全文获取类型
收费全文 | 880篇 |
免费 | 214篇 |
国内免费 | 347篇 |
专业分类
测绘学 | 26篇 |
大气科学 | 172篇 |
地球物理 | 271篇 |
地质学 | 691篇 |
海洋学 | 172篇 |
天文学 | 9篇 |
综合类 | 46篇 |
自然地理 | 54篇 |
出版年
2024年 | 9篇 |
2023年 | 24篇 |
2022年 | 31篇 |
2021年 | 36篇 |
2020年 | 45篇 |
2019年 | 40篇 |
2018年 | 44篇 |
2017年 | 44篇 |
2016年 | 48篇 |
2015年 | 63篇 |
2014年 | 71篇 |
2013年 | 55篇 |
2012年 | 67篇 |
2011年 | 56篇 |
2010年 | 70篇 |
2009年 | 59篇 |
2008年 | 68篇 |
2007年 | 80篇 |
2006年 | 75篇 |
2005年 | 53篇 |
2004年 | 50篇 |
2003年 | 49篇 |
2002年 | 47篇 |
2001年 | 35篇 |
2000年 | 29篇 |
1999年 | 22篇 |
1998年 | 28篇 |
1997年 | 22篇 |
1996年 | 21篇 |
1995年 | 24篇 |
1994年 | 11篇 |
1993年 | 7篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1441条查询结果,搜索用时 15 毫秒
421.
建立了3,5-二硝基苯甲酸工业品的高效液相色谱-紫外光谱的指纹图谱。首先,在Kromasil C18色谱柱上,以水-甲醇-0.10%高氯酸水溶液(体积比为25:45:30)为流动相,流动相流速1.0mL/min,检测波长254nm,对3,5-二硝基苯甲酸及其相关杂质进行了分离分析。在此基础上,通过运行大量样品,筛选共有组分,绘制具有共同特性的指纹图谱。根据待测样品色谱峰的保留时间、紫外光谱及其色谱峰面积,与色谱指纹图谱进行分析对比,建立了控制3,5-二硝基苯甲酸产品质量的新方法。该方法在产品含量测定方面结果准确、可靠,在产品质量控制方面直观、方便。阐述了“整体性”和“明确性”是精细化工中间体指纹图谱的基本属性和发展方向。 相似文献
422.
通过分析当前巨厚松散层套管起拔存在的问题,从套管设计、起拔工艺及抑制地层水化等各方面,均提出新的措施和解决方案,经实践证明是可行的。 相似文献
423.
Influence of drizzle on Z–M relationships in warm clouds 总被引:1,自引:0,他引:1
This paper addresses the sensitivity of the relationships between radar reflectivity (Z) and liquid water content (M) for liquid water clouds to microphysical drizzle parameters by means of simulated radar observation at a frequency of 3 GHz of modeled cumulus clouds. A power law relationship for non drizzling clouds with water content as high as 3 gm− 3: Zc = 0.026 Mc1.61 is numerically derived and agreed with previous empirical relationships relative to cumulus and stratocumulus. This relationship is then used to explore the influence of drizzle on the correlation between radar reflectively and water content. Due to their large diameters with respect to cloud droplets, drizzle sized drops dominate radar reflectivity but do not carry the cloud water content so that reflectivity and liquid water content are expected to be not correlated in clouds containing drizzle. It is shown that for congestus or extreme congestus cumuli, microphysical conditions for which the Zc–Mc relationship can be used with a tolerance of 5 and 10% are provided whereas for humilis or mediocris cumuli, the presence of drizzle breaks down the Zc–Mc relationship whatever the situations. 相似文献
424.
425.
SANG Zunan XIA Bin ZHOU Yongsheng & JIN Zhenmin . Guangzhou Institute of Geochemistry Chinese Academy of Sciences Guangzhou China . Wuhan University Wuhan China . Institute of Geology China Seismological Bureau Beijing China . Faculty of Earth Sciences China University of Geosciences Wuhan China 《中国科学D辑(英文版)》2005,48(4):496-505
The magma immiscibility is that an originallyuniform magma split into two liquids with differentcompositions and properties because of the changes oftemperature, pressure and composition in the mag-matic processes. The phenomenon is ubiquitous in thenature and industrial production. For example, magmaimmiscibility has been widely regarded as the mainmechanism of formation of the Cu-Ni sulphide depositAs early as the 1920s, some geologists[1] noted that anon-silicate magma, which is mainly com… 相似文献
426.
Influence of liquid bridges on the mechanical behaviour of polydisperse granular materials 总被引:1,自引:0,他引:1
We investigate a polydisperse granular material in which the particle interactions are governed by a capillary force law. The cohesion force for a grain‐pair with unequal diameters is expressed as an explicit function of the inter‐particle distance and the volume of the liquid bridge. This analytical relation is validated by experiments on a reference material. Then, it is completed by a rupture criterion and cast in the form of a force law that accounts for solid contact, capillary force and rupture characteristics of a grain‐pair. Finally, in order to evaluate the influence of capillary cohesion on the macroscopic behaviour, radial and axial compression tests on cylindrical assemblies of wet particles are simulated using a 3D distinct element method. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
427.
A. Kasper-Giebl A. Koch R. Hitzenberger H. Puxbaum 《Journal of Atmospheric Chemistry》2000,35(1):33-46
Cloud water and interstitial aerosol samples collected at Mt. Sonnblick (SBO) were analyzed for sulfate and aerosol carbon to calculate in-cloud scavenging efficiencies. Scavenging efficiencies for sulfate (SO) ranged from 0.52 to 0.99 with an average of 0.80. Aerosol carbon was scavenged less efficiently with an average value (AC) of 0.45 and minimum and maximum values of 0.14 and 0.81, respectively. Both SO and AC showed a marked, but slightly different, dependence on the liquid water content (LWC) of the cloud. At low LWC, SO increased with rising LWC until it reached a relatively constant value of 0.83 above an LWC of 0.3 g/m3. In the case of aerosol carbon, we obtained a more gradual increase of AC up to an LWC of 0.5 g/m3. At higher LWCs, _ remained relatively constant at 0.60. As the differences between SO and A varied across the LWC range observed at SBO, we assume that part of the aerosol carbon was incorporated into the cloud droplets independently from sulfate. This hypothesis is supported by size classified aerosol measurements. The differences in the size distributions of sulfate and total carbon point to a partially external mixture. Thus, the different chemical nature and the differences in the size and mixing state of the aerosol particles are the most likely candidates for the differences in the scavenging behavior. 相似文献
428.
429.
建筑结构利用TLCD减振的神经网络智能控制 总被引:14,自引:0,他引:14
本文提出了建筑结构利用调谐液体柱型阻尼器(TLCD)减振的神经网络智能控制方法。首先阐述了确定TLCD半主动控制策略;然后利用BP人工神经网络方法计算并控制TLCD隔板孔洞的面积,以调节和控制阻尼比&T,实现对建筑结构的智能控制。地震作用下的数值分析表明,本文所述的方法是十分有效的。 相似文献
430.