全文获取类型
收费全文 | 51252篇 |
免费 | 874篇 |
国内免费 | 522篇 |
专业分类
测绘学 | 1391篇 |
大气科学 | 3746篇 |
地球物理 | 9983篇 |
地质学 | 18398篇 |
海洋学 | 4566篇 |
天文学 | 11544篇 |
综合类 | 112篇 |
自然地理 | 2908篇 |
出版年
2021年 | 442篇 |
2020年 | 508篇 |
2019年 | 559篇 |
2018年 | 1228篇 |
2017年 | 1215篇 |
2016年 | 1435篇 |
2015年 | 807篇 |
2014年 | 1395篇 |
2013年 | 2648篇 |
2012年 | 1588篇 |
2011年 | 2084篇 |
2010年 | 1880篇 |
2009年 | 2419篇 |
2008年 | 2126篇 |
2007年 | 2128篇 |
2006年 | 2095篇 |
2005年 | 1549篇 |
2004年 | 1556篇 |
2003年 | 1423篇 |
2002年 | 1363篇 |
2001年 | 1244篇 |
2000年 | 1255篇 |
1999年 | 1016篇 |
1998年 | 1007篇 |
1997年 | 1042篇 |
1996年 | 809篇 |
1995年 | 835篇 |
1994年 | 821篇 |
1993年 | 660篇 |
1992年 | 660篇 |
1991年 | 585篇 |
1990年 | 657篇 |
1989年 | 578篇 |
1988年 | 570篇 |
1987年 | 623篇 |
1986年 | 544篇 |
1985年 | 710篇 |
1984年 | 721篇 |
1983年 | 734篇 |
1982年 | 698篇 |
1981年 | 580篇 |
1980年 | 630篇 |
1979年 | 524篇 |
1978年 | 494篇 |
1977年 | 482篇 |
1976年 | 425篇 |
1975年 | 430篇 |
1974年 | 429篇 |
1973年 | 408篇 |
1972年 | 266篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
291.
292.
293.
N. Callegari Jr S. Ferraz-Mello T. A. Michtchenko 《Celestial Mechanics and Dynamical Astronomy》2006,94(4):381-397
This paper considers the dynamics of two planets, as the planets B and C of the pulsar PSR B1257+12, near a 3/2 mean-motion resonance. A two-degrees-of-freedom model, in the framework of the general three-body planar problem, is used and the solutions are analyzed through surfaces of section and Fourier techniques in the full phase space of the system.On the possibility of existence of a fourth planet in distant orbit, see Wolszczan et al., 2000 相似文献
294.
Yannis F. Dafalias Majid T. Manzari Achilleas G. Papadimitriou 《国际地质力学数值与分析法杂志》2006,30(12):1231-1257
SANICLAY is a new simple anisotropic clay plasticity model that builds on a modification of an earlier model with an associated flow rule, in order to include simulations of softening response under undrained compression following Ko consolidation. Non‐associativity is introduced by adopting a yield surface different than the plastic potential surface. Besides, the isotropic hardening of the yield surface both surfaces evolve according to a combined distortional and rotational hardening rule, simulating the evolving anisotropy. Although built on the general premises of critical state soil mechanics, the model induces a critical state line in the void ratio–mean effective stress space, which is a function of anisotropy. To ease interpretation, the model formulation is presented firstly in the triaxial stress space and subsequently, its multiaxial generalization is developed systematically, in a form appropriate for implementation in numerical codes. The SANICLAY is shown to provide successful simulation of both undrained and drained rate‐independent behaviour of normally consolidated sensitive clays, and to a satisfactory degree of accuracy of overconsolidated clays. The new model requires merely three constants more than those of the modified Cam clay model, all of which are easily calibrated from well‐established laboratory tests following a meticulously presented procedure. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
295.
296.
M. T. Murphy S. J. Curran J. K. Webb 《Monthly notices of the Royal Astronomical Society》2003,342(3):830-836
We describe initial results of a search for redshifted molecular absorption towards four millimetre-loud, optically faint quasars. A wide frequency bandwidth of up to 23 GHz per quasar was scanned using the Swedish–ESO Submillimetre Telescope at La Silla. Using a search list of commonly detected molecules, we obtained nearly complete redshift coverage up to z abs = 5 . The sensitivity of our data is adequate to have revealed absorption systems with characteristics similar to those seen in the four known redshifted millimetre-band absorption systems, but none were found. Our frequency-scan technique nevertheless demonstrates the value of wide-band correlator instruments for searches such as these. We suggest that a somewhat larger sample of similar observations should lead to the discovery of new millimetre-band absorption systems. 相似文献
297.
298.
The mean state of the tropical atmosphere is important as the nature of the coupling between the ocean and the atmosphere
depends nonlinearly on the basic state of the coupled system. The simulation of the annual cycle of the tropical surface wind
stress by 17 atmospheric general circulation models (AGCMs) is examined and intercompared. The models considered were part
of the Atmospheric Model Intercomparison Project (AMIP) and were integrated with observed sea surface temperature (SST) for
the decade 1979–1988. Several measures have been devised to intercompare the performance of the 17 models on global tropical
as well as regional scales. Within the limits of observational uncertainties, the models under examination simulate realistic
tropical area-averaged zonal and meridional annual mean stresses. This is a noteworthy improvement over older generation low
resolution models which were noted for their simulation of surface stresses considerably weaker than the observations. The
models also simulate realistic magnitudes of the spatial distribution of the annual mean surface stress field and are seen
to reproduce realistically its observed spatial pattern. Similar features are observed in the simulations of the annual variance
field. The models perform well over almost all the tropical regions apart from a few. Of these, the simulations over Somali
are interesting. Over this region, the models are seen to underestimate the annual mean zonal and meridional stresses. There
is also wide variance between the different models in simulating these quantities. Large model-to-model variations were also
seen in the simulations of the annual mean meridional stress field over equatorial Indian Ocean, south central Pacific, north
east Pacific and equatorial eastern Pacific oceans. It is shown that the systematic errors in simulating the surface winds
are related to the systematic errors in simulating the Inter-Tropical Convergence Zone (ITCZ) in its location and intensity.
Weaker than observed annual mean southwesterlies simulated by most models over Somali is due to weaker than observed southwesterlies
during the Northern Hemisphere summer. This is related to the weaker than observed land precipitation simulated by most models
during the Northern Hemisphere summer. The diversity in simulation of the surface wind over Somali and equatorial Indian ocean
is related to the diversity of AGCMs in simulating the precipitation zones in these regions.
Received: 2 August 1996 / Accepted: 7 February 1997 相似文献
299.
E. Tóth F. Deak C. S. Gyurkócza Z. S. Kasztovszky R. Kuczi G. Marx B. Nagy S. Oberstedt L. Sajó-Bohus C. S. Sükösd G. Toth N. Vajda 《Environmental Geology》1997,31(1-2):123-127
A steady radon exhalation is assumed in most publications. In a village of North-East Hungary, however, high radon concentrations
have been measured, differing strongly in neighbouring houses and varying in time, due to the interplay of geochemical phenomena.
Received: 20 November 1995 · Accepted: 18 June 1996 相似文献
300.
In laboratory investigations with model waters, the behaviour of selected cation-exchange resins (Amberlite 200 C, Duolite C-25, Lewatit S-100, Wofatit KPS and Wofatit KS-10) is tested. The usable volume capacity of the resins in the forms of H, Na and NH4 as well as the water content and the total volume capacity after 25 cycles of loading/regeneration are determined. It is recommended to use Amberlite 200 C and Wofatit KS-10. 相似文献