全文获取类型
收费全文 | 103202篇 |
免费 | 6129篇 |
国内免费 | 8258篇 |
专业分类
测绘学 | 3903篇 |
大气科学 | 12027篇 |
地球物理 | 21187篇 |
地质学 | 43738篇 |
海洋学 | 9232篇 |
天文学 | 15651篇 |
综合类 | 5038篇 |
自然地理 | 6813篇 |
出版年
2023年 | 613篇 |
2022年 | 1580篇 |
2021年 | 2088篇 |
2020年 | 1908篇 |
2019年 | 2002篇 |
2018年 | 7131篇 |
2017年 | 6270篇 |
2016年 | 5644篇 |
2015年 | 2472篇 |
2014年 | 3593篇 |
2013年 | 4408篇 |
2012年 | 4178篇 |
2011年 | 6236篇 |
2010年 | 5456篇 |
2009年 | 6272篇 |
2008年 | 5302篇 |
2007年 | 5739篇 |
2006年 | 3375篇 |
2005年 | 2824篇 |
2004年 | 2806篇 |
2003年 | 2690篇 |
2002年 | 2503篇 |
2001年 | 2121篇 |
2000年 | 2255篇 |
1999年 | 2451篇 |
1998年 | 2274篇 |
1997年 | 2239篇 |
1996年 | 1895篇 |
1995年 | 1774篇 |
1994年 | 1575篇 |
1993年 | 1384篇 |
1992年 | 1223篇 |
1991年 | 1054篇 |
1990年 | 936篇 |
1989年 | 837篇 |
1988年 | 791篇 |
1987年 | 727篇 |
1986年 | 650篇 |
1985年 | 731篇 |
1984年 | 770篇 |
1983年 | 666篇 |
1982年 | 634篇 |
1981年 | 571篇 |
1980年 | 536篇 |
1979年 | 508篇 |
1978年 | 472篇 |
1977年 | 375篇 |
1976年 | 357篇 |
1975年 | 360篇 |
1973年 | 345篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
94.
The reservoir quality of Jurassic and Triassic fluvial and lacustrine-deltaic sandstones of the Yanchang Oil Field in the Ordos Basin is strongly influenced by the burial history and facies-related diagenetic events. The fluvial sandstones have a higher average porosity (14.8%) and a higher permeability (12.7×10?3 ?m2) than those of the deltaic sandstones (9.8% and 5.8 ×10?3 ?m2, respectively). The burial compaction, which resulted in 15% and 20% porosity loss for Jurassic and Triassic sandstones, respectively, is the main factor causing the loss of porosity both for the Jurassic and Triassic sandstones. Among the cements, carbonate is the main one that reduced the reservoir quality of the sandstones. The organic acidic fluid derived from organic matter in the source rocks, the inorganic fluid from rock-water reaction during the late diagenesis, and meteoric waters during the epidiagenesis resulted in the formation of dissolution porosity, which is the main reason for the enhancement of reservoir-quality. 相似文献
95.
The problem of the diversity of the geochemical types of carbon dioxide waters (CDW) in petrografically and mineralogically uniform crystalline rock masses is solved with allowance made for the effect of different boundary conditions (physicochemical parameters) on the geochemical effect of interaction in the rock–water system. The formation of the entire geochemical spectrum of CDW in crystalline rock masses is shown to be explicable on the basis of a model of interaction in granite–water systems at different mass ratios of reacting rock (S) and water (L), different temperatures T, and equilibrium concentrations of dissolved CO2 (P
CO2). 相似文献
96.
97.
98.
99.
Samples of dune sands, surveys of the morphology and field measurements of wind velocity and direction of a simple linear dune in Taklimakan Sand Sea show that the airflow and sand flux vary with the change of wind direction on the dune surface. Decrease of the airflow stress on the lee flank does not result in much decrease of the sand flux because of the low threshold shear velocities and the airflow conditions. There are no significant relations between the sand flux on the lee flank and the angle of incidence of the airflow. The low threshold shear velocities and the maintenance of the sand flux at the lee flank are the main mechanisms keeping the linear shape of the dunes. Measurements of the sand flux shows that it reaches a maximum on the crest of the dune. The grain size of the transported sands has some differences compared to that of the dune surface. The sands transported are finer than that on the dune surface, but better sorted under the influence of the medium to low wind activity. The field experiment results exhibit that it is possible for the dunes to be shaped as linear dunes during the processes of accumulation and elongation. 相似文献
100.