全文获取类型
收费全文 | 61934篇 |
免费 | 1302篇 |
国内免费 | 1350篇 |
专业分类
测绘学 | 1490篇 |
大气科学 | 4488篇 |
地球物理 | 12122篇 |
地质学 | 23194篇 |
海洋学 | 5864篇 |
天文学 | 13767篇 |
综合类 | 302篇 |
自然地理 | 3359篇 |
出版年
2022年 | 538篇 |
2021年 | 852篇 |
2020年 | 892篇 |
2019年 | 963篇 |
2018年 | 1838篇 |
2017年 | 1744篇 |
2016年 | 1991篇 |
2015年 | 1188篇 |
2014年 | 1905篇 |
2013年 | 3290篇 |
2012年 | 2293篇 |
2011年 | 2963篇 |
2010年 | 2613篇 |
2009年 | 3272篇 |
2008年 | 2809篇 |
2007年 | 2900篇 |
2006年 | 2765篇 |
2005年 | 1840篇 |
2004年 | 1709篇 |
2003年 | 1588篇 |
2002年 | 1578篇 |
2001年 | 1366篇 |
2000年 | 1305篇 |
1999年 | 1066篇 |
1998年 | 1130篇 |
1997年 | 1049篇 |
1996年 | 916篇 |
1995年 | 857篇 |
1994年 | 810篇 |
1993年 | 687篇 |
1992年 | 674篇 |
1991年 | 626篇 |
1990年 | 730篇 |
1989年 | 570篇 |
1988年 | 554篇 |
1987年 | 691篇 |
1986年 | 528篇 |
1985年 | 704篇 |
1984年 | 769篇 |
1983年 | 674篇 |
1982年 | 688篇 |
1981年 | 589篇 |
1980年 | 623篇 |
1979年 | 525篇 |
1978年 | 520篇 |
1977年 | 481篇 |
1976年 | 447篇 |
1975年 | 450篇 |
1974年 | 449篇 |
1973年 | 484篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
The South Karaku
oil field is located in southeast Turkey, and produces, from the Late Cretaceous Mardin Group, carbonate reservoirs consisting of the Karababa, Derdere, Sabunsuyu and Areban Formations. The Karababa Formation is divided into three members, of which the productive Karababa-C member, discussed here, is composed of shallow marine bioclastic mudstone to wackestone. It is affected by early to late diagenetic processes that caused modification of the original pore system by cementation, dissolution and fracturing. Two petrophysical-petrologic facies can be discriminated by principal component analysis, and linear, multiple and stepwise multiple regression analysis of petrophysical data. These correspond to vuggy-moldic porosity and microporosity dominated reservoirs. 相似文献
993.
A. I. Ryabinin S. A. Bobrova L. V. Saltykova E. A. Danilova 《Physical Oceanography》2012,21(5):320-328
We study the space-and-time variations of the delivery of fluxes of 26 elements (Na, K, Rb, Cs, Cu, Ag, Au, Ca, Sr, Ba, Zn,
Cd, Hg, Hf, Ta, As, Sb, Cr, Se, Mo, W, Mn, Br, Fe, Co and Ni) with atmospheric precipitations to the sea surface in the regions
of Sevastopol and the South Coast of Crimea. It is established A series of general regularities of the delivery of the sum
of these elements and their soluble and insoluble forms. We also give the characteristics of their space-time variability. 相似文献
994.
A computational method for diagnosing three-dimensional atmospheric fronts from temperature, wind, and geopotential fields
on a three-dimensional regular grid is proposed. The criterion, which serves for the diagnosis of atmospheric fronts, is discussed.
The weights of the input information about the mentioned fields are optimized based on the maximal difference between the
correlation functions for (a) pairs of particles separated by the front and (b) pairs from one synoptic mass. These weights
were different for different baric levels. The correlation functions and the optimization of weights were estimated on the
basis of the archive of fields of the NCEP objective analysis on the half-degree latitude-longitude grid and data from aerological
observations. The results of numerical experiments on the construction of atmospheric fronts are presented. Applying the described
method to fields predicted for a term of up to 36 h showed that errors in the prognostic models introduce a relatively weak
distortion into the geometry of atmospheric fronts. 相似文献
995.
Avianna F. Zhukovskaya Nina N. Belcheva Valentina S. Slobodskova Viktor P. Chelomin 《Ocean Science Journal》2012,47(3):189-195
Organisms have evolved a cellular response called stress protein response that increases their tolerance in adverse environmental conditions. Well known stress proteins that bind essential and toxic metals are metallothionein (MT). The scallop Mizuhopecten yessoensis is the most interesting organism because it is able to accumulate toxic cadmium in its digestive gland. However, in the tissue of the digestive gland of Mizuhopecten yessoensis MT (metallothioneins) have not been found. Eastern scallops, Mizuhopecten yessoensis, were collected from two locations ?? one clean and one polluted site. The concentrations of cadmium (Cd), copper (Cu) and zinc (Zn) were measured in the digestive gland. There was a significant increase in Cd concentrations in this studied tissue. We found that in the presence of cadmium Mizuhopecten yessoensis can induce high molecular proteins. The results of experiments have shown that Cd-binding ligands have a number of properties similar to MT: acetone and temperature stability; the ability to bind some metals, including Cd, Cu and Zn. Protein chromatography (FPLC, Superosa 12) from the digestive gland of scallop M. yessoensis has shown that cadmium is associated with high molecular weight Cd-binding proteins (72 kDa and 43 kDa). The major cadmium-binding protein 72 kDa is glycoprotein. In experiments we have demonstrated that Cd-binding proteins can be induced when there is cadmium exposure. The results of this study strongly suggest that the far eastern scallop Mizuhopecten yessoensis has a unique and well-developed system for the detoxification of heavy metals and it allows for biochemical systems to be maintained in a relatively stable manner in the presence of heavy metals. 相似文献
996.
997.
Johanna Mattila Glen Chaplin Michele R. Eilers Kenneth L. Heck Jr. Jonathan P. O'Neal John F. Valentine 《Journal of Sea Research》1999,41(4):209
Fish, epibenthos and macroinfauna were collected in a Zostera marina bed and nearby unvegetated sediments in the estuary of the Damariscotta River, on the mid-coast of Maine. Samples of epibenthic fauna and fish were collected at low tides both during day and night, and samples of infauna at low tides during the day. The mean density of Zostera shoots in the study area was 335 m−2. Abundance and species number of fish were greater at night than during the day and greater in eelgrass beds (Z. marina) than in unvegetated habitats. Daytime fish collections were dominated by Atlantic silversides (Medinia medinia), while juvenile winter flounder (Pseudopleuronectes americanus) dominated night collections. Also Zostera-associated epifaunal abundances and number of species were significantly higher at night than during the day. Mysis stenolepis, Idotea balthica and Littorina obtusata were dominant species in the epifauna samples. Of the total of 37 invertebrate species encountered, only five occurred both in the infaunal and epifaunal samples. Nineteen different taxa were collected from the benthic core samples. The most abundant invertebrate infaunal taxa were sipunculids, the polychaete Nereis virens, and oligochaetes. Infaunal invertebrate abundances and species diversity were significantly higher in eelgrass beds than in unvegetated sediments. The abundance and number of species of benthic invertebrates were also positively correlated to seagrass biomass. Community diversity values (H′) were relatively low but fit well in the general pattern of decreasing diversity towards northern latitudes. 相似文献
998.
A study was conducted to understand the mechanisms driving observed subtidal variability in the stratification of Saldanha Bay, located in the southern Benguela system. It was found that the 6–8 day period variability in bay stratification was caused by the inflow and outflow of cold upwelled water driven by changing baroclinic pressure gradients between the coastal and bay domains. The direction and magnitude of the pressure gradients were governed by coastal upwelling activity and a lag in the response of the bay to changes in density structure in the coastal ocean. When the pressure gradients were bayward and cold water was being driven into the bay the cycle was termed to be in an ‘ active phase ’ and the reverse was termed the ‘ relaxation phase ’. The upwelling-favourable equatorward wind stress impacted the bay stratification in two ways: on the regional scale, wind drives upwelling and governs the inflow–outflow of cold upwelled bottom water, which strengthens stratification; conversely, on the local bay scale, wind drives vertical mixing, which weakens stratification. A four-phase model is used to describe the observed variability in stratification in the bay. The associated density-driven exchange flows are capable of flushing the bay in 6–8 days, about one-third of the time for tidal exchange alone (c. 25 days). These inflows of cold bottom water are ecologically critical as they supply nutrients to the bay and thus impose a control on new production within the bay environment. Further ecological implications of this bay–ocean exchange include export of phytoplankton new production to the coast, limitation of the risk of harmful algal blooms (HABs) and the division of the system into two distinct ecosystems (bay and lagoon). 相似文献
999.
1000.
Oceanology - The multidisciplinary expedition “European Arctic-2020” on board the R/V Akademik Mstislav Keldysh took place from July 31 to August 26, 2020. The investigations were... 相似文献