全文获取类型
收费全文 | 2915篇 |
免费 | 452篇 |
国内免费 | 307篇 |
专业分类
测绘学 | 140篇 |
大气科学 | 59篇 |
地球物理 | 718篇 |
地质学 | 1684篇 |
海洋学 | 112篇 |
天文学 | 13篇 |
综合类 | 124篇 |
自然地理 | 824篇 |
出版年
2024年 | 13篇 |
2023年 | 47篇 |
2022年 | 92篇 |
2021年 | 104篇 |
2020年 | 111篇 |
2019年 | 94篇 |
2018年 | 70篇 |
2017年 | 93篇 |
2016年 | 106篇 |
2015年 | 91篇 |
2014年 | 130篇 |
2013年 | 142篇 |
2012年 | 121篇 |
2011年 | 154篇 |
2010年 | 122篇 |
2009年 | 184篇 |
2008年 | 242篇 |
2007年 | 197篇 |
2006年 | 169篇 |
2005年 | 149篇 |
2004年 | 163篇 |
2003年 | 125篇 |
2002年 | 110篇 |
2001年 | 102篇 |
2000年 | 124篇 |
1999年 | 95篇 |
1998年 | 94篇 |
1997年 | 71篇 |
1996年 | 58篇 |
1995年 | 50篇 |
1994年 | 56篇 |
1993年 | 45篇 |
1992年 | 48篇 |
1991年 | 36篇 |
1990年 | 25篇 |
1989年 | 19篇 |
1988年 | 11篇 |
1987年 | 1篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有3674条查询结果,搜索用时 15 毫秒
91.
92.
介绍了当前湖泊水下地形测量的一般方法和作业过程。针对逐点插入构建不规则三角网算法,本文提出了效率改正算法和格网索引号快速计算算法。基于不规则三角网,给出了湖泊水下数字高程模型的一般应用模型——任意点高程计算、填挖方计算模型及等深线计算模型。 相似文献
93.
Multi-parameter studies (stable isotopes in carbonate and organic matter, pigment,organic carbon and nitrogen contents) from a 660-yr continuous sediment core from Lake Cheng-hai, a closed, eutropic lake in southern China, provide information on lake historical eutrophi-cation. During the last 660 years, great changes have taken place in productivity and eutrophi-cation of Lake Chenghai in response to human activities. In 1690, the productivity of the lakebegan to increase as Lake Chenghai became closed from agriculture in the lake‘‘ s watershed. In 1942, Lake Chenghai evolved to eutrophic state, marked by an increase in organic carbon, ni-trogen, CaC03, pigment contents and obvious negative values of stable isotopes, which is more or less simultaneous with the large-scale population immigration during the period. In 1984, in-tensive human activities induced modern lacustrine productivity and eutrophic level. Human-in-duced trophic changes during the past few decades have affected the Lake Chenghai ecosystem tosuch an extent that it has never experienced before in the last 660 years. 相似文献
94.
莱州湾南岸平原是指西起小清河口,东至胶莱河口的广大沿岸地区,这一地区近年来是我国工农业发展较快的地区,也是我国地下咸水入侵较为严重的地区。历史上,莱州湾南岸平原地区曾有一些湖泊存在,如巨淀湖、黑冢泊、别画湖,但现在早已荡然无存了。研究这些古湖泊的消亡原因对于恢复该区古地理环境以及确立湖迹区今后的发展方向具有十分重要的意义。本文运用查阅历史文献、地层剖面分析、地名考证、遥感解译等多种方法,对莱州湾南岸古湖泊的消亡原因进行了研究与分析,并指出该区古湖泊消亡的原因是气候变干、河流变迁、人类活动影响等,其中气候变化是古湖泊消亡的根本原因,河流变迁是古湖泊消亡的直接原因,而人类活动则加速了古湖泊消亡的进程。 相似文献
95.
96.
Following recent applications of numerical modelling and remote sensing to the thermal bar phenomenon, this paper seeks to review the current state of knowledge on the effect of its circulation on lacustrine plankton ecosystems. After summarising the literature on thermal bar hydrodynamics, a thorough review is made of all plankton observations taken in the presence of a thermal bar. Two distinct plankton growth regimes are found, one with production favoured throughout the inshore region and another with a maximum in plankton biomass near the position of the thermal bar. Possible explanations for the observed distributions are then discussed, with reference to numerical modelling studies, and the scope for future study of this interdisciplinary topic is outlined. 相似文献
97.
98.
Analysis of the Chiufengershan landslide triggered by the 1999 Chi-Chi earthquake in Taiwan 总被引:18,自引:0,他引:18
A disastrous earthquake rocked Taiwan on September 21, 1999, with magnitude ML=7.3 and an epicenter near the small town of Chi-Chi in central Taiwan. The Chi-Chi earthquake triggered landslide on the dip slope at the Chiufengershan. In this study, a review of the topography and geology of this area was followed by field investigations. Laboratory testing was applied to understand the geomaterial composing the slope. Then, based on a series of limit equilibrium analyses, the failure mechanism of this landslide and the risk of the residual slope were studied.
According to the stability analyses, the pre-quake slope is quite stable, with factor of safety of 1.77 (dry) to 1.35 (full groundwater level); explaining why there is no written record of a landslide here for the past 100 years. In contrast, a back analysis shows that the Chi-Chi earthquake-induced dynamic loading is far more than the dip slope can sustain, due in part to the short distance to the epicenter. A Monte Carlo type probability analysis suggests that the residual slope is more dangerous than the pre-quake slope and needs more attention. 相似文献
99.
Spatial probabilistic modeling of slope failure using an integrated GIS Monte Carlo simulation approach 总被引:4,自引:0,他引:4
Spatial probabilistic modeling of slope failure using a combined Geographic Information System (GIS), infinite-slope stability model and Monte Carlo simulation approach is proposed and applied in the landslide-prone area of Sasebo city, southern Japan. A digital elevation model (DEM) for the study area has been created at a scale of 1/2500. Calculated results of slope angle and slope aspect derived from the DEM are discussed. Through the spatial interpolation of the identified stream network, the thickness distribution of the colluvium above Tertiary strata is determined with precision. Finally, by integrating an infinite-slope stability model and Monte Carlo simulation with GIS, and applying spatial processing, a slope failure probability distribution map is obtained for the case of both low and high water levels. 相似文献
100.