首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   814篇
  免费   128篇
  国内免费   86篇
测绘学   25篇
大气科学   96篇
地球物理   218篇
地质学   375篇
海洋学   91篇
天文学   47篇
综合类   65篇
自然地理   111篇
  2023年   3篇
  2022年   33篇
  2021年   26篇
  2020年   25篇
  2019年   30篇
  2018年   41篇
  2017年   39篇
  2016年   43篇
  2015年   45篇
  2014年   51篇
  2013年   41篇
  2012年   41篇
  2011年   44篇
  2010年   39篇
  2009年   54篇
  2008年   68篇
  2007年   38篇
  2006年   33篇
  2005年   32篇
  2004年   19篇
  2003年   25篇
  2002年   29篇
  2001年   16篇
  2000年   9篇
  1999年   28篇
  1998年   25篇
  1997年   22篇
  1996年   20篇
  1995年   11篇
  1994年   11篇
  1993年   9篇
  1992年   5篇
  1991年   4篇
  1990年   13篇
  1989年   7篇
  1988年   8篇
  1987年   6篇
  1986年   6篇
  1985年   5篇
  1984年   4篇
  1983年   1篇
  1982年   1篇
  1981年   2篇
  1980年   3篇
  1979年   1篇
  1978年   2篇
  1977年   3篇
  1976年   3篇
  1975年   2篇
  1973年   1篇
排序方式: 共有1028条查询结果,搜索用时 314 毫秒
81.
1项目区基本情况临沂市试点工作涉及2个县,9个乡镇,19个行政村,挂钩周转指标总规模175.61 hm2。其中,沂南县界湖、大庄、苏村、葛沟、湖头、青驼6个乡镇15个行政村,总规模144.98 hm2;河东区汤头、刘店子、凤凰岭3个乡镇4个行政村,总规模97.3 hm2。沂南县需安置692户,主要使用新  相似文献   
82.
83.
平阴县土壤中重金属元素异常成因研究   总被引:1,自引:0,他引:1  
通过对平阴县周边及其西部农田区采样调查,平阴县周边元素异常具有异常衬度较高,富集系数大等特征,西部农田区异常具有各元素套合关系好,多数异常衬度不高,富集系数小的特点。结果表明,西部农田区异常是以As,Cd为主要成分的异常,元素含量与SiO2,Al2O3,Fe2O3等常量组分间具有显著的相关性,随SiO2含量的增加而降低,随Al2O3,Fe2O3含量的增加而增加,说明土壤常量组分及其所决定的土壤质地是导致异常形成的主要因素;而平阴城区异常是以S,Hg,As,Zn,Mn等元素为主的异常,是典型的人为综合因素(化工烟尘、工厂污水、生活垃圾)产生的异常。  相似文献   
84.
We conducted this study to assess the diversity of bacteria associated with the surfaces of algae based on 16S rDNA sequence analyses.Twelve strains of bacteria were obtained from the surfaces of the following four species of algae:Gracilaria textorii,Ulva pertusa,Laminaria japonica,and Polysiphonia urceolata.The isolated strains of bacteria can be divided into two groups:Halomonas and Vibrio,in physiology,biochemical characteristics and 16S rDNA sequence analyses.The phylogenetic tree constructed based on ...  相似文献   
85.
Although it has been shown that the potential of tight‐sand gas resources is large, the research into the mechanisms of hydrocarbon charging of tight sandstone reservoirs has been relatively sparse. Researchers have found that there is a force balance during hydrocarbon charging, but discriminant models still have not been established. Based on the force balance conditions observed during gas migration from source rocks to tight sandstone reservoirs, a calculation formula was established. A formula for identifying effective source rocks was developed with the gas expulsion intensity as the discrimination parameter. The critical gas expulsion intensity under conditions of various burial depths, temperatures, and pressures can be obtained using the calculation formula. This method was applied in the Jurassic tight sandstone reservoirs of the eastern Kuqa Depression, Tarim Basin, and it was calculated that the critical expulsion intensity range from 6.05 × 108 m3/km2 to 10.07 × 108 m3/km2. The critical gas charging force first increases with depth and later decreases with greater depths. The distribution range of effective gas source rocks and total expelled gas volume can be determined based on this threshold. This method provides new insight into and method for predicting favourable tight‐sand gas‐bearing regions and estimating their resource potentials. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
86.
Combined with the actual geological settings, tight oil is the oil that occurs in shale or tight reservoirs, which has permeability less than 1 mD and is interbedded with or close to shale, including tight dolomitic oil and shale oil. The Fengcheng area (FA), at the northwest margin of the Junggar Basin, northwest China, has made significant progress in the tight oil exploration of the Fengcheng (P1f) Formation recently, which indicates that the tight oil resources have good exploration prospects. Whereas the lack of recognition of hydrocarbon generation and expulsion characteristics of Permian P1f source rocks results in the misunderstanding of tight oil resource potential. Based on the comprehensive analysis of geological and geochemical characteristics of wells, seismic inversion, sedimentary facies, tectonic burial depth, etc., the characteristics of P1f source rocks were investigated, and the horizontal distributions of the following aspects were predicted: the thickness of source rocks, abundance and type of organic matter. And on this basis, an improved hydrocarbon generation potential methodology together with basin simulation techniques was applied to unravel the petroleum generation and expulsion characteristics of P1f source rocks in FA. Results show that the P1f source rocks distribute widely (up to 2039 km2), are thick (up to 260 m), have high total organic content (TOC, ranging from 0.15 to 4 wt%), are dominated by type II kerogen and have entered into low mature–mature stage. The modeling results indicate that the source rocks reached hydrocarbon generation threshold and hydrocarbon expulsion threshold at 0.5% Ro and 0.85% Ro and the comprehensive hydrocarbon expulsion efficiency was about 46%. The amount of generation and expulsion from the P1f source rocks was 31.85 × 108 and 15.31 × 108 t, respectively, with a residual amount of 16.54 × 108 t within the source rocks. Volumetrically, the geological resource of shale oil is up to 15.65 × 108 t. Small differences between the amounts calculated by the volumetric method compared with that by hydrocarbon generation potential methodology may be due to other oil accumulations present within interbedded sands associated with the oil shales. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
87.
We have analyzed the continuum emission of limb spectra acquired by the Cassini/CIRS infrared spectrometer in order to derive information on haze extinction in the 3–0.02 mbar range (∼150–350 km). We focused on the 600–1420 cm−1 spectral range and studied nine different limb observations acquired during the Cassini nominal mission at 55°S, 20°S, 5°N, 30°N, 40°N, 45°N, 55°N, 70°N and 80°N. By means of an inversion algorithm solving the radiative transfer equation, we derived the vertical profiles of haze extinction coefficients from 17 spectral ranges of 20-cm−1 wide at each of the nine latitudes. At a given latitude, all extinction vertical profiles retrieved from various spectral intervals between 600 and 1120 cm−1 display similar vertical slopes implying similar spectral characteristics of the material at all altitudes. We calculated a mean vertical extinction profile for each latitude and derived the ratio of the haze scale height (Hhaze) to the pressure scale height (Hgas) as a function of altitude. We inferred Hhaze/Hgas values varying from 0.8 to 2.4. The aerosol scale height varies with altitude and also with latitude. Overall, the haze extinction does not show strong latitudinal variations but, at 1 mbar, an increase by a factor of 1.5 is observed at the north pole compared to high southern latitudes. The vertical optical depths at 0.5 and 1.7 mbar increase from 55°S to 5°N, remain constant between 5°N and 30°N and display little variation at higher latitudes, except the presence of a slight local maximum at 45°N. The spectral dependence of the haze vertical optical depth is uniform with latitude and displays three main spectral features centered at 630 cm−1, 745 cm−1 and 1390 cm−1, the latter showing a wide tail extending down to ∼1000 cm−1. From 600 to 750 cm−1, the optical depth increases by a factor of 3 in contrast with the absorbance of laboratory tholins, which is generally constant. We derived the mass mixing ratio profiles of haze at the nine latitudes. Below the 0.4-mbar level all mass mixing ratio profiles increase with height. Above this pressure level, the profiles at 40°N, 45°N, 55°N, at the edge of the polar vortex, display a decrease-with-height whereas the other profiles increase. The global increase with height of the haze mass mixing ratio suggest a source at high altitudes and a sink at low altitudes. An enrichment of haze is observed at 0.1 mbar around the equator, which could be due to a more efficient photochemistry because of the strongest insolation there or an accumulation of haze due to a balance between sedimentation and upward vertical drag.  相似文献   
88.
本文对长庆油田测井仪器遇卡的种类、遇卡的具体原因、预防遇卡事故的措施、解卡的处理方法及解卡的理论分析等方面进行了阐述,主要目的是提高测井效率,降低安全风险,确保裸眼井筒作业优质高效.  相似文献   
89.
浙江八面山萤石矿床流体包裹体地球化学研究   总被引:2,自引:1,他引:1  
八面山萤石矿床流体包裹体可分为三大类型:Ⅰ气液包裹体,Ⅱ气体包裹体,Ⅲ含子矿物的多相包裹体;矿床成矿温度变化不大,主要集中在120~240°C之间。细粒条带状萤石矿石包裹体温度变化在115~250℃之间;巨晶块状萤石矿石和石英脉型萤石矿石包裹体温度集中在135~170℃之间。萤石矿床流体包裹体以低盐度成矿流体为主。成矿过程中起作用的成矿流体为KCl-H2O体系和CO2-CaF2-H2O体系,成矿溶液的离子类型属K+-Ca2+-HCO--F-型,KCl-H2O体系反映岩浆期后热液作用的结果,而CO2-CaF2-H2O体系可能反映了寒武纪矿源层成矿体系。通过包裹体研究,认为八面山萤石矿床是受地层-岩体-层间断裂共同控制"三位一体"的热液成因矿床。  相似文献   
90.
了解高喷注浆过程及其效果对于实际工程具有重要意义,而高密度电法是对其实施动态监测的一项有效手段。基于Archie法则,对高密度电法所测得之数据进行转换、预处理和反演,可得到注浆过程各时段的电阻率以及不同时段的电阻率剖面图。结果表明,注浆区测点的基体电阻率曲线与水泥浆电阻率变化曲线具有相似的特征,而非注浆区的测点则没有。因而高密度电法可广泛应用于监测注浆过程,并对其效果进行检测,从而为探寻地下工程的可视化施工方式提供技术参考。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号