全文获取类型
收费全文 | 3071篇 |
免费 | 466篇 |
国内免费 | 564篇 |
专业分类
测绘学 | 365篇 |
大气科学 | 252篇 |
地球物理 | 823篇 |
地质学 | 1037篇 |
海洋学 | 284篇 |
天文学 | 1001篇 |
综合类 | 147篇 |
自然地理 | 192篇 |
出版年
2024年 | 13篇 |
2023年 | 32篇 |
2022年 | 81篇 |
2021年 | 96篇 |
2020年 | 116篇 |
2019年 | 142篇 |
2018年 | 90篇 |
2017年 | 113篇 |
2016年 | 139篇 |
2015年 | 160篇 |
2014年 | 172篇 |
2013年 | 161篇 |
2012年 | 155篇 |
2011年 | 160篇 |
2010年 | 145篇 |
2009年 | 235篇 |
2008年 | 207篇 |
2007年 | 269篇 |
2006年 | 234篇 |
2005年 | 184篇 |
2004年 | 193篇 |
2003年 | 170篇 |
2002年 | 132篇 |
2001年 | 130篇 |
2000年 | 97篇 |
1999年 | 98篇 |
1998年 | 95篇 |
1997年 | 32篇 |
1996年 | 48篇 |
1995年 | 30篇 |
1994年 | 29篇 |
1993年 | 35篇 |
1992年 | 21篇 |
1991年 | 23篇 |
1990年 | 20篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有4101条查询结果,搜索用时 15 毫秒
991.
热带气旋穿越副热带高压的数值试验 总被引:1,自引:0,他引:1
用简单的准地转正压涡度方程模式,通过比较与多组不同计算参数相对应的台风路径的相似程度,确定出合理的计算参数:即求解Poisson方程的迭代精度可取为1.0×10-4;时间积分步长可取为20分钟。 相似文献
992.
吴忠良 《地震地磁观测与研究》1998,19(5):1-7
本文讨论了渐近式地震速报和地震信息服务的工作程序的设想。随着通讯技术和数字地震观测技术的发展,地震速报工作已经开始逼近地震参数快速测定的地震学极限,即地震波传播速度的有限性和震相分析的复杂性带来的极限,从而使同时提高速度和精度存在档大的困难,中国方面,防震减灾工作以地震快速反应的要求却不一定是速度与精度的同时提高,而 分阶段的、依距地震发生的时间而不同的,这就使得渐近式的地震速报程序成为可能。从更 相似文献
993.
部分输入未知条件下的结构系统识别研究 总被引:24,自引:3,他引:21
本文研究输入信息不完备条件下结构的参数识别问题,在对传统识别算法的特点进行分析的基础上提出了一种新的识别方法-全量补偿法。文中给出了算法理论证明和具体的数值算例。 相似文献
994.
Source extent parameters of the 1988 Lancang earthquake (M
s=7.6) were estimated by computing the second-central moment of displacement pulses of far field long period SH waves. We inverted
the source duration T, the fault length L and the directivity parameter D by the least squares, and obtained that T=11.77 s, D=15.05 km·s, and L=70.94 km. We also find that this event is a symmetrically bilateral rupture and fault segments in two opposite rupture directions
have the same value of 35 km in length. Combining analysis of aftershock distribution, the results would imply that there
is an area in the joint part of the rupture area of two main shocks, which is not broken yet during the main shocks. Due to
the dislocation accompanied during the main shocks, the strain would be rearranged. The joint part has enough strength to
accumulate enough strain energy to excite a larger aftershock. 相似文献
995.
根据工作区潜在震源区划分、潜在震源区地震活动性参数和地震动衰减关系, 进行场地地震危险性分析, 得到不同概率水平下场区相应地震烈度和基岩水平加速度峰值及其反应谱。根据场地工程地震条件划分不同地质单元及相应的场地类别, 进行不同概率水平的地震反应分析计算, 确定地震动设计参数。 相似文献
996.
Mark Cropper Gavin Ramsay & Kinwah Wu 《Monthly notices of the Royal Astronomical Society》1998,293(3):222-232
One method of obtaining the mass of the white dwarf in magnetic cataclysmic variables (mCVs) is through their hard X-ray spectra. However, previous mass estimates using this method give lower limits because the temperature of the plasma in the post-shock region (where the hard X-rays are emitted) is lower than the temperature of the shock itself. In AM Her systems, the additional cooling of the post-shock plasma by cyclotron emission will further lower the derived mass. Here we present estimates of the masses of the white dwarf in 13 mCVs derived using Ginga data and a model in which X-rays are emitted from a multi-temperature emission region with the appropriate temperature and density profile. We include in the model reflection from the surface of the white dwarf and a partially ionized absorber. We are able to achieve good fits to the data. We compare the derived masses with previous estimates and the masses for larger samples of isolated white dwarfs and those in CVs. 相似文献
997.
RobertSchmidt Rachel L.Webster Geraint F.Lewis 《Monthly notices of the Royal Astronomical Society》1998,295(2):488-496
In the gravitational lens system Q2237+0305 the cruciform quasar image geometry is twisted by 10c by the lens effect of a bar in the lensing galaxy. This effect can be used to measure the mass of the bar. We construct a new lensing model for this system with a power-law elliptical bulge and a Ferrers bar. The observed ellipticity of the optical isophotes of the galaxy leads to a nearly isothermal elliptical profile for the bulge, with a total quasar magnification of 16+5 −4 . We measure a bar mass of (7.5 ∼ 1.5) −108 h −1 75 M⊙ in the region inside the quasar images. 相似文献
998.
Pritchard Tobin Clark & Guinan 《Monthly notices of the Royal Astronomical Society》1998,297(1):278-290
Using improved techniques, high-quality CCD uvbyVI C photometry has been obtained for the 14th magnitude eclipsing binaries HV 1620 in the Small Magellanic Cloud (SMC) and HV 2241 in the Large Magellanic Cloud (LMC). IUE ultraviolet spectrophotometry was also obtained. These data have been analysed using the Wilson & Devinney synthetic light-curve code and Kurucz model atmospheres. Both systems are semi-detached and appear to have undergone mass exchange. In HV 1620 the mass ratio and the effective temperatures of the primary and secondary are q = M 2 / M 1 = 0.68 ± 0.03, T eff,1 = 33 000 ± 4500 K and T eff,2 = 24 000 ± 3500 K. The corresponding values for HV 2241 are 0.53 ± 0.01, 27 000 ± 3000 K and 20 200 ± 1500 K. Using the radial-velocity curves obtained by Niemela & Bassino with a 1-m telescope, we find that both systems are massive, as expected. Reddening considerations suggest both systems may lie towards the rear of their respective Clouds. 相似文献
999.
1000.
Julien E. G. Devriendt Shiv K. Sethi Bruno Guiderdoni & Biman B. Nath 《Monthly notices of the Royal Astronomical Society》1998,298(3):708-718
We estimate the evolution of the contribution of galaxies to the cosmic background flux at 912 Å by means of a semi-analytic model of galaxy formation and evolution. Such modelling has been quite successful in reproducing the optical properties of galaxies. We assume that high-redshift damped Lyman α systems are the progenitors of present-day galaxies, and we design a series of models that are consistent with the evolution of cosmic comoving emissivities in the available near-infrared, optical, ultraviolet and far-infrared bands along with the evolution of the neutral hydrogen content and average metallicity of damped Lyman α systems. We use these models to compute the galactic contribution to the Lyman-limit emissivity and background flux for 0 ≃ z ≤ 4. We take into account the absorption of Lyman-limit photons by H I and dust in the interstellar medium of the galaxies. We find that the background Lyman-limit flux due to galaxies might dominate (or be comparable to) the contribution from quasars at almost all redshifts if the absorption by H I in the interstellar medium is neglected. Such H I absorption would result in a severe diminishing of this flux — by almost three orders of magnitude at high redshifts and by one to two orders at z ≃ 0. Though the resulting galaxy flux is completely negligible at high redshifts, it is comparable to the quasar flux at z ≃ 0. 相似文献