全文获取类型
收费全文 | 433篇 |
免费 | 25篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 31篇 |
地球物理 | 92篇 |
地质学 | 191篇 |
海洋学 | 15篇 |
天文学 | 109篇 |
自然地理 | 20篇 |
出版年
2020年 | 5篇 |
2019年 | 7篇 |
2018年 | 6篇 |
2017年 | 6篇 |
2016年 | 16篇 |
2015年 | 15篇 |
2014年 | 18篇 |
2013年 | 19篇 |
2012年 | 15篇 |
2011年 | 23篇 |
2010年 | 21篇 |
2009年 | 20篇 |
2008年 | 14篇 |
2007年 | 14篇 |
2006年 | 13篇 |
2005年 | 6篇 |
2004年 | 21篇 |
2003年 | 8篇 |
2002年 | 14篇 |
2001年 | 13篇 |
2000年 | 12篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1997年 | 5篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 16篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1980年 | 11篇 |
1979年 | 4篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 8篇 |
1974年 | 5篇 |
1973年 | 3篇 |
1971年 | 5篇 |
1970年 | 4篇 |
1967年 | 4篇 |
1966年 | 2篇 |
1964年 | 3篇 |
1962年 | 4篇 |
排序方式: 共有462条查询结果,搜索用时 15 毫秒
91.
本文介绍用电子束CT作冠状动脉可视化造影的方法,说明本项成就的特征和在应用这项技术的局限性,并指出这种技术在临床上,可能成为新无创伤性的诊断工具。 相似文献
92.
Stable carbon isotope distribution of particulate organic matter in the ocean: a model study 总被引:4,自引:0,他引:4
Matthias Hofmann Dieter A. Wolf-Gladrow Taro Takahashi Steward C. Sutherland Katharina D. Six Ernst Maier-Reimer 《Marine Chemistry》2000,72(2-4)
The stable carbon isotopic composition of particulate organic matter in the ocean, δ13CPOC, shows characteristic spatial variations with high values in low latitudes and low values in high latitudes. The lowest δ13CPOC values (−32‰ to −35‰) have been reported in the Southern Ocean, whereas in arctic and subarctic regions δ13CPOC values do not drop below −27‰. This interhemispheric asymmetry is still unexplained. Global gradients in δ13CPOC are much greater than in δ13CDIC, suggesting that variations in isotopic fractionation during organic matter production are primarily responsible for the observed range in δ13CPOC. Understanding the factors that control isotope variability is a prerequisite when applying δ13CPOC to the study of marine carbon biogeochemistry. The present model study attempts to reproduce the δ13CPOC distribution pattern in the ocean. The three-dimensional (3D) Hamburg Model of the Oceanic Carbon Cycle version 3.1 (HAMOCC3.1) was combined with two different parametrizations of the biological fractionation of stable carbon isotopes. In the first parametrization, it is assumed that the isotopic fractionation between CO2 in seawater and the organic material produced by algae, P, is a function of the ambient CO2 concentration. The two parameters of this function are derived from observations and are not based on an assumption of any specific mechanism. Thus, this parametrization is purely empirical. The second parametrization is based on fractionation models for microalgae. It is supported by several laboratory experiments. Here the fractionation, P, depends on the CO2 concentration in seawater and on the (instantaneous) growth rates, μi, of the phytoplankton. In the Atlantic Ocean, where most field data are available, both parametrizations reproduce the latitudinal variability of the mean δ13CPOC distribution. The interhemispheric asymmetry of δ13CPOC can mostly be attributed to the interhemispheric asymmetry of CO2 concentration in the water. However, the strong seasonal variations of δ13CPOC as reported by several authors, can only be explained by a growth rate-dependent fractionation, which reflects variations in the cellular carbon demand. 相似文献
93.
We have investigated the interacting winds model (IWM) in which the shapes of elliptical Planetary Nebulae (PNe) can be explained
by the asymmetric mass loss produced by a rotating AGB star. The mass loss mechanism is based on a dust driven wind calculated
for stationary situations. Already for small rotation rates of the AGB star we get a significantly angle-dependent mass loss
which is concentrated towards the equatorial plane. This pole to equator density variation in the space surrounding the star
influences the shape of the later developed PN. We compare these theoretical shapes with observed PNe and for some objects
with well known quantities our model can fit the observations quite well.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
94.
Noah Brosch Elchanan Almoznino Dieter Engels Stuart Bowyer Michael Lampton 《Monthly notices of the Royal Astronomical Society》2000,316(1):58-70
We analyse a UV observation with FAUST in the direction of the North Galactic Pole. The region includes a cirrus cloud (G251.2+73.3) and a dark globule, and the FAUST image contains 75 UV sources. We discuss the UV source detection and their identification with optical counterparts. We use, for the first time, low-resolution spectral information as the primary means of identifying possible optical counterparts. This is complemented, and sometimes modified, by optical information available from existing data bases. The results are interpreted with the help of maps of the distribution of far-infrared emission and of the neutral hydrogen gas. We discuss the types of objects found, the degree of matching with the predictions of our UV Galaxy model, and the general behaviour of the Galactic UV extinction in this Milky Way part. We compare the UV results for this region with similar observations in the same neighbourhood, which are less affected by dust, and attempt to explain the peculiar distribution of UV magnitudes as a result of a peculiar distribution of foreground dust, which does not follow the accepted dust-to-gas relation. 相似文献
95.
Dieter Lorenz-Petzold 《Astrophysics and Space Science》1984,103(2):397-399
We present the most general triaxial BDT-Bianchi type-V radiation solution. The solution is the simplest generalization of the GRT solution first given by Ruban. 相似文献
96.
Dieter Lorenz-Petzold 《Astrophysics and Space Science》1985,115(1):197-198
The inhomogeneous Bianchi type-VI0 perfect fluid solution given recently by Roy and Narain (1985) is shown to be identical with the solution first given by Tomita (1978). 相似文献
97.
Dieter Biskamp 《Astrophysics and Space Science》1996,242(1-2):165-207
A review of the present status of the theory of magnetic reconnection is given. In strongly collisional plasmas reconnection proceeds via resistive current sheets, i.e. quasi-stationary macroscopic Sweet-Parker sheets at intermediate values of the magnetic Reynolds numberR
m
, or mirco-current sheets in MHD turbulence, which develops at highR
m
. In hot, dilute plasmas the reconnection dynamics is dominated by nondissipative effects, mainly the Hall term and electron inertia. Reconnection rates are found to depend only on the ion mass, being independent of the electron inertia and the residual dissipation coefficients. Small-scale whistler turbulence is readily excited giving rise to an anomalous electron viscosity. Hence reconnection may be much more rapid than predicted by conventional resistive theory. 相似文献
98.
Dieter Lorenz-Petzold 《Astrophysics and Space Science》1985,108(2):419-421
We wish to point out that the Brans-Dicke-Bianchi type-VI0 stiff matter solution recently given by Ram and Singh is not the most general solution of the corresponding field equations. Moreover, this solution has no vacuum limit and the general relativistic limit is obtained only after making an asymptotic expansion. In this paper we rediscuss the entire problem in a different way. In the limit =const., , we obtain both the stiff matter and the vacuum relativistic limit first given by Ellis and MacCallum (1969) in analytic form. 相似文献
99.
Michael Schnabel Dieter Franke Martin Engels Karl Hinz Snke Neben Volkmar Damm Stefan Grassmann Hugo Pelliza Paulo Ricardo Dos Santos 《Tectonophysics》2008,454(1-4):14-22
It is well established that the Argentine passive margin is of the rifted volcanic margin type. This classification is based primarily on the presence of a buried volcanic wedge beneath the continental slope, manifested by seismic data as a seaward dipping reflector sequence (SDRS). Here, we investigate the deep structure of the Argentine volcanic margin at 44°S over 200 km from the shelf to the deep oceanic Argentine Basin. We use wide-angle reflection/refraction seismic data to perform a joint travel time inversion for refracted and reflected travel times. The resulting P-wave velocity-depth model confirms the typical volcanic margin structure. An underplated body is resolved as distinctive high seismic velocity (vp up to 7.5 km/s) feature in the lower crust in the prolongation of a seaward dipping reflector sequence. A remarkable result is that a second, isolated body of high seismic velocity (vp up to 7.3 km/s) exists landward of the first high-velocity feature. The centres of both bodies are 60 km apart. The high-velocity lower-crustal bodies likely were emplaced during transient magmatic–volcanic events accompanying the late rifting and initial drifting stages. The lateral variability of the lower crust may be an expression of a multiple rifting process in the sense that the South Atlantic rift evolved by instantaneous breakup of longer continental margin segments. These segments are confined by transfer zones that acted as rift propagation barriers. A lower-crustal reflector was detected at 3 to 5 km above the modern Moho and probably represents the lower boundary of stretched continental crust. With this finding we suggest that the continent–ocean boundary is situated 70 km more seaward than in previous interpretations. 相似文献
100.
Hugen ZhU Associate Prof Dept. Of Civil Eng. Hefei University of Technology Hefei China Zhaoyin WANG Prof Dr. International Research Training Center on Erosion Sedimentation P.O. Box Beijing China Dieter PRINZ Prof. 《国际泥沙研究》1997,(3)
LIN~DUCnONTheHuaiheBasinislOCatedbetWeen31"-36"llorthemlahtudeand112"-121"easternlongitude,andcoversatotalareaofabout269,000sq.kin,OfwhichthemountainousandhillyareasocCUPyl/3,theplainsandlow-iringland2/3.ThebasinelicitSsalientphysicalgeographicalfeatllTesasfollowsf(l)Thereisnoobviousmountaindividebe~ntheWatershedoftheriVerandtheYellowforerBasinaswellastheYangtZeRadBasin.MostofthetributariesinthenoalbudoftheHuaiheforertakethesouthdikesOftheYellowherasthedivide.(2)TheriVerbedofthetr… 相似文献