全文获取类型
收费全文 | 37843篇 |
免费 | 308篇 |
国内免费 | 238篇 |
专业分类
测绘学 | 727篇 |
大气科学 | 1754篇 |
地球物理 | 7258篇 |
地质学 | 14804篇 |
海洋学 | 3591篇 |
天文学 | 9001篇 |
综合类 | 107篇 |
自然地理 | 1147篇 |
出版年
2022年 | 494篇 |
2021年 | 716篇 |
2020年 | 769篇 |
2019年 | 835篇 |
2018年 | 1722篇 |
2017年 | 1559篇 |
2016年 | 1674篇 |
2015年 | 639篇 |
2014年 | 1456篇 |
2013年 | 2076篇 |
2012年 | 1654篇 |
2011年 | 1937篇 |
2010年 | 1830篇 |
2009年 | 2029篇 |
2008年 | 1808篇 |
2007年 | 2011篇 |
2006年 | 1766篇 |
2005年 | 924篇 |
2004年 | 842篇 |
2003年 | 835篇 |
2002年 | 761篇 |
2001年 | 783篇 |
2000年 | 641篇 |
1999年 | 426篇 |
1998年 | 446篇 |
1997年 | 487篇 |
1996年 | 353篇 |
1995年 | 369篇 |
1994年 | 339篇 |
1993年 | 290篇 |
1992年 | 286篇 |
1991年 | 296篇 |
1990年 | 342篇 |
1989年 | 275篇 |
1988年 | 262篇 |
1987年 | 266篇 |
1986年 | 198篇 |
1985年 | 307篇 |
1984年 | 308篇 |
1983年 | 302篇 |
1982年 | 278篇 |
1981年 | 250篇 |
1980年 | 266篇 |
1979年 | 205篇 |
1978年 | 242篇 |
1977年 | 206篇 |
1976年 | 178篇 |
1975年 | 185篇 |
1974年 | 173篇 |
1973年 | 207篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
V. Delouille J. De Patoul J. F. Hochedez L. Jacques J. P. Antoine 《Solar physics》2005,228(1-2):301-321
The extreme ultraviolet imaging telescope (EIT) of SOHO offers a unique record of the solar atmosphere for its sampling in
temperature, field of view, resolution, duration, and cadence. To investigate globally and locally its topology and evolution
during the solar cycle, we consider a multi-scale approach, and more precisely we use the wavelet spectrum.
We present three results among the applications of such a procedure. First, we estimate the typical dimension of the supergranules
as seen in the 30.4 nm passband, and we show that the evolution of the characteristic network scale is almost in phase with
the solar cycle. Second, we build pertinent time series that give the evolution of the signal energy present in the corona
at different scales. We propose a method that detects eruptions and post-flaring activity in EUV image sequences. Third, we
introduce a new way to extract active regions in EIT images, with perspectives in, e.g., long-term irradiance analysis. 相似文献
12.
13.
14.
We discuss long-time changes of polar activity of the Sun using the new observational data sets in the optical range during
1872–2001. A study of the secular and cycle variations of the magnetic activity at the high-latitude regions is the main goal
that includes polar magnetic field reversals during 1872–2001 and secular changes of the duration of polar activity cycles.
The secular increase of the area of polar zones during the minimum activity in the last 120 years and as consequence a decrease
of coronal temperature of the Sun in the high-latitude zones during the last 50 years. Correlation between the polar cycles
of Caii-K bright points with the Wolf sunspot numbers cycles, W(t), and the 22-year polar magnetic cycles of Caii-K bright points at the high latitudes during 1905–1995 is discussed. 相似文献
15.
V. Parro J.A. Rodríguez-Manfredi C. Compostizo E. Vez M. Moreno-Paz P. Fernández-Calvo J. Pérez-Mercader J. Gómez-Elvira 《Planetary and Space Science》2005,53(7):729-737
Recent findings by the MER rover opportunity confirming the presence of iron minerals that can only be formed in the presence of water emphasize the study of analogous environments to Mars on Earth. The study of chemolithoautotrophic communities living in acidic iron-rich habitats is highly relevant in order to identify Mars analog environment-specific biomarkers. Iron oxidizing bacteria like Leptospirillum ferrooxidans and Acidithiobacillus ferrooxidans have ways of life for which it is feasible to identify a past or present hypothetical niche on Mars. We have developed a strategy for biomarker identification based on: (i) search for biosignatures on acid and metal-rich environments; (ii) development of an immunosensor microarray; and (iii) integration into an instrument for autonomous and remote operation. The instrument that we have built, called Signs Of LIfe Detector (SOLID), is capable of processing a variety of samples for the detection of specific biomarkers. Antibodies against several bacterial strains have been developed and tested in a microarray biosensor on SOLID. Tests with field samples have been successfully performed, allowing the detection of L. ferrooxidans, A. ferrooxidans present in sediment samples. 相似文献
16.
17.
18.
19.
We present results from a new simulation code that accounts for the evolution of the reservoirs of carbon dioxide on Mars, from its early years to the present. We establish a baseline model parameter set that produces results compatible with the present (i.e., Patm?6.5 mbar with permanent CO2 ice cap) for a wide range of initial inventories. We find that the initial inventory of CO2 broadly determines the evolutionary course of the reservoirs of CO2. The reservoirs include the atmosphere, ice cap, adsorbed CO2 in the regolith, and carbonate rocks. We track the evolution of the free inventory: the atmosphere, ice cap and regolith. Simulations begin at 4.53 Gyr before present with a rapid loss of free inventory to space in the early Noachian. Models that assume a relatively small initial inventory (?5 bar) have pronounced minima in the free inventory of CO2 toward the end of the Noachian. Under baseline parameters, initial inventories below ∼4.5 bar result in a catastrophic loss of the free inventory to space. The current free inventory would be then determined by the balance between outgassing, sputtering losses and chemical weathering following the end of the late bombardment. We call these “thin” models. They generically predict small current free inventories in line with expectations of a small present CO2 ice cap. For “thick” models, with initial inventories ?5 bar, a surplus of 300-700 mbar of free CO2 remains during the late-Noachian. The histories of free inventory in time for thick models tend to converge within the last 3.5 Gyr toward a present with an ice cap plus atmospheric inventory of about 100 mbar. For thick models, the convergence is largely due to the effects of chemical weathering, which draws down higher free inventories more rapidly than the low. Thus, thick models have ?450 mbar carbonate reservoirs, while thin models have ?200 mbar. Though both thick and thin scenarios can reproduce the current atmospheric pressure, the thick models imply a relatively large current CO2 ice cap and thin models, little or none. While the sublimation of a massive cap at a high obliquity would create a climate swing of greenhouse warming for thick models, under the thin model, mean temperatures and pressures would be essentially unaffected by increases in obliquity. 相似文献
20.
V. Berezinsky 《Astroparticle Physics》2002,17(4):575-514
Comparison of solar-neutrino signals in SNO [Phys. Rev. Lett. 87 (2001) 071301] and Super-Kamiokande (SK) [Phys. Rev. Lett. 86 (2001) 5651] detectors results in discovery of νe→νμ,τ oscillations at level 3.1–3.3σ [Phys. Rev. Lett. 87 (2001) 071301]. This comparison involves the assumption of neutrino spectrum and a choice for the thresholds of detection in both experiments. In this paper we obtain an exact formula for the comparison of the signals which is valid for arbitrary spectra and thresholds. We find that the no-oscillation hypothesis (astrophysical solutions) is excluded at 3.3σ. If the energy-dependent component of the survival probability for electron neutrinos is small as compared with the average value, i.e. in the case of small distortion of the observed spectrum, the oscillation hypothesis can also be tested to similar accuracy. The oscillation to sterile neutrino only, is excluded at 3.3σ level, and oscillation to active neutrinos is confirmed at 2.8σ. 相似文献