全文获取类型
收费全文 | 1209篇 |
免费 | 90篇 |
国内免费 | 18篇 |
专业分类
测绘学 | 25篇 |
大气科学 | 77篇 |
地球物理 | 371篇 |
地质学 | 464篇 |
海洋学 | 132篇 |
天文学 | 157篇 |
综合类 | 9篇 |
自然地理 | 82篇 |
出版年
2024年 | 3篇 |
2022年 | 10篇 |
2021年 | 31篇 |
2020年 | 22篇 |
2019年 | 28篇 |
2018年 | 52篇 |
2017年 | 50篇 |
2016年 | 84篇 |
2015年 | 60篇 |
2014年 | 74篇 |
2013年 | 71篇 |
2012年 | 69篇 |
2011年 | 86篇 |
2010年 | 67篇 |
2009年 | 95篇 |
2008年 | 81篇 |
2007年 | 43篇 |
2006年 | 55篇 |
2005年 | 52篇 |
2004年 | 36篇 |
2003年 | 23篇 |
2002年 | 31篇 |
2001年 | 16篇 |
2000年 | 15篇 |
1999年 | 19篇 |
1998年 | 32篇 |
1997年 | 14篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1990年 | 10篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 8篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有1317条查询结果,搜索用时 218 毫秒
11.
The passivation of calcite by acid mine water. Column experiments with ferric sulfate and ferric chloride solutions at pH 2 总被引:2,自引:1,他引:1
Josep M. Soler Marco Boi Jos Luis Mogolln Jordi Cama Carlos Ayora Peter S. Nico Nobumichi Tamura Martin Kunz 《Applied Geochemistry》2008,23(12):3579-3588
Column experiments, simulating the behavior of passive treatment systems for acid mine drainage, have been performed. Acid solutions (HCl or H2SO4, pH 2), with initial concentrations of Fe(III) ranging from 250 to 1500 mg L−1, were injected into column reactors packed with calcite grains at a constant flow rate. The composition of the solutions was monitored during the experiments. At the end of the experiments (passivation of the columns), the composition and structure of the solids were measured. The dissolution of calcite in the columns caused an increase in pH and the release of Ca into the solution, leading to the precipitation of gypsum and Fe–oxyhydroxysulfates (Fe(III)–SO4–H+ solutions) or Fe–oxyhydroxychlorides (Fe(III)–Cl–H+ solutions). The columns worked as an efficient barrier for some time, increasing the pH of the circulating solutions from 2 to 6–7 and removing its metal content. However, after some time (several weeks, depending on the conditions), the columns became chemically inert. The results showed that passivation time increased with decreasing anion and metal content of the solutions. Gypsum was the phase responsible for the passivation of calcite in the experiments with Fe(III)–SO4–H+ solutions. Schwertmannite and goethite appeared as the Fe(III) secondary phases in those experiments. Akaganeite was the phase responsible for the passivation of the system in the experiments with Fe(III)–Cl–H+ solutions. 相似文献
12.
13.
The EU Green Paper on Maritime Policy is the European response to the new generation of ocean strategies based on science, technology and innovation aimed at new objectives, such as the strengthening of security and access to new resources. The European character of the proposal is found in the presence of social, cultural and historical elements, what is called the “European vision”. The viability of a European vision of the oceans and the idea of maritime empire as an extension of the current concept of empire within the general context of emerging ocean strategies are the elements offered up for debate on this European Union initiative. 相似文献
14.
Freezing as a method of sample preservation for the analysis of dissolved inorganic nutrients in seawater 总被引:1,自引:0,他引:1
John E. Dore Terrence Houlihan Dale V. Hebel Georgia Tien Luis Tupas David M. Karl 《Marine Chemistry》1996,53(3-4)
It is often desirable or necessary to store collected seawater samples prior to analysis for dissolved inorganic nutrients. It is therefore important to establish preservation and storage techniques that will ensure sample integrity and will not alter the precision or accuracy of analysis. We have performed a series of experiments on the storage of nutrient samples collected at the oligotrophic North Pacific benchmark Station ALOHA, using both standard autoanalyses and low-level techniques. Our results reveal that for oligotrophic oceanic waters, the immediate freezing of an unfiltered water sample in a clean polyethylene bottle is a suitable preservation method. This procedure is simple, it avoids potentially contaminating sample manipulations and chemical additions, and it adequately preserves the concentrations of nitrate + nitrite, soluble reactive phosphate, and soluble reactive silicate within a single water sample. 相似文献
15.
16.
17.
Crystallization under confinement conditions is a very important process in geochemistry and geophysics. Computer simulations of fluids in nanometer scale pore spaces can provide a unique microscopic insight into the structure, dynamics and forces arising from the crystallization process. We discuss in this paper molecular dynamics computer simulations of crystallization in pores of nanometer dimensions. The crystallization pressure due to the freezing of a model of Argon in a nanopore is computed using molecular dynamics simulations. We also investigate the influence of pore geometry in determining the dynamics of confined fluids, as well as mass separation in binary mixtures. It turns out that the pore geometry reveals itself as an important variable, leading to 1) new mechanisms for fast diffusion in confined spaces, and 2) accumulation of solute in specific regions inside the pore. 相似文献
18.
Leticia Gmez-Mendoza Ernesto Vega-Pea M. Isabel Ramírez Jos Luis Palacio-Prieto Leopoldo Galicia 《Applied geography (Sevenoaks, England)》2006,26(3-4):276-290
The objective of study was to explore short-term trends of processes that determine land-use change in Sierra Norte of Oaxaca (SNO), Mexico. Land use and land cover changes (LULCC) were estimated in a complex mosaic of vegetation in the SNO from 1980 to 2000, and projected them to 2020 through a Markovian model. SNO is highly vulnerable to climatic change according to a 2050 GCM scenario. However, 3% annual rate of tropical and temperate forest deforestation from agriculture and livestock encroachment, suggest the threat from land-use change is higher than that from climatic change for this study site. Productive land-use strategies are needed to reduce such high deforestation rates for tropical regions. Controlling deforestation would also reduce short-term effects of CO2 emissions to the atmosphere. Because of the necessity to evaluate anthropogenic ecosystem changes, it is imperative to separate short-term influences such as deforestation, from long-term influences such as climatic change. 相似文献
19.
Groundwater-flow modeling in the Yucatan karstic aquifer, Mexico 总被引:1,自引:0,他引:1
Roger González-Herrera Ismael Sánchez-y-Pinto José Gamboa-Vargas 《Hydrogeology Journal》2002,10(5):539-552
The current conceptual model of the unconfined karstic aquifer in the Yucatan Peninsula, Mexico, is that a fresh-water lens
floats above denser saline water that penetrates more than 40 km inland. The transmissivity of the aquifer is very high so
the hydraulic gradient is very low, ranging from 7–10 mm/km through most of the northern part of the peninsula. The computer
modeling program AQUIFER was used to investigate the regional groundwater flow in the aquifer. The karstified zone was modeled
using the assumption that it acts hydraulically similar to a granular, porous medium. As part of the calibration, the following
hypotheses were tested: (1) karstic features play an important role in the groundwater-flow system; (2) a ring or belt of
sinkholes in the area is a manifestation of a zone of high transmissivity that facilitates the channeling of groundwater toward
the Gulf of Mexico; and (3) the geologic features in the southern part of Yucatan influence the groundwater-flow system. The
model shows that the Sierrita de Ticul fault, in the southwestern part of the study area, acts as a flow barrier and head
values decline toward the northeast. The modeling also shows that the regional flow-system dynamics have not been altered
despite the large number of pumping wells because the volume of water pumped is small compared with the volume of recharge,
and the well-developed karst system of the region has a very high hydraulic conductivity.
Electronic Publication 相似文献
20.