全文获取类型
收费全文 | 4059篇 |
免费 | 838篇 |
国内免费 | 1065篇 |
专业分类
测绘学 | 100篇 |
大气科学 | 1234篇 |
地球物理 | 1295篇 |
地质学 | 1368篇 |
海洋学 | 942篇 |
天文学 | 188篇 |
综合类 | 207篇 |
自然地理 | 628篇 |
出版年
2024年 | 28篇 |
2023年 | 73篇 |
2022年 | 154篇 |
2021年 | 169篇 |
2020年 | 201篇 |
2019年 | 236篇 |
2018年 | 172篇 |
2017年 | 193篇 |
2016年 | 199篇 |
2015年 | 229篇 |
2014年 | 297篇 |
2013年 | 322篇 |
2012年 | 262篇 |
2011年 | 283篇 |
2010年 | 251篇 |
2009年 | 269篇 |
2008年 | 265篇 |
2007年 | 283篇 |
2006年 | 261篇 |
2005年 | 219篇 |
2004年 | 169篇 |
2003年 | 155篇 |
2002年 | 180篇 |
2001年 | 119篇 |
2000年 | 120篇 |
1999年 | 111篇 |
1998年 | 118篇 |
1997年 | 93篇 |
1996年 | 100篇 |
1995年 | 67篇 |
1994年 | 68篇 |
1993年 | 48篇 |
1992年 | 48篇 |
1991年 | 41篇 |
1990年 | 25篇 |
1989年 | 20篇 |
1988年 | 20篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 14篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1973年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有5962条查询结果,搜索用时 15 毫秒
131.
132.
133.
134.
Kinetic parameters were determined for the first time, via open-system pyrolyses, on algaenans (highly resistant biomacromolecules that are selectively preserved during kerogen formation) isolated from extant microalgae. Parallel studies were also carried out on 10 kerogens exhibiting, with one exception, a low level of maturity. These kerogens included samples chiefly derived from the selective preservation of the above algaenans and samples mainly, or almost exclusively, derived from the “natural vulcanization” pathway. Important differences in activation energy (Ea) distributions were observed between the four algaenans investigated and correlated with their chemical structures. The kerogens predominantly derived from algaenan-selective preservation (Pula alginite, NE 70 and BJ 248 Torbanites, Rundle Oil Shale) also exhibited pronounced differences in Ea distributions. These distributions provided: (i) information on the diversity of the source materials; and (ii) reflected the occurrence of important differences in chemical structures and thermal behaviour between three of the tested kerogens, even though they are all classified as low maturity type I. The Kimmeridge Clay samples and the Lorca Oil Shale showed broad Ea distributions shifted to low energies when compared with the above algaenans and kerogens. Such shifts reflect an important (or even almost exclusive for some of these kerogens) contribution of materials originating from sulphur incorporation into various lipids during early diagenesis. Finally, the kinetic data derived for the nine low maturity fossil samples were extrapolated to a very low, geological heating rate of 3°C Ma−1 and the generation rate curves and cumulative yield curves thus obtained were compared. 相似文献
135.
着重介绍了CuInSe2的结构和光、电学特性;讨论了多各上薄膜沉积技术;评价了主要的合成装置及其作途;综述了制备CuInSe2太阳电池器件的工艺和材料,提出了一种能成功地生产大面积太阳电池薄膜的经济有铲的沉积技术。 相似文献
136.
137.
介绍了刃具斜切入破岩的试验装置及试验结果,推导出了跃进载荷的计算公式,并对试验结果进行了理论分析,探讨了影响刃具侵入岩石难易的因素和影响破岩比功大小的因素。 相似文献
138.
139.
140.
Measurements of the activation energy of electrical conductance and desiccation rates on subtidal marine algae from Florida
were compared to similar data from the Bay of Fundy, Nova Scotia, on intertidal marine algae frequently subjected to long
periods of exposure to air. We have developed a method for calculating the reaction rate constant of desiccation of fully
hydrated marine algae. Values of activation energies and desiccation rate constants are consistent with the requirements for
survival of these algae under widely different environmental conditions. 相似文献