全文获取类型
收费全文 | 8610篇 |
免费 | 267篇 |
国内免费 | 147篇 |
专业分类
测绘学 | 253篇 |
大气科学 | 782篇 |
地球物理 | 2069篇 |
地质学 | 3648篇 |
海洋学 | 421篇 |
天文学 | 1446篇 |
综合类 | 89篇 |
自然地理 | 316篇 |
出版年
2022年 | 72篇 |
2021年 | 100篇 |
2020年 | 87篇 |
2019年 | 75篇 |
2018年 | 287篇 |
2017年 | 278篇 |
2016年 | 397篇 |
2015年 | 234篇 |
2014年 | 412篇 |
2013年 | 509篇 |
2012年 | 395篇 |
2011年 | 357篇 |
2010年 | 410篇 |
2009年 | 454篇 |
2008年 | 349篇 |
2007年 | 306篇 |
2006年 | 310篇 |
2005年 | 242篇 |
2004年 | 212篇 |
2003年 | 177篇 |
2002年 | 160篇 |
2001年 | 157篇 |
2000年 | 148篇 |
1999年 | 149篇 |
1998年 | 172篇 |
1997年 | 144篇 |
1996年 | 150篇 |
1995年 | 103篇 |
1994年 | 92篇 |
1993年 | 104篇 |
1992年 | 68篇 |
1991年 | 78篇 |
1990年 | 65篇 |
1989年 | 72篇 |
1988年 | 61篇 |
1987年 | 82篇 |
1986年 | 81篇 |
1985年 | 73篇 |
1984年 | 87篇 |
1983年 | 90篇 |
1982年 | 83篇 |
1981年 | 68篇 |
1980年 | 68篇 |
1979年 | 76篇 |
1978年 | 57篇 |
1977年 | 57篇 |
1976年 | 48篇 |
1975年 | 67篇 |
1974年 | 58篇 |
1973年 | 61篇 |
排序方式: 共有9024条查询结果,搜索用时 46 毫秒
921.
T. M. Lenton R. Marsh A. R. Price D. J. Lunt Y. Aksenov J. D. Annan T. Cooper-Chadwick S. J. Cox N. R. Edwards S. Goswami J. C. Hargreaves P. P. Harris Z. Jiao V. N. Livina A. J. Payne I. C. Rutt J. G. Shepherd P. J. Valdes G. Williams M. S. Williamson A. Yool 《Climate Dynamics》2007,29(6):591-613
We have used the Grid ENabled Integrated Earth system modelling (GENIE) framework to undertake a systematic search for bi-stability
of the ocean thermohaline circulation (THC) for different surface grids and resolutions of 3-D ocean (GOLDSTEIN) under a 3-D
dynamical atmosphere model (IGCM). A total of 407,000 years were simulated over a three month period using Grid computing.
We find bi-stability of the THC despite significant, quasi-periodic variability in its strength driven by variability in the
dynamical atmosphere. The position and width of the hysteresis loop depends on the choice of surface grid (longitude-latitude
or equal area), but is less sensitive to changes in ocean resolution. For the same ocean resolution, the region of bi-stability
is broader with the IGCM than with a simple energy-moisture balance atmosphere model (EMBM). Feedbacks involving both ocean
and atmospheric dynamics are found to promote THC bi-stability. THC switch-off leads to increased import of freshwater at
the southern boundary of the Atlantic associated with meridional overturning circulation. This is counteracted by decreased
freshwater import associated with gyre and diffusive transports. However, these are localised such that the density gradient
between North and South is reduced tending to maintain the THC off state. THC switch-off can also generate net atmospheric
freshwater input to the Atlantic that tends to maintain the off state. The ocean feedbacks are present in all resolutions,
across most of the bi-stable region, whereas the atmosphere feedback is strongest in the longitude–latitude grid and around
the transition where the THC off state is disappearing. Here the net oceanic freshwater import due to the overturning mode
weakens, promoting THC switch-on, but the atmosphere counteracts this by increasing net freshwater input. This increases the
extent of THC bi-stability in this version of the model.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
922.
The results of experimentally investigating the fluctuation parameters of four slight-mechanical-displacement meters via the method of “force cooling” of their low-Q-factor mechanical oscillators are presented. In the course of the experiment at the temperature T = 300 K during continuous observation of the coordinate of a test weight of an oscillator in the steady nonequilibrium state, it was demonstrated that the standard quantum limit (SQL) can be overcome. 相似文献
923.
High-pressure granulite from Western Kunlun,northwestern China: Its metamorphic evolution,zircon SHRIMP U-Pb ages and tectonic implication 总被引:1,自引:0,他引:1
QU JunFeng ZHANG LiFei AI YongLiang L Zeng WANG JianPing ZHOU Hui & WANG ShiYan MOE Key Laboratory of Orogenic Belts Crustal Evolution School of Earth Space Science Peking University Beijing China Henan Polytechnic University Jiaozuo China Geological Survey of Henan Province Zhengzhou China 《中国科学D辑(英文版)》2007,50(7):961-971
High-pressure mafic granulites occurring as lenticular bodies within garnet-amphibolites in Kangxiwar Fault have been first reported in this paper. The P-T conditions of two metamorphic stages were ob-tained using calibrated geothermal barometers and ThermoCalc Program. The peak metamorphic con-dition of these high-pressure granulites is about 760―820℃,1.0―1.2 GPa and the retrograde meta-morphic condition is about 620―720℃,0.7―0.8 GPa. The petrological studies show that they have a near-isobaric cooling P-T... 相似文献
924.
Kinder A Sierts-Herrmann A Biselli S Heinzel N Hühnerfuss H Kammann U Reineke N Theobald N Steinhart H 《Marine environmental research》2007,63(5):506-515
Heat shock proteins 70 (hsp70) are known to be induced by a great variety of chemical stressors. The effects of different environmental contaminants, which were identified in sediments of the North Sea and the Baltic Sea as main contaminants or as contaminants of special toxicological interest, on the extent of expression of hsp70 in a permanent cell line Epithelioma papulosum cyprini (EPC) were investigated. Concentrations of the single contaminants leading to elevated hsp70 levels were compared to the respective concentrations of these contaminants encountered in the sediment extracts thus allowing an assessment of their contribution to the toxicity of these sediments. Analysis of hsp70 was performed using western blotting techniques with subsequent comparative quantification by densitometry. Eleven of thirteen contaminants have shown a dose-dependent increase in hsp70 levels. An expression of hsp70 was observed in most cases between 0.1 and 10 microg/mL test solution. Some of the investigated stressors led to extremely high hsp70 contents even at low concentrations. However, in most cases contaminant concentrations in sediments were too low to cause an effect. For this reason, effects of the tested sediments are attributed to other contaminants or rather to mixtures of stressors. 相似文献
925.
We present our synchronous spectroscopy and photometry of DI Cep, a classical T Tauri star. The equivalent widths and radial velocities of the individual components and Hα, Hβ, D1 and D2 Na I, and HeI λ5876 Å emission line profiles exhibit variability. We have found a clear positive correlation between the brightness and equivalent width for the Hα and Hβ emission lines. The photometric and spectroscopic data are satisfactorily described in phases of a 9-day period. The expected magnetic field of the star has been estimated using existing magnetospheric models to be 655–1000 G. The star is suspected to be a binary. 相似文献
926.
Modification of fluid inclusions in quartz by deviatoric stress I: experimentally induced changes in inclusion shapes and microstructures 总被引:1,自引:1,他引:0
Alexandre Tarantola Larryn W. Diamond Holger Stünitz 《Contributions to Mineralogy and Petrology》2010,160(6):825-843
Fluid inclusions in quartz are known to modify their shapes and microstructures (textures) during weak plastic deformation.
However, such changes have not been experimentally demonstrated and criteria are not available to relate them to paleostress
conditions. To address these issues, quartz crystals containing natural CO2–H2O–NaCl fluid inclusions have been experimentally subjected to compressive deviatoric stresses of 90–250 MPa at 700°C and ~600 MPa
confining pressure. Strains of up to 1% cause the inclusions to develop irregular shapes and to generate microcracks in crystallographic
planes oriented subperpendicular to the major compression axis, σ
1. The uniform alignment of the microcracks imparts a planar fabric to the samples. The microcracks heal and form swarms of
tiny satellite inclusions. These new inclusions lose H2O by diffusion, thereby triggering plastic deformation of the surrounding quartz via H2O-weakening. Consequently, the quartz samples deform plastically only in domains originally rich in inclusions. This study
shows that fluid inclusions deformed by deviatoric stresses may indeed record information on paleostress orientations and
that they play a key role in facilitating crystal-plastic deformation of quartz. 相似文献
927.
928.
A. V. Tatarinov E. V. Danilova L. I. Yalovik D. D. Barkhutova Z. B. Namsaraev A. V. Bryanskaya A. M. Plyusnin 《Geochemistry International》2010,48(2):152-162
Hoito Gol hot spring of weakly mineralized warm (36–29°C) neutral and partly alkaline nitrogen-carbon dioxide waters belongs
to the hydrogeological structure of the actively water-flooded fault marked by the Sentsy River at the southwestern termination
of the Baikal rift system. The spatiotemporal evolution of the major parameters of the underground aqueous ecosystem of this
spring is controlled mainly by geological and geodynamic factors, whereas the parameters of the surface system are determined
mostly by bacterial factors. Variations in these factors are correlated with changes in the composition, structure, and spatial
distribution of the bacterial communities. 相似文献
929.
Wan Guojiang Zheng Xiangdong Lee H N Bai Z G Wan Enyuan Wang Shilu Yang Wei 《地球科学进展》2010,25(5):492-504
It′s essential to measure air concentrations and depositional fluxes of environmental radionuclides in different regions for modeling global contamination transfer and validation, tracing deposition process and dating, referencing watershed erosion trace and assessing natural radiation of ecosystem. This study introduces the research background and methods and explains weekly variations of 210Pb and 7Be concentrations in surface air and precipitation at Mt. Guanfeng/Guiyang since 2001. The results indicate that 210Pb and 7Be concentrations in surface air fluctuate periodically at 2~6 week interval because of the meteorological condition changes. The annual trend in 210Pb air concentration is overall influenced by air temperature variation and periodical rainfall. 7Be air concentration varies up and down regualarly. The synchronization of low concentrations for both 210Pb and 7Be in surface air and high ratio (210Pb/7Be ≥ 0.8) indicate oceanic poor 210Pb-7Be air mass invasion. The synchronization of high concentrations of 210Pb and 7Be in surface air and low ratio (210Pb/7Be ≤ 0.7) implies rich 7Be air mass invasion from altostratus atmosphere. Weekly concentrations of 210Pb and 7Be in precipitation and the Kd coefficients are high in late Autumn to Spring, and low in late Spring to Autumn. Although 210Pb and 7Be concentrations vary seasonally, their weekly concentrations in precipitation increase with that of air concentration. The 210Pb and 7Be weekly concentrations for seasonal division is about 0.2 Bq/L and 1 Bq/L, respectively. However, the Kd coefficient decreases when 210Pb and 7Be air concentrations increase. Deposition of 210Pb and 7Be with precipitation mainly take place in Spring and Summer; The weekly fallout of 210Pb and 7Be increases with increasing precipitation; the increase of 7Be is triple of that of 210Pb and 2.5 when precipitation nears to zero. The weekly-high fallout of 210Pb and 7Be with precipitation corresponds with the dramatic decrease of their air concentrations within or vicinal weeks. The ratio of 210Pb to 7Be in rainfall is overall ≤ 0.5 and varies synchronously with the ratio in surface air, indicating that the two radionuclides are cleaned by precipitation from air at close speed. In the extreme freezing disaster in 2008, both 210Pb and 7Be air concentrations were low and coupling with coexist of low concentration of aerosol and high nuclides activities. Weekly concentration of 7Be in surface air at Mt. Guanfeng demonstrates the anticipated concentration level in the low-latitude and high-elevation region; the short-term fluctuations of 7Be concentration indicated the hysteresis was influcenced by the strong air current submersion and the low-elevation air mass rising differently at Mt. Guanfeng and Mt. Waliguan. 相似文献
930.