全文获取类型
收费全文 | 6061篇 |
免费 | 1223篇 |
国内免费 | 1779篇 |
专业分类
测绘学 | 445篇 |
大气科学 | 1404篇 |
地球物理 | 1507篇 |
地质学 | 3358篇 |
海洋学 | 644篇 |
天文学 | 281篇 |
综合类 | 722篇 |
自然地理 | 702篇 |
出版年
2024年 | 40篇 |
2023年 | 151篇 |
2022年 | 291篇 |
2021年 | 369篇 |
2020年 | 292篇 |
2019年 | 298篇 |
2018年 | 405篇 |
2017年 | 333篇 |
2016年 | 382篇 |
2015年 | 343篇 |
2014年 | 371篇 |
2013年 | 379篇 |
2012年 | 317篇 |
2011年 | 331篇 |
2010年 | 407篇 |
2009年 | 347篇 |
2008年 | 324篇 |
2007年 | 335篇 |
2006年 | 249篇 |
2005年 | 240篇 |
2004年 | 192篇 |
2003年 | 177篇 |
2002年 | 154篇 |
2001年 | 181篇 |
2000年 | 194篇 |
1999年 | 256篇 |
1998年 | 250篇 |
1997年 | 236篇 |
1996年 | 209篇 |
1995年 | 158篇 |
1994年 | 152篇 |
1993年 | 146篇 |
1992年 | 113篇 |
1991年 | 88篇 |
1990年 | 62篇 |
1989年 | 66篇 |
1988年 | 59篇 |
1987年 | 31篇 |
1986年 | 32篇 |
1985年 | 20篇 |
1984年 | 14篇 |
1983年 | 14篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1975年 | 7篇 |
1960年 | 4篇 |
1959年 | 2篇 |
1958年 | 7篇 |
排序方式: 共有9063条查询结果,搜索用时 15 毫秒
131.
132.
133.
乌和尔楚鲁图钼矿床位于国内重要的二连东乌旗钼矿成矿带中,为近几年新发现的斑岩型钼矿床.本次就该矿床成矿岩体的地球化学及其U-Pb年代学开展相关研究.结果表明: 矿区中的成矿岩体属过铝质、高钾钙碱性系列;富集大离子亲石元素(LILE)、亏损高场强元素(HFSE),具有与南岭型花岗岩相似的地球化学特征.锆石LA-ICP-MS U-Pb定年显示,与乌和尔楚鲁图钼矿床成矿有关的花岗斑岩形成于中侏罗世((160 ± 1)Ma).因此,可推测乌和尔楚鲁图钼矿床斑岩型钼矿的成矿时代为燕山早期.综合研究认为乌和尔楚鲁图斑岩型钼矿床形成于后碰撞的构造环境. 相似文献
134.
Zhaochu Hu Yongsheng Liu Ming Li Shan Gao Laishi Zhao 《Geostandards and Geoanalytical Research》2009,33(3):319-335
New analytical results are reported for rarely determined elements Be, B, Ge, As, Mo, Rh, Pd, Ag, Cd, In, Sn, Sb, W, Re, Ir, Pt, Au, Tl and Bi in MPI‐DING and USGS (BCR‐2G, BHVO‐2G, BIR‐1G) silicate glasses and the NIST SRM 610‐614 synthetic soda‐lime glasses using 193 nm ArF excimer laser ablation and quadrupole ICP‐MS. The method used involved external calibration against GOR132‐G for Ir and NIST SRM 610 for other elements, internal standardisation using Ca, and ablation with a crater diameter of 160 μm and a pulsed laser repetition rate of 10 Hz. Small amounts of nitrogen (5 ml min?1) were added to the central channel gas of the plasma to improve the limits of detection for most of these elements by a factor of 1.2–2.5 and to reduce the oxide interference level to 0.02% (ThO+/Th+). Under these conditions, the LODs for most of these rarely determined elements were within the range 0.1 to 10 ng g?1. The operating conditions that were required to minimise ICP‐induced fractionation (U+/Th+≈ 1) in the mode without nitrogen were accompanied by a 50–60% reduction in sensitivity for elements such as Ca, Au and Pt. In contrast, ICP‐induced fractionation could be minimised (U+/Th+≈ 1) with no loss of analyte sensitivity in the nitrogen mode. Interferences of CuAr+, ZnAr+, Cd+, Pb2+ and Sn+ on Pd+, Rh+, Cd+ and In+ were corrected. Oxide interferences were not considered due to their lower production rate. Analytical precision, as given by one relative standard deviation (% RSD) was less than 15% for most of the elements present at concentrations greater than 0.1 μg g?1. A significant negative correlation was found between logarithmic concentration and logarithmic RSD, with a correlation coefficient of ?0.76. This trend indicates that possible chemical heterogeneities for most of these elements are smaller than the analytical uncertainty. Our results for Be, B, Ge, Sb and W are generally in good agreement with their reference values. In contrast, other elements in many of the reference glasses have only information values, upper limits or even no values, which restrict any detailed evaluation of the accuracy of the determined values. However, concentrations from multiple isotopes of one element analysed in this study showed excellent agreement, which guarantee the quality of our data to a certain extent. 相似文献
135.
Trace Elements in Fluid Inclusions in the Carlin—Type Gold Deposits,Southwestern Guizhou Province 总被引:2,自引:1,他引:2
Fluid inclusions in quartz from the Lannigou and Yata Carlin-type gold deposits in southwestern Guizhou were analyzed by inductively coupled plasma-mass spectrometry for their trace elements(Co,Ni,Cu,Pb,Zn,Pt,etc.).The results show that quartz fluid inclusions entrapped at different ore-forming stages contain higher Co,Ni,Cu,Pb and Zn.It has been found for the first time that the ore-forming fluids responsible for the Carlin-type gold deposits are rich in Pt.From this it can be concluded that basic volcanic rocks seem to be one of the important sources of ore-forming materials for the Carlin-type gold deposits. 相似文献
136.
山东招远大尹格庄金矿成矿流体特征 总被引:18,自引:13,他引:18
大尹格庄金矿位于中国胶北地体西北部招平断裂带下盘的蚀变花岗质碎裂岩 (绢英岩 )带中 ,断裂上盘为胶东群变质岩系。金主要产于黄铁绢英岩和黄铁矿±多金属硫化物 石英±碳酸盐脉 -细网脉中 ,构成细脉 -浸染状矿石。对蚀变围岩和金矿石中流体包裹体的研究表明钾长石化岩 (钾长石 -石英脉 )和绢英岩 (第 I和第 II阶段 )的石英中含有丰富的 CO2 -H2 O包裹体 ,而金 -硫化物矿石和石英 -碳酸盐脉 (第 III和第 IV阶段 )中 CO2 - H2 O包裹体数量逐渐减少。显微测温指示 ,钾长石化岩和绢英岩石英中的 CO2 - H2 O包裹体的均一温度范围为 2 80~ 36 0℃ ;而金 -黄铜矿和金 -方铅矿 -闪锌矿矿石中包裹体的均一温度分别为 2 40~ 2 75℃和 180~ 2 5 0℃。显微测温和激光拉曼探针分析表明 ,第 I和第 II阶段的成矿流体含 10~ 2 5mol% CO2 ;而第 III和第 IV阶段的含 <5~ 10 mol% CO2 ,并含少量至可观数量 CH4,H2 S和 SO2 等。广泛的黄铁矿化、碳酸盐化蚀变以及缺乏较高盐度的水包裹体说明金很可能是以硫络合物和碳络合物形式被搬运。金的沉淀与温度下降、由裂隙的(重复 )开放引起明显的压力降低和原始流体的不混溶作用有关 ,具多阶段成矿特点 相似文献
137.
Successional stages of biological soil crusts and their microstructure variability in Shapotou region (China) 总被引:5,自引:1,他引:5
In order to investigate succession of biological soil crusts (BSCs) and their microstructure variability, we conducted this
work in Shapotou revegetation region at the southeast edge of Tengger Deser. The results showed that BSCs generally succeeded
as a pathway of “Algae crusts, algae–lichen crusts, lichen crusts, lichen–moss crusts and moss crusts”. Occasionally mosses
directly occurred on algae crusts, and BSCs succeeded from algae crusts to moss crusts. Crust vertical stratification was
a common phenomenon, from top to bottom an inorganic layer, algae-dense layer and algae-sparse layer were divided in algae
crusts; a thallus layer, rhizoid layer and sub-rhizoid layer in lichen crusts; a “stem-leaf” layer, rhizoid layer and sub-rhizoid
layer in moss crusts, respectively. The main crust binding organisms varied from filamental cyanobacteria (dominated by Microcoleus) in algae crusts to lichen rhizoids, free-living cyanobacterial filaments and fungal hyphaes in lichen crusts, and to moss
rhizoids and fungal hyphaes in moss crusts. The dominant phototrophic organisms varied from Microcoleus (algae) in algae crusts to Collema (lichens) in lichen crusts, and to Bryum (or Didymodon and Tortula; mosses) in moss crusts. Total phototrophic biomass increased while the free-living algal biomass decreased with the succession
of BSCs. In addition, exopolysaccharides and fine particles accumulated in the course of development and succession of BSCs,
all of which lead to a gradual increase in crust thickness and porosity, while decrease in the bulk density. 相似文献
138.
笔者对沧参1井石炭、二叠纪地层中的粘土矿物特征进行研究,并对不同深度的粘土矿物进行了K-Ar、40Ar-39Ar及Rb-Sr法同位素地质年龄测定,得出至少存在三期伊利石的结论;碎屑伊利石,年龄为400Ma左右,在235—243Ma时受到热扰动;海西期末一印支早期形成的高温伊利石,其年龄为214—234Ma,在145Ma时经受一次热扰动;早侏罗世时期形成的伊利石,年龄为180Ma左右,分布比较普遍。这一研究结果无疑将有助于深入探讨区域地热场的演化,以及进一步研究有关地层的生、储油气能力。 相似文献
139.
硅橡胶作为特种橡胶体系的一个重要成员,以其耐高温、耐寒、耐候及电气特性等优良品质得到国防、航天航空、电子、医疗卫生等行业的青睐[1]。然而,目前工业上主要采用价格昂贵的气相白炭黑作硅橡胶的增强剂,使硅橡胶制品成本偏高,限制了硅橡胶的普及应用,阻碍了硅... 相似文献
140.
利用电子显微镜(EM)及能谱仪(EDS),分析研究了变生热液形成的载金石英的化学成分、离子扩散作用以及金在石英中的赋存状态等问题,探讨了它们的形成和变化机理。研究结果表明:Al~(3+)、Ti~(3+)、TFe、Na~(+)、K~(+)、Ca~(2+)等在石英中为类质同像混入物;石英和黄铁矿之间的离子相互扩散作用,表现为石英中Al离子的带出和Fe离子的带入,黄铁矿中Fe离子的带出和Al离子的带入;石英中呈分散状态分布的金主要为离子金,它们充填在石英结构中,起平衡电价的作用。 相似文献