number and critical radii at onset of cellular structure were obtained. The results show that an increase in initial pressure leads to a decrease in the unstretched laminar burning velocities. Laminar burning velocities give their peak values at the equivalence ratio o... 相似文献
145.
WANG Bin & ZHANG GuoWei Department of Geology Northwest University Xi’an China 《科学通报(英文版)》2010,55(14):1423-1429
A paleomagnetic study was carried out on Early-Middle Jurassic sediments in the Zhenba area, the western South-dabashan orogenic belt. Stepwise thermal demagnetization isolated the characteristic high temperature component (HTC) (D=37.1°, I=46.1°, α95=10.1°), which passed the fold test. By comparing the corresponding pole of HTC (57.6°N, 196.6°E, A95=9.9°) with coeval reference poles for the Sichuan basin, we detected a 26.5°±9.0° clockwise rotation of the study area relative to the stable Sichuan basin. We... 相似文献
146.
变电站人性化的安全管理 总被引:1,自引:0,他引:1
王金同 《科技情报开发与经济》2010,20(8):190-191
阐述了变电站的重要性与特点,分析了西铭矿玉门变电站的现状,探讨了变电站安全管理中的若干问题。 相似文献
147.
Xueya Yang Baixiao Chen Feilin Qi National Key Lab for Radar Signal Processing Xidian University Xi’ an P. R. China 《系统工程与电子技术(英文版)》2010,21(1):9-15
To enhance the resolution of parameter estimation with limited samples received by a short passive array, an iterative nonparametric algorithm for estimating the frequencies and direction-of-arrivals (DOAs) of signals is proposed. The cost function is constructed using l2-norm Gaussian entropy combined with an additional constraint, l2-norm constraint or linear constraint. By minimizing the cost functions in the temporal and the spatial dimensions using corresponding iteration algorithms respectively, the s... 相似文献
148.
研究了非对称RSA加密算法及PE文件结构,基于Derome的RSA密钥快速生成方法,提出了利用高级语言ASM编写嵌入RSA验证DLL和直接修改PE文件来加密Win32平台下的PE可执行文件的方法。该方法避免了耗时的Euclidean算法,可并行处理,同时在PE文件验证时嵌入了DLL来实现,具有很好的安全强度。 相似文献
149.
为研究射流式调制声源的发射和传播特性,文中搭建了多种室外声场声压测试平台,提出具有普适性的大功率气流扬声器声压级量测方法,测试射流式调制声源的低频发射特性和传播特性。实验结果表明:(1)声发射方面,在不同海拔高度的对比试验发现,高海拔(4 000 m)地区声压级较低海拔(70 m)地区声压级下降4 dB;(2)声传播方面,在号筒的作用下低频声波在号筒附近呈现出一定的指向性;声压级在传播方向上呈现指数函数衰减形式。本研究对射流式调制声源的低频强声发射能力的技术边界和低频声波在大气中的传播规律给出定量描述。 相似文献
150.
中药废水高效生物处理技术生产性试验研究 总被引:5,自引:0,他引:5
采用CSTR产酸发酵反应罐-UASBAF复合厌氧反应池-CAR交叉流好氧反应池这一高效生物处理工艺治理了哈尔滨中药二厂的生产废水,并进行了生产性试验研究,结果表明,此工艺可以有效地处理该厂高浓度难降解有机中药废水,在进水浓度为7000-40000mg/L时,COD总去除率可达99%以上,出水可以达到松花江水系排放标准。 相似文献