全文获取类型
收费全文 | 4690篇 |
免费 | 695篇 |
国内免费 | 1520篇 |
专业分类
测绘学 | 52篇 |
大气科学 | 119篇 |
地球物理 | 404篇 |
地质学 | 4820篇 |
海洋学 | 694篇 |
天文学 | 283篇 |
综合类 | 255篇 |
自然地理 | 278篇 |
出版年
2024年 | 23篇 |
2023年 | 59篇 |
2022年 | 139篇 |
2021年 | 185篇 |
2020年 | 166篇 |
2019年 | 225篇 |
2018年 | 183篇 |
2017年 | 157篇 |
2016年 | 235篇 |
2015年 | 196篇 |
2014年 | 337篇 |
2013年 | 283篇 |
2012年 | 298篇 |
2011年 | 291篇 |
2010年 | 257篇 |
2009年 | 285篇 |
2008年 | 333篇 |
2007年 | 332篇 |
2006年 | 314篇 |
2005年 | 317篇 |
2004年 | 271篇 |
2003年 | 243篇 |
2002年 | 214篇 |
2001年 | 176篇 |
2000年 | 232篇 |
1999年 | 180篇 |
1998年 | 194篇 |
1997年 | 141篇 |
1996年 | 124篇 |
1995年 | 97篇 |
1994年 | 89篇 |
1993年 | 72篇 |
1992年 | 68篇 |
1991年 | 34篇 |
1990年 | 39篇 |
1989年 | 14篇 |
1988年 | 23篇 |
1987年 | 17篇 |
1986年 | 16篇 |
1985年 | 14篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有6905条查询结果,搜索用时 265 毫秒
991.
苏北废黄河三角洲经历了150多a的侵蚀演变过程,目前仍处在侵蚀演变中.据2007-08和2008-07废黄河口附近断面调查结果显示,沉积类型出现粗化趋势,10 m以浅的浅水区,砂粒含量达60%以上,平均粒径达0.06 mm,物质粗化显著,岸滩呈现了强烈的波蚀作用;10 m以深至15 m的深水区,泥粒含量增多,平均粒径为... 相似文献
992.
LI Xujun FAN Zhenhua FAN Wenliang REN Shanfeng . College of Earth Sciences Jilin University Changchun China . Haigou Gold Mining Company Ltd. Antu Jilin 《东北亚地学研究》2011,(2)
Lode 28 is the largest gold-bearing quartz vein in Haigou gold deposit,and the lode itself contains more than 30t of gold. Geochemical study shows that 12 trace elements related gold mineralization can be divided into 5 metallogenic factors(element assemblages) .The high values of F1,F2 and F4 together indicate overlapped of multiple stages of gold mineralization,revealing high potential of gold mineralization at depth;the single high value of F4 represents the root of an existing ore body while high values... 相似文献
993.
Geochemistry and genesis on saturated hydrocarbon of crude oils in Gas Hure Oilfield in Qaidam Basin
Gas Hure Oilfield is the biggest one in the Qaidam Basin.Through intensive sampling and GC-MS analysis,the authors analyzed the geochemical characteristics of the crude oils in the Gas Hure Oilfield.The results show that the crude oils have even-odd carbon predominance for n-alkanes.In shallow reservoir,part of crude oils suffered biogenic degradation.As for normal oils,they have low Pr/Ph ratios with abundant gammacerane and C35 homohopane,which indicate that the crude oils are formed in strong reducing sa... 相似文献
994.
Phytoplankton pigment patterns and community composition in the northern South China Sea during winter 总被引:1,自引:0,他引:1
Phytoplankton pigment patterns and community composition were investigated in the northern South China Sea using high-performance liquid chromatography and the CHEMTAX software from February 11 to 23, 2009. We recognized four different vertical distribution patterns of pigments: chlorophyll a (Chl a)-like type, divinyl chlorophyll a (DV Chl a) type, even distribution type, and surface type. The average value of ratios of accessory photo-protective pigments (APP) to accessory photo-synthetic pigments was 0.89±0.63 in the upper 50 m and 0.16±0.06 below 50 m depth. With increasing depth, APP decreased and photo-synthetically active radiation was attenuated. There was an obvious succession in the phytoplankton community from inshore to the open sea. Diatoms were dominant in the inshore region, while pelagophytes, Prochlorococcus, cyanobacteria and prymnesiophytes were dominant in the open sea. The vertical distribution of phytoplankton also differed greatly from inshore to the open sea. In the coastal and shelf region, diatoms were important components in the whole water column. Cyanobacteria also had a high abundance at the Subsurface Chlorophyll a Maxima (SCM) in the shelf region. In the slope and open sea, Prochlorococcus and cyanobacteria were important groups above the SCM, while pelagophytes dominated below the SCM. 相似文献
995.
在对应用集成及其发展分析的基础上,将Web Services技术运用到空间信息应用集成,提出和建立了面向服务的空间信息应用集成框架,包括Web应用层、服务集成层、服务层和UDDI等4个组成部分。通过该框架,可以实现空间信息集成、服务集成和应用集成。论文解决了空间信息应用集成框架中的2个关键问题:(1)提出了分别从数据层次和业务层次对原有系统集成的解决方案,在数据层次上,提出了基于XML/GML的空间数据封装和基于Web服务接口的空间数据封装策略;在业务层次上,提出根据系统的功能模块和业务逻辑分别进行封装的策略;(2)提出了空间信息Web服务链接和服务组合的串联、并联和混联模式,通过三种模式服务链的设计,可以实现多个服务的链接和组合,从而完成空间信息以及应用集成。 相似文献
996.
辽宁瓦房店金刚石矿区金伯利岩中的石榴石一直被当作镁铝榴石。为了确定矿区颜色复杂的石榴石种类,本文对矿区的石榴石进行了系统的采样分析,测定了112件石榴石样品的晶胞参数、50件样品的微区化学成分和40件样品的红外光谱。利用石榴石晶胞参数、红外光谱、化学成分和化学分子式方法对矿区石榴石进行分类,结果显示:晶胞参数分类法误差大,容易得出错误结论;红外图谱分类法准确度不高,只能作为参考方法;化学成分分类法太过笼统,达不到详细划分石榴石种类的目的;化学分子式分类法可把矿区的石榴石详细划分6个矿种:镁钙铁-铝铬铁榴石、镁铁钙-铝铬铁榴石、镁钙铁-铝铬榴石、镁钙-铝铬铁镁榴石、镁铁钙-铝铬榴石、镁铁钙-铝铁铬榴石,每种石榴石都充分反映了A、B离子的种类及占位特征,是4种分类方法中最为科学的方法。研究认为瓦房店金刚石矿区金伯利岩中石榴石A端元成分以Mg2+离子占位为主;B端元成分以Al3+离子占位为主。由于阳离子替代普遍,A、B端元成分复杂,瓦房店金伯利岩中不存在单纯意义上的镁铝榴石。 相似文献
997.
湘东锡田A型花岗岩的年代学、Hf同位素、地球化学特征及其地质意义 总被引:5,自引:1,他引:4
对湘东锡田岩体进行的LA-ICP-MS定年结果表明,2个第一期中(细)粒斑状黑云母二长花岗岩样品的年龄分别为(220.9±0.6) Ma及(220.7±0.7)Ma;第二期中细粒二云母二长花岗岩的年龄为(154.4±0.7)Ma.两期花岗岩均为高钾、富碱、弱过铝质岩石.稀土元素总量较高,富集U、Th,亏损Ti、P等高场强元素和Ba、Sr等大离子亲石元素,具高的104 Ga/Al,显示A型花岗岩特征.印支期花岗岩略富集轻稀土元素,Eu异常较弱;燕山期花岗岩轻、重稀土元素分异不明显,Eu异常显著.Hf同位素研究显示,两期次花岗岩均具有较低的εHf(t)(-4.91~-11.04),亏损地幔二阶段模式年龄集中在1.6~1.8 Ga,与华夏地块古老的变质基底年龄一致.因此,锡田岩体是华夏地块古元古代地壳物质在伸展的构造背景下部分熔融的产物.锡田A型花岗岩复式岩体的确定,对于研究湖南东部在中生代印支、燕山两期构造事件中所处的构造背景具有重要意义,同时也为华南地区存在印支期A型花岗岩钨锡成矿作用增加了证据. 相似文献
998.
We present absorption cross sections of propane (C3H8) at temperatures from 145 K to 297 K in the 690–1550 cm−1 region. Pure and N2-broadened spectra were measured at pressures from 3 Torr to 742 Torr using a Bruker IFS125 FT-IR spectrometer at JPL. The gas absorption cell, developed at Connecticut College, was cooled by a closed-cycle helium refrigerator. The cross sections were measured and compiled for individual spectra recorded at various experimental conditions covering the planetary atmosphere and Titan. In addition to the cross sections, a propane pseudoline list with a frequency grid of 0.005 cm−1, was fitted to the 34 laboratory spectra. Line intensities and lower state energies were retrieved for each line, assuming a constant width. Validation tests showed that the pseudoline list reproduces discrete absorption features and continuum, the latter contributed by numerous weak and hot band features, in most of the observed spectra within 3%. Based on the pseudoline list, the total intensity in the 690–1550 cm−1 region was determined to be 52.93 (±3%) × 10−19 cm−1/(molecule cm−2) at 296 K; this value is within 3% of the average from four earlier studies. Finally, the merit of the pseudoline approach is addressed for heavy polyatomic molecules in support of spectroscopic observation of atmospheres of Titan and other planets. The cold cross sections will be submitted to the HITRAN database (hitran.harvard.edu), and the list of C3H8 pseudolines will be available from a MK-IV website of JPL (http://mark4sun.jpl.nasa.gov/data/spec/Pseudo). 相似文献
999.
André C. Colonese Giovanni Zanchetta Catherine Perlès Russell N. Drysdale Giuseppe Manganelli Ilaria Baneschi Elissavet Dotsika Hélène Valladas 《Quaternary Research》2013
This paper investigates the stable isotopic composition from late Pleistocene–Holocene (~ 13 to ~ 10.5 cal ka BP) shells of the land snail Helix figulina, from Franchthi Cave (Greece). It explores the palaeoclimatic and palaeoenvironmental implications of the isotope palaeoecology of archaeological shells at the time of human occupation of the cave. Modern shells from around the cave were also analysed and their isotopic signatures compared with those of the archaeological shells. The carbon isotope composition of modern shells depicts the consumption of C3 vegetation. Shell oxygen isotopic values are consistent with other Mediterranean snail shells from coastal areas. Combining empirical linear regression and an evaporative model, the δ18Os suggest that modern snails in the study area are active during periods of higher relative humidity and lower rainfall δ18O, probably at night. Late glacial and early Holocene δ18Os show lower values compared to modern ones. Early Holocene δ18Os values likely track enhanced moisture and isotopic changes in the precipitation source. By contrast, lower late glacial δ18O could reflect lower temperatures and δ18Op, compared to the present day. Shell carbon isotope values indicate the presence of C3 vegetation as main source of carbon to late glacial and early Holocene snails. 相似文献
1000.
阿荣旗谢永贵家庭农场一带土壤化探的数学地质异常提取 总被引:2,自引:0,他引:2
应用数学地质方法对阿荣旗谢永贵家庭农场一带1:1万土壤化探数据进行了分析,得出该区异常主要受中下泥盆统泥鳅河组泥质板岩、沙质板岩与安山岩体接触带形成的矿化异常控制。研究区土壤地球化学R型聚类分析表明,10种微量元素可以分为3类:第一类为Cu、Ag、Au、As、Mo,第二类为Pb、Zn、Bi、Hg,还有一类为Sb。第一类反映了石英脉或蚀变岩型矿化的指示元素组合,第二类反映了中温的矿化元素组合。对研究区元素采用因子得分趋势面分析提取其反映局部异常变化的剩余异常,再对剩余异常进行多因子叠加法成图。在该区共圈定出4个异常靶区,以石英脉或蚀变岩型金矿化为主,是下一步重点的找矿区域。 相似文献