全文获取类型
收费全文 | 31561篇 |
免费 | 811篇 |
国内免费 | 340篇 |
专业分类
测绘学 | 895篇 |
大气科学 | 2455篇 |
地球物理 | 6499篇 |
地质学 | 11267篇 |
海洋学 | 2637篇 |
天文学 | 7294篇 |
综合类 | 80篇 |
自然地理 | 1585篇 |
出版年
2022年 | 144篇 |
2021年 | 322篇 |
2020年 | 380篇 |
2019年 | 407篇 |
2018年 | 911篇 |
2017年 | 903篇 |
2016年 | 1122篇 |
2015年 | 703篇 |
2014年 | 1043篇 |
2013年 | 1793篇 |
2012年 | 1192篇 |
2011年 | 1409篇 |
2010年 | 1293篇 |
2009年 | 1613篇 |
2008年 | 1378篇 |
2007年 | 1347篇 |
2006年 | 1317篇 |
2005年 | 988篇 |
2004年 | 998篇 |
2003年 | 882篇 |
2002年 | 848篇 |
2001年 | 718篇 |
2000年 | 720篇 |
1999年 | 629篇 |
1998年 | 619篇 |
1997年 | 609篇 |
1996年 | 451篇 |
1995年 | 462篇 |
1994年 | 474篇 |
1993年 | 355篇 |
1992年 | 336篇 |
1991年 | 294篇 |
1990年 | 367篇 |
1989年 | 298篇 |
1988年 | 278篇 |
1987年 | 319篇 |
1986年 | 264篇 |
1985年 | 351篇 |
1984年 | 372篇 |
1983年 | 360篇 |
1982年 | 347篇 |
1981年 | 287篇 |
1980年 | 286篇 |
1979年 | 240篇 |
1978年 | 226篇 |
1977年 | 238篇 |
1976年 | 196篇 |
1975年 | 206篇 |
1974年 | 196篇 |
1973年 | 188篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
41.
42.
O. Tamuz T. Mazeh S. Zucker † 《Monthly notices of the Royal Astronomical Society》2005,356(4):1466-1470
We suggest a new algorithm to remove systematic effects in a large set of light curves obtained by a photometric survey. The algorithm can remove systematic effects, such as those associated with atmospheric extinction, detector efficiency, or point spread function changes over the detector. The algorithm works without any prior knowledge of the effects, as long as they linearly appear in many stars of the sample. The approach, which was originally developed to remove atmospheric extinction effects, is based on a lower rank approximation of matrices, an approach which has already been suggested and used in chemometrics, for example. The proposed algorithm is especially useful in cases where the uncertainties of the measurements are unequal. For equal uncertainties, the algorithm reduces to the Principal Component Analysis (PCA) algorithm. We present a simulation to demonstrate the effectiveness of the proposed algorithm and we point out its potential, in the search for transit candidates in particular. 相似文献
43.
Lawrence M. Mayer Peter T. Rahaim William Guerin Stephen A. Macko Les Watling Franz E. Anderson 《Estuarine, Coastal and Shelf Science》1985,20(4):491-503
A variety of measures of organic matter concentration and quality were made on samples collected from the top few mm of intertidal mudflat sediment over the course of a year, in order to assess the relative importance of biological and sedimentological influences on sedimentary organic matter. Winter and summer were times of relatively fine-grained sediment accumulation, caused by biological deposition or stabilization processes and resulting in higher organic matter concentrations. Stable carbon isotope and Br:C ratios indicated a planktonic source of bulk organic matter. Ratios of organic carbon to specific surface area of the sediments were consistent with an organic monolayer coverage of sediment grains. Correction for changing grain size during the year showed no change in the organic concentration per unit surface area, in spite of organic matter inputs by in situ primary production, buildup of heterotroph biomass and mucus coatings, and biodeposition of organic-rich seston. There were also no indications of changes in bulk organic quality, measured as hydrolyzable carbohydrates and amino acids, in response to these biological processes. It is concluded that biological processes on a seasonal time scale affect the bulk organic matter of these sediments via a modulation of grain size rather than creation or decay of organic matter. 相似文献
44.
45.
B. Ahmed G. J. Alner H. Araujo J. C. Barton A. Bewick M. J. Carson D. Davidge J. V. Dawson T. Gamble S. P. Hart R. Hollingworth A. S. Howard W. G. Jones M. K. Joshi V. A. Kudryavtsev T. B. Lawson V. Lebedenko M. J. Lehner J. D. Lewin P. K. Lightfoot I. Liubarsky R. Lüscher J. E. McMillan B. Morgan G. Nicklin S. M. Paling R. M. Preece J. J. Quenby J. W. Roberts M. Robinson N. J. T. Smith P. F. Smith N. J. C. Spooner T. J. Sumner D. R. Tovey 《Astroparticle Physics》2003,19(6):691-702
The NAIAD experiment (NaI Advanced Detector) for weakly interacting massive particle (WIMP) dark matter searches at Boulby mine (UK) is described. The detector consists of an array of encapsulated and unencapsulated NaI(Tl) crystals with high light yield. Six crystals are collecting data at present. Data accumulated by four of them (10.6 kg × year exposure) have been used to set upper limits on the WIMP–nucleon spin-independent and WIMP–proton spin-dependent cross-sections. Pulse shape analysis has been applied to discriminate between nuclear recoils, as may be caused by WIMP interactions, and electron recoils due to gamma background. Various calibrations of crystals are presented. 相似文献
46.
47.
With the advent of either sensitive space-born infrared cameras, or their high-resolution ground-based siblings, we are uncovering
a new category of star clusters: the dust-enshrouded super-star clusters. These manifest themselves only beyond a few microns,
as their shroud of dust is able to block all light emitted by the stars themselves. Here we present our results on the spectacular
cluster in SBS 0335-052, a very metal-poor galaxy. We also point to the growing number of galaxy analogs to SBS 0335-052,
revealing the possibility that these clusters signal a major mode of star formation in starbursts. We conclude by listing
a number of open points these clusters raise, in particular with respect to high-redshift counterparts.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
48.
A type IV radio burst accompanied by several normal- and reverse-drifting type III bursts, multiple long-term quasi-periodic pulsations and spikes was observed with the radio spectrometers (1.0–2.0 and 2.6–3.8 GHz) at National Astronomical Observatories of China (NAOC) on 23 September 1998. In combination with the images of Siberian Solar Radio Telescope (SSRT) of Russia, the complex and multiple magnetic structures inferred from the radio bursts reveal the existence of both large-scale and small-scale magnetic structures. This event suggests that the geometries of coronal magnetic fields contain multiple discrete electron acceleration/injection sites at different heights, and extended open and closed magnetic field lines. It can be shown that the energetic electrons gain access to open, diverging and closed field lines thus producing different types of radio bursts. From the characteristics of position, polarization, dispersion and displacement of the sources, the model of the type IV event is supported, which involves synchrotron emission from the electrons confined by the rapid scattering through the interaction of hydromagnetic wave with particles. 相似文献
49.
Florent Deleflie Gilles Métris Pierre Exertier 《Celestial Mechanics and Dynamical Astronomy》2006,94(1):83-104
This paper studies the long period variations of the eccentricity vector of the orbit of an artificial satellite, under the
influence of the gravity field of a central body. We use modified orbital elements which are non-singular at zero eccentricity.
We expand the long periodic part of the corresponding Lagrange equations as power series of the eccentricity. The coefficients
characterizing the differential system depend on the zonal coefficients of the geopotential, and on initial semi-major axis,
inclination, and eccentricity. The differential equations for the components of the eccentricity vector are then integrated
analytically, with a definition of the period of the perigee based on the notion of “free eccentricity”, and which is also
valid for circular orbits. The analytical solution is compared to a numerical integration. This study is a generalization
of (Cook, Planet. Space Sci., 14, 1966): first, the coefficients involved in the differential equations depend on all zonal coefficients (and not only on
the very first ones); second, our method applies to nearly circular orbits as well as to not too eccentric orbits. Except
for the critical inclination, our solution is valid for all kinds of long period motions of the perigee, i.e., circulations
or librations around an equilibrium point. 相似文献
50.