全文获取类型
收费全文 | 37649篇 |
免费 | 2132篇 |
国内免费 | 3193篇 |
专业分类
测绘学 | 1260篇 |
大气科学 | 3626篇 |
地球物理 | 7332篇 |
地质学 | 16280篇 |
海洋学 | 4319篇 |
天文学 | 6751篇 |
综合类 | 1039篇 |
自然地理 | 2367篇 |
出版年
2023年 | 350篇 |
2022年 | 958篇 |
2021年 | 1310篇 |
2020年 | 1169篇 |
2019年 | 1257篇 |
2018年 | 1888篇 |
2017年 | 1745篇 |
2016年 | 1776篇 |
2015年 | 1090篇 |
2014年 | 1647篇 |
2013年 | 2183篇 |
2012年 | 1770篇 |
2011年 | 2050篇 |
2010年 | 1900篇 |
2009年 | 2037篇 |
2008年 | 1806篇 |
2007年 | 1976篇 |
2006年 | 1754篇 |
2005年 | 958篇 |
2004年 | 884篇 |
2003年 | 938篇 |
2002年 | 1028篇 |
2001年 | 934篇 |
2000年 | 728篇 |
1999年 | 691篇 |
1998年 | 597篇 |
1997年 | 623篇 |
1996年 | 505篇 |
1995年 | 509篇 |
1994年 | 461篇 |
1993年 | 360篇 |
1992年 | 364篇 |
1991年 | 286篇 |
1990年 | 281篇 |
1989年 | 288篇 |
1988年 | 231篇 |
1987年 | 240篇 |
1986年 | 224篇 |
1985年 | 244篇 |
1984年 | 235篇 |
1983年 | 229篇 |
1982年 | 225篇 |
1981年 | 193篇 |
1980年 | 183篇 |
1979年 | 204篇 |
1978年 | 171篇 |
1977年 | 155篇 |
1976年 | 146篇 |
1975年 | 157篇 |
1973年 | 179篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Quasi-steady high-temperature current sheets are an energy source during the main or hot phase of solar flares. Such sheets are shown to be stabilized with respect to the tearing instability by a small transverse component of magnetic field existing in the sheets. 相似文献
22.
The joint evolution of organic matter and silica in petroliferous sequences is considered in the terms of the laws of transformation of dispersion systems. The dispersion systems are transformed under conditions of low-temperature solid-phase processes accompanied by the silica phase transition and dehydration that favors the evolution of organic matter. 相似文献
23.
9711号北上台风演变及暴雨过程的位涡诊断分析 总被引:6,自引:2,他引:6
通过对 971 1号台风登陆北上穿过山东造成山东特大暴雨过程的湿位涡的分析 ,并从湿位涡的角度研究了台风演变及山东特大暴雨的形成机制 ,揭示了冷空气在台风演变及暴雨过程中的重要作用。结果表明 :倾斜涡度发展是暴雨产生和台风加强的重要机制之一 ,暴雨产生在 θe线陡立密集区内 ;湿位涡在这次暴雨过程中对流层低层具有 MPV1 <0 ,MPV2 >0的特征 ,此次暴雨产生在负的MPV1等值线密集区中 ;对流层上部及平流层下部高位涡的下传使得低层斜压性增大 ,引起低层的对流稳定度减小 ,促使气旋性涡度发展 ,有利于位势不稳定能量的释放 ,使得暴雨增幅 ,导致台风的加强并演变为温带气旋。 相似文献
24.
Trends in emigration from Ireland over time are reviewed. "During the eighteenth and nineteenth centuries overseas migration to the United States and seasonal harvest migration to Britain were the main types of movement, but over the past 100 years the Irish have developed a special affinity for settling in British towns. Although the outflow was halted for a time during the 1970s, when return migration took over, the 1980s have seen a renewal of the exodus. This time, however, the character of the flow has changed from predominantly low-skill construction and factory workers to embrace better-educated emigrants, including many graduates. This shift reflects Ireland's changing position in the international market for labour." 相似文献
25.
26.
27.
28.
Mantra IB 《The Indonesian journal of geography》1984,14(47):19-34
Internal migration trends in Indonesia are reviewed using 1971 and 1980 census data. The author notes that although migration in 1971 was primarily to Jakarta and Lampung, by 1980 it was more diversified, with significant migration to some of the outer islands. The importance of the national transmigration program is noted. 相似文献
29.
The laboratory simulation experiments on volatilization from the melts formed due to micrometeoroid impacts on the lunar surface were carried out. The simulation was performed using modulated laser pulses incident on rocks and minerals in vacuum; in so doing microcraters on the targets, glass particles, condensates were formed and gases solved in the bulk of the rock and mineral grains were released. It is shown that volatilization from only the crater glass layers is negligible, which fully confirms the theoretical predictions of Nussinov and Chernyak.The volatilizations from the drops formed by the micrometeoric impacts can be noticeable. For micron-sized drops, predominant among the others after the impact, the volatilization of Na, K and other volatiles can be up to 10 to 20%. For larger-sized (d102 m) drops the volatilization should lead to the appearance of the significant gradients of the element concentrations over the particle cross-section and as a result of their normalization it leads to the surface enrichment by some elements (Si and others).The mechanism of dust formation due to the surface rocks attack by volatilizing alkaline metals (Naughtonet al.) on the Moon probably is not effective. It is the consequence of such a fact that the condensate of the target materials evaporated due to other simultaneous micrometeoric impacts and had the same (as the target has) elemental composition is the very strong background for volatilizing and condensating alkaline elements.Preliminary conclusions about a possible correlation between the composition and the sizes of dust particles in the Solar system and in the Universe (at similar initial composition) have been drawn. 相似文献
30.