全文获取类型
收费全文 | 5086篇 |
免费 | 627篇 |
国内免费 | 791篇 |
专业分类
测绘学 | 333篇 |
大气科学 | 524篇 |
地球物理 | 892篇 |
地质学 | 2200篇 |
海洋学 | 504篇 |
天文学 | 871篇 |
综合类 | 334篇 |
自然地理 | 846篇 |
出版年
2024年 | 17篇 |
2023年 | 57篇 |
2022年 | 148篇 |
2021年 | 195篇 |
2020年 | 188篇 |
2019年 | 202篇 |
2018年 | 134篇 |
2017年 | 155篇 |
2016年 | 124篇 |
2015年 | 203篇 |
2014年 | 242篇 |
2013年 | 257篇 |
2012年 | 276篇 |
2011年 | 261篇 |
2010年 | 218篇 |
2009年 | 316篇 |
2008年 | 306篇 |
2007年 | 335篇 |
2006年 | 335篇 |
2005年 | 282篇 |
2004年 | 312篇 |
2003年 | 255篇 |
2002年 | 234篇 |
2001年 | 201篇 |
2000年 | 195篇 |
1999年 | 159篇 |
1998年 | 184篇 |
1997年 | 107篇 |
1996年 | 123篇 |
1995年 | 100篇 |
1994年 | 87篇 |
1993年 | 69篇 |
1992年 | 51篇 |
1991年 | 46篇 |
1990年 | 36篇 |
1989年 | 26篇 |
1988年 | 17篇 |
1987年 | 17篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有6504条查询结果,搜索用时 15 毫秒
1.
2.
E.A. Evstigneeva R.R. de Carvalho A.L. Ribeiro H.V. Capelato 《Astrophysics and Space Science》2003,284(2):487-490
We present the preliminary results of a study of how small stellar systems merge to form larger ones. As we display the families
of galaxies in the μe - Re plane (effective surface brightness versus effective radius) we realize that different morphological types occupy different
loci, evidencing the different physical mechanisms operating in each family. As proposed by Capaccioli et al. (1992) this
diagram is the logical equivalent of the HR diagram for stars. Here we take some initial steps in understanding of how we
can establish the evolutionary tracks, solely due to dynamical processes, in the μe - Re plane, ultimately making a dwarf elliptical to turn into a normal elliptical galaxy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
调查了潜蝇在湛江市的发生与为害情况,结果表明,美洲斑潜蝇(LiriomyzaSatiuaeBlanchard)是为害作物潜蝇的优势种,包括有6个科18种,年间发生有6个为害高峰期。应用绿潜宝、乐果、巴丹等药剂在发生为害高峰期的峰前、中、后三次用药,防治效果维持70%以上。 相似文献
4.
5.
This research paper analyses the grain-size characteristics of the Quaternary deposits at Xingshan near Siping, Jilin province in China by employing graphic measures to study the grain size distribution and its mode of transport and deposition. The Quaternary deposits at Xingshan lie unconformable on Cretaceous rocks made of siltstone, mudstone and sandstone. The average grain size is between 8.06 to 8.55Φ (0.002 6 ~0.003 7 mm). The Quaternary deposits at Xingshan mainly compose of very fine silt to clay. The compositions of the grade are clay 63% and silt 37%. The clay size components are weathered debris transported and deposited by flowing water from the SE highlands or hills to the low lying NW Xingshan plains whereas the silty components accumulated by aoelian process. The Quaternary deposits at Xingshan accumulated in the middle and late Pleistocene interglacial periods from (459.12~39.03) ka to (88.92~7.56) ka. The standard deviation ranged from 0.96 to 1.36Φ, indicating that the sediments are moderately to poorly sorted, Coefficient of skewness ranged from 0.16~0.31 with an average skewness of 0.218, (Positively skewed towards fine). Kurtosis values (0.84~1.05) from the grain size distribution and visual inspection of the frequency curves indicate platykurtic to mesokurtic curves and unimodal to bimodal grain-size distribution. The type of deposit formation is sand dune and the source is at a distal from its provenance. 相似文献
6.
A. S. Oliveira J. E. Steiner D. Cieslinski 《Monthly notices of the Royal Astronomical Society》2003,346(3):963-967
The star WR 7a, also known as SPH 2, has a spectrum that resembles that of V Sagittae stars although no O vi emission has been reported. The Temporal Variance Spectrum – TVS – analysis of our data shows weak but strongly variable emission of O vi lines which is below the noise level in the intensity spectrum.
Contrary to what is seen in V Sagittae stars, optical photometric monitoring shows very little, if any, flickering. We found evidence of periodic variability. The most likely photometric period is Pphot = 0.227(±14) d , while radial velocities suggest a period of P spec = 0.204(±13) d . One-day aliases of these periods can not be ruled out. We call attention to similarities with HD 45166 and DI Cru (= WR 46), where multiple periods are present. They may be associated to the binary motion or to non-radial oscillations.
In contrast to a previous conclusion by Pereira et al., we show that WR 7a contains hydrogen. The spectrum of the primary star seems to be detectable as the N v 4604 Å absorption line is visible. If so, it means that the wind is optically thin in the continuum and that it is likely to be a helium main sequence star.
Given the similarity to HD 45166, we suggests that WR 7a may be a qWR – quasi Wolf–Rayet – star. Its classification is WN4h/CE in the Smith, Shara & Moffat three-dimensional classification system. 相似文献
Contrary to what is seen in V Sagittae stars, optical photometric monitoring shows very little, if any, flickering. We found evidence of periodic variability. The most likely photometric period is P
In contrast to a previous conclusion by Pereira et al., we show that WR 7a contains hydrogen. The spectrum of the primary star seems to be detectable as the N v 4604 Å absorption line is visible. If so, it means that the wind is optically thin in the continuum and that it is likely to be a helium main sequence star.
Given the similarity to HD 45166, we suggests that WR 7a may be a qWR – quasi Wolf–Rayet – star. Its classification is WN4h/CE in the Smith, Shara & Moffat three-dimensional classification system. 相似文献
7.
杨吉 《地球科学与环境学报》2003,25(3):16-20
北秦岭侵入岩带中的中酸性侵入岩主要形成于晋宁旋回的中晚期阶段。主要岩石类型包括辉石闪长岩、闪长岩、石英闪长岩、英云闪长岩、花岗闪长岩、斜长花岗岩、花岗岩和钾长花岗岩。岩石化学、稀土元素和微量元素地球化学研究证明,这些岩石主要形成于B型俯冲和碰撞造山的构造环境中,而钾长花岗岩形成于后造山的伸展阶段。据此,该侵入岩带揭示了北秦岭褶皱带在晋宁旋回中晚期阶段的演化过程。 相似文献
8.
9.
J.-M. Carquillat N. Ginestet J.-L. Prieur Y. Debernardi 《Monthly notices of the Royal Astronomical Society》2003,346(2):555-564
We present the results of a radial-velocity study of eight Am stars (HD 341, 55822, 61250, 67317, 93991, 162950, 224890 and 225137) observed at Observatoire de Haute-Provence with the CORAVEL instrument. We find that these systems are single-line spectroscopic binaries whose orbital elements are determined for the first time. 相似文献
10.