全文获取类型
收费全文 | 35923篇 |
免费 | 5468篇 |
国内免费 | 7354篇 |
专业分类
测绘学 | 1862篇 |
大气科学 | 6284篇 |
地球物理 | 8298篇 |
地质学 | 17894篇 |
海洋学 | 4451篇 |
天文学 | 2711篇 |
综合类 | 3268篇 |
自然地理 | 3977篇 |
出版年
2024年 | 113篇 |
2023年 | 497篇 |
2022年 | 1483篇 |
2021年 | 1779篇 |
2020年 | 1565篇 |
2019年 | 1744篇 |
2018年 | 2143篇 |
2017年 | 1955篇 |
2016年 | 2134篇 |
2015年 | 1608篇 |
2014年 | 2071篇 |
2013年 | 2167篇 |
2012年 | 2048篇 |
2011年 | 2195篇 |
2010年 | 2049篇 |
2009年 | 2009篇 |
2008年 | 1822篇 |
2007年 | 1845篇 |
2006年 | 1550篇 |
2005年 | 1223篇 |
2004年 | 912篇 |
2003年 | 1008篇 |
2002年 | 1059篇 |
2001年 | 980篇 |
2000年 | 980篇 |
1999年 | 1325篇 |
1998年 | 1051篇 |
1997年 | 1152篇 |
1996年 | 1040篇 |
1995年 | 904篇 |
1994年 | 767篇 |
1993年 | 674篇 |
1992年 | 545篇 |
1991年 | 386篇 |
1990年 | 316篇 |
1989年 | 279篇 |
1988年 | 247篇 |
1987年 | 185篇 |
1986年 | 158篇 |
1985年 | 111篇 |
1984年 | 89篇 |
1983年 | 84篇 |
1982年 | 75篇 |
1981年 | 51篇 |
1980年 | 57篇 |
1979年 | 55篇 |
1978年 | 32篇 |
1977年 | 28篇 |
1976年 | 27篇 |
1975年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
黑色高岭石粘土岩,是铜川王石凹煤矿石炭纪煤系地层顶部,五号煤层的上部一层稳定的煤矸石。经偏光显微镜及费氏台测试光性特征、化学试验及分析鉴定表明,这是一种由高岭石组成的,成分很纯、颗粒大、结晶良好的高岭石粘土岩。据微量元素含量分析,此高岭石系淡水沉积物。 相似文献
92.
A. B. Pushkarev D. C. Gabuzda Yu. N. Vetukhnovskaya V. E. Yakimov 《Monthly notices of the Royal Astronomical Society》2005,356(3):859-871
We present the results of multifrequency (15 + 8 + 5 GHz) polarization Very Long Baseline Array (VLBA) observations of the three BL Lacertae objects 0745+241, 1418+546 and 1652+398 together with 5-GHz VLBI Space Observatory Programme (VSOP) observations of 1418+546 and 1.6- and 5-GHz VSOP observations of the blazar 1055+018. The jets of all these sources have polarization structure transverse to the jet axis, with the polarization E vectors aligned with the jet along the jet spine and 'sheaths' of orthogonal E vectors at one or both edges of the jet. The presence of polarization aligned with the jet near the 'spine' may indicate that the jets are associated with helical B fields that propogate outward with the jet flow; the presence of orthogonal polarization near the edges of the jet may likewise be a consequence of a helical jet B field, or may be owing to an interaction with the ambient medium on parsec scales. We have tentatively detected interknot polarization in 1055+018 with E aligned with the local jet direction, consistent with the possibility that the jet of this source is associated with a helical B field. 相似文献
93.
The characteristics of red karst weathering crust in the research region can be divided into three subtypes. The first one includes the silicon to aluminum ratio, the composition of the clay minerals, etc., and reflects the weak action of de-silicon and aluminum enrichment. The second one, for example the granularity, shows that the viscous action is strong. The third one, such as the CaCO3 content and pH value, has regional difference in a large scale, which is consistent with the condition of modern scenery, so it is not important as for the ancient environment.
相似文献94.
1 INTRODUCTION Active oxygen free radicals can damage cell structure, even kill the cells, causing aging and cer- tain serious diseases (Bors et al., 1989). Usually, the production and scavenging of active oxygen free radicals are in balance in healthy hu… 相似文献
95.
We study a model of mergers affecting only the progenitors of present E/SO. We adopt the standard scenarios of star formation as prescribed by Guiderdoni & Rocca-Volmerange. The merging process is parametrized under the assumptions of(1) self-similarity of the Schechter MF and(2) mass conservation. Nine models are discussed. The predictions are compared with counts ofB
J
,U
+,F
+,N
+ bands. E/SO mergers account for the excess of the faintest blue galaxies without causing excess in redder bands. However, as we no longer have enough mergers at brighter magnitudes, a plain E/SO merging model fits less tightly for the redshift and the colour distributions. Detection effect, a steeper slope of LF may be ways to improve. Our models predict acceptable merger frequencies atz = 0.5 although some models predict more interacting galaxies than observation atz = 0. 相似文献
96.
A numerical study of gas flow through a porous cometary mantle is presented. A kinetic model based on the well-known Test Particle Monte Carlo Method for the solution of rarefied gas dynamics problems is proposed. The physical model consists of two spatial plane regions: the condensed ice phase and a porous dust mantle. The structure of the porous dust layer is described as a bundle of cylindrical inclined channels not crossing each other. A vertical temperature gradient may exist across the dust mantle. The aim is to investigate how the characteristics of molecular flow depend on the capillary length, inclination angle, and temperature gradient. Examples illustrating a significant deviation of some results from equilibrium values are shown. In particular, the gas velocity distribution at both ends of the pore is strongly non-Maxwellian if there is an important temperature contrast across the pore. The emergent gas flow rate is found to vary with the pore length/radius ratio in excellent agreement with Clausing's empirical formula. The degree of collimation of the flow is quantitatively studied as a function of the length/radius ratio, and consequences for the jet force of outgassing through a dust mantle or, indeed, a rough surface are estimated. 相似文献
97.
Yu. A. Rylov 《Astrophysics and Space Science》1987,132(2):353-386
In the spherically-symmetric case, a computer simulation of the electron acceleration inside the outflow channel of the pulsar magnetosphere is produced. The stationary motion of electrons is shown to be unstable in the case of > c, where is a parameter describing inhomogeneity of the background charge, and c is its critical value. The arising non-stationary motion of electrons leads to a formation of electron bunches, which move chaotically. The mean electron energy appears to be much greater at the non-stationary motion, than at the stationary one. The time-averaged parameters of the non-stationary electron flow and their dependence upon have been investigated. Distributions of the mean values of parameters (charge density, electron velocity, electric field energy density, pressure, and internal energy of the gas composed of the electron bunches) over the magnetosphere altitude have been investigated. The mean spectra of the charge density have been obtained. The results of numerical investigation of the spherically-symmetric model are used for estimation of the electron energy and of the electron flux in the case of the more realistic model. The radioemission loss is estimated, and is shown to be large enough for explaining the radiopulsar phenomenon as a thermal radioemission of the pulsar magnetosphere. In particular, such common properties of the pulsar radioemission as the high bright temperature, the sharp radioemission directivity, and the characteristic turn-over of the radioemission spectrum at the frequency of the order 108 Hz are found a natural explanation in frames of this model. 相似文献
98.
99.
G. Z. Xie F. K. Liu Y. Y. Zhu J. H. Fan R. W. Lu 《Astrophysics and Space Science》1991,179(2):321-329
It has become clear in recent years that relativistic beaming is a good explanation for the BL Lac phenomenon. Of studies based on the relativistic beaming model of BL Lac objects, we note that the orientation of jet's axis to the line-of-sight is very small and, therefore, the observed flux emitted from a rapidly moving source is orders of magnitude higher than the flux in its rest-frame:F
obs = 3 +
F
intr, where is the bulk relativistic Doppler factor. Then the observed apparent magnitudem
v
must be corrected for this effect. For our 39 samples, the corrected apparent magnitudem
v
corr
and logZ have a good correlation. 相似文献
100.
We found that the structure of the Universe can be characterized by a set of actions
s
. This means that some discontinuous phenomena in the Universe can be considered as large-scale quantum effects. The behaviour of matter on a typical scale is determined by the behaviour of matter on other scales through the interactions. 相似文献