全文获取类型
收费全文 | 516篇 |
免费 | 23篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 13篇 |
大气科学 | 86篇 |
地球物理 | 108篇 |
地质学 | 193篇 |
海洋学 | 28篇 |
天文学 | 98篇 |
综合类 | 2篇 |
自然地理 | 13篇 |
出版年
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 24篇 |
2017年 | 27篇 |
2016年 | 53篇 |
2015年 | 28篇 |
2014年 | 40篇 |
2013年 | 30篇 |
2012年 | 14篇 |
2011年 | 22篇 |
2010年 | 27篇 |
2009年 | 26篇 |
2008年 | 15篇 |
2007年 | 17篇 |
2006年 | 11篇 |
2005年 | 6篇 |
2004年 | 7篇 |
2003年 | 8篇 |
2002年 | 6篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1998年 | 11篇 |
1997年 | 7篇 |
1996年 | 12篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 13篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1981年 | 3篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1971年 | 5篇 |
1970年 | 3篇 |
1969年 | 4篇 |
1965年 | 4篇 |
1963年 | 2篇 |
排序方式: 共有541条查询结果,搜索用时 0 毫秒
91.
92.
A new finite element model to analyze the seismic response of deformable rocking bodies and rocking structures is presented. The model comprises a set of beam elements to represent the rocking body and zero‐length fiber cross‐section elements at the ends of the rocking body to represent the rocking surfaces. The energy dissipation during rocking motion is modeled using a Hilber–Hughes–Taylor numerically dissipative time step integration scheme. The model is verified through correct prediction of the horizontal and vertical displacements of a rigid rocking block and validated against the analytical Housner model solution for the rocking response of rigid bodies subjected to ground motion excitation. The proposed model is augmented by a dissipative model of the ground under the rocking surface to facilitate modeling of the rocking response of deformable bodies and structures. The augmented model is used to compute the overturning and uplift rocking response spectra for a deformable rocking frame structure to symmetric and anti‐symmetric Ricker pulse ground motion excitation. It is found that the deformability of the columns of a rocking frame does not jeopardize its stability under Ricker pulse ground motion excitation. In fact, there are cases where a deformable rocking frame is more stable than its rigid counterpart. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
93.
Aleksandra Šajnović Ksenija Stojanović Branimir Jovančićević Olga Cvetković 《Chemie der Erde / Geochemistry》2008,68(4):395-411
In this study, the molecular composition and biomarker distribution of lacustrine sediments from Val-1 drillhole in the central zone of the western part of the Valjevo-Mionica basin were investigated at depth interval of 0–400 m. Former investigations have shown that the core material can be separated into six depth intervals based on bulk geochemical, mineralogical and sedimentological characteristics. Concerning the quality of organic matter, presence of specific minerals, and high salinity and anoxicity, or alkalinity, three zones are of highest interest, defined at depth intervals of 15–75 m (A), 75–200 m (B) and 360–400 m (F). The first aim of the study was to identify which biomarkers characterize these specific intervals. The second aim, addressing the transitions zones of these intervals, was to extend the changes in the characteristics of the organic substance, to reflect the changes of conditions in the depositional environment as well as to define biomarker parameters which are the most sensitive sedimentological indicators.The sediments from the hypersaline anoxic and alkaline environment show high contribution of algal precursor biomass, what is in accordance with the good quality of organic substances in the sediments from these zones. High squalane content and low content of regular isoprenoid C25 are typical for hypersaline anoxic environment, whereas sediments from alkaline environment have high regular isoprenoid C25 content.Transition to specific sedimentation zones is characterized by change in total organic matter content, and of both free and pyrolysis-derived, and change in hydrogen index value. In the biomarker distributions, more significant changes were detected in distributions of n-alkanes and isoprenoids, compared to polycyclic alkanes. The most intensive changes in alkane distribution are reflected in changes in n-C17 content compared to n-C27, and phytane compared to n-C18. In addition, significant sensitivity was seen in ratios between squalane and n-alkane C26 (hypersaline depositional environment), or isoprenoid C25 and n-alkane C22 for high alkalinity environment.This study showed that Sq/n-C26 ratio can be used to assess the quality of organic substance in immature lacustrine sediments. 相似文献
94.
Nenad Grba Aleksandra Šajnović Ksenija Stojanović Vladimir Simić Branimir Jovančićević Goran Roglić Vladisav Erić 《Chemie der Erde / Geochemistry》2014
Sedimentary rocks from the saline formation of the Lopare Basin were investigated. Sediments contain a moderate amount of immature to marginally mature algal organic matter deposited under slightly reducing to anoxic and slightly saline to hypersaline conditions. Almost all of the samples contain β-carotane in a relatively high quantity, and in some, it represents the most abundant compound in the total distribution of hydrocarbons. The objective of the study was to determine the conditions that are favourable to precursors of β-carotene and/or the preservation of the carotenoid hydrocarbon skeleton. Moreover, the dominant transformation pathways of β-carotene under different redox and salinity conditions, which lead to the formation of aromatic carotenoids were defined. 相似文献
95.
Dr. Stjepko Golubić 《Aquatic Sciences - Research Across Boundaries》1965,27(2):218-232
Ohne Zusammenfassung
Die vorliegende Arbeit entstand dank der Unterstützung der Alexander-von-Humboldt-Stiftung, Bad Godesberg. 相似文献
96.
97.
We discuss the contribution of cosmic-ray protons at all energies above 1 MeV to the absorbed doses of the surface layers of a comet. Since there exists no calculation which takes into account proton energy losses by means of losses to electrons and nuclear collisions (in a cascade process), and losses due to the low energy end-products of the cascade, we have made a rough estimate of all of these contributions. An analytical formula is proposed that allows a rapid estimate of ranges and the dose absorbed at any depth. We give dose-depth curves for two extreme values of the energy at which nuclear collisions begin to dominate the slowing-down process, and for an intermediate value we display the dose-depth curve down to 20 m from the surface. The relevance of these findings to dosimetry in comets and some alterations of cometary material are considered. The need for improving the analytical expression proposed is stressed. 相似文献
98.
A. Šajnović K. Stojanović V. Simić G. S. Pevneva A. K. Golovko B. Jovančiećević 《Geochemistry International》2011,49(10):1022-1034
Liquid thermolysis products of various types of immature kerogen from sedimentary lacustrine rocks from the Valjevo-Mionica
basin in Serbia were studied to evaluate the generation potential of kerogen contained in the organic matter (OM) of the rocks,
determine the composition of the biomarkers and alkylaromatics in the liquid thermolysis products, and elucidate the effect
of Pt4+ and Ru3+ ions (which were added in the form of inorganic salts) on the yield and hydrocarbon composition of the liquid thermolysis
products. For this purpose, representative bitumen-free samples A and B of the sedimentary rocks were subjected to thermolysis
under various conditions. Rock A contains high amount of immature organic matter, which is dominated by kerogen type I/II
and was generated under strongly reduced sedimentation conditions at a high salinity. Sample B is poorer in immature OM than
sample A, and the OM of the former contains kerogen type II/III and was generated predominantly in a reduced environment.
The content of the liquid products and the concentrations of hydrocarbons obtained in the course of thermolysis of bitumen-free
sample A and the typical oil distribution of the biomarkers and alkylaromatics in the thermolysis products confirm a high
generation potential of OM in this rock. In all of our experiments on the thermolysis of bitumen-free sample B, the yield
of liquid products and hydrocarbons is low. According to the kerogen type, the thermolysis of this rock generates much gases.
The Pt4+ and Ru3+ ions (added in the form of simple inorganic salts) increased the yield of liquid (kerogen type I/II) and gaseous (kerogen
type II/III) products. During the thermolysis of various type of immature kerogen in the lacustrine sedimentary rocks at a
temperature of 400°C, the OM attained maturation corresponding to the early catagenesis level. Saturated biomarkers and alkylaomatics
in the thermolysis products of both samples display typical oil distributions. The type of the source OM most strongly affects
the composition of n-alkanes and alkylnaphthalenes. The metal ions used in this research served as catalysts for the methylation process during
the thermolysis of immature kerogen, regardless of its type. The effect of the Pt4+ and Ru3+ ions on other transformations of the hydrocarbons, for example, the destruction of high-molecular n-alkanes to low-molecular ones and on isomerization reactions in molecules of polycyclic biomarkers and alkylaromatics to
thermodynamically more stable isomers in the thermolysis products is controlled, first of all, by the type of the source OM. 相似文献
99.
100.
Mateja Jemec Auflič Matjaž Mikoš Timotej Verbovšek Željko Arbanas Snježana Mihalić Arbanas 《Landslides》2018,15(2):381-384
The 3rd Regional Symposium on Landslides in the Adriatic-Balkan Region (3rd ReSyLAB) was held in Ljubljana, Slovenia, from June 11 to 13, 2017, with 70 participants from nine countries (Austria, Bosnia and Hercegovina, Croatia, Czech Republic, Italy, Republic of Macedonia, Serbia, Slovenia, Spain)—scientists, engineers, researchers, students, experts, politicians, and other decision-makers working in the area of landslide risk reduction in the region. The ReSyLAB is a biannual event organized by the Adriatic-Balkan Network of the International Consortium on Landslides (ICL ABN). Being an important form of activities of this ICL regional network comprising of six ICL members from four countries, it was also a contribution of the International Consortium on Landslides (ICL) to the implementation of the Sendai Framework for Disaster Risk Reduction 2015–2030. This article reports on the main outcomes of the 3rd ReSyLAB Symposium. Altogether, 41 abstracts were published in the symposium book of abstracts, and the symposium proceedings with over 20 reviewed full papers are under preparation to be printed early in 2018. During the 3rd ReSyLAB, a five invited keynote lectures have been presented, and 28 oral presentations are given to the audience. An important part of the symposium was a Round Table entitled “Enhancing cooperation between landslide research community and end users.” On the last day of the symposium, over 30 experts participated in two post-symposium study tours in Slovenia. 相似文献