全文获取类型
收费全文 | 46117篇 |
免费 | 20475篇 |
国内免费 | 44378篇 |
专业分类
测绘学 | 3699篇 |
大气科学 | 23226篇 |
地球物理 | 15562篇 |
地质学 | 40583篇 |
海洋学 | 17106篇 |
天文学 | 1469篇 |
综合类 | 5658篇 |
自然地理 | 3667篇 |
出版年
2024年 | 196篇 |
2023年 | 511篇 |
2022年 | 1092篇 |
2021年 | 1463篇 |
2020年 | 2461篇 |
2019年 | 5893篇 |
2018年 | 6224篇 |
2017年 | 5883篇 |
2016年 | 6039篇 |
2015年 | 5281篇 |
2014年 | 4908篇 |
2013年 | 5459篇 |
2012年 | 5101篇 |
2011年 | 4910篇 |
2010年 | 4797篇 |
2009年 | 4223篇 |
2008年 | 3423篇 |
2007年 | 3413篇 |
2006年 | 3037篇 |
2005年 | 2902篇 |
2004年 | 3042篇 |
2003年 | 2815篇 |
2002年 | 2616篇 |
2001年 | 2459篇 |
2000年 | 2091篇 |
1999年 | 2315篇 |
1998年 | 2250篇 |
1997年 | 2259篇 |
1996年 | 1857篇 |
1995年 | 1716篇 |
1994年 | 1579篇 |
1993年 | 1478篇 |
1992年 | 1255篇 |
1991年 | 941篇 |
1990年 | 888篇 |
1989年 | 728篇 |
1988年 | 624篇 |
1987年 | 457篇 |
1986年 | 381篇 |
1985年 | 293篇 |
1984年 | 315篇 |
1983年 | 184篇 |
1982年 | 241篇 |
1981年 | 157篇 |
1980年 | 124篇 |
1979年 | 115篇 |
1978年 | 53篇 |
1977年 | 49篇 |
1971年 | 53篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
概略地叙述了西宁地区的泥石流形成条件和形成机理,并将西宁地区泥石流划分为稀性泥石流类及泥石质泥石流种类。在此基础上提出防治泥石流灾害的意见。 相似文献
33.
本文在已有数据处理方法的基础上,利用近代数值逼近理论,给出了从时空域角度描述地壳垂直运动过程的一种具体的函数解析形式。最后给出了一个实际算例。 相似文献
34.
35.
Yunfei Bao Shengbo Chen 《东北亚地学研究》2006,9(1):100-108
IntroductionThe radiance leaving the earth-atmosphere sys-tem which can be sensed by a satellite borne ra-diometer is the sum of radiation emission fromtheearth surface and each atmospheric level that aretransmittedtothe top of the atmosphere.The radia-tion emissionfromthe earthsurface andthe radianceof each atmospheric level can be separated fromtheradiance at the top the atmospheric level a satellitemeasured.Thus,the earth surface parameters willbe retrieved from the surface radiance after a… 相似文献
36.
37.
Hong-Guang Wang Guo-Jun Qiao Ren-Xin XuDepartment of Astronomy Peking University Beijing 《中国天文和天体物理学报》2003,3(5):443-452
The inner vacuum gap model has become the foundation stone of most theories on pulsar radio emission. The fundamental picture of this model is the sparking, which was conjectured to be induced by magnetic absorption of background gamma photons. However, a question is, can the sparking be triggered in the millisecond pulsars (MSPs) with magnetic fields (B) only about 108 G? We investigate this problem by including the pair production above the inner gap. Under the assumption that the magnetic field is dipolar, our results show the background gamma-ray emission can not be the key factor that triggers the sparking, at least not in MSPs with B - 108 G, if the temperature in the polar cap region is only so high as is observed (< 4 × 106 K). Some other mechanisms are required. 相似文献
38.
H. L. Xu S. Svanberg R. D. Cowan P.-H. Lefèbvre P. Quinet E. Biémont 《Monthly notices of the Royal Astronomical Society》2003,346(2):433-440
Radiative lifetime measurements were performed with time-resolved laser-induced fluorescence techniques for 24 levels of Nd ii in the energy range 20 500–32 500 cm−1 . For 17 levels, no previous experimental data exist. These results have allowed the testing of new theoretical calculations with the relativistic Hartree–Fock method taking configuration interactions and core-polarization effects into account, and a satisfying agreement has been found for this complex ion. A new set of calculated oscillator strengths, accurate within a few per cent for the strongest transitions, is presented for 107 lines of astrophysical interest appearing in the wavelength range 358.0–1100.0 nm. These results will be useful to evaluate abundance values of neodymium in chemically peculiar stars in relation with cosmochronology. 相似文献
39.
Spencer John Buie Marc Young Leslie Guo Yanping Stern Alan 《Earth, Moon, and Planets》2003,92(1-4):483-491
Development of the New Horizons mission to Pluto and the Kuiper Belt is now fully funded by NASA (Stern and Spencer, this volume). If all goes well, New Horizons will be launched in January 2006, followed by a Jupiter gravity assist in 2007, with Pluto arrival expected in either 2015 or 2016, depending on the launch vehicle chosen. A backup launch date of early 2007, without a Jupiter flyby, would give a Pluto arrival in 2019 or 2020. In either case, a flyby of at least one Kuiper Belt object (KBO) is planned following the Pluto encounter, sometime before the spacecraft reaches a heliocentric distance of 50 AU, in 2021 or 2023 for the 2006 launch, and 2027 or 2029 for the 2007 launch. However, none of the almost 1000 currently-known KBOs will pass close enough to the spacecraft trajectory to be targeted by New Horizons, so the KBO flyby depends on finding a suitable target among the estimated 500,000 KBOs larger than 40 km in diameter. This paper discusses the issues involved in finding one or more KBO targets for New Horizons. The New Horizons team plans its own searches for mission KBOs but will welcome other U.S, or international team who wish to become involved in exchange for mission participation at the KBO. 相似文献
40.
Polypeptide fromChlamys farreri (PCF), a topical polypeptide isolated fromChlamys farreri, was used in this experiment aimed to investigate the photoprotective effect of PCF against chronic skin damage induced by
ultraviolet A (UVA) and ultraviolet B (UVB) radiation. The chronic ultraviolet-irradiated guinea pig model was established,
and visible changes in the skin including wrinkling, sagging and erythema were observed. Malondialdehyde (MDA) and antioxidant
enzymes including superoxide dismutase (SOD) and glutathione peroxidase (GSH-px) in the dorsal skin were determined using
biochemical methods. The results showed: (1) PCF (5 % and 20%) could greatly protect the dorsal skin of guinea pig against
wrinkling, sagging and erythema induced by UV radiation in a concentration-dependent manner. (2) PCF could reduce MDA formation
in the dorsal skin caused by UV irradiation, while increasing the activities of SOD and GSH-px. (3) The differences among
the PCF groups and UV model group were significant (P<0.05,P<0.01). These results indicated that topical application, of PCF provided broad solar UV spectrum photoprotection; and that
the antioxidant property of PCF might play a role in photoprotection.
Project No. 39970638 supported by the NSFC, and the Science and Technology Bureau of Qingdao (No. 2001-28-50). 相似文献