全文获取类型
收费全文 | 733篇 |
免费 | 31篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 13篇 |
大气科学 | 50篇 |
地球物理 | 211篇 |
地质学 | 279篇 |
海洋学 | 33篇 |
天文学 | 150篇 |
自然地理 | 31篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 11篇 |
2020年 | 14篇 |
2019年 | 8篇 |
2018年 | 23篇 |
2017年 | 23篇 |
2016年 | 27篇 |
2015年 | 36篇 |
2014年 | 28篇 |
2013年 | 36篇 |
2012年 | 37篇 |
2011年 | 44篇 |
2010年 | 38篇 |
2009年 | 51篇 |
2008年 | 24篇 |
2007年 | 25篇 |
2006年 | 32篇 |
2005年 | 35篇 |
2004年 | 24篇 |
2003年 | 30篇 |
2002年 | 13篇 |
2001年 | 10篇 |
2000年 | 11篇 |
1999年 | 9篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 12篇 |
1993年 | 4篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1988年 | 4篇 |
1986年 | 4篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1971年 | 7篇 |
1965年 | 4篇 |
1961年 | 3篇 |
1958年 | 5篇 |
1957年 | 3篇 |
排序方式: 共有767条查询结果,搜索用时 93 毫秒
81.
D. Chochol T. Pribulla M. Vaňko P. Mayer M. Wolf P. G. Niarchos K. D. Gazeas V. N. Manimanis L. Brát M. Zejda 《Astrophysics and Space Science》2006,304(1-4):93-96
Orbital period changes of the eclipsing binaries GO Cyg and GW Cep are explained by the light-time effect for the first time. New minima of the eclipsing binary AR Aur improve the predicted light-time orbit. The light-time orbit with the quadratic ephemeris of the binary matches the new observations of V505 Sgr better than the linear one. As the light-time effect fits in corresponding O − C diagrams of all four systems have been reaching extreme values, the observations of minima times in forthcoming years are highly desirable. 相似文献
82.
The paper presents an optimization routine especially developed for the identification of model parameters in soil plasticity on the basis of different soil tests. Main focus is put on the mathematical aspects and the experience from application of this optimization routine. Mathematically, for the optimization, an objective function and a search strategy are needed. Some alternative expressions for the objective function are formulated. They capture the overall soil behaviour and can be used in a simultaneous optimization against several laboratory tests. Two different search strategies, Rosenbrock's method and the Simplex method, both belonging to the category of direct search methods, are utilized in the routine. Direct search methods have generally proved to be reliable and their relative simplicity make them quite easy to program into workable codes. The Rosenbrock and simplex methods are modified to make the search strategies as efficient and user‐friendly as possible for the type of optimization problem addressed here. Since these search strategies are of a heuristic nature, which makes it difficult (or even impossible) to analyse their performance in a theoretical way, representative optimization examples against both simulated experimental results as well as performed triaxial tests are presented to show the efficiency of the optimization routine. From these examples, it has been concluded that the optimization routine is able to locate a minimum with a good accuracy, fast enough to be a very useful tool for identification of model parameters in soil plasticity. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
83.
Black hole spin in GRS 1915+105 总被引:2,自引:0,他引:2
84.
85.
86.
The H N method, employed for studies in neutron transport theory, is used to establish numerical results basic to the vector equation describing the transfer of polarized light in a Rayleigh scattering atmosphere with true absorption. The method has been applied to the classical Milne problem. The exit distribution is defined as a series in powers of the zenith observation angle. The numerical results are computed and compared with exact values obtained using the exit distribution in terms of the H-matrix. The numerical results are in good agreement with previously published findings. 相似文献
87.
88.
I.?Tongu? UysalEmail author Arthur?J.?Mory Suzanne?D.?Golding Robert?Bolhar Kenneth?D.?Collerson 《Contributions to Mineralogy and Petrology》2005,149(5):576-590
Chaotically structured diamictite from the inner ring syncline surrounding the central uplift of the Woodleigh impact structure contains shocked metamorphic and impact melt-rock fragments, largely derived from Ordovician and Devonian target sandstones. Coarse illite fractions (<2 m) from the sandstones containing no K-feldspar yield K–Ar ages of around 400 Ma, whereas the K–Ar ages of authigenic clays of >0.2 m fractions from the diamictite without smectite and K-feldspar cluster around 360 Ma, consistent with Rb–Sr data. Crystallisation of newly formed illite in the impact melt rock clasts and recrystallisation of earlier formed illite in the sandstone clasts preserved in the diamictite, are attributed to impact-induced hydrothermal processes in the Late Devonian. The illitic clays from the diamictite and from the sandstones have very similar trace element compositions, with significantly enriched incompatible lithophile elements, which increase in concentrations correlatively with those of the compatible ferromagnesian elements. The unusual trace element associations in the clays may be due to the involvement of hot gravity-driven basinal fluids that interacted with rocks of the Precambrian craton to the east of the study area, or with such material transported and reworked in the studied sedimentary succession. 相似文献
89.
Model parameterization through adjustment to field data is a crucial step in the modeling and the understanding of the drainage network response to tectonic or climatic perturbations. Using as a test case a data set of 18 knickpoints that materialize the migration of a 0.7-Ma-old erosion wave in the Ourthe catchment of northern Ardennes (western Europe), we explore the impact of various data fitting on the calibration of the stream power model of river incision, from which a simple knickpoint celerity equation is derived. Our results show that statistical least squares adjustments (or misfit functions) based either on the stream-wise distances between observed and modeled knickpoint positions at time t or on differences between observed and modeled time at the actual knickpoint locations yield significantly different values for the m and K parameters of the model. As there is no physical reason to prefer one of these approaches, an intermediate least-rectangles adjustment might at first glance appear as the best compromise. However, the statistics of the analysis of 200 sets of synthetic knickpoints generated in the Ourthe catchment indicate that the time-based adjustment is the most capable of getting close to the true parameter values. Moreover, this fitting method leads in all cases to an m value lower than that obtained from the classical distance adjustment (for example, 0.75 against 0.86 for the real case of the Ourthe catchment), corresponding to an increase in the non-linear character of the dependence of knickpoint celerity on discharge. 相似文献
90.
We study the influence of X-rays on the wind structure of selected O stars. For this purpose we use our non-local thermodynamic equilibrium (NLTE) wind code with inclusion of additional artificial source of X-rays, assumed to originate in the wind shocks.
We show that the influence of shock X-ray emission on wind mass-loss rate is relatively small. Wind terminal velocity may be slightly influenced by the presence of strong X-ray sources, especially for stars cooler than Teff ≲ 35 000 K .
We discuss the origin of the LX / L ∼ 10−7 relation. For stars with thick wind this relation can be explained assuming that the cooling time depends on wind density. Stars with optically thin winds exhibiting the 'weak wind problem' display enhanced X-ray emission which may be connected with large shock cooling length. We propose that this effect can explain the 'weak wind problem'.
Inclusion of X-rays leads to a better agreement of the model ionization structure with observations. However, we do not find any significant influence of X-rays on P v ionization fraction implying that the presence of X-rays cannot explain the P v problem.
We study the implications of modified ionization equilibrium due to shock emission on the line transfer in the X-ray region. We conclude that the X-ray line profiles of helium-like ions may be affected by the line absorption within the cool wind. 相似文献
We show that the influence of shock X-ray emission on wind mass-loss rate is relatively small. Wind terminal velocity may be slightly influenced by the presence of strong X-ray sources, especially for stars cooler than T
We discuss the origin of the L
Inclusion of X-rays leads to a better agreement of the model ionization structure with observations. However, we do not find any significant influence of X-rays on P v ionization fraction implying that the presence of X-rays cannot explain the P v problem.
We study the implications of modified ionization equilibrium due to shock emission on the line transfer in the X-ray region. We conclude that the X-ray line profiles of helium-like ions may be affected by the line absorption within the cool wind. 相似文献