全文获取类型
收费全文 | 1641篇 |
免费 | 47篇 |
国内免费 | 51篇 |
专业分类
测绘学 | 153篇 |
大气科学 | 161篇 |
地球物理 | 300篇 |
地质学 | 702篇 |
海洋学 | 145篇 |
天文学 | 217篇 |
综合类 | 17篇 |
自然地理 | 44篇 |
出版年
2022年 | 17篇 |
2021年 | 22篇 |
2020年 | 19篇 |
2019年 | 16篇 |
2018年 | 39篇 |
2017年 | 53篇 |
2016年 | 74篇 |
2015年 | 33篇 |
2014年 | 58篇 |
2013年 | 118篇 |
2012年 | 55篇 |
2011年 | 62篇 |
2010年 | 46篇 |
2009年 | 63篇 |
2008年 | 48篇 |
2007年 | 46篇 |
2006年 | 59篇 |
2005年 | 43篇 |
2004年 | 38篇 |
2003年 | 30篇 |
2002年 | 40篇 |
2001年 | 42篇 |
2000年 | 37篇 |
1999年 | 44篇 |
1998年 | 30篇 |
1997年 | 29篇 |
1996年 | 29篇 |
1995年 | 17篇 |
1994年 | 23篇 |
1993年 | 20篇 |
1992年 | 19篇 |
1991年 | 18篇 |
1990年 | 27篇 |
1989年 | 18篇 |
1988年 | 22篇 |
1987年 | 27篇 |
1986年 | 24篇 |
1985年 | 27篇 |
1984年 | 29篇 |
1983年 | 26篇 |
1982年 | 24篇 |
1981年 | 22篇 |
1980年 | 22篇 |
1979年 | 22篇 |
1978年 | 16篇 |
1975年 | 17篇 |
1974年 | 14篇 |
1973年 | 23篇 |
1972年 | 16篇 |
1971年 | 22篇 |
排序方式: 共有1739条查询结果,搜索用时 0 毫秒
11.
Summary. The contributions from the oceanic and ionospheric dynamos, Lo and LI respectively, to the geomagnetic lunar daily variation, L , at Alibag, a coastal station in the Indian equatorial region, are calculated from the L harmonics derived from a 41–yr long series of observations. The analysis in the calendar months shows a steady and significant ocean dynamo contribution in the vertical component, Z, in all the months except April. Examination, by an analysis of the data year by year, of the association of Lo and LI with varying solar and magnetic activities reveals, surprisingly, a stable correlation between the magnetic activity index A P and the oceanic part in the horizontal and vertical components but not in declination, which probably indicates the influence of induced currents, along the latitudes, on L o . 相似文献
12.
R. Pandiyan S. V. Subbarao T. Nagamani Chaitra Rao N. Hari Prasad Rao Harish Joglekar Naresh Kumar Surya Ratna Prakash Dumpa Anshu Chauhan B. P. Dakshayani 《Journal of Astrophysics and Astronomy》2017,38(2):35
On 28th September 2015, India launched its first astronomical space observatory AstroSat, successfully. AstroSat carried five astronomy payloads, namely, (i) Cadmium Zinc Telluride Imager (CZTI), (ii) Large Area X-ray Proportional Counter (LAXPC), (iii) Soft X-ray Telescope (SXT), (iv) Ultra Violet Imaging Telescope (UVIT) and (v) Scanning Sky Monitor (SSM) and therefore, has the capability to observe celestial objects in multi-wavelength. Four of the payloads are co-aligned along the positive roll axis of the spacecraft and the remaining one is placed along the positive yaw axis direction. All the payloads are sensitive to bright objects and specifically, require avoiding bright Sun within a safe zone of their bore axes in orbit. Further, there are other operational constraints both from spacecraft side and payloads side which are to be strictly enforced during operations. Even on-orbit spacecraft manoeuvres are constrained to about two of the axes in order to avoid bright Sun within this safe zone and a special constrained manoeuvre is exercised during manoeuvres. The planning and scheduling of the payloads during the Performance Verification (PV) phase was carried out in semi-autonomous/manual mode and a complete automation is exercised for normal phase/Guaranteed Time Observation (GuTO) operations. The process is found to be labour intensive and several operational software tools, encompassing spacecraft sub-systems, on-orbit, domain and environmental constraints, were built-in and interacted with the scheduling tool for appropriate decision-making and science scheduling. The procedural details of the complex scheduling of a multi-wavelength astronomy space observatory and their working in PV phase and in normal/GuTO phases are presented in this paper. 相似文献
13.
D. P. Rao 《Journal of the Indian Society of Remote Sensing》1977,5(2):67-70
Visual Interpretation of LANDSAT imagery of Eastern Ghats-Godavari delta area on scale 1:1,000,000 on spectral bands 5 and 7 was attempted. A neotectonic and geomorphic map was prepared from these images showing among other features major and minor lineaments. The importance of some of these lineaments for sedimentation, oil migration and localisation of ore bodies is discussed. 相似文献
14.
An examination of day-to-day and monthly mean positions of the electrojet axis in relation to the changes in the apparent solar declination, in the Indian equatorial region shows marked association between the two. For relatively quiet days, significant correlations are observed between the solar declination and each of the parameters, the northernSq focal latitude, the jet axis and the line of maximumSq(H). From the significant mutual association of these parameters, it has been suggested that the equatorial electrojet could be a part of the world-wideSq current system. 相似文献
15.
16.
D. P. sharma A. K. Jain S. C. Chakravarty K. Kasturirangan K. R. Ramanathan U. R. Rao 《Astrophysics and Space Science》1972,17(2):409-425
The electron production rates in the night-time D-region arising from the transit of strong celestial X-ray sources Sco X-1,
Tau X-1 and Galactic Center are estimated and compared with the ambient electron production rates resulting from other known
stable agencies. Using the experimentally measured values of the night-time electron densities, the number of additional electrons/cc
expected from the passage of these sources is computed. For the 164 kHz transmission from Tashkent, received at Ahmedabad,
the associated enhancement in the attenuation is calculated using the full wave admittance technique of Barron and Budden.
Reasonable agreement is shown to exist between the calculated values of the attenuation and those of direct observations. 相似文献
17.
N. Kameswara Rao V. R. Venugopal A. R. Patnaik 《Journal of Astrophysics and Astronomy》1987,8(3):227-230
VLA observations at 6 cm have been obtained for three hydrogen-deficient objects υ Sgr, V 348 Sgr, and A bell 58. A bell 58
was also observed at 2 cm. Only upper limits to the flux density could be set for these sources. A new radio source at 6 cm
was found in the field of υ Sgr.
The upper limit for 6 cm flux density of V348 Sgr sets an upper limit to its reddening asE(B–V) ≤ 0.65. The hydrogen deficient planetary nebula A 58 shows much lower radio flux than expected from the infrared-radio flux
density relationship of planetary nebulae.
National Radio Astronomy Observatory’s Very Large Array is operated by Associated Universities Inc. under contract with National
Science Foundation, USA. 相似文献
18.
Rama Rao Karri Abhijit Badwe Xuan Wang Ghada El Serafy Julius Sumihar Vladan Babovic Herman Gerritsen 《Ocean Dynamics》2013,63(1):43-61
Hydrodynamic models are commonly used for predicting water levels and currents in the deep ocean, ocean margins and shelf seas. Their accuracy is typically limited by factors, such as the complexity of the coastal geometry and bathymetry, plus the uncertainty in the flow forcing (deep ocean tide, winds and pressure). In Southeast Asian waters with its strongly hydrodynamic characteristics, the lack of detailed marine observations (bathymetry and tides) for model validation is an additional factor limiting flow representation. This paper deals with the application of ensemble Kalman filter (EnKF)-based data assimilation with the purpose of improving the deterministic model forecast. The efficacy of the EnKF is analysed via a twin experiment conducted with the 2D barotropic Singapore regional model. The results show that the applied data assimilation can improve the forecasts significantly in this complex flow regime. 相似文献
19.
20.
Brice Ménard Daniel Nestor David Turnshek Anna Quider Gordon Richards Doron Chelouche Sandhya Rao 《Monthly notices of the Royal Astronomical Society》2008,385(2):1053-1066
Using a sample of almost 7000 strong Mg ii absorbers with W 0 > 1 Å and 0.4 < z < 2.2 detected in the SDSS DR4 data set, we investigate the gravitational lensing and dust extinction effects they induce on background quasars. After carefully quantifying several selection biases, we isolate the reddening effects as a function of redshift and absorber rest equivalent width, W 0 . We find the amount of dust to increase with cosmic time as τ( z ) ∝ (1 + z )−1.1±0.4 , following the evolution of cosmic star density or integrated star formation rate. We measure the reddening effects over a factor of 30 in E ( B − V ) and we find that τ∝ ( W 0 )1.9±0.1 , providing us with an important scaling for theoretical modelling of metal absorbers. We also measure the dust-to-metal ratio and find it similar to that of the Milky Way. In contrast to previous studies, we do not detect any gravitational magnification by Mg ii systems. We measure the upper limit μ < 1.10 and discuss the origin of the discrepancy. Finally, we estimate the fraction of absorbers missed due to extinction effects and show that it rises from 1 to 50 per cent in the range 1 < W 0 < 6 Å . We parametrize this effect and provide a correction for recovering the intrinsic ∂ N /∂ W 0 distribution. 相似文献