全文获取类型
收费全文 | 2546篇 |
免费 | 55篇 |
国内免费 | 35篇 |
专业分类
测绘学 | 64篇 |
大气科学 | 145篇 |
地球物理 | 628篇 |
地质学 | 847篇 |
海洋学 | 313篇 |
天文学 | 408篇 |
综合类 | 13篇 |
自然地理 | 218篇 |
出版年
2021年 | 26篇 |
2020年 | 35篇 |
2019年 | 33篇 |
2018年 | 59篇 |
2017年 | 46篇 |
2016年 | 92篇 |
2015年 | 55篇 |
2014年 | 75篇 |
2013年 | 157篇 |
2012年 | 71篇 |
2011年 | 132篇 |
2010年 | 94篇 |
2009年 | 111篇 |
2008年 | 90篇 |
2007年 | 105篇 |
2006年 | 99篇 |
2005年 | 97篇 |
2004年 | 89篇 |
2003年 | 64篇 |
2002年 | 78篇 |
2001年 | 44篇 |
2000年 | 44篇 |
1999年 | 45篇 |
1998年 | 28篇 |
1997年 | 34篇 |
1996年 | 33篇 |
1995年 | 43篇 |
1994年 | 33篇 |
1993年 | 27篇 |
1992年 | 26篇 |
1991年 | 34篇 |
1990年 | 23篇 |
1989年 | 24篇 |
1988年 | 34篇 |
1987年 | 28篇 |
1986年 | 25篇 |
1985年 | 35篇 |
1984年 | 38篇 |
1983年 | 42篇 |
1982年 | 32篇 |
1981年 | 30篇 |
1980年 | 27篇 |
1979年 | 32篇 |
1978年 | 25篇 |
1977年 | 33篇 |
1976年 | 31篇 |
1975年 | 26篇 |
1973年 | 19篇 |
1972年 | 22篇 |
1971年 | 18篇 |
排序方式: 共有2636条查询结果,搜索用时 15 毫秒
81.
Gregory K. Druschel Robert J. Hamers George W. Luther III Jillian F. Banfield 《Aquatic Geochemistry》2003,9(2):145-164
The oxidation kinetics of trithionate (S3O62-
) and tetrathionate (S4O
6
2-
) with hydroxyl radicals (OH*) have been investigated in systems analogous to acid mine drainage (AMD) environments. The discovery of hydroxyl radical
(OH*) formation on pyrite surfaces (Borda et al., 2003) suggests hydroxyl radicals may affect the oxidation kinetics of intermediate
sulfur species such as tetrathionate. Cyclic voltammetry experiments in acidic solutions indicate that the reaction of S4O
6
2-
with OH* goes through an unknown intermediate, tentatively assigned as S3O
4
n-
. An outer-sphere electron transfer mechanism for the reaction of S4O
6
2-
with OH* to form S3O
4
n-
is proposed based on experimental results. Oxidation rates for trithionate and tetrathionate in the presence of Fenton's
reagent (which forms hydroxyl radicals) are too fast to be directly measured using UV-Vis spectrophotometry, electrochemical,
or stop-flow spectrophotometry methods. Competitive reaction kinetics within the context of the Haber—Weiss mechanism suggests
that the rate constant for the oxidation of trithionate and tetrathionate with OH* is in excess of 108 M-1 sec-1. 相似文献
82.
83.
Kohei Cho 《ISPRS Journal of Photogrammetry and Remote Sensing》1997,52(6):277-280
The first ISPRS software contest for computer-assisted teaching, CATCON, took place on July 12, 1996 at the ISPRS Congress in Vienna. The main objective of the contest was to promote the development and dissemination of good/user-friendly software packages for computer-assisted teaching. Ten software packages and one data set from six countries were nominated. All the software and the data set were demonstrated at the contest, and prizes were given to three software packages and to one data set. 相似文献
84.
85.
86.
87.
88.
Dynamic stochastic estimation of physical variables 总被引:1,自引:0,他引:1
A fundamental problem facing the physical sciences today is analysis of natural variations and mapping of spatiotemporal processes. Detailed maps describing the space/time distribution of groundwater contaminants, atmospheric pollutant deposition processes, rainfall intensity variables, external intermittency functions, etc. are tools whose importance in practical applications cannot be overestimated. Such maps are valuable inputs for numerous applications including, for example, solute transport, storm modeling, turbulent-nonturbulent flow characterization, weather prediction, and human exposure to hazardous substances. The approach considered here uses the spatiotemporal random field theory to study natural space/time variations and derive dynamic stochastic estimates of physical variables. The random field model is constructed in a space/time continuum that explicitly involves both spatial and temporal aspects and provides a rigorous representation of spatiotemporal variabilities and uncertainties. This has considerable advantages as regards analytical investigations of natural processes. The model is used to study natural space/time variations of springwater calcium ion data from the Dyle River catchment area, Belgium. This dataset is characterized by a spatially nonhomogeneous and temporally nonstationary variability that is quantified by random field parameters, such as orders of space/time continuity and random field increments. A rich class of covariance models is determined from the properties of the random field increments. The analysis leads to maps of continuity orders and covariances reflecting space/time calcium ion correlations and trends. Calcium ion estimates and the associated statistical errors are calculated at unmeasured locations/instants over the Dyle region using a space/time kriging algorithm. In practice, the interpretation of the results of the dynamic stochastic analysis should take into consideration the scale effects. 相似文献
89.
Porewater pressure increases in soil and rock from underground chemical and nuclear explosions 总被引:3,自引:0,他引:3
Wayne A. Charlie George E. Veyera Deanna S. Durnford Donald O. Doehring 《Engineering Geology》1996,43(4):225-236
A review and analysis of chemical and nuclear explosive-induced porewater pressure increases and induced rise in groundwater table elevations (groundwater mounding) is presented. Our analysis indicates that residual pore pressure increases and groundwater mounding can be induced by underground chemical and nuclear explosions to scaled distances of 879 m/(kt)1/3. This relationship is linear over seven orders of magnitude of explosive energy ranging from a 0.01 kg chemical explosion to a 100 kt nuclear explosion and is valid for a wide variety of saturated geological profiles. Underground chemical explosions, and probably underground nuclear explosions have the potential to induce liquefaction of water-saturated soils to scaled distances of about 260 m/(kt)1/3. 相似文献
90.
Lake Koronia, a Ramsar site, is shallow, polymictic, hypertrophic and until recently was aerially the fourth largest lake in Greece. Although exceeding 5 m in the past, lake depth has declined progressively from 3.8 m in 1980 to < 1 m in 1997, reducing surface area and water volume by 50% and 80%, respectively. Specific conductivityincreased from 1300 μS cm−1 in 1977 to >6000 μS cm−1 in 1991. Increased phosphate concentrations from the late 1970's (8–45 μg L−1) to the late 1990's (100–1000 μg L−1) document that the previously eutrophic system with a limited littoral zone switched to hypertrophy dominated by massive cyanobacteria blooms. Oxygen saturation of the water column increased progressively from about 80% in 1983 to full saturation about 1993, after which it decreased progressively to only 20% saturation in 1997. In spite of cyanobacteria dominance, community metabolism of the lake switched from progressively increasing autotrophy to rapidly advancing heterotrophy associated with progressive water-level reduction leading to fish extirpation in the lake. 相似文献