全文获取类型
收费全文 | 60271篇 |
免费 | 420篇 |
国内免费 | 333篇 |
专业分类
测绘学 | 1556篇 |
大气科学 | 3532篇 |
地球物理 | 10795篇 |
地质学 | 25155篇 |
海洋学 | 4997篇 |
天文学 | 12718篇 |
综合类 | 284篇 |
自然地理 | 1987篇 |
出版年
2022年 | 530篇 |
2021年 | 786篇 |
2020年 | 827篇 |
2019年 | 915篇 |
2018年 | 4064篇 |
2017年 | 3606篇 |
2016年 | 3013篇 |
2015年 | 846篇 |
2014年 | 1678篇 |
2013年 | 2438篇 |
2012年 | 2576篇 |
2011年 | 4140篇 |
2010年 | 3667篇 |
2009年 | 4120篇 |
2008年 | 3461篇 |
2007年 | 4083篇 |
2006年 | 2049篇 |
2005年 | 1382篇 |
2004年 | 1319篇 |
2003年 | 1342篇 |
2002年 | 1194篇 |
2001年 | 965篇 |
2000年 | 869篇 |
1999年 | 561篇 |
1998年 | 594篇 |
1997年 | 619篇 |
1996年 | 437篇 |
1995年 | 467篇 |
1994年 | 436篇 |
1993年 | 366篇 |
1992年 | 342篇 |
1991年 | 368篇 |
1990年 | 415篇 |
1989年 | 335篇 |
1988年 | 323篇 |
1987年 | 352篇 |
1986年 | 266篇 |
1985年 | 395篇 |
1984年 | 389篇 |
1983年 | 391篇 |
1982年 | 354篇 |
1981年 | 339篇 |
1980年 | 368篇 |
1979年 | 283篇 |
1978年 | 314篇 |
1977年 | 270篇 |
1976年 | 231篇 |
1975年 | 242篇 |
1974年 | 233篇 |
1973年 | 264篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
961.
A. G. Massevitch E. I. Popova A. V. Tutukov L. R. Yungelson 《Astrophysics and Space Science》1979,62(2):451-463
Evolution of massive stars losing mass with the rateM H L/V
C is computed (for =1,2,7). It is shown that observed mass loss rates correspond to 0.3 and, therefore, mass loss by stellar wind cannot play any significant role in the evolution of normal massive stars. However, for several types of massive stars (WR, OH/IR, X-ray sources) enhanced mass loss explains their peculiar features. Computations of evolutionary sequences of massive stars with convective overshooting taken into account (as a formal increase of the convective core) show that a significant broadening of the hydrogen-burning band in the H-R diagram may be obtained. 相似文献
962.
A mission out of the planetary system, launched about the year 2000, could provide valuable data concerning characteristics of the heliopause, the interstellar medium, stellar distances (by parallax measurements), low-energy cosmic rays, interplanetary gas distribution, and mass of the solar system. Secondary objectives include investigation of Pluto. Candidate science measurements, instruments, and instrument development needs are discussed. The mission should extend from 400 to 1000 AU from the Sun. A heliocentric hyperbolic escape velocity of 50–100 km/sec or more is needed to attain this distance within a reasonable mission duration (20–50 years). The trajectory should be toward the incoming interstellar gas. For a year 2000 launch, a Pluto encounter and orbiter can be included. A second mission targeted parallel to the solar axis would also be worthwhile. 相似文献
963.
The paper presents an analysis of the coronal data of emission line 530.3 nm. The analysis was carried out with data recorded at the coronal station of Lomnický tít for the period 1965–1976. Up till now the observed time and latitudal changes of the shape of the corona as well as the existence of two maxima have been fully proved. The development of intensities has, in many cases, different characters in the southern and northern hemispheres. Apart from this, the third increase of intensities in the course of the cycle was observed nearly at all latitudes in the coincidence with sunspot numbers in 1974–1975 years. The maximum of intensities of this impulse of activity was observed at latitudes around 60° in both hemispheres. 相似文献
964.
Electric fields and currents in the ionosphere generated by field-aligned currents observed by TRIAD
On the basis of the experimental data on the ionospheric conductivities and field-aligned currents the electric fields and currents in the ionosphere generated by the field-aligned currents were computated for various magnetic activity conditions. The model of the ionospheric conductivities by Vanyan and Osipova (1975) was used taking into account the influence of the universal time seasons and magnetic activity. The field-aligned current patterns and their change with magnetic activity was set on the basis of the TRIAD data. It is shown that the calculated patterns of the ionospheric electric fields and currents are in agreement with the measured electric fields and the equivalent current systems of the magnetic disturbances in high latitudes. The conclusion is made that the magnetospheric field-aligned currents are the main sources of the presently known polar magnetic disturbances. 相似文献
965.
A.B. Shvartsburg V.G. Korobeinikov M.G. Deminov A.V. Razmadze 《Planetary and Space Science》1979,27(2):159-163
The non-linear stationary temperature waves (domains) is analysed. The exact analytical solutions of the non-linear equation of the heat conductivity determine the region of existence of such domains and the critical values of plasma parameters, correspond to the increase of the periodical temperature profiles in the plasma. A stationary source of heating (photo-electrons or electric fields) may stimulate the existence of domains, when the power of the source reaches a critical value. Conditions in the F-region of the ionosphere near the equator favour the increase of the domains. 相似文献
966.
This paper reports the study concerning the latitudinal dispalacement of the auroral oval as a function of the northward orientation of the Bz-component IMF and the relation between southward Bz and the auroral dynamics in the night sector. 相似文献
967.
The data on optical, X-ray and gamma emission from proton flares, as well as direct observations of flare-associated phenomena, show energetic proton acceleration in the corona rather than in the flare region. In the present paper, the acceleration of protons and accompanying relativistic electrons is accounted for by a shock wave arising during the development of a large flare. We deal with a regular acceleration mechanism due to multiple reflection of resonance protons and fast electrons from a collisionless shock wave front which serves as a moving mirror. The height of the most effective acceleration in the solar corona is determined. The accelerated particle energy and density are estimated. It is shown in particular that a transverse collisionless shock wave may produce the required flux of protons with energy of 10 MeV and of relativistic electrons of 1–10 MeV.The proposed scheme may also serve as an injection mechanism when the protons are accelerated up to relativistic energies by other methods. 相似文献
968.
Skylab S-054 data have been used to examine the flux from X-ray bright points with 90 s time resolution. There is evidence of a steady heating input, similar to one reported for active region loops. Also observed are impulsive brightenings of bright points and rapid decays which are consistent with a sudden turn-off of the steady heating. 相似文献
969.
Photoelectric observations on five consecutive nights yield a period of rotation of 80 ± 2 hr with an amplitude of 0.7 magnitude for 182 Elsa, making it the longest period of rotation known to date. 182 Elsa is classed as an S object with a diameter of 48 km. 相似文献
970.
Io's neutral sodium emission cloud was monitored during the period of Voyager 1 encounter from two independent ground-based sites. Observations from Table Mountain Observatory verified the continued existence of the “near-Io cloud” (d < 1.5 × 105 km, for 4πI > 1 kR; R denotes Rayleigh) while those from Wise Observatory showed a deficiency in the weaker emission at greater distances from Io. The sodium cloud has been monitored from both observatories for several years. These and other observations demonstrate that the behavior of the cloud is complex since it undergoes a variety of changes, both systematic and secular, which can have both time and spatial dependencies. The cloud also displays some characteristics of stability. Table Mountain images and high-dispersion spectra (resolution ) indicate that the basic shape and intensity of the “near cloud” have remained relatively constant at least since imaging observations began in 1976. Wise Observatory low-dispersion spectra (resolution ) which have been obtained since 1974 demonstrate substantial variability of the size and intensity of the “far cloud” (d ? 1.5 × 105 km) on a time scale of months or less. Corresponding changes in the state of the plasma associated with the Io torus are suggested, with the period of Voyager 1 encounter represented as a time of unusually high plasma temperature and/or density. Dynamic models of the sodium cloud employing Voyager 1 plasma data provide a reasonable fit to the Table Mountain encounter images. The modeling assumptions of anisotropic ejection of neutral sodium atoms from the leading, inner hemisphere of Io with a velocity distribution characteristic of sputtering adequately explain the overall intensity distribution of the “near cloud”. During the Voyager 1 encounter period there appeared a region of enhanced intensity projecting outward from Io's orbit and inclined to the orbital plane. This region is clearly distinguished from the sodium emission normally aligned with the plane of Io's orbit. The process responsible for this phenomenon is not yet understood. Similar but less pronounced features are also present in several Table Mountain images obtained over the past few years. 相似文献