全文获取类型
收费全文 | 483篇 |
免费 | 46篇 |
国内免费 | 94篇 |
专业分类
测绘学 | 17篇 |
大气科学 | 22篇 |
地球物理 | 166篇 |
地质学 | 201篇 |
海洋学 | 92篇 |
天文学 | 52篇 |
综合类 | 41篇 |
自然地理 | 32篇 |
出版年
2022年 | 3篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 8篇 |
2018年 | 15篇 |
2017年 | 13篇 |
2016年 | 3篇 |
2015年 | 7篇 |
2014年 | 20篇 |
2013年 | 15篇 |
2012年 | 11篇 |
2011年 | 23篇 |
2010年 | 20篇 |
2009年 | 29篇 |
2008年 | 30篇 |
2007年 | 25篇 |
2006年 | 37篇 |
2005年 | 36篇 |
2004年 | 36篇 |
2003年 | 45篇 |
2002年 | 29篇 |
2001年 | 21篇 |
2000年 | 18篇 |
1999年 | 11篇 |
1998年 | 8篇 |
1997年 | 9篇 |
1996年 | 7篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 18篇 |
1992年 | 23篇 |
1991年 | 16篇 |
1990年 | 5篇 |
1989年 | 14篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1985年 | 5篇 |
1983年 | 4篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1966年 | 1篇 |
1933年 | 2篇 |
1927年 | 3篇 |
1924年 | 2篇 |
排序方式: 共有623条查询结果,搜索用时 31 毫秒
91.
92.
青藏高原东北部黄河源区大暖期气候特征 总被引:1,自引:0,他引:1
本文通过孢粉、有机碳和粘土矿物的分析,探讨了黄河源区全新世的气候变迁,重点论述了大暖期的气候特点。在全新世,黄河源区的气候总体凉干,属于高原的高寒气候。在大暖期,该区的气候较现今高2~3℃,显得湿润些,但波动较频繁,尤其是大暖期的后期波动剧烈,并在5.0kaBP前后发生一次剧烈的降温。记录表明,黄河源区的大暖期始于9.0kaBP,止于2.30kaBP,较我国其他地区开始得早,而结束得晚,其鼎盛时期为6.0kaBP前后。 相似文献
93.
Evolution of the shear wave velocity during shaking modeled in centrifuge shaking table tests 总被引:2,自引:1,他引:1
Chung-Jung Lee Chung-Ru Wang Yui-Chen Wei Wen-Yi Hung 《Bulletin of Earthquake Engineering》2012,10(2):401-420
Two in-flight shear wave velocity measurement systems were developed to perform the subsurface exploration of shear wave velocity
in a centrifuge model. The bender elements test and the pre-shaking test used in the study provided reliable and consistent
shear wave velocity profiles along the model depth before and after shaking in the centrifuge shaking table tests. In addition,
the use of the bender elements measurement system particularly developed here allowed continuous examination of the evolution
of shear wave velocity not only during and after the shaking periods in the small shaking events but also during the dissipation
period of excess pore water pressure after liquefaction in the large shaking events. The test results showed that the shear
wave velocity at different values of excess pore water pressure ratio varied as the effective mean stress to the power of
0.27, to a first approximation. Consequently, a relationship between the shear wave velocity evolution ratio and the excess
pore water pressure ratio is proposed to evaluate the changes in shear wave velocity due to excess pore water generation and
dissipation during shaking events. This relation will assist engineers in determining the shear stiffness reduction ratio
at various ru levels when a sand deposit is subjected to different levels of earthquake shaking. 相似文献
94.
95.
Natural Hazards - Survey-based studies of household natural hazard preparedness have often relied on individual-level data to predict household-level preparedness behaviors, in doing so neglecting... 相似文献
96.
Analysis of ground vibrations due to underground trains by 2.5D finite/infinite element approach 总被引:1,自引:1,他引:0
The 2.5D finite/infinite element approach is adopted to study wave propagation problems caused by underground moving trains.
The irregularities of the near field, including the tunnel structure and parts of the soil, are modeled by the finite elements,
and the wave propagation properties of the far field extending to infinity are modeled by the infinite elements. One particular
feature of the 2.5D approach is that it enables the computation of the three-dimensional response of the half-space, taking
into account the load-moving effect, using only a two-dimensional profile. Although the 2.5D finite/infinite element approach
shows a great advantage in studying the wave propagation caused by moving trains, attention should be given to the calculation
aspects, such as the rules for mesh establishment, in order to avoid producing inaccurate or erroneous results. In this paper,
some essential points for consideration in analysis are highlighted, along with techniques to enhance the speed of the calculations.
All these observations should prove useful in making the 2.5D finite/infinite element approach an effective one. 相似文献
97.
In view of water pollutants becoming more complex, both anionic and cationic pollutants need to be removed. The multi‐pollutants simultaneous removal is paid more and more attention. Hence, development composite materials for treatment complex wastewater are the aim of this study. In this research, iron–nickel nanoparticles deposited onto aluminum oxide (α‐Al2O3) and carbon nanotubes (CNTs) to form nanocomposite materials Fe–Ni/Al2O3 and Fe–Ni/CNTs, respectively, were used as adsorbents. The adsorption capacities of Fe–Ni/Al2O3 and Fe–Ni/CNTs for AO7, HSeO, and Pb2+ were observed to be 5.46, 8.28, 27.02, and 25.6 mg/g, 15.29 and 17.12 mg/g, separately. The composite materials with negative charges were superior in adsorption of anionic pollutants. Using orthogonal experimental design and analysis of variance to co‐treat dye AO7, HSeO and Pb2+ in aqueous solutions, seven testing factors were included: (1) adsorbent types, (2) amount of iron, (3) solution pHs, (4) AO7 concentrations, (5) Pb2+ concentrations, (6) HSeO concentrations and (7) reaction time. The experimental results showed that the removal of complex pollutants AO7, HSeO, and Pb2+ on Fe–Ni/CNTs could reach up to 90% in the optimal treatment conditions. When using Fe–Ni/CNTs as the adsorbent, the sorption isothermals were well fitted in the Freundlich isotherm, and R2 could reach up to 0.98. 相似文献
98.
99.
Rayleigh wave dispersion signals are significant to underground investigation.Tradition-ally,uniformed trace spacing is employed in surface wave surveys.In some cases,however,uneven trace spacing is often encountered because of the limitations of the site condition.In order to study the influence of uneven trace spacing on the dispersion data construction of Rayleigh waves,data acquisi-tion is performed based on a 2.5D field layout with a linear array of geophones fixed and a mobile source.The observation d... 相似文献
100.
The aim of the present work is to investigate the distribution of arsenic(As) in sewage ir-rigation area,to deduce the migration and transformation mechanism of As in soil and groundwater,and to infer the source of As in soil and groundwater.This study is carried out in a sewage irrigation area of the Pearl River Delta,China.Surface water samples,soil samples,and groundwater samples from sewage irrigation area were analyzed for As and other elements.As contents in water samples were analyzed by hydride gene... 相似文献