全文获取类型
收费全文 | 2913篇 |
免费 | 741篇 |
国内免费 | 1157篇 |
专业分类
测绘学 | 317篇 |
大气科学 | 849篇 |
地球物理 | 645篇 |
地质学 | 1679篇 |
海洋学 | 488篇 |
天文学 | 181篇 |
综合类 | 278篇 |
自然地理 | 374篇 |
出版年
2024年 | 23篇 |
2023年 | 87篇 |
2022年 | 197篇 |
2021年 | 255篇 |
2020年 | 203篇 |
2019年 | 231篇 |
2018年 | 240篇 |
2017年 | 187篇 |
2016年 | 204篇 |
2015年 | 179篇 |
2014年 | 180篇 |
2013年 | 198篇 |
2012年 | 215篇 |
2011年 | 204篇 |
2010年 | 211篇 |
2009年 | 169篇 |
2008年 | 170篇 |
2007年 | 132篇 |
2006年 | 159篇 |
2005年 | 117篇 |
2004年 | 93篇 |
2003年 | 68篇 |
2002年 | 92篇 |
2001年 | 100篇 |
2000年 | 92篇 |
1999年 | 114篇 |
1998年 | 81篇 |
1997年 | 90篇 |
1996年 | 108篇 |
1995年 | 80篇 |
1994年 | 71篇 |
1993年 | 52篇 |
1992年 | 42篇 |
1991年 | 33篇 |
1990年 | 22篇 |
1989年 | 29篇 |
1988年 | 22篇 |
1987年 | 15篇 |
1986年 | 9篇 |
1985年 | 3篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1958年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有4811条查询结果,搜索用时 109 毫秒
441.
The atmospheric circulation over the mid-high latitudes in Asia has an important influence on regional climate, yet its long-term variation has not been fully explored. The main task of this study is to reveal the interdecadal variation features of summer atmospheric circulation over Asian mid-high latitudes in recent decades. The results show that the atmospheric circulation over mid-high latitudes of Asia has stronger interdecadal fluctuations than that over low latitudes and one significant change center appears near Lake Baikal. It is found that the atmospheric circulation near Lake Baikal has a significant interdecadal change around 1996 and a deep anomalous anticyclonic circulation has been controlling this region since then, which contributes to the significant increase in the surface temperature near Lake Baikal since 1997 and makes the region a remarkable warming center in Asia in recent 40 years. During 1997-2015, the pattern of less precipitation in the north and more precipitation in the south of east China is closely related to the anomalous anticyclonic circulation near Lake Baikal. Especially, this anomalous circulation near Lake Baikal has been found to contribute to the obvious interdecadal decrease of the precipitation in northeast China and north China near 1997. The sea surface temperature (SST) of northwestern Atlantic is an important influence factor to the interdecadal change in the atmospheric circulation near Lake Baikal around 1996. 相似文献
442.
利用1961-2017年辽宁省61个气象站逐月降水数据,以5-8月为研究时段建立旱涝急转指数(drought-flood abrupt alternation index,DFAI)序列,采用线性倾向法、趋势分析、阶段性分析、T检验、ArcGIS空间插值等方法对辽宁省降水集中期的旱涝急转现象进行时空特征分析。结果表明:1961-2017年辽宁省降水集中期DFAI总体以-0.7/(10 a)的速率下降,有13 a出现旱转涝,有19 a出现涝转旱;DFAI强度以0.1/(10 a)的速率略呈上升趋势。近57 a,辽宁省旱转涝多发生在20世纪60年代,涝转旱多发生在20世纪70年代和20世纪初之后,1989年出现了涝转旱的突变,发生频率呈增多趋势,1994年又出现旱转涝的突变,发生频率呈减少趋势。典型旱转涝年(2013年),DFAI的高值区分布在中、西部地区;典型涝转旱年(2014年),DFAI绝对值的高值区分布在东北部和中西部地区。DFAI变化率在空间分布上具有明显的中、北部增多,东、西部减少的趋势差异。 相似文献
444.
Bingliang Zhuang Qian Liu Tijian Wang Changqin Yin Shu Li Min Xie Fei Jiang Huiting Mao 《Theoretical and Applied Climatology》2013,114(3-4):651-672
A Regional Climate Chemistry Modeling System that employed empirical parameterizations of aerosol-cloud microphysics was applied to investigate the spatial distribution, radiative forcing (RF), and climate effects of black carbon (BC) over China. Results showed high levels of BC in Southwest, Central, and East China, with maximum surface concentrations, column burden, and optical depth (AOD) up to 14 μg?m?3, 8 mg?m?2, and 0.11, respectively. Black carbon was found to result in a positive RF at the top of the atmosphere (TOA) due to its direct effect while a negative RF due to its indirect effect. The regional-averaged direct and indirect RF of BC in China was about +0.81 and ?0.95 W?m?2, respectively, leading to a net RF of ?0.15 W?m?2 at the TOA. The BC indirect RF was larger than its direct RF in South China. Due to BC absorption of solar radiation, cloudiness was decreased by 1.33 %, further resulting in an increase of solar radiation and subsequently a surface warming over most parts of China, which was opposite to BC’s indirect effect. Further, the net effect of BC might cause a decrease of precipitation of ?7.39 % over China. Investigations also suggested large uncertainties and non-linearity in BC’s indirect effect on regional climate. Results suggested that: (a) changes in cloud cover might be more affected by BC’s direct effect, while changes in surface air temperature and precipitation might be influenced by BC’s indirect effect; and (b) BC second indirect effect might have more influence on cloud cover and water content compared to first indirect effect. This study highlighted a substantial role of BC on regional climate changes. 相似文献
445.
Qian Shengbang Yang Yuangui Zhu Liying He Jiajia Yuan Jingzhao 《Astrophysics and Space Science》2006,304(1-4):25-28
The formations of the blue straggler stars and the FK Com-type stars are unsolved problems in stellar astrophysics. One of the possibilities for their formations is from the coalescence of W UMa-type overcontact binary systems. Therefore, deep (f > 50%), low-mass ratio (q < 0.25) overcontact binary stars are a very important source to understand the phenomena of Blue Straggler/FK Com-type stars. Recently, 12 W UMa-type binary stars, FG Hya, GR Vir, IK Per, TV Mus, CU Tau, V857 Her, V410 Aur, XY Boo, SX CrV, QX And, GSC 619-232, and AH Cnc, were investigated photometrically. Apart from TV Mus, XY boo, and GSC 619-232, new observations of the other 9 binaries were obtained. Complete light curves of the 10 systems, FG Hya, GR Vir, IK Per, TV Mus, CU Tau, V857 Her, GSC 619-232, V410 Aur, XY Boo, and AH Cnc, were analyzed with the 2003 version of the W-D code. It is shown that all of those systems are deep (f > 50%), low-mass ratio (q < 0.25) overcontact binary stars. We found that the system GSC 619-232 has the highest degree of overcontact (f = 93.4%). The derived photometric mass ratio of V857 Her, q = 0.0653, indicates that it is the lowest-mass ratio system among W UMa-type binaries.Of the 12 sample stars, long-term period changes of 11 systems were found. About 58% (seven) of the sample binaries show cyclic period oscillation. No cyclic period changes were discovered for the other 5 systems, which may be caused by the short observational time interval or by insufficient observations. Therefore, we think that all W UMa-type binary stars may contain cyclic period variations. By considering the long-term period changes (both increase and decrease) of those binary stars, we proposed two evolutionary scenarios evolving from deep, low-mass ratio overcontact binaries into Blue Straggler/FK Com-type stars. 相似文献
446.
447.
448.
Qian Shengbang 《Astrophysics and Space Science》2002,282(2):399-409
Orbital period changes of four neglected short-period semidetached Algols, SX Dra, AV Del, CU Peg and DK Peg, are presented
based on the analysis of their O–C observations. It is found that the three systems, AV Del, CU Peg and DK Peg, show rapid
period increase at rates of dP/dt =+3.15 × 10-6, +2.00 × 10-6 and +4.88 × 10-7days/year respectively. For the other system, SX Dra, a possible periodic variation in the orbital period is discovered to
superimpose on a very rapid period increase (dP/dt = +1.09 × 10-5 days/year). The period increases of the four Algols can be explained by a mass transfer from the secondary to the more massive
primary, which is in agreement with the semi-detached configurations of these systems. However, since the period increases
are rather rapid, the mass transfer should be on a dynamical time scale. The cyclic period change in SX Dra suggests that
there may exist a third body in this system.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
449.
本文讨论Blazar天体中光学射电大爆发频谱演化的理论模型.考虑沿喷流传播的相对论性激波所注入或加速的相对论性电子,受到康普顿、同步辐射和绝热膨胀三种损耗,并计及相对论电子能谱的高能截断.假定喷流轴线与观测者方向构成很小角度.文中给出了大爆发频谱三阶段连续演化的特性,即康普顿阶段,同步辐射阶段和绝热膨胀阶段的爆发特性.频谱演化用(Sm-vm)关系表达(见图2,图中Sm为频谱反转流量,vm为反转频率),它与一些Blazar天体中观测到的典型形式相符合. 相似文献
450.