全文获取类型
收费全文 | 3544篇 |
免费 | 99篇 |
国内免费 | 92篇 |
专业分类
测绘学 | 72篇 |
大气科学 | 416篇 |
地球物理 | 904篇 |
地质学 | 1082篇 |
海洋学 | 676篇 |
天文学 | 330篇 |
综合类 | 46篇 |
自然地理 | 209篇 |
出版年
2023年 | 12篇 |
2022年 | 22篇 |
2021年 | 53篇 |
2020年 | 50篇 |
2019年 | 69篇 |
2018年 | 138篇 |
2017年 | 133篇 |
2016年 | 142篇 |
2015年 | 92篇 |
2014年 | 178篇 |
2013年 | 238篇 |
2012年 | 153篇 |
2011年 | 213篇 |
2010年 | 202篇 |
2009年 | 201篇 |
2008年 | 177篇 |
2007年 | 185篇 |
2006年 | 162篇 |
2005年 | 137篇 |
2004年 | 118篇 |
2003年 | 106篇 |
2002年 | 107篇 |
2001年 | 82篇 |
2000年 | 85篇 |
1999年 | 58篇 |
1998年 | 49篇 |
1997年 | 44篇 |
1996年 | 34篇 |
1995年 | 40篇 |
1994年 | 24篇 |
1993年 | 21篇 |
1992年 | 21篇 |
1991年 | 20篇 |
1990年 | 21篇 |
1989年 | 17篇 |
1988年 | 15篇 |
1987年 | 26篇 |
1986年 | 15篇 |
1985年 | 19篇 |
1984年 | 30篇 |
1983年 | 37篇 |
1982年 | 24篇 |
1981年 | 21篇 |
1980年 | 27篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1977年 | 18篇 |
1975年 | 18篇 |
1974年 | 10篇 |
1973年 | 10篇 |
排序方式: 共有3735条查询结果,搜索用时 15 毫秒
31.
Occurrence and exploration of gas hydrate in the marginal seas and continental margin of the Asia and Oceania region 总被引:5,自引:0,他引:5
Ryo Matsumoto Byong-Jae Ryu Sung-Rock Lee Saulwood Lin Shiguo Wu Kalachand Sain Ingo Pecher Michael Riedel 《Marine and Petroleum Geology》2011,28(10):1751-1767
Supplies of conventional natural gas and oil are declining fast worldwide, and therefore new, unconventional forms of energy resources are needed to meet the ever-increasing demand. Amongst the many different unconventional natural resources are gas hydrates, a solid, ice-like crystalline compound of methane and water formed under specific low temperature and high pressure conditions. Gas hydrates are believed to exist in large quantities worldwide in oceanic regions of continental margins, as well as associated with permafrost regions in the Arctic. Some studies to estimate the global abundance of gas hydrate suggest that the total volume of natural gas locked up in form of gas hydrates may exceed all known conventional natural gas reserves, although large uncertainties exist in these assessments. Gas hydrates have been intensively studied in the last two decades also due to connections between climate forcing (natural and/or anthropogenic) and the potential large volumes of methane trapped in gas hydrate accumulations. The presence of gas hydrate within unconsolidated sediments of the upper few hundred meters below seafloor may also pose a geo-hazard to conventional oil and gas production. Additionally, climate variability and associated changes in pressure-temperature regimes and thus shifts in the gas hydrate stability zone may cause the occurrence of submarine slope failures.Several large-scale national gas hydrate programs exist especially in countries such as Japan, Korea, Taiwan, China, India, and New Zealand, where large demands of energy cannot be met by domestic supplies from natural resources. The past five years have seen several dedicated deep drilling expeditions and other scientific studies conducted throughout Asia and Oceania to understand gas hydrates off India, China, and Korea. This thematic set of publications is dedicated to summarize the most recent findings and results of geo-scientific studies of gas hydrates in the marginal seas and continental margin of the Asia, and Oceania region. 相似文献
32.
An analytical solution for the coupling problem of a two-dimensional tension leg structure interacting with a monochromatic linear wave train in an inviscid and incompressible fluid is presented. The tension legs are considered to be linearly elastic. The flow is further assumed to be irrotational and single-valued velocity potentials can then be defined.The boundary value problem is incorporated into a scattering and a radiation problem. The boundary value problems are then solved separately and combined to resolve all unknowns. The complete solutions of the velocity potentials are represented by the series of eigen-functions, and the surge motion of the structure is described in terms of the incident wave properties.The analytical solution is compared with a computer-coded numerical solution utilizing the boundary element method. The solutions agree very well, and both predict a resonant frequency for a specific structure which is different from the natural frequency of the structure due to the presence of the evanescent waves caused by the structure. 相似文献
33.
The seasonal circulation in the southeastern Huanghai Sea has been studied with hydrographic data,which were observed in February and June 1994 and bimonthly during 1970-1990,and numerical model results.Horiwntal distributions of temperature and salinity in 1994 are quite different due to strong tidal mixing so that we need a analysis to see the real distributions of water masses.The mixing ratio analysis with the data of 1970-1990 shows the connection of the waters in the west coasts of Kotea Peninsula with warm and saline waters from the south in summer,which means northward inflows along the west coasts of Korea Peninsula in summer.With this flow,the seasonal circulations,which are deduced from the seasonal change of water mass distributions in the lower layer,are warm inflows in winter and mld outflows in summer in the central Huanghai Sea,and cold outflows in winter and warm inflows in summer along the west coasts of Korea Peninsula.The seasonally changed inflows might be the Huanghai Sea Warm Current.The monsoon winds can drive such circulations.However,summer monsoon winds are weak and irregular.As one of other possible dynamics,the variation of Kuroshio transport is numerically studied with allowing sea level fluctuations.Although it should be studied more,it possibly drives the summer circulations.The real circulations seem to be driven by both of them. 相似文献
34.
Aerosol optical thickness (AOT) was retrieved from the Geostationary Ocean Color Imager (GOCI) on board the Communication, Ocean, and Meteorological Satellite (COMS) for the first time. AOT values were retrieved over the ocean at a spatial scale of 0.5 × 0.5 km2 by using the look-up table (LUT)-based separation technique. The radiative transfer model (RTM) was used for different models of atmosphere-ocean environmental conditions, taking into account the realistic variability of scattering and absorption. Ocean surface properties affected by whitecaps and pigment content were also taken into account. The results show that the radiance observed by the GOCI amounts to only 5% of the radiation that penetrated the ocean and, consequently, 95% of the radiation is scattered in the atmosphere or reflected at the ocean surface in the visible wavelengths longer than 0.6 ìm. Within these wavelengths, radiance variations at the top of atmosphere (TOA) due to pigment variations are within 10%, while the radiance variation due to wind speed is considerably higher. For verification of GOCI-retrieved AOTs, comparison between GOCI and ground-based sunphotometer measurement at Gosan, Korea (126.10°E, 33.23°N)) showed good correlation (r = 0.99). The GOCI observations obtained by using the proposed technique showed promising results for the daily monitoring of atmospheric aerosol loading as well as being useful for environmental supervisory authorities. 相似文献
35.
Ocean Science Journal - This study examines the different effects of high and low freshwater discharge on the water physical structure of the water column and plankton community in a tide-dominated... 相似文献
36.
Ocean Science Journal - The carbon isotopic compositions (δ13C) of n-alkanes in various environmental samples have been previously proposed as suitable fingerprints for assessing the origin of... 相似文献
37.
Ocean Science Journal - The high load of protozoan parasites in marine bivalves often leads to mass mortalities of the hosts. On the west coast of Korea in the Yellow Sea, the protozoan parasite... 相似文献
38.
The scattering of water waves by bottom-mounted vertical circular cylinders is solved by using the null-field integral equations in conjunction with degenerate kernels and Fourier series to avoid calculating the Cauchy and Hadamard principal values. In the implementation, the null-field point can be exactly located on the real boundary owing to the introduction of degenerate kernels for fundamental solutions. An adaptive observer system of polar coordinates is considered to fully employ the properties of degenerate kernels. For the hypersingular equation, vector decomposition for the radial and tangential gradients is carefully considered. This method can be seen as a semi-analytical approach since errors attribute from the truncation of Fourier series. Neither hypersingularity in the Burton and Miller approach nor the CHIEF concept was required to deal with the problem of irregular frequencies. Five advantages of free of calculating principal value, well-posed algebraic system, convergence rate of exponential order, meshfree and elimination of boundary-layer effect, are achieved by using the present approach. Numerical results are given for the forces and free-surface elevation around the circular boundaries. Also, the near-trapped behavior arisen from the physical resonance is detected. A general-purpose program for water wave impinging several circular cylinders with arbitrary number, radii, and positions was developed. Several examples of water wave structure interaction by vertical circular cylinders were demonstrated to see the validity of the present formulation. 相似文献
39.
Anja Engel Lynn Abramson Jennifer Szlosek Zhanfei Liu Gillian Stewart David Hirschberg Cindy Lee 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(18):1408-1419
The quantitative relationship between organic carbon and mineral contents of particles sinking below 1800 m in the ocean indicates that organisms with mineral shells such as coccolithophores are of special importance for transporting carbon into the deep sea. Several hypotheses about the mechanism behind this relationship between minerals and organic matter have been raised, such as mineral protection of organic matter or enhanced sinking rates through ballast addition. We examined organic matter decomposition of calcifying and non-calcifying Emiliania huxleyi cultures in an experiment that allowed aggregation and settling in rotating tanks. Biogenic components such as particulate carbon, particulate nitrogen, particulate volume, pigments, transparent exopolymer particles (TEP), and particulate amino acids in suspended particles and aggregates were followed over a period of 30 d. The overall pattern of decrease in organic matter, the amount of recalcitrant organic matter left after 30 d, and the compositional changes within particulate organic matter indicated that cells without a shell are more subject to loss than calcified cells. It is suggested that biogenic calcite helps in the preservation of particulate organic matter (POM) by offering structural support for organic molecules. Over the course of the experiment, half the particulate organic carbon in both calcifying and non-calcifying cultures was partitioned into aggregates and remained so until the end of the experiment. The partial protection of particulate organic matter from solubilization by biominerals and by aggregation that was observed in our experiment may help explain the robustness of the relationship between organic and mineral matter fluxes in the deep ocean. 相似文献
40.
Ultraviolet-B (UV-B) radiation (0.5, 1.0, 1.5, and 3.0 W m?2) induced higher H2O2 production and lipid peroxidation in alga Gelidium amansii inhabiting in lower subtidal regions than upper subtidal alga Ptercladiella capillacea. Compared to G. amansii, mycosporine-like amino acid (MAA) concentration in P. capillacea was higher and can be increased by 0.5–1.0 W m?2 UV-B, while carotenoid concentration was lower but also increased by 1.5–3.0 W m?2 UV-B. UV-B increased ascorbate concentration, but to a higher degree in P. capillacea. UV-B decreased glutathione concentration, but to a higher degree in G. amansii. UV-B increased ascorbate peroxidase (APX) and glutathione reductase (GR) activities in P. capillacea but decreased them in G. amansii. UV-B increased superoxide dismutase and catalase activities, but to a higher degree in G. amansii. So, G. amansii suffered greater oxidative stress from UV-B radiation. P. capillacea can effectively reduce UV-B sensitivity by increasing sunscreen ability and antioxidant defense capacity. 相似文献