全文获取类型
收费全文 | 8503篇 |
免费 | 350篇 |
国内免费 | 97篇 |
专业分类
测绘学 | 205篇 |
大气科学 | 576篇 |
地球物理 | 1993篇 |
地质学 | 3077篇 |
海洋学 | 779篇 |
天文学 | 1292篇 |
综合类 | 19篇 |
自然地理 | 1009篇 |
出版年
2021年 | 89篇 |
2020年 | 114篇 |
2019年 | 115篇 |
2018年 | 167篇 |
2017年 | 167篇 |
2016年 | 233篇 |
2015年 | 198篇 |
2014年 | 202篇 |
2013年 | 480篇 |
2012年 | 259篇 |
2011年 | 312篇 |
2010年 | 291篇 |
2009年 | 357篇 |
2008年 | 335篇 |
2007年 | 287篇 |
2006年 | 334篇 |
2005年 | 252篇 |
2004年 | 296篇 |
2003年 | 271篇 |
2002年 | 276篇 |
2001年 | 177篇 |
2000年 | 177篇 |
1999年 | 151篇 |
1998年 | 148篇 |
1997年 | 112篇 |
1996年 | 118篇 |
1995年 | 119篇 |
1994年 | 130篇 |
1993年 | 117篇 |
1992年 | 116篇 |
1991年 | 111篇 |
1990年 | 107篇 |
1989年 | 87篇 |
1988年 | 91篇 |
1987年 | 123篇 |
1986年 | 104篇 |
1985年 | 169篇 |
1984年 | 192篇 |
1983年 | 150篇 |
1982年 | 143篇 |
1981年 | 135篇 |
1980年 | 117篇 |
1979年 | 128篇 |
1978年 | 124篇 |
1977年 | 108篇 |
1976年 | 98篇 |
1975年 | 96篇 |
1974年 | 72篇 |
1973年 | 90篇 |
1972年 | 50篇 |
排序方式: 共有8950条查询结果,搜索用时 15 毫秒
131.
In mammals, the induction of cytochrome P4501A forms by chlorinated dibenzo-p-dioxins, chlorinated dibenzofurans, and halogenated biphenyls is under control of a soluble protein known as the Ah (aromatic hydrocarbon) receptor. Little is known about the presence and properties of the Ah receptor in other vertebrate and invertebrate species. In these studies, we sought evidence for an Ah receptor in the liver or liver-equivalent of 20 species of marine and freshwater animals, using the photoaffinity ligand 2-azido-3-[125I] iodo-7,8-dibromodibenzo-p-dioxin (N3[125I]Br2DD). Specific labeling of cytosolic proteins by N3[125I]Br2DD was observed in seven species of teleost and elasmobranch fish, in PLHC-I fish hepatoma cells, and in beluga whales. No specifically labeled proteins were found in cytosol from two species of agnathan fish nor in any of nine invertebrate species representing eight classes of four phyla. The presence or absence of specifically labeled polypeptides corresponds with the inducibility of cytochrome P4501A and sensitivity to the toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin and related planar halogenated aromatic hydrocarbons in many of these groups. Thus, Ah receptor function may have arisen early invertebrate evolution and has been conserved from elasmobranch and teleost fish to mammals. 相似文献
132.
133.
Kinetic studies have been carried out on the dissolution of 10μm beads of silica and of the siliceous tests of two species of diatoms (Thalassiosira fluviatus andSkeletonema costatum) in sea water at 10–50°C and over the pH range 6–9. At all temperatures dissolution of the biogenous silica occurred most
rapidly at pH 8 and most slowly at pH 6. First order kinetics were closely followed when the silica was present in a considerable
excess over that required for saturation, the rate being proportional to the area of the silica. Apparent deviation from this
type of kinetics occurred when there was insufficient silica to bring about saturation. This was undoubtedly due to the progressive
decrease in the surface area which takes place as the particle dissolves. Application of the rather simplistic model developed
by Kamataniet al. (1980), which makes allowance for this decrease, gave a close correspondence with the data until ∼ 90% of the silica had
dissolved. 相似文献
134.
135.
Textural isotopic and microfossil data from two gravity cores obtained in Saguenay Fjord, Quebec, suggest that a distinctive sandy clay bed was deposited as the result of a major landslide in the Saguenay River basin. Pb-210 dating of the cores indicate that the bed is of similar age to the magnitude 7 earthquake of February 5, 1663. The slide involved sensitive marine clays and may have occurred in two stages. Slide sediments carried into the Saguenay River channel were probably reworked and subsequently transported down the Fjord basin as two distinct cohesionless mass flows. Fine clay laminae that overlie the older mass flow bed record the modulation of depositional processes by tidal currents for several weeks after this event. 相似文献
136.
John D. Wang 《Ocean Engineering》1987,14(3)
A 3-dimensional model methodology for predicting the upper ocean currents under the combined influence of Gulf Stream and hurricane is described. Predicted currents are highly dependent on the turbulence closure scheme and nonlinear interactions. New field data will be required to determine the appropriate formulation for turbulent momentum transfer. However, the model points out the importance of nonlinear terms in the equations of motions for preserving the jet-like structure of the Gulf Stream and for properly accounting for interaction between the Gulf Stream and a hurricane. A potentially worst case condition is obtained for the so-called resonant hurricane. 相似文献
137.
138.
Multi-proxy evidence of long-term changes in ecosystem structure in a Danish marine estuary, linked to increased nutrient loading 总被引:3,自引:0,他引:3
Marianne Ellegaard Annemarie L. Clarke Nina Reuss Simon Drew Kaarina Weckstrm Stephen Juggins N. John Anderson Daniel J. Conley 《Estuarine, Coastal and Shelf Science》2006,68(3-4):567
This paper presents a study of changes in eutrophication over the past 100 years in a fertile estuary. The Danish estuary Mariager Fjord is a long, narrow sill-fjord with a permanently anoxic basin. In 1997 anoxia spread from the basin to the entire inner estuary, killing almost all eukaryotes and prompting debate on the causes. This paper reports a multi-proxy survey of 210Pb-dated sediment cores from the anoxic basin. Analyses of diatoms, dinoflagellates, pigments and geochemical proxies were used to determine changes in ecosystem structure over the past 100 years. The aim was to establish ‘base-line conditions’, for management purposes, of the biological structure prior to 1900, and to examine possible causes of changes observed. Geochemical proxies total nitrogen (TN), total carbon (TC) and biogenic silica (BSi) were consistently high throughout the sediment record. Increased concentrations of pigments and natural isotopes (δ13C, δ15N) suggested increasing production and nutrient loading. The main changes in the biological proxies occurred between 1915 and the 1940s, and indicated that the estuary has been somewhat eutrophic since 1900, but that the eutrophication process increased over the past 100 years. A reconstruction of TN concentration by a diatom-based transfer function supports this interpretation, with inferred TN ca. 1900 around 60 μmol l−1, and an increase in TN concentration over the past century to ca. 130 μmol l−1 by 1995. Inferred TN decreased to ca. 100 μmol l−1 by 2001, similar to present day monitoring data. 相似文献
139.
John K. Hall 《Marine Geophysical Researches》2006,27(1):1-5
This special issue of Marine Geophysical Researches presents five papers dealing with GEBCO, the General Bathymetric Chart
of the Oceans, which celebrated its Centennial in April 2003, hosted by the International Hydrographic Bureau and the Principality
of Monaco. Over the past 103 years GEBCO has been the sole body dedicated to compiling all available data to produce standardized
maps of the oceans and seas covering 71% of planet Earth. Over time GEBCO has undergone a complete transformation as sparse
500 m contours on paper charts were replaced by digital grids with ever-increasing resolution. The 2003 Centennial saw the
release on two CDROMS with the first global 1′ grid, produced by methods unheard of in 1984, when GEBCO’s last 6th Edition
paper chart set was published. In GEBCO’s second century, the thrust is towards global grids that will capture the resolutions
available with evolving deep-water swath mapping technologies, as well as vast improvement in the details of the shallow continental
shelves that have traditionally been the preserve of the hydrographic community. As little more than 10% of the oceans have
been mapped to the desired level of detail, there is much to be done. However refinements in satellite altimetry appear to
offer an interim stop-gap as more multi-beam sonars ply the oceans and as the littoral countries of the world map their adjacent
marine areas for submission under Article 76 of UNCLOS (United Nations, 1983, 1999). In addition GEBCO is becoming increasingly proactive, with outreach to the public via the internet and a new GEBCO Map
of the World, active data-scrounging, and encouraging development of the first drifting buoys for acquiring data in the inaccessible
areas of the Antarctic, SW Pacific, and Arctic Oceans. 相似文献
140.
A 15-month study of zooplankton ingestion by farmed mussels (Mytilus edulis) in Bantry Bay, Southwest Ireland 总被引:4,自引:1,他引:4
There is a growing body of evidence to suggest that bivalve molluscs routinely ingest zooplankton. To elucidate further these observations, a 15-month study of zooplankton ingestion by farmed mussels was conducted using mussel long-lines in Bantry Bay, Ireland. Stomach content analysis of the mussels showed that there was evidence of zooplankton ingestion throughout the sampling period, but that highest mean numbers of zooplankters were ingested by mussels in the spring and summer months. Various zooplankton species were present in mussel stomachs. Harpacticoid copepods were found more often in stomach contents than calanoid copepods, probably due to their proximity to the bivalves' inhalent siphons. Barnacle cyprids featured in large numbers in stomach contents, but only for a period of 3 months which broadly corresponded with their pelagic phase. Sizes of ingested zooplankton ranged from 126 μm to 6 mm, but more of the smaller zooplankters (e.g. crustacean nauplii) were ingested. When lengths of ingested copepods were compared with those found in plankton net samples, it was found that the net-sampled copepods were significantly larger than those found in mussel stomachs, suggesting that mussels select for smaller categories within the zooplankton available to them. Soft bodied zooplankton was rarely found in mussel stomachs but their absence may be due to rapid digestion or they may have been destroyed in the preservation process. Ingestion of zooplankton by bivalves is discussed in the context of the impacts mussel farms have on resident zooplankton populations. 相似文献