全文获取类型
收费全文 | 3513篇 |
免费 | 85篇 |
国内免费 | 52篇 |
专业分类
测绘学 | 394篇 |
大气科学 | 299篇 |
地球物理 | 631篇 |
地质学 | 1545篇 |
海洋学 | 170篇 |
天文学 | 472篇 |
综合类 | 57篇 |
自然地理 | 82篇 |
出版年
2023年 | 19篇 |
2022年 | 64篇 |
2021年 | 74篇 |
2020年 | 68篇 |
2019年 | 80篇 |
2018年 | 270篇 |
2017年 | 253篇 |
2016年 | 261篇 |
2015年 | 154篇 |
2014年 | 229篇 |
2013年 | 313篇 |
2012年 | 193篇 |
2011年 | 177篇 |
2010年 | 168篇 |
2009年 | 154篇 |
2008年 | 140篇 |
2007年 | 98篇 |
2006年 | 85篇 |
2005年 | 64篇 |
2004年 | 55篇 |
2003年 | 38篇 |
2002年 | 26篇 |
2001年 | 28篇 |
2000年 | 51篇 |
1999年 | 31篇 |
1998年 | 25篇 |
1997年 | 19篇 |
1996年 | 20篇 |
1995年 | 16篇 |
1994年 | 26篇 |
1993年 | 25篇 |
1992年 | 19篇 |
1991年 | 47篇 |
1990年 | 26篇 |
1989年 | 26篇 |
1988年 | 20篇 |
1987年 | 36篇 |
1986年 | 24篇 |
1985年 | 22篇 |
1984年 | 20篇 |
1983年 | 20篇 |
1982年 | 14篇 |
1981年 | 11篇 |
1980年 | 15篇 |
1979年 | 17篇 |
1978年 | 13篇 |
1976年 | 14篇 |
1974年 | 17篇 |
1973年 | 9篇 |
1972年 | 10篇 |
排序方式: 共有3650条查询结果,搜索用时 15 毫秒
121.
122.
Chin-Fu Tsang Jan-Erik Rosberg Prabhakar Sharma Theo Berthet Christopher Juhlin Auli Niemi 《Hydrogeology Journal》2016,24(6):1333-1341
Drilling of a deep borehole does not normally allow for hydrologic testing during the drilling period. It is only done when drilling experiences a large loss (or high return) of drilling fluid due to penetration of a large-transmissivity zone. The paper proposes the possibility of conducting flowing fluid electrical conductivity (FFEC) logging during the drilling period, with negligible impact on the drilling schedule, yet providing important information on depth locations of both high- and low-transmissivity zones and their hydraulic properties. The information can be used to guide downhole fluid sampling and post-drilling detailed testing of the borehole. The method has been applied to the drilling of a 2,500-m borehole at Åre, central Sweden, firstly when the drilling reached 1,600 m, and then when the drilling reached the target depth of 2,500 m. Results unveil eight hydraulically active zones from 300 m down to borehole bottom, with depths determined to within the order of a meter. Further, the first set of data allows the estimation of hydraulic transmissivity values of the six hydraulically conductive zones found from 300 to 1,600 m, which are very low and range over one order of magnitude. 相似文献
123.
AbstractThis research deals with the surface dynamics and key factors – hydrological regime, sediment load, and erodibility of floodplain facies – of frequent channel shifting, intensive meandering, and lateral instability of the Bhagirathi River in the western part of the Ganga-Brahmaputra Delta (GBD). At present, the floodplain of the Bhagirathi is categorized as a medium energy (specific stream power of 10–300 W m?2), non-cohesive floodplain, which exhibits a mixed-load and a meandering channel, an entrenchment ratio >2.2, width–depth ratio >12, sinuosity >1.4, and channel slope <0.02. In the study area, since 1975, four meander cutoffs have been shaped at an average rate of one in every 9–10 years. In the active meander belt and sand-silt dominated floodplains of GBD, frequent shifting of the channel and meander migration escalate severe bank erosion (e.g. 2.5 × 106 m3 of land lost between 1999 and 2004) throughout the year. Remote sensing based spatio-temporal analysis and stratigraphic analysis reveal that the impact of the Farakka barrage, completed in 1975, is not the sole factor of downstream channel oscillation; rather, hydrogeomorphic instability induced by the Ajay–Mayurakshi fluvial system and the erodibility of floodplain sediments control the channel dynamics of the study area. 相似文献
124.
The Housing Market and Population Vulnerabilities: Perceptions in a Fordist and a Post‐Fordist Context
下载免费PDF全文
![点击此处可从《Geographical review》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Madhuri Sharma 《Geographical review》2016,106(4):588-613
Drawing on qualitative interviews and participatory urban‐appraisal tools, this paper analyzes household perceptions on the five elements of Lawrence and Su‐Yeul's market‐led pluralism (M‐LP) framework (2008). It uses post‐Fordist Columbus, Ohio, and Fordist Milwaukee, Wisconsin, as testing grounds for these household perspectives. M‐LP suggests that at the center of contemporary housing market lie five elements: developers/builders who unveil new urban spaces with culturally open communities; lending agencies that offer affordable mortgages to all; real estate brokers/agents who have moved past discriminatory practices; consumers whose preferences emphasize class‐type elements; and communities that impose development agendas. While many felt that the housing market of the mid‐2000s was racially blind, race still played a crucial role in driving home‐buying decisions, especially in Milwaukee. Columbus respondents aligned more closely with M‐LP, putting greater emphasis on class, but they also used phrases and words to blur race and class distinction. Both metropolises, though, illustrated complex intertwining between class and culture. 相似文献
125.
126.
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
127.
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
128.
129.
130.