全文获取类型
收费全文 | 257篇 |
免费 | 8篇 |
专业分类
测绘学 | 13篇 |
大气科学 | 37篇 |
地球物理 | 61篇 |
地质学 | 70篇 |
海洋学 | 20篇 |
天文学 | 39篇 |
自然地理 | 25篇 |
出版年
2023年 | 1篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 5篇 |
2018年 | 5篇 |
2017年 | 5篇 |
2016年 | 19篇 |
2015年 | 13篇 |
2014年 | 9篇 |
2013年 | 8篇 |
2012年 | 23篇 |
2011年 | 16篇 |
2010年 | 8篇 |
2009年 | 15篇 |
2008年 | 11篇 |
2007年 | 15篇 |
2006年 | 9篇 |
2005年 | 17篇 |
2004年 | 13篇 |
2003年 | 10篇 |
2002年 | 10篇 |
2001年 | 6篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1970年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有265条查询结果,搜索用时 78 毫秒
161.
C.‐I. Lagerkvist O. Karlsson G. Hahn St. Mottola A. Doppler A. Gndig U. Carsenty 《Astronomische Nachrichten》2002,323(5):475-483
We have used the ESO Schmidt telescope during the apparitions 1996, 1997 and 1998 to study the preceding Lagrangian cloud of Jupiter, L4. In our observed field of view, about 700 square degrees, during 1996 we found 399 moving objects that we classified as Trojans. From this we conclude that down to absolute magnitude H ≤ 13.0 there are ≈ 1100 Trojans in the L4 cloud. Proper elements of 696 numbered and multiopposition Trojans were calculated and one of these in the L5 cloud were found to be a non Trojan. A discussion of the Trojan proper elements is also presented. 相似文献
162.
A combination of retention pond and reed bed was tested for its effectiveness in reducing non-point source runoff pollution from an urban area. This paper presents data on the development of reed plants (Phragmites australis Cav. Trin.), on the effectiveness of runoff purification and on the accumulation of contaminants in the pond sediment and the reed bed for the years 1993–1995. P. australis was well established and grew according to normal development. The measured length and biomass values of P. australis were larger on sand than on gravel and coarse materials. Toxic levels of heavy metals in the plants were not reached. Harvested plants can be composted. The purification system is effective within the following ranges: The rate of retention of suspended solids and heavy metals varies between 16% and 91%. For chemical oxygen demand the average values is 25%. Poor retention rates usually occur along with very low input concentrations. Generally retention within the reed bed is higher than in the pond. Between 1993 and 1995 the concentration of contaminants within the organic layer of the reed bed increased by 50% for lead and by 90% for poly aromatic hydrocarbons. Until 1994 the concentrations of mineral oil hydrocarbons also increased by 60%. Between 1994 and 1995 however the concentration of mineral oil hydrocarbons in the reed bed decreased rapidly by more than 50%: Mineral oil hydrocarbons underlie biological degradation within the reed bed. In the pond sediment a significant accumulation of heavy metals, poly aromatic hydrocarbons and mineral oil hydrocarbons has also been found. The concentrations of these contaminants are still far from inhibiting the function of the system. 相似文献
163.
Volatile emission during the eruption of Baitoushan Volcano (China/North Korea) ca. 969 AD 总被引:33,自引:1,他引:32
3 [magma volume (DRE): 24 ± 5 km3]. The main phase (ca. 95 vol.%) is represented by comenditic tephra deposited dominantly as widespread fallout blankets and
proximal ignimbrites. The eruption column is estimated to have reached ca. 25 km and thus entered the stratosphere. A late
phase (5 vol.%) is represented by trachyte emplaced chiefly as moderately welded ignimbrites. The comendites contain ∼ 3,
and the trachytes 10–20 vol.% phenocrysts, mainly anorthoclase, hedenbergite, and fayalite. Primary glassy melt inclusions
with no signs of leakage were found only in phenocrysts in the comenditic tephra, whereas those in phenocrysts in the trachytes
are devitrified. The comendite magma is interpreted to have been generated by fractional crystallization from a trachyte magma
represented by melt inclusions in the phenocrysts in the comendite tephra. The mass of volatiles emitted to the atmosphere
during the eruption was estimated using the petrologic method. The average H2O concentration of the comenditic matrix glass is 1.5 wt.% (probably largely secondary) and of the corresponding melt inclusions
∼ 5.2 wt.%. Melt inclusions in feldspar and quartz present the highest halogen concentrations with a calculated average for
chlorine of 4762 ppm and for fluorine of 4294 ppm. The comenditic matrix glasses are represented by a fluorine-rich (3992 ppm
F) and fluorine-poor group (2431 ppm F), averaging 3853 ppm for chlorine. Only 20% of all sulfur analyses of the comenditic
matrix glasses and melt inclusions are above the detection limit of ≥ 250 ppm S. The difference between pre- and post-eruptive
concentration of H2O is at least 3.7 ± 0.6 wt.% H2O taking into consideration re-hydration of the matrix glass and possible leakage of melt inclusions. The difference between
pre- and post-eruptive concentrations of the halogens amounts to 909 ± 90 ppm Cl, and 1863 ± 280 ppm and 302 ± 40 ppm F. The
difference for S was estimated based on the average of the maximum S concentrations in the melt inclusions (455 ppm S) and
the detection limit, resulting in 205 ± 40 ppm S. The calculated mass of volatiles injected into the atmosphere, based on
the erupted magma volume and volatile data, is 1796 ± 453 megatons for H2O, 45 ± 10 megatons for chlorine, 42 ± 11 megatons for fluorine, and 2 ± 0.6 megatons for sulfur. The 969 ± 20 AD eruption
of Baitoushan Volcano, one of the largest eruptions of the past 2000 years, is thought to have had a substantial but possibly
short-lived effect on climate.
Received: 25 July 1998 / Accepted: 8 September 1999 相似文献
164.
165.
166.
Sources and fate of nutrients in a subtropical reservoir 总被引:1,自引:0,他引:1
Michele?A.?BurfordEmail author Susanne?A.?Green Andrew?J.?Cook Suzanne?A.?Johnson Jason?G.?Kerr Katherine?R.?O’Brien 《Aquatic Sciences - Research Across Boundaries》2012,74(1):179-190
This study examined the sources and fate of nutrient inputs from two principal tributaries to the eutrophic subtropical Wivenhoe
reservoir: an unregulated river and a dammed river with regular releases, during a period of declining reservoir water levels.
Nutrient budgets were constructed over a period of 6 years, and combined with short-term data on nutrient concentrations and
forms, and δ15N stable isotope data. Our study found that over a 6 year period, there was net retention of phosphorus (P) in the reservoir,
with 60% of inputs retained. Most of the P input load came from the unregulated river, with an agricultural catchment, during
periods of high flow. During one event half of the total TP load from the unregulated river in the study period was delivered
in only 12 days. Much of the P was dissolved inorganic P (DIP) and was derived from high P concentrations in soils and sediments.
This highlights the importance of appropriate catchment management practices to reduce P losses from terrestrial systems because
retention of P in reservoir sediments reduces the availability of this nutrient for agricultural production. In contrast,
there was negligible retention of nitrogen (N). The unregulated river was an important source of N derived from N fixation
in the river and adjacent soils, while the source from the dammed river was mostly reprocessed N. The high retention of P
relative to N is consistent with relatively higher accumulation of P in sediments. 相似文献
167.
Tectonic and climate control of oil shale deposition in the Upper Cretaceous Qingshankou Formation (Songliao Basin, NE China) 总被引:4,自引:0,他引:4
Jianliang Jia Zhaojun Liu Achim Bechtel Susanne A. I. Strobl Pingchang Sun 《International Journal of Earth Sciences》2013,102(6):1717-1734
Oil shales were deposited in the Songliao Basin (NE China) during the Upper Cretaceous period, representing excellent hydrocarbon source rocks. High organic matter (OM) contents, a predominance of type-I kerogen, and a low maturity of OM in the oil shales are indicated by bulk geochemical parameters and biomarker data. A major contribution of aquatic organisms and minor inputs from terrigenous land plants to OM input are indicated by n-alkane distribution patterns, composition of steroids, and organic macerals. Strongly reducing bottom water conditions during the deposition of the oil shale sequences are indicated by low pristane/phytane ratios, high C14-aryl-isoprenoid contents, homohopane distribution patterns, and high V/Ni ratios. Enhanced salinity stratification with mesosaline and alkaline bottom waters during deposition of the oil shales are indicated by high gammacerane index values, low MTTC ratios, high β-carotene contents, low TOC/S ratios, and high Sr/Ba ratios. The stratified water column with anoxic conditions in the bottom water enhanced preservation of OM. Moderate input of detrital minerals during the deposition of the oil shale sequences is reflected by titanium concentrations. In this study, environmental conditions in the paleo-lake leading to OM accumulation in the sediments are related to sequence stratigraphy governed by climate and tectonics. The first Member of the Qingshankou Formation (K2qn1) in the Songliao Basin, containing the oil shale sequence, encompasses a third-order sequence that can be divided into three system tracts (transgressive system tract—TST, highstand system tract—HST, and regressive system tract—RST). Enrichment of OM changed from low values during TST-I to high-moderate values during TST-II/III and HST-I/II. Low OM enrichment occurs during RST-I and RST-II. Therefore, the highest enrichment of OM in the sediments is related to stages of mid-late TST and early HST. 相似文献
168.
Uwe Ulbrich Gerd Bürger Dierk Schriever Hans von Storch Susanne L Weber Gerhard Schmitz 《Climate Dynamics》1993,8(6):277-285
The sensitivity of the atmospheric circulation to an increase in ocean surface roughness in the Southern Hemisphere storm track is investigated in a paired general circulation model experiment. Such a change in sea roughness could be induced by ocean waves generated by storms. Two extended permanent-July runs are made. One with standard sea surface roughness, the other with ten times as a large surface roughness over open sea poleward of 40° S. The regional increase in ocean surface roughness significantly modifies the tropospheric circulation in the Southern Hemisphere. The strongest effect is the reduction of tropospheric winds (by 2 m/s or 10%) above the area with increased roughness. The poleward eddy momentum flux is reduced in the upper troposphere and the meridional eddy sensible heat flux is reduced in the lower troposphere. Zonal mean and eddy kinetic energy are consistently reduced. 相似文献
169.
Jun A. Zhang Kristina B. Katsaros Peter G. Black Susanne Lehner Jeffrey R. French William M. Drennan 《Boundary-Layer Meteorology》2008,128(2):173-189
Boundary-layer secondary circulations or ‘roll vortices’ can have a significant influence on the turbulent exchange of momentum,
sensible heat and moisture throughout the hurricane boundary layer. In this study, analyses of data from a WP-3D aircraft
of the National Oceanic and Atmospheric Administration (NOAA) are presented. As part of the Coupled Boundary Layer Air-Sea
Transfer (CBLAST)-hurricane experiment sponsored through the Office of Naval Research and NOAA’s annual hurricane research
program, flights were conducted to investigate energy exchange across the air–sea interface. We present the first in-situ
aircraft-based observations of rolls in the hurricane boundary layer and investigate their influence on energy and momentum
exchange. The rolls detected in Hurricane Isidore (year 2002) have a characteristic wavelength of about 900 m, in good agreement
with analyses of data from a synthetic aperture radar image captured by the Canadian Space Agency’s RADARSAT satellite in
the same storm. Our analyses of the airborne data suggest that roll vortices may be a significant factor modulating the air–sea
momentum exchange. 相似文献
170.
Justin FILIBERTO Emily CHIN James M. D. DAY Ian A. FRANCHI Richard C. GREENWOOD Juliane GROSS Sarah C. PENNISTON‐DORLAND Susanne P. SCHWENZER Allan H. TREIMAN 《Meteoritics & planetary science》2012,47(8):1256-1273
Abstract— The newly found meteorite Northwest Africa 6234 (NWA 6234) is an olivine (ol)‐phyric shergottite that is thought, based on texture and mineralogy, to be paired with Martian shergottite meteorites NWA 2990, 5960, and 6710. We report bulk‐rock major‐ and trace‐element abundances (including Li), abundances of highly siderophile elements, Re‐Os isotope systematics, oxygen isotope ratios, and the lithium isotope ratio for NWA 6234. NWA 6234 is classified as a Martian shergottite, based on its oxygen isotope ratios, bulk composition, and bulk element abundance ratios, Fe/Mn, Al/Ti, and Na/Al. The Li concentration and δ7Li value of NWA 6234 are similar to that of basaltic shergottites Zagami and Shergotty. The rare earth element (REE) pattern for NWA 6234 shows a depletion in the light REE (La‐Nd) compared with the heavy REE (Sm‐Lu), but not as extreme as the known “depleted” shergottites. Thus, NWA 6234 is suggested to belong to a new category of shergottite that is geochemically “intermediate” in incompatible elements. The only other basaltic or ol‐phyric shergottite with a similar “intermediate” character is the basaltic shergottite NWA 480. Rhenium‐osmium isotope systematics are consistent with this intermediate character, assuming a crystallization age of 180 Ma. We conclude that NWA 6234 represents an intermediate compositional group between enriched and depleted shergottites and offers new insights into the nature of mantle differentiation and mixing among mantle reservoirs in Mars. 相似文献