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排序方式: 共有1364条查询结果,搜索用时 15 毫秒
931.
Vaccination rates in Illinois schools are decreasing as more parents opt for nonmedical exemptions (NMEs). At the local scale, higher levels of exemptions affect herd immunity levels. Few studies have previously conducted or proposed methods to conduct local-scale spatial and temporal cluster pattern analysis. This study used vaccination exemption data from the Illinois School Board of Education’s annual Immunization School Survey for the 2003–2004 and 2013–2014 academic years. The Getis–Ord General G statistic was used to identify cluster detection by individual vaccine at the school level. The Getis–Ord Gi* statistic was used with two different parameter models to identify hot and cold spots. This study found that NMEs are highly clustered. More clusters of high and low NMEs were identified for the 2013–2014 academic year than for 2003–2004. The percentages of schools that were neither hot nor cold averaged 94.0 percent for the 2003–2004 school year and 78.7 percent for the 2013–2014 school year. NME rates in Illinois are rising. The increase in hot and cold spots is evidence that the polarity of vaccination choice is growing. As vaccination exemption rates continue to polarize U.S. society, it is essential for public health efforts to monitor and conduct local-level studies. Key Words: antivaccination, hot spot analysis, medical geography, nonmedical exemption, spatial statistics.  相似文献   
932.
This article explores the use of visual research methodologies for understanding the everyday political desires and behavior of individuals. Its goal is to extend conversations in geography about the use of visual methods for interpreting the relationships between society and space, specifically the ways in which photovoice techniques can help geographers better understand the ways in which intergenerational emplaced memories motivate and shape contemporary political action. Using an urban community in Costa Rica built through hybrid housing–antiviolence movements in the 1980s and 1990s as a case study, this article illustrates the material and metaphorical pathways that participants trace between historical social movements and contemporary social issues through their photo essays. Participant images are made in tandem with practices and movement in the present but recall and represent family histories and narratives of historical struggle in the past. Significantly, as savvy users embedded in visual worlds, participants use these moments of intersection between past and present to mobilize political arguments about value and justice in their community. In this way, visual methods reveal the political mundane: how individuals shape their political opinions through conversation between contemporary embodiment and experiences with social issues and family histories of social movement participation. Key Words: photovoice, urban social movements, visual research methods.  相似文献   
933.
Desalination is an increasingly important water source for the sunny, arid city of El Paso, Texas. As the city’s population grows, El Paso Water, the city’s water utility, has had to drill deeper into the Hueco Bolson aquifer, a primary water source for El Paso. This deeper drilling into the Hueco Bolson, however, has yielded progressively more saline water. In response, El Paso Water and administrators from Fort Bliss jointly constructed a reverse osmosis desalination plant to protect the Hueco Bolson’s freshwater supplies and expand the city’s water sources. Reverse osmosis water desalination, however, is an expensive, energy-intensive process currently dependent on carbon-heavy fossil fuels. Solar energy, however, is an abundant, carbon-free energy source that could potentially reduce the energy costs and carbon footprint of the reverse osmosis desalination process. We hypothesize that building a solar microgrid that supplies El Paso’s desalination plant with energy in tandem with the regional grid will reduce the plant’s energy expenditures in the long term compared to solely buying energy from the regional grid. We used the Hybrid Optimization for Multiple Energy Resources (HOMER) model created by the National Renewable Energy Laboratory. The results suggest that a solar microgrid whose modules use one axis tracker could reduce the plant’s energy expenses. Key Words: desalination, solar energy, water resources.  相似文献   
934.
The phase space structure around L 4 in the restricted three-body problem is investigated. The connection between the long period family emanating from L 4 and the very complex structure of the stability region is shown by using the method of Poincarés surface of section. The zero initial velocity stability region around L 4 is determined by using a method based on the calculation of finite-time Lyapunov characteristic numbers. It is shown that the boundary of the stability region in the configuration space is formed by orbits suffering slow chaotic diffusion.  相似文献   
935.
KAr analyses on whole rock and minerals are reported for the Kokoumi anorogenic pluton and alkaline volcanics of the Benue valley, west of Garoua (northern Cameroon), which belong to the northern part of the ‘Cameroon Line’. The two formations yield similar ages of 39 and 37 Ma, respectively. These values likely correspond to the time of emplacement. They are in agreement with the interpretation considering the ‘Cameroon Line’ as a huge lithospheric crack tapping a hot deep asthenospheric zone. To cite this article: R. Montigny et al., C. R. Geoscience 336 (2004).  相似文献   
936.
刘东生 《第四纪研究》2003,23(4):345-356
文章试图通过德日进神父自己的记述、与亲友的通信以及人们的回忆寻找他对中国科学做出贡献的发生发展过程,追踪德日进在其事业不同阶段的经历,了解他是如何在极端困难和复杂的条件下取得如此崇高的、科学和哲学的统一.德日进神父(1881~1955年),法国人,1923年来到中国.从在宁夏银川的水洞沟黄土层中发现了旧石器时起,1929年担任中国地质调查所新生代研究室顾问,指导了周口店的发掘研究,经历了第二次世界大战的困难时期,完成了他的名著<智慧圈>及<人的现象>.直至1946年离开中国,他在中国前后生活了23年(1923~1946年).在这23年中,他对中国的地质、古生物科学、考古科学等许多方面进行了大量的调查和研究,培养了人才,撰写了许多科学论文和专著,以及重要的哲学著作.德日进神父在中国受到人们的尊敬和爱戴,被称为中国古脊椎动物学的奠基者和领路人.一个人成就的伟大,往往不在于他意料之中,而是在于出乎他的意想之外.德日进神父是中西科学文化交流历史上、20世纪这一旋回中,连接西方和东方之路的无声的开拓者.他是把自然科学和哲学完美联结在一起的一座看不见的桥梁.文章按时间顺序分别描述德日进神父对东方的印象和思考,包括:1)对东方的憧憬--童年和<马可@波罗游记>;2)对东方的企盼--浪漫主义的东方;3)对东方的失望--长城边上的落日;4)对东方的希望--他们将自己站稳;5)对东方的升华--"智慧圈"和<人的现象>.谨以此文纪念80年前德日进神父来华所开辟的东西方科学交流之道路,和科学与哲学的结合.  相似文献   
937.
德日进"亚洲干极"理论的现实意义   总被引:8,自引:3,他引:5       下载免费PDF全文
"亚洲干极"是德日进总结中国北方中生代以来不断干旱化得出的观点.构造运动驱动气候变干是其主导思想.德日进关于中国新生代古地理演化的基本框架至今仍然适用,当代研究补充和深化了"亚洲干极"的理论,老第三纪行星风系的干热气候逐渐在新第三纪被季风气候取代,代表干旱气候的粉尘沉积逐步扩大空间范围,湖相沉积则逐渐收缩.22MaB.P.,8.5MaB.P.,3.6MaB.P.和1.2MaB.P.是"亚洲于极"逐步加强的关键时段.  相似文献   
938.
The volcano-tectonic evolution of Concepción,Nicaragua   总被引:1,自引:1,他引:0  
We describe the evolution of Concepción volcano by integrating regional geology, eruptive activity, morphology, stratigraphy, petrology, structure and active deformation data. This Nicaraguan volcano is set close to the back limb of the northwest-trending Tertiary Rivas anticline, a regional structure that bounds the southwest side of Lake Nicaragua. Concepción rises 1,600 m above a 1-km-thick sequence of Quaternary lacustrine mud-stones. There is no record of volcanism in the lake prior to Concepción. In addition, the only nearby volcano, Maderas volcano, has not deposited material on Concepción because of the trade winds. Thus, Concepción (and Made ras, too) can be considered as pristine volcanic environments, unaffected by other centres. A topographic rise forms an annulus 20 km in diameter around the cone. The rise is created by thrust-related folds at the western base, where the trade winds have accumulated a thick sequence of tephra, and by mud diapirs at the eastern base where only lake mudstones are present. Four magmatic-eruptive episodes exist in the stratigraphic record. The first begins with primitive low-alumina basalt and subsequently evolves to dacitic compositions. The following three episodes begin with high-alumina basalts and evolve only to silicic andesites. The occurrence of the high-alumina basalt after the first episode is indicative of crystal fractionation at lower crustal depths. The first episode may be associated with a compressive phase of volcano evolution. In this phase, the edifice load compresses substrata, allowing a longer magma residence time and differentiation in a shallow reservoir (possibly located at the density contrast between the lake sediments and the Tertiary flysch). During the next three episodes the weak sediments below the volcano started to rupture and yield under its increasing load, beginning a thrusting/diapiring phase of volcano evolution. Because of outward thrusting, vertical and horizontal stresses above the chamber were reduced, allowing magma to erupt more easily and to reach a lesser degree of evolution. If we consider the future evolution of Concepción, the differentiation in the shallow reservoir has probably generated a cumulitic complex, which eventually will start to deform and spread, beginning another, this time plutonic, spreading phase. This phase, which may be beginning now, could allow less evolved magmas to be erupted again. Four components influence the phases of volcano evolution: (1) the regional geology that is the boundary condition of the environment, (2) the substrata rheology that controls deformation, (3) the load of the volcanic edifice and (4) the magma, which provides the input of mass and energy. Our model of volcanic evolution suggests that Concepción is a complex geologic environment. The volcanic activity, tectonics and hazards can only be constrained through a complete knowledge of the many components of this environment. Published online: 20 February 2003 Editorial responsibility: R. Cioni  相似文献   
939.
We investigated the acceleration of solar cosmic rays (SCRs) by the shock waves produced by coronal mass ejections. We performed detailed numerical calculations of the SCR spectra produced during the shock propagation in the solar corona in terms of a model based on the diffusive transport equation using a realistic set of physical parameters for the corona. The resulting SCR energy spectrum N(ε) ∝ ε exp [? (ε/εmax)α] is shown to include a power-law portion with an index γ?2 that ends with an exponential tail with α ? 2.5 ? β, where β is the spectral index of the background Alfvén turbulence. The maximum SCR energy lies within the range εmax = 1–300 MeV, depending on the shock velocity. Because of the steep spectrum of the SCRs, their backreaction on the shock structure is negligible. The decrease in the Alfvén Mach number of the shock due to the increase in the Alfvén velocity with heliocentric distance r causes the efficient SCR acceleration to terminate when the shock reaches a distance of r = 2–3R. Since the diffusive SCR propagation in this case is faster than the shock expansion, SCR particles intensively escape from the shock vicinity. A comparison of the calculated SCR fluxes expected near the Earth’s orbit with available experimental data indicates that the theory satisfactorily explains all of the main observed features.  相似文献   
940.
Avrum J. Shriar 《Geoforum》2006,37(1):104-112
Many studies have examined the impacts of new roads in tropical forest frontiers. In general, these have led to substantial deforestation because they provide access to peasant farmers in need of land for food production and income generation. But few studies have investigated the impacts of improvements made to existing roads in frontier regions, and more specifically, their effects on the rural economy, land use, and land cover. This paper discusses the results of a 2001 study of these impacts, following the recent paving of the main road between Petén, a lowland frontier region in northern Guatemala, and the more densely populated highland regions of the country. This improvement, completed in late 1999, has yielded a major reduction in travel time between Flores, Petén and Guatemala City, the capital, from 12 to 14 h, or more, previously, to 7-8 h currently. The effects of this substantial change were examined through interviews and discussions with farmers, market vendors, and representatives of governmental and non-governmental organizations in the region, and through analyzing the limited available data on imports to Petén from other parts of the country. The results indicate that to date, the farmers in the study area have not altered their land use patterns because the prices they receive from intermediaries have not changed, and no market for new crops has emerged. However, more agricultural products raised in other regions of Guatemala are now being sold in Petén. Therefore, producers in Petén seemingly face greater competition from those elsewhere in the country. This trend has important implications regarding the impacts of regional integration, and for the difficult challenge of improving agricultural and environmental conditions in Petén.  相似文献   
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