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141.
Larry N. Smith 《Quaternary Research》2006,66(2):311-322
Glacial Lake Missoula, a source of Channeled Scabland flood waters, inundated valleys of northwest Montana to altitudes of ∼ 1265 m and to depths of >600 m, as evidenced by shorelines and silty lacustrine deposits. This study describes previously unrecognized catastrophic lake-drainage deposits that lie stratigraphically beneath the glacial-lake silts. The unconsolidated gravelly flood alluvium contains imbricated boulder-sized clasts, cross-stratified gravel with slip-face heights of 2-> 35 m, and 70- to 100-m-high gravel bars which all indicate a high-energy, high-volume alluvial environment. Gravel bars and high scablands were formed by catastrophic draining of one or possibly more early, high lake stands (1200-1265 m). Most glacial-lake silt, such as the Ninemile section, was deposited stratigraphically above the earlier deposits, represents a lower lake stand(s) (1050-1150 m), and was not deposited in lake(s) responsible for the highest discharge events. The glaciolacustrine silt-covered benches are incised by relict networks of valleys formed during the drainage of the last glacial lake. Significant erosion associated with the last lake draining was confined to the inner Clark Fork River canyon. 相似文献
142.
1990~2003年洪湖水体环境质量演变分析 总被引:16,自引:0,他引:16
以详细的水质监测资料为基础,采用标准指数法并结合实地调查,分析了1990~2003年洪湖水质的变化状况。结果表明,14 a间,洪湖水质类别以Ⅲ类和Ⅳ类为主。水质恶化的驱动因子是氮、磷及其它有机污染物。1991年到1994年期间,水体中氨氮(NH4 -N)占溶解无机氮(D IN)的比例逐年增高;1995~2003年,以氨氮和硝酸盐(NO3--N)同时作为水体中溶解无机氮的主要存在形式,与1990~1994年的水质状况相比,亚硝酸盐(NO2--N)所占的比例呈增加之势。氨氮、硝酸盐和亚硝酸盐的年际变化表明,洪湖水体自净能力在逐渐降低。以总磷(TP)、总氮(TN)和溶解无机氮(D IN)作为评价指标,洪湖水体已属中富营养型湖泊。洪湖水质演变与该区域人类活动(围湖造田、围网养殖等)以及江湖连通的变化对水环境的作用相耦合。 相似文献
143.
梁子湖水体P的季节变化与沉积物P释放初步研究 总被引:4,自引:0,他引:4
采用分级测定的方法对梁子湖沉积物中无机磷酸盐进行了分析,测定了梁子湖水体P的季节变化,并以室内模拟的方法研究梁子湖沉积物在pH值和温度控制下P的释放特征。研究表明,梁子湖水体P的含量呈明显的季节变化,冬季高,夏季低。沉积物无机磷(P i)中以钙磷(Ca—P)为主(55%~61%),铁磷(Fe—P)次之(28%~33%),铝磷(A l—P)最少(3%~5%)。在梁子湖的入水口和出水口,由于沉积环境影响到P的形态,P的释放明显较湖心高。在试验初期,由于扰动的影响,使得P的释放在第1天比第2天和第3天高,其后P的释放量则迅速增加。温度对P释放影响明显,其具体表现为,30℃时P释放达到峰值的时间比4℃时提前4 d,而且前者峰值比后者高出9倍。pH值对沉积物P释放同样有明显的影响,与正常状态下的湖水条件(pH值为8.5)相比,偏酸(pH值为5.5)和偏碱(pH值为11.5)条件下,P的释放量增加。 相似文献
144.
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147.
Pirouz Mojtahed-Zadeh 《GeoJournal》2006,66(4):273-283
Erratum to: GeoJournal 62: 51–58 DOI 10.1007/s10708-005-8562-2 The erroneous version of this article was originally published in GeoJournal 62: 51–58. This amended version corrects the formatting errors which are evident in the original version.Abstract It is universally accepted that the need for defining precise lines of separation and points of contacts between states is the byproduct of the emergence of nation-states and ‘world economy’ in the nineteenth century Europe. Nevertheless, it is hard to overlook the fact that these modern notions are rooted in periods prior to the emergence in Europe of nation-states. There are indications that ancient civilizations were familiar with the notion of ‘state’ in connection with the concepts of territory and boundary. Ancient texts reveal that this basic principle existed in ancient Persian literature in respect of matters of state, territory, and boundary. Similarly, the likelihood exists that these Persian notions could have influenced Roman civilization. It is widely believed that a combination of ancient Greco-Roman and Persian civilizations is a major contributor to what culturally constitutes ‘West’. Later in the Sassanid period the inter-linked notions of state, territory, and boundary developed substantially, coming quite close to their contemporary forms. On the other hand, considering that ‘justice’ was the corner stone of ancient Persian Political philosophy, the idea that ancient␣Iranian spatial arrangement might have contributed to the evolution of the concept of democracy in the West may not be too difficult to contemplate.The online version of the original article can be found at 相似文献
148.
David W. Kelley Stefanie A. Brachfeld Edward A. Nater Herbert E. Wright Jr. 《Journal of Paleolimnology》2006,35(1):193-206
Sediments from Lake Pepin on the Mississippi River, southeastern Minnesota, are used as provenance tracers to assess variations
in hydrology and sediment-transport during the middle Holocene. Three rivers contribute sediment to Lake Pepin, and each catchment
is characterized by a distinctly different geologic terrain. The geochemical fingerprint for each drainage basin was determined
from the elemental composition of heavy minerals in the silt-sized fraction of modern sediment samples. Down-core elemental
abundances were compared with these fingerprints by use of a chemical-mass-balance model that apportions sediment to the source
areas. We observed a decreased contribution from the Minnesota River during the interval ~6700–5500 14C yr BP, which we attribute to decreased discharge of the Minnesota River, likely controlled by a combination of precipitation,
snow melt, and groundwater input to the river. This hydrologic condition coincides with the mid-Holocene prairie period recorded
by fossil pollen data. The occurrence of this feature in a proxy record for hydrologic variations supports the hypothesis
that the mid-Holocene prairie period reflects drier conditions than before or after in midwestern North America. 相似文献
149.
Sven O. Franz Lorenz Schwark Cathrin Brüchmann Burkhard Scharf Ralf Klingel Jon D. Van Alstine Namık Çagatay Umut B. Ülgen 《Journal of Paleolimnology》2006,35(4):715-736
A limnogeological reconnaissance study was carried out on Lake Iznik, located in the southeast of the Marmara region of Turkey,
involving a seismic survey and collection of short sediment cores. This lake is located on the middle branch of the North
Anatolian Fault Zone (NAFZ), a transform plate boundary between the Eurasian and Anatolian Plates. It is, therefore, tectonically
active and offers an opportunity to investigate the interplay of sedimentary and seismo-tectonic processes, as well as climate
change and human impact in the region. Short cores of the three sub-basins, maximum length of 35.5 cm, recovered non-laminated,
blackish clays and silts with varying amounts of biogenic and minerogenic (allochthonous, autochthonous) material, which documented
almost the last 80 years of deposition and environmental history. High sedimentation rates in the deeper core sections are
accompanied by changes in land use (conversion of woodland to farmland) in the northern areas of Lake Iznik, which caused
the deposition of more weathered material (high K/Na ratios) and higher contents of Mn in the lake. A tendency towards eutrophic
conditions within the last 20 years is indicated by high nutrient content (N, TOC, P), decreasing C/N-ratios, and characteristic
diatom and cladoceran associations. Also increased pollution is revealed by higher Pb, Cu, and Zn contents and increased supply
of human and animal faeces (high coprostanol content) during the last two decades. But simultaneous lower sedimentation rates
towards the core tops complicate the reconstruction of recent and past eutrophication and pollution states of Lake Iznik.
This requires an extension of the pilot study and deeper sediment cores, to recover non-anthropogenic influenced sediment
levels. 相似文献
150.
Authigenic vivianite and siderite microconcretions were found, respectively, in hemipelagic and deltaic facies of 600-m-long BDP-98 sediment section from Lake Baikal. Textural investigations of these microconcretions show that they are typically <1 mm in size, irregular in shape and composed of aggregated crystallites. Dissimilar orientation of vivianite and siderite crystallites suggests formation at different depths in the sediment; up to tens of centimeters for vivianite and tens of meters for siderite. Chemical analyses of both the vivianite and the siderite indicate cation composition characterized by minor amounts of Mn, Ca and Mn apart from the dominating Fe. Rather limited and distinctive carbon isotopic composition of the siderite, with δ
13CVPDB values between about +13 and +16‰, implies formation of the mineral in the methanogenic zone of diagenesis. Isotopic composition of oxygen in the siderite (δ
18OVPDB values between about −10 and -11‰ ) is consistent with crystallization temperature at about 10–30°C and water δ
18OSMOW values between about −10 and -16‰ . The distribution of the authigenic minerals in the section suggests changes in both sedimentary facies and climate, where vivianite formation was controlled by hemipelagic depositional conditions during the Pliocene and Quaternary, whereas siderite reflects impact of deltaic conditions during the Miocene. 相似文献