全文获取类型
收费全文 | 10309篇 |
免费 | 2117篇 |
国内免费 | 2253篇 |
专业分类
测绘学 | 1520篇 |
大气科学 | 1707篇 |
地球物理 | 3300篇 |
地质学 | 4620篇 |
海洋学 | 1014篇 |
天文学 | 969篇 |
综合类 | 825篇 |
自然地理 | 724篇 |
出版年
2024年 | 64篇 |
2023年 | 159篇 |
2022年 | 287篇 |
2021年 | 380篇 |
2020年 | 399篇 |
2019年 | 489篇 |
2018年 | 352篇 |
2017年 | 440篇 |
2016年 | 456篇 |
2015年 | 507篇 |
2014年 | 566篇 |
2013年 | 614篇 |
2012年 | 668篇 |
2011年 | 676篇 |
2010年 | 535篇 |
2009年 | 667篇 |
2008年 | 579篇 |
2007年 | 753篇 |
2006年 | 675篇 |
2005年 | 541篇 |
2004年 | 514篇 |
2003年 | 509篇 |
2002年 | 439篇 |
2001年 | 398篇 |
2000年 | 406篇 |
1999年 | 377篇 |
1998年 | 355篇 |
1997年 | 310篇 |
1996年 | 286篇 |
1995年 | 223篇 |
1994年 | 226篇 |
1993年 | 190篇 |
1992年 | 144篇 |
1991年 | 111篇 |
1990年 | 98篇 |
1989年 | 87篇 |
1988年 | 70篇 |
1987年 | 42篇 |
1986年 | 14篇 |
1985年 | 13篇 |
1984年 | 11篇 |
1983年 | 2篇 |
1982年 | 12篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
对在上海市建设用地勘测定界过程中涉及的土地权属界线认定、原土地用途划分时所现的若干问题进行了详细探讨,同时从政策角度、技术角度提出了以上问题的相应解决途径。 相似文献
62.
邢东矿井位于太行山隆起带与华北沉陷带的过渡带,通过区域构造应力-应变场分析,本区先后经历了由挤压-拉张的变形过程,变形强度由弱到强。海西期构造应力影响较弱,印支期-中燕山期构造应力作用较为强烈,形成了大量的挤压结构面和压缩构造.燕山晚期-喜山期是构造形成的最终阶段,以拉张伸展变形为主,现今的多数正断层的断裂结构面仍保存有先期的挤压结构面特征。区内构造以断裂构造为主要形式,断层组合形式多样,这些构造形成期次不同,北西向断裂对北东向断裂具有限制作用。 相似文献
63.
在系统地分析了目前各种测震学地震预报方法科学思路的基础上,认为测震学地震预报方法基本上可以分为两大类。一类是以已经发生的一些地震作为未来可能发生的地震的“因”,即由于已经发生的地震对区域应力场的影响,导致未来发生较强地震。这一类包括的预报方法较多,如空区、条带、b值、地震迁移、相关地震等等及其由此衍生出来的各种方法。另一类是把已经发生的一些地震作为区域应力场增强的“果”,即已经发生的地震是区域应力场增强过程中的一种反映,而未来地震不一定是已经发生的地震所导致的结果。这一类包括“地震窗口”、小震群活动等方法。针对第一类方法,各种预报方法都是力图从地震三要素中提取未来地震的信息,而具体作法又都是利用地震三要素这个多维空间的某个剖面。为了从地震活动诸要素的多维空间提取综合信息,我们对每个地震加入了破裂面方位,构成了地震第四要素,并依据地震4要素建立了地震综合效应场函数。地震综合效应场函数概括了多种测震学地震预报方法的科学思路和预报经验,从而可以形成测震学的综合预报方法。 相似文献
64.
We investigate the global evolution of a turbulent protoplanetary disk incorporating the effects of Maxwell stress due to a large-scale magnetic field permeating the disk. A magnetic field is produced continuously by an dynamo and the resultant Maxwell stress assists the viscous stress in p roviding the means for disk evolution. The most striking feature of magnetized disk evolution is the presence of the surface density bulge located in the magnetic gap, the region of the disk where the degree of ionization is too low to allow for coupli ng between the magnetic field and the gas. The bulge persists for a time of the order of 105–106 yr. The presence and persistence of the surface density bulge may have important implications for the process of planet formation and the overall characteristics of resultant planetary systems.Operated by USRA under contract No. NASW-4574 with NASA. 相似文献
65.
新地球观 总被引:11,自引:0,他引:11
One of the most important achivements on science in 20th century is the new recognition on the Earth:the Earth,out of the other planets, exhibits very peculiar features because it has an extremely complex and active periphery part (surfacial layers). This periphery part is an open system sustained by inputting solar energe , which is captured , transfered and stored by life. Through the system , cyclings of matters and energe flow are driven and regulated by life activities. This system is self-equilibrated,self-controlled and far away from astrophysical and thermodynamic equilibria mainly because of life and life activities.
Development of human calture influences increasingly on流Earth's periphery system , at last , the natural biosphere that has existed for 3 billion years on the Earth's surface will inavoidably be replaced by so called "noosphere",which is man一reconstructed,man-controlled and unstable system. Thus the fate of the Earth,to a great extent,will be determined by the direction of human calture evolution.
相似文献
Development of human calture influences increasingly on流Earth's periphery system , at last , the natural biosphere that has existed for 3 billion years on the Earth's surface will inavoidably be replaced by so called "noosphere",which is man一reconstructed,man-controlled and unstable system. Thus the fate of the Earth,to a great extent,will be determined by the direction of human calture evolution.
相似文献
66.
Tectonic relation between northeastern China and the Korean peninsula revealed by interpretation of GRACE satellite gravity data 总被引:2,自引:0,他引:2
The major continental blocks in northeastern Asia are the North China block and the South China block, which have collided starting from the Korean peninsula. Geologic and geophysical interpretations reveal a well defined suture zone in northeastern China from Qinling through Dabie to Jiaodong. The discovery of high-pressure metamorphic rocks in the Hongseong area of the Korean peninsula, prominent evidence for the collision zone, indicates extension of the collision zone in northeastern China into the Korean peninsula. Interpretation of the GRACE satellite gravity dataset shows two prominent structural boundaries in the Yellow Sea. One extends from the Jiaodong Belt in eastern China to the Imjingang Belt in the Korean peninsula. The other extends from near Nanjing, eastern China, to Hongseong. Tectonic movement in or near the suture zone may be responsible for seismic activity in the western Korean peninsula and the development of the Yellow Sea sedimentary basin. 相似文献
67.
Seismic activity associated with the subducting motion of the Philippine Sea plate beneath the Kanto district, Japan 总被引:1,自引:1,他引:1
Sadaki Hori 《Tectonophysics》2006,417(1-2):85
The Pacific plate and the Philippine Sea plate overlap and subduct underneath the Kanto region, central Japan, causing complex seismic activities in the upper mantle. In this research, we used a map selection tool with a graphic display to create a data set for earthquakes caused by the subducting motion of the Philippine Sea plate that are easily determined. As a result, we determined that there are at least four earthquake groups present in the upper mantle above the Pacific plate. Major seismic activity (Group 1) has been observed throughout the Kanto region and is considered to originate in the uppermost part of mantle in the subducted Philippine Sea plate, judging from the formation of the focal region and comparison with the 3D structure of seismic velocity. The focal mechanism of these earthquakes is characterized by the down-dip compression. A second earthquake layer characterized by down-dip extension (Group 2), below the earthquakes in this group, is also noted. The focal region for those earthquakes is considered to be located at the lower part of the slab mantle, and the Pacific plate located directly below is considered to influence the activity. Earthquakes located at the shallowest part (Group 3) form a few clusters distributed directly above the Group 1 focal region. Judging from the characteristics of later phases in these earthquakes and comparing against the 3D structure of seismic velocity, the focal regions for the earthquakes are considered to be located near the upper surface of the slab. Another earthquake group (Group 4) originates further below Group 2; it is difficult to consider these earthquakes within a single slab. The seismic activities representing the upper area of the Philippine Sea plate are Group 3. This paper proposes a slab geometry model that is substantially different from conventional models by strictly differentiating the groups. 相似文献
68.
Mineralogy, geochemistry, and Nd isotope composition of the Rainbow hydrothermal field, Mid-Atlantic Ridge 总被引:3,自引:0,他引:3
Petrological, geochemical, and Nd isotopic analyses have been carried out on rock samples from the Rainbow vent field to assess the evolution of the hydrothermal system. The Rainbow vent field is an ultramafic-hosted hydrothermal system located on the Mid-Atlantic Ridge characterized by vigorous high-temperature venting (∼365°C) and unique chemical composition of fluids: high chlorinity, low pH and very high Fe, and rare earth element (REE) contents (Douville et al., Chemical Geology 184:37–48, 2002). Serpentinization has occurred under a low-temperature (<270°C) retrograde regime, later overprinted by a higher temperature sulfide mineralization event. Retrograde serpentinization reactions alone cannot reproduce the reported heat and specific chemical features of Rainbow hydrothermal fluids. The following units were identified within the deposit: (1) nonmineralized serpentinite, (2) mineralized serpentinite—stockwork, (3) steatite, (4) semimassive sulfides, and (5) massive sulfides, which include Cu-rich massive sulfides (up to 28wt% Cu) and Zn-rich massive sulfide chimneys (up to 5wt% Zn). Sulfide mineralization has produced significant changes in the sulfide-bearing rocks including enrichment in transition metals (Cu, Zn, Fe, and Co) and light REE, increase in the Co/Ni ratios comparable to those of mafic Cu-rich volcanic-hosted massive sulfide deposits and different 143Nd/144Nd isotope ratios. Vent fluid chemistry data are indicative of acidic, reducing, and high temperature conditions at the subseafloor reaction zone where fluids undergo phase separation most likely under subcritical conditions (boiling). An explanation for the high chlorinity is not straightforward unless mixing with high salinity brine or direct contribution from a magmatic Cl-rich aqueous fluid is considered. This study adds new data, which, combined with the current knowledge of the Rainbow vent field, brings compelling evidence for the presence, at depth, of a magmatic body, most likely gabbroic, which provides heat and metals to the system. Co/Ni ratios proved to be good tools used to discriminate between rock units, degree of sulfide mineralization, and positioning within the hydrothermal system. Deeper units have Co/Ni <1 and subsurface and surface units have Co/Ni >1. 相似文献
69.
大气CO2浓度升高对土壤中不同粒级碳的影响 总被引:4,自引:0,他引:4
不同粒级土壤中的碳有着不同的周转规律,在高CO2浓度条件下,它们含量的变化将在一定程度上反映土壤碳是累积还是减少,对明确土壤碳的变化趋势有重要意义.采用田间培养试验初步模拟研究在高CO2浓度条件下土壤不同粒级碳的分布.结果表明,加入秸秆培养1年,由于CO2浓度升高的原因导致在低氮(LN)、常规氮(NN)和高氮(HN)水平下土壤中碳分别增加0.01、1.10、1.22g/kg,表现为粒级〈53μm土壤颗粒中碳分别增加1.53、2.19、2.70g/kg.粒级〈53μmm土壤颗粒碳量的增加,主要是由于其重量分配百分数显著增加36.2%,碳浓度增加5.4%;粒级〉250μm和250~53μm土壤颗粒部分虽然其碳浓度分别增加20.8%和17.3%(P〈0.05),怛由于重量分配百分数分别显著降低22.8%和36.1%,结果碳量降低.试验表明高CO2浓度导致不同粒级土壤的分配及碳浓度的变化;高氮施肥水平下有增加土壤碳量特别是小粒级土壤碳量的趋势. 相似文献
70.
从分析大湾铀矿田各矿床(点)的铀镭平衡系数变化特征出发,结合放射性同位素比值特征分析铀镭迁移富集行为,指出了各矿床(点)氧化带的深度,以了解各铀矿床(点)潜在的工业价值. 相似文献