全文获取类型
收费全文 | 56526篇 |
免费 | 21781篇 |
国内免费 | 46676篇 |
专业分类
测绘学 | 3673篇 |
大气科学 | 24858篇 |
地球物理 | 18093篇 |
地质学 | 46798篇 |
海洋学 | 17747篇 |
天文学 | 2142篇 |
综合类 | 6941篇 |
自然地理 | 4731篇 |
出版年
2024年 | 238篇 |
2023年 | 705篇 |
2022年 | 1424篇 |
2021年 | 1853篇 |
2020年 | 2806篇 |
2019年 | 6168篇 |
2018年 | 6679篇 |
2017年 | 6268篇 |
2016年 | 6540篇 |
2015年 | 5601篇 |
2014年 | 5413篇 |
2013年 | 5846篇 |
2012年 | 5454篇 |
2011年 | 5708篇 |
2010年 | 5465篇 |
2009年 | 4982篇 |
2008年 | 3843篇 |
2007年 | 3844篇 |
2006年 | 3482篇 |
2005年 | 3332篇 |
2004年 | 3710篇 |
2003年 | 3294篇 |
2002年 | 2885篇 |
2001年 | 2632篇 |
2000年 | 2377篇 |
1999年 | 2824篇 |
1998年 | 2683篇 |
1997年 | 2694篇 |
1996年 | 2188篇 |
1995年 | 2030篇 |
1994年 | 1846篇 |
1993年 | 1843篇 |
1992年 | 1544篇 |
1991年 | 1130篇 |
1990年 | 942篇 |
1989年 | 823篇 |
1988年 | 685篇 |
1987年 | 525篇 |
1986年 | 433篇 |
1985年 | 335篇 |
1984年 | 330篇 |
1983年 | 200篇 |
1982年 | 251篇 |
1981年 | 175篇 |
1980年 | 130篇 |
1979年 | 129篇 |
1978年 | 61篇 |
1977年 | 55篇 |
1976年 | 47篇 |
1971年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
中国南极新站选择在维多利亚地特拉诺瓦湾难言岛上进行建设,其气象环境状况是开展科学研究的基础工作,也是考察队员生命安全保障的基础资料。因此,通过2013年度难言岛气象站的观测资料,结合附近地区历史气象资料,对该区域气象要素特征进行了分析。结果表明:(1)由于地处罗斯海与东南极冰盖交界处,难言岛年均气压为987.8 h Pa,与中山站非常接近;(2)年均温为-16.1℃,最低气温为-39.3℃,且冬季气温波动较大,标准差可达±6.0℃;(3)年均相对湿度为42.1%,年均比湿为0.6 g·kg-1且冬季比湿极低,空气非常干燥,降水量非常低;(4)盛行风向为WNW,5—7级风出现频率超过50%,但夏季风速明显低于冬季风速,一般不超过8.0 m·s~(-1),有利于中国在夏季开展工程建设和补给;(5)难言岛年总辐射量为3 342.8 MJ·m~(-2),明显低于中山站,但两站反照率非常接近。 相似文献
172.
Non-erodible elements, for its disturbance to the near-surface airflow, have been widely used in arid and semi-arid regions to protect the surface from wind erosion. Roughness length was usually used to evaluate the protection effect of non-erodible elements from wind erosion. In this study, the wind profiles above five types of non-erodible surfaces including gravel, wheat straw checkerboard barriers, cotton stem checkerboard barriers, shrubs, and herbs were measured and analyzed. The wind velocities above these surfaces increased with height approximately in logarithmic functions. The roughness length of different non-erodible surfaces was calculated by the functions of wind profiles. The results reveal that:(1) Roughness length increased with wind velocity in given wind velocity ranges. (2) On vegetative surfaces, wind did not effectively bend the stems. The threshold wind velocity for bending the stems of Achnatherum splendens was 4 m/s, 10 m/s for Agropyron cristatum, and for Artemisia ordosica, no obvious bending of stems even for wind velocity reaching 12 m/s. (3) Correlation analysis results show that the vegetation''s coverage and frontal area affect the roughness length more significantly than the other parameters. (4) The protective results of these non-erodible elements were evaluated. The checkerboard sand barriers made of cotton stem could provide more effective protection than that made of wheat straw. In the same coverage conditions, vegetation could provide more effective protection from wind erosion than gravel, and the blending of different non-erodible elements especially the combination of blending of vegeation and checkerboard sand barriers could provide more effective protection to the surface. 相似文献
173.
平邑左庄石膏矿区曾发生过3次地面塌陷,但井下实地调查发现,该矿区地面塌陷并非地下采空塌陷波及地表后而引发的地面塌陷。根据矿区地质环境条件、采矿方法及井巷工程布置等因素,分析认为地面塌陷原因是矿山布置的第一开采中段未预留出足够的顶柱厚度,致使井下回采时揭穿矿房顶柱接触到上覆第四纪松散盖层,第四纪孔隙水携带泥砂泄入矿坑发生潜蚀作用,在矿房顶柱与第四纪松散盖层之间形成"天窗式"砂漏,第四纪松散盖层中逐渐形成土洞,土洞扩大并塌陷后引发地面塌陷。 相似文献
174.
????????????????д????????ò???????????????????????????ε??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????硢??????????????????Ч??????????????????????????????????????????С?? 相似文献
175.
According to the meteorological observation data of 72 stations from 1960 to 2010 in the Huanghe (Yellow) River Watershed, China, the long-term variations of potential evapotranspiration, calculated in the modified Penman-Monteith model of Food and Agriculture Organization of the United Nations, were presented, as well as the meteorological causes for the decrease of potential evapotranspiration were discussed. Since 1960, temperature has risen significantly and potential evapotranspiration a decreasing trend, which indicated the existence of "Evaporation paradox" in the Huanghe River Watershed. This phenomenon was not consistent spatially or temporally with the increase of temperature, potential evapotranspiration decreased in spring, summer and winter, mainly over most parts of Shanxi and Henan, and some parts of Gansu, Ningxia, Inner Mongolia, and Shaanxi. During the recent half century, the trends of temperature and potential evapotranspiration were negatively correlated at most of the stations, while precipitation and potential evapotranspiration exhibited a contrary trend. Calculated in multiple regressions, the contribution to potential evapotranspiration change of related meteorological factors was discussed, including mean pressure, maximum and minimum temperature, sunshine hours, relative humidity and average wind speed. The decrease of wind speed in the Huanghe River Watershed may be the dominating factor causing potential evapotranspiration decreasing. 相似文献
176.
<正>1 Introduction After the successful implementation of large-scale shale gas exploration、development and utilization in United States,the domestic shale gas exploration and development is in a rapid development.However,the progress of exploration and understanding of the highEvolution shale gas in the complex structure zone of the outer basin are relatively slow,the evaluation method and 相似文献
177.
SORPTION AND DESORPTION CHARACTERISTICS OF CADMIUM BY FOUR DIFFERENT SOILS IN NORTHEAST CHINA 总被引:3,自引:0,他引:3
ZHANG Lei SONG Feng-bin 《中国地理科学(英文版)》2005,15(4):343-347
1IN TR O D U C TIO NA s a persistentand toxic pollutant, cadm ium (C d) canresultin m any adverse health effects in a variety oftis-suesand organssuch asthe lung,kidney,urinary,blad-der,pancreas,breast and prostate (SA TA R U G etal.,2003).C adm ium in so… 相似文献
178.
179.
随着科学技术的进步,地理空间数据的分析处理面临着数据量膨胀和计算量高速增长的双重挑战,为了解决海量数据处理速度慢的问题,本文针对空间分布不均匀的点数据,从数据并行的角度,以保持数据的空间邻近性及保证数据分组后各组数据量负载均衡为目标,提出基于N-KD树(Number-K Dimension Tree)数据动态分组的方法,其是一种面向实时变化(数据量和数据空间范围变化)的空间数据动态分组方法。该方法借鉴K-D树的创建和最临近点搜索的思想,通过方差判断数据分布稀疏程度,利用最临近点搜索方法处理边界点,实现空间范围的不均等切分,保证数据分组后各组数据量基本均衡。试验表明,该方法具有较好的动态分组效果与较高的计算效率;支持各种分布状态的空间点数据的分组;分组后各组数据量负载均衡;分组算法本身有支持并行、支持分布式协同工作模式的特点。 相似文献
180.