全文获取类型
收费全文 | 83492篇 |
免费 | 18986篇 |
国内免费 | 27186篇 |
专业分类
测绘学 | 12272篇 |
大气科学 | 13828篇 |
地球物理 | 17253篇 |
地质学 | 50478篇 |
海洋学 | 13960篇 |
天文学 | 1940篇 |
综合类 | 8022篇 |
自然地理 | 11911篇 |
出版年
2024年 | 491篇 |
2023年 | 1641篇 |
2022年 | 4596篇 |
2021年 | 5443篇 |
2020年 | 4433篇 |
2019年 | 5377篇 |
2018年 | 5062篇 |
2017年 | 4784篇 |
2016年 | 4941篇 |
2015年 | 5378篇 |
2014年 | 5583篇 |
2013年 | 6371篇 |
2012年 | 6778篇 |
2011年 | 6896篇 |
2010年 | 6939篇 |
2009年 | 6412篇 |
2008年 | 6429篇 |
2007年 | 6084篇 |
2006年 | 5500篇 |
2005年 | 4808篇 |
2004年 | 3657篇 |
2003年 | 2756篇 |
2002年 | 2701篇 |
2001年 | 2583篇 |
2000年 | 2470篇 |
1999年 | 2080篇 |
1998年 | 1388篇 |
1997年 | 1232篇 |
1996年 | 1123篇 |
1995年 | 963篇 |
1994年 | 832篇 |
1993年 | 752篇 |
1992年 | 618篇 |
1991年 | 473篇 |
1990年 | 379篇 |
1989年 | 321篇 |
1988年 | 277篇 |
1987年 | 168篇 |
1986年 | 167篇 |
1985年 | 112篇 |
1984年 | 127篇 |
1983年 | 91篇 |
1982年 | 77篇 |
1981年 | 66篇 |
1980年 | 35篇 |
1979年 | 56篇 |
1978年 | 21篇 |
1958年 | 30篇 |
1957年 | 19篇 |
1954年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Quasi-electrostatic electron and ion-cyclotron instabilities are studied. The result indicates that the higher harmonic ion cyclotron instabilities (ICI) can be excited while the fast ions produced from reconnection are injected into a coronal loop. Part of the energetic ions can be dragged out of the magnetic mirror turning points and a negative plasma potential is generated. The plasma potential may directly accelerate the electrons up to the relativistic velocity within a short time. This acceleration is similar to the processes occurring in the magnetic mirror devices of controlled thermonuclear fusion. The spectrum and flux of accelerated electrons have also been obtained. Some observational results during the solar flare might be explained by this acceleration mechanism. 相似文献
92.
本文在Thorne工作的基础上讨论了吸积盘中黑洞的有关参量的演化,以及由Schwarzschild黑洞吸积盘向Kerr黑洞吸积盘演化过程中对吸积盘辐射通量的影响,最后针对几个典型的辐射过程,分别讨论了黑洞吸积盘在牛顿框架中的温度分布方程与广义相对论的温度分布方程的热不稳定性,并给出此类问题的热不稳定性的判据。 相似文献
93.
我们于1989年11月30日晚对PG0027+260进行了时间分辨率为108秒的高速CCD测光,得到了一条完整的光变曲线,从而确认其为激变食变星系统,轨道周期0.146~d 相似文献
94.
西南低涡是对流层下层的中尺度扰动。本文在零级近似条件下,采用p坐标系的基本方程组,在边界层内设计两层模式。通过一定的简化方程组后,得到:当Z≤1/2[kL~2/(μ~2Knu~*)] 时,摩擦效应具有二重性,一方面使扰动减弱;另一方面使扰动增强,而前者的影响略大于后者,最终使扰动消失。频率随高度Z的降低而增加。当Z>1/2[kL~2/(μ~2Knμ~*)]时,摩擦作用甚微,几乎可以忽略不计。频率虽然有两个值,但随高度Z的增加,他们趋于一个常值。 相似文献
95.
96.
97.
Three continuous marine fish cell lines of FG (i. e., Hounder Gill) from flounder (Paralichthys olivaceus) gill, SPH (i. e. , Sea Perch Heart) from sea perch (Lateolabrax japonicus) heart and RSBF (i.e., Red Sea Bream Fin) from red sea bream (Pagrosomus major) fin, were characterized by lactate dehydrogenase (LDH) isozyme and morphological analysis. The LDH isozyme patterns of these three cell lines and their corresponding tissues of origin were investigated and compared. The results showed: (1) No difference was found in the LDH isozyme patterns of FG and flounder gill tissue. However, the LDH isozyme patterns of SPH and RSBF were significantly different from their corresponding tissues of origin; (2) LDH isozyme patterns of FG, SPH and RSBF were markedly different from each other and could serve as genetic markers for species identification and detection of cross contamination. Morphological change analysis of these three cell lines in comparison to their original tissues indicated that FG cells still appeared epithelioid without morphological transformation. However, morphological changes were found in SPH and RSBF compared to their original tissues. Therefore, the cellular morphology was still plastic in the relatively stable culture conditions, and it was possible that change of LDH patterns wasrelated to morphological changes of fish cells in vitro. 相似文献
98.
WANG Yachun 《东北亚地学研究》2002,(1)
The paper deals with the methods of formation pressure evaluation for a single well by using the very common ac-cepted parameters, such as drilling exponent , and flowline temperature , etc. which is part of compiling the end well report. 相似文献
99.
100.
Technique for Controlling Spread of Limnotic Oncomelania 总被引:1,自引:0,他引:1
Schistosomiasis is a parasitic disease mostly found in areas along the Changjiang River of China. The disease is spread solely through an intermediary named oncomelania, so its spread of schistosomiasis can be controlled by properly designing water intakes which prevent oncomelania from entering farming land or residential areas. This paper reports a successful design process and a new oncomelania-free intake device. The design of the new intake is based on a sound research program in which extensive experimental studies were carried out to gain knowledge of oncomelania eco-hydraulic behavior and detailed flow field information through CFD simulation. 相似文献