全文获取类型
收费全文 | 7831篇 |
免费 | 156篇 |
国内免费 | 315篇 |
专业分类
测绘学 | 215篇 |
大气科学 | 604篇 |
地球物理 | 1633篇 |
地质学 | 2895篇 |
海洋学 | 647篇 |
天文学 | 1856篇 |
综合类 | 30篇 |
自然地理 | 422篇 |
出版年
2023年 | 45篇 |
2022年 | 52篇 |
2021年 | 59篇 |
2020年 | 66篇 |
2019年 | 83篇 |
2018年 | 235篇 |
2017年 | 192篇 |
2016年 | 275篇 |
2015年 | 163篇 |
2014年 | 263篇 |
2013年 | 414篇 |
2012年 | 241篇 |
2011年 | 406篇 |
2010年 | 289篇 |
2009年 | 459篇 |
2008年 | 363篇 |
2007年 | 325篇 |
2006年 | 341篇 |
2005年 | 308篇 |
2004年 | 295篇 |
2003年 | 273篇 |
2002年 | 250篇 |
2001年 | 220篇 |
2000年 | 208篇 |
1999年 | 180篇 |
1998年 | 169篇 |
1997年 | 162篇 |
1996年 | 154篇 |
1995年 | 139篇 |
1994年 | 115篇 |
1993年 | 93篇 |
1992年 | 78篇 |
1991年 | 88篇 |
1990年 | 79篇 |
1989年 | 83篇 |
1988年 | 59篇 |
1987年 | 101篇 |
1986年 | 64篇 |
1985年 | 64篇 |
1984年 | 70篇 |
1983年 | 71篇 |
1982年 | 72篇 |
1981年 | 68篇 |
1980年 | 54篇 |
1979年 | 51篇 |
1977年 | 49篇 |
1976年 | 47篇 |
1975年 | 35篇 |
1974年 | 30篇 |
1973年 | 41篇 |
排序方式: 共有8302条查询结果,搜索用时 15 毫秒
61.
Generation, migration and accumulation of petroleum in a sedimentary basin is a function of geologic, hydrodynamic and thermodynamic development of the basin and the type and amount of organic matter. Temperature history not only determines rate of hydrocarbon generation, but also affects paleohydrodynamics and physical and thermal properties vs depth relationships. Therefore, paleotemperature is the most important parameter. Paleohydrodynamics together with geologic history of the basin is important in shaping secondary migration patterns and accumulation of hydrocarbons.Quantification of all the above processes is complicated. Steps in constructing a deterministic dynamic model for calculation of petroleum potential during a sedimentary basin development are stated and analyzed in this paper. The effect of paleotemperature variations on petroleum generation and on physical properties of sedimentary sequences are illustrated by numerical examples. Computer models will enable exploration geologists to make quantitative exploration predictions in sedimentary basins. 相似文献
62.
This paper proposes a numerical model for jointed rock masses within the 3‐D numerical manifold method (NMM) framework equipped with a customized contact algorithm. The strength of rock sample containing a few sets of discontinuities is first investigated. The results of models with simple geometries are compared with the available analytical solutions to verify the developed computer code, whereas models with complex geometries are simulated to better understand the fundamental behavior and failure mechanism of jointed rock mass. Furthermore, the stability of jointed rock mass in an underground excavation is studied, where rock failure process is determined by the 3‐D NMM simulation. The simulation results provide valuable guidance on excavation process design and stabilization design in rock engineering practice. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
63.
64.
A geochemical baseline provides the means to distinguish between the pedogenic origin and the anthropogenic origin of the
trace element in the environmental compartments. We collected 271 soil samples representative of different parent rocks and
soil types from the whole territory of Hong Kong and analyzed the composition of clay mineralogy and the contents of 15 chemical
elements (Fe, Cd, As, etc.) for these samples. The baseline was predicted with the method of the normalization procedure combined
with the relative cumulative frequency curve. The result indicated that Fe was the best reference element for the normalization
procedure among the five potential reference elements (Fe, Al, Sc, Ti, and Mn), followed by Sc and Ti. A poor correlation
was found between Sc, Ti, and Cu. The predicted baseline was much lower than the A-value of the Dutch List used usually in screening the polluted soil of Hong Kong, implying that the extent of heavy metal
pollution might have been underestimated with respect to local lands. We also applied the cluster analysis to distinguish
the geochemical associations of the trace elements due to its importance to the baseline. Approximately three major associations
including the Fe–Mn-oxides related, Al oxides or Al-bearing-clay-mineralogy related and sulfide- related associations were
observed from the dendrogram. 相似文献
65.
An analytical solution for rainfall infiltration into an unsaturated infinite slope and its application to slope stability analysis 总被引:1,自引:0,他引:1
Surficial slope failures in residual soils are common in tropical and subtropical regions as a result of rainfall infiltration. This study develops an analytical solution for simulating rainfall infiltration into an infinite unsaturated soil slope. The analytical solution is based on the general partial differential equation for water flow through unsaturated soils. It can accept soil–water characteristic curve and unsaturated permeability function of the exponential form into account. Numerical simulations are conducted to verify the assumptions of the analytical solution and demonstrate that the proposed analytical solution is acceptable for the coarse soils with low air entry values. The pore‐water pressure (pwp) distributions obtained from the analytical solution can be incorporated into a limit equilibrium method to do infinite slope stability analysis for a rain‐induced shallow slip. The analysis method takes into account the influence of the water content change on unit weight and hence on factor of safety. A series of analytical parametric analyses have been performed using the developed model. The analyses indicate that when the residual soil slope, consisting of a completely decomposed granite layer underlain by a less permeable layer, is subjected to a continuous heavy rainfall, the loss of negative pwp and the reduction in factor of safety were found to be most significant for the shallow soil layer and during the first 12 h. The antecedent and subsequent rainfall intensity, depth of a less permeable layer and slope angle all have a significant influence on the pwp response and hence the slope stability. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
66.
A new method for the determination of the critical slip surfaces of slopes is proposed in this paper.In this paper,the original critical slip field method is extended in terms of the total residual moment,values of residual work as well as the unbalanced thrust force at the exit point for a given non-circular slip surface.The most critical slip surface with the maximum representative value for a prescribed factor of safety will be optimized and located using the harmony search algorithm.The prescribed factor of safety is modified with certain tiny interval in order to find the critical slip surface where the maximum representative value is zero.The aforementioned approach to the location of the critical slip surface is greatly different from the traditional limit equilibrium procedure.Three typical soil slopes are evaluated by use of the proposed method,and the comparisons with the classical approaches have illustrated the applicability of the proposed method. 相似文献
67.
Common carp (Cyprinus carpio L.) exhibits significant morphological variability in the shape and size of the caudal fin. In this study, we used 190 progeny from two F1 parents to identify and map quantitative trait loci (QTLs) that influence caudal fin length (CFL) and the ratio (RCS) between caudal fin length and standard length (SL) based on a microsatellite genetic map of common carp. A total of 15 QTLs were detected in seven different linkage groups. One significant and eight suggestive QTLs affecting CFL were identified on LG8, LG14, LG29, LG32 and LG44, which explained 8.0%–22.1% of the phenotypic variation; six suggestive QTLs affecting RCS were detected on LG8, LG32, LG46 and LG48, which explained 7.0%–15.4% of the phenotypic variation. The QTLs for caudal fin length detected in this study may serve as a starting point for identification of genes involved in caudal fin development in common carp. 相似文献
68.
Variations in the quantity and composition of seston from an estuary in southern Chile on different temporal scales 总被引:1,自引:0,他引:1
O.R. Chaparro C.J. Segura Y.A. Montiel R.J. Thompson J.M. Navarro 《Estuarine, Coastal and Shelf Science》2008,76(4):845-860
Estuaries are characterised by highly variable environmental conditions largely driven by tidal and atmospheric forces. This study investigates variation in the physical environment and the composition of the seston on various temporal scales in the Quempillén estuary, southern Chile. The water column was sampled throughout the tidal cycle at various times of the year. Total particulate matter, particulate inorganic matter, particulate organic matter, particle numbers, total particle volume, proximate biochemical composition and energy content of the seston, chlorophyll a and chloropigments were routinely measured. In each of the months in which sampling took place, two or three tidal cycles were examined. The information not only helps to explain the dynamics of the estuary, but is essential for an understanding of the physiology and ecology of the suspension-feeders which exploit the seston as a food source, the most dominant being the gastropod Crepipatella dilatata. Temperature and salinity were generally highest during summer, but seston quality, defined by energy content and biochemical composition (lipid, protein and carbohydrate) was higher at the end of winter and during spring. Chlorophyll a values were greatest in late spring (November). Many of the variables studied changed frequently according to the phase of the tidal cycle, and in several cases significant differences were observed among tidal cycles from the same month of the same year. In general the variables measured did not exhibit consistent patterns linked to the tidal cycle, possibly because any such patterns were masked by atmospheric conditions (wind and rain) that dominate the region and greatly influence the estuary. The quantity and quality of the seston available to suspension-feeders is largely determined by these atmospheric forces, which cause an influx of terrigenous material from adjacent areas and also resuspend bottom sediment. These effects are magnified by the shallowness of the estuary (<2 m depth). The food supply for C. dilatata and other suspension-feeders therefore varies on temporal scales varying from hourly (tidal cycle) to daily/weekly (atmospheric forces) to monthly (seasonal influences), but inhibition of feeding by low salinity sometimes limits the ability of C. dilatata to exploit fully the available organic matter. 相似文献
69.
Tatiana Y. Shvareva Drew Gorman-Lewis Peter C. Burns Jeremy B. Fein 《Geochimica et cosmochimica acta》2011,75(18):5269-5282
Boltwoodite and uranophane are uranyl silicates common in oxidized zones of uranium ore deposits. An understanding of processes that impact uranium transport in the environment, especially pertaining to the distribution of uranium between solid phases and aqueous solutions, ultimately requires determination of thermodynamic parameters for such crystalline materials. We measured formation enthalpies of synthetic boltwoodites, K(UO2)(HSiO4)·H2O and Na(UO2)(HSiO4)·H2O, and uranophane, Ca(UO2)2(HSiO4)2·5H2O, by high temperature oxide melt solution calorimetry. We also studied the aqueous solubility of these phases from both saturated and undersaturated conditions at a variety of pH. The combined data permit the determination of standard enthalpies, entropies and Gibbs free energies of formation for each phase and analysis of its potential geological impact from a thermodynamic point of view. 相似文献
70.
Ananiev R. A. Dmitrevsky N. N. Roslyakov A. G. Chernykh D. V. Moroz E. A. Zarayskaya Y. A. Semiletov I. P. 《Oceanology》2022,62(1):127-132
Oceanology - The emission of natural gas from the seafloor to the surface in shelf areas of the Arctic seas is of increasing interest among researchers. Recently, various types of acoustic... 相似文献