全文获取类型
收费全文 | 38869篇 |
免费 | 630篇 |
国内免费 | 241篇 |
专业分类
测绘学 | 754篇 |
大气科学 | 2580篇 |
地球物理 | 7637篇 |
地质学 | 14070篇 |
海洋学 | 3545篇 |
天文学 | 8725篇 |
综合类 | 87篇 |
自然地理 | 2342篇 |
出版年
2022年 | 257篇 |
2021年 | 441篇 |
2020年 | 499篇 |
2019年 | 576篇 |
2018年 | 1014篇 |
2017年 | 1014篇 |
2016年 | 1081篇 |
2015年 | 584篇 |
2014年 | 1035篇 |
2013年 | 1851篇 |
2012年 | 1191篇 |
2011年 | 1629篇 |
2010年 | 1441篇 |
2009年 | 1796篇 |
2008年 | 1629篇 |
2007年 | 1692篇 |
2006年 | 1558篇 |
2005年 | 1059篇 |
2004年 | 1074篇 |
2003年 | 1114篇 |
2002年 | 997篇 |
2001年 | 869篇 |
2000年 | 798篇 |
1999年 | 724篇 |
1998年 | 716篇 |
1997年 | 724篇 |
1996年 | 589篇 |
1995年 | 573篇 |
1994年 | 501篇 |
1993年 | 453篇 |
1992年 | 409篇 |
1991年 | 424篇 |
1990年 | 437篇 |
1989年 | 391篇 |
1988年 | 369篇 |
1987年 | 400篇 |
1986年 | 415篇 |
1985年 | 508篇 |
1984年 | 545篇 |
1983年 | 542篇 |
1982年 | 496篇 |
1981年 | 454篇 |
1980年 | 429篇 |
1979年 | 408篇 |
1978年 | 375篇 |
1977年 | 384篇 |
1976年 | 344篇 |
1975年 | 353篇 |
1974年 | 340篇 |
1973年 | 370篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
301.
We outline some main results from recent analytical modelling of axisymmetric jets from the coronae of young stars and compare them to disk-wind and X-wind models. We emphazise the roles of the magnetic rotator and the disk in the formation and the evolution of the jet. We conjecture that with time both the efficiency of the magnetic rotator and the role of the disk as a primary source for the wind decline. 相似文献
302.
303.
A. J. Zhang E. R. G. Hill B. A. Hobbs 《Physics of the Earth and Planetary Interiors》1990,60(1-4):40-52
An important stage in two-dimensional magnetotelluric modelling is the calculation of the Earth's response functions for an assumed conductivity model and the calculation of the associated Jacobian relating those response functions to the model parameters. The efficiency of the calculation of the Jacobian will affect the efficiency of the inversion modelling. Rodi (1976) produced all the Jacobian elements by inverting a single matrix and using an approximate first-order algorithm. Since only one inverse matrix required calculation the procedure speeded up the inversion. An iterative scheme to improve the approximation to the Jacobian information is presented in this paper. While this scheme takes a little longer than Rodi's algorithm, it enables a more accurate determination of the Jacobian information. It is found that the Jacobian elements can be produced in 10% of the time required to calculate an inverse matrix or to calculate a 2D starting model. A modification of the algorithm can further be used to improve the accuracy of the original inverse matrix calculated in a 2D finite difference program and hence the solution this program produces. The convergence of the iteration scheme is found to be related both to the originally calculated inverse matrix and to the change in the newly formed matrix arising from perturbation of the model parameter. A ridge regression inverse algorithm is used in conjunction with the iterative scheme for forward modelling described in this paper to produce a 2D conductivity section from field data. 相似文献
304.
We have used photometric images of ten barred galaxies in the B and I bands to infer the geometrical and dynamical parameters of their bars: Their length, (R
bar), their strengths, (S
b), and their corotation radii, (R
CR).These parameters have been obtained studying azimuthal profiles from the B and I band images of the galaxies. We find that R
CR is in all cases slightly larger than R
bar, with mean values close to 1.2 R
bar. We have also found a dependence of the ratio R
CR/R
bar on S
bar.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
305.
J. Geiswiller J.G. Trotignon C. Béghin E. Kolesnikova 《Astrophysics and Space Science》2001,277(1-2):317-318
The Rosetta spacecraft (S/C), which is planned to meet comet 46P/Wirtanen in 2011, will carry a set of five wave and plasma
instruments (i.e. the Rosetta Plasma Consortium). This is to measure the cometary plasma properties from the minimum value
of activity of the comet to its maximum value at perihelion. The mutual impedance probe, MIP, is one of those (Trotignon et al., 1999) five.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
306.
307.
S. H. Zisk C. A. Hodges H. J. Moore R. W. Shorthill T. W. Thompson E. A. Whitaker D. E. Wilhelms 《Earth, Moon, and Planets》1977,17(1):59-99
The region including the Aristarchus Plateau and Montes Harbinger is probably the most diverse, geologically, of any area of comparble size on the Moon. This part of the northwest quadrant of the lunar near side includes unique dark mantling material; both the densest concentration and the largest of the sinuous rilles; apparent volcanic vents, sinks, and domes; mare materials of various ages and colors; one of the freshest large craters (Aristarchus) with ejecta having unique colors and albedos; and three other large craters in different states of flooding and degradation (krieger, Herodotus, and Prinz). The three best-authenticated lunar transient phenomena were also observed here.This study is based principally on photographic and remote sensing observations made from Earth and Apollo orbiting space craft. Results include (1) delineation of geologic map units and their stratigraphic relationships; (2) discussion of the complex interrelationships between materials of volcanic and impact origin, including the effects of excavation, redistribution and mixing of previously deposited materials by younger impact craters; (3) deduction of physical and chemical properties of certain of the geologic units, based on both the remote-sensing information and on extrapolation of Apollo data to this area; and (4) development of a detailed geologic history of the region, outlining the probable sequence of events that resulted in its present appearance.A primary concern of the investigation has been anomalous red dark mantle on the Plateau. Based on an integration of Earth- and lunar orbit-based data, this layer seems to consist of fine-grained, block-free material containing a relatively large fraction of orange glass. It is probably of pyroclastic origin, laid down at some time during the Imbrian period of mare flooding. 相似文献
308.
On three nights in February 1976 we carried out polarimetric measurements, in V, of the short periodic eclipsing binary XY UMa, covering a complete cycle. The results are as follows:
- Within all phase intervals the linear polarization does not exceed 0.1%.
- In the phase range 0 p .95–1 p .35 the scatter of the Stokes parametersQ andU is about twice that within the phase interval 0 p .35–0 p .95.
- A periodogram analysis of these data revealed a period of 21000 s, which is equal to half the orbital periodP o=0d.47899 within 1.5%.
309.
G. M. Tovmasyan R. Kh. Oganesyan R. A. Epremyan S. E. Nersesyan M. A. Mkrtchyan Yu. M. Khodzhayants M. N. Krmoyan A. L. Kashin D. Huguenin S. I. Serova Yu. V. Romanenko A. P. Aleksandrov V. G. Titov M. Kh. Manarov 《Astrophysics》1990,32(1):1-5
Byurakan Astrophysical Observatory; SKB Granit; Geneva Observatory; Flight Control Center. Translated from Astrofizika, Vol. 32, No. 1, p. 5–13, January–February, 1990. 相似文献
310.
A Kelvin-Helmholtz instability has been identified numerically on an azimuthally symmetric Alfvén resonant layer in an axially bounded, straight cylindrical coronal loop. The physical model employed is an incompressible, reduced magnetohydrodynamic (MHD) model including resistivity, viscosity, and density variation. The set of equations is solved numerically as an initial value problem. The linear growth rate of this instability is shown to be approximately proportional to the Alfvén driving amplitude and inversely proportional to the width of the Alfvén resonant layer. It is also shown that the linear growth rate increases linearly with m - 1 up to a certain m, reaches its maximum value for the mode whose half wavelength is comparable to the Alfvén resonant layer width, and decreases at higher m's. (m is the azimuthal mode number.) 相似文献