首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   48080篇
  免费   795篇
  国内免费   301篇
测绘学   1330篇
大气科学   3817篇
地球物理   9066篇
地质学   15833篇
海洋学   4172篇
天文学   11647篇
综合类   108篇
自然地理   3203篇
  2020年   338篇
  2019年   332篇
  2018年   822篇
  2017年   810篇
  2016年   1038篇
  2015年   662篇
  2014年   1142篇
  2013年   2423篇
  2012年   1075篇
  2011年   1514篇
  2010年   1400篇
  2009年   1902篇
  2008年   1737篇
  2007年   1737篇
  2006年   1651篇
  2005年   1512篇
  2004年   1468篇
  2003年   1386篇
  2002年   1345篇
  2001年   1215篇
  2000年   1107篇
  1999年   1067篇
  1998年   1003篇
  1997年   990篇
  1996年   768篇
  1995年   823篇
  1994年   778篇
  1993年   724篇
  1992年   692篇
  1991年   664篇
  1990年   759篇
  1989年   659篇
  1988年   626篇
  1987年   720篇
  1986年   595篇
  1985年   810篇
  1984年   930篇
  1983年   894篇
  1982年   843篇
  1981年   804篇
  1980年   718篇
  1979年   685篇
  1978年   687篇
  1977年   620篇
  1976年   589篇
  1975年   514篇
  1974年   588篇
  1973年   582篇
  1972年   358篇
  1971年   330篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Shakirov  R. B.  Cuong  Do Huy  Obzhirov  A. I.  Valitov  M. G.  Lee  N. S.  Legkodimov  A. A.  Kalgin  V. Yu.  Yeskova  A. I.  Proshkina  Z. N.  Telegin  Yu. A.  Storozhenko  A. V.  Ivanov  M. V.  Pletnev  S. P.  Sedin  V. T.  Bulanov  A.V.  Shvalov  D. A.  Lipinskaya  N. A.  Bovsun  M. A.  Makseev  D. S.  Thanh  Nguyen Trung  Anh  Le Duc  Luong  Le Duc 《Oceanology》2021,61(1):147-149
Oceanology - Abstract—The paper gives brief results of comprehensive studies in the South China Sea obtained from a joint Russian–Vietnamese expedition in November 2019 (cruise 88 of...  相似文献   
2.
Field measurement and modelling of soil erosion provides insights into landscape systems as well as the potential for enhanced landscape management. There are a number of field and numerical methods by which soil erosion and deposition can be quantified. Here we examine the capability of the SIBERIA landscape evolution model to quantify short-term erosion and deposition on a well-managed cattle grazing landscape on the east coast of Australia. The model is calibrated by two methods (1) a geomorphological approach using a site digital elevation model (DEM) and soil data and (2) a laboratory-scale flume. The two calibration processes resulted in similar model input parameters and estimated erosion rates of 3.1 t ha−1 year−1 and 4.4 t ha−1 year−1, respectively. These were found to closely match erosion rates estimated using the environmental tracer 137Cs (2.7–4.8 t ha−1 year−1). However, erosion and deposition estimated at individual points along the hillslope was not well correlated with 137Cs at the same position due to the temporal averaging of the model and microtopography. Sensitivity analysis showed the model was more sensitive to parameterisation than sub-DEM-scale topography. This places confidence in the model's ability to estimate erosion and deposition across an entire hillslope and catchment on decadal time scales. We also highlight the robustness and flexibility of the calibration methods.  相似文献   
3.
Geomagnetism and Aeronomy - The total electron content (TEC) data obtained from the ground-based GPS receiver stations of the Nigerian GNSS network of stations (NIGNET) have been used in this study...  相似文献   
4.
Surveys in Geophysics - Over the last 15 years, the satellite constellation of the global positioning system (GPS) has been modernized for more precise applications, with the introduction...  相似文献   
5.
The 33 086 ha mixed land use Fall Creek watershed in upstate New York is part of the Great Lakes drainage system. Results from more than 3500 water samples are available in a data set that compiles flow data and measurements of various water quality analytes collected between 1972 and 1995 in all seasons and under all flow regimes in Fall Creek and its tributaries. Data is freely accessible at https://ecommons.cornell.edu/handle/1813/8148 and includes measurements of suspended solids, pH, alkalinity, calcium, magnesium, potassium, sodium, chloride, nitrate nitrogen (NO3-N), sulphate sulphur (SO4-S), phosphorus (P) fractions molybdate reactive P (MRP) and total dissolved P (TDP), percent P in sediment, and ammonium nitrogen (NH4-N). Methods, sub-watershed areas, and coordinates for sampling sites are also included. The work represented in this data set has made important scientific contributions to understanding of hydrological and biogeochemical processes that influence loading in mixed use watersheds and that have an impact on algal productivity in receiving water bodies. In addition, the work has been foundational for important regulatory and management decisions in the region.  相似文献   
6.
Over recent decades, sustained economic growth in Indonesia has lifted many millions of Indonesians out of poverty. But despite these developments, 28 per cent of the population still live below the official poverty line and many more remain vulnerable to falling into poverty. Coastal and fishing communities represent some of the poorer populations across Indonesia, their livelihoods increasingly threatened by deleterious environmental impacts and overfishing. This paper draws on an analysis of household surveys from two Sama Bajo fishing settlements in coastal Southeast Sulawesi. A predominantly maritime language community, Sama Bajo livelihoods are shaped by seasonal patterns of fishing and marine based harvesting and trading. Using a modified poverty survey instrument, the paper explores comparative patterns of poverty and prosperity in these two communities with a focus on livelihood dynamics, seasonality effects, and the enduring patron‐client relationships that sustain their market‐oriented way of life. Key findings highlight the vulnerability of female headed households given the highly gendered access to fishing success, and the significance of relational co‐dependencies between patron‐client networks that sustain the current patterns of fishing livelihoods. The paper highlights the need for more focussed livelihood research among vulnerable populations in Indonesia and smallholder fishing communities in particular.  相似文献   
7.
Water Resources - The forked channel is a rare and poorly known type of branching channel, the distribution of flow in which is of key importance for water transport, economic activities, and water...  相似文献   
8.
Ephemeral gully (EG) erosion has an important impact on agricultural soil losses and increases field surface hydrology connectivity and transport of pollutants to nearby water bodies. Watershed models including an EG component are scarce and not yet properly evaluated. The objective of this study is to evaluate the capacity of one such tool, AnnAGNPS, to simulate the evolution of two EG formed in a conservation tillage system. The dataset for model testing included runoff measurements and EG morphological characteristics during 3 years. Model evaluation focused on EG evolution of volume, width, and length model outputs, and included calibration and testing phases and a global sensitivity analysis (GSA). While the model did not fully reproduce width and length, the model efficiency to simulate EG volume was satisfactory for both calibration and testing phases, supporting the watershed management objectives of the model. GSA revealed that the most sensitive factors were EG depth, critical shear stress, headcut detachment exponent coefficient b, and headcut detachment leading coefficient a. For EG outputs the model was additive, showing low sensitivity to interactions between the inputs. Prediction of EG spatial evolution on conservation tillage systems requires improved development of gully erosion components, since many of the processes were developed originally for traditional tillage practices or larger channel systems. Our results identify the need for future research when EG form within conservation tillage systems, in particular to study gully headcut, soil erodibility, and width functions specific to these practices.  相似文献   
9.
Geomagnetism and Aeronomy - The total solar eclipse on July 2, 2019, has been studied by using data of the La Serena ground magnetic station in Chile located in the path of the totality (at...  相似文献   
10.
Kravtsova  V. I.  Vachnina  O. V.  Chalova  E. R. 《Water Resources》2021,48(4):474-484
Water Resources - Based on images from the Sentinel-2 satellite taken in 2017–2019, a map of shallows in the Yenisei delta was compiled. This paper highlighted the methodological problems...  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号