全文获取类型
收费全文 | 6082篇 |
免费 | 1180篇 |
国内免费 | 1683篇 |
专业分类
测绘学 | 293篇 |
大气科学 | 1327篇 |
地球物理 | 1815篇 |
地质学 | 2865篇 |
海洋学 | 921篇 |
天文学 | 265篇 |
综合类 | 635篇 |
自然地理 | 824篇 |
出版年
2024年 | 24篇 |
2023年 | 101篇 |
2022年 | 279篇 |
2021年 | 329篇 |
2020年 | 238篇 |
2019年 | 334篇 |
2018年 | 393篇 |
2017年 | 320篇 |
2016年 | 361篇 |
2015年 | 323篇 |
2014年 | 404篇 |
2013年 | 336篇 |
2012年 | 390篇 |
2011年 | 377篇 |
2010年 | 374篇 |
2009年 | 358篇 |
2008年 | 348篇 |
2007年 | 310篇 |
2006年 | 285篇 |
2005年 | 245篇 |
2004年 | 197篇 |
2003年 | 235篇 |
2002年 | 199篇 |
2001年 | 173篇 |
2000年 | 212篇 |
1999年 | 233篇 |
1998年 | 229篇 |
1997年 | 202篇 |
1996年 | 177篇 |
1995年 | 193篇 |
1994年 | 156篇 |
1993年 | 148篇 |
1992年 | 101篇 |
1991年 | 57篇 |
1990年 | 51篇 |
1989年 | 53篇 |
1988年 | 48篇 |
1987年 | 48篇 |
1986年 | 26篇 |
1985年 | 14篇 |
1984年 | 14篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1958年 | 5篇 |
排序方式: 共有8945条查询结果,搜索用时 930 毫秒
161.
162.
一种基于向量序结构关系的多值形态变换 总被引:1,自引:0,他引:1
提出了一种向量型数据全序关系建立的一般方法,并以此为基础建立了多值形态变换的基本形式,并对其性质进行了讨论。多值形态变换作为数学形态学在多值图像空间中的扩展.具有与灰值形态变换类似的功能和作用,可有效地应用于多值图像的处理和目标形状特征的提取。 相似文献
163.
164.
Introduction The research on the structure and physical property of ancient hidden hill, igneous rocks and basement is relatively difficult by using seismic data only. If we combine seismic data, magneto-telluric (MT) data and geophysical data together, better results can be obtained for the above problem. A number of geophysicists at home and abroad, such as CHEN and WANG (1990), Siri-punvarapor and Egbert (2000) have tried many methods to solve the problem by the inversion of seismic da… 相似文献
165.
Introduction In recent years, with the development of earthquake observation technology, increasing ofobservation stations and improvement of observation instruments which are digitalized and con-nected by network, a great deal of data is recorded, to some extend, which brings difficulty for usto manage and store them. It leads to traditional methods, which use the file system to managemass data, could not satisfy our requirement, and it is necessary to find a new method in place oftradit… 相似文献
166.
挤扩支盘桩极限承载力的预测 总被引:2,自引:0,他引:2
用双曲线方法对110根挤扩支盘桩的极限承载力进行预测,并与直杆桩预测结果进行对比。结果表明由于支盘桩受力性状复杂,加载前期和中期预测精度较高,后期较低,误差超过15%;支盘桩的沉降曲线出现台阶时预测值与实测值误差较大;支盘桩极限承载力的预测精度与工程地质条件和桩本身的参数密切相关,桩身参数和地质条件相同条件下各桩预测精度比较接近。总体上直杆桩的预测结果优于支盘桩。 相似文献
167.
Situated in a climatically stressful environment, alpine grassland is sensitive to subtle climate changes in its productivity. We remedy the current deficiency in studying grassland productivity by taking the integrated effect of all relevant factors into consideration. The relative importance of temperature, rainfall and evaporation to the alpine grassland productivity in western China was determined through analysis of their relationship with the normalized difference vegetation index (NDVI) between 1981 and 2000. Climate warming stimulated grassland productivity in the 1980s, but hampered it in the 1990s. Temperature is more important than rainfall to grassland productivity early in the growing season. However, their relative importance is reversed late in the growing season. Monthly summer month rainfall modified by maximum monthly temperature is a good predictor of alpine grassland productivity at 62.0 per cent. However, the best predictor is water deficiency, which is able to improve the estimation accuracy to 78.3 per cent. Hence, the impact of temperature on grassland productivity is better studied indirectly through evaporation. 相似文献
168.
Sedimentation rates in the Wanggang salt marshes, Jiangsu 总被引:1,自引:0,他引:1
WANGAijun GAOShu JIAJianjun PANShaoming 《地理学报(英文版)》2005,15(2):199-209
1 IntroductionLand-ocean interaction in coastalzone is one of the key m atters of the International G eosphereand Biosphere Program (IG BP). The key problem s of the second phase in the next decadeinclude the m aterial cycle, the system evolution process … 相似文献
169.
170.
The Karst Feature Database (KFD) of Minnesota is a relational GIS-based Database Management System (DBMS). Previous karst feature datasets used inconsistent attributes to describe karst features in different areas of Minnesota. Existing metadata were modified and standardized to represent a comprehensive metadata for all the karst features in Minnesota. Microsoft Access 2000 and ArcView 3.2 were used to develop this working database. Existing county and sub-county karst feature datasets have been assembled into the KFD, which is capable of visualizing and analyzing the entire data set. By November 17 2002, 11,682 karst features were stored in the KFD of Minnesota. Data tables are stored in a Microsoft Access 2000 DBMS and linked to corresponding ArcView applications. The current KFD of Minnesota has been moved from a Windows NT server to a Windows 2000 Citrix server accessible to researchers and planners through networked interfaces. 相似文献