全文获取类型
收费全文 | 15444篇 |
免费 | 2839篇 |
国内免费 | 3703篇 |
专业分类
测绘学 | 804篇 |
大气科学 | 3167篇 |
地球物理 | 4117篇 |
地质学 | 7626篇 |
海洋学 | 1833篇 |
天文学 | 715篇 |
综合类 | 1731篇 |
自然地理 | 1993篇 |
出版年
2024年 | 51篇 |
2023年 | 209篇 |
2022年 | 694篇 |
2021年 | 757篇 |
2020年 | 671篇 |
2019年 | 765篇 |
2018年 | 870篇 |
2017年 | 790篇 |
2016年 | 930篇 |
2015年 | 732篇 |
2014年 | 912篇 |
2013年 | 870篇 |
2012年 | 824篇 |
2011年 | 911篇 |
2010年 | 911篇 |
2009年 | 853篇 |
2008年 | 743篇 |
2007年 | 791篇 |
2006年 | 618篇 |
2005年 | 499篇 |
2004年 | 462篇 |
2003年 | 467篇 |
2002年 | 465篇 |
2001年 | 438篇 |
2000年 | 498篇 |
1999年 | 695篇 |
1998年 | 618篇 |
1997年 | 608篇 |
1996年 | 499篇 |
1995年 | 474篇 |
1994年 | 488篇 |
1993年 | 378篇 |
1992年 | 316篇 |
1991年 | 213篇 |
1990年 | 187篇 |
1989年 | 143篇 |
1988年 | 147篇 |
1987年 | 88篇 |
1986年 | 64篇 |
1985年 | 62篇 |
1984年 | 60篇 |
1983年 | 46篇 |
1982年 | 54篇 |
1981年 | 43篇 |
1980年 | 19篇 |
1979年 | 21篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1975年 | 4篇 |
1958年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 937 毫秒
51.
1 INTRODUCTION Active oxygen free radicals can damage cell structure, even kill the cells, causing aging and cer- tain serious diseases (Bors et al., 1989). Usually, the production and scavenging of active oxygen free radicals are in balance in healthy hu… 相似文献
52.
In this paper, the equilibrium configurations of rapid rotating compact stars and some gravitational effects are studied within the general relativity by use of the Harrison-Wheeler equation of state and by the self-consistent field method. Numerical calculations show that the equilibrium configuration of a rotating star is a spheroid. For large spin velocities, say, ω > 3.0 × 102 sec−1 the eccentricity and mass increase very rapidly as the angular velocity increases, for the critical angular velocity of the rotating star, the eccentricity is about 0.7, the increase in mass is about 10–35%. The difference of the gravitational redshifts at the surface of the star caused by rotation, and the difference of the light bending when the beam moves in the direction of rotation or in the opposite direction are obvious. 相似文献
53.
54.
Gang Zhao Yonggheng Zhao Jtasheng Huang Lonlong Feng Keliang Huang Qiuhe Peng Tan Lu 《Astrophysics and Space Science》1988,141(1):169-176
In this paper, the neutrino mass has been determined from SN1987a observation in a manner that the simultaneity of neutrino emission is not regarded as the starting point, but is itself defined through the analysis by Monte-Carlo simulation. The result is that the neutrino mass lies in 3–4 eV, possiblym
v
3.6 eV. Neutrino luminosity variation and neutrino spectrum are also obtained. Comparison with theories gives further support to the mass determination, and also predicts the mass of progenitor star of SN1987a to be in the range of 12–25M
.The project supported by the National Natural Science Foundation of China. 相似文献
55.
56.
57.
Yi-Sui Sun 《Celestial Mechanics and Dynamical Astronomy》1983,30(1):7-19
In this paper, using two methods: LCN'S (Lyapunov characteristic numbers) method and slice cutting method, we study numerically two mappings with odd dimension: $$T_1 :\left\{ {\begin{array}{*{20}c} {x_{n + 1} = x_n + z_n ,} \\ {y_{n + 1} = y_n + x_{n + 1} , (\bmod 2\pi )} \\ {z_{n + 1} = z_n + A\sin y_{n + 1} ,} \\ \end{array} } \right. T_2 :\left\{ {\begin{array}{*{20}c} {x_{n + 1} = x_n + y_n + B \sin z_n ,} \\ {y_{n + 1} = y_n + A \sin x_{n + 1} , (\bmod 2\pi ),} \\ {z_{n + 1} = z_n + B \sin y_{n + 1} ,} \\ \end{array} } \right.$$ whereA, B are parameters. For the mappingT 1 the whole region is stochastic; however, we find two-dimensional invariant manifolds for the mappingT 2. 相似文献
58.
Uranium-series dating of oxygen and carbon isotope records for stalagmite SJ3 collected in Songjia Cave, central China, shows significant variation in past climate and environment during the period 20-10 ka. Stalagmite SJ3 is located more than 1000 km inland of the coastal Hulu Cave in East China and more than 700 km north of the Dongge Cave in Southwest China and, despite minor differences, displays a clear first-order similarity with the Hulu and Dongge records. The coldest climatic phase since the Last Glacial Maximum, which is associated with the Heinrich Event 1 in the North Atlantic region, was clearly recorded in SJ3 between 17.6 and 14.5 ka, in good agreement in timing, duration and extent with the records from Hulu and Dongge caves and the Greenland ice core. The results indicate that there have been synchronous and significant climatic changes across monsoonal China and strong teleconnections between the North Atlantic and East Asia regions during the period 20-10 ka. This is much different from the Holocene Optimum which shows a time shift of more than several thousands years from southeast coastal to inland China. It is likely that temperature change at northern high latitudes during glacial periods exerts stronger influence on the Asian summer monsoon relative to insolation and appears to be capable of perturbing large-scale atmospheric/oceanic circulation patterns in the Northern Hemisphere and thus monsoonal rainfall and paleovegetation in East Asia. Climatic signals in the North Atlantic region propagate rapidly to East Asia during glacial periods by influencing the winter land-sea temperature contrast in the East Asian monsoon region. 相似文献
59.
Decoupling of stalagmite-derived Asian summer monsoon records from North Atlantic temperature change during marine oxygen isotope stage 5d 总被引:2,自引:0,他引:2
Houyun Zhou Jianxin Zhao Chuan-Chou Shen Yuexing Feng Huazheng Guan Chen-Feng You 《Quaternary Research》2008,70(2):315-321
The Asian monsoon is an important component of the global climate system. Seasonal variations in wind, rainfall, and temperature associated with the Asian monsoon systems affect a vast expanse of tropical and subtropical Asia. Speleothem-derived summer monsoon variation in East Asia was previously found to be closely associated with millennial-scale change in temperature in the North Atlantic region between 75 and 10 ka. New evidence recovered from East Asia, however, suggests that the teleconnection between summer monsoon in East Asia and temperature change in the North Atlantic region may have significantly reduced during 120 to ~ 110 ka, a period directly after the full last interglaciation and corresponding roughly to marine oxygen isotope stage 5d. This reduction may be due to the low ice volume in the North Hemisphere at that time, which makes the millennial-scale change in temperature in the North Atlantic region less effective in influencing the Asian summer monsoon. This is important for investigating the mechanisms controlling the Asian summer monsoon and the paleoclimatic teleconnection between East Asia and the North Atlantic region, and for predicting monsoon-associated precipitation in East Asia under a global-warming trend. 相似文献
60.
Chang-Guk Sun Sung-Ho Chun Tae-Gyun Ha Choong-Ki Chung Dong-Soo Kim 《Computers and Geotechnics》2008,35(3):436-449
An integrated GIS-based tool (GTIS) was constructed to estimate site effects related to the earthquake hazards in the Gyeongju area of Korea. To build the GTIS for the study area, intensive site investigations and geotechnical data collections were performed and a walk-over site survey was additionally carried out to acquire surface geo-knowledge data in accordance with the procedure developed to build the GTIS. For practical applications of the GTIS used to estimate the site effects associated with the amplification of ground motion, seismic microzoning maps of the characteristic site period and the mean shear wave velocity to a depth of 30 m were created and presented as a regional synthetic strategy addressing earthquake-induced hazards. Additionally, based on one-dimensional site response analyses, various seismic microzoning maps for short- and mid-period amplification potentials were created for the study area. Case studies of seismic microzonations in the Gyeongju area verified the usefulness of the GTIS for predicting seismic hazards in the region. 相似文献