全文获取类型
收费全文 | 62646篇 |
免费 | 22408篇 |
国内免费 | 46874篇 |
专业分类
测绘学 | 4348篇 |
大气科学 | 25946篇 |
地球物理 | 19127篇 |
地质学 | 48431篇 |
海洋学 | 18459篇 |
天文学 | 2468篇 |
综合类 | 7489篇 |
自然地理 | 5660篇 |
出版年
2024年 | 279篇 |
2023年 | 852篇 |
2022年 | 1782篇 |
2021年 | 2274篇 |
2020年 | 3125篇 |
2019年 | 6460篇 |
2018年 | 7039篇 |
2017年 | 6599篇 |
2016年 | 6957篇 |
2015年 | 5921篇 |
2014年 | 5897篇 |
2013年 | 6360篇 |
2012年 | 5871篇 |
2011年 | 5717篇 |
2010年 | 5598篇 |
2009年 | 5028篇 |
2008年 | 4151篇 |
2007年 | 4190篇 |
2006年 | 3679篇 |
2005年 | 3455篇 |
2004年 | 3480篇 |
2003年 | 3215篇 |
2002年 | 2885篇 |
2001年 | 2716篇 |
2000年 | 2600篇 |
1999年 | 3138篇 |
1998年 | 2838篇 |
1997年 | 2825篇 |
1996年 | 2397篇 |
1995年 | 2206篇 |
1994年 | 1999篇 |
1993年 | 1806篇 |
1992年 | 1503篇 |
1991年 | 1158篇 |
1990年 | 1015篇 |
1989年 | 874篇 |
1988年 | 761篇 |
1987年 | 533篇 |
1986年 | 469篇 |
1985年 | 374篇 |
1984年 | 359篇 |
1983年 | 213篇 |
1982年 | 262篇 |
1981年 | 188篇 |
1980年 | 141篇 |
1979年 | 133篇 |
1978年 | 62篇 |
1977年 | 45篇 |
1976年 | 47篇 |
1971年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
81.
Journal of Geographical Sciences - The Interconnected River System Network (IRSN) plays a crucial role in water resource allocation, water ecological restoration and water quality improvement. It... 相似文献
82.
The magmatic activity mechanism of the fossil spreading center in the Southwest sub-basin,South China Sea 总被引:1,自引:0,他引:1
Petrogeochemical data indicate that after the end of seafloor spreading,residual magmatic activity still exists in the deep basin of the South China Sea.By using different viscous structure models beneath the fossil spreading center of the Southwest sub-basin we simulated the amount of melt produced,the length of the melting period,and the thermal evolution process in terms of geothermics and the buoyant decompression melting mechanism.We compared the results of our model with observed heat flow,seismic,and petrogeochemistry data.The results show that depletion buoyancy induced by buoyant decompression melting plays an important role in the melting process,while retention buoyancy,thermal buoyancy,and viscous shear force have only a weak influence on the melting process.From the length of the melting period,we determined that for the three viscous structures models the magmatic activity lasted about 5,12,and 15 Ma.Under the effect of buoyant depression melting,local high-temperature areas will develop under the basin,which can explain the low-velocity layer detected by seismic exploration in the middle and upper lithosphere of the Southwest sub-basin.We also simulated the possible lithology distribution beneath the fossil spreading center with the physical conditions of different viscous structure,different temperature structure,and different melting fraction,which provided a greater understanding of the rock petrogeochemical data of the deep sea basin in the South China Sea. 相似文献
83.
During the development of Qaidam Basin, which is an arid area in Northwest China, rational water resources utilization and optimization are primal prerequisites, and the main restrictive factors include the following facts: scarcy water resources are non-substitutional and uneven distributed in time and space. Based on the essential principle of sustainable development, this paper adopts Multiple Targets Decision by the Closest Value Model, and succeeds in getting the best plan, which can o… 相似文献
84.
本文利用地震学分析预报方法程式指南和“八五”攻关成果中提出的地震b值定量预测方法,对辽宁及邻区1969年以来发生的8次地震震例作了回顾性检验研究。在此基础上,根据震前b值的变化特征,总结出了可能适用于辽宁地区半年左右尺度的b值预测方法的异常羊别指标及预报规则。 相似文献
85.
86.
Analyses of trace elements of the Lower Palaeozoic carbonate rock strata in Beijing show that the contents of As, Hg, F increase from primary carbonate rocks to weathered carbonate rocks and from primary carbonate rocks to the soil coexisting with carbonate rocks, but the distribution regularity of S is not obvious. In the whole weathered stages, the sorption of As is mainly affected by Fe2O3. In soil Fe2O3 is also the main affecting factor of Hg enrichment. The main existing forms of Hg in primary carbonate rocks should simply be physical adsorption, coprecipitation and false isomorphous form between surface of carbonate rock and Hg. In soil the enrichment of F has little relationship with sul-fides and Fe2O3. In primary carbonate rocks, F is mainly absorbed by sulfides and clay minerals, etc. Weathered samples have closer genetic relationships with primary carbonate rocks. This also implies that weathered carbonate rocks have the close existing forms to that of primary carbonate rocks. In primary carbonate rocks FeS2 and FeS are the main forms of S, and sulfides have fixation effect on some heavy metals, whereas in weathered carbonate rocks and soil the fixation effect is weakened. 相似文献
87.
The periodogram spectral analysis method applicable to equallyspaced time series is discussed, and the method is tested first with a simulated data series. It is confirmed that this method is effective for noisy series. Then, applying this method to the analysis of the light periods of the quasars 3C 279 and 3C 345 as well as the BL Lac objects OJ 287 and ON 231, we obtain their light periods to be 7.14 yr, 10.00 yr, 11.76 yr and 6.80 yr, respectively. These results obtained by periodogram spectral analysis are consistent with those obtained by the Jurkevich method in the literature. We have analyzed the effects of different window functions, and commented on their correct selection in practical applications. 相似文献
88.
PEI Xiandeng KONG Lingwang ZHU Yuanhong HUANG Hao 《地球空间信息科学学报》2005,8(4):306-310
IntroductionIn color reproduction and communication, met-amer exists inherently when the conventionalcondition matching used. Therefore , the colordifference introduced makes the accuracy of colorrepresentation be lowered.In order to eli minatemetamer CIE developed the scheme so-calledspectra matching in Publication 15 .2 and speci-fied that using band-pass filters with 5 nminter-val to sample and then reconstruct the originalcolor signal ,thus the color difference will disap-pear[1].Spectra… 相似文献
89.
自1988年11月至1989年3月,对南极乔治王岛的长城湾沿岸水域中的海洋生物和环境因子进行了调查,1988年11月20日在2号站采得的冰芯中部有一层约5cm的棕色层,而1988年11月17日、20日和26日在5号站采得的冰芯样中有二层棕色层。固定冰中叶绿素a浓度范围在2.55~56.8mg/m~3之间,而且大部分含量集中在海冰的中间层中,而不象其它海区如昭和、戴维斯、凯西和麦克默多等站,大部分叶绿素a集中在海冰的底部,造成这种差别的原因、可能是由于海冰的结构和形成过程不同所致。 相似文献
90.
萨拉乌苏河流域150 ka BP以来的粒度旋回 总被引:18,自引:1,他引:18
萨拉乌苏河流域米浪沟湾地层剖面150kaBP以来古流动砂丘砂与河湖相和古土壤在粒度上具有多次显著的粗细韵律交替变化,粒度参数-Mz、σ、Sk、Kg和SC/D亦随之响应为多波动峰谷交替的态势,同时,粒度特征值-φ5、φ16φ、φ25、φ50、φ84、φ9相应地表现为非常有节奏地跳动,据此,将米浪沟湾剖面划分为27个粒度粗细沉积旋回,并认为其是150kaBP以来在东亚冬夏古代季风交替影响下沙漠演变的一个颇为完整的气候-地质过程记录。 相似文献