全文获取类型
收费全文 | 1062篇 |
免费 | 274篇 |
国内免费 | 177篇 |
专业分类
测绘学 | 55篇 |
大气科学 | 79篇 |
地球物理 | 389篇 |
地质学 | 646篇 |
海洋学 | 240篇 |
天文学 | 30篇 |
综合类 | 29篇 |
自然地理 | 45篇 |
出版年
2024年 | 2篇 |
2023年 | 4篇 |
2022年 | 25篇 |
2021年 | 12篇 |
2020年 | 23篇 |
2019年 | 27篇 |
2018年 | 31篇 |
2017年 | 58篇 |
2016年 | 56篇 |
2015年 | 48篇 |
2014年 | 82篇 |
2013年 | 67篇 |
2012年 | 63篇 |
2011年 | 132篇 |
2010年 | 54篇 |
2009年 | 85篇 |
2008年 | 76篇 |
2007年 | 84篇 |
2006年 | 81篇 |
2005年 | 58篇 |
2004年 | 67篇 |
2003年 | 55篇 |
2002年 | 51篇 |
2001年 | 31篇 |
2000年 | 25篇 |
1999年 | 28篇 |
1998年 | 33篇 |
1997年 | 26篇 |
1996年 | 28篇 |
1995年 | 28篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 13篇 |
1991年 | 2篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1986年 | 1篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1978年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有1513条查询结果,搜索用时 953 毫秒
71.
72.
本文比较了从油田压裂资料获得的应力值与专门的水压致裂应力测量结果。研究结果表明,前者的最小水平主应力可以和后者的精度相当,最大水平主应力的精度略低。以长庆油田岭261—2井1985年11月15日实际压裂记录结果和吉林油田东33—35井的压裂记录为例,提出了处理油田资料的方法,给出了相应的处理结果 相似文献
73.
本文记述了在扶余油田采用井间电磁波和声波CT方法进行的试验。阐述了试验的意义、理论基础、计算方法、实施方案及成果几方面。试验结果表明电磁波的工作频率应降低到至少几百KHz以下才能适于油田应用。100m井间距的声波成像获得了成功,两个油层均有清晰显示。最后,对技术的发展提出了建议。 相似文献
74.
G. A. Herbert R. C. Schnell H. A. Bridgman B. A. Bodhaine S. J. Oltmans G. E. Shaw 《Journal of Atmospheric Chemistry》1989,9(1-3):17-48
The second Arctic Gas and Aerosol Sampling Program (AGASP-II) was conducted across the Alaskan and Canadian Arctic in April 1986, to study the in situ aerosol, and the chemical and optical properties of Arctic haze. The NOAA WP-3D aircraft, with special instrumentation added, made six flights during AGASP-II. Measurements of wind, pressure, temperature, ozone, water vapor, condensation nuclei (CN) concentration, and aerosol scattering extinction (bsp) were used to determine the location of significant haze layers. The measurements made on the first three flights, over the Arctic Ocean north of Barrow and over the Beaufort Sea north of Barter Island, Alaska are discussed in detail in this report of the first phase of AGASP II. In the Alaskan Arctic the WP-3D detected a large and persistent region of haze between 960 and 750 mb, in a thermally stable layer, on 2, 8, and 9 April 1986. At its most dense, the haze contained CN concentrations >10,000 cm–3 and bsp of 80×10–6 m–1 suggesting active SO2 to H2SO4 gas-to-particle conversion. Calculations based upon observed SO2 concentrations and ambient relative humidities suggest that 104–105 small H2SO4 droplets could have been produced in the haze layers. High concentrations of sub-micron H2SO4 droplets were collected in haze. Ozone concentrations were 5–10 ppb higher in the haze layers than in the surrounding troposphere. Outside the regions of haze, CN concentrations ranged from 100 to 400 cm–3 and bsp values were about (20–40)×10–6 m–1. Air mass trajectories were computed to depict the air flow upwind of regions in which haze was observed. In two cases the back trajectories and ground measurements suggested the source to be in central Europe. 相似文献
75.
Bogdana Izmailow 《地球表面变化过程与地形》1984,9(2):143-151
Eolian processes were the subject of detailed studies in the high-mountain area of the Tatra Mts. The field investigations in 1975–80 attempted to determine the amount of deflation and eolian deposition and to improve understanding of their mechanism. The net rates of these processes were determined from repeated survey of deflational forms and of eolian deposits. Observations of the mechanism of material displacement were based on field experiments carried out during strong winds. All the investigations were conducted using simple methods and traps. Relationships between the course and intensity of processes and wind conditions and soil properties were obtained. 相似文献
76.
Methods for the determination of three compound classes, i. e. diaminotoluenes, nitrophenols, and chloroaromatics in groundwater of a former ammunition plant are reported. Diaminotoluenes were extracted by discontinuous liquid/liquid-, nitrophenols by continuous liquid/liquid-extraction using dichloromethane, and chloroaromatics by solid-phase extraction. These compound classes may be analyzed by gas chromatography (GC) or gas chromatography coupled to mass spectrometry (GC/MS) without derivatization or after derivatization with N-methyl-bis(trifluoroacetamide) (MBTFA) or heptafluorobutyric anhydride (HFBA) in the case of diaminotoluenes and HFBA or acetic anhydride in the case of nitrophenols. An atomic emission detector (AED) coupled to a gas chromatograph may be employed for the analysis of chloroaromatics. High selectivity can be achieved using the characteristic wavelengths of chlorine. A variety of these compounds were identified and quantified in a groundwater sample from the former ammunition plant Elsnig (Saxony, Germany). Concentrations were in the lower ppb range. Thus, dichlorobenzenes which may have been used as substituents at the end of World War II could be identified in groundwater samples at this site. 相似文献
77.
采用与实测较接近的二次函数来表达Ekman层中的湍流粘性系数K,在圆形气压场条件下,求得了山地上空边界层中的风速,进而求得散度、涡度和垂直速度等场变量随高度的分布。并作图分析了这些场变量的一些动力学特征。改进了以往在求解析解时,略去运动方程中湍流粘性力项中的关于高度的一阶导数项,以及取山坡面上风速为零作下边界条件等欠合理欠精确的做法。所求得的风速、散度、涡度和垂直速度均用简单的初等函数表示出来,有助于边界层参数化和深化对边界层动力学的认识。 相似文献
78.
采用二进小波变换,构造了位场基小波,通过简单模型,分析了位场信号小波分解与重构的物理实质,阐明了小波变换的频带分布与“归一化”位场空间分布的一致性,以及小波重构的规律,并叙述了小波重构与异常分解的关系. 相似文献
79.
Recent improvements in both Infra-red spectroscopy and equilibrator techniqueshave allowed to determine, for the first time, pCO2using simultaneously and continuously both the direct and indirect methods in an estuary where pCO2 values range from 500 to 8500 atm and salinity from 0 to 30. Our results show that both methods are in excellent agreement in the wholeestuary (r2 = 0.999, n = 1075, p < 0.0001). Thus, the NBS (US National Bureau of Standards) scale, although inadequate for seawater samples, is appropriate for estuarine waters and can be applied with confidence to calculate pCO2. 相似文献
80.
加油站的雷电防护设计 总被引:7,自引:1,他引:7
通过对加油站所处环境特点、系统特点中雷电灾害各因素的分析,对加油棚、油罐及附属建筑的直击雷防护和接地,加油站电源、信号系统的雷电系统防护和静电防护等,依据GB50057、IEC61312、GB50156—2002标准对雷电防护的要求,提出了系统的解决方案。 相似文献