全文获取类型
收费全文 | 30818篇 |
免费 | 570篇 |
国内免费 | 381篇 |
专业分类
测绘学 | 791篇 |
大气科学 | 2811篇 |
地球物理 | 6353篇 |
地质学 | 10767篇 |
海洋学 | 2378篇 |
天文学 | 6754篇 |
综合类 | 70篇 |
自然地理 | 1845篇 |
出版年
2020年 | 179篇 |
2019年 | 196篇 |
2018年 | 492篇 |
2017年 | 481篇 |
2016年 | 689篇 |
2015年 | 448篇 |
2014年 | 674篇 |
2013年 | 1404篇 |
2012年 | 739篇 |
2011年 | 1026篇 |
2010年 | 873篇 |
2009年 | 1240篇 |
2008年 | 1058篇 |
2007年 | 941篇 |
2006年 | 1043篇 |
2005年 | 874篇 |
2004年 | 848篇 |
2003年 | 869篇 |
2002年 | 867篇 |
2001年 | 746篇 |
2000年 | 788篇 |
1999年 | 660篇 |
1998年 | 629篇 |
1997年 | 666篇 |
1996年 | 575篇 |
1995年 | 541篇 |
1994年 | 483篇 |
1993年 | 427篇 |
1992年 | 420篇 |
1991年 | 416篇 |
1990年 | 422篇 |
1989年 | 398篇 |
1988年 | 380篇 |
1987年 | 466篇 |
1986年 | 435篇 |
1985年 | 464篇 |
1984年 | 558篇 |
1983年 | 560篇 |
1982年 | 501篇 |
1981年 | 490篇 |
1980年 | 447篇 |
1979年 | 433篇 |
1978年 | 447篇 |
1977年 | 394篇 |
1976年 | 355篇 |
1975年 | 355篇 |
1974年 | 405篇 |
1973年 | 389篇 |
1972年 | 245篇 |
1971年 | 224篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Kunde Yang Yuanliang Ma Chao Sun Miller J.H. Potty G.R. 《Oceanic Engineering, IEEE Journal of》2004,29(4):964-972
This paper discusses the results of geoacoustic inversion carried out using explosive charge data from the Asian Seas International Acoustic Experiment (ASIAEX) East China Sea (ECS) Experiment. A multifrequency incoherent matched-field inversion processor and a genetic algorithm (GA) are used for the inversion. A multistep matched field inversion approach is presented, which makes use of the varying sensitivities of wave fields at various frequencies to reduce the inversion problem into a sequence of smaller inversions with fewer unknowns to estimate at each stage. Different parameters are estimated using data at different frequencies according to their sensitivities. Inversion results for different areas in the ECS region are summarized and compared with core data. 相似文献
32.
The occultation of Io by Ganymede as observed on 10 June 1985 is reported. The middle of the occultation minimum was found to occur at 14h 14m 5.7s UT. In the plane perpendicular to the line of sight the centres of the two satellite disks passed to within ~ 2530 km of each other, at a relative velocity, in this plane, of about 11 kms–1. The values of these last two quantities, however, depend on what assumptions are made about the light distribution over io's disk. 相似文献
33.
H. W. Urbarz 《Astrophysics and Space Science》1996,243(1):203-207
The list of mass ejections published in Solar Geophysical Data during the period of Jan. 1981 to Oct. 1987 contains about 1300 Surges, Sprays and Type II bursts. The relationship between the mass ejection events and the shock front events is investigated by means of correlation of time and position. The result shows that type II bursts start as frequently after the mass ejections as prior to them. 相似文献
34.
35.
Long-term measurements from Advanced Very High Resolution Radiometer (AVHRR) onboard the National Oceanic and Atmospheric Administration satellites were evaluated to assess variability in cloud-top temperatures over central and eastern Europe that saw radical infrastructural changes after the fall of the East Bloc in 1989 that has affected the pollution levels and hence cloud albedo. Four years in the late 1980s (1985-1988) and in the late 1990s (1997-2000) were chosen, as these are distinctively marked as episodes of very high and lower air pollution (sulphates and particulate matter). During the late 1980s, low- and medium-level clouds were colder by more than 2 K and convective clouds even by 4 K. Cloud-tops over and around polluted regions are higher, and their temperatures showed stronger variability, suggesting an indirect aerosol effect in the thermal spectral range as well. 相似文献
36.
Andrea PATZER Jochen SCHLÜTER Ludolf SCHULTZ Dolores H. HILL William V. BOYNTON 《Meteoritics & planetary science》2005,40(6):869-879
Abstract— Mineralogical and chemical studies of Dar al Gani 983 show that this meteorite is a eucrite. Its texture is that of an impact breccia. It contains cumulate pyroxene and feldspar megacrysts, a variety of recrystallized melt clasts, clasts of subophitic basalt, and mesostasis. These components are embedded in a matrix of fragmental pyroxene and plagioclase. In addition, the entire rock is penetrated by glassy melt veins and patches, and displays features of strong shock. The mineralogical and chemical evidence obtained for DaG 983 indicates that this meteorite experienced a complex evolutionary history. The presence of cumulate silicate crystals implies substantial, large scale cratering events on the HED asteroid. As a result of these impacts, rocks from different intrusive bodies to extrusive surface layers were laterally and vertically transported to form a thoroughly mixed megaregolith. DaG 983 represents a sample of this megabreccia. 相似文献
37.
38.
39.
Distances to nine dark globules are determined by a method using optical ( VRI ) and near-infrared (near-IR) ( JHK ) photometry of stars projected towards the field containing the globules. In this method, we compute intrinsic colour indices of stars projected towards the direction of the globule by dereddening the observed colour indices using various trial values of extinction A V and a standard extinction law. These computed intrinsic colour indices for each star are then compared with the intrinsic colour indices of normal main-sequence stars and a spectral type is assigned to the star for which the computed colour indices best match with the standard intrinsic colour indices. Distances ( d ) to the stars are determined using the A V and absolute magnitude ( MV ) corresponding to the spectral types thus obtained. A distance versus extinction plot is made and the distance at which A V undergoes a sharp rise is taken to be the distance to the globule. All the clouds studied in this work are in the distance range 160–400 pc. The estimated distances to dark globules LDN 544, LDN 549, LDN 567, LDN 543, LDN 1113, LDN 1031, LDN 1225, LDN 1252 and LDN 1257 are 180 ± 35, 200 ± 40, 180 ± 35, 160 ± 30, 350 ± 70, 200 ± 40, 400 ± 80, 250 ± 50 and 250 ± 50 pc, respectively. Using the distances determined, we have estimated the masses of the globules and the far-IR luminosity of the IRAS sources associated with them. The mass of the clouds studied are in the range 10–200 M⊙ . 相似文献
40.
The great continental ice sheets of the Pleistocene represented a significant topographic obstacle to the westerly winds
in northern midlatitudes. This work explores how consequent changes in the atmospheric stationary wave pattern might have
affected the shape and growth of the ice sheets themselves. A one dimensional (1-D) model is developed which permits an examination
of the types and magnitudes of the feedbacks that might be expected. When plausible temperature perturbations are introduced
at the ice-sheet margin which are proportional to the stationary wave amplitude, the equilibrium shape of the ice sheet is
significantly altered, and depends on the sign of the perturbation. The proposed feedback also affects the response of the
ice sheet to time-varying climate forcing. The results suggest that the evolution of a continental-scale ice sheet with a
land-based margin may be significantly determined by the changes it induces in the atmospheric circulation.
Received: 1 October 1999 / Accepted: 17 July 2000 相似文献