全文获取类型
收费全文 | 3005篇 |
免费 | 566篇 |
国内免费 | 868篇 |
学科分类
地球科学 | 4439篇 |
出版年
2024年 | 15篇 |
2023年 | 49篇 |
2022年 | 144篇 |
2021年 | 197篇 |
2020年 | 145篇 |
2019年 | 145篇 |
2018年 | 167篇 |
2017年 | 179篇 |
2016年 | 184篇 |
2015年 | 153篇 |
2014年 | 203篇 |
2013年 | 199篇 |
2012年 | 223篇 |
2011年 | 196篇 |
2010年 | 190篇 |
2009年 | 182篇 |
2008年 | 156篇 |
2007年 | 174篇 |
2006年 | 123篇 |
2005年 | 135篇 |
2004年 | 104篇 |
2003年 | 78篇 |
2002年 | 87篇 |
2001年 | 92篇 |
2000年 | 101篇 |
1999年 | 101篇 |
1998年 | 121篇 |
1997年 | 108篇 |
1996年 | 75篇 |
1995年 | 68篇 |
1994年 | 76篇 |
1993年 | 57篇 |
1992年 | 46篇 |
1991年 | 40篇 |
1990年 | 25篇 |
1989年 | 23篇 |
1988年 | 22篇 |
1987年 | 15篇 |
1986年 | 16篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1958年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有4439条查询结果,搜索用时 15 毫秒
81.
根据天山中段8套四分量钻孔应变仪观测资料,利用自洽方程计算应变观测的信度,用信度指标检验数据的可靠性,从而进一步用自洽方程计算实际各元件灵敏度的相对大小,并用相对标定的结果,对观测数据进行校正。结果表明:①石场、巴仑台、巴音沟、雀儿沟、榆树沟和库米什台经过校正后,数据观测信度有了明显提升,其中石场和雀儿沟台的数据信度最高;②库米什台校正前数据观测信度较高,因个别“坏点”影响,校正后,观测信度反而下降;③小泉沟和新源台数据信度较低,存在从自洽到失洽的情况,分析认为这可能与系统自身存在问题有关,也有可能是前兆异常,有待进一步研究。 相似文献
82.
Six sediment samples collected from the Gulf of Mexico were analyzed. Total concentrations of the PAHs ranged from 52 to 403 ng g−1 dry weight. The lowest PAH concentration without 5–6 rings PAHs appeared in S-1 sample associated with gas hydrate or gas venting. Moreover, S-1 sample had the lowest organic carbon content with 0.85% and highest reduced sulfur level with 1.21% relative to other samples. And, analysis of the sources of PAHs in S-1 sample indicated that both pyrogenic and petrogenic sources, converserly, while S-8, S-10 and S-11 sample suggested petrogenic origin. The distribution of dibenzothiophene, fluorine and dibenzofuran and the maturity parameters of triaromatic steranes suggested that organic matters in S-1 sample were different from that in S-8, S-10 and S-11 sample. This study suggested that organic geochemical data could help in distinguish the characteristic of sediment associated with gas hydrate or with oil seepage. 相似文献
83.
Phosphorus removal from secondary effluents through integrated constructed treatment system 总被引:1,自引:0,他引:1
The treatment capacity of an integrated constructed treatment system (CTS) was explored which was designed to reduce phosphorus (P) from secondary effluents. The integrated CTS was combined with vertical-flow constructed wetland, floating bed and sand filter. The vertical wetland was filled from the bottom to the top with gravels, steel slag and peat. Vetiverzizanioides (L.) Nash was selected to grow in the vertical constructed wetland while Coixlacrymajobi L. was grown in floating bed. The results suggested that integrated CTS displayed excellent removal efficiency for chemical oxygen demand (COD), dissolved phosphorus (DP), and total phosphorus (TP). The average COD removal efficiency of the integrated CTS was 90.45% after 40 days of operation, the average DP and TP removal efficiencies of the integrated CTS were 97.43% and 96.40%, respectively. The integrated CTS has good potential in removing COD as well as P from secondary effluents. 相似文献
84.
Origin and Evolution of Aquitard Porewater in the Western Coastal Plain of Bohai Bay,China 总被引:2,自引:0,他引:2 下载免费PDF全文
High‐salinity paleowater from low‐permeability aquitards in coastal areas can be a major threat to groundwater resources; however, such water has rarely been studied. The chemical and isotopic compositions of porewater extracted from a 200‐m‐thick Quaternary sedimentary sequence in the western coastal plain of Bohai Bay, China, were analyzed to investigate the salinity origin and chemical evolution of porewater in aquitards. Porewater samples derived at depths shallower than 32 m are characterized by Cl‐Na type saline water (total dissolved solids [TDS], 10.9–84.3 g/L), whereas those at depths greater than 32 m comprise Cl·SO4‐Na type brackish water (TDS, 2.2–6.3 g/L). Saline porewater is interpreted as evaporated seawater prior to halite saturation, as evidenced by Cl‐Br relationships. Although substantial dilution of saline porewater with meteoric water is supported by a wider Cl? range and δ2H‐δ18O covariance, the original marine waters were not completely flushed out. The deeper brackish porewater is determined to be a mixture of fresher porewater and brine groundwater and had a component of old brine of less than 10%, as indicated by a mixing model defined using δ2H and Cl? tracers. Porewater δ2H‐δ18O relationships and negative deuterium excess ranging from ?25.9‰ to ?2.9‰ indicate the existence of an arid climate since Late Pleistocene in Tianjin Plain. The aquitard porewaters were chemically modified through water‐rock interactions due to the long residence time. 相似文献
85.
A probability-based analytical model for predicting the seismic residual deformation of bilinear single-degreeof-freedom(SDOF) systems with a kinematic/Takeda hysteretic model is proposed based on a statistical analysis of the nonlinear time history response,and the proposed model explicitly incorporates the influence of record-to-record variability.In addition,the influence of primary parameters such as the natural vibration period,relative yield force coefficient,stiffness ratio and peak groun... 相似文献
86.
87.
A large‐scale survey for offshore aggregates is carried out on the northern shelf of the East China Sea. Results show that most of them are directly exposed in the Yangtze Shoal and the linear sand ridges system at water depths 25–55 m and 60–120 m, respectively. The components of these deposits belong to fine aggregates in terms of the fineness modulus. The potential resources are as high as 147.8 × 1012 kg for the Yangtze Shoal yet only 36.68 × 1012 kg for the sand ridges area, respectively. A preliminary feasibility analysis suggests that the Yangtze Shoal is suitable for dredging under the present conditions of technology and economy. 相似文献
88.
Zeng Jingjing Qu Jiansheng Pei Huijuan Dong Liping Liao Qin Liu Yanfei Zhang Zhiqiang 《地球科学进展》2015,30(11):1210-1217
The international climate change negotiation has been carried out over 20 years. The issue of climate change has shifted from a scientific question into a complex political matter which is related to the sustainable development of mankind. Based on the overview of major processes and stages of international climate conferences, this paper analyzed the key measures that major countries have taken to address climate change, as well as the primary tasks of Paris climate conference and recent international actions. The recent international climate policy issues were also analyzed in order to provide suggestions for China’s activel participation in the development of a new round of international climate change system. 相似文献
89.
以东江流域的岳城、胜前、东坑、蓝塘和九州五个子流域为例,应用前四个子流域分析DEM分辨率和流域大小对地形指数和TOPMODEL模型模拟结果的影响,探讨TOPMODEL模型对DEM分辨率的依赖性.结果表明:DEM分辨率对地形指数有着显著的影响,且径流模拟精度依赖于DEM空间分辨率,随着DEM空间分辨率的降低模拟得到的确定性系数逐渐减小.为了克服TOPMODEL模型难以考虑降雨空间分布不均对径流过程的影响,建立基于子流域的TOPMODEL模型,将基于子流域的TOPMODEL模型和整个流域的TOPMODEL模型应用九州子流域进行模拟比较,发现基于子流域的TOPMODEL模型能够得到精度更好的模拟效果,而且可以得到不同子流域对流域出口流量过程的贡献度,进而能够分析不同降雨情况下的流域出口洪水过程. 相似文献
90.