全文获取类型
收费全文 | 1806篇 |
免费 | 71篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 77篇 |
大气科学 | 282篇 |
地球物理 | 442篇 |
地质学 | 664篇 |
海洋学 | 59篇 |
天文学 | 272篇 |
综合类 | 2篇 |
自然地理 | 85篇 |
出版年
2021年 | 26篇 |
2020年 | 23篇 |
2019年 | 17篇 |
2018年 | 56篇 |
2017年 | 54篇 |
2016年 | 85篇 |
2015年 | 66篇 |
2014年 | 76篇 |
2013年 | 122篇 |
2012年 | 62篇 |
2011年 | 57篇 |
2010年 | 69篇 |
2009年 | 81篇 |
2008年 | 56篇 |
2007年 | 60篇 |
2006年 | 62篇 |
2005年 | 31篇 |
2004年 | 19篇 |
2003年 | 43篇 |
2002年 | 36篇 |
2001年 | 36篇 |
2000年 | 39篇 |
1999年 | 26篇 |
1998年 | 22篇 |
1997年 | 40篇 |
1996年 | 25篇 |
1995年 | 33篇 |
1994年 | 30篇 |
1993年 | 18篇 |
1991年 | 23篇 |
1990年 | 19篇 |
1988年 | 13篇 |
1987年 | 22篇 |
1986年 | 13篇 |
1984年 | 18篇 |
1983年 | 27篇 |
1982年 | 15篇 |
1981年 | 15篇 |
1980年 | 16篇 |
1979年 | 15篇 |
1978年 | 21篇 |
1976年 | 16篇 |
1975年 | 15篇 |
1974年 | 19篇 |
1973年 | 20篇 |
1972年 | 14篇 |
1970年 | 12篇 |
1969年 | 12篇 |
1968年 | 12篇 |
1965年 | 14篇 |
排序方式: 共有1883条查询结果,搜索用时 421 毫秒
951.
Christine Däumling 《洁净——土壤、空气、水》2012,40(8):779-789
Emissions from construction products may have a significant impact on the quality of indoor air, particularly in energy‐efficient buildings, where the normal rate of air exchange with fresh ambient air may be limited. In this context, reduction strategies to mitigate the concentration of chemicals in the indoor environment have become even more important. German authorities wanted to foster the development of low‐emission products, and as a result it was necessary to quantify and qualify these emissions in a reliable and objective manner. The core principles for evaluation of the standardized measurements in emission tests were established by the “Committee for Health‐Related Evaluation of Building Products” (AgBB) and published in the so‐called “AgBB scheme”. Relevant for evaluation are: (i) Assessment of the emission levels of substances with known toxicological properties; (ii) limits for non‐assessable or unknown substances; (iii) limits for the total amount of chemical emissions. This review describes the stepwise implementation of the test procedure in Germany and the experience gained in evaluation of product emissions over the years. A comprehensive overview of the philosophy, history, current practices, and future directions of the German AgBB scheme for VOC emissions is also provided. Special emphasis is given to the evaluation of a list of about 170 single substances which have an agreed “lowest concentration of interest” (LCI) value for the indoor environment – values that are updated periodically according to present toxicological knowledge. 相似文献
952.
B. M. Schäfer 《Monthly notices of the Royal Astronomical Society》2008,388(3):1394-1402
In this paper, I investigate the family of mixed three-point correlation functions 〈τ q γ3− q 〉, q = 0, 1, 2 , between the integrated Sachs–Wolfe (iSW) temperature perturbation τ and the galaxy overdensity γ as a tool for detecting the gravitational interaction of cosmic microwave background (CMB) photons with the potentials of non-linearly evolving cosmological structures. Both the iSW-effect and the galaxy overdensity are derived in hyperextended perturbation theory to second order and I emphasize the different parameter sensitivities of the linear and non-linear iSW-effect. I examine the configuration dependence of the relevant bispectra, quantify their sensitivities and discuss their degeneracies with respect to the cosmological parameters Ωm , σ8 , h and the dark energy equation of state parameter w . I give detection significances for combining Planck CMB data and galaxy sample of a survey like Dark UNiverse Explorer (DUNE) by using a quadratic approximation for the likelihood with Λ cold dark matter (ΛCDM) as the fiducial cosmology: the combination of Planck with DUNE should be able to reach a cumulative signal-to-noise ratio of ≃0.6 for the bispectrum 〈τγ2 〉 up to ℓ= 2000, which is too weak to be detected. The most important noise source is the primary CMB fluctuations as the Poisson noise in the galaxy number density is almost negligible for a survey like DUNE. 相似文献
953.
954.
Magnetotelluric (MT) studies represent the structure of crust and mantle in terms of conductivity anomalies, while geodynamic modelling predicts the deformation and evolution of crust and mantle subject to plate tectonic processes. Here, we review the first attempts to link MT models with geodynamic models. An integration of MT with geodynamic modelling requires the use of relationships between conductivity and rheological parameters such as viscosity and melt fraction, which are provided by laboratory measurements of rock properties. Owing to present limitations in our understanding of these relationships, and in interpreting the trade-off between scale and magnitude of conductivity anomalies from MT inversions, most studies linking MT and geodynamic models are qualitative rather than providing hard constraints. Some recent examples attempt a more quantitative comparison, such as a study from the Himalayan continental collision zone, where rheological parameters have been calculated from a resistivity model and compared to predictions from geodynamic modelling. We conclude by demonstrating the potential in combining MT results and geodynamic modelling with examples that directly use MT results as constraints within geodynamic models of ore bodies and studies of an active volcano-tectonic rift. 相似文献
955.
Ángeles I. Díaz Guillermo F. Hägele Elena Terlevich Roberto Terlevich 《Astrophysics and Space Science》2009,324(2-4):209-214
A study of circumnuclear star-forming regions (CNSFRs) in several early-type spirals has been carried out in order to investigate their main properties: stellar and gas kinematics, dynamical masses, ionising stellar masses, chemical abundances and other properties of the ionised gas. Both high resolution (R~20,000) and moderate resolution (R~5000) have been used. In some cases, these regions (about 100–150 pc in size) are composed of several individual star clusters with sizes between 1.5 and 4.9 pc, estimated from Hubble Space Telescope images. Stellar and gas velocity dispersions are found to differ by about 20 to 30 km?s?1, with the Hβ emission lines being narrower than both the stellar lines and the [Oiii]λ5007 Å lines. The twice ionised oxygen, on the other hand, shows velocity dispersions comparable to those of stars. We have applied the virial theorem to estimate dynamical masses of the clusters, assuming that the systems are gravitationally bounded and spherically symmetric, and using previously measured sizes. The measured values of the stellar velocity dispersions yield dynamical masses of the order of 107 to 108 M⊙ for the full CNSFRs. We obtain oxygen abundances which are comparable to those found in high-metallicity disc Hii regions from direct measurements of electron temperatures and consistent with solar values within the errors. The region with the highest oxygen abundance is R3+R4 in NGC3504, 12+log(O/H)=8.85, about 1.5 times solar. The derived N/O ratios are, on average, larger than those found in high-metallicity disc Hii regions, and they do not seem to follow the trend of N/O vs. O/H which marks the secondary behaviour of nitrogen. On the other hand, the S/O ratios span a very narrow range—between 0.6 and 0.8 times solar. Compared to high-metallicity disc Hii regions, CNSFRs show values of the O23 and the N2 parameters whose distributions are shifted to lower and higher values, respectively. Hence, even though their derived oxygen and sulphur abundances are similar, higher values would in principle be obtained for the CNSFRs if pure empirical methods were used to estimate abundances. CNSFRs also exhibit lower ionisation parameters than their disc counterparts, as derived from [Sii]/[Siii]. Their ionisation structure also seems to be different, with CNSFRs showing radiation-field properties more similar to Hii galaxies than to disc high-metallicity Hii regions. 相似文献
956.
Pierre Kaufmann Gérard Trottet C. Guillermo Giménez de Castro Jean-Pierre Raulin Säm Krucker Albert Y. Shih Hugo Levato 《Solar physics》2009,255(1):131-142
The presence of a solar burst spectral component with flux density increasing with frequency in the sub-terahertz range, spectrally
separated from the well-known microwave spectral component, bring new possibilities to explore the flaring physical processes,
both observational and theoretical. The solar event of 6 December 2006, starting at about 18:30 UT, exhibited a particularly
well-defined double spectral structure, with the sub-THz spectral component detected at 212 and 405 GHz by the Solar Submilimeter
Telescope (SST) and microwaves (1 – 18 GHz) observed by the Owens Valley Solar Array (OVSA). Emissions obtained by instruments
onboard satellites are discussed with emphasis to ultra-violet (UV) obtained by the Transition Region And Coronal Explorer
(TRACE), soft X-rays from the Geostationary Operational Environmental Satellites (GOES) and X- and γ-rays from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The sub-THz impulsive component had its closer temporal
counterparts only in the higher energy X- and γ-rays ranges. The spatial positions of the centers of emission at 212 GHz for the first flux enhancement were clearly displaced
by more than one arc-minute from positions at the following phases. The observed sub-THz fluxes and burst source plasma parameters
were difficult to be reconciled with a purely thermal emission component. We discuss possible mechanisms to explain the double
spectral components at microwaves and in the THz ranges. 相似文献
957.
A number of X-ray instruments have been active in observing the solar coronal X-ray radiation this decade. We have compared
XSM observations with simultaneous GOES and RHESSI observations. We present flux calibrations for all instruments and compare
XSM and GOES total emission measures (TEM) and temperatures (T). 相似文献
958.
S. Schiller G. M. Tino P. Gill C. Salomon U. Sterr E. Peik A. Nevsky A. Görlitz D. Svehla G. Ferrari N. Poli L. Lusanna H. Klein H. Margolis P. Lemonde P. Laurent G. Santarelli A. Clairon W. Ertmer E. Rasel J. Müller L. Iorio C. Lämmerzahl H. Dittus E. Gill M. Rothacher F. Flechner U. Schreiber V. Flambaum Wei-Tou Ni Liang Liu Xuzong Chen Jingbiao Chen Kelin Gao L. Cacciapuoti R. Holzwarth M. P. Heß W. Schäfer 《Experimental Astronomy》2009,23(2):573-610
The Einstein Gravity Explorer mission (EGE) is devoted to a precise measurement of the properties of space-time using atomic
clocks. It tests one of the most fundamental predictions of Einstein’s Theory of General Relativity, the gravitational redshift,
and thereby searches for hints of quantum effects in gravity, exploring one of the most important and challenging frontiers
in fundamental physics. The primary mission goal is the measurement of the gravitational redshift with an accuracy up to a
factor 104 higher than the best current result. The mission is based on a satellite carrying cold atom-based clocks. The payload includes
a cesium microwave clock (PHARAO), an optical clock, a femtosecond frequency comb, as well as precise microwave time transfer
systems between space and ground. The tick rates of the clocks are continuously compared with each other, and nearly continuously
with clocks on earth, during the course of the 3-year mission. The highly elliptic orbit of the satellite is optimized for
the scientific goals, providing a large variation in the gravitational potential between perigee and apogee. Besides the fundamental
physics results, as secondary goals EGE will establish a global reference frame for the Earth’s gravitational potential and
will allow a new approach to mapping Earth’s gravity field with very high spatial resolution. The mission was proposed as
a class-M mission to ESA’s Cosmic Vision Program 2015–2025.
相似文献
S. SchillerEmail: |
959.
Thierry Appourchaux Raymond Burston Yanbei Chen Michael Cruise Hansjörg Dittus Bernard Foulon Patrick Gill Laurent Gizon Hugh Klein Sergei Klioner Sergei Kopeikin Hans Krüger Claus Lämmerzahl Alberto Lobo Xinlian Luo Helen Margolis Wei-Tou Ni Antonio Pulido Patón Qiuhe Peng Achim Peters Ernst Rasel Albrecht Rüdiger Étienne Samain Hanns Selig Diana Shaul Timothy Sumner Stephan Theil Pierre Touboul Slava Turyshev Haitao Wang Li Wang Linqing Wen Andreas Wicht Ji Wu Xiaomin Zhang Cheng Zhao 《Experimental Astronomy》2009,23(2):491-527
ASTROD I is a planned interplanetary space mission with multiple goals. The primary aims are: to test general relativity with
an improvement in sensitivity of over three orders of magnitude, improving our understanding of gravity and aiding the development
of a new quantum gravity theory; to measure key solar system parameters with increased accuracy, advancing solar physics and
our knowledge of the solar system; and to measure the time rate of change of the gravitational constant with an order of magnitude
improvement and the anomalous Pioneer acceleration, thereby probing dark matter and dark energy gravitationally. It is an
international project, with major contributions from Europe and China and is envisaged as the first in a series of ASTROD
missions. ASTROD I will consist of one spacecraft carrying a telescope, four lasers, two event timers and a clock. Two-way,
two-wavelength laser pulse ranging will be used between the spacecraft in a solar orbit and deep space laser stations on Earth,
to achieve the ASTROD I goals. A second mission, ASTROD (ASTROD II) is envisaged as a three-spacecraft mission which would
test General Relativity to 1 ppb, enable detection of solar g-modes, measure the solar Lense–Thirring effect to 10 ppm, and
probe gravitational waves at frequencies below the LISA bandwidth. In the third phase (ASTROD III or Super-ASTROD), larger
orbits could be implemented to map the outer solar system and to probe primordial gravitational-waves at frequencies below
the ASTROD II bandwidth.
相似文献
Wei-Tou NiEmail: |
960.
N.J.T. Edberg A.I. Eriksson U. Auster S. Barabash A. Bößwetter C.M. Carr S.W.H. Cowley E. Cupido M. Fränz K.-H. Glassmeier R. Goldstein M. Lester R. Lundin R. Modolo H. Nilsson I. Richter M. Samara J.G. Trotignon 《Planetary and Space Science》2009,57(8-9):1085-1096
We present the first two-spacecraft near-simultaneous observations of the Martian bow shock (BS), magnetic pileup boundary (MPB) and photo-electron boundary (PEB) obtained by the plasma instruments onboard Rosetta and Mars Express during the Rosetta Mars flyby on February 25, 2007. Our observations are compared with shape models for the BS and MPB derived from previous statistical studies. The MPB is found at its expected position but the BS for this event is found significantly closer to the planet than expected for the rather slow and moderately dense solar wind. Cross-calibration of the density measurements on the two spacecraft gives a density profile through the magnetosheath, indicating an increasing solar wind flux during the Rosetta passage which is consistent with the multiple BS crossings at the Rosetta exit. 相似文献