全文获取类型
收费全文 | 1651篇 |
免费 | 42篇 |
国内免费 | 21篇 |
专业分类
测绘学 | 53篇 |
大气科学 | 98篇 |
地球物理 | 347篇 |
地质学 | 587篇 |
海洋学 | 116篇 |
天文学 | 344篇 |
综合类 | 16篇 |
自然地理 | 153篇 |
出版年
2021年 | 8篇 |
2020年 | 23篇 |
2019年 | 22篇 |
2018年 | 31篇 |
2017年 | 23篇 |
2016年 | 31篇 |
2015年 | 25篇 |
2014年 | 37篇 |
2013年 | 73篇 |
2012年 | 50篇 |
2011年 | 69篇 |
2010年 | 87篇 |
2009年 | 94篇 |
2008年 | 78篇 |
2007年 | 66篇 |
2006年 | 59篇 |
2005年 | 57篇 |
2004年 | 50篇 |
2003年 | 64篇 |
2002年 | 53篇 |
2001年 | 27篇 |
2000年 | 39篇 |
1999年 | 25篇 |
1998年 | 21篇 |
1997年 | 22篇 |
1996年 | 22篇 |
1995年 | 23篇 |
1994年 | 27篇 |
1993年 | 25篇 |
1992年 | 23篇 |
1991年 | 8篇 |
1990年 | 21篇 |
1989年 | 24篇 |
1988年 | 26篇 |
1987年 | 21篇 |
1986年 | 20篇 |
1985年 | 34篇 |
1984年 | 32篇 |
1983年 | 28篇 |
1982年 | 22篇 |
1981年 | 36篇 |
1980年 | 24篇 |
1979年 | 16篇 |
1978年 | 15篇 |
1977年 | 20篇 |
1976年 | 14篇 |
1975年 | 12篇 |
1974年 | 19篇 |
1973年 | 16篇 |
1971年 | 8篇 |
排序方式: 共有1714条查询结果,搜索用时 187 毫秒
161.
Subsolidus and melting reactions involving calcic plagioclase in pelitic assemblages in the K-Na-Ca model system occur at higher temperatures than their K-Na counterparts. For the most calcic plagioclase compositions observed in high-grade pelitic rocks (An25-An40) the equilibria are rarely extended by more than 30 ° C above those in KA1O2-NaAlO2-Al2O3-SiO2-H2O, although all discontinuities in facies inferred for the K-Na system are continuously displaced when they involve Ca-bearing plagioclase. The maximum pressure-temperature overlap between muscovite dehydration and initial melting reactions occurs in the pressure range of 4–6 kbar between about 640 ° and 720 ° C. This provides optimum conditions for anatectic melt generation in felsic rocks of the appropriate compositions progressively metamorphosed in kyanite-sillimanite facies series. Progressive regional metamorphism at pressures of 2–4 kbar, corresponding to andalusite-sillimanite facies series, shows little overlap between muscovite dehydration and initial melting reactions. Consequently anatectic melt generation in andalusite-sillimanite facies series would require the participation of biotite in dehydration-melting reactions. Felsic intrusive rock in andalusite-sillimanite terranes could have risen upward from their anatectic sites in high grade kyanite-sillimanite facies series at depth. Many andalusite-sillimanite facies series terranes culminating in migmatites could represent upward movement of kyanite-sillimanite facies series rocks to shallower depths with uplift rates faster than cooling rates. 相似文献
162.
163.
164.
Compositional profiles of a series of garnets, extracted from a pelitic schist occurring in the Moinian rocks of Northern Sutherland, have been established. The profiles are complex and do not conform to a simple fractionation model. A model to explain them is suggested. 相似文献
165.
Vitrinite reflectance data for two sections of the Kootenay Formation are different, but increase with depth. Illite crystallinities (XRD) are irregular with depth but detailed S.E.M. examination shows that crystal size and morphology increase with depth.At Elk Valley (low reflectance) S.E.M. examination shows kaolinite + dolomite as the authigenic assemblage. At Mt Allan (45 km north, higher reflectance) kaolinite disappears at 265 m and chlorite + calcite appears implying the equilibrium 5 CaMg(CO3)2 + Al2Si2O5(OH)4 + SiO2 + H2OagMg5Al2Si3O10(OH)8 + 5CaCO3 + 5CO2. (1)Equilibrium (1) involves CO2 and H2O which form an immiscible fluid at diagenetic conditions. Thermochemical data, activity coefficients for the fluid mixture (Margules solution model), and fugacity coefficients allow the position of intersection of the miscibility surface and equilibria similar to (1) to be calculated. Maximum temperatures (180–250°C) in water-rich fluids are in accord with geothermal gradients of 33°C/km and temperatures from vitrinite reflectance (220°C). It is suggested that produced CO2 may be responsible for the development of secondary porosity during deep burial. 相似文献
166.
167.
J. Alan Chalmers 《Pure and Applied Geophysics》1964,57(1):189-192
Summary The definition of a generator in atmospheric electricity is considered, and various phenomena are discussed as to whether they can be described as generators. 相似文献
168.
169.
Surendra K. Saxena Alan Benimoff Nicholas E. Pingitore Jr. 《Contributions to Mineralogy and Petrology》1977,60(1):77-90
The chemical composition of 2188 terrestrial igneous rocks ranging from ultrabasic to granitic composition was analyzed statistically using the method of factor analysis (principal components). The resultant first and second factors were: $$\begin{gathered} {\text{ }}F_1 = 0.933{\text{ Na}}_{\text{2}} {\text{O + 0}}{\text{.143 SiO}}_{\text{2}} + 0.206{\text{ K}}_{\text{2}} {\text{O}} - 0.346{\text{ CaO}} - 0.263{\text{ MgO}} - \hfill \\ .203{\text{ FeO}} \pm \cdot \cdot \cdot \hfill \\ {\text{ }}F_2 = 0.979{\text{ Al}}_{\text{2}} {\text{O}}_{\text{3}} - 0.269{\text{ MgO}} - 0.151{\text{ SiO}}_{\text{2}} - 0.112{\text{ FeO}} \pm \cdot \cdot \cdot \hfill \\ \end{gathered} $$ where oxides are in weight percent. A plot of the first factor against the second results in a useful igneous variation diagram. When the compositions of the 2188 terrestrial rocks and 604 lunar rocks are plotted on this diagram, the two groups of rocks are clearly separated within an albite-anorthite-forsterite-fayalite-quartz polygon. None of the terrestrial differentiation trends are significant for lunar rocks. The major difference in the chemistry of lunar and terrestrial rocks lies in the former being albite poor. Removal of most of the albite from the compositions of terrestrial layered intrusives such as the Skaergaard results in an excellent match between the compositions of the two groups of rocks. Albite subtracted compositions of Skaergaard rocks in particular cover the entire range of chemical variation in the lunar rocks. The statistical results prompt us to speculate further on the similarity of the moon and Skaergaard. We note that the average composition of the moon (Wanke et al., 1974) is similar to the albite subtracted composition of the Skaergaard magma. The lunar crust and a significant part of the lunar interior may match the albite subtracted and somewhat Mg enriched Skaergaard magma. 相似文献
170.
Alan B Blaxland 《Lithos》1977,10(1):1-8
RbSr isotopic analyses of 10'whole-rock samples from the controversial peralkaline Norra Kärr complex of southern Sweden suggest an age (1580±62 m.y.) considerably older than had previously been anticipated, and indicate an initial 87Sr/86Sr ratio of 0.7072±0.0035 (errors at 2σ). The isotopic data are consistent with a primary magmatic origin for the Norra Kärr agpaites, but data from 8 mineral separates show that they have experienced at least one period of metamorphic disturbance since the original intrusion; the last episode of isotopic readjustment must have occurred after 1250 m.y. before present, and is attributed to the Sveconorwegian (Grenville) metamorphism. 相似文献