全文获取类型
收费全文 | 110585篇 |
免费 | 1905篇 |
国内免费 | 1052篇 |
专业分类
测绘学 | 2477篇 |
大气科学 | 7707篇 |
地球物理 | 21636篇 |
地质学 | 39614篇 |
海洋学 | 10221篇 |
天文学 | 25028篇 |
综合类 | 325篇 |
自然地理 | 6534篇 |
出版年
2022年 | 686篇 |
2021年 | 1181篇 |
2020年 | 1291篇 |
2019年 | 1419篇 |
2018年 | 2975篇 |
2017年 | 2752篇 |
2016年 | 3342篇 |
2015年 | 1795篇 |
2014年 | 3169篇 |
2013年 | 5833篇 |
2012年 | 3533篇 |
2011年 | 4658篇 |
2010年 | 4158篇 |
2009年 | 5403篇 |
2008年 | 4687篇 |
2007年 | 4778篇 |
2006年 | 4399篇 |
2005年 | 3330篇 |
2004年 | 3200篇 |
2003年 | 3037篇 |
2002年 | 2964篇 |
2001年 | 2588篇 |
2000年 | 2560篇 |
1999年 | 2119篇 |
1998年 | 2139篇 |
1997年 | 2027篇 |
1996年 | 1766篇 |
1995年 | 1695篇 |
1994年 | 1449篇 |
1993年 | 1387篇 |
1992年 | 1301篇 |
1991年 | 1331篇 |
1990年 | 1287篇 |
1989年 | 1135篇 |
1988年 | 1069篇 |
1987年 | 1231篇 |
1986年 | 1125篇 |
1985年 | 1354篇 |
1984年 | 1528篇 |
1983年 | 1461篇 |
1982年 | 1357篇 |
1981年 | 1265篇 |
1980年 | 1117篇 |
1979年 | 1064篇 |
1978年 | 1061篇 |
1977年 | 893篇 |
1976年 | 878篇 |
1975年 | 874篇 |
1974年 | 853篇 |
1973年 | 922篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
11.
Abstract— Active capture is a new process for the incorporation of large quantities of heavy noble gases into growing surfaces. Adsorption in the conventional sense involves surface bonding by polarization (Van der Waals forces). What is referred to as “anomalous adsorption” of heavy noble gases involves chemical bonds and can occur when other (more chemically active) species are not available to preempt sites with unfilled bonds. Anomalous adsorption has been observed under conditions of fracture, vacuum deposition and ionizing radiation. Active capture depends upon anomalous adsorption to retain noble gases on a surface long enough to be captured in a growing surface film as it is deposited. The fundamental principle may be the impingement onto the growing film with sufficient energy to liberate surface electrons (work function energy of a few electronvolts) so that they are retained by anomalous adsorption long enough to be entrapped in the growing surface. Trapping efficiencies of ?1% have been observed for Kr and Xe in laboratory experiments, implying a fundamentally new mechanism for the incorporation of heavy noble gases onto surfaces. It may play a role in explaining the large concentrations of planetary noble gases contained in phase‐Q. 相似文献
12.
Zhi-gen Yang Wen-yao Zhu C. K. Shum Feng-chun Shu 《Chinese Astronomy and Astrophysics》2002,26(4):303-502
The vertical deformation rates (VDRs) and horizontal deformation rates (HDRs) of Shanghai VLBI station in China and Kashima and Kashima34 VLBI stations in Japan were re-analysed using the baseline length change rates from Shanghai to 13 global VLBI stations, and from Kashima to 27 stations and from Kashima34 to 12 stations, based on the NASA VLBI global solution glb1123 (Ma, 1999). The velocity vectors of the global VLBI stations were referred to the ITRF97 reference frame, and the Eulerian vectors of different models of plate motion were used for comparative solutions. The VDR of Shanghai station is estimated to be −1.91±0.56 mm/yr, and those of Kashima and Kashima34 stations, −3.72±0.74mm/yr and −8.81±0.84mm/yr, respectively. The difference between the last two was verified by further analysis. Similar estimates were also made for the Kokee, Kauai and MK_VLBA VLBI stations in mid-Pacific. 相似文献
13.
We present our observations of the galaxy UGS 5600 with a long-slit spectrograph (UAGS) and a multipupil field spectrograph (MPFS) attached to the 6-m Special Astrophysical Observatory telescope. Radial-velocity fields of the stellar and gaseous components were constructed for the central region and inner ring of the galaxy. We proved the existence of two nearly orthogonal kinematic subsystems and conclude that UGC 5600 is a galaxy with an inner polar ring. In the circumnuclear region, we detected noncircular stellar motions and suspected the existence of a minibar. The emission lines are shown to originate in H II regions. We estimated the metallicity from the intensity ratio of the [N II]λ6583 and Hα lines to be nearly solar, which rules out the possibility that the polar ring was produced by the accretion of gas from a dwarf companion. 相似文献
14.
The mass ratio of Charon to Pluto is a basic parameter describing the binary system and is necessary for determining the individual masses and densities of these two bodies. Previous measurements of the mass ratio have been made, but the solutions differ significantly (Null et al., 1993; Young et al., 1994; Null and Owen, 1996; Foust et al., 1997; Tholen and Buie, 1997). We present the first observations of Pluto and Charon with a well-calibrated astrometric instrument—the fine guidance sensors on the Hubble Space Telescope. We observed the motion of Pluto and Charon about the system barycenter over 4.4 days (69% of an orbital period) and determined the mass ratio to be 0.122±0.008 which implies a density of 1.8 to 2.1 g cm−3 for Pluto and 1.6 to 1.8 g cm−3 for Charon. The resulting rock-mass fractions for Pluto and Charon are higher than expected for bodies formed in the outer solar nebula, possibly indicating significant postaccretion loss of volatiles. 相似文献
15.
16.
We present our spectroscopic observations of the novae V1425, V1493, and V1494 Aql carried out with the 125-cm telescope at the Crimean Station of the Sternberg Astronomical Institute in the wavelength range 4000–11000 Å. We measured the emission-line intensities, determined the nova shell expansion velocities from the line profile FWHMs and components, and estimated the interstellar reddening from the first members of the Balmer series. The chemical composition of the nova shells is analyzed. Nitrogen and oxygen were found to be overabundant in V1425 and V1494 Aql; the helium abundance turned out to be normal in the two stars. 相似文献
17.
The magnetic-field distribution outside a flat, infinitely conductive unbounded disk in the field of a point magnetic dipole is determined. A relationship is established between the problem of magnetic-field determination and the problem of the flow of an ideal incompressible fluid around an infinitely thin disk. 相似文献
18.
19.
20.