全文获取类型
收费全文 | 1101篇 |
免费 | 163篇 |
国内免费 | 215篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 214篇 |
地球物理 | 247篇 |
地质学 | 600篇 |
海洋学 | 228篇 |
天文学 | 90篇 |
综合类 | 25篇 |
自然地理 | 73篇 |
出版年
2024年 | 5篇 |
2023年 | 20篇 |
2022年 | 24篇 |
2021年 | 34篇 |
2020年 | 41篇 |
2019年 | 25篇 |
2018年 | 27篇 |
2017年 | 34篇 |
2016年 | 30篇 |
2015年 | 32篇 |
2014年 | 37篇 |
2013年 | 40篇 |
2012年 | 35篇 |
2011年 | 48篇 |
2010年 | 44篇 |
2009年 | 62篇 |
2008年 | 73篇 |
2007年 | 67篇 |
2006年 | 80篇 |
2005年 | 64篇 |
2004年 | 76篇 |
2003年 | 58篇 |
2002年 | 55篇 |
2001年 | 38篇 |
2000年 | 71篇 |
1999年 | 59篇 |
1998年 | 44篇 |
1997年 | 43篇 |
1996年 | 36篇 |
1995年 | 23篇 |
1994年 | 29篇 |
1993年 | 26篇 |
1992年 | 16篇 |
1991年 | 4篇 |
1990年 | 21篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1978年 | 2篇 |
排序方式: 共有1479条查询结果,搜索用时 531 毫秒
941.
942.
A. L.?Huber M.?Heuer K. T.?FehrEmail author K.?Bente E.?Schmidbauer G. D.?Bromiley 《Physics and Chemistry of Minerals》2004,31(2):67-79
Clinopyroxenes along the solid solution series hedenbergite (CaFeSi2O6)–petedunnite (CaZnSi2O6) were synthesized under hydrothermal conditions and different oxygen fugacities at temperatures of 700 to 1200 °C and pressures of 0.2 to 2.5 GPa. Properties were determined by means of X-ray diffraction, electron microprobe analysis and 57Fe Mössbauer spectroscopy at 298 K. Unit-cell parameters display a linear dependency with changing composition. Parameters a0 and b0 exhibit a linear decrease with increasing Zn content while the monoclinic angle increases linearly. Parameter c0 is not affected by composition and remains constant at a value of 5.248 Å. The molar volume can be described according to the equation Vmol (ccm mol–1)=33.963(16)–0.544(31)*Zn pfu. The isomer shifts of ferrous iron on the octahedral M1 site in hedenbergite are not affected by composition along the hedenbergite–petedunnite solid solution series and remain constant at an average value of 1.18 mm s–1. Quadrupole splittings of Fe2+ on the M1 are, however, strongly affected by composition, and they decrease linearly with increasing petedunnite component in hedenbergite, ranging from 2.25 mm s–1 for pure hedenbergite end member to 1.99 mm s–1 for a solid solution containing 84 mole% petedunnite. The half-widths of intermediate solid solutions vary between 0.26 and 0.33 mm s–1, indicating, in accordance with the microprobe analyses and X-ray diffraction, that samples are homogeneous and well-crystallized. The data from this study demonstrate that the crystallinity of hedenbergitic clinopyroxenes can be improved by using oxide mixtures as starting materials. Crystal sizes for intermediate compositions range up to 70 m, suitable for standard single-crystal X-ray analysis.This paper is dedicated to Prof. Dr. Georg Amthauer, Salzburg, on occasion of his 60th birthday 相似文献
943.
Craig Stroud Sasha Madronich Elliot Atlas Christopher Cantrell Alan Fried Brian Wert Brian Ridley Fred Eisele Lee Mauldin Richard Shetter Barry Lefer Frank Flocke Andy Weinheimer Mike Coffey Brian Heikes Robert Talbot Donald Blake 《Journal of Atmospheric Chemistry》2004,47(2):107-138
Local ozone production and loss rates for the arctic free troposphere (58–85° N, 1–6 km, February–May) during the TroposphericOzone Production about the Spring Equinox (TOPSE) campaign were calculated using a constrained photochemical box model. Estimates were made to assess the importance of local photochemical ozone production relative to transport in accounting for the springtime maximum in arctic free tropospheric ozone. Ozone production and loss rates from our diel steady-state box model constrained by median observations were first compared to two point box models, one run to instantaneous steady-state and the other run to diel steady-state. A consistent picture of local ozone photochemistry was derived by all three box models suggesting that differences between the approaches were not critical. Our model-derived ozone production rates increased by a factor of 28 in the 1–3 km layer and a factor of 7 in the 3–6 kmlayer between February and May. The arctic ozone budget required net import of ozone into the arctic free troposphere throughout the campaign; however, the transport term exceeded the photochemical production only in the lower free troposphere (1–3 km) between February and March. Gross ozone production rates were calculated to increase linearly with NOx mixing ratiosup to 300 pptv in February and for NOx mixing ratios up to 500 pptv in May. These NOx limits are an order of magnitude higher thanmedian NOx levels observed, illustrating the strong dependence ofgross ozone production rates on NOx mixing ratios for the majority of theobservations. The threshold NOx mixing ratio needed for netpositive ozone production was also calculated to increase from NOx 10pptv in February to 25 pptv in May, suggesting that the NOx levels needed to sustain net ozone production are lower in winter than spring. This lower NOx threshold explains how wintertime photochemical ozone production can impact the build-up of ozone over winter and early spring. There is also an altitude dependence as the threshold NOx neededto produce net ozone shifts to higher values at lower altitudes. This partly explains the calculation of net ozone destruction for the 1–3 km layerand net ozone production for the 3–6 km layer throughout the campaign. 相似文献
944.
Over the last 25 years, considerable changes have been observed in the littoral vegetation of 11 lakes within the Sejny Lake District. In eight lakes (Dowcień, Jurkowo, Kunis, Miałkie, Pilwie, Płaskie, Wiłkokuk, Zelwa) where Chara species dominated, their communities declined or disappeared completely. In four of these lakes (Dowcień, Jurkowo, Kunis and Miałkie), charophytes were replaced by communities of the class Potametea (mainly Nupharo-Nymphaeetum albae and Ceratophylletum demersi). In three other lakes (Pilwie, Płaskie and Wiłkokuk), the area covered by charophyte communities decreased. In Lake Zelwa, Charetum rudis and Charetum jubatae disappeared while Charetum tomentosae and Charetum fragilis expanded. A total area of charophyte communities remained approximately the same. A considerable increase in the water total hardness and concentration was noted in each of the eight lakes. In most of them increased levels of dissolved organic matter (measured as COD-KMnO4) and pH were detected as well. However, the increase in the concentration was smaller in Lakes Wiłkokuk and Zelwa in which only slight changes in the vegetation were observed. In the above two lakes, the concentration of dissolved organic matter decreased and low water colour values are now noted. In three lakes (Długie, Dmitrowo and Gajlik), the charophyte communities tended to expand under the condition of moderate or high (Lake Długie) concentration, while dissolved organic matter concentrations were low. These lakes are also characterized by low values of colour. Charophyte communities may persist in lakes for a long period of time even when there is a moderate increase in concentration until the colour of water distinctly increases (>20 mg Pt L−1). 相似文献
945.
Thomas A. Douglas 《Chemical Geology》2006,231(3):236-251
The draw down of CO2 from the atmosphere during mineral weathering plays a major role in the global budget of this greenhouse gas. Silicate minerals remove twice the CO2 of carbonate minerals per mole of calcium in runoff during weathering. Bedrock weathering chemistry was investigated in the White River watershed of northeastern USA to investigate whether there are seasonal differences in carbonate and silicate weathering chemistry. Geographic Information Systems analyses of bedrock geology were combined with major element concentrations in river waters to gain an understanding of the consistency of mineral weathering during three seasons. The percent of carbonate mineralogy comprising the bedrock in tributaries of the White River varied from less than 5% to 45% by area. A mass balance calculation using major element concentrations in waters was applied to estimate the seasonal relationships between bedrock geology and bicarbonate flux. In all tributaries and the main stem of the White River the highest calculated percent of bicarbonate from carbonate mineral weathering was measured in the late fall. The results suggest that carbonate and silicate bedrock weathering processes are seasonally controlled. Thus single season sampling could not accurately represent an entire year's geochemical budget. In the White River, water samples obtained solely during the summer would consistently underestimate the total yearly source of bicarbonate from carbonate bedrock weathering. The same sample set would also provide data that would lead to an underestimation of the yearly atmospheric CO2 draw down by bedrock weathering in the watershed. For example at four of the seven locations studied there was an almost two-fold difference between summer and spring calculated atmospheric CO2 consumption rates. 相似文献
946.
Jianmei Cheng Jennifer C. McIntosh Xinong Xie Jiu Jimmy Jiao 《Journal of Geochemical Exploration》2006,88(1-3):86
The Sanzhao depression and Qijia-gulong depression are two of the most important hydrocarbon-bearing sub-depressions in the Songliao basin, dominated by Cretaceous fluvial and lacustrine strata with volcanic and volcaniclastic rocks. In this paper, the pressure distributions and hydrochemistry variations in those two depressions are investigated. It is found that the Qijia-gulong depression is dominated by overpressure, but the Sanzhao depression is dominated by underpressure, especially in the Quantou formation. The salinity of formation water ranges from 1.0 g/L to 20 g/L, with a mean of 4 g/L in most formations. Water composition is dominated by NaHCO3 water type but varies greatly in salinity and ionic ratios in the different depressions. The results of mass balance calculation reveal that, fluid chemistry in the Qijia-gulong depression is dominated by dissolution of silicate minerals and halite, whereas in the Sanzhao depression it is dominated by silicate mineral dissolution, evaporite dissolution (halite and gypsum), carbonate mineral dissolution/precipitation, and cation exchange. 相似文献
947.
948.
Sphene is very common in rocks including albitized granite, dioritic porphyrite, calcsilicate rock and breccia from the eastern fold belt of Mount Isa Inlier, Cloncurry. Two stages of sphenes are present in these rocks. First-staged sphene is relatively fine, euhedral, some grains show round or patchy zoning; second-staged sphene is relatively large, anhedral to subhedral, some grains show patchy zoning;both possibly contain rutile, ilmenite and magnetite inclusions. All sphenes are of low-Al type. The second-staged sphene has lesser Fe apfu than the first-staged sphene. Light-color part of the sphene has bigger Fe apfu than the dark-color part, as observed on one individual grain of sphene with patchy zoning, the average Xro of the sphene with patchy zoning is greater than that of the sphene without patchy zoning. Because the sphenes are taken from different types of rocks, Si, Ti, and Al have variable relations with F OH apfu. Si and Ti are not correlated with OH F in all analyzed samples ; Fe is correlated with OH F in the sphene just from granite and dioritic porphyrite; Al is correlated with OH F in the sphene fromgranite and breccia and is not correlated with OH F in the sphene from the dioritic porphyrite and calcsilicate rocks. The first-staged sphenes were possibly formed in the processes of magmatism and metamorphism. The second-staged sphenes were formed as a result of the breakdown of hornblendes and biotites in the process of Na (Ca) -metasomatism. 相似文献
949.
F. Di Benedetto G. P. Bernardini D. Borrini W. Lottermoser G. Tippelt G. Amthauer 《Physics and Chemistry of Minerals》2005,31(10):683-690
A combined 57Fe and 119Sn Mössbauer study is performed on the whole solid solution stannite-kesterite consisting of natural and synthetic samples. No discontinuous change of the Mössbauer parameters of 57Fe as well as of 119Sn as function of the composition is observed, thus confirming the existence of a complete solid solution between both compounds. 相似文献
950.
The water of Bosten Lake was released to lower reaches of the Tarim River for 5 times from 2000 to 2002. The changes of total dissolved solid (TDS) and the major ions (SO2-4, Cl-, Na+, Ca2+, Mg2+ and HCO-3) were analyzed during this period. It was found out that TDS and the concentrations of the major ions initially and quickly increased and then decreased, but finally increased again. These changes were different at different distances from the river, which indicated that the groundwater changes relied on the distance from the river. In addition, the salt in groundwater was only diluted but not removed by the water. It was suggested that ecological measures should be sought to really promote the quality of the groundwater at the lower reaches of the Tarim River. 相似文献