全文获取类型
收费全文 | 2676篇 |
免费 | 73篇 |
国内免费 | 51篇 |
专业分类
测绘学 | 271篇 |
大气科学 | 256篇 |
地球物理 | 491篇 |
地质学 | 1231篇 |
海洋学 | 130篇 |
天文学 | 318篇 |
综合类 | 48篇 |
自然地理 | 55篇 |
出版年
2023年 | 16篇 |
2022年 | 52篇 |
2021年 | 61篇 |
2020年 | 61篇 |
2019年 | 65篇 |
2018年 | 243篇 |
2017年 | 226篇 |
2016年 | 213篇 |
2015年 | 128篇 |
2014年 | 188篇 |
2013年 | 247篇 |
2012年 | 154篇 |
2011年 | 150篇 |
2010年 | 130篇 |
2009年 | 130篇 |
2008年 | 114篇 |
2007年 | 71篇 |
2006年 | 65篇 |
2005年 | 45篇 |
2004年 | 36篇 |
2003年 | 29篇 |
2002年 | 21篇 |
2001年 | 16篇 |
2000年 | 26篇 |
1999年 | 18篇 |
1998年 | 14篇 |
1997年 | 16篇 |
1996年 | 9篇 |
1995年 | 9篇 |
1994年 | 18篇 |
1993年 | 13篇 |
1992年 | 6篇 |
1991年 | 23篇 |
1990年 | 18篇 |
1989年 | 14篇 |
1988年 | 10篇 |
1987年 | 17篇 |
1986年 | 14篇 |
1985年 | 15篇 |
1984年 | 11篇 |
1982年 | 6篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1975年 | 6篇 |
1974年 | 11篇 |
1973年 | 5篇 |
1972年 | 8篇 |
1971年 | 5篇 |
1969年 | 5篇 |
排序方式: 共有2800条查询结果,搜索用时 0 毫秒
81.
82.
Abhishek Kumar Singh Anirban Lakshman Amares Chattopadhyay 《Geomechanics and Geoengineering》2016,11(3):201-218
Heterogeneity, being a trivial feature inside the earth or in a geostructure, makes a strong basis for its consideration in the study of geomechanics. Inclusion of the concept of heterogeneity along with irregularity in the medium brings a novelty to the existing literature related to the study of the moving load. The present study investigates the effects of linear and exponential heterogeneity on the dynamic response due to a normal load moving with constant velocity on a rough irregular heterogeneous isotropic half-space in a comparative approach. Expressions for both normal and shear stresses for either case of heterogeneity have been established in closed form. Substantial effects of the affecting parameters such as depth, irregularity factor, maximum depth of irregularity, frictional coefficient, linear heterogeneity parameter and exponential heterogeneity parameter on normal and shear stresses for both the cases of heterogeneity have been observed. Numerical computation has been carried out and the effects of said parameters have been meticulously examined by means of graphs. Moreover, different cases of heterogeneity and homogeneity along with various types of irregularity namely rectangular, parabolic and no irregularity are compared which serve as a focal theme of the study. 相似文献
83.
B. Kiran K. Pathak R. Kumar D. Deshmukh N. Rani 《International Journal of Environmental Science and Technology》2016,13(7):1823-1832
Microalgal lipids can be enhanced through varying nitrogen (N) content, and limited supply of nitrogen source seems to be valuable approach for increased lipid accumulation in microalgae. In this study, Chlorella sp. IM-02 was observed under fluorescence microscope for increased number of lipid bodies under nitrogen scarcity. Fourier transform infrared spectroscopy was used to determine spectral changes due to varying lipid content under nitrogen-starved (N0, without sodium nitrate), nitrogen-limited (N0.1, N0.25, N0.5 and N1.0 representing 0.1, 0.25, 0.5 and 1.0 g/L of sodium nitrate, respectively) and nitrogen-sufficient (N1.5, i.e., 1.5 g/L sodium nitrate) setting. Chlorophyll content was also monitored under these conditions as growth indicator. Various biochemical components viz. total carbohydrates, total proteins and total lipids were also estimated under varying nitrogen levels spectrophotometrically. On fourth day itself, maximum lipid productivity was observed in case of N0.5, which is having one-third of nitrogen concentration present in original growth media, BG-11. This concludes N0.5 as suitable nitrogen provision for better production of lipids in Chlorella sp. IM-02 without much compromising the biomass production as both growth and lipid quantity are key parameters affecting the lipid productivity of any microalgal strain. 相似文献
84.
85.
86.
87.
88.
89.
90.