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151.
152.
Juan Pablo Corella Adel El Amrani Javier Sigró Mario Morellón Eugenio Rico Blas Lorenzo Valero-Garcés 《Journal of Paleolimnology》2011,46(3):469-485
We present a high-resolution, multiproxy reconstruction of the depositional history of Lake Arreo, northern Spain, for the
last 60 years. We conducted sedimentological, geochemical and diatom analyses in short cores and made a detailed comparison
with regional instrumental climate data (1952–2007), limnological monitoring of the lake (1992–2008) and recent land use changes
that affect the lake catchment. Chronology is based on “floating” discontinuous varve counts and 137Cs and 14C dates. Four periods were identified in the Lake Arreo recent history: (1) prior to 1963, varved facies intercalated with
fine turbidite deposits, and diatom assemblages dominated by Cyclotella taxa indicate predominantly meromictic conditions, (2) from 1964 to 1978, permanent anoxia persisted in bottom waters, as shown
by similar facies and diatom assemblages as before, though detrital layers were coarser, (3) from 1979 to 1994, sediment delivery
to the lake increased and laminated, clastic facies were deposited, and (4) from 1995 to 2008, dominance of massive facies
and an increase in Fragilaria tenera and Achnanthes minutissima reflect relatively lower lake levels, less frequent bottom anoxia with more frequent water column mixing, similar to modern
conditions. The period 1952–1979 was a time of meromixis and varved facies deposition, and was characterized by higher rainfall
and less intense agricultural pressure in the watershed. There were two short humid periods (1992–1993 and 1996–1998) when
monitoring data show more anoxic weeks per year and relatively higher lake levels. Increased cultivation of small landholdings
in 1963, and particularly after 1979, caused a large increase in sediment delivery to the lake. The inferred lake evolution
is in agreement with monitoring data that suggest a transition from dominantly meromictic conditions prior to 1993–1994 to
a predominantly monomictic pattern of circulation since then, particularly after 2000. The synergistic effects of intensive
water extraction for irrigation and lower rainfall since 1979, and particularly since 1994, brought the long period of meromictic
conditions in Lake Arreo to an end. Water balance and sediment delivery to the lake are dominant factors that control the
limnological and mixing conditions in Lake Arreo and they must be considered in management and restoration plans. 相似文献
153.
Although China was one of the countries with the fastest-growing aging population in the world, limited scholarly attention has been paid to migration among older adults in China. The full picture of their migration in the entire country over time remains unknown. This study examines the spatial patterns of older interprovincial migration flows and their drivers in China over the period 1995 to 2015, using four waves of census data and intercensal population sample survey data. Results from eigenvector spatial filtering negative binomial regressions indicate that older adults tend to migrate away from low cost-of-living rural areas to high cost-of-living urban and rural areas, moving away from areas with extreme temperature differences. The location of their grandchildren is among the most important attractions. Our findings suggest that family-oriented migration is more common than amenity-led migration among retired Chinese older adults, and the cost-of-living is an indicator of economic opportunities for adult children and the quality of senior care services. 相似文献
154.
基于旅游经济联系模型,运用GIS技术手段,构建中国入境旅游城市的旅游经济联系网络,并对1997年和2010年的Top1、Top5和Top10网络的结构演变特征进行研究。研究发现:① 整体网络规模在缩小,但是最大联系强度和平均联系强度却明显增长,且最大联系强度一直出现在广州和深圳之间;② 整体网络结构处于核心极化阶段,总体呈现“东部强,中西弱”的“L”型分布,一级节点城市北京、上海和广州的集聚作用显著,且进一步增强;③ 旅游城市联系以东部区内联系为主,东部地区城市的集聚作用愈加明显,中部和西部地区城市的集聚作用在减弱;④ 中国入境旅游城市可分为三大体系,形成三极多核的空间格局。 相似文献
155.
以企鹅珍珠贝、菲律宾蛤仔和锯齿巴非蛤全脏器为原料,经酶解、离心去蛋白、醇沉、分离、洗涤、干燥,得糖胺聚糖(GAG)粗制品,分别测定并比较3种贝类的GAG的含量和得率。结果表明,企鹅珍珠贝的GAG质量分数为22.35%,菲律宾蛤仔为18.69%,锯齿巴非蛤为20.36%,由此得出企鹅珍珠贝的GAG的含量比其他两种贝类高,是较好的GAG来源。 相似文献
156.
通过大量野外观察、分析测试和综合研究,结合覆盖全区不同比例尺的区域地质调查资料,对柴达木盆地及其邻区早—中二叠世构造岩相古地理格局进行了研究,并探讨了其形成机制.结果表明:柴达木盆地及其邻区中、北部早—中二叠世为陆内盆山裂谷系统,主体处于伸展构造背景,总体表现为堑垒相间的构造古地理格局;南部为巴颜喀拉洋盆,早—中二叠世是巴颜喀拉洋盆扩张最为剧烈且规模最大的时期,巴颜喀拉洋盆中洋岛、海山遍布;早—中二叠世晚期强烈的华力西构造运动使古板块间的相对运动加剧,巴颜喀拉洋盆大洋岩石圈板块向北强烈俯冲,形成东昆仑陆缘岩浆弧及其南部增生带,东昆仑陆缘岩浆弧岩浆活动十分强烈,宗务隆山—西秦岭陆源裂谷盆地进一步发育,形成十分复杂的构造岩相古地理格局.早—中二叠世是研究区地球动力学机制从强烈扩张到强烈汇聚的转折时期,加强其构造岩相古地理研究对建立该区地层序列、探讨其地质演化历史以及指导找矿等均具有重要意义. 相似文献
157.
158.
WANG Pu-jun HOU Qi-jun SHU Ping HUANG Yu-long GUO Zhen-hua LI Jin-long College of Earth Sciences Jilin University Changchun Jilin China Jilin Petroleum Company Songyuan Jilin China Daqing Petroleum Company Daqing HeiLongjiang China 《东北亚地学研究》2005,(Z1)
Volcanic rocks of the late Mesozoic are very important reservoirs for the commercial natural gases including hydrocarbon, carbon dioxide and rare gases in the northern Songliao Basin. The reservoir volcanic rocks include rhyolite, andesite, trachyte, basalt and tuff. Facies of the volcanic rocks can be classified into 5 categories and 15 special types. Porosity and permeability of the volcanic reservoirs are facies-controlled. Commercial reservoirs were commonly found among the following volcanic subfacies: volcanic neck (I1) , underground-explosive breccia (I3), pyroclastic-bearing lava flow (II3), upper effusive (III3) and inner extrusive ones (IV1). The best volcanic reservoirs are generally evolved in the interbedded explosive and effusive volcanics. Rhyolites show in general better reservoir features than other types of rocks do. 相似文献
159.
Concepción L. Alados Fernando G. Barroso Antonio Aguirre Juan Escós 《Journal of Arid Environments》1996,34(4):455-463
To determine if defoliation of a woody plant affects foraging by folivorous insects, we examined the infection rate (number of leaves damaged per total number of leaves sampled on marked stems) ofAnthyllis cytisoidesunder three experimental treatments: 10, 50 and 90% plant defoliation. Observations were made for three age classes, established by trunk base perimeter (equal to or lower than 11 cm, between 11 and 20 cm, larger than 20 cm). Plants respond positively to artificial defoliation by increasing total vegetative length of the stem and total inflorescence length. This response is most evident in young individuals.Response to herbivory was measured as overall infection rate and also as infection rate by different feeding guilds—chewing, mining, or sucking insects. We found that increased defoliation elicited increased resistance of leaves to insect attack. This was particularly evident in young plants. Different insect guilds respond in different ways. Attack by chewing insects declines with defoliation for all plant age classes; only sucking insects which feed on the oldest plants reduce feeding rate with plant defoliation. Finally, mining insects present the opposite trend in young and senescent plants. 相似文献
160.
基于DEM的交通线文化景观感知与功能分段研究——紫荆关长城景观的实证 总被引:2,自引:1,他引:2
在已有景观感知度概念和模型基础上,根据景观规模和特征将交通线某一具体位置的景观感知度划分为单点景观、多点景观和组景观感知度,并提出了基于集合表达的交通线景观感知度模型,以解决在一组特定的线性空间单元或区域上开展景观感知的研究和计算问题。以紫荆关长城文化景观为例,利用DEM进行景观视域分析,并引入资源价值、遗存现状等权重因子,实现了紫荆关附近公路和铁路线的景观感知度定量计算。根据景观感知度的空间格局,准确划分了敌台、烽火台和马面等单点景观、墙体景观及各类组景观和综合景观的最佳感知功能路段和最佳观赏位置。总体来看,紫荆关附近的公路线可感知位置连续性更强,铁路线高感知位置相对离散,公路感知效果整体优于铁路感知。交通线景观感知度模型特别适合用于大型造型地貌、宏伟建筑群等景观感知分析,是对旅游景观规划设计方法的一种扩充,能够将旅游景观规划设计从旅游地内部拓展到旅游地外围,对于提高旅游景观导引设计的精准性、提升旅游文化传播效率和增加传播途径等均有理论参考意义和实践应用价值。 相似文献