全文获取类型
收费全文 | 4829篇 |
免费 | 946篇 |
国内免费 | 1360篇 |
专业分类
测绘学 | 558篇 |
大气科学 | 955篇 |
地球物理 | 1076篇 |
地质学 | 2708篇 |
海洋学 | 562篇 |
天文学 | 182篇 |
综合类 | 443篇 |
自然地理 | 651篇 |
出版年
2024年 | 22篇 |
2023年 | 68篇 |
2022年 | 213篇 |
2021年 | 271篇 |
2020年 | 206篇 |
2019年 | 247篇 |
2018年 | 266篇 |
2017年 | 252篇 |
2016年 | 272篇 |
2015年 | 243篇 |
2014年 | 286篇 |
2013年 | 320篇 |
2012年 | 362篇 |
2011年 | 301篇 |
2010年 | 302篇 |
2009年 | 279篇 |
2008年 | 247篇 |
2007年 | 245篇 |
2006年 | 216篇 |
2005年 | 212篇 |
2004年 | 196篇 |
2003年 | 215篇 |
2002年 | 337篇 |
2001年 | 322篇 |
2000年 | 185篇 |
1999年 | 170篇 |
1998年 | 143篇 |
1997年 | 146篇 |
1996年 | 99篇 |
1995年 | 80篇 |
1994年 | 93篇 |
1993年 | 61篇 |
1992年 | 49篇 |
1991年 | 51篇 |
1990年 | 32篇 |
1989年 | 27篇 |
1988年 | 29篇 |
1987年 | 17篇 |
1986年 | 19篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1958年 | 2篇 |
1957年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有7135条查询结果,搜索用时 15 毫秒
1.
Barley(Hordeum vulgare L.) is one of the earliest domesticated crop species and ranked as the fourth largest cereal production worldwide. Forward genetic studies in barley have greatly advanced plant genetics during the last century; however, most genes are identified by the conventional mapping method. Array genotyping and exome-capture sequencing have also been successfully used to target the causal mutation in barley populations, but these techniques are not widely adopted because of associated costs and partly due to the huge genome size of barley. This review summarizes three mapping cases of barley cuticle mutants in our laboratory with the help of RNA-sequencing. The causal mutations have been successfully identified for two of them and the target genes are located in the pericentromeric regions. Detailed information on the mapping-by-sequencing, mapping-and-sequencing, and RNA-sequencing assisted linkage mapping are presented and some limitations and challenges on the mapping assisted by RNA sequencing are also discussed. The alternative and elegant methods presented in this review may greatly accelerate forward genetics of barley mapping, especially for laboratories without large funding. 相似文献
2.
Zhi Xu Cheng Fang Wei-Qun Can Astronomy Department of Nanjing University Nanjing Purple Mountain Observatory Chinese Academy of Sciences Nanjing 《中国天文和天体物理学报》2005,5(5):519-530
Chromospheric lines, including Ha, Lyα, Lyβand CaⅡK, CaⅡ8542, are systemically and quantitatively investigated with respect to the non-thermal excitation and ionization due to particle beam bombardment for a series of solar semi-empirical atmospheric models. As a result we propose to use the contrast in the integrated intensity of hydrogen lines to estimate the total energy flux of the bombarding beam during the solar flare impulsive phase. Partial frequency redistribution is considered in the Lyαline calculation and a smaller intensity enhancement in the Ha line-centers is found than in the previous results of Fang et al. 相似文献
3.
4.
5.
Microwave Type III bursts with positive frequency drifting rate were found by Stahli and Benz (1987) for first time. Type III events are especially interesting because they are well-known to be signatures of electron beams in coronal plasma, and they are effective means for diagnosting of source plasma. A microwave burst consisting of some microwave type III burst groups was registered at Beijing Astronomical Observatory with the 2545–2645–2840 MHz synchronous observing system. The distributions of frequency drifting rate, half power duration, and intensity for each impulse in the groups have been statistically analysed. From this analysis, some important parameters for the dynamic process in the flare are deduced and discussed. 相似文献
6.
本文讨论了彗星中尘埃粒子的充电机制 ,带电特性和平衡电势的变化规律 ,分析了彗星尘埃的破碎特性和临界半径 ,得出了很有意义的结果 相似文献
7.
1 INTRODUCTIONIn the previous paper (on et al. 1999, hereafter Paper I), we investigated the wavelength-dependence of four colltribution functions (CFs) derived from dmerent formal solutions andreferring to different emergellt quantities in the unpolarized case. Because one cannot generallyassign a single formation region to the whole line band in a real stellar atmosphere, e.g., the solaratmosphere, instead, the line formation region can be defined as the layers deviating farthestfrom t… 相似文献
8.
应用地壳波浪与镶嵌构造学说对富氏谱分析法提取地壳垂直形变信息的科学性做了地质学意义上的阐释 ,并提出了根据多期形变资料提取特定波段上构造策应力的数学模型 相似文献
9.
Qin Chengzhi 《中国地震研究》2004,18(2):178-187
The migration of strong earthquakes is an important research topic because the migration phenomena reflect partly the seismic mechanism and involve the prediction of tendency of seismic activity. Research on migration of strong earthquakes has mostly focused on finding the phenomena. Some attempts on getting regularity were comparatively subjective. This paper suggests that there should be indices of migration in earthquake dataset and the indexes should have statistical meaning if there is regularity in the migration of strong earthquakes. In this study, three derivative attributes of migration, i.e., migration orientation, migration distance and migration time interval, were statistically analyzed. Results in the North China region show that the migration of strong earthquakes has statistical meaning. There is a dominant migration orientation (W by S to E by N), a dominant distance (≤100km and on the confines of 300~700km), and a dominant time interval (≤1a and on the confines of 3~4a). The results also show that the migration will differ slightly with different magnitude range or earthquake activity phase. 相似文献
10.
本文叙述南天区 5GHzVLBI普查中新发现的视超光速射电源 ,0 4 2 0— 0 1 4,1 334—1 2 7和 2 345— 1 67,这些结果尚待进一步的观测加以证实 相似文献