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991.
镁铁-超镁铁层状侵入体研究现状 总被引:1,自引:0,他引:1
本文主要探讨了镁铁 -超镁铁层状侵入体的一般特征及成因机制 ,并对世界上著名的斯开利戛德、布什维尔德、斯蒂尔沃特层状侵入体和我国攀西层状侵入体的岩石学和地球化学特征进行了总结和对比。 相似文献
992.
华北陆块南缘熊耳群形成时代讨论 总被引:53,自引:0,他引:53
分布于豫、晋、陕3省的熊耳群火山岩系不整合覆盖于太古界及下元古界结晶基底之上,其上被汝阳群、官道口群等陆源碎屑岩-碳酸盐岩地层不整合覆盖.已有的各种熊耳群年龄资料为1.40~1.85 Ga,故常认为其形成标志着中元古代的开始,并将它与蓟县剖面的长城系对比.豫西熊耳山地区马家河组顶部的流纹斑岩和侵入于鸡蛋坪组的辉石闪长岩的单颗粒锆石U-Pb和激光探针等离子体质谱(LP-ICPMS)年龄表明:熊耳群形成于古元古代1.75~1.95 Ga,早于长城系;火山喷发开始于1.95 Ga±,中心可能在豫西的熊耳山或崤山地区,形成豫西崤山、熊耳山、外方山地区的许山组和鸡蛋坪组;大约在1.85 Ga±,火山活动可能以崤山地区为中心呈三叉裂谷系分别向西、东和北3个方向发展,形成覆盖全区的马家河组;末期(1.75 Ga±)可能仅在豫西地区形成次火山-侵入岩——辉石闪长岩类.不整合覆盖于熊耳群之上的汝阳群云梦山组和官道口群高山河组的形成时代相当于长城系. 相似文献
993.
994.
天山西南段乌恰—柯坪地区航磁磁场特征与成矿远景预测 总被引:2,自引:0,他引:2
本文以1998年1:20万航空磁测资料为基础,参考地质和化探资料,对工作区磁场特征、岩浆岩、断裂构造与矿产分布的关系进行探讨,研究地质成矿环境,建立寻找热液型和火山-沉积型的铜、铅、锌、金、铁、锰矿找矿标志,对本区找矿远景进行了预测。 相似文献
995.
996.
Delineation of capture zones for municipal wells in fractured dolomite, Sturgeon Bay, Wisconsin, USA 总被引:1,自引:1,他引:1
A wellhead protection study for the city of Sturgeon Bay, Wisconsin, USA, demonstrates the necessity of combining detailed
hydrostratigraphic analysis with groundwater modeling to delineate zones of contribution for municipal wells in a fractured
dolomite aquifer. A numerical model (MODFLOW) was combined with a particle tracking code (MODPATH) to simulate the regional
groundwater system and to delineate capture zones for municipal wells. The hydrostratigraphic model included vertical and
horizontal fractures and high-permeability zones. Correlating stratigraphic interpretations with field data such as geophysical
logs, packer tests, and fracture mapping resulted in the construction of a numerical model with five high-permeability zones
related to bedding planes or facies changes. These zones serve as major conduits for horizontal groundwater flow. Dipping
fracture zones were simulated as thin high-permeability layers. The locations of exposed bedrock and surficial karst features
were used to identify areas of enhanced recharge. Model results show the vulnerability of the municipal wells to pollution.
Capture zones for the wells extend several kilometers north and south from the city. Travel times from recharge areas to all
wells were generally less than one year. The high seasonal variability of recharge in the study area made the use of a transient
model necessary.
Electronic Publication 相似文献
997.
Radiocarbon dating of dissolved inorganic carbon in groundwater from confined parts of the Upper Floridan aquifer, Florida, USA 总被引:3,自引:1,他引:3
Geochemical reaction models were evaluated to improve radiocarbon dating of dissolved inorganic carbon (DIC) in groundwater
from confined parts of the Upper Floridan aquifer in central and northeastern Florida, USA. The predominant geochemical reactions
affecting the 14C activity of DIC include (1) dissolution of dolomite and anhydrite with calcite precipitation (dedolomitization), (2) sulfate
reduction accompanying microbial degradation of organic carbon, (3) recrystallization of calcite (isotopic exchange), and
(4) mixing of fresh water with as much as 7% saline water in some coastal areas. The calculated cumulative net mineral transfers
are negligibly small in upgradient parts of the aquifer and increase significantly in downgradient parts of the aquifer, reflecting,
at least in part, upward leakage from the Lower Floridan aquifer and circulation that contacted middle confining units in
the Floridan aquifer system. The adjusted radiocarbon ages are independent of flow path and represent travel times of water
from the recharge area to the sample point in the aquifer. Downgradient from Polk City (adjusted age 1.7 ka) and Keystone
Heights (adjusted age 0.4 ka), 14 of the 22 waters have adjusted 14C ages of 20–30 ka, indicating that most of the fresh-water resource in the Upper Floridan aquifer today was recharged during
the last glacial period. All of the paleowaters are enriched in 18O and 2H relative to modern infiltration, with maximum enrichment in δ18O of approximately 2.0‰.
Electronic Publication 相似文献
998.
TAN Fuwen PAN Guitang XU Qiang Chengdu Institute of Geology Mineral Resources Chengdu 《Continental Dynamics》2001,(1)
1. Introduction The uplift and evolution of the Qinghai Tibet Plateau has been the most important projects for studying the dynamic process of the plateau, and the uplift mechanism and history are the essential problems. Researches have been done extensively in terms of tectonics, sedimentology, geophysics, paleontology, paleoclimate and paleomagnetism for several tens of years. Many evolution models have been suggested but so far none of them have been explained perfectly. In recent years,… 相似文献
999.
1000.
Transport properties (permeability and electrical conductivity) have been measured at different hydrostatic pressure runs on 7 crystalline rocks (gneisses and amphibolites) sampled from the KTB drilling project. The decrease of permeability by pressure are compared with the pressure-dependent data of the electrical conductivity (formation factor) resulting from complex impedance measurements. According to the equivalent-channel model (ECM), there exists a linear relationship between these parameters by representing both properties on logarithmic scales. The results show that it is possible to extrapolate high-pressure permeability from low-pressure (< 60 MPa) permeability data by using the pressure-dependent electrical conductivity (up to 300 MPa). 相似文献