全文获取类型
收费全文 | 85218篇 |
免费 | 1378篇 |
国内免费 | 525篇 |
专业分类
测绘学 | 1755篇 |
大气科学 | 5606篇 |
地球物理 | 16254篇 |
地质学 | 30783篇 |
海洋学 | 7867篇 |
天文学 | 19904篇 |
综合类 | 222篇 |
自然地理 | 4730篇 |
出版年
2022年 | 619篇 |
2021年 | 1046篇 |
2020年 | 1115篇 |
2019年 | 1247篇 |
2018年 | 2550篇 |
2017年 | 2360篇 |
2016年 | 2718篇 |
2015年 | 1353篇 |
2014年 | 2616篇 |
2013年 | 4486篇 |
2012年 | 2861篇 |
2011年 | 3692篇 |
2010年 | 3373篇 |
2009年 | 4263篇 |
2008年 | 3716篇 |
2007年 | 3830篇 |
2006年 | 3550篇 |
2005年 | 2521篇 |
2004年 | 2445篇 |
2003年 | 2282篇 |
2002年 | 2272篇 |
2001年 | 1970篇 |
2000年 | 1954篇 |
1999年 | 1536篇 |
1998年 | 1595篇 |
1997年 | 1465篇 |
1996年 | 1243篇 |
1995年 | 1242篇 |
1994年 | 1042篇 |
1993年 | 1007篇 |
1992年 | 934篇 |
1991年 | 967篇 |
1990年 | 935篇 |
1989年 | 817篇 |
1988年 | 751篇 |
1987年 | 883篇 |
1986年 | 773篇 |
1985年 | 946篇 |
1984年 | 1070篇 |
1983年 | 1031篇 |
1982年 | 950篇 |
1981年 | 891篇 |
1980年 | 792篇 |
1979年 | 748篇 |
1978年 | 726篇 |
1977年 | 618篇 |
1976年 | 626篇 |
1975年 | 613篇 |
1974年 | 589篇 |
1973年 | 656篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
Despite the fact that BaP is a carcinogen, mammalian immunosuppressant, and ubiquitous aquatic pollutant, knowledge regarding the effects of BaP on the immune system of fish is still lacking. To begin to fill this gap, studies were conducted in medaka to examine the effects and mechanisms by which BaP exposure might alter host immunocompetence. Fish, exposed by IP injection of BaP (2-600 microg/g BW), were examined after 48 h for effects upon immune function and CYP1A expression/activity. Benzo[a]pyrene, at a concentration below that which increased levels of CYPIA expression/activity (2 microg BaP/g BW) suppressed lymphocyte proliferation. Concentrations of BaP at 20 and 200 microg/g BW. suppressed antibody-forming cell (AFC) numbers, superoxide production, and host resistance against bacteria. In contrast, exposure to the low affinity aryl hydrocarbon receptor (AhR) agonist, benzo[e]pyrene (BeP), neither induced CYP1A expression nor altered immune function. Given the lack of immunosuppressive effects produced by BeP, and the fact that exposure to the AhR antagonist (and CYP1A inhibitor) alpha-naphthoflavone (ANF) ameliorated the suppressive effects of BaP upon AFC numbers, the AhR pathway (including CYP1A-mediated production of reactive BaP metabolites) appears important in mediating BaP-induced immunotoxicity in fish, as in mammals. In the past, the medaka has proven a successful model for assessing carcinogenic agents. These studies have demonstrated its utility for also determining the immunosuppressive effects of an important aquatic contaminant. 相似文献
994.
Recent events concerning Atlantic salmon escapees in the Pacific 总被引:1,自引:0,他引:1
995.
A. Mascle R. Vially E. Deville B. Biju-Duval J.P. Roy 《Marine and Petroleum Geology》1996,13(8):941-961
The Southeast Basin of France is the thickest onshore French sedimentary basin which contains locally as much as 10 km of Mesozoic-Cenozoic sediment. Basin development occurred in several stages between late Carboniferous and late Cretaceous times. Partial tectonic inversion took place during two compressive events, the so-called ‘Pyrenean’ and ‘Alpine’ phases of late Cretaceous-early Tertiary and late Tertiary ages respectively. They are separated by an intervening stretching event of Oligocene age, which further south resulted in the opening of the western Mediterranean oceanic basin. As a result of this complex tectonic history, structural traps were difficult to image on the seismic data shot during the first phase of exploration prior to 1980. Oil and gas natural seeps, and shows in several wells, indicate that some petroleum systems are, or have been active, at least in some places.The present erosional western margin of the basin is more or less superimposed on the initial Triassic-Jurassic margin. Margin subsidence and Tertiary inversion are discussed using regional sections on which the polyphase history of the entire basin is well shown. These sections are located on three major segments where the Mesozoic margin is either partly preserved (Ardèche), or has been partly inverted in late Tertiary times (Vercors-Chartreuse), or has been completely inverted in early Tertiary times (Corbières-eastern Pyrenees). 1-D ‘Genex’ basin modelling on the Ardèche segment, and 2-D ‘Thrustpack’ structural-maturity modelling in the Vercors-Chartreuse segment are used to further assess the remaining petroleum plays. 相似文献
996.
Steven A. Hughes 《Coastal Engineering》1993,20(3-4)
Most coastal and ocean engineering laboratories employ techniques that use two or three spatially separated wave gages to estimate reflection of irregular waves in two-dimensional wave flumes. This paper presents a frequency domain method for separating incident and reflected wave spectra from co-located gages (gages located on the same vertical line). The technique is based on linear wave theory, and it can be applied to time series of sea surface elevation and horizontal water velocity collected in a vertical array, or it can be used with horizontal and vertical water velocity time series collected at the same point in the water column. Application of the method is limited to those frequencies showing good coherence between time series signals. Outside the range of good coherence, gross inaccuracies occur.The utility of the co-located gage method is illustrated using water velocity data collected in a wave flume with a laser Doppler velocimeter, and the method is validated for the case of complete reflection by a vertical wall. Side-by-side comparison to the spatially-separated wave gage method of Goda and Suzuki (1976) exhibited close agreement for a variety of irregular wave trains being weakly reflected by a mild sloping beach. The co-located gage method is useful in situations where there are spatial variations in the wavelength, such as on a mildly sloping bottom, or in the region close to highly reflective structures where errors arising from spatial variations in characteristic wave parameters would corrupt estimates made using the spatially-separated wave gage method. 相似文献
997.
Keith A. W. Crook 《Geo-Marine Letters》1986,5(4):203-209
Multichannel seismic reflection profiles recorded in the northern Red Sea show structures that we interpret to be a result of the intrusion of uppermost Miocene salt. We believe that the evaporites are underlaid by attenuated continental crust and the flow of salt is due to renewed faulting of basement in the Pliocene when sea floor spreading began between latitudes 21°N and 15°30°N. 相似文献
998.
999.
The potential of heterotrophs to degrade aromatic hydrocarbons derived from oil in water and sediments in the northern North Sea around the Brent, Beryl, Forties and Murchison oilfields and at a number of stations, from the Forties field to the Firth of Forth, was estimated using 1-14C naphthalene and 7, 10-14C benzo(a)pyrene. The degradation of uniformly labelled 14C mixed 1-amino acids was used as a measure of total heterotrophic activity. Results showed that microorganisms have the potential to degrade the smaller aromatic hydrocarbon molecules rapidly in the water column and in surface sediments. Close to the Beryl platform, where diesel-washed drill cuttings have been continuously dumped, the rate of input of hydrocarbons to the sediment has exceeded the rate of degradation. Mineralization of benzo(a)pyrene, estimated in the sediments only, was minimal. Close to production platforms the biodegradation rate of mixed 1-amino acids showed no increase comparable with that found for naphthalene, suggesting that existing microbial populations had not increased but adapted to degrade oil in water and sediments. 相似文献
1000.