全文获取类型
收费全文 | 362篇 |
免费 | 12篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 26篇 |
地球物理 | 86篇 |
地质学 | 118篇 |
海洋学 | 21篇 |
天文学 | 88篇 |
综合类 | 3篇 |
自然地理 | 18篇 |
出版年
2022年 | 2篇 |
2019年 | 5篇 |
2018年 | 18篇 |
2017年 | 6篇 |
2016年 | 13篇 |
2015年 | 4篇 |
2014年 | 12篇 |
2013年 | 17篇 |
2012年 | 16篇 |
2011年 | 13篇 |
2010年 | 17篇 |
2009年 | 17篇 |
2008年 | 15篇 |
2007年 | 18篇 |
2006年 | 20篇 |
2005年 | 15篇 |
2004年 | 11篇 |
2003年 | 12篇 |
2002年 | 12篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 8篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1990年 | 4篇 |
1989年 | 9篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1973年 | 3篇 |
1959年 | 2篇 |
1958年 | 1篇 |
1956年 | 1篇 |
1955年 | 2篇 |
1953年 | 1篇 |
1950年 | 3篇 |
1949年 | 3篇 |
1948年 | 1篇 |
1941年 | 1篇 |
排序方式: 共有376条查询结果,搜索用时 15 毫秒
161.
162.
Two toxic polypeptides BTTX I and BTTX II were isolated from the sea anemone Bolocera tuediae. Toxin isolation was achieved by alcoholic extraction of the homogenized tentacles and filaments, batchwise adsorption onto ion-exchangers (QAE-Sephadex A25, CM-Cellulose, Se-Cellulose, Sp-Sephadex C25), gel filtration on Sephadex G50 and G25 and ion-exchange chromatography on SP-Sephadex C25 and QAE-Sephadex A25. The toxins were tested on the shore crab Carcinus maenas by intramuscular injection. LD100 for BTTX I is 500 μg kg−1 C. maenas, whereas the BTTX II it is 40 μg kg−1. The molecular weights of both toxins are estimated to be 5000 Dalton. 相似文献
163.
Time-series of surface water CO2 and oxygen measurements on a platform in the central Arkona Sea (Baltic Sea): Seasonality of uptake and release 总被引:1,自引:1,他引:1
Joachim Kuss Wolfgang Roeder K.-Peter Wlost Michael D. DeGrandpre 《Marine Chemistry》2006,101(3-4):220-232
High resolution measurements of carbon dioxide and oxygen were made in surface waters of the central Arkona Sea (Baltic Sea) from May 2003 to September 2004. Sensors for CO2 partial pressure (pCO2w) and oxygen (O2) concentration were mounted in 7 m depth on a moored platform which is used for hydrographic and meteorological monitoring. The pCO2w data were obtained in half hour intervals and O2 was measured each hour as an average of a 10 min measurement. To check the performance of the sensors, pCO2w and O2 were determined by shipboard measurements on a research vessel which visited the site in 1–2 month intervals. In addition, pCO2w was measured on a “volunteer observing ship” (VOS) passing the platform each second day at a distance of about 25 km. Minima of 220 to 250 μatm of pCO2w were observed at the time of the spring bloom and a cyanobacteria bloom in mid-summer. During winter the pCO2w was mostly close to equilibrium with the atmosphere but maxima of 430 to 530 μatm were also observed. The seasonality of oxygen and pCO2w showed an opposing pattern. From a multiple regression analysis, we concluded that two processes primarily controlled pCO2w during our study: biological turnover and mixing. A parameterization, based on apparent oxygen utilisation (AOU) and salinity (S) only (pCO2w = 1.23 AOU + 43 S), reproduced the seasonality of pCO2w in surface water reasonably well. Based on our pCO2, salinity, and temperature data set, we attempted to separate processes changing total inorganic carbon concentrations (CT) by using an alkalinity–salinity relation for the area. The contribution of CO2 gas exchange and mixing were calculated and from this the biological turnover was deduced to reveal the calculated CT changes.The net annual uptake of CO2 in the central Arkona Sea was estimated to be about 1.5 Tg (1.5·1012 g) which was approximately balanced by a net oxygen release considering the uncertainties of the flux calculations. Near-coast CO2 emission due to episodic upwelling partly compensated the uptake of the central part of the Arkona Sea reducing the overall magnitude of the CO2 uptake. 相似文献
164.
165.
Jef Guelinckx Joachim Maes Loreto De Brabandere Frank Dehairs Frans Ollevier 《Estuarine, Coastal and Shelf Science》2006,66(3-4):612-623
Large numbers of young of the year herring (Clupea harengus L.) and sprat (Sprattus sprattus (L.)) typically enter and remain within North Sea estuaries during the winter months. The main purpose of this study was to examine their migration dynamics between the North Sea and the Schelde estuary using C and N stable isotopes. Prior to this, stomach contents were used to verify the isotopic differences between the food sources at the sampling stations. From May 2000 to April 2001 fish were collected monthly in the upper and lower estuary. Muscle tissue and stomach contents were analyzed for δ13C and δ15N using an EA-IRMS. Based on the stomach contents, it was demonstrated that δ15N could not be used as a tracer for fish migration because the longitudinal estuarine δ15N gradient had reversed completely during autumn. The δ13C gradient, however, was found to be reliable for studying fish movement in the Schelde estuary.Seasonal movements of clupeoids in the Schelde estuary were analyzed by separating the temporal abundance patterns into migration groups based on their muscle isotopic composition. Immigration and emigration seem to occur continuously throughout the year. Most exchange occurred in November. During winter, immigration remained high but gradually decreased. Although the herring and sprat abundance further declined in the estuary during February and March, large seaward emigration was not fully demonstrated. As temporal overlap between immigration and emigration is concluded the results support the hypothesis that migration to estuarine nurseries is individually based. 相似文献
166.
VGDI – Advancing the Concept: Volunteered Geo‐Dynamic Information and its Benefits for Population Dynamics Modeling 下载免费PDF全文
Christoph Aubrecht Dilek Özceylan Aubrecht Joachim Ungar Sérgio Freire Klaus Steinnocher 《Transactions in GIS》2017,21(2):253-276
The concept of Volunteered Geographic Information (VGI) has progressed from being an exotic prospect to making a profound impact on GIScience and geography in general, as initially anticipated. However, while massive and manifold data is continuously produced voluntarily and applications are built for information and knowledge extraction, the initially introduced concept of VGI lacks certain methodological perspectives in this regard which have not been fully elaborated. In this article we highlight and discuss an important gap in this concept, i.e. the lack of formal acknowledgment of temporal aspects. By coining the proposed advanced framework ‘Volunteered Geo‐Dynamic Information’ (VGDI), we attempt to lay the ground for full conceptual and applied spatio‐temporal integration. To illustrate that integrative approach of VGDI and its benefits, we describe the potential impact on the field of dynamic population distribution modeling. While traditional approaches in that domain rely on survey‐based data and statistics as well as static geographic information, the use of VGDI enables a dynamic setup. Foursquare venue and user check‐in data are presented for a test site in Lisbon, Portugal. Two core modules of spatio‐temporal population assessment are thereby addressed, namely time use profiling and target zone characterization, motivated by the potential integration in existing population dynamics frameworks such as the DynaPop model. 相似文献
167.
The goal of this work is to derive the physical properties of dust envelopes around post-AGB stars by means of radiative transfer calculations. The model spectral energy distributions (SEDs) have been compared with observational data of the post-AGB stars IRAS 10215-5916, 16342-3814, 17150-3224, and 19500-1709 in the wavelength range from 0.4 to 1300µm. The match between our model SEDs and the observational data is very satisfactory. As a result, we have obtained estimates of the inner and outer radii, the density, the temperature, and the mass of the envelopes of the four objects. 相似文献
168.
169.
Joachim Bartz 《International Journal of Earth Sciences》1949,37(1):113-114
Ohne Zusammenfassung 相似文献
170.