全文获取类型
收费全文 | 27291篇 |
免费 | 2041篇 |
国内免费 | 2983篇 |
专业分类
测绘学 | 1125篇 |
大气科学 | 3150篇 |
地球物理 | 5376篇 |
地质学 | 12114篇 |
海洋学 | 3324篇 |
天文学 | 4182篇 |
综合类 | 1043篇 |
自然地理 | 2001篇 |
出版年
2024年 | 80篇 |
2023年 | 235篇 |
2022年 | 794篇 |
2021年 | 1049篇 |
2020年 | 949篇 |
2019年 | 1035篇 |
2018年 | 1519篇 |
2017年 | 1362篇 |
2016年 | 1407篇 |
2015年 | 917篇 |
2014年 | 1307篇 |
2013年 | 1583篇 |
2012年 | 1399篇 |
2011年 | 1600篇 |
2010年 | 1473篇 |
2009年 | 1511篇 |
2008年 | 1407篇 |
2007年 | 1422篇 |
2006年 | 1263篇 |
2005年 | 742篇 |
2004年 | 675篇 |
2003年 | 692篇 |
2002年 | 749篇 |
2001年 | 680篇 |
2000年 | 581篇 |
1999年 | 531篇 |
1998年 | 463篇 |
1997年 | 475篇 |
1996年 | 368篇 |
1995年 | 383篇 |
1994年 | 343篇 |
1993年 | 277篇 |
1992年 | 232篇 |
1991年 | 201篇 |
1990年 | 187篇 |
1989年 | 175篇 |
1988年 | 155篇 |
1987年 | 160篇 |
1986年 | 135篇 |
1985年 | 148篇 |
1984年 | 136篇 |
1983年 | 143篇 |
1982年 | 124篇 |
1981年 | 104篇 |
1980年 | 120篇 |
1979年 | 113篇 |
1978年 | 103篇 |
1977年 | 93篇 |
1975年 | 84篇 |
1973年 | 81篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
11.
ENVIRONMENTAL SUSTAINABILITY AND SCENARIOS OF URBANIZATION IN ARID AREA——A Case Study in Wuwei City of Gansu Province 总被引:1,自引:0,他引:1
YOUFei LIYu DONGSuo-cheng 《中国地理科学(英文版)》2005,15(2):120-130
1IN T R O D U C T IO N The western China isfacinggrowing problems of eco- logicaland economic development. The disparitiebse- tween the socio-economy of the western and eastern China were enlarging, and the major ecologicalprob- lems stilelvolve as past(H… 相似文献
12.
MohammedHazaea HUKe MohammedMattash CHENBing M.O.AI-JabaliAref MohammedAbdussalam 《东北亚地学研究》2004,7(2):181-184
The chemical composition of several thermal springs around Changbaishan area has been investigated. Cenozoic basaltic rocks are widely distributed in Northeast China and geothermal characteristics have been described. About one hundred hot springs exist around Changhaishan Volcano at the border between China and D.P.R.Korea with high temperature about 82~C. The pH values of the spring water range from 6.9 to 7.1 and the total flow rate is about 4.8 L/sec. The chemical composition of the thermal springs is sodium carbonate; the high-mineral contents of thermal water are believed to have medicinal properties. Bathhouses are already built along the hot springs to take the advantage of the supposed healing properties. The high quality of those hot springs is believed to be utilitized for mineral water. The chemical equilibrium temperatures were estimated at about 160℃ based on the Na-K-Ca geochemical thermometer. 相似文献
13.
Methyl-galactosides were oxidized at room temperature by galactose oxidase in a one-step reaction and afforded methyl-galactoaldehyde
in excellent yield and high purity. The resulting galactoaldehyde as a useful intermediate can be directly used in glycopeptide
synthesis. 相似文献
14.
本文通过对1980年以来长江上游10次洪涝过程的500hpa环流形势分析,并用车比雪夫多项式对500hpa高度场进行展开,研究了各类洪涝过程的中期演变特征,发现代表不同洪涝过程环流形势变化的不同的车氏系数值都有明显的特征变化,结合欧洲中心中期数值预告96小时500hpa高度场的车氏系数分析,可为洪涝暴雨的中期预报提供一种新的思路。 相似文献
15.
Baolin Tan Haisheng Ji Guangli Huang Tuanhui Zhou Qiwu Song Yu Huang 《Solar physics》2006,239(1-2):137-148
Using one-minute cadence vector magnetograms from Big Bear Solar Observatory (BBSO), we analyze the temporal behavior of derived
longitudinal electric currents associated with two flares on July 26, 2002. One of the events is an M1.0 flare which occurred
in active region NOAA 10044, while the other is an M8.7 flare in the adjacent region 10039. Rapid changes of magnetic fields
in the form of flux emergence are found to be associated with both of these events. However, the temporal behavior of electric
currents are very different. For the M1.0 flare, the longitudinal electric current density drops rapidly near the flaring
neutral line; while for the M8.7 flare, the current density rapidly increases, confirming the picture of the current-carrying
flux emergence. We offer a possible explanation for such a difference: magnetic reconnection at different heights for the
two events, near the photosphere for the M1.0 flare, and higher up for the M8.7 flare. 相似文献
16.
17.
In the first paper of this series, we presented EBAS – Eclipsing Binary Automated Solver, a new fully automated algorithm to analyse the light curves of eclipsing binaries, based on the ebop code. Here, we apply the new algorithm to the whole sample of 2580 binaries found in the Optical Gravitational Lensing Experiment (OGLE) Large Magellanic Cloud (LMC) photometric survey and derive the orbital elements for 1931 systems. To obtain the statistical properties of the short-period binaries of the LMC, we construct a well-defined subsample of 938 eclipsing binaries with main-sequence B-type primaries. Correcting for observational selection effects, we derive the distributions of the fractional radii of the two components and their sum, the brightness ratios and the periods of the short-period binaries. Somewhat surprisingly, the results are consistent with a flat distribution in log P between 2 and 10 d. We also estimate the total number of binaries in the LMC with the same characteristics, and not only the eclipsing binaries, to be about 5000. This figure leads us to suggest that (0.7 ± 0.4) per cent of the main-sequence B-type stars in the LMC are found in binaries with periods shorter than 10 d. This frequency is substantially smaller than the fraction of binaries found by small Galactic radial-velocity surveys of B stars. On the other hand, the binary frequency found by Hubble Space Telescope ( HST ) photometric searches within the late main-sequence stars of 47 Tuc is only slightly higher and still consistent with the frequency we deduced for the B stars in the LMC. 相似文献
18.
We have investigated the central regions of the galaxies in the NGC 3169/NGC 3166/NGC 3156 group with the multipupil fiber spectrograph of the 6-m telescope; the first (central) galaxy in the group is a spiral (Sa) one and the other two galaxies are lenticular ones. The group is known to have an extended HI cloud with a size of more than 100 kpc that is associated in its position, orientation, and rotation with the central galaxy NGC 3169. The mean age of the stellar populations in the centers of all three galaxies has been found to be approximately the same, ~1 Gyr. Since the galaxies are early-type ones and since NGC 3166 and NGC 3156 show no global star formation, we are dealing here with a synchronous star formation burst in the centers of all three galaxies. 相似文献
19.
O.V.Chumak 《中国天文和天体物理学报》2003,3(2):175-182
We present a study of the relationship between integral area and corresponding total magnetic flux for solar active regions. It is shown that some of these relationships are satisfied to simple power laws. Fractal examination showed that some of these power laws can not be justified inside the simple models of stationary magnetic flux tube aggregation. All magnetic fluxes and corresponding areas were calculated using the data measured with the Solar Magnetic Field Telescope of the Huairou Solar Observing Station in Beijing. 相似文献
20.