全文获取类型
收费全文 | 29184篇 |
免费 | 1146篇 |
国内免费 | 2109篇 |
专业分类
测绘学 | 1806篇 |
大气科学 | 2729篇 |
地球物理 | 5572篇 |
地质学 | 14352篇 |
海洋学 | 1601篇 |
天文学 | 1945篇 |
综合类 | 2538篇 |
自然地理 | 1896篇 |
出版年
2024年 | 35篇 |
2023年 | 107篇 |
2022年 | 247篇 |
2021年 | 299篇 |
2020年 | 256篇 |
2019年 | 301篇 |
2018年 | 4986篇 |
2017年 | 4276篇 |
2016年 | 2824篇 |
2015年 | 505篇 |
2014年 | 373篇 |
2013年 | 331篇 |
2012年 | 1251篇 |
2011年 | 2999篇 |
2010年 | 2292篇 |
2009年 | 2580篇 |
2008年 | 2178篇 |
2007年 | 2626篇 |
2006年 | 236篇 |
2005年 | 399篇 |
2004年 | 579篇 |
2003年 | 573篇 |
2002年 | 440篇 |
2001年 | 265篇 |
2000年 | 214篇 |
1999年 | 189篇 |
1998年 | 155篇 |
1997年 | 152篇 |
1996年 | 110篇 |
1995年 | 102篇 |
1994年 | 74篇 |
1993年 | 72篇 |
1992年 | 80篇 |
1991年 | 39篇 |
1990年 | 43篇 |
1989年 | 38篇 |
1988年 | 39篇 |
1987年 | 15篇 |
1986年 | 19篇 |
1985年 | 14篇 |
1984年 | 13篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 28篇 |
1980年 | 24篇 |
1979年 | 4篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 11篇 |
1958年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
The Magellan seamounts began forming as large submarine shield volcanoes south of the equator during the Cretaceous. These
volcanoes formed as a cluster on the small Pacific plate in a period when tectonic stress was absent. Thermal subsidence of
the seafloor led to sinking of these volcanoes and the formation of guyots as the seamounts crossed the equatorial South Pacific
(10–0°S) sequentially and ocean surface temperatures became too high for calcareous organisms to survive. Guyot formation
was completed between about 59 and 45 Ma and the guyots became phosphatized at about 39–34 and 27–21 Ma. Ferromanganese crusts
began formation as proto-crusts on the seamounts and guyots of the Magellan Seamount cluster towards the end of the Cretaceous
up to 55 Ma after the formation of the seamounts themselves. The chemical composition of these crusts evolved over time in
a series of steps in response to changes in global climate and ocean circulation. The great thickness of these crusts (up
to 15–20 cm) reflects their very long period of growth. The high Co contents of the outer parts of the crusts are a consequence
of the increasing deep circulation of the ocean and the resulting deepening of the oxygen minimum zone with time. Growth of
the Co-rich Mn crusts in the Magellan Seamount cluster can be considered to be the culmination of a long journey through time. 相似文献
93.
Ryoko Tokeshi Kaoru Ichikawa Satoshi Fujii Kenji Sato Shoichiro Kojima 《Journal of Oceanography》2007,63(4):711-720
A method to extract geostrophic current in the daily mean HF radar data in the Kuroshio upstream region is established by
comparison with geostrophic velocity determined from the along-track altimetry data. The estimated Ekman current in the HF
velocity is 1.2% (1.5%) and 48° (38°)-clockwise rotated with respect to the daily mean wind in (outside) the Kuroshio. Furthermore,
additional temporal smoothing is found necessary to remove residual ageostrophic currents such as the inertial oscillation.
After removal of the ageostrophic components, the HF geostrophic velocity agrees well with that from the altimetry data with
rms difference 0.14 (0.12) m/s in (outside) the Kuroshio. 相似文献
94.
95.
近1300年来古胶州港位置的变迁 总被引:4,自引:0,他引:4
本文主要依据有关方志、文史资料,着重考证了近1300年来古胶州港位置的变迁,研究发现,古胶州港的位置自唐代至清末近1300年间,沿胶州湾西、北岸大致经历了7次变更,特别自明代开始,港口位置变迁尤为频繁,作者初步分析认为这与历史时期胶州湾内西、北岸的不断淤涨和胶莱南河、大沽河口的冲淤作用有关。 相似文献
96.
Floating tephra was deposited together with ice core,snow layer,abyssal sediment,lake sediments,and other geological records.It is of great significance to interpret the impact on the climate change of volcanic eruptions from these geological records.It is the first time that volcanic glass was discovered from the peat of Jinchuan(金川)Maar,Jilin(吉林)Province,China.And it is in situ sediments from a near-source explosive eruption according to particle size analysis and identification results.The tephra were neither from Tianchi(天池)volcano eruptions,Changbai(长白)Mountain,nor from Jinlongdingzi(金龙顶子)volcano about 1 600 aBP eruption,but maybe from an unknown eruption of Longgang(龙岗)volcano group according to their geochemistry and distribution.Geochemical characters of the tephra are similar to those of Jingiongdingzi,which are poor in s.Jica,deficient in alkali,Na20 content is more than K20 content,and are similar to distribution patterns of REE and incompatible elements,which helps to speculate that they originated from the same mantle magma with rare condemnation,and from basaltic explosive eruption of Longgang volcano group.The tephra,from peat with age proved that the eruption possibly happened in 15 BC-26 AD,is one of Longgang volcano group eruption that was not recorded and is earlier than that of Jinglongdingzi about 1 600 aBP eruption.And the sedimentary time of tephra is during the period of low temperature alteration.which may be the influence of eruption toward the local climate according to the correlativity of eruption to local temperature curve of peat cellulose oxygen isotope. 相似文献
97.
基于传统吸附烃概念的烃类检测新技术 总被引:5,自引:1,他引:4
烃类是地表油气地球化学勘查地下油气藏的直接指标.目前我国油气化探中常用的酸解烃法检测出的烃类,不应定义为"吸附烃",它是介质吸收的产物,属结合态烃类,应定义为"吸收烃".地表酸解烃异常十分稳定,重现性好,能够很好地证明地质历史上曾经有过的烃类运移过程,但在反映目前深部油气信息方面具有多解性.针对酸解烃法的弱点,依据烃类垂向运移理论和物质吸附作用原理,自行设计开发、研制了一套吸附烃脱气装置,建立了土壤吸附烃提取新技术和检测方法.该方法有利于在近地表获取油气系统的动态信息,强化烃类测量法对其信息源的探测,可以提高地表油气化探预测油气分布的成功率. 相似文献
98.
Xin Li Dongliang Wang Baoquan Liu Chunling Ren Jianying Guo Xuefeng Su Jian Wang 《中国地球化学学报》2008,27(4):412-419
The northern margin of the Qaidam Basin is one of the main oil-gas exploration areas in western China, where source rocks are composed mostly of Middle and Lower Jurassic dark mud shale, carbargillite and coal. A large number of subsurface and outcrop samples differing in lithology with different types of organic matter were selected for resource evaluation, research and calculation. And among them, 13 samples were used for simulation experiment on hydrocarbon generating potential of various source rocks. At first, two kinds of heating modes were compared through simulation experiment, including single temperature-step heating and continual heating. Perhaps, the process of hydrocarbon generation and expulsion occurred naturally between a close system and an open system. In addition, the first heating mode was convenient, and all its reaction products were involved in the whole thermal evolution, and the final simulation experimental results were basically in consistency with the natural evolution trend Therefore, the first heating mode was adopted and the hydrocarbon yield of every sample was worked out. According to the type and lithology of organic matter and the hydrocarbon yield of samples for simulation experiment, hydrocarbon generation and expulsion mode with three kinds of lithology and five types of source rock has been established to provide the basis for hydrocarbon generation evaluation, research and resource calculation. 相似文献
99.
K. S. Rao Y. S. Rao H. K. Al Jassar 《Journal of the Indian Society of Remote Sensing》2008,36(2):123-136
Spaceborne Imaging Radar (SIR-C) data acquired over Gujarat, India in 1994 were processed and analysed using differnet techniques
applicable to polarimetric SAR data such as polarization signatures, polarization index, decomposition of the signal and polarization
phase difference and limited groundtruth data. It has been observed that multi-frequency polarimetric data enhances the potential
of retrieving geo-physical parameters. The polarization signatures are found to vary with the nature of the target. Target
decomposition of the returned signal will be useful for the classification of various features. Polarization Phase Difference
(PPD) gives good information about the vegetation parameters. 相似文献
100.
The Bayesian detection of discontinuities in a polynomial regression and its application to the cycle-slip problem 总被引:4,自引:1,他引:3
Maria Clara de Lacy Mirko Reguzzoni Fernando Sansò Giovanna Venuti 《Journal of Geodesy》2008,82(9):527-542
This paper deals with the problem of detecting and correcting cycle-slips in Global Navigation Satellite System (GNSS) phase
data by exploiting the Bayesian theory. The method is here applied to undifferenced observations, because repairing cycle-slips
already at this stage could be a useful pre-processing tool, especially for a network of permanent GNSS stations. If a dual
frequency receiver is available, the cycle-slips can be easily detected by combining two phase observations or phase and range
observations from a single satellite to a single receiver. These combinations, expressed in a distance unit form, are completely
free from the geometry and depend only on the ionospheric effect, on the electronic biases and on the initial integer ambiguities;
since these terms are expected to be smooth in time, at least in a short period, a cycle-slip in one or both the two carriers
can be modelled as a discontinuity in a polynomial regression. The proposed method consists in applying the Bayesian theory
to compute the marginal posterior distribution of the discontinuity epoch and to detect it as a maximum a posteriori (MAP)
in a very accurate way. Concerning the cycle-slip correction, a couple of simultaneous integer slips in the two carriers is
chosen by maximazing the conditional posterior distribution of the discontinuity amplitude given the detected epoch. Numerical
experiments on simulated and real data show that the discontinuities with an amplitude 2 or 3 times larger than the noise
standard deviation are successfully identified. This means that the Bayesian approach is able to detect and correct cycle-slips
using undifferenced GNSS observations even if the slip occurs by one cycle. A comparison with the scientific software BERNESE
5.0 confirms the good performance of the proposed method, especially when data sampled at high frequency (e.g. every 1 s or
every 5 s) are available. 相似文献