全文获取类型
收费全文 | 43901篇 |
免费 | 7875篇 |
国内免费 | 10099篇 |
专业分类
测绘学 | 4184篇 |
大气科学 | 5199篇 |
地球物理 | 7542篇 |
地质学 | 26457篇 |
海洋学 | 4770篇 |
天文学 | 3377篇 |
综合类 | 3156篇 |
自然地理 | 7190篇 |
出版年
2024年 | 224篇 |
2023年 | 603篇 |
2022年 | 1521篇 |
2021年 | 1817篇 |
2020年 | 1700篇 |
2019年 | 2235篇 |
2018年 | 1611篇 |
2017年 | 1836篇 |
2016年 | 1895篇 |
2015年 | 2096篇 |
2014年 | 2647篇 |
2013年 | 2541篇 |
2012年 | 2807篇 |
2011年 | 2937篇 |
2010年 | 2522篇 |
2009年 | 2986篇 |
2008年 | 2959篇 |
2007年 | 3046篇 |
2006年 | 2990篇 |
2005年 | 2788篇 |
2004年 | 2425篇 |
2003年 | 2272篇 |
2002年 | 1945篇 |
2001年 | 1757篇 |
2000年 | 1689篇 |
1999年 | 1489篇 |
1998年 | 1301篇 |
1997年 | 952篇 |
1996年 | 808篇 |
1995年 | 689篇 |
1994年 | 651篇 |
1993年 | 537篇 |
1992年 | 417篇 |
1991年 | 345篇 |
1990年 | 217篇 |
1989年 | 164篇 |
1988年 | 146篇 |
1987年 | 84篇 |
1986年 | 47篇 |
1985年 | 36篇 |
1984年 | 21篇 |
1983年 | 19篇 |
1982年 | 14篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1978年 | 14篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1954年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
L. I. Matveenko 《Astronomy Letters》2001,27(11):686-690
The core (injector) and the jet (relativistic plasma outflow) of AGN objects are surrounded by an ionized medium, an H II region observed in emission lines. The synchrotron radiation from the core and the jet is observed through a thin screen that cocoons the structure under consideration. The screen transparency depends on wavelength and distance from the injector. We consider the objects 3C 345 and 1803+784 whose core emission at decimeter wavelengths is absorption by more than 25 dB. The visible bright compact component is the bright nearby portion of the jet that extends outside the dense part of the screen. We explore the possibility of measuring the screen transparency from absorption in Hα recombination lines with different quantum numbers at centimeter wavelengths. 相似文献
104.
105.
106.
Abstract The high-grade metamorphic rocks of southern Brittany underwent a complex tectonic evolution under various P-T conditions (high-P, high-T), related to stacking of nappes during Palaeozoic continentcontinent collision. The east to west thrusting observed in the whole belt is strongly perturbed by vertical movements attributed to the ascent of anatectic granites in the high-T area. The field reconstruction of subvertical, closed elliptical structures in gneisses and migmatites, associated with the subhorizontal, doubly radial pattern of stretching lineation in the mica schists, suggests the existence of an elliptical diapiric body buried at depth beneath the present erosion level. Deformation is associated with a complex P-T evolution partly recorded in aluminous gneisses (kinzigites, e.g. morbihanites). A chronology of successive episodes of mineral growth at different compositions is established by detailed studies of the mineral-microstructure relationships in X-Z sections, using the deformation-partitioning concept (low- and high-strain zones). Several thermometric and barometric calibrations are applied to mineral pairs either in contact or not in contact but in equivalent microstructiiral positions with respect to the deformation history. This methodology provides a continuous microstructural control of P-T variations through time and leads to three P-T-t-d paths constructed from numerous successive P-T estimations. Path 1 is a clockwise retrograde path preserved in low-strain zones, which records general exhumation movements after crustal thickening. Paths 2 and 3 are clockwise prograde/retrograde paths from high-strain zones; they are interpreted and discussed in the light of models of crustal anatexis and upward movement of magma (diapirism). Deformation and P-T effects induced by diapirism can be distinguished from the general deformation-metamorphic history of a belt, and would seem to be produced during a late stage of its history. The present microstructural-petrological approach to defining successive mineral equilibria in relation to progressive deformation steps provides a far more accurate evaluation of the metamorphic evolution than is possible by ‘standard’thermobarometry. 相似文献
107.
108.
109.
110.