全文获取类型
收费全文 | 15703篇 |
免费 | 3451篇 |
国内免费 | 5300篇 |
专业分类
测绘学 | 967篇 |
大气科学 | 1945篇 |
地球物理 | 2564篇 |
地质学 | 12126篇 |
海洋学 | 3077篇 |
天文学 | 34篇 |
综合类 | 1212篇 |
自然地理 | 2529篇 |
出版年
2024年 | 77篇 |
2023年 | 287篇 |
2022年 | 677篇 |
2021年 | 787篇 |
2020年 | 778篇 |
2019年 | 1027篇 |
2018年 | 805篇 |
2017年 | 853篇 |
2016年 | 897篇 |
2015年 | 940篇 |
2014年 | 1218篇 |
2013年 | 1101篇 |
2012年 | 1183篇 |
2011年 | 1210篇 |
2010年 | 983篇 |
2009年 | 1072篇 |
2008年 | 1130篇 |
2007年 | 1135篇 |
2006年 | 1152篇 |
2005年 | 949篇 |
2004年 | 867篇 |
2003年 | 755篇 |
2002年 | 673篇 |
2001年 | 606篇 |
2000年 | 530篇 |
1999年 | 451篇 |
1998年 | 397篇 |
1997年 | 356篇 |
1996年 | 295篇 |
1995年 | 241篇 |
1994年 | 257篇 |
1993年 | 200篇 |
1992年 | 170篇 |
1991年 | 122篇 |
1990年 | 60篇 |
1989年 | 51篇 |
1988年 | 52篇 |
1987年 | 29篇 |
1986年 | 17篇 |
1985年 | 16篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 1篇 |
1979年 | 8篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1954年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
掌握澳门附近海域沉积物的污染状况及特征,对于合理安排澳门海洋海岸工程疏浚泥的海洋倾倒,防止造成海洋污染有十分重要的意义。根据1997—1999年连续三年对澳门附近主要区域的海洋沉积物采样测定结果,通过分析认为澳门附近海域沉积物污染具有下列特征:1)沉积物中重金属和油类含量普遍较高,除了总Hg外均高于珠江口海区的其他港口;2)沉积物中污染物的分布受人类活动的影响明显,澳门内港受船只排污、码头作业、陆地工业和生活污水排放的影响,是澳门附近海域沉积物污染最为严重区域;3)受水质交换的影响明显,澳门外港、路环岛东北等区域受珠江径流影响水质交换较快,沉积物中污染物的含量较低,而内港由于水质交换较差,沉积物中污染物的含量相对较高;4)与沉积物的成分组成(吸附)有关,大部分污染物与沉积物中粉砂有较好的相关性,表明粉砂对污染物质有较广泛性的吸附能力,尤其是Cu、Zn、Cd、油类、有机质。 相似文献
22.
利用高光谱数据进行植被生化成分反演方法研究 总被引:3,自引:0,他引:3
高光谱数据包含着丰富光谱信息,能够定量地分析物质成分[1]。由高光谱数据,可以运用多元逐步线性回归方法反演植被生化组分含量,从而达到监测植被生长状况的目的[2]。本文具体介绍了多元逐步线性回归方法,及其在氮、木质素和纤维素含量估算中的应用。 相似文献
23.
FUZZY COMPREHENSIVE EVALUATION OF CONTAINER TRANSPORTATION MODES ALONG THE CHANGJIANG RIVER MAIN LINE AND ITS DELTA AREA 总被引:1,自引:0,他引:1
ZHANGShi-yu XIAOHan-liang 《中国地理科学(英文版)》2003,13(3):259-261
The Changjiang River (Yangtze) is one of the fastest growth areas of container transportation in Chi-na. Rail, road and water transportation have competed against each other for container transportation in the Chang-jiang River main line and its delta area. It is of significance to assess these different transportation modes scientifi-cally in order to organize container transportation efficiently in this area and make decision for integral plan and construction of transportation system in this area. This paper outlines application of fuzzy comprehensive evaluation to appraise different modes of typical direction of containers. Twelve assessment indexes were decided. Membership functions were formulated. Evaluation results indicated that road transportation was optimal mode in the Changjiang River delta area, however water transportation was the primary way in the Changjiang River main line. 相似文献
24.
本文系统描述了中国南部二叠、三叠纪“混生生物群”。根据笔者的统计,目前巳经发现有“二叠纪型”分子36属53种与三叠纪菊石、双壳类、牙形剌共生。 笔者认为中国南部可以以牙形剌Anchignathodus parvus 的出现作为三叠系的底界,双壳类Pteria ussurica variabilis,菊石 Hypophiceras的出现可以作为三叠系开始的辅助标志。文中还将这一界线与世界上其它地区的二叠、三叠系界线进行了对比。 相似文献
25.
In the northern limb of the 2.06-Ga Bushveld Complex, the Platreef is a platinum group elements (PGE)-, Cu-, and Ni-mineralized
zone of pyroxenite that developed at the intrusion margin. From north to south, the footwall rocks of the Platreef change
from Archaean granite to dolomite, hornfels, and quartzite. Where the footwall is granite, the Sr-isotope system is more strongly
perturbed than where the footwall is Sr-poor dolomite, in which samples show an approximate isochron relationship. The Nd-isotope
system for samples of pyroxenite and hanging wall norite shows an approximate isochron relationship with an implied age of
2.17 ± 0.2 Ga and initial Nd-isotope ratio of 0.5095. Assuming an age of 2.06 Ga, the ɛNd values range from −6.2 to −9.6 (ave.
−7.8, n = 17) and on average are slightly more negative than the Main Zone of the Bushveld. These data are consistent with local
contamination of an already contaminated magma of Main Zone composition. The similarity in isotope composition between the
Platreef pyroxenites and the hanging wall norites suggests a common origin. Where the country rock is dolomite, the Platreef
has generally higher plagioclase and pyroxene δ
18O values, and this indicates assimilation of the immediate footwall. Throughout the Platreef, there is considerable petrographic
evidence for sub-solidus interaction with fluids, and the Δ
plagioclase–pyroxene values range from −2 to +6, which indicates interaction at both high and low temperatures. Whole-rock and mineral δD values suggest that the Platreef interacted with both magmatic and meteoric water, and the lack of disturbance to the Sr-isotope
system suggests that fluid–rock interaction took place soon after emplacement. Where the footwall is granite, less negative
δD values suggest a greater involvement of meteoric water. Consistently higher values of Δ
plagioclase–pyroxene in the Platreef pyroxenites and hanging wall norites in contact with dolomite suggest prolonged interaction with CO2-rich fluid derived from decarbonation of the footwall rocks. The overprint of post crystallization fluid–rock interaction
is the probable cause of the previously documented lack of correlation between PGE and sulfide content on the small scale.
The Platreef in contact with dolomite is the focus of the highest PGE grades, and this suggests that dolomite contamination
played a role in PGE concentration and deposition, but the exact link remains obscure. It is a possibility that the CO2 produced by decarbonation of assimilated dolomite enhanced the process of PGE scavenging by sulfide precipitation. 相似文献
26.
D. Lange J. Cembrano A. Rietbrock C. Haberland T. Dahm K. Bataille 《Tectonophysics》2008,455(1-4):14-24
A temporal seismic network recorded local seismicity along a 130 km long segment of the transpressional dextral strike-slip Liquiñe-Ofqui fault zone (LOFZ) in southern Chile. Seventy five shallow crustal events with magnitudes up to Mw 3.8 and depths shallower than 25 km were observed in an 11-month period mainly occurring in different clusters. Those clusters are spatially related to the LOFZ, to the volcanoes Chaitén, Michinmahuida and Corcovado, and to active faulting on secondary faults. Further activity along the LOFZ is indicated by individual events located in direct vicinity of the surface expression of the LOFZ. Focal mechanisms were calculated using deviatoric moment tensor inversion of body wave amplitude spectra which mostly yield strike-slip mechanisms indicating a NE–SW direction of the P-axis for the LOFZ at this latitude. The seismic activity reveals the present-day activity of the fault zone. The recent Mw 6.2 event near Puerto Aysén, Southern Chile at 45.4°S on April 21, 2007 shows that the LOFZ is also capable of producing large magnitude earthquakes and therefore imposing significant seismic hazard to this region. 相似文献
27.
28.
藏北南羌塘盆地毕洛错地区下侏罗统曲色组石膏岩层 总被引:1,自引:0,他引:1
对西藏自治区北部南羌塘盆地毕洛错地区下侏罗统曲色组石膏岩层进行了研究。根据岩石地层和生物地层资料,确认毕洛错地区的石膏岩层和油页岩为曲色组的一部分,地质时代为早侏罗世,并确认下侏罗统曲色组在区域上可能是寻找油气、油页岩资源的重要层位之一。 相似文献
29.
华南寒武系年代地层系统的修订及相关问题 总被引:10,自引:3,他引:7
将早先提出的华南寒武系4统9阶的年代地层系统,修订成4统10阶,除王村阶的底界略高于全球鼓山阶(Drumian Stage)的底界外,其余界线都与目前的全球4统10阶的年代地层界线一致。新系统采纳了在我国华南建立的全球芙蓉统、排碧阶和古丈阶,在原桃源阶的上部另建"牛车河阶"。原王村阶和桃源阶的时限因这一修订有所缩减。全球鼓山阶的底界与台江阶上部的Ptychagnostus atavus带底界可以精确对比。滇东统包含晋宁阶和梅树村阶(狭义)两个年代地层单位,晋宁阶的底界采用全球寒武系的底界,梅树村阶的底界采用罗惠麟等1994年正式修订后的定义,即位于梅树村剖面的"B"点。梅树村阶的原始定义仅指梅树村剖面的磷块岩层(即现今的中谊村段),它的底界高于现在的以Tricophycus pedum首现定义的全球寒武系底界。 相似文献
30.