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11.
Dauphiné twinning and texture memory in polycrystalline quartz. Part 3: texture memory during phase transformation 总被引:1,自引:0,他引:1
Hans-Rudolf?WenkEmail author N.?Barton M.?Bortolotti S.?C.?Vogel M.?Voltolini G.?E.?Lloyd G.?B.?Gonzalez 《Physics and Chemistry of Minerals》2009,36(10):567-583
Samples of quartz-bearing rocks were heated above the α (trigonal)–β (hexagonal) phase transformation of quartz (625–950°C)
to explore changes in preferred orientation patterns. Textures were measured both in situ and ex situ with neutron, synchrotron
X-ray and electron backscatter diffraction. The trigonal–hexagonal phase transformation does not change the orientation of
c- and a-axes, but positive and negative rhombs become equal in the hexagonal β-phase. In naturally deformed quartzites measured by
neutron diffraction a perfect texture memory was observed, i.e. crystals returned to the same trigonal orientation they started
from, with no evidence of twin boundaries. Samples measured by electron back-scattered diffraction on surfaces show considerable
twinning and memory loss after the phase transformation. In experimentally deformed quartz rocks, where twinning was induced
mechanically before heating, the orientation memory is lost. A mechanical model can explain the memory loss but so far it
does not account for the persistence of the memory in quartzites. Stresses imposed by neighboring grains remain a likely cause
of texture memory in this mineral with a very high elastic anisotropy. If stresses are imposed experimentally the internal
stresses are released during the phase transformation and the material returns to its original state prior to deformation.
Similarly, on surfaces there are no tractions and thus texture memory is partially lost. 相似文献
12.
In Europe, the Wide Wheel abrasion (WWA) test and the B?hme abrasion (BA) test are among the most widely used standard test
methods for determining abrasion resistance of natural stones, the former being the reference test method in EN 14157 Standard.
However, it is stated in the Annex-A (Informative) of EN 14157 Standard that very limited data are available to provide correlations
between these two test methods. To be able to fill this gap, in this study, 25 different natural stones belonging to sedimentary,
metamorphic and igneous groups were tested for their abrasion resistance as well as physico-mechanical properties. Also, for
a better interpretation of abrasion resistance characteristics of the tested stone materials, relationships between abrasion
resistance and physico-mechanical properties were statistically examined. A statistically significant linear correlation (R
2 = 0.85; P value = 0.000) was established between the WWA test and the BA test, which could be used in practice for converting the measured
abrasion resistance values from one testing method to another. It was also found that the correlation between these two test
methods improved significantly (R
2 = 0.93; P value = 0.001) when relatively high-porosity stone materials (porosity ≥1%) were separately evaluated. Both methods of abrasion
resistance employed in the present study showed statistically significant linear correlations with uniaxial compressive strength
and Brazilian tensile strength, the former proving to be a more influencing parameter on resistance to abrasion. Also, from
the point view of representing actual abrasion mechanism of stone materials in practice, the necessity of simulating multi-directional
foot traffic in abrasion testing methods was discussed. In this respect, the reference test method in the EN 14157 Standard
was criticized for not fully meeting this requirement. It was also pointed out that the reference method could have some drawbacks
when applied to coarse-grained granitic rocks having cleavable minerals such as plagioclase and orthoclase feldspars. 相似文献
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Kristie?L.?EbiEmail author Jessica?Hartman Nathan?Chan John?Mcconnell Michael?Schlesinger John?Weyant 《Climatic change》2005,73(3):375-393
Climate is one factor that determines the potential range of malaria. As such, climate change may work with or against efforts
to bring malaria under control. We developed a model of future climate suitability for stable Plasmodium falciparum malaria transmission in Zimbabwe. Current climate suitability for stable malaria transmission was based on the MARA/ARMA
model of climatic constraints on the survival and development of the Anopheles vector and the Plasmodium falciparum malaria parasite. We explored potential future geographic distributions of malaria using 16 projections of climate in 2100.
The results suggest that, assuming no future human-imposed constraints on malaria transmission, changes in temperature and
precipitation could alter the geographic distribution of malaria in Zimbabwe, with previously unsuitable areas of dense human
population becoming suitable for transmission. Among all scenarios, the highlands become more suitable for transmission, while
the lowveld and areas with low precipitation show varying degrees of change, depending on climate sensitivity and greenhouse
gas emission stabilization scenarios, and depending on the general circulation model used. The methods employed can be used
within or across other African countries. 相似文献
16.
Muhammad Ali Salman Tariq Khalid Mahmood Asim Daud Adila Batool Zia-ul-Haq 《Asia-Pacific Journal of Atmospheric Sciences》2014,50(2):153-162
It is well established that aerosols affect the climate in a variety of ways. In order to understand these effects, we require an insight into the properties of aerosols. In this paper we present a study of aerosol properties such as aerosol optical depth (AOD), single scattering albedo (SSA) and aerosol radiative forcing (ARF) over mega city of Lahore (Pakistan). The data from Aerosol Robotic Network (AERONET) have been used for the period December 2009 to October 2011. The seasonal average values of AOD, asymmetry parameter (ASY) and volume size distribution in coarse mode were observed to be highest in summer. On the other hand, the average values of Angstrom exponent (AE) and imaginary part of refractive index (RI) were found to be maximum in winter. The average value of real part of RI was found to be higher in spring than in all other seasons. The SSA exhibited an increasing trend with wavelength in the range 440 nm–1020 nm in spring, summer and fall indicating the dominance of coarse particles (usually dust). However, a decreasing trend was found in winter in the range 675 nm–1020 nm pointing towards the dominance of biomass and urban/industrial aerosols. As far as aerosol radiative forcing (ARF) is concerned, we have found that during the spring season ARF was lowest at the surface of Earth and highest at top of the atmosphere (TOA). This indicates that the atmosphere was warmer in spring than in all the remaining seasons. 相似文献
17.
Jian Zhou Yingui Qiu Danial Jahed Armaghani Wengang Zhang Chuanqi Li Shuangli Zhu Reza Tarinejad 《地学前缘(英文版)》2021,(3):201-213
A reliable and accurate prediction of the tunnel boring machine(TBM) performance can assist in minimizing the relevant risks of high capital costs and in scheduling tunneling projects.This research aims to develop six hybrid models of extreme gradient boosting(XGB) which are optimized by gray wolf optimization(GWO), particle swarm optimization(PSO), social spider optimization(SSO), sine cosine algorithm(SCA), multi verse optimization(MVO) and moth flame optimization(MFO), for estimation of the TBM penetration rate(PR).To do this, a comprehensive database with 1286 data samples was established where seven parameters including the rock quality designation, the rock mass rating, Brazilian tensile strength(BTS), rock mass weathering, the uniaxial compressive strength(UCS), revolution per minute and trust force per cutter(TFC), were set as inputs and TBM PR was selected as model output.Together with the mentioned six hybrid models, four single models i.e., artificial neural network, random forest regression, XGB and support vector regression were also built to estimate TBM PR for comparison purposes.These models were designed conducting several parametric studies on their most important parameters and then, their performance capacities were assessed through the use of root mean square error, coefficient of determination, mean absolute percentage error, and a10-index.Results of this study confirmed that the best predictive model of PR goes to the PSO-XGB technique with system error of(0.1453, and 0.1325), R~2 of(0.951, and 0.951), mean absolute percentage error(4.0689, and 3.8115), and a10-index of(0.9348, and 0.9496) in training and testing phases, respectively.The developed hybrid PSO-XGB can be introduced as an accurate, powerful and applicable technique in the field of TBM performance prediction.By conducting sensitivity analysis, it was found that UCS, BTS and TFC have the deepest impacts on the TBM PR. 相似文献
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Sardar M. Balaky Irfan Sh. Asaad Ali Ismail Al-Juboury 《Arabian Journal of Geosciences》2016,9(20):747
Facies and sequence stratigraphic analysis of the Kometan Formation (Upper Cretaceous) were studied from Kometan village, Kurdistan region of northeastern Iraq. Lithologically, the formation consists of 44 m of white weathering, light grey, thin to medium-bedded highly fractured limestones with chert nodules. Petrographic study of the carbonates shows that both skeletal and non-skeletal grains were present. The skeletal grains include a variety of planktonic foraminifera (including Oligostegina), calcispheres, ostracods, pelecypods, larva ammonite, and echinoderms. Non-skeletal grains include peloids only. Three main microfacies types are distinguished in the studied formation. The results of stable carbon and oxygen isotopes of the studied carbonate samples show negative values of δ18O. These indicate that the seawater was warm with low salinity during precipitation of the carbonates in the Kometan Formation in northeastern Iraq. The positive δ13C values of carbonate samples, in the middle part of the formation, reflect the widespread deposition of organic-rich marine sediments during a transgression and deepening of the basin. Petrographic, facies and stable isotopic analyses revealed that the Kometan Formation was deposited in a warm, basinal, pelagic (open marine) environment with low salinity. The Kometan Formation consists of one complete third-order depositional sequence, separated by a sequence boundary (SB) of type 2. The third-order sequence is subdivided into a transgressive systems tract (TST) and highstand systems tract (HST). This reflects episodes of transgression and still stands of the relative sea level. The TSTs are topped by maximum flooding surface (MFS) characterized by deepening-/fining-upward parasequences implying a retrogradational stacking pattern. The HST is marked by shallowing-/coarsening-upward parasequences implying a progradational stacking pattern. 相似文献