全文获取类型
收费全文 | 6185篇 |
免费 | 490篇 |
国内免费 | 1447篇 |
专业分类
测绘学 | 401篇 |
大气科学 | 667篇 |
地球物理 | 2285篇 |
地质学 | 2716篇 |
海洋学 | 830篇 |
天文学 | 231篇 |
综合类 | 473篇 |
自然地理 | 519篇 |
出版年
2024年 | 28篇 |
2023年 | 81篇 |
2022年 | 79篇 |
2021年 | 88篇 |
2020年 | 93篇 |
2019年 | 89篇 |
2018年 | 102篇 |
2017年 | 37篇 |
2016年 | 76篇 |
2015年 | 74篇 |
2014年 | 133篇 |
2013年 | 125篇 |
2012年 | 230篇 |
2011年 | 310篇 |
2010年 | 160篇 |
2009年 | 178篇 |
2008年 | 298篇 |
2007年 | 303篇 |
2006年 | 349篇 |
2005年 | 344篇 |
2004年 | 320篇 |
2003年 | 267篇 |
2002年 | 264篇 |
2001年 | 248篇 |
2000年 | 291篇 |
1999年 | 173篇 |
1998年 | 157篇 |
1997年 | 164篇 |
1996年 | 187篇 |
1995年 | 176篇 |
1994年 | 196篇 |
1993年 | 239篇 |
1992年 | 192篇 |
1991年 | 271篇 |
1990年 | 206篇 |
1989年 | 212篇 |
1988年 | 187篇 |
1987年 | 165篇 |
1986年 | 107篇 |
1985年 | 145篇 |
1984年 | 125篇 |
1983年 | 97篇 |
1982年 | 71篇 |
1981年 | 59篇 |
1980年 | 95篇 |
1978年 | 20篇 |
1964年 | 21篇 |
1959年 | 22篇 |
1958年 | 23篇 |
1957年 | 24篇 |
排序方式: 共有8122条查询结果,搜索用时 46 毫秒
91.
Planetary-Scale Wave Structures of the Earth’s Atmosphere Revealed from the COSMIC Observations 总被引:1,自引:0,他引:1 下载免费PDF全文
S. K. A. V. Prasad Rao ANISETTY P. S. BRAHMANANDAM G. UMA A. Narendra BABU HUANG Ching-Yuang G. Anil KUMAR S. Tulasi RAM WANG Hsiao-Lan CHU Yen-Hsyang 《Acta Meteorologica Sinica》2014,28(2):281-295
GPS radio occultation(GPS RO) method,an active satellite-to-satellite remote sensing technique,is capable of producing accurate,all-weather,round the clock,global refractive index,density,pressure,and temperature profiles of the troposphere and stratosphere.This study presents planetary-scale equatorially trapped Kelvin waves in temperature profiles retrieved using COSMIC(Constellation Observing System for Meteorology,Ionosphere,and Climate) satellites during 2006-2009 and their interactions with background atmospheric conditions.It is found that the Kelvin waves are not only associated with wave periods of higher than 10 days(slow Kelvin waves) with higher zonal wave numbers(either 1 or 2),but also possessing downward phase progression,giving evidence that the source regions of them are located at lower altitudes.A thorough verification of outgoing longwave radiation(OLR) reveals that deep convection activity has developed regularly over the Indonesian region,suggesting that the Kelvin waves are driven by the convective activity.The derived Kelvin waves show enhanced(diminished) tendencies during westward(eastward) phase of the quasi-biennial oscillation(QBO) in zonal winds,implying a mutual relation between both of them.The El Nino and Southern Oscillation(ENSO) below 18 km and the QBO features between 18 and 27km in temperature profiles are observed during May 2006-May 2010 with the help of an adaptive data analysis technique known as Hilbert Huang Transform(HHT).Further,temperature anomalies computed using COSMIC retrieved temperatures are critically evaluated during different phases of ENSO,which has revealed interesting results and are discussed in light of available literature. 相似文献
92.
在龙门山中段小鱼洞地区映秀-北川断裂和彭县-灌县断裂发生了同震位移,同时在该地区新出现了一条北西向的同震破裂带——小鱼洞断裂的破裂带,并分割了两条近于平行的北东向逆冲-走滑型的主断裂。汶川特大地震发生后重点对小鱼洞断裂的地表破裂开展了详细的野外地质填图,利用全站仪和GPS对地表破裂进行了精确的测量。初步调查的结果表明,小鱼洞断裂位于映秀-北川断裂与彭县-灌县断裂之间,走向近于北西向,延伸约15km,以脆性破裂为特征,穿过小鱼洞大桥,并切割了多种类型的地貌单元,使道路发生拱曲、破坏和桥梁垮塌或移位。单个破裂长度在几米到300m不等,其南西盘为上升盘,北东盘为下降盘,平均垂直位错为1.0m,平均水平位错为2.3m,垂直与水平位错量之比1 ∶1~1 ∶2,显示为逆冲分量小于或等于左旋走滑分量,并以左旋走滑作用为主。同时,研究表明小鱼洞断裂属于映秀-北川断裂与彭县-灌县断裂之间的捩断层,其主要特征包括: 1)是在汶川地震中由于龙门山逆冲体之间的差异逆冲运动过程中而形成的断裂; 2)其走向近于北西向,垂直于龙门山北东向的主干断裂,而平行于逆冲体的逆冲运动方向; 3)具有高角度断面的断层,以左旋走滑作用为主。 相似文献
93.
内蒙古草地土壤水分动态监测预测模式的研究 总被引:3,自引:0,他引:3
利用土壤水分平衡参数模拟的方法,建立了内蒙古草地0-50cm土层土壤水分动态监测预测模式。通过8个站点两年的检验和试用,效果较好。 相似文献
94.
在绿片岩、角闪岩和麻粒岩和变质岩层中,电气石岩和富电气石的沉积物与喷气矿化伴生,它们遭受了中等到强烈的变形,呈连续层状分布于褶皱构造附近,显示出诸如层理、递变层理、交错层理、层内滑动等沉积构造和拉裂构造。在高级变质作用区,它们显示变质结构,通常被再活化而成的石英-电气石脉所穿切。富电气石岩出现在由海底喷气而形成的Pb-Zn-Ag、Cu-Co、Cu-Bi、W、Sn、Au和稀土元素矿化的下部、内部及矿化之上,且在横向上与矿化同期的地层中。在一些地方,电气石岩没有上述矿化现象,也不与花岗质岩石相伴生。电气石的成分是黑电气石-镁电气石,虽反映了其全岩成分,但不能作为矿化的标志。虽然电气石是与花岗岩、交代岩、角砾岩简伴生的普通矿物,但本文描述的富电气石层为山硅电气石前身的变质作用产生的富硼硅质铁建造。它们是一种常见的喷气岩类型,并且常常出现在早-中元古代厚层的泥质变沉积岩和蒸发岩层序中。这就说明硼是由含硼的粘土的淋滤作用或由含硼酸盐的蒸发岩的淋滤作用产生的。 相似文献
95.
Overview of integrative tools and methods in assessing ecological integrity in estuarine and coastal systems worldwide 总被引:8,自引:1,他引:8
Borja A Bricker SB Dauer DM Demetriades NT Ferreira JG Forbes AT Hutchings P Jia X Kenchington R Carlos Marques J Zhu C 《Marine pollution bulletin》2008,56(9):1519-1537
In recent years, several sets of legislation worldwide (Oceans Act in USA, Australia or Canada; Water Framework Directive or Marine Strategy in Europe, National Water Act in South Africa, etc.) have been developed in order to address ecological quality or integrity, within estuarine and coastal systems. Most such legislation seeks to define quality in an integrative way, by using several biological elements, together with physico-chemical and pollution elements. Such an approach allows assessment of ecological status at the ecosystem level ('ecosystem approach' or 'holistic approach' methodologies), rather than at species level (e.g. mussel biomonitoring or Mussel Watch) or just at chemical level (i.e. quality objectives) alone. Increasing attention has been paid to the development of tools for different physico-chemical or biological (phytoplankton, zooplankton, benthos, algae, phanerogams, fishes) elements of the ecosystems. However, few methodologies integrate all the elements into a single evaluation of a water body. The need for such integrative tools to assess ecosystem quality is very important, both from a scientific and stakeholder point of view. Politicians and managers need information from simple and pragmatic, but scientifically sound methodologies, in order to show to society the evolution of a zone (estuary, coastal area, etc.), taking into account human pressures or recovery processes. These approaches include: (i) multidisciplinarity, inherent in the teams involved in their implementation; (ii) integration of biotic and abiotic factors; (iii) accurate and validated methods in determining ecological integrity; and (iv) adequate indicators to follow the evolution of the monitored ecosystems. While some countries increasingly use the establishment of marine parks to conserve marine biodiversity and ecological integrity, there is awareness (e.g. in Australia) that conservation and management of marine ecosystems cannot be restricted to Marine Protected Areas but must include areas outside such reserves. This contribution reviews the current situation of integrative ecological assessment worldwide, by presenting several examples from each of the continents: Africa, Asia, Australia, Europe and North America. 相似文献
96.
Bassam A. ABUAMARAH Mokhles K. AZER Paul D. ASIMOW Habes GHREFAT Heba S. MUBARAK 《《地质学报》英文版》2021,95(2):459-480
The Abu Dabbab albite granite(ADAG), in the central Eastern Desert of Egypt, hosts the most significant rare metal ore deposit in the northern part of the Neoproterozoic Arabian-Nubian Shield. Here, we report detailed field,petrographic, mineralogical and geochemical investigation of the ADAG, an isolated stock-like granitic body with sharp intrusive contacts against metamorphic country rocks, probably emplaced at about 600 Ma. The fine-grained porphyritic upper unit is a preserved remnant of the shallowly-emplaced apex of the magma chamber, whereas the medium-grained lower unit crystallized at deeper levels under subvolcanic conditions. The peraluminous leucocratic ADAG shares common geochemical characteristics with post-collisional intraplate A-type magmas. In addition to the conspicuous enrichment in Na2 O, the ADAG is remarkable for its anomalous concentrations of Ta, Nb, Li, Hf, Ga, Sn, Zn and heavy rare-earth elements. Nb-Ta minerals in the ADAG are mixed with Fe-Mn oxides, forming black patches that increase in abundance toward of the base of the intrusion. Columbite-tantalite, cassiterite and wolframite are the most important ore minerals.Pronounced negative Eu anomalies(Eu/Eu* = 0.10–0.24) reflect extreme magmatic fractionation and perhaps the effects of late fluid-rock interaction. The ADAG was most likely generated by partial melting of the juvenile middle crust of the ANS as the geotherm was elevated by erosional uplift following lithospheric delamination and it was emplaced at the intersection of lineations of structural weakness. Although formation of the ADAG and its primary enrichment in rare metals are essentially due to magmatic processes, late-stage metasomatism caused limited redistribution of rare metals. Fluid-driven subsolidus modification was limited to the apex of the magma chamber and drove development of greisen, amazonite, and quartz veins along fracture systems. 相似文献
97.
引言大约在一个世纪以前人们就在世界范围内发现了金矿床和铁建造具有共同伴生组合关系。金矿床中金的来源有同生的,也有后生的。在加拿大除了由砂矿床转变而来的金矿外,大多数金矿产在岩脉、剪切带和破碎带里。可见在金矿的沉淀过程中构造因素是十分重要的。铁建造是原来的化学沉积物,它一方面作为同生金的来源,另一方面,这些硬而脆的燧石质岩石又为矿脉的形成提供了一个有利的环境。岩石的构造控制了金的 相似文献
98.
In recent years,scholars at home and abroad have method,and that vanous disasters would be analyzed assynthetically studied natural dlsaste‘theoretically and an Integral.SHI Peilun(1991)putforwad a scientificmethodologlcally,as well as its cases analys。s(CND,term—regional disaster system,which Indicates that1987; MA et al,1990; MARBLE,1990; NE et al,the situation of a disaster(calamity loss)results from1999; PATAK et al,1982; SHI,1991;VAN et al,h… 相似文献
99.
Pressure solution is a common phenomenon in massive sulphide zinc-lead deposits of western Canada and may have been an important factor leading to the mobilization of ore-forming materials during diagenesis, deformation and metamorphism of sedimentary ores.The control of ductile shear zones over gold mineralization could be explained in view of pressure solution of gold-bearing miner-als under shearing stress and the tesultant mobilization of this metal. 相似文献
100.
双刺镰状水蚤Drepanopus bispinosus为南极沿海伯尔顿盐湖(Burton lake)中的越冬种类之一,其雌性性成熟大约于每年的初冬季节,在随后8个多月的生活史中,经历了一个盐度从33(5月份)到39(11月份)的环境变化.本文报道了该水蚤雌性成体对环境盐度适应的季节差异,动物在冬季的耐低盐能力较夏季强,从冬季到夏季,动物对盐度的适应范围明显地向高盐度方向偏移,这与环境盐度对动物的驯化有关.在低盐水中,动物的呼吸率增高,且夏季大于冬季,因而进一步证实了环境盐度的变化对动物盐度适应性的影响. 相似文献