全文获取类型
收费全文 | 85731篇 |
免费 | 14327篇 |
国内免费 | 20211篇 |
专业分类
测绘学 | 8550篇 |
大气科学 | 10920篇 |
地球物理 | 16354篇 |
地质学 | 48027篇 |
海洋学 | 10701篇 |
天文学 | 6468篇 |
综合类 | 6224篇 |
自然地理 | 13025篇 |
出版年
2024年 | 346篇 |
2023年 | 909篇 |
2022年 | 2508篇 |
2021年 | 2904篇 |
2020年 | 3052篇 |
2019年 | 3824篇 |
2018年 | 2815篇 |
2017年 | 3337篇 |
2016年 | 3428篇 |
2015年 | 3867篇 |
2014年 | 4703篇 |
2013年 | 4872篇 |
2012年 | 5143篇 |
2011年 | 5467篇 |
2010年 | 4685篇 |
2009年 | 5701篇 |
2008年 | 5692篇 |
2007年 | 6255篇 |
2006年 | 6095篇 |
2005年 | 5474篇 |
2004年 | 4919篇 |
2003年 | 4607篇 |
2002年 | 4015篇 |
2001年 | 3523篇 |
2000年 | 3398篇 |
1999年 | 3089篇 |
1998年 | 2686篇 |
1997年 | 2193篇 |
1996年 | 1921篇 |
1995年 | 1591篇 |
1994年 | 1601篇 |
1993年 | 1360篇 |
1992年 | 1048篇 |
1991年 | 754篇 |
1990年 | 613篇 |
1989年 | 532篇 |
1988年 | 382篇 |
1987年 | 253篇 |
1986年 | 178篇 |
1985年 | 121篇 |
1984年 | 62篇 |
1983年 | 50篇 |
1982年 | 48篇 |
1981年 | 34篇 |
1980年 | 33篇 |
1979年 | 32篇 |
1978年 | 48篇 |
1977年 | 30篇 |
1976年 | 7篇 |
1954年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 812 毫秒
311.
In view of rapid developments in iterative solvers, it is timely to re‐examine the merits of using mixed formulation for incompressible problems. This paper presents extensive numerical studies to compare the accuracy of undrained solutions resulting from the standard displacement formulation with a penalty term and the two‐field mixed formulation. The standard displacement and two‐field mixed formulations are solved using both direct and iterative approaches to assess if it is cost‐effective to achieve more accurate solutions. Numerical studies of a simple footing problem show that the mixed formulation is able to solve the incompressible problem ‘exactly’, does not create pressure and stress instabilities, and obviate the need for an ad hoc penalty number. In addition, for large‐scale problems where it is not possible to perform direct solutions entirely within available random access memory, it turns out that the larger system of equations from mixed formulation also can be solved much more efficiently than the smaller system of equations arising from standard formulation by using the symmetric quasi‐minimal residual (SQMR) method with the generalized Jacobi (GJ) preconditioner. Iterative solution by SQMR with GJ preconditioning also is more elegant, faster, and more accurate than the popular Uzawa method. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
312.
313.
314.
315.
316.
尚永亮 《广东海洋大学学报》2003,23(2):27-29
古代荆湘之地域的特殊性使其成为朝廷贬官吏的首选之地和贬官的中转之地。在此 ,这些被贬官首创了大量关于贬谪的文学作品。其作品物色鲜明 ,楚地风情突出 ,具有近乎凝固化了的悲怨传统 ,早期逐臣、作品及谪地成为凝定的贬谪代码和符号 ,生成并积淀了深厚的人文精神。 相似文献
317.
WANGWei-wu ZHULi-zhong WANGRen-chao SHIYong-jung 《中国地理科学(英文版)》2003,13(1):39-47
Urban heat environmental quality(UHEQ) is affected by the interacting of weather condition and underlying surface framework of urban area .In the last two decades,many researchers from domestic and overseas have studied many problems at the aspect of urban heat environment such as urban heat islands ,urban air temperature and their rela-tion with urban land cover,city population,air pollution etc,In the recent years,Hangzhou,acting as a center city of Zhejiang Province in China,its urbanization quantum and quantity have both changed greatly,in particular ,representing as business affairs building,resident real property and all kins of specialty market having arisen in built-up zone,Based on Landsat TM images data in 1991 and 1999,urban underlying surface temperature value and Normalized Difference Vegetation Index (NDVI) were calculated using image interpreting and supervised classification technique by remote sensing software ERDAS image 8.4,The relation model between urban underlying surface temperature (UUST )and urban air temperature was setup according to the certain correlation patten .Reference to the relational standard of assessing human comfort and other meteorology data of Hangzhou City in summer,the spatial distribution characteristic and the spatial varia-tion degree of human comfort of heat environmental quality are estimated and mapped on a middle scale,that is ,in six districts of Hangzhou City .Then the paper reveals the main characteristic of spatial variation from 1991 to 1999.Lastly,the change mechanism is analyzed and discussed from the viewpoint of city planning,construction and environmental protec-tion. 相似文献
318.
319.
320.
Sea‐surface temperature and salinity changes in the northwest Pacific since the Last Glacial Maximum
The oxygen isotope records of both benthic and planktonic Foraminifera in five piston cores, collected from the region between the Oyashio and Kuroshio Currents near Japan, clearly show the marked latitudinal shifts of these two currents during the past 25 kyr. Under the present hydrographic condition, a clear relationship between the sea‐surface temperature (SST) and oxygen isotope differences from benthic to planktonic Foraminifera is observed in this region. Using this relationship, we find decreased SSTs of 12–13°C (maximum 15°C) in the southernmost core site at the Last Glacial Maximum (LGM), indicating the Oyashio Current shifted southward. The SSTs at the southern two core sites abruptly increased more than 10°C at 10–11 ka, suggesting the Kuroshio Current shifted northward over these sites at 10–11 ka. In contrast, the northern two core sites have remained under the influence of the cold Oyashio Current for the past 25 kyr. With the reasonable estimate of bottom‐water temperature decrease of 2.5°C at the LGM, the SSTs estimated by this new method give exactly the same SST values calculated from Mg/Ca ratio of planktonic Foraminifera, allowing palaeosea‐surface salinities to be reconstructed. The result suggests that the ice volume effect was 1.0 ± 0.1‰ at the LGM. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献