全文获取类型
收费全文 | 70281篇 |
免费 | 13009篇 |
国内免费 | 15718篇 |
专业分类
测绘学 | 4350篇 |
大气科学 | 10113篇 |
地球物理 | 11845篇 |
地质学 | 41214篇 |
海洋学 | 8106篇 |
天文学 | 9282篇 |
综合类 | 4112篇 |
自然地理 | 9986篇 |
出版年
2024年 | 275篇 |
2023年 | 944篇 |
2022年 | 2270篇 |
2021年 | 2726篇 |
2020年 | 2648篇 |
2019年 | 2988篇 |
2018年 | 2546篇 |
2017年 | 2910篇 |
2016年 | 3017篇 |
2015年 | 3212篇 |
2014年 | 4295篇 |
2013年 | 4513篇 |
2012年 | 4416篇 |
2011年 | 4759篇 |
2010年 | 4228篇 |
2009年 | 5316篇 |
2008年 | 5092篇 |
2007年 | 5257篇 |
2006年 | 4881篇 |
2005年 | 4431篇 |
2004年 | 3846篇 |
2003年 | 3505篇 |
2002年 | 3026篇 |
2001年 | 2667篇 |
2000年 | 2571篇 |
1999年 | 2316篇 |
1998年 | 1996篇 |
1997年 | 1464篇 |
1996年 | 1210篇 |
1995年 | 1063篇 |
1994年 | 979篇 |
1993年 | 851篇 |
1992年 | 662篇 |
1991年 | 502篇 |
1990年 | 382篇 |
1989年 | 313篇 |
1988年 | 268篇 |
1987年 | 127篇 |
1986年 | 107篇 |
1985年 | 85篇 |
1984年 | 68篇 |
1983年 | 41篇 |
1982年 | 47篇 |
1981年 | 28篇 |
1980年 | 36篇 |
1979年 | 13篇 |
1978年 | 38篇 |
1977年 | 26篇 |
1976年 | 6篇 |
1954年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
111.
112.
113.
114.
We present new 1.45-1.75 μm spectra of Europa's dark non-ice material with a spectral resolution (λ/δλ) of 1200, obtained by using adaptive optics on the Keck telescope to spatially separate the spectrum of the non-ice material from that of the surrounding ice-rich regions. Despite the great increase in spectral resolution over the previous best spectra of the non-ice material, taken with Galileo's near-infrared mapping spectrometer (NIMS) with λ/δλ=66, no new fine-scale spectral structure is revealed. The smoothness of the spectra is inconsistent with available laboratory spectra of crystalline hydrated salts at Europa temperatures, but is more consistent with various combinations of non-crystalline hydrated salts and/or hydrated sulfuric acid, as have been matched to the lower-resolution NIMS spectra. 相似文献
115.
116.
蛤蜊科3种贝类16SrRNA基因片段及ITS2核苷酸序列分析 总被引:4,自引:0,他引:4
利用PCR技术分别扩增连云港及启东沿海蛤蜊科的西施舌(Coelomactra antiquata)、中国蛤蜊(Mactra chinensis)和四角蛤蜊(Mactra veneriformis)3种双壳贝的16SrRNA基因片段和ITS2核苷酸序列.测序后用DNAstar软件分析了核苷酸差异。结果显示:三种贝类16SrRNA基因片段长度相同,均为306bp(去除引物).核苷酸存在多态性。共有45个变异位点,54个核苷酸发生了变异。全部为碱基置换。西施舌与中国蛤蜊此片段核苷酸的同源性为88.9%.与四角蛤蜊的同源性为88.6%.中国蛤蜊与四角蛤蜊的同源性为90.6%。三种蛤蜊ITS2序列分别为390bp(西施舌)、441bp(四角蛤蜊)和466bp(中国蛤蜊)。存在长度多态性.ITS2核苷酸差异分析结果显示.西施舌与中国蛤蜊的同源性为70.9%-71.1%,西施舌与四角蛤蜊的为70.5%-71.0%。中国蛤蜊与四角蛤蜊的同源性为88.1%-88.8%。ITS2序列分析结果与16SrRNA基因片段分析结果一致.2种分子分析法均显示中国蛤蜊与四角蛤蜊的亲缘关系近。 相似文献
117.
Flavio Scappini Cesare Cecchi-Pestellini Harvey Smith William Klemperer Alexander Dalgarno 《Monthly notices of the Royal Astronomical Society》2003,341(2):657-661
We consider sulphur depletion in dense molecular clouds, and suggest hydrated sulphuric acid, H2 SO4 · n H2 O, as a component of interstellar dust in icy mantles. We discuss the formation of hydrated sulphuric acid in collapsing clouds and its instability in heated regions in terms of the existing hot core models and observations. We also show that some features of the infrared spectrum of hydrated sulphuric acid have correspondence in the observed spectra of young stellar objects. 相似文献
118.
We present warm dark matter (WDM) as a possible solution to the missing satellites and angular momentum problem in galaxy
formation and introduce improved initial conditions for numerical simulations of WDM models, which avoid the formation of
unphysical haloes found in earlier simulations. There is a hint, that because of that the mass function of satellite haloes
has been overestimated so far, pointing to higher values for the WDM particle mass.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
119.
120.
We present a new general scheme for calculating the structure and dynamics of radiation-pressure-driven photoionized flows. The new method goes one step beyond the Sobolev approximation. It involves a numerical solution of the radiative transfer in absorption lines, including the effects of differential expansion and line interactions such as line locking and blanketing. We also present a new scheme for calculating the radiation pressure due to trapped line photons in finite, differentially expanding flows. We compare our results for the radiation pressure force with those obtained using the Sobolev approximation and show the limitations of the latter. In particular, we demonstrate that the Sobolev method gives a poor approximation near discontinuity surfaces and its neglect of line blanketing can lead to erroneous results in high-velocity flows. We combine the newly calculated radiation pressure force with self-consistent photoionization and thermal calculations to study the dynamics and spectral features of broad absorption-line flows and highly ionized gas flows in active galactic nuclei (AGN). A comparison with Sobolev-type calculations shows that the latter overestimates the terminal velocity of the flow and, conversely, underestimates its opacity. We also show that line locking on broad emission lines can have a significant effect on the dynamics and spectral features of AGN flows. 相似文献