全文获取类型
收费全文 | 1448篇 |
免费 | 113篇 |
国内免费 | 490篇 |
专业分类
测绘学 | 36篇 |
大气科学 | 251篇 |
地球物理 | 600篇 |
地质学 | 730篇 |
海洋学 | 181篇 |
天文学 | 65篇 |
综合类 | 62篇 |
自然地理 | 126篇 |
出版年
2024年 | 9篇 |
2023年 | 32篇 |
2022年 | 30篇 |
2021年 | 21篇 |
2020年 | 24篇 |
2019年 | 34篇 |
2018年 | 58篇 |
2017年 | 15篇 |
2016年 | 35篇 |
2015年 | 28篇 |
2014年 | 70篇 |
2013年 | 54篇 |
2012年 | 89篇 |
2011年 | 110篇 |
2010年 | 46篇 |
2009年 | 67篇 |
2008年 | 101篇 |
2007年 | 95篇 |
2006年 | 101篇 |
2005年 | 93篇 |
2004年 | 84篇 |
2003年 | 52篇 |
2002年 | 74篇 |
2001年 | 48篇 |
2000年 | 52篇 |
1999年 | 21篇 |
1998年 | 28篇 |
1997年 | 27篇 |
1996年 | 37篇 |
1995年 | 27篇 |
1994年 | 22篇 |
1993年 | 59篇 |
1992年 | 33篇 |
1991年 | 44篇 |
1990年 | 43篇 |
1989年 | 36篇 |
1988年 | 30篇 |
1987年 | 37篇 |
1986年 | 22篇 |
1985年 | 34篇 |
1984年 | 19篇 |
1983年 | 18篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 20篇 |
1977年 | 4篇 |
1947年 | 4篇 |
1946年 | 3篇 |
1935年 | 3篇 |
1933年 | 4篇 |
排序方式: 共有2051条查询结果,搜索用时 15 毫秒
71.
Previous studies have identified two emission modes in PSR B1859+07: a normal mode that has three prominent components in the average profile, with the trailing one being the brightest, and an anomalous mode(i.e., the A mode) where emissions seem to be shifted to an earlier phase. Within the normal mode, further analysis has revealed the presence of two submodes, i.e., the cW mode and c B mode, where the central component can appear either weak or bright. As for the anomalous mode, a new bright ... 相似文献
72.
Dong-Xiang Shen Jin-Zhong Liu Chun-Hua Zhu Guo-Liang Lü Yu Zhang Cheng-Long Lü Hao-Zhi Wang Lei Li Xi-Zhen Lu Jin-Long Yu Abdurepqet Rustem 《天文和天体物理学研究(英文版)》2023,(1):20-33
We first present the multicolor photometry results of the rapidly rotating magnetic star HD 345439 using the Nanshan One-meter Wide-field Telescope.From the photometric observations,we derive a rotational period of 0.7699±0.0014 day.The light curves of HD 345439 are dominated by the double asymmetric S-wave feature that arises from the magnetic clouds.Pulsating behaviors are not observed in Sector 41 of the Transiting Exoplanet Survey Satellite.No evidence is found of the occurrence of centrifug... 相似文献
73.
Ronan Connolly Willie Soon Michael Connolly Sallie Baliunas Johan Berglund C. J. Butler Rodolfo Gustavo Cionco Ana G. Elias Valery M. Fedorov Hermann Harde Gregory W. Henry Douglas V. Hoyt Ole Humlum David R. Legates Nicola Scafetta Jan-Erik Solheim László Szarka Víctor M. Velasco Herrera Hong Yan Weijia Zhang 《天文和天体物理学研究(英文版)》2023,(10):369-388
Since 2007, the Intergovernmental Panel on Climate Change(IPCC) has heavily relied on the comparison between global climate model hindcasts and global surface temperature(ST) estimates for concluding that post-1950s global warming is mostly human-caused. In Connolly et al., we cautioned that this approach to the detection and attribution of climate change was highly dependent on the choice of Total Solar Irradiance(TSI) and ST data sets.We compiled 16 TSI and five ST data sets and found by alter... 相似文献
74.
We present the first detailed photometric analysis of ATO J108.6991+27.8306(hereinafter as J108). The shortperiod close binary J108 was observed by the Nanshan 1 m Wide Field Telescope of the Xinjiang Astronomical Observatory. The obtained BVRI-band light curves were used to determine the photometric solution by using the 2003 version of the Wilson-Devinney code. J108 is a typical deep( f > 50%), low mass ratio(q < 0.25)overcontact binary system with a mass ratio of q = 0.1501 and a fill-o... 相似文献
75.
Harmful algal blooms(HABs) have become a recurring problem, posing severe impacts on marine ecosystems, fisheries, mariculture industry, and even public health. In this study, the geographic information system(GIS) was utilized to determine spatial and temporal characteristics of HAB events in the coastal waters of Guangdong from 1980–2016. We analyzed distribution patterns and characteristics of HABs by dividing the coast of Guangdong into well-known bays, estuary and coastal waters. Results showed that there were a total of 337 HABs recorded in Guangdong coastal waters. Spatial and temporal distributions varied among dif ferent regions. Most HABs occurred in the Mirs Bay, followed by the west coast of Daya Bay, while a few occurred in the west and east coasts of Guangdong but with an increasing trend in the past two decades. HABs occurred mostly in warmer months of March to May in the western coast of Guangdong, March and April in Mirs Bay, April in Zhujiang(Pearl) River estuary, November in eastern coast of Guangdong. For Daya Bay, most HABs were reported between March and September.The most frequently occurring HABs species were Noctiluca scintillans, P haeocystis globosa, Skeletonema costatum and Scrippsiella trochoidea, occurring mostly in Mirs Bay, western Guangdong coast area, eastern Guangdong coast area and Zhujiang River estuary and Daya Bay, respectively. Ichthyotoxic blooms were more common than toxic blooms, and Heterosigma akashiwo, Chattonella marina, Karenia mikimotoi and P haeocystis globosa were the most common ichthyotoxic species. Our results provide baseline information useful for policy making and management of HABs in the region. 相似文献
76.
E. Puga Antonio M. alvarez- Valero J. Galindo- Zaldlvar F. Bohoyo A. Maldonado A.Maldonado L. Somoza F. J. Gonzaezz L. Somoza 蔡观强 《海洋地质》2009,(1)
本研究对来自DOVE盆地(Scotia海南部)中部火山山脊的拖网样品进行了详细的岩石学、地球化学分析,辅以K—Ar年代学分析。研究区水深2000~3000m,地理坐标范围为59°21~23′S和42°27~31′w。本研究的目的在于,通过比较研究区火成岩和形成Scotia、Antartic—Phoenix洋中脊及南设得兰群岛的火山岩之间的地球化学特征和同位素特征,厘定研究区岩浆形成的地球动力学背景以及岩浆作用的绝对年龄。 相似文献
77.
Almroth BC Sturve J Stephensen E Holth TF Förlin L 《Marine environmental research》2008,66(2):271-277
The use of fish in environmental monitoring has become increasingly important in recent years as anthropogenic substances, many of which function as prooxidants, are accumulating in aquatic environments. We have measured a battery of antioxidant defenses as a measure of oxidative status, as well as protein carbonylation as a measure of oxidative damage, in corkwing wrasse (Symphodus melops) captured near a disused copper mine, where water and sediment are contaminated with heavy metals, and an aluminum smelter, a site contaminated with PAHs. Results were compared to two different reference sites. Fish at the heavy metal site had lower glucose-6-phosphate dehydrogenase activity and elevated protein carbonyls (1.8 times) compared to fish from the reference site. At the PAH site, EROD was increased 2-fold, while total glutathione and methemoglobin reductase concentration, were decreased. No differences were seen in protein carbonyl levels at the PAH site. Measures of both antioxidant defenses and oxidative damage should be used when assessing effects of xenobiotics on oxidative stress in fish species. 相似文献
78.
Marsili L Casini S Bucalossi D Porcelloni S Maltese S Fossi MC 《Marine environmental research》2008,66(1):151-153
The aim of the present study was to propose the immunofluorescence technique in cultured fibroblasts from Mediterranean cetaceans as a new "in vitro" tool to explore the susceptibility of these marine mammals to different xenobiotic compounds. The cell lines were cultured from integument biopsies of free-ranging and stranded cetaceans (dead within 12h). Using the indirect immunofluorescence assay, we detected endogenous proteins induced by different contaminants. Here we present the method used for qualitative and quantitative evaluation of cytochromes P450 (CYP1A1 and CYP2B) induced by some POPs (DDTs and PCBs) and emerging contaminants (PBDEs) in fibroblast cell cultures of striped dolphin (Stenella coeruleoalba) and bottlenose dolphin (Tursiops truncatus). Immunofluorescence was quantified with a specially designed Olympus macro, DetectIntZ. A major result was the possibility of using this "in vitro" assay to quantify induction of endogenous proteins. 相似文献
79.
Krishnan KP Fernandes SO Loka Bharathi PA Krishna Kumari L Nair S Pratihary AK Rao BR 《Marine environmental research》2008,65(5):445-455
Studies on the Arabian Sea coastal anoxia have been of immense interest, but despite its ecological significance there is sparse understanding of the microbes involved. Hence, observations were carried out off Goa (15 degrees 30'N, 72 degrees 40'E to 15 degrees 30'N, 72 degrees 59'E) to understand the processes that mediate the changes in various inorganic nitrogen species in the water column during anoxia. Water column chemistry showed a clear distinct oxic environment in the month of April and anoxic condition in October. Our study based on microbial signatures indicated that oxygen deficit appeared as a well-defined nucleus almost 40 km away from the coast during the oxic period (April) and spreads there after to the entire water column synchronizing with the water chemistry. Striking results of net changes in inorganic nitrogen species in nitrification blocked and unblocked experimental systems show that denitrification is the predominant process in the water column consuming available nitrate ( approximately 0.5 microM) to near zero levels within approximately 72 h of incubation. These observations have been supported by concomitant increase in nitrite concentration ( approximately 4 microM). Similar studies on denitrification-blocked incubations, demonstrate the potential of nitrification to feed denitrification. Nitrification could contribute almost 4.5 microM to the total nitrate pool. It was found that the relation between ammonium and total dissolved inorganic nitrogen (DIN) pool (r=0.98, p<0.001, n=122) was significant compared to the latter with nitrite and nitrate. The occurrence of high ammonium under low phosphate conditions corroborates our observations that ammonium does not appear to be locked under low oxygen regimes. It is suggested that ammonium actively produced by detrital breakdown (ammonification) is efficiently consumed through nitrification process. The three processes in concert viz. ammonification, nitrification and denitrification appear to operate in more temporal and spatial proximity than hitherto appreciated in these systems and this gives additional cues on the absence of measurable nitrate at surface waters, which was earlier attributed only to efficient algal uptake. Hence we hypothesize that the alarming nitrous oxide input into the atmosphere could be due to high productivity driven tighter nitrification-denitrification coupling, rather than denitrification driven by extraneous nitrate. 相似文献
80.
Diagnosis of trace metal contamination in sediments: the example of Ensenada and El Sauzal, two harbors in Baja California, Mexico 总被引:1,自引:0,他引:1
Huerta-Diaz MA Delgadillo-Hinojosa F Hernández-Ayón M Segovia-Zavala JA García-Esquivel Z López-Zárate H Siqueiros-Valencia A Galindo-Bect S 《Marine environmental research》2008,66(3):345-358
Total metal concentrations in sediments from within Ensenada and El Sauzal Harbors are generally higher than at the mouths. Grain-size analyses suggested that this enrichment could be due to the presence of fine-grained sediments in the inner part of the harbors rather than to anthropogenic perturbations. The (Me/Al)(sample) ratios for Pb, Co, Ni and Fe were significantly higher for Ensenada Harbor relative to El Sauzal Harbor, whereas the ratios for Cd, Mn, Zn and Cu were statistically equivalent for both harbors. Calculated enrichment factors [EF(Me)=(Me/Al)(sample)/(Me/Al)(shale)] indicated that the metals showing slight enrichment were those associated with anthropogenic contamination (Pb, Zn), or probably related to primary productivity in the water column (Cd, Co). The levels of most of the metals were not greatly enriched, a consideration that is of the utmost importance when contamination issues are at stake. 相似文献