全文获取类型
收费全文 | 95809篇 |
免费 | 1602篇 |
国内免费 | 693篇 |
专业分类
测绘学 | 2213篇 |
大气科学 | 7079篇 |
地球物理 | 19588篇 |
地质学 | 32880篇 |
海洋学 | 8475篇 |
天文学 | 21094篇 |
综合类 | 216篇 |
自然地理 | 6559篇 |
出版年
2021年 | 735篇 |
2020年 | 918篇 |
2019年 | 989篇 |
2018年 | 1826篇 |
2017年 | 1805篇 |
2016年 | 2262篇 |
2015年 | 1469篇 |
2014年 | 2273篇 |
2013年 | 4697篇 |
2012年 | 2482篇 |
2011年 | 3553篇 |
2010年 | 3107篇 |
2009年 | 4249篇 |
2008年 | 3855篇 |
2007年 | 3693篇 |
2006年 | 3617篇 |
2005年 | 2877篇 |
2004年 | 2985篇 |
2003年 | 2821篇 |
2002年 | 2659篇 |
2001年 | 2347篇 |
2000年 | 2281篇 |
1999年 | 1971篇 |
1998年 | 1955篇 |
1997年 | 1951篇 |
1996年 | 1688篇 |
1995年 | 1628篇 |
1994年 | 1430篇 |
1993年 | 1314篇 |
1992年 | 1233篇 |
1991年 | 1125篇 |
1990年 | 1313篇 |
1989年 | 1156篇 |
1988年 | 1027篇 |
1987年 | 1213篇 |
1986年 | 1140篇 |
1985年 | 1400篇 |
1984年 | 1593篇 |
1983年 | 1528篇 |
1982年 | 1379篇 |
1981年 | 1319篇 |
1980年 | 1168篇 |
1979年 | 1121篇 |
1978年 | 1153篇 |
1977年 | 1074篇 |
1976年 | 1011篇 |
1975年 | 966篇 |
1974年 | 967篇 |
1973年 | 1000篇 |
1972年 | 626篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
932.
933.
C. Ravaut S. Operto L. Improta J. Virieux A. Herrero P. Dell'Aversana 《Geophysical Journal International》2004,159(3):1032-1056
934.
Hans J. Albrecht 《Meteorology and Atmospheric Physics》1958,11(1):84-92
Summary This paper presents new results of the author's investigations on ionospheric propagation in Australia from 1952 to 1957. Considerations on path attenuation are followed by a discussion on the propagation paths to North America and Western Europe. Conclusions are in agreement with the author's previous publications in this field.
With 1 Figure 相似文献
Zusammenfassung In dieser Arbeit behandelt der Verfasser neue Ergebnisse seiner Untersuchungen über ionosphärische Ausbreitung in Australien von 1952 bis 1957. Auf eine Betrachtung über die Signalschwächung folgt eine Diskussion über die Ausbreitungswege nach Nordamerika und Westeuropa. Die Folgerungen stimmen mit den früheren Veröffentlichungen des Verfassers auf diesem Gebiet überein.
Résumé L'auteur expose les nouveaux résultats de ses recherches sur la propagation ionosphérique en Australie de 1952 à 1957; il considère l'affaiblissement de la propagation des signaux et les chemins suivis par les ondes vers l'Amérique du Nord et vers l'Europe occidentale. Ces résultats concordent avec ceux qu'il a publiés précédemment.
With 1 Figure 相似文献
935.
936.
Although emerging technologies like carbon capture and storage and advanced nuclear are expected to play leading roles in greenhouse gas mitigation efforts, many engineering and policy-related uncertainties will influence their deployment. Capital-intensive infrastructure decisions depend on understanding the likelihoods and impacts of uncertainties such as the timing and stringency of climate policy as well as the technological availability of carbon capture systems. This paper demonstrates the utility of stochastic programming approaches to uncertainty analysis within a practical policy setting, using uncertainties in the US electric sector as motivating examples. We describe the potential utility of this framework for energy-environmental decision making and use a modeling example to reinforce these points and to stress the need for new tools to better exploit the full range of benefits the stochastic programming approach can provide. Model results illustrate how this framework can give important insights about hedging strategies to reduce risks associated with high compliance costs for tight CO2 caps and low CCS availability. Metrics for evaluating uncertainties like the expected value of perfect information and the value of the stochastic solution quantify the importance of including uncertainties in capacity planning, of making precautionary low-carbon investments, and of conducting research and gathering information to reduce risk. 相似文献
937.
E. P. Veselov 《Russian Meteorology and Hydrology》2008,33(2):98-101
A formula is obtained for calculation of wind speed in tornado, as proportional to the speed of convective updraft. Results are presented of wind speed calculation using the formula for 57 tornadoes observed at different time and in different regions of the world. Possibilities are shown of tornado wind speed forecasting taking into account criteria of tornado danger of the Cb clouds. 相似文献
938.
Daniel D. Riemer Eric C. Apel John J. Orlando Geoffrey S. Tyndall William H. Brune Eric J. Williams William A. Lonneman James D. Neece 《Journal of Atmospheric Chemistry》2008,61(3):227-242
As part of the 2000 Texas Air Quality Study (TexAQS), we studied the isoprene oxidation process under ambient conditions to
discern the presence of chlorine atom (Cl) chemistry in the Houston, Texas urban area. By measuring chloromethylbutenone (CMBO)
and an isomer of chloromethylbutenal (CMBA), we clearly observed sixteen episodes of active Cl chemistry during the 24-day
experiment. Estimated median Cl concentration during each of these episodes was between the detection limit of ~102 atoms cm−3 and 50 - 30 + 70 ×104 50_{ - 30}^{ + 70} \times {10^4} atoms cm−3. Cl concentration during all the episodes averaged 7.6 - 2.0 + 4.7 ×104 7.6_{ - 2.0}^{ + 4.7} \times {10^4} atoms cm−3 and thus amounted to less than 3% of the OH concentration during the same periods. During the episodes, the fraction of oxidation
chemistry initiated by Cl ranged from 3–43% and was strongly dependent on the quantity and type of hydrocarbons present in
the atmosphere. Because of its intermittent presence and low concentration, Cl is not a broadly influential oxidant in the
Houston, Texas urban area. 相似文献
939.
940.
The stability functions for momentum and heat under a Richardson number formulation are derived from the nondimensional shear functions under a Monin-Obukhov formulation. The Prandtl number is also derived as a function of the Richardson number. Previously, this has been done only in a limited sense. Because the Richardson number formulation is expressed in closed form, iterative techniques are no longer needed in numerical models that use Monin-Obukhov similarity theory. This time-saving approach is made possible by deriving expressions for the friction velocity and temperature in terms of the Richardson-number-dependent stability functions. In addition, the Richardson number approximation in the lowest layer is made to depend explicitly upon the surface roughness. 相似文献