全文获取类型
收费全文 | 54051篇 |
免费 | 554篇 |
国内免费 | 478篇 |
专业分类
测绘学 | 1448篇 |
大气科学 | 3813篇 |
地球物理 | 9924篇 |
地质学 | 19264篇 |
海洋学 | 4919篇 |
天文学 | 12969篇 |
综合类 | 208篇 |
自然地理 | 2538篇 |
出版年
2022年 | 370篇 |
2021年 | 658篇 |
2020年 | 698篇 |
2019年 | 750篇 |
2018年 | 1587篇 |
2017年 | 1508篇 |
2016年 | 1875篇 |
2015年 | 990篇 |
2014年 | 1746篇 |
2013年 | 2866篇 |
2012年 | 1855篇 |
2011年 | 2373篇 |
2010年 | 2068篇 |
2009年 | 2677篇 |
2008年 | 2295篇 |
2007年 | 2347篇 |
2006年 | 2193篇 |
2005年 | 1621篇 |
2004年 | 1638篇 |
2003年 | 1548篇 |
2002年 | 1472篇 |
2001年 | 1298篇 |
2000年 | 1218篇 |
1999年 | 993篇 |
1998年 | 1039篇 |
1997年 | 947篇 |
1996年 | 816篇 |
1995年 | 782篇 |
1994年 | 685篇 |
1993年 | 604篇 |
1992年 | 592篇 |
1991年 | 593篇 |
1990年 | 622篇 |
1989年 | 493篇 |
1988年 | 504篇 |
1987年 | 528篇 |
1986年 | 487篇 |
1985年 | 610篇 |
1984年 | 673篇 |
1983年 | 590篇 |
1982年 | 562篇 |
1981年 | 499篇 |
1980年 | 469篇 |
1979年 | 477篇 |
1978年 | 458篇 |
1977年 | 368篇 |
1976年 | 345篇 |
1975年 | 357篇 |
1974年 | 308篇 |
1973年 | 342篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
G. Tamburello E.P. Kantzas A.J.S. McGonigle A. Aiuppa G. Giudice 《Journal of Volcanology and Geothermal Research》2011,199(1-2):47-52
The UV camera is becoming an important new tool in the armory of volcano geochemists to derive high time resolution SO2 flux measurements. Furthermore, the high camera spatial resolution is particularly useful for exploring multiple-source SO2 gas emissions, for instance the composite fumarolic systems topping most quiescent volcanoes. Here, we report on the first SO2 flux measurements from individual fumaroles of the fumarolic field of La Fossa crater (Vulcano Island, Aeolian Island), which we performed using a UV camera in two field campaigns: in November 12, 2009 and February 4, 2010. We derived ~ 0.5 Hz SO2 flux time-series finding fluxes from individual fumaroles, ranging from 2 to 8.7 t d?1, with a total emission from the entire system of ~ 20 t d?1 and ~ 13 t d?1, in November 2009 and February 2010 respectively. These data were augmented with molar H2S/SO2, CO2/SO2 and H2O/SO2 ratios, measured using a portable MultiGAS analyzer, for the individual fumaroles. Using the SO2 flux data in tandem with the molar ratios, we calculated the flux of volcanic species from individual fumaroles, and the crater as a whole: CO2 (684 t d?1 and 293 t d?1), H2S (8 t d?1 and 7.5 t d?1) and H2O (580 t d?1 and 225 t d?1). 相似文献
132.
The annealing characteristics of fission tracks in allanite have been studied. All the tracks in the mineral fade at 720° C for one hour heating. The activation energy of allanite ranges from 1.4 to 3.4 eV. 相似文献
133.
As a recent trend, the continuous increase of new technologies for space observations of new missions to Mars, Venus, and Titan, has stimulated vigorous experimental and theoretical studies on the collision process induced by interactions between plasma and planetary atmosphere. In order to facilitate the comprehension of these processes, this brief paper chose a collection of cross section data not always easily accessible. With the purpose of making a useful collection of such data we have collected both experimental and theoretical estimate for most of the expected collisions processes. 相似文献
134.
U. S. Chaubey 《Astrophysics and Space Science》1982,81(1-2):283-293
The light curves of eclipsing binary DI Pegasi inU, B. andV filters have been presented and discussed. Photometric elements of the system have been determined. Using the colour indices, we estimate absolute dimensions and discuss the evolutionary status of the system. 相似文献
135.
J. S. Mani 《Natural Hazards》2004,31(2):523-536
Chennai coast, right from the inception of Madras harbourin the year 1876, has been experiencinghostile conditions such as (i) coastal erosion, (ii) sandbar formation at the entrance to inlets, (iii) sea water ingression and (iv) change insea bed elevation, etc. In addition, construction of a new satellite harbour, about18 km north of Madras harbour has produced a negative impact on the delicatecoastal features such as (i) Pulicat lake, (ii) Ennore shoals, etc. Construction ofthis satellite harbour has led to the accumulation of sand south of the southbreakwater of the harbour and its accelerated growth is of concern to an inletlocated 2.6~km south of the harbour. `Coastal erosion', a perennial problemassociated with north Chennai sea front for the past 100 years has been addressedin this paper. The paper discusses on a long term solution and details of themethodologies to be adopted for effective management of the coast. Thesolution presented in this paper is based on numerical model study consideringthe nearshore currents and wave induced sediment transports. 相似文献
136.
137.
H.S. Yoon O.A. El-Samni A.T. Huynh H.H. Chun H.J. Kim A.H. Pham I.R. Park 《Ocean Engineering》2009,36(9-10):697-707
The present study numerically investigates the characteristics of three-dimensional turbulent flow in a wavy channel. For the purpose of a careful observation of the effect of the wave amplitude on the turbulent flow, numerical simulations are performed at a various range of the wave amplitude to wavelength ratio (0.01?α/λ?0.05), where the wavelength is fixed with the same value of the mean channel height (H). The immersed boundary method is used to handle the wavy surface in a rectangular grid system, using the finite volume method. The Reynolds number (Re=UbH/ν) based on the bulk velocity (Ub) is fixed at 6760. The present computational results for a wavy surface are well compared with those of references. When α/λ=0.02, the small recirculating flow occurs near the trough at the instant, but the mean reverse flow is not observed. In the mean flow field, the reverse flow appears from α/λ=0.03 among the wave amplitude considered in this study. The domain of the mean reverse flow defined by the locations of separation and reattachment depends strongly on the wave amplitude. The pressure drag coefficient augments with increasing the wave amplitude. The friction drag coefficient shows the increase and decrease behavior according to the wave amplitude. The quantitative information about the flow variables such as the distribution of pressure and shear stress on the wavy surface is highlighted. 相似文献
138.
139.
J. I. S. Zonneveld Dr. 《GeoJournal》1983,7(2):121-129
Modern geography is based on ecological thinking. In this paper some geoecological notions are discussed: the scales and levels regarding spatial magnitude and complexity, the “hierarchy” of landscape units and espcially the scale of time and the concept of the supper-imposing “stamps”. This last mentioned concept is very important in relation to the problem regarding regionalization and its possibilities. Three “stamps” are recognized: 1. the substrate, 2. the climatic conditions, 3. the human (noötic) influence. Holistic regionalization in which all elements (including the human influences) are telling to full advantage, is unsatisfactory. 相似文献
140.
M.R. Kaplan A. Coronato N.R.J. Hulton J.O. Rabassa P.W. Kubik S.P.H.T. Freeman 《Geomorphology》2007,87(4):284-301
We measured in situ 10Be, 26Al and36Cl on glacial deposits as old as 1.1 Myr in the southernmost part of Patagonia and on northern Tierra del Fuego to understand boulder and moraine and, by inference, landscape changes. Nuclide concentrations indicate that surface boulders have been exposed for far less time than the ages of moraines they sit upon. The moraine ages are themselves constrained by previously obtained 40Ar/39Ar ages on interbedded lava flows or U-series and amino acid measurements on related (non-glacial) marine deposits. We suggest that a combination of boulder erosion and their exhumation from the moraine matrix could cause the erratics to have a large age variance and often short exposure histories, despite the fact that some moraine landforms are demonstrably 1 Myr old. We hypothesize that fast or episodic rates of landscape change occurred during glacial times or near the sea during interglacials. Comparison with boulder erosion rates and exhumation histories derived for the middle latitudes of semi-arid Patagonia imply different geomorphic processes operating in southernmost South America. We infer a faster rate of landscape degradation towards the higher latitudes where conditions have been colder and wetter. 相似文献