全文获取类型
收费全文 | 47188篇 |
免费 | 1048篇 |
国内免费 | 1110篇 |
专业分类
测绘学 | 1162篇 |
大气科学 | 3493篇 |
地球物理 | 9527篇 |
地质学 | 17601篇 |
海洋学 | 4348篇 |
天文学 | 10132篇 |
综合类 | 285篇 |
自然地理 | 2798篇 |
出版年
2022年 | 412篇 |
2021年 | 632篇 |
2020年 | 613篇 |
2019年 | 681篇 |
2018年 | 1341篇 |
2017年 | 1217篇 |
2016年 | 1444篇 |
2015年 | 871篇 |
2014年 | 1400篇 |
2013年 | 2373篇 |
2012年 | 1725篇 |
2011年 | 2234篇 |
2010年 | 2020篇 |
2009年 | 2534篇 |
2008年 | 2182篇 |
2007年 | 2221篇 |
2006年 | 2080篇 |
2005年 | 1495篇 |
2004年 | 1398篇 |
2003年 | 1268篇 |
2002年 | 1224篇 |
2001年 | 1046篇 |
2000年 | 1048篇 |
1999年 | 808篇 |
1998年 | 874篇 |
1997年 | 826篇 |
1996年 | 671篇 |
1995年 | 674篇 |
1994年 | 581篇 |
1993年 | 501篇 |
1992年 | 479篇 |
1991年 | 466篇 |
1990年 | 540篇 |
1989年 | 429篇 |
1988年 | 422篇 |
1987年 | 527篇 |
1986年 | 420篇 |
1985年 | 526篇 |
1984年 | 618篇 |
1983年 | 545篇 |
1982年 | 530篇 |
1981年 | 476篇 |
1980年 | 504篇 |
1979年 | 436篇 |
1978年 | 422篇 |
1977年 | 412篇 |
1976年 | 361篇 |
1975年 | 351篇 |
1974年 | 378篇 |
1973年 | 401篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A method of separating electric field in the flare region in the potential and vortex (induced) parts is discussed. According to the proposed model, the motion of flare ribbons from the central line of the flare region is caused by the vortex component of the coronal electric field, while the motion of bright spots within the flare region towards the central line is driven by the potential component of that field. The intensity of both the components of the flare region electric field is estimated to equal approximately 1–3 V cm–1, which provides the input of the electromagnetic energy into the active region at a rate of about 1010 erg cm–2 s–1. 相似文献
992.
NLTE calculations of carbon abundance in Peg atmosphere revealed a slight deficiency of this element ([C/H] =–0.25). A short discussion of this result is given. The list of CII that could be used for LTE calculation of carbon abundance in hot stars is presented. 相似文献
993.
McKay CP Grunthaner FJ Lane AL Herring M Bartman RK Ksendzov A Manning CM Lamb JL Williams RM Ricco AJ Butler MA Murray BC Quinn RC Zent AP Klein HP Levin GV 《Planetary and Space Science》1998,46(6-7):769-777
The MOx instrument was developed to characterize the reactive nature of the martian soil. The objectives of MOx were: (1) to measure the rate of degradation of organics in the martian environment; (2) to determine if the reactions seen by the Viking biology experiments were caused by a soil oxidant and measure the reactivity of the soil and atmosphere: (3) to monitor the degradation, when exposed to the martian environment, of materials of potential use in future missions; and, finally, (4) to develop technologies and approaches that can be part of future soil analysis instrumentation. The basic approach taken in the MOx instrument was to place a variety of materials composed as thin films in contact with the soil and monitor the physical and chemical changes that result. The optical reflectance of the thin films was the primary sensing-mode. Thin films of organic materials, metals, and semiconductors were prepared. Laboratory simulations demonstrated the response of thin films to active oxidants. 相似文献
994.
C. Simon Jeffery & Don L. Pollacco 《Monthly notices of the Royal Astronomical Society》1998,298(1):179-184
Intermediate dispersion spectroscopy of a sample of 40 hot subdwarf B stars between 5500 and 9000Å has been obtained. The sample includes a large fraction of targets which have been studied photometrically. Seven targets show strong lines arising from the infrared Ca ii triplet, the unequivocal signature of a cool companion. The positive Ca ii identifications include known photometric binaries and new targets; all are associated with a photometric red excess. Assuming a canonical value for the subdwarf luminosity, all of the detected companions are overluminous compared with the main sequence. The detection procedure indicates an improved and more secure method for the measurement of the binary frequency of hot subdwarfs. 相似文献
995.
Coryn A. L. Bailer-Jones Mike Irwin & Ted von Hippel 《Monthly notices of the Royal Astronomical Society》1998,298(4):1061-1068
We describe a method for the extraction of spectra from high-dispersion objective prism plates. Our method is a catalogue-driven plate solution approach, making use of the right ascension and declination coordinates for the target objects. In contrast to existing methods of photographic plate reduction, we digitize the entire plate and extract spectra off-line. This approach has the advantages that it can be applied to CCD objective prism images and spectra can be re-extracted (or additional spectra extracted) without having to re-scan the plate. After a brief initial interactive period, the subsequent reduction procedure is completely automatic, resulting in fully reduced, wavelength-justified spectra. We also discuss a method of removing stellar continua using a combination of non-linear filtering algorithms. The method described is used to extract over 12 000 spectra from a set of 92 objective prism plates. These spectra are used in an associated project to develop automated spectral classifiers based on neural networks. 相似文献
996.
L. G. Kiseleva J. Colin B. Dauphole & P. Eggleton 《Monthly notices of the Royal Astronomical Society》1998,301(3):759-766
In this paper we present numerical results on the decay of small stellar systems under different initial conditions (multiplicity 3 ≤ N ≤ 10, and various mass spectra, initial velocities and initial configurations). The numerical treatment uses the CHAIN1 code (Mikkola &38; Aarseth). Particular attention is paid to the distribution of high-velocity escapers: we define these as stars with velocity above 30 km s−1 . These numerical experiments confirm that small N -body systems are dynamically unstable and produce cascades of escapers in the process of their decay. It is shown that the fraction of stars that escape from small dense stellar systems with an escape velocity greater than 30 km s−1 is ∼1 per cent for all systems treated here. This relatively small fraction must be considered in relation to the rate of star formation in the Galaxy in small groups: this could explain some moderately high-velocity stars observed in the Galactic disc and possibly some young stars with relatively high metallicity in the thick disc. 相似文献
997.
998.
999.
The methods used to derive effective temperatures, projected rotational velocities and surface gravities of a sample of low
and high-amplitude δ Sct stars are presented here. Effective temperatures were derived using Hα and Hβ line profiles whereas
rotational velocities were calculated following the method described in Solano & Fernley (1997). Surface gravities were obtained
using Hipparcos parallaxes and evolutionary models (Claret 1995). The results of this analysis will be published in a subsequent
paper (Solano & Pintado 1999).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
1000.
We study the motion of an infinitesimal mass point under the gravitational action of three mass points of masses μ, 1–2μ and
μ moving under Newton's gravitational law in circular periodic orbits around their center of masses. The three point masses
form at any time a collinear central configuration. The body of mass 1–2μ is located at the center of mass. The paper has
two main goals. First, to prove the existence of four transversal ejection–collision orbits, and second to show the existence
of an uncountable number of invariant punctured tori. Both results are for a given large value of the Jacobi constant and
for an arbitrary value of the mass parameter 0<μ≤1/2.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献