全文获取类型
收费全文 | 3085篇 |
免费 | 62篇 |
国内免费 | 53篇 |
专业分类
测绘学 | 85篇 |
大气科学 | 363篇 |
地球物理 | 661篇 |
地质学 | 1029篇 |
海洋学 | 211篇 |
天文学 | 688篇 |
综合类 | 20篇 |
自然地理 | 143篇 |
出版年
2021年 | 18篇 |
2020年 | 22篇 |
2019年 | 19篇 |
2018年 | 54篇 |
2017年 | 52篇 |
2016年 | 66篇 |
2015年 | 46篇 |
2014年 | 73篇 |
2013年 | 120篇 |
2012年 | 87篇 |
2011年 | 124篇 |
2010年 | 99篇 |
2009年 | 137篇 |
2008年 | 139篇 |
2007年 | 121篇 |
2006年 | 109篇 |
2005年 | 130篇 |
2004年 | 102篇 |
2003年 | 90篇 |
2002年 | 100篇 |
2001年 | 83篇 |
2000年 | 85篇 |
1999年 | 96篇 |
1998年 | 93篇 |
1997年 | 77篇 |
1996年 | 72篇 |
1995年 | 73篇 |
1994年 | 54篇 |
1993年 | 53篇 |
1992年 | 47篇 |
1991年 | 57篇 |
1990年 | 44篇 |
1989年 | 43篇 |
1988年 | 23篇 |
1987年 | 33篇 |
1986年 | 35篇 |
1985年 | 31篇 |
1984年 | 51篇 |
1983年 | 34篇 |
1982年 | 40篇 |
1981年 | 42篇 |
1980年 | 39篇 |
1979年 | 33篇 |
1978年 | 32篇 |
1977年 | 20篇 |
1976年 | 26篇 |
1975年 | 15篇 |
1974年 | 30篇 |
1973年 | 17篇 |
1971年 | 22篇 |
排序方式: 共有3200条查询结果,搜索用时 359 毫秒
991.
Zhuravskiy D. M. Prokhorova U. V. Ivanov B. V. Yanjura A. S. Kuprikov N. M. Kurapov M. V. 《Izvestiya Atmospheric and Oceanic Physics》2020,56(9):927-935
Izvestiya, Atmospheric and Oceanic Physics - The results of using an original procedure for estimating albedo from the photogrammetric data and exposure parameters by an unmanned aerial vehicle... 相似文献
992.
The unicellular cyanobacterium Synechocystis sp. PCC 6803, a model organism known for its unique combination of highly desirable molecular genetic, physiological and morphological characteristics, was employed in the present study. The species was cultured in BG11 liquid medium contained various initial concentrations of Pb2+ and Cd2+ (0, 0.5, 1, 2, 4, 6 and 8 mg/L). The experiment was conducted for six days and the metal induced alterations in the ultrastructure, growth and pigment contents were assessed. Alterations in the ultrastructure of the Synechocystis sp. PCC 6803 ceils became evident with the increased (>4 mg/L Pb2+) metal concentration. The photosynthetic apparatus (thylakoid membranes) were found to be the worst affected. Deteriorated or completely destroyed thylakoid membranes have made large empty spaces in the cell interior. In addition, at the highest concentration (8 mg/L pb2+), the polyphosphate granules became more prominent both in size and number. Despite the initial slight stimulations (0.2, 3.8 and 6.5% respectively at 0.5, 1 and 2 mg/L Pb2+), both metals inhibited the growth in a dose-dependent manner as incubation progressed. Pigment contents (chlorophyll a, βcarotene and phycocyanin) were also decreased with increasing metal concentration. Cells exposed to 6 mg/L Pb2+, resulted in 36.56, 37.39 and 29.34% reductions of chlorophyll a, β carotene and phycocyanin respectively over the control. Corresponding reductions for the same Cd2+concentrations were 57.83, 48.94 and 56.90%. Lethal concentration (96 h LC50) values (3.47 mg/L Cd2+ and 12.11 mg/L Pb2+) indicated that Synechocystis sp. PCC 6803 is more vulnerable to Cd2+ than Pb2+. 相似文献
993.
994.
A series of experiments have been carried out in a developed liquid sloshing setup to estimate the pressure developed on the tank walls and the free surface displacement of water from the mean static level. The square tank attached to a shaking table can be moved to and fro by a cam arrangement driven by a DC motor. Pressure and displacement studies are done on the basis of changing excitation frequency of the shaking table and fill level in the tank. Experiments were carried out without and with baffles, and the consequent changes in the parameters are observed. 相似文献
995.
G. Espinosa-Paredes A. Morales-Díaz U. Olea-González J.J. Ambriz-Garcia 《Marine and Petroleum Geology》2009
A strategy based on proportional-integral (PI) feedback control was applied to solve an inverse heat transfer problem for estimating static formation temperatures (SFTs) from logged temperatures in oil wells. The PI control feedbacks the error between logged and simulated temperatures during the shut-in time process, existing SFT proposal. Thus, mathematically speaking an inverse heat transfer problem was solved in this way, since SFT represents the initial conditions (which are unknown) to solve the partial differential equations governing the heat transfer process in the wellbore-formation system. The mathematical model considers transient convective heat transfer due to circulation losses to the rock surrounding a well. The methodology was tested analyzing two oil wells (MB-3007 and MB-3009) from the Gulf of Mexico and results were compared against two classic methods. The method presented in this work needs only one temperature measurement for each fixed depth to estimate the SFT. 相似文献
996.
Jeomshik Hwang Steven J. Manganini Daniel B. Montluon Timothy I. Eglinton 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(10):1792-1803
The Northwest Atlantic margin is characterized by high biological productivity in shelf and slope surface waters. In addition to carbon supply to underlying sediments, the persistent, intermediate depth nepheloid layers emanating from the continental shelves, and bottom nepheloid layers maintained by strong bottom currents associated with the southward flowing Deep Western Boundary Current (DWBC), provide conduits for export of organic carbon over the margin and/or to the interior ocean. As a part of a project to understand dynamics of particulate organic carbon (POC) cycling in this region, we examined the bulk and molecular properties of time-series sediment trap samples obtained at 968 m, 1976 m, and 2938 m depths from a bottom-tethered mooring on the New England slope (water depth, 2988 m). Frequent occurrences of higher fluxes in deep relative to shallower sediment traps and low Δ14C values of sinking POC together provide strong evidence for significant lateral transport of aged organic matter over the margin. Comparison of biogeochemical properties such as aluminum concentration and flux, and iron concentration between samples intercepted at different depths shows that particles collected by the deepest trap had more complex sources than the shallower ones. These data also suggest that at least two modes of lateral transport exist over the New England margin. Based on radiocarbon mass balance, about 30% (±10%) of sinking POC in all sediment traps is estimated to be derived from lateral transport of resuspended sediment. A strong correlation between Δ14C values and aluminum concentrations suggests that the aged organic matter is associated with lithogenic particles. Our results suggest that lateral transport of organic matter, particularly that resulting from sediment resuspension, should be considered in addition to vertical supply of organic matter derived from primary production, in order to understand carbon cycling and export over continental margins. 相似文献
997.
Anil Sood B. U. Choudhury S. S. Ray S. K. Jalota P. K. Sharma Shushma Panigrahy 《Journal of the Indian Society of Remote Sensing》2009,37(3):483-491
A remote sensing-based approach was applied to study the impact of changes in cropping system on the exploitation of water
resources in two districts namely Ludhiana in central Punjab and Muktsar in South-Western Punjab. Rice-wheat remained dominant
rotation in Ludhiana while cottonwheat rotation was replaced partially by rice-wheat in Muktsar within a span of over five
years (1998–99 to 2003–04). The solo rice-wheat system in Ludhiana district has resulted in large-scale ground water exploitation
as is evident from the faster decline in water table (up to 0.9m year−1) and higher tube-wells density (440 per 1000 ha). As a result, nearly 60 per cent of the total area of Ludhiana district
has the water table depth greater than 10m and in some blocks, it has reached to a depth of 22 m. In Muktsar district, corresponding
rise in water table is 0.2m per year and tube well density is 114 per 1000 ha. Irrigation water associated with paddy cultivation
in Ludhiana and adjoining areas moves laterally through the buried paleo-channels of Sutlaj in the deeper soil profile and
gets accumulated in the basin lands of Muktsar and adjoining areas and causes an extra water flux and subsequent rise in water
table, recorded at 3 to 7m depth. To minimize the hydrological imbalance of the state, it is suggested to diversify some of
the area in the central districts from irrigation water intensive rice-wheat system to less water intensive cropping system. 相似文献
998.
999.
Gas hydrates and active mud volcanism on the South Shetland continental margin, Antarctic Peninsula 总被引:1,自引:0,他引:1
During the Antarctic summer of 2003–2004, new geophysical data were acquired from aboard the R/V OGS Explora in the BSR-rich area discovered in 1996–1997 along the South Shetland continental margin off the Antarctic Peninsula. The
objective of the research program, supported by the Italian National Antarctic Program (PNRA), was to verify the existence
of a potential gas hydrate reservoir and to reconstruct the tectonic setting of the margin, which probably controls the extent
and character of the diffused and discontinuous bottom simulating reflections. The new dataset, i.e. multibeam bathymetry,
seismic profiles (airgun and chirp), and two gravity cores analysed by computer-aided tomography as well as for gas composition
and content, clearly shows active mud volcanism sustained by hydrocarbon venting in the region: several vents, located mainly
close to mud volcanoes, were imaged during the cruise and their occurrence identified in the sediment samples. Mud volcanoes,
vents and recent slides border the gas hydrate reservoir discovered in 1996–1997. The cores are composed of stiff silty mud.
In core GC01, collected in the proximity of a mud volcano ridge, the following gases were identified (maximum contents in
brackets): methane (46 μg/kg), pentane (45), ethane (35), propane (34), hexane (29) and butane (28). In core GC02, collected
on the flank of the Vualt mud volcano, the corresponding data are methane (0 μg/kg), pentane (45), ethane (22), propane (0),
hexane (27) and butane (25). 相似文献