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911.
鲁西新太古代济宁群含铁岩系形成时代——SHRIMP U-Pb锆石定年 总被引:12,自引:7,他引:5
济宁群以隐伏的地质体分布于华北克拉通鲁西地区,以往被划归古元古代。近年来在济宁群的钻探和地球物理研究中,发现存在较大规模条带状硅铁建造,其形成时代引起地学界极大关注。本文对济宁群变质碎屑沉积岩和长英质火山岩进行了锆石SHRIMP年龄测定。含砾绿泥绢云千枚岩的碎屑锆石年龄主要集中在~2.7Ga,可靠的最年轻碎屑锆石年龄为2.61±0.01Ga。变质长英质火山岩岩浆锆石年龄为2.56±0.02Ga。研究表明,济宁群形成于新太古代晚期,而不是以往认为的古元古代。华北克拉通条带状铁建造主要形成于新太古代晚期。济宁群在岩石组合、变质作用方面与鞍山、冀东以及五台地区同时代含硅铁建造的表壳岩系有差别,但是与本溪南芬铁矿的岩石组合有相似之处。这些可能为我国的隐伏太古宙BIF铁矿的研究与勘探提供了重要依据。 相似文献
912.
General approximate analytical solutions are developed for one-dimensional consolidation with consideration of the threshold gradient under a time-dependent loading. A comparison is made between the present solution and some available numerical solutions for a particular case, and the results show that the approach employed in this article is reasonable. The influence of the threshold gradient and the loading period on consolidation behaviour is investigated, and the results show that the moving boundary of seepage moves downward gradually. The greater the threshold gradient is, the slower the boundary moves. The excess pore pressure will not be completely dissipated at the end of consolidation, and the larger the threshold gradient is, the greater the residual excess pore pressure is. The average degree of consolidation considering the threshold gradient defined by settlement is different from that defined by pore pressure. Moreover, the greater the threshold gradient is, the larger the average degree of consolidation in terms of strain, whereas the smaller the average degree of consolidation in terms of stress. It is also shown that the longer the loading period is, the longer the time moving boundary takes to reach the bottom of the layer, and the greater the average degree of consolidation is. 相似文献
913.
Gray crystalline hematite on Mars has been detected in three regions, Sinus Meridiani, Aram Chaos, and Valles Marineris, first by the Thermal Emission Spectrometer (TES) onboard the Mars Global Surveyor (MGS) orbiter, and then confirmed by other instruments. The hematite-rich spherules were also detected by the Mars Exploration Rover (MER) Opportunity at Meridiani Planum (Sinus Meridiani). Formation mechanisms of the hematite-rich spherules have been discussed widely since then. Here, we argue for an alternative formation mechanism, that is, the spherules originally formed at Valles Marineris due to the interaction of volcanic deposits and acidic hydrothermal fluids, and then were transported to and deposited at Meridiani Planum and Aram Chaos as alluvial/fluvial sedimentary deposits with other materials such as sulfates and rock fragments during the wash-out flows from Valles Marineris to Meridiani Planum and Aram Chaos. Diagenesis of the hematite-rich spherules may have also been a possible mechanism following sediment transport and emplacement. The hypothesis is consistent with available relevant information to date and provides an insight into the understanding of Martian surficial processes. 相似文献
914.
Zhifu Xie 《Celestial Mechanics and Dynamical Astronomy》2010,107(3):353-376
In this paper, we consider the inverse problem of central configurations of n-body problem. For a given \({q=(q_1, q_2, \ldots, q_n)\in ({\bf R}^d)^n}\), let S(q) be the admissible set of masses denoted \({ S(q)=\{ m=(m_1,m_2, \ldots, m_n)| m_i \in {\bf R}^+, q}\) is a central configuration for m}. For a given \({m\in S(q)}\), let S m (q) be the permutational admissible set about m = (m 1, m 2, . . . , m n ) denotedThe main discovery in this paper is the existence of a singular curve \({\bar{\Gamma}_{31}}\) on which S m (q) is a nonempty set for some m in the collinear four-body problem. \({\bar{\Gamma}_{31}}\) is explicitly constructed by a polynomial in two variables. We proved:
相似文献
$S_m(q)=\{m^\prime | m^\prime\in S(q),m^\prime \not=m \, {\rm and} \, m^\prime\,{\rm is\, a\, permutation\, of }\, m \}.$
- (1)If \({m\in S(q)}\), then either # S m (q) = 0 or # S m (q) = 1.
- (2)#S m (q) = 1 only in the following cases:
- (i)If s = t, then S m (q) = {(m 4, m 3, m 2, m 1)}.
- (ii)If \({(s,t)\in \bar{\Gamma}_{31}\setminus \{(\bar{s},\bar{s})\}}\), then either S m (q) = {(m 2, m 4, m 1, m 3)} or S m (q) = {(m 3, m 1, m 4, m 2)}.
- (i)
915.
长江北支口门圆陀角附近潮滩沉积物粒度记录及其对环境变化的响应 总被引:7,自引:6,他引:1
江苏圆陀角位于长江口北支与江苏海岸交汇处,海岸沉积动力环境复杂,潮滩沉积物粒度变化记录了潮滩环境变化的信息.根据2007年4月采集的表层样和钻孔岩芯粒度分析,圆陀角附近Yyb断面表层沉积物粒度在互花米草滩前缘较粗,大堤前岸滩最粗,光滩和互花米草滩粒度较细.YY孔岩芯沉积物粒度组成以砂质粉砂为主,粒度变化自下向上呈先由粗变细再变粗的特点,表层样和钻孔岩芯粒度变化反映了潮滩沉积物对风暴潮、潮汐海洋动力、大米草和互花米草种植以及大规模围垦的综合响应.173Cs测年结果推算出YY孔岩芯1954年以来、1963年以来、1975年以来和1986年以来的平均沉积速率分别为2.38cm/a,2.23cm/a,2.44cm/a和1.24cm/a.岩芯沉积物的沉积速率总体随潮滩淤积增高而下降,1975~1986年间沉积速率的快速增加,主要与圆陀角附近互花米草的快速淤积有关. 相似文献
916.
917.
Geochemistry of soil gas in the seismic fault zone produced by the Wenchuan Ms 8.0 earthquake, southwestern China 总被引:2,自引:0,他引:2
Xiaocheng Zhou Jianguo Du Zhi Chen Jianwu Cheng Yi Tang Liming Yang Chao Xie Yueju Cui Lei Liu Li Yi Panxin Yang Ying Li 《Geochemical transactions》2010,11(1):1-10
The spatio-temporal variations of soil gas in the seismic fault zone produced by the 12 May 2008 Wenchuan Ms 8.0 earthquake were investigated based on the field measurements of soil gas concentrations after the main shock. Concentrations of He, H2, CO2, CH4, O2, N2, Rn, and Hg in soil gas were measured in the field at eight short profiles across the seismic rupture zone in June and December 2008 and July 2009. Soil-gas concentrations of more than 800 sampling sites were obtained. The data showed that the magnitudes of the He and H2 anomalies of three surveys declined significantly with decreasing strength of the aftershocks with time. The maximum concentrations of He and H2 (40 and 279.4 ppm, respectively) were found in three replicates at the south part of the rupture zone close to the epicenter. The spatio-temporal variations of CO2, Rn, and Hg concentrations differed obviously between the north and south parts of the fault zone. The maximum He and H2 concentrations in Jun 2008 occurred near the parts of the rupture zone where vertical displacements were larger. The anomalies of He, H2, CO2, Rn, and Hg concentrations could be related to the variation in the regional stress field and the aftershock activity. 相似文献
918.
Genming Luo Junhuang Huang Shucheng Xie Paul B. Wignall Xinyan Tang Xianyu Huang Hongfu Yin 《International Journal of Earth Sciences》2010,99(4):775-784
This paper investigates kerogen carbon isotopes, the difference between carbonate and kerogen carbon isotopes (Δ13Ccarb-kero = δ
13Ccarb − δ
13Ckero) and the difference between carbonate and n-C19 alkane compound-specific carbon isotopes (Δ13Ccarb-n-C19 = δ
13Ccarb − δ
13C
n-C19) during the Permian–Triassic transition at Meishan, South China. The results show that kerogen carbon isotopes underwent
both gradual and sharp shifts in beds 23–25 and 26–29, respectively. The differences between carbonate and organic carbon
isotopes, both the Δ13Ccarb-kero and Δ13Ccarb-n-C19, which are mainly affected by CO2-fixing enzyme and pCO2, oscillated frequently during the Permian–Triassic transition. Both the variations of Δ13Ccarb-n-C19 and Δ13Ccarb-kero coupled with the alternation between cyanobacteria and green sulfur bacteria indicated by biomarkers. The episodic low values
of Δ13Ccarb-n-C19 corresponded to episodic blooms of green sulfur bacteria, while the episodic high values of Δ13Ccarb-n-C19 corresponded to episodic blooms of cyanobacteria. The relationships between the variation of carbon isotopes and biota show
that the microbes which flourished after the extinction of macroorganism affected the carbon isotope fractionation greatly.
Combining the carbon isotope compositions and the pattern of size variation of the conodont Neogondolella, this paper supposes that anoxia of the photic zone at bed 24 was episodic and it would be caused by the degradation of terrigenous
organic matters by sulfate reducing bacteria in the upper water column. Considered together with results from previous research,
the high resolution variation of the biogeochemistry presents the sequence of the important geo-events during the Permian–Triassic
crisis. 相似文献
919.
Mingqun Huo Qian Sun Yuhua Bai Peng Xie Zhaorong Liu Jinlong Li Xuesong Wang Sihua Lu 《Journal of Atmospheric Chemistry》2010,67(1):29-43
Rainwater samples were collected at four sites, including Beijing and Mazhuang Town in the north of China, Shenzhen and Mangdang
Mountain in the south of China. Character of atmospheric particles and gases were also measured at Mazhuang Town and Mangdang
Mountain. Both of Beijing and Shenzhen are urban sites; Mazhuang Town and Mangdang Mountain are rural and remote sites respectively.
The atmospheric pollution at rural plain site in the north of China was more serious than that at remote mountain site in
the south of China. At Beijing, Mazhuang Town, Shenzhen and Mangdang Mountain the average pH values in rainwater were 6.02,
5.97, 4.72 and 4.81, respectively and the concentrations of total ions in rainwater were 1454, 1125, 187 and 191 μeq/l, respectively.
While the acidity of the rain was higher in the south than that in the north, the rainwater in the north of China was more
severely polluted than that in the south. The major acidic ion in the rainwater is SO42-, and NH4+ is the most important neutralizing ion in rainwater at the four sites, followed by Ca2+. The amounts of organic acid in precipitation were compared with other sites in the world. The ratios of organic acid to
total free acid in rainwater at Mangdang Mountain was 13.8% and the influence of organic acid on acidity of rainwater at mountain
site in the south of China is more important. The variation of atmospheric particles, gases and components in rainwater and
cloud-fog water during special rain and cloud-fog events was discussed. The importance of washout process varied with atmospheric
species. The impacts of rainfall, rain duration time and wind speed on wash-out process were estimated by regression analysis. 相似文献
920.
The governing equations for one‐dimensional consolidation of layered structured soils under time‐dependent loading are established. Using simplified k‐σ′ and mv‐σ′ models, n‐layered structured soils are transformed into (n + 1) or (n + 2)‐layered soils in which the thickness of upper and lower layers are gradually changing. The approximate solutions for the governing equations are then obtained under two types of boundary conditions, and the computer program is developed. Based on the solutions and computer program, the consolidation behavior of layered structured soils with soft interlayer is studied. It is shown that the permeability and compressibility of the soft interlayer have the greatest influences on the rate of settlement and rate of the dissipation of excess pore water pressure. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献