全文获取类型
收费全文 | 53519篇 |
免费 | 297篇 |
国内免费 | 280篇 |
专业分类
测绘学 | 1361篇 |
大气科学 | 2993篇 |
地球物理 | 9480篇 |
地质学 | 22856篇 |
海洋学 | 4309篇 |
天文学 | 11227篇 |
综合类 | 246篇 |
自然地理 | 1624篇 |
出版年
2022年 | 489篇 |
2021年 | 708篇 |
2020年 | 756篇 |
2019年 | 827篇 |
2018年 | 3973篇 |
2017年 | 3530篇 |
2016年 | 2839篇 |
2015年 | 727篇 |
2014年 | 1444篇 |
2013年 | 2042篇 |
2012年 | 2371篇 |
2011年 | 3925篇 |
2010年 | 3474篇 |
2009年 | 3829篇 |
2008年 | 3194篇 |
2007年 | 3868篇 |
2006年 | 1781篇 |
2005年 | 1151篇 |
2004年 | 1084篇 |
2003年 | 1129篇 |
2002年 | 971篇 |
2001年 | 792篇 |
2000年 | 669篇 |
1999年 | 418篇 |
1998年 | 437篇 |
1997年 | 474篇 |
1996年 | 337篇 |
1995年 | 358篇 |
1994年 | 335篇 |
1993年 | 281篇 |
1992年 | 284篇 |
1991年 | 290篇 |
1990年 | 337篇 |
1989年 | 272篇 |
1988年 | 258篇 |
1987年 | 261篇 |
1986年 | 191篇 |
1985年 | 301篇 |
1984年 | 303篇 |
1983年 | 295篇 |
1982年 | 275篇 |
1981年 | 262篇 |
1980年 | 285篇 |
1979年 | 203篇 |
1978年 | 242篇 |
1977年 | 204篇 |
1976年 | 181篇 |
1975年 | 184篇 |
1974年 | 171篇 |
1973年 | 206篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
511.
M. Aglietta P. Antonioli G. Badino G. Bologna C. Castagnoli A. Castellina V. L. Dadykin W. Fulgione P. Galeotti F. F. Khalchukov E. V. Korolkova P. V. Kortchaguin V. B. Kortchaguin V. A. Kudryavtsev A. S. Malguin L. Periale V. G. Ryassny O. G. Ryazhskaya O. Saavedra G. Trinchero S. Vernetto C. Vigorito V. F. Yakushev G. T. Zatsepin 《Astrophysics and Space Science》1995,231(1-2):355-358
A search for low energy neutrinos of all flavours in correlation with 553 ray bursts detected by BATSE aboard the Compton Observatory has been performed by the LSD (Liquid Scintillator Detector) neutrino telescope. No excess ofe,, orv
e,, candidate has been detected by LSD during the time interval in which BATSE detected the 90% of the photon flux for any of the GRBs analyzed. Upper limits on the neutrino fluxes are given in the paper. 相似文献
512.
The spectra of 26 IRAS sources have been fitted using experimental optical data obtained in our laboratory for different types of carbon and silicon carbide (SiC) submicronic particles. Laboratory data are the main input for a radiative transfer model, which, taking into account several important parameters of the circumstellar matter and of the central star, evaluates the temperature gradient across the envelope and hence the emission best-fit spectrum. In this way it has been possible to fit, with good accuracy, most of the examined IRAS spectra in the range 8 - 100µm. The sources have been chosen among those showing SiC feature around 11µm and the best fits have been obtained by carefully assessing the amount and the type ( &) of SiC particles present in the grain mixtures. 相似文献
513.
K. Golap N. H. Issur R. Somanah R. Dodson M. Modgekar S. Sachdev N. Udaya Shankar Ch. V. Sastry 《Astrophysics and Space Science》1995,228(1-2):373-377
The Mauritius Radiotelescope (MRT) is a T-shaped array of helical antennas with a 2048 m EW arm and a 890 m South arm. The primary objective of the telescope is to produce a sky survey in the declination zone -15° to -65° with a point source sensitivity of 200 mJy and an angular resolution of 4'×4.6'cosec(z) at 151.6 MHz, z being the zenith angle . This paper describes the telescope and the present status 相似文献
514.
V. M. Bogod V. Garimov G. B. Gelfreikh K. R. Lang R. F. Willson J. N. Kile 《Solar physics》1995,160(1):133-149
Solar radio and microwave sources were observed with the Very Large Array (VLA) and the RATAN-600, providing high spatial resolution at 91 cm (VLA) and detailed spectral and polarization data at microwave wavelengths (1.7 to 20 cm - RATAN). The radio observations have been compared with images from the Soft X-ray Telescope (SXT) aboard theYohkoh satellite and with full-disk phoptospheric magnetic field data from the Kislovodsk Station of the Pulkovo Observatory. The VLA observations at 91 cm show fluctuating nonthermal noise storm sources in the middle corona. The active regions that were responsible for the noise storms generally had weaker microwave emission, fainter thermal soft X-ray emission, as well as less intense coronal magnetic fields than those associated with other active regions on the solar disk. The noise storms did, however, originate in active regions whose magnetic fields and radiation properties were evolving on timescales of days or less. We interpret these noise storms in terms of accelerated particles trapped in radiation belts above or near active regions, forming a decimetric coronal halo. The particles trapped in the radiation belts may be the source of other forms of nonthermal radio emission, while also providing a reservoir from which energetic particles may drain down into lower-lying magnetic structures.Presented at the CESRA-Workshop on Coronal Magnetic Energy Release at Caputh near Potsdam in May 1994. 相似文献
515.
Possibilities to explain the observed 1/a-distribution are discussed in the light of improved understanding of the dynamical evolution of long-period comets. It appears that the fading problem applies both to single-injection and continuous-injection models. Although uncertainties due to nongravitational effects do not allow detailed results to be drawn from the observed 1/a-distribution at small perihelion distance q, that for q 1.5 AU shows that a constant fading probability cannot explain all the features of the observed distribution. Assuming that comets can reappear following a period of fading, values for the assumed constant fading and renewal probabilities, and the total cometary flux have been estimated for q > 1.5 AU. 相似文献
516.
We give the results of photographic, photoelectric, and spectral observations of the flare star PP Ori. The 109 photographic observations used, which were obtained on the 40 Schmidt telescope of the Byurakan Observatory over a period of about 20 years, and four spectra obtained on the same telescope with a4° objective prism show no variation in brightness. Photoelectric observations in the UBVR bands using the 50cm and 60cm telescopes of the high-altitude Maidanak station of the Tashkent Astronomical Institute in 1987 and 1989 give grounds for suspecting a variation in brightness much larger than observational errors. Spectral observations of the star PP Ori made on the 2.6m telescope of the Byurakan Observatory show weak H emission. The results of all these observations show that PP Ori is an Orion variable of spectral class K7-M0 with absolute visual magnitude7
m
5–8
m
5.Translated fromAstrofizika, Vol. 38, No. 2, 1995. 相似文献
517.
A. V. Krivov L. L. Sokolov V. V. Dikarev 《Celestial Mechanics and Dynamical Astronomy》1995,63(3-4):313-339
This paper deals with dynamics of impact ejecta from Phobos and Deimos initially on near-circular equatorial orbits around Mars. For particles emitted in a wide size regime of 1 micron and greater, and taking into account the typical particle lifetimes to be less than 100 years, the motion is governed by two perturbing forces: solar radiation pressure and influence of Mars' oblateness. The equations of motion of particles in Lagrangian non-singular elements are deduced and solved, both analytically and numerically, for different-sized ejecta. We state that the coupled effect of both forces above is essential so that on no account can the oblateness of Mars are be neglected. The dynamics of grains prove to be quite different for the ejecta of Phobos and Deimos. For Deimos, the qualitative results are relatively simple and imply oscillations of eccentricity and long-term variations of orbital inclination, with amplitudes and periods both depending on grain size. For Phobos, the dynamics are shown to be much more complicated, and we discuss it in detail. We have found an intriguous peculiar behavior of debris near 300 µm in size. Another finding is that almost all the Phobos ejecta with radii less than 30 µm (against the values of 5 to 20 µm adopted earlier by many authors) should be rapidly lost by collisions with martian surface. The results of the paper may be the base for constructing an improved model of dust belts that presumably exist around Mars. 相似文献
518.
Interpretation of X-ray eclipses in SS 433 binary system in the framework of wind-wind collision model yields high value of mass ratioq =m
x
/m
v
> 1 which implies high mass of relativistic objectm
x
> 8M
. 相似文献
519.
We have calculated the circumstellar extinction curves produced by dust grains which absorb and scatter the stellar radiation in the shells of pre-main-sequence stars. A Monte Carlo method was used to model the radiative transfer in non-spherical shells. The dependence on the particle size distribution and the dust shell parameters has been examined.The application of the theoretical results to explain the extinction and polarization of the Herbig Be star HD 45677 shows that the dust shell is not disk-like and that very small grains are absent in it. 相似文献
520.
An exact analysis of Hall current on hydromagnetic free convection with mass transfer in a conducting liquid past an infinite vertical porous plate in a rotating fluid has been presented. Exact solution for the velocity field has been obtained and the effects ofm (Hall parameter),E (Ekman number), andS
c (Schmidt number) on the velocity field have been discussed.Nomenclature
C
species concentration
-
C
w
concentration at the porous plate
-
C
species concentration at infinity
-
C
p
specific heat at constant pressure
-
D
chemical molecular diffusivity
-
g
acceleration due to gravity
-
E
Ekman number
-
G
Grashof number
-
H
0
applied magnetic field
-
j
x, jy, jz
components of the current densityJ
-
k
thermal conductivity
-
M
Hartman number
-
m
Hall parameter
-
P
Prandtl number
-
Q
heat flux per unit area
-
S
c
Sehmidt number
-
T
temperature of the fluid near the plate
-
T
w
temperature of the plate
-
T
temperature of the fluid in the free-stream
-
u, v, w
components of the velocity fieldq,
-
U
uniform free stream velocity
-
w
0
suction velocity
-
x, y, z
Cartesian coordinates
-
Z
dimensionless coordinate normal to the plate.
Greek symbols
coefficient of volume expansion
- *
coefficient of expansion with concentration
- e
cyclotron frequency
-
dimensionless temperature
- *
dimensionless concentration
-
v
kinematic viscosity
-
density of the fluid in the boundary layer
-
coefficient of viscosity
- e
magnetic permeability
-
angular velocity
-
electrical conductivity of the fluid
- e
electron collision time
- u
skin-friction in the direction ofu
- v
skin-friction in the direction ofv 相似文献