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991.
Bohloul Alijani 《山地科学学报》2008,5(3):218-231
In order to examine the effect of the Zagros Mountains on precipitation, first, the annual and Seasonal rainfall indices (rain days frequency, rain amount, daily rainfall intensity, and heavy rains) from 43 stations in 1995 - 2004 between the 30° N to 35° N parallels over the mountain range were analyzed. Second, the effect of the Zagros Mountains was studied through the computation of the spatial correlations between the precipitation parameters and the topographic indices (station site elevation, station mean elevation within a radius of 2.5 km, mean elevation of 9 blocks along each of the eight Cartesian directions, and the elevation differences of these 9 blocks from the station mean elevation). The results showed that in the cold season the maximal rainfall occurs on the upper range of west slope, while in warm season it spreads over the study area. The correlations between precipitation and elevation indices were positive on the north of the stations and negative on the south of the stations, that is, the higher elevations of the stations to the north force the uplifting of the moist air masses and increase rainfall at the stations, while the lower elevations to their south lead the movement of the moist air masses to the stations. This is due to the fact that these stations or slopes are exposed to the moist air masses coming from the Mediterranean Sea and the Persian Gulf. The heavy rain days and the summer sporadic rain events do not show significant correlations with the topographic indices. The findings indicate that the Zagros Mountains intensify the cold period frontal rains especially over the west slope and block the moist air masses from entering the interior parts of the country. Moreover, these mountains play a secondary role in creating rain days. But they are very important in the production of precipitation in the area. Therefore, their absence will decrease the amount of rainfall to their west and, in return, expand the dry climates of their west and east. 相似文献
992.
现有恐怖团伙关系挖掘方法因其难以顾及恐怖组织特有的结构复杂、行动灵活、生存期长等特点而难以应用于反恐研究中.为此,本文从时空角度出发,通过引入时空邻近与团伙时空同现模式等概念,将多元独立分布的团伙关系发现问题建模为时空同现模式的频繁度评价问题,提出一种点模式分布下的团伙关系挖掘方法.基于此方法构建团伙关系网络,进而提出... 相似文献
993.
城乡要素流动贯穿城乡发展全过程,是构建城乡能否实现融合发展的核心,探究城乡实体要素流动对城乡融合发展的作用机制,能够为城乡融合发展破局提供科学指导。论文基于TOPSIS模型对全国292个城市的城乡融合发展水平进行评价,采用普通最小二乘法(OLS)和地理加权回归(GWR)模型探究城乡实体要素流动对城乡融合的影响机制。研究结果表明:(1)中国城市层面的城乡融合发展水平存在较大空间分异特征,达到深度融合水平的多为经济发达城市。相较而言,东部地区的城乡融合发展最为平衡。(2)全局上看,土地要素与人才要素的流动对城乡融合发展的影响最为显著,且两者驱动作用为负;局部上看,各城乡实体要素流动对城乡融合发展的影响具有明显的地域差异性。(3)土地要素流失使乡村失去了生产要素和发展空间,而人才要素无有效路径回流至乡村,使其限制了城乡融合;政府投资促进实体要素集聚并降低要素流动成本,城乡产业实现分工协作、功能互补,信息要素有效流动降低其他实体要素配置成本并提高配置效率,这益于城乡融合。 相似文献
994.
受限于个体流动数据的获取制约,以往人口流动研究多采用交通网络强度来模拟城市间的人口流动强度,忽视了二者之间的偏离。论文以铁路、公路车次构建交通网络,以腾讯位置大数据的铁路出行、公路出行数据构建人口流动网络,运用社会网络分析法、QAP模型,对比分析两者之间的偏离和关联。研究发现:(1)东北地区铁路人口流动和其交通网络格局均呈现出以“哈大”走廊为轴的南密北疏、东众西寡的特征。铁路人口流动网络结构较为分散,铁路交通网络的极化效应明显。(2)公路人口流动和其交通网络的偏离较大。公路和铁路之间存在竞争和互补关系,在铁路交通不太发达的地区,公路人口流动强度和其交通网络强度较高。(3)人口流动与交通网络存在一定关联,但人口流动受多方面因素影响,综合联系网络模型则能更准确地模拟城市间人口流动。其他影响因素中,经济联系、人口规模等因素对人口流动的影响不够明显,而城市间的邻接关系对人口流动有显著影响。(4)铁路人口流动与其交通网络的关联程度较公路人口与其交通网络的关联程度高。论文定量说明了人口流动与其交通网络的相关程度,为交通网络模拟人口流动提供了理论和实际操作层面的参考。 相似文献
995.
A theoretical analysis of interactive coercing effects between urbanization and eco-environment 总被引:3,自引:0,他引:3
Objectively, a complex interactive coercing relationship exists between urbanization and eco-environment, and the research of this relationship is primarily divided into three schools, i.e., interactive coercion theory, interactive promotion theory and coupling symbiosis theory. Harmonizing the relationship between urbanization and eco-environment is not only an important proposition for the national development plan but also the only way to promote healthy urbanization. Based on an analysis of urbanization process and its relationship with the eco-environment, this article analyzes interactive coercing effects between urbanization and eco-environment from three perspectives of population urbanization, economic urbanization and spatial urbanization, respectively, and analyzes risk effects of the interactive coercion. Further, it shows six basic laws followed by interactive coercion between urbanization and eco-environment, namely, coupling fission law, dynamic hierarchy law, stochastic fluctuation law, non-linear synergetic law, threshold value law and forewarning law, and divides the interactive coercing process into five stages, namely, low-level coordinate, antagonistic, break-in, ameliorative and high-grade coordinate. Based on the geometric derivation, the interactive coercing relationship between urbanization and eco-environment is judged to be non-linear and it can be explained by a double-exponential function formed by the combination of power and exponential functions. Then, the evolutionary types of the interactive coercing relationship are divided into nine ones: rudimentary coordinating, ecology-dominated, synchronal coordinating, urbanization lagging, stepwise break-in, exorbitant urbanization, fragile ecology, rudimentary break-in and unsustainable types. Finally, based on an interactive coercion model, the degree of interactive coercion can be examined, and then, an evolutionary cycle can be divided into four phases, namely rudimentary symbiosis, harmonious development, utmost increasing and spiral type rising. The study results offer a scientific decision-making of healthy urbanization for achieving the goal of eco-environment protection and promoting urbanization. 相似文献
996.
997.
998.
A primary magma not only represents the starting point of a fractional crystallization process, but also is the product of an equilibrium or fractional partial melting process in a mantle.Element abundance relationships in the primary magma obey both law of power function for fractional crystallization and the law of fractional linear function for equilibrium partial melting .Based on this double nature of the primary magma, the authors advanced a principle to restore the primary magma composition from that of an igneous rock series with petrogenesis of fractional crystallization and put forward an approach of estimating the element abundance of the primary magma, exempli-fied by the rar-earth elements in the Andes volcanic rock series. 相似文献
999.
米兰科维奇理论认为,北半球高纬夏季太阳辐射变化是驱动第四纪冰期旋回的主因。这个理论的核心是单一敏感区的触发驱动机制,即北半球高纬气候变化信号被放大、传输进而影响全球。最近,由于大量高分辨率及精确定年的气候变化记录的获得,从以下4个方面构成了对米氏理论的挑战:1)一些低纬地区并没有明显的10万年冰量周期,而是以2万年岁差周期为主,表明北半球冰盖的扩张、收缩变化并没有完全控制低纬区的气候变化;2)在最近几次冰消期时,南半球和低纬区的温度增高,要早于北半球冰盖的融化,表明冰消期的触发机制并非是北半球高纬夏季太阳辐射;3)大气CO2浓度在第2冰消期的增加同南极升温相一致,表明该时大气CO2浓度增加亦有可能早于北半球冰盖消融;4)南半球的末次冰盛期有可能早于北半球。这就说明单一敏感区触发驱动机制已难以圆满解释所有观察事实,天文因素控制下轨道尺度气候变化机制研究正面临理论突破的新需求和新机遇。 相似文献
1000.
邓肯E-B模型无法描述软化土体的应力应变关系以及土体的剪胀效应;采用抛物线型体应变曲线的南水模型破坏时的剪胀率趋于定值,与实际土体不符。但南水模型适合描述应力应变峰值点前或最大剪胀率前土体的本构关系,邓肯模型适合描述的应变范围更小。因此,若要进行土工结构渐进破坏的分析计算,则需要建立一个适合于描述直至破坏的更大应变范围的土体本构关系。采用损伤扰动概念,将变形过程中的土体视为“相对完整”的未损伤土体和“完全调整”扰动土体的混合体,其应力应变关系可根据损伤扰动程度,由各自的应力应变关系组合确定。并根据试验提出了确定损伤扰动函数的计算公式。对体应变曲线,则采用抛物线加双曲线的形式加以描述。 相似文献