全文获取类型
收费全文 | 10266篇 |
免费 | 808篇 |
国内免费 | 826篇 |
专业分类
测绘学 | 3183篇 |
大气科学 | 592篇 |
地球物理 | 755篇 |
地质学 | 2123篇 |
海洋学 | 320篇 |
天文学 | 26篇 |
综合类 | 1223篇 |
自然地理 | 3678篇 |
出版年
2024年 | 30篇 |
2023年 | 87篇 |
2022年 | 285篇 |
2021年 | 376篇 |
2020年 | 360篇 |
2019年 | 398篇 |
2018年 | 302篇 |
2017年 | 473篇 |
2016年 | 481篇 |
2015年 | 474篇 |
2014年 | 571篇 |
2013年 | 727篇 |
2012年 | 720篇 |
2011年 | 728篇 |
2010年 | 564篇 |
2009年 | 520篇 |
2008年 | 553篇 |
2007年 | 610篇 |
2006年 | 603篇 |
2005年 | 515篇 |
2004年 | 483篇 |
2003年 | 414篇 |
2002年 | 350篇 |
2001年 | 301篇 |
2000年 | 214篇 |
1999年 | 165篇 |
1998年 | 144篇 |
1997年 | 118篇 |
1996年 | 66篇 |
1995年 | 55篇 |
1994年 | 53篇 |
1993年 | 36篇 |
1992年 | 25篇 |
1991年 | 22篇 |
1990年 | 20篇 |
1989年 | 10篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
942.
943.
944.
Effects of Crop Growth and Development on Land Surface Fluxes 总被引:2,自引:0,他引:2
In this study, the Crop Estimation through Resource and Environment Synthesis model (CERES3.0) was coupled into the Biosphere-Atmosphere Transfer Scheme (BATS), which is called BATS CERES, to represent interactions between the land surface and crop growth processes. The effects of crop growth and development on land surface processes were then studied based on numerical simulations using the land surface models. Six sensitivity experiments by BATS show that the land surface fluxes underwent substantial changes when the leaf area index was changed from 0 to 6 m2 m-2. Numerical experiments for Yucheng and Taoyuan stations reveal that the coupled model could capture not only the responses of crop growth and development to environmental conditions, but also the feedbacks to land surface processes. For quantitative evaluation of the effects of crop growth and development on surface fluxes in China, two numerical experiments were conducted over continental China: one by BATS CERES and one by the original BATS. Comparison of the two runs shows decreases of leaf area index and fractional vegetation cover when incorporating dynamic crops in land surface simulation, which lead to less canopy interception, vegetation transpiration, total evapotranspiration, top soil moisture, and more soil evaporation, surface runoff, and root zone soil moisture. These changes are accompanied by decreasing latent heat flux and increasing sensible heat flux in the cropland region. In addition, the comparison between the simulations and observations proved that incorporating the crop growth and development process into the land surface model could reduce the systematic biases of the simulated leaf area index and top soil moisture, hence improve the simulation of land surface fluxes. 相似文献
945.
城市化极大地改变了城市下垫面的性质,这有可能增加灰霾天气发生的概率和强度.利用Landsat-7 ETM+和HJ-1A卫星多光谱遥感数据,通过人工解译获得2002年和2012年武汉市土地利用情况,并对武汉市土地利用规划图进行数字化和尺度转换.在此基础上,针对武汉市典型灰霾天气过程,对不同土地类型(历史、现状和规划)利用WRF-NAQPMS空气质量数值模式进行了不同情景的模拟.同时,对比分析和揭示了不同情境下,大气风场和主要大气污染物浓度场的变化,解析了下垫面对灰霾天气的影响.可为从灰霾天气防治的角度完善城市土地规划和建设提供科学依据. 相似文献
946.
947.
基于关系型数据库管理系统,构建了河南省气候业务数据库系统,用于存储全省各气象台站建站以来的逐日数据、月统计数据、年统计数据等。利用可视化开发环境,采用面向对象编程语言,开发了气候业务数据库应用系统,具备数据库记录实时追加、信息化文件采集、数据库记录修改、数据库记录查询统计、数据质量检测等功能。系统投入使用后,提高了气候... 相似文献
948.
949.
Tele-connecting local consumption to global land use 总被引:1,自引:0,他引:1
Globalization increases the interconnectedness of people and places around the world. In a connected world, goods and services consumed in one country are often produced in other countries and exchanged via international trade. Thus, local consumption is increasingly met by global supply chains oftentimes involving large geographical distances and leading to global environmental change. In this study, we connect local consumption to global land use through tracking global commodity and value chains via international trade flows. Using a global multiregional input–output model with sectoral detail allows for the accounting of land use attributed to “unusual” sectors – from a land use perspective – including services, machinery and equipment, and construction. Our results show how developed countries consume a large amount of goods and services from both domestic and international markets, and thus impose pressure not only on their domestic land resources, but also displace land in other countries, thus displacing other uses. For example, 33% of total U.S. land use for consumption purposes is displaced from other countries. This ratio becomes much larger for the EU (more than 50%) and Japan (92%). Our analysis shows that 47% of Brazilian and 88% of Argentinean cropland is used for consumption purposes outside of their territories, mainly in EU countries and China. In addition, consumers in rich countries tend to displace land by consuming non-agricultural products, such as services, clothing and household appliances, which account for more than 50% of their total land displacement. By contrast, for developing economies, such as African countries, the share of land use for non-agricultural products is much lower, with an average of 7%. The emerging economies and population giants, China and India, are likely to further increase their appetite for land from other countries, such as Africa, Russia and Latin America, to satisfy their own land needs driven by their fast economic growth and the needs and lifestyles of their growing populations. 相似文献
950.