全文获取类型
收费全文 | 125526篇 |
免费 | 2036篇 |
国内免费 | 1223篇 |
专业分类
测绘学 | 3417篇 |
大气科学 | 8993篇 |
地球物理 | 24921篇 |
地质学 | 44732篇 |
海洋学 | 10870篇 |
天文学 | 28444篇 |
综合类 | 490篇 |
自然地理 | 6918篇 |
出版年
2022年 | 726篇 |
2021年 | 1313篇 |
2020年 | 1472篇 |
2019年 | 1452篇 |
2018年 | 3286篇 |
2017年 | 3096篇 |
2016年 | 3924篇 |
2015年 | 2282篇 |
2014年 | 3786篇 |
2013年 | 6698篇 |
2012年 | 3953篇 |
2011年 | 5321篇 |
2010年 | 4505篇 |
2009年 | 5887篇 |
2008年 | 5272篇 |
2007年 | 5099篇 |
2006年 | 4873篇 |
2005年 | 3783篇 |
2004年 | 3697篇 |
2003年 | 3549篇 |
2002年 | 3363篇 |
2001年 | 3014篇 |
2000年 | 2888篇 |
1999年 | 2351篇 |
1998年 | 2470篇 |
1997年 | 2336篇 |
1996年 | 2053篇 |
1995年 | 2011篇 |
1994年 | 1750篇 |
1993年 | 1586篇 |
1992年 | 1524篇 |
1991年 | 1433篇 |
1990年 | 1567篇 |
1989年 | 1344篇 |
1988年 | 1265篇 |
1987年 | 1502篇 |
1986年 | 1286篇 |
1985年 | 1576篇 |
1984年 | 1761篇 |
1983年 | 1618篇 |
1982年 | 1574篇 |
1981年 | 1363篇 |
1980年 | 1283篇 |
1979年 | 1182篇 |
1978年 | 1174篇 |
1977年 | 1064篇 |
1976年 | 995篇 |
1975年 | 959篇 |
1974年 | 957篇 |
1973年 | 971篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
122.
The paper presents the results of a photometric study of the hydroxyl bands (7–2) and (8–3) in the night airglow spectrum at Mt. Abu in the winter and spring of 1966–1972. The observed nocturnal variation differs from the variation expected from the theoretical studies of Hesstvedt, Hunt, Shimazaki and others. Instead of a gradual fall in intensity after sunset to shortly before sunrise, a peak in intensity is found at a time which changes from month to month and roughly coincides with the transit times of the X-ray star TAU (XR-1)-Crab Nebula. Anexplanation of the observed phenomenon is offered in terms of the increased energy output into the D and E regions of the atmospheres, increased eddy diffusion, and production, of additional O(3P) and O3 in the region 80–95 km. O3 reacting with H gives rise to OH*. 相似文献
123.
Randall S. Babcock 《Lithos》1973,6(3):279-290
It is possible to calculate quantitative models of chemical transfer by metasomatic processes if rock density values are available with chemical analyses. A unique solution for the magnitude and sign of chemical transfer can be obtained only if the volume change or absolute variation in any chemical constituent can be established. However, even if evidence for volume change and chemical behavior is ambiguous, constraints can be placed on the chemical and physical characteristics of the chemical transfer process by making calculations based on reasonable assumptions. 相似文献
124.
125.
126.
A computer-generated model of a coal-bearing delta would be desirable if it included enough detail to reproduce the cyclical nature of the sediments. At the present stage of development of computers, and with the present state of knowledge of the quantitative aspects of transportation and sedimentation, it is not yet possible to set up such a model. However, the logical arrangement in a flow-diagram of the processes and parameters involved in delta formation strongly suggests that cyclical sedimentation can occur without the need for an external cyclical cause, such as tectonic or climatic oscillations. Attempts to provide for appropriate checks of a computer model bring out overall regularities in the assemblages of cyclic types in three different coal basins. 相似文献
127.
128.
R. E. Bevan A.C.I.S. F. Insp. P.C. 《Aquatic Sciences - Research Across Boundaries》1969,31(2):322-334
Ohne Zusammenfassung 相似文献
129.
130.