全文获取类型
收费全文 | 2004篇 |
免费 | 68篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 31篇 |
大气科学 | 136篇 |
地球物理 | 457篇 |
地质学 | 612篇 |
海洋学 | 154篇 |
天文学 | 425篇 |
综合类 | 5篇 |
自然地理 | 260篇 |
出版年
2021年 | 12篇 |
2020年 | 15篇 |
2019年 | 20篇 |
2018年 | 48篇 |
2017年 | 32篇 |
2016年 | 30篇 |
2015年 | 53篇 |
2014年 | 52篇 |
2013年 | 111篇 |
2012年 | 46篇 |
2011年 | 83篇 |
2010年 | 82篇 |
2009年 | 100篇 |
2008年 | 79篇 |
2007年 | 93篇 |
2006年 | 77篇 |
2005年 | 67篇 |
2004年 | 76篇 |
2003年 | 67篇 |
2002年 | 65篇 |
2001年 | 45篇 |
2000年 | 62篇 |
1999年 | 25篇 |
1998年 | 29篇 |
1997年 | 45篇 |
1996年 | 37篇 |
1995年 | 42篇 |
1994年 | 21篇 |
1993年 | 30篇 |
1992年 | 34篇 |
1991年 | 32篇 |
1990年 | 28篇 |
1989年 | 24篇 |
1988年 | 13篇 |
1987年 | 19篇 |
1986年 | 23篇 |
1985年 | 28篇 |
1984年 | 35篇 |
1983年 | 29篇 |
1982年 | 24篇 |
1981年 | 27篇 |
1980年 | 24篇 |
1979年 | 17篇 |
1978年 | 23篇 |
1977年 | 31篇 |
1976年 | 16篇 |
1975年 | 18篇 |
1974年 | 18篇 |
1973年 | 16篇 |
1971年 | 9篇 |
排序方式: 共有2080条查询结果,搜索用时 15 毫秒
181.
C.T. Russell 《Physics of the Earth and Planetary Interiors》1979,20(2-4):237-246
The magnetic field measurements of the Mars 2, 3 and 5 spacecraft have been interpreted by Dolginov and co-workers to be consistent with an intrinsic planetary magnetic moment of 2.5 × 1022 gauss cm3. They base this interpretation mainly on the apparent size of the obstacle responsible for deflecting the solar wind, the lack of dependence of the sign of the magnetic field in the wake region of the planet on the sign of the component of the interplanetary field radially out from the sun, and an apparent encounter of the Mars spacecraft with the planetary field. When examined in detail this evidence is very suspect. A detailed criticism of the arguments by Dolginov and co-workers for an intrinsic field has appeared elsewhere. Herein we summarize this criticism and present, in an appendix, a compendium of the Mars 3 and 5 magnetic field data transformed into a coordinate system in which the details of the interaction are more easily visualized. Many of these data have not been published in this form previously. 相似文献
182.
183.
184.
Melanoidins, acidic polymeric products of amino acid/sugar condensation reactions, are shown to be capable of reacting with and binding functionalized lipid molecules. Pyrolysis gas chromatography is used to monitor the inclusion of lipids (alcohols and acids) into, and to monitor the changes in composition caused by artificial diagenesis of, the melanoidins. Artificial diagenesis of the lipidcontaining melanoidins produces a material resembling kerogen. The possible role of melanoidins in the formation of kerogens is discussed as are internal transformations within kerogens during diagenesis. 相似文献
185.
186.
The effect of mineral matter on the laboratory pyrolysis of sediments, kerogens and coals, and of coal macerals mixed with either alumina, bentonite, kaolinite, or calcium carbonate has been investigated. Some minerals are more active than others in effecting changes in the composition of the pyrolysate. The relative content of low molecular weight pyrolysis products is higher for kerogens pyrolyzed in a mineral matrix than for isolated kerogens. Our limited data suggests that this is due to both condensation and gasification of higher molecular weight constituents in the ‘primary’ pyrolysate. Differences in the content of aromatic versus aliphatic compounds have been noted when pyrograms from coal macerals are compared with pyrograms from coal maceral-mineral mixtures. We conclude that mineralogy is important in controlling the composition of kerogen pyrolysis products. 相似文献
187.
Terry Russell 《Sedimentary Geology》1980,25(4):277-290
Clasts of the Late Devonian Keepit Conglomerate of northeastern New South Wales, Australia, are predominantly andesites of isotropic nature that lack any apparent initial shape controls. Given adequate time in a particular environment, these clasts could be reasonably expected to develop shapes characteristic of abrasion within that environment.Clasts from both fluvial and marine resedimented conglomerates of the Keepit Conglomerate possess shape characteristics indicative of shaping within a fluvial environment. Maximum projection sphericity, and a plot of sphericity against either the oblate-prolate index or the flatness parameter C/A, were the most useful in indicating fluvial shaping processes. In addition, the Index and the dominant form classes of the Sneed and Folk Sphericity-Form diagram were in support of a fluvial history for the clasts.The occurrence of clasts exhibiting typical fluvial shapes in marine resedimented conglomerates indicates a lack of time and/or insufficient energy in a beach environment for reshaping of the clasts prior to resedimentation into deeper-water submarine-fan environments. This interpretation is consistent with and lends support to the interpretation, based on all other available data, for the Keepit Conglomerate of a history of rapid progradation of fluvial gravels into a relatively low-energy coastline environment, with periodic resedimentation of coarse sediment into deeper water. 相似文献
188.
189.
Henry P Schwarcz Russell S Harmon Peter Thompson Derek C Ford 《Geochimica et cosmochimica acta》1976,40(6):657-665
Fluid inclusions found trapped in speleothems (cave deposited travertine) are interpreted as samples of seepage water from which enclosing calcium carbonate was deposited. The inclusions are assumed to have preserved their D/H ratios since the time of deposition. Initial 18O/16O ratios can be inferred from δD because rain- and snow-derived seepage waters fall on the meteoric water line (δD = 8δ18O + 10). Estimates of temperature of deposition of the carbonate can be calculated from inclusion D/H ratios and δ18O of enclosing calcite in Pleistocene speleothems. For most speleothems investigated (0–200,000 yr old) δ18O of calcite appears to have decreased with increasing temperature of deposition indicating that the dominant cause of climate-dependent change in δ18O of calcite was the change in Kcw, the isotope fractionation equilibrium constant, with temperature; δ18O of meteoric precipitation generally increased with increasing temperature, but not sufficiently to compensate for the decrease in Kcw. 相似文献
190.
Douglas S. Davison 《Boundary-Layer Meteorology》1976,10(2):167-180
Davenport's geometric similarity is applied to the temperature field in the unstable atmospheric surface layer for displacements in all three orthogonal directions. The decay constants for lateral displacements are over 50 times as large as for vertical displacements. Such large lateral decay constants mean that the measurement of longitudinal constants will be very difficult.Some of the assumptions inherent in geometric similarity were not satisfied. Two regimes, plume scales and larger scales, having different decay constants, were observed. The possibility of a similar scale dependency of the decay constants for the wind field is discussed. 相似文献