全文获取类型
收费全文 | 655篇 |
免费 | 25篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 55篇 |
地球物理 | 175篇 |
地质学 | 233篇 |
海洋学 | 34篇 |
天文学 | 136篇 |
综合类 | 1篇 |
自然地理 | 34篇 |
出版年
2021年 | 5篇 |
2018年 | 18篇 |
2017年 | 14篇 |
2016年 | 20篇 |
2015年 | 25篇 |
2014年 | 19篇 |
2013年 | 28篇 |
2012年 | 30篇 |
2011年 | 47篇 |
2010年 | 33篇 |
2009年 | 42篇 |
2008年 | 23篇 |
2007年 | 26篇 |
2006年 | 14篇 |
2005年 | 16篇 |
2004年 | 16篇 |
2003年 | 18篇 |
2002年 | 10篇 |
2001年 | 10篇 |
2000年 | 19篇 |
1999年 | 14篇 |
1998年 | 17篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 10篇 |
1992年 | 10篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 10篇 |
1987年 | 5篇 |
1986年 | 8篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1973年 | 7篇 |
1970年 | 9篇 |
1969年 | 5篇 |
1968年 | 4篇 |
1952年 | 6篇 |
1951年 | 4篇 |
1950年 | 4篇 |
1949年 | 4篇 |
排序方式: 共有684条查询结果,搜索用时 15 毫秒
21.
Ulrich Einsle 《Aquatic Sciences - Research Across Boundaries》1988,50(2):136-165
The long-term development of crustacean associations in the Obersee of Lake Constance was studied at one central station from
1962 to 1986. In a simultaneously managed program with four additional stations from the eastern part (Bregenz Bay) to the
western überlinger See mainly the differences in horizontal distribution were focussed. It was one aim of these investigations,
to get an idea or an indication of a connexion between the recently observed eutrophication of the Obersee, and its crustacean
communities.
Due to the immigration of several species (cyclopids) or genotypes (Daphnia), the communities had changed in genetical structures, in reproduction rates and in predation or grazing impact. Dependent
on the specific annual cycles, there resulted an extermination (Heterocope, Diaphanosoma), or a long-term decrease in annual means (Mesocyclops, Cyclops abyssorum) of the “old-settled” species.
A general tendency was seen in an increase of annual averages until the middle of the seventies, and a following decrease
of population density of most of the species.
The horizontal differences in the species associations were remarkable. The Bregenz Bay showed an own aspect in its crustacean
community with high total numbers and in earlier spring development. Most of the newcomers were concentrated in the eastern
part of the lake. 相似文献
22.
23.
Benjamin D. Santer Karl E. Taylor Tom M. L. Wigley Joyce E. Penner Philip D. Jones Ulrich Cubasch 《Climate Dynamics》1995,12(2):77-100
It has been hypothesized recently that regional-scale cooling caused by anthropogenic sulfate aerosols may be partially obscuring
a warming signal associated with changes in greenhouse gas concentrations. Here we use results from model experiments in which
sulfate and carbon dioxide have been varied individually and in combination in order to test this hypothesis. We use centered
[R (t)] and uncentered [C (t)] pattern similarity statistics to compare observed time-evolving surface temperature change patterns with the model-predicted
equilibrium signal patterns. We show that in most cases, the C (t) statistic reduces to a measure of observed global-mean temperature changes, and is of limited use in attributing observed
climate changes to a specific causal mechanism. We therefore focus on R (t), which is a more useful statistic for discriminating between forcing mechanisms with different pattern signatures but similar
rates of global mean change. Our results indicate that over the last 50 years, the summer (JJA) and fall (SON) observed patterns
of near-surface temperature change show increasing similarity to the model-simulated response to combined sulfate aerosol/CO2 forcing. At least some of this increasing spatial congruence occurs in areas where the real world has cooled. To assess the
significance of the most recent trends in R (t) and C (t), we use data from multi-century control integrations performed with two different coupled atmosphere-ocean models, which
provide information on the statistical behavior of 'unforced' trends in the pattern correlation statistics. For the combined
sulfate aerosol/CO2 experiment, the 50-year R (t) trends for the JJA and SON signals are highly significant. Results are robust in that they do not depend on the choice of
control run used to estimate natural variability noise properties. The R (t) trends for the CO2-only signal are not significant in any season. C (t) trends for signals from both the CO2-only and combined forcing experiments are highly significant in all seasons and for all trend lengths (except for trends
over the last 10 years), indicating large global-mean changes relative to the two natural variability estimates used here.
The caveats regarding the signals and natural variability noise which form the basis of this study are numerous. Nevertheless,
we have provided first evidence that both the largest-scale (global-mean) and smaller-scale (spatial anomalies about the global
mean) components of a combined CO2/anthropogenic sulfate aerosol signal are identifiable in the observed near-surface air temperature data. If the coupled-model
noise estimates used here are realistic, we can be highly confident that the anthropogenic signal that we have identified
is distinctly different from internally generated natural variability noise. The fact that we have been able to detect the
detailed spatial signature in response to combined CO2 and sulfate aerosol forcing, but not in response to CO2 forcing alone, suggests that some of the regional-scale background noise (against which we were trying to detect a CO2-only signal) is in fact part of the signal of a sulfate aerosol effect on climate. The large effect of sulfate aerosols found
in this study demonstrates the importance of their inclusion in experiments designed to simulate past and future climate change.
Received: 10 November 1994 / Accepted: 19 July 1995 相似文献
24.
Henry D. Schreiber G.Bryan Balazs Andrew P. Shaffer P.Lynne Jamison 《Geochimica et cosmochimica acta》1982,46(10):1891-1901
The production of metallic iron in silicate melts by the chemical reactions, 2Ti3+(melt) + Fe2+(melt) → 2Ti4+(melt) + Fe0(crystal)2Cr2+(melt) + Fe2+(melt) → 2Cr3+(melt) + Fe0(crystal)2Eu2+(melt)+ Fe2+(melt) → 2Eu3+(melt) + Fe0(crystal) has been demonstrated under experimental conditions in a simplified basaltic liquid, Such reactions may occur in lunar basalts and other reduced systems, and, thus, may aid in the understanding of the reduced nature of lunar basalts. The reactions were studied in a glass-forming Na-Ca-Mg-Al-silicate composition at a melt temperature of 1250°C and an imposed oxygen fugacity at the C/CO buffer (1 atm total pressure). Microtitrations of individually-doped samples were used in the quantitative assessment of their redox ratios and for the calibration of visible and near-infrared spectral absorptions. These spectral absorptions were then applied to the evaluation of the mutual redox interactions in dual-doped samples. 相似文献
25.
26.
27.
28.
29.
Hans Güsten Günther Heinrich Ralf W. H. Schmidt Ulrich Schurath 《Journal of Atmospheric Chemistry》1992,14(1-4):73-84
A small, lightweight (1.5 kg) and fast-response ozone sensor for direct eddy flux measurements has been built. The basis for detection is the chemiluminescence of an organic dye adsorbed on dry silica gel in the reaction with ozone. The chemiluminescence is monitored with a cheap and small blue-sensitive photomultiplier. At a flow rate of 100 l min-1 the ozone sensor has a 90% response time of significantly better than 0.1 s with a detection limit lower than 50 ppt at S/N=3. There are no interferences from other atmospheric trace gases like NOx, H2O2 and PAN. Water vapour and SO2 enhance the chemiluminescence efficiency of the ozone sensor. Since their response times are 22 seconds and 30 minutes, respectively, no correlation between rapid ozone fluctuations and those of these two trace gases is noticed by the ozone sensor when operating at a frequency of 10 Hz.The ozone sensor was tested for several weeks in continuous measurements of ozone fluxes and deposition velocities over different croplands using the eddy correlation technique. Good agreement was found between ozone dry deposition velocities derived from profile measurements and by eddy correlation. 相似文献
30.