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81.
    
《Astronomische Nachrichten》2018,339(2-3):183-197
New time‐series VI CCD photometry of the globular cluster NGC 6362 is studied with the aim of estimating the reddening, mean metallicity, and distance of the cluster from its population of RR Lyrae stars. The Fourier decomposition of carefully selected single‐mode RR Lyrae light curves, and the use of well‐established semiempirical calibrations and revised zero points, lead to the values of [Fe/H]UVES −1.066 ± 0.126 and −1.08 ± 0.16 and distances of 7.93 ± 0.32 and 8.02 ± 0.15 kpc from the RRab and RRc stars, respectively. The distribution of RR Lyrae stars in the horizontal branch shows a neat segregation of pulsating modes about the red edge of the first overtone instability strip, which is not necessarily expected in an OoI‐type cluster like NGC 6362. Four RRab stars are found to be likely advanced in their evolution toward the AGB. One new foreground SX Phe star, some 4 kpc in front of the cluster and projected onto the field of our images, is reported. We comment on the heavy light contamination, by a very close neighbouring star, of the peculiar double‐mode V37 variable, recently postulated as a non‐typical RRc variable.  相似文献   
82.
    
Recent XMM‐Newton observations of the B2 type star ρ Oph A indicated a periodicity of 1.205 day, which was ascribed to rotational modulation. Since variability of X‐ray emission in massive stars is frequently the signature of a magnetic field, we investigated whether the presence of a magnetic field can indeed be invoked to explain the observed X‐ray peculiarity. Two FORS 2 spectropolarimetric observations in different rotation phases revealed the presence of a negative (⟨Bzall = − 419 ± 101 G) and positive (⟨Bzall = 538 ± 69 G) longitudinal magnetic field, respectively. We estimate a lower limit for the dipole strength as Bd = 1.9 ± 0.2 kG. Our calculations of the Kepler and Alfvén radii imply the presence of a centrifugally supported, magnetically confined plasma around ρ Oph A. The study of the spectral variability indicates a behavior similar to that observed in typical magnetic early‐type Bp stars.  相似文献   
83.
    
《Astronomische Nachrichten》2017,338(2-3):299-304
The CHEERS (CHEmical enrichment reflection grating spectrometer sample) observations of clusters of galaxies with XMM ‐Newton have shown to be valuable to constrain the chemical evolution of the universe. The soft X‐ray spectrum contains lines of the most abundant metals from N to Ni, which provide relatively accurate abundances that can be compared to supernova enrichment models. The accuracy of the abundances is currently limited by systematic uncertainties introduced by the available instruments and uncertainties in the modeling of the spectra, which are of the order of 20–30%. We discuss the possible gain of extending the current samples at low and high redshift. We conclude that expanding the samples would be expensive in terms of exposure time, but will not yield significantly improved results, because the current samples already reach the systematic limits. New instrumentation, like Astro‐H2 and ATHENA , as well as improvements to the atomic databases, are needed to make significant advances in this field.  相似文献   
84.
大、小洋山建港总体规划中的水流泥沙问题   总被引:7,自引:0,他引:7  
水流、泥沙一直是建港中关键问题之一。从现场水文泥沙条件分析和数学模型计算等方面,分析比选了洋山港规划方案,提出了洋山港总体规划以单通道方案为宜,不但能简化现场的复杂的水流,选择合适的口门宽度还能维持深槽水流、水深条件,经计算分析提出了西口门宽度为3.5km的规划方案较好,此外还从平衡水深的角度对单通道方案的维持水深进行了计算。  相似文献   
85.
天然气水合物研究进展   总被引:5,自引:0,他引:5  
全面回顾了近几十年来国际天然气水合物从发现到商业化开发的研究历程。一方面,从纵向时间角度追溯水合物研究的3大历史阶段(早期的发现阶段、20世纪六七十年代的调研阶段;大规模的详查阶段);另一方面,从横向学科联合发展角度探讨水合物实验室模拟的热力学与动力学过程,概述水合物的全球分布与资源量评价,归纳钻、采、储、运4大工程的主要内容与要点;阐述了世界范围内天然气水合物的研究趋势(定量化、一体化、低能高效化)及阶段性进展。  相似文献   
86.
Based on the theoretical spectral model of inertial internal wave breaking(fine structure) proposed previously, in which the effects of the horizontal Coriolis frequency component f-tilde on a potential isopycnal are taken into account, a parameterization scheme of vertical mixing in the stably stratified interior below the surface mixed layer in the ocean general circulation model(OGCM) is put forward preliminarily in this paper. Besides turbulence, the impact of sub-mesoscale oceanic processes(including inertial internal wave breaking product) on oceanic interior mixing is emphasized. We suggest that adding the inertial internal wave breaking mixing scheme(F-scheme for short) put forward in this paper to the turbulence mixing scheme of Canuto et al.( T-scheme for short) in the OGCM, except the region from 15°S to 15°N. The numerical results of F-scheme by using WOA09 data and an OGCM(LICOM, LASG/IAP climate system ocean model) over the global ocean are given. A notable improvement in the simulation of salinity and temperature over the global ocean is attained by using T-scheme adding F-scheme, especially in the mid- and high-latitude regions in the simulation of the intermediate water and deep water. We conjecture that the inertial internal wave breaking mixing and inertial forcing of wind might be one of important mechanisms maintaining the ventilation process. The modeling strength of the Atlantic meridional overturning circulation(AMOC) by using T-scheme adding F-scheme may be more reasonable than that by using T-scheme alone, though the physical processes need to be further studied, and the overflow parameterization needs to be incorporated. A shortcoming in F-scheme is that in this paper the error of simulated salinity and temperature by using T-scheme adding F-scheme is larger than that by using T-scheme alone in the subsurface layer.  相似文献   
87.
A 3×3 complete diallel cross comprising three families of the clam Meretrix meretrix(P1, P2 and P3) was used to determine the combining ability of parental families and heterosis of F1 under indoor and openair environments for growth traits. Analysis of variance for shell length and whole body weight indicated highly significant cross effects, environment effects and the interaction of cross by environment. General combining ability(GCA) and specific combing ability exhibited great variation among crosses and between two environments. Pooled over environments, P2 was the top combiner among the three parental families for both traits studied. The cross of P1 and P3 had the highest SCA. Additionally, significant reciprocal effects were observed. For individual environment, about half of the crossbred combinations showed favorable Mid-parent heterosis(MPH)(1%) for the shell length and whole body weight. Our data has shown that non-additive genetic and reciprocal effects constituted the major sources of genetic variation for both shell length and whole body weight, which indicates that crossbreeding among selective families could further explore the heterotic effects.  相似文献   
88.
基于模糊综合评判理论的过驳系统效率计算方法   总被引:2,自引:2,他引:0  
如何计算整个系统的运转效率,特别是受不确定因素影响的系统(如过驳系统),仍然是一个非常重要的研究课题。文章提出基于模糊综合评判方法的效率计算方法,是一种新的尝试,这种方法较好的避免了人的主观随意性,更符合实际情况,同时又可以弥补统计方法的不足。文章对某沿海地区的一过驳系统进行了效率计算,取得比较好的效果。  相似文献   
89.
    
This paper describes the large scale aspects of the seasonal surface heat budget and discusses its main forcing mechanisms in the tropical Western Pacific Ocean. The high-resolution general circulation model (Semtner & Chervin, 1992) used in this study reproduced well the observed upper-layer thermal structure and circulation. It is shown that at least on the average of the study region (20 °S–20 °N, west boundary −160 °E) the semiannual variation is a dominant signal for all heat budget components and is presumably due to the sun’s passing across the equator twice a year, but that the components have substantial differences in amplitude. The local Ekman divergence in the region does not change significantly through the year. As a result, the change in surface heat content is roughly half due to ocean-atmosphere heat exchange and half due to heat advection by remotely forced vertical motion. Horizontal currents do not play a significant role directly by advection, because the water which enters the region is not very much different in temperature from the water which leaves it.  相似文献   
90.
We present preliminary results from a 150 ks Suzaku observation of the Seyfert 1 galaxy NGC 3516. Suzaku 's wide bandpass has enabled us to deconvolve the broadband emitting and absorbing components in this object, breaking model degeneracies inherent in previous, smaller‐bandpass spectra. The primary power‐law continuum is absorbed by an ionized absorber as well as a partial‐covering absorber; the column density of the ionized absorber has increased by a factor of ∼3 since XMM‐Newton observations in 2001. We detect a soft power‐law component which may be scattered emission. We confirm the presence of the broad Fe line, finding a eV equivalent width line that indicates emission extending down to a few Schwarzschild radii. Models which exclude either the broad line or the partial‐covering absorber are rejected. Suzaku 's high effective area and low background near 6 keV also allow us to resolve the narrow Fe K emission line; we find a FWHM velocity width near 4000 km s–1, commensurate with Broad Line Region velocities. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
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