全文获取类型
收费全文 | 7648篇 |
免费 | 1120篇 |
国内免费 | 964篇 |
专业分类
测绘学 | 651篇 |
大气科学 | 968篇 |
地球物理 | 2380篇 |
地质学 | 3639篇 |
海洋学 | 632篇 |
天文学 | 380篇 |
综合类 | 387篇 |
自然地理 | 695篇 |
出版年
2024年 | 29篇 |
2023年 | 77篇 |
2022年 | 178篇 |
2021年 | 184篇 |
2020年 | 134篇 |
2019年 | 158篇 |
2018年 | 588篇 |
2017年 | 499篇 |
2016年 | 367篇 |
2015年 | 307篇 |
2014年 | 240篇 |
2013年 | 297篇 |
2012年 | 869篇 |
2011年 | 664篇 |
2010年 | 337篇 |
2009年 | 345篇 |
2008年 | 285篇 |
2007年 | 341篇 |
2006年 | 347篇 |
2005年 | 1008篇 |
2004年 | 1001篇 |
2003年 | 752篇 |
2002年 | 271篇 |
2001年 | 159篇 |
2000年 | 94篇 |
1999年 | 40篇 |
1998年 | 20篇 |
1997年 | 25篇 |
1996年 | 15篇 |
1992年 | 5篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 6篇 |
1987年 | 5篇 |
1985年 | 3篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1973年 | 3篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1965年 | 3篇 |
1963年 | 2篇 |
1961年 | 2篇 |
1959年 | 2篇 |
1955年 | 2篇 |
1954年 | 3篇 |
1951年 | 2篇 |
1948年 | 2篇 |
排序方式: 共有9732条查询结果,搜索用时 953 毫秒
991.
DONGSheng GANBuhong HAOXiaoli 《中国海洋大学学报(英文版)》2004,3(1):111-114
1 Introduction InChina ,coastalcitiesaremostlyregionaleconomicdevelopmentcenters.Becauseoftheirspecialgeogra phiclocations ,typhoonsandassociatedstormsurgescauseheavylossesoflivesandproperties.In 1 992 Qing daowasfloodedduetothecoincidenceoftheastrono m… 相似文献
992.
993.
从环流形势、单站气象要素及中尺度滤波分析等几方面对2004年7月28日新乡市大暴雨过程进行分析,结果表明这次暴雨、大暴雨天气过程是副热带高压西伸北抬和西风槽东移及北方南下冷空气的共同影响造成的,副高西伸北抬的"突变"过程,是造成大暴雨的直接原因;中低层切变线的生成,为强对流天气的产生提供了动力条件;低空西南急流不仅输送暖湿空气,增强层结的不稳定性,而且可以产生低层扰动,触发不稳定能量的释放,新乡地区东南部位于深厚急流区入口处的左侧,是暴雨、大暴雨产生的关键部位;用T213的初始流场经滤波分析后,能清晰显示出形成大暴雨的中尺度辐合系统,对暴雨、大暴雨预报有一定的指示意义. 相似文献
994.
Antonio?Acosta-VigilEmail author David?London George?B.?Morgan 《Contributions to Mineralogy and Petrology》2006,151(5):539-557
We have experimentally investigated the kinetics of melting of an aplitic leucogranite (quartz+sodic plagioclase of ≈Ab90+K-feldspar+traces of biotite) at 690, 740, and 800°C, all at 200 MPa H2O. Leucogranite cylinders, 3.5 mm in diameter and 7 mm in length, were run in the presence of excess H2O using cold-seal pressure vessels for 11–2,925 h. At 690 and 740°C and any experimental time, and 800°C and short run times, silicate glass (melt at run conditions) occurs as interconnected films along most of the mineral boundaries and in fractures, with the predominant volume occurring along quartz/feldspars boundaries and quartz/plagioclase/K-feldspar triple junctions. Glass film thickness is roughly constant throughout a given experimental charge and increases with experimental temperature and run duration. The results indicate that H2O-saturated partial melting of a quartzo-feldspathic protolith will produce an interconnected melt phase even at very low degrees (<5 vol%) of partial melting. Crystal grain boundaries are therefore completely occluded with melt films even at the lowest degrees of partial melting, resulting in a change in the mechanism of mass transport through the rock from advection of aqueous vapor to diffusion through silicate melt. At 690 and 740°C the compositions of glasses are homogeneous and (at both temperatures) close to, but not on, the H2O-saturated 200 MPa haplogranite eutectic; glass compositions do not change with run duration. At 800°C glasses are heterogeneous and plot away from the minimum, although their molar ratios ASI (=mol Al2O3/CaO+Na2O+K2O) and Al/Na are constant throughout the entire charge at any experimental time. Glass compositions within individual 800°C experiments form linear trends in (wt%) normative quartz–albite–orthoclase space. The linear trends are oriented perpendicular to the 200 MPa H2O haplogranite cotectic line, reflecting nearly constant albite/orthoclase ratio versus variable quartz/feldspar ratio, and have endpoints between the 800°C isotherms on the quartz and feldspar liquidus surfaces. With increasing experimental duration the trends migrate from the potassic side of the minimum toward the bulk rock composition located on the sodic side, due to more rapid (and complete) dissolution of K-feldspar relative to plagioclase. The results indicate that partial melting at or slightly above the solidus (690–740°C) is interface reaction-controlled, and produces disequilibrium melts of near-minimum composition that persist metastably for up to at least 3 months. Relict feldspars show no change in composition or texture, and equilibration between melt and feldspars might take from a few to tens of millions of years. Partial melting at temperatures well above the solidus (800°C) produces heterogeneous, disequilibrium liquids whose compositions are determined by the diffusive transport properties of the melt and local equilibrium with neighboring mineral phases. Feldspars recrystallize and change composition rapidly. Partial melting and equilibration between liquids and feldspars might take from a few to tens of years (H2O-saturated conditions) at these temperatures well above the solidus. 相似文献
995.
Cristina?PerinelliEmail author Pietro?Armienti Luigi?Dallai 《Contributions to Mineralogy and Petrology》2006,151(3):245-266
Peridotite xenoliths found in Cenozoic alkali basalts of northern Victoria Land, Antarctica, vary from fertile spinel-lherzolite
to harzburgite. They often contain glass-bearing pockets formed after primary pyroxenes and spinel. Few samples are composite
and consist of depleted spinel lherzolite crosscut by amphibole veins and/or lherzolite in contact with poikilitic wehrlite.
Peridotite xenoliths are characterized by negative Al2O3–Mg# and TiO2–Mg# covariations of clino- and orthopyroxenes, low to intermediate HREE concentrations in clinopyroxene, negative Cr–Al trend
in spinel, suggesting variable degrees of partial melting. Metasomatic overprint is evidenced by trace element enrichment
in clinopyroxene and sporadic increase of Ti–Fetot. Preferential Nb, Zr, Sr enrichments in clinopyroxene associated with high Ti–Fetot contents constrain the metasomatic agent to be an alkaline basic melt. In composite xenoliths, clinopyroxene REE contents
increase next to the veins suggesting metasomatic diffusion of incompatible element. Oxygen isotope data indicate disequilibrium
conditions among clinopyroxene, olivine and orthopyroxene. The highest δ18O values are observed in minerals of the amphibole-bearing xenolith. The δ18Ocpx correlations with clinopyroxene modal abundance and geochemical parameters (e.g. Mg# and Cr#) suggest a possible influence
of partial melting on oxygen isotope composition. Thermobarometric estimates define a geotherm of 80°C/GPa for the refractory
lithosphere of NVL, in a pressure range between 1 and 2.5 GPa. Clinopyroxene microlites of melt pockets provide P–T data close
to the anhydrous peridotite solidus and confirm that they originated from heating and decompression during transport in the
host magma. All these geothermometric data constrain the mantle potential temperature to values of 1250–1350°C, consistent
with the occurrence of mantle decompressional melting in a transtensive tectonic regime for the Ross Sea region. 相似文献
996.
地图内容质量特征和数量特征概括的数学模型 总被引:1,自引:1,他引:0
在分类的定义下,根据概念外延的包含关系,给出了质量特征概括的数学模型。在定义数量的基础上,推导出级距概念,并根据两个不同级距的偏序集中大级距子集包含多个小级距子集的关系,给出了数量特征概括的数学模型。本文给出的地物质量特征和数量特征概括的数学模型,可对地图编制过程中诸如随地图比例尺缩小而缩减分类,扩大级差等经验事实,作出定量的描述和理论阐释。 相似文献
997.
Evaluation of an ensemble of Arctic regional climate models: spatiotemporal fields during the SHEBA year 总被引:1,自引:1,他引:0
A.?RinkeEmail author K.?Dethloff J.?J.?Cassano J.?H.?Christensen J.?A.?Curry P.?Du E.?Girard J.-E.?Haugen D.?Jacob C.?G.?Jones M.?K?ltzow R.?Laprise A.H.?Lynch S.?Pfeifer M.?C.?Serreze M.?J.?Shaw M.?Tjernstr?m K.?Wyser M.??agar 《Climate Dynamics》2006,26(5):459-472
Simulations of eight different regional climate models (RCMs) have been performed for the period September 1997–September
1998, which coincides with the Surface Heat Budget of the Arctic Ocean (SHEBA) project period. Each of the models employed
approximately the same domain covering the western Arctic, the same horizontal resolution of 50 km, and the same boundary
forcing. The models differ in their vertical resolution as well as in the treatments of dynamics and physical parameterizations.
Both the common features and differences of the simulated spatiotemporal patterns of geopotential, temperature, cloud cover,
and long-/shortwave downward radiation between the individual model simulations are investigated. With this work, we quantify
the scatter among the models and therefore the magnitude of disagreement and unreliability of current Arctic RCM simulations.
Even with the relatively constrained experimental design we notice a considerable scatter among the different RCMs. We found
the largest across-model scatter in the 2 m temperature over land, in the surface radiation fluxes, and in the cloud cover
which implies a reduced confidence level for these variables.
An erratum to this article can be found at 相似文献
998.
999.
卫星重力梯度测量数据的粗差探测 总被引:1,自引:0,他引:1
分别讨论了阈值法、Dixon检验法和小波算法应用于卫星重力梯度数据粗差探测的效果。为了克服这3种单一粗差探测方法的不足,提出了卫星重力梯度数据的粗差探测组合方案,即联合Dixon检验和小波算法,以及联合Dixon检验、阈值法和小波算法的组合方案。模拟结果表明,两种组合方案均能有效改善粗差探测的效果。 相似文献
1000.