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181.
Acrochaete leptochaete (Huber) Nielsen (Chaetophoraceae, Chlorophyta) was isolated from the macroalgae Chaetomorpha collected from intertidal pools in Rongcheng, Shandong, China. 18S rDNA combined with ITS regions were used to ascertain the morphological identification of the isolated material. Based on the unialgal culture, asexual reproduction and growth characteristics of A. leptochaete were investigated over wide ranges of temperature and irradiance. Results revealed that asexual reproduction of A. leptochaete could be realized by biflagellate zoospores. The zoospores germinated directly to give self- replicating generations. Zoospore germination was bipolar. A temperature range from 13-21°C and a lower irradiance of 36 μmol/(m2·s) were most favorable for the growth of A. leptochaete. Thallus organization, an important taxonomic criterion for the genus Acrochaete, was affected markedly by temperature and irradiance. Our results extend the knowledge about the species’ general biology and its morphological plasticity. For classification and identification of a simple microphytic algae like A. leptochaete, which are traditionally placed in the class Chaetophoraceae, we propose that molecular tools associated with culture observations are applied. 相似文献
182.
天然磁铁矿化学改性及其在水体除砷中的应用 总被引:4,自引:2,他引:2
铁氧化物及其复合氧化物(如菱铁矿、水铁矿)的表面电荷高、比表面积大,在特定条件下对亚砷酸盐和砷酸盐有较强的结合能力和亲和性,以铁氧化物作为吸附剂处理高砷水已经成为研究热点之一。天然磁铁矿的主要成分为Fe_3O_4,但其本身活性较弱,直接应用于处理高砷水的除砷率低。本文对天然磁铁矿采取酸化、碱化、不同温度灼烧、不同灼烧时间等简易的方法进行改性,达到有效去除水中砷的目的。实验结果表明:经0.5 mol/L盐酸浸泡、150℃灼烧10 min的改性磁铁矿分别处理As(Ⅲ)溶液和As(Ⅴ)溶液时,As(Ⅴ)去除率达98%,吸附能力显著增强,达到预期目标;溶液中As(Ⅲ)浓度从1000μg/L下降到250μg/L,去除率达75%,即As吸附能力明显优于未改性的天然磁铁矿,与其他改性铁矿除砷能力相近,而改性方法更加简便、易行。本文研究的改性天然磁铁矿吸附剂为控制高砷水的砷含量提供了一种切实可用的吸附材料。 相似文献
183.
Samples of suspended particulate matters(SPMs),surface sediment and road dust were collected from the Yangtze estuarine and nearby coastal areas,coastal rivers,and central Shanghai.The samples were analyzed for the presence of 16 polycyclic aromatic hydrocarbons(PAHs)in the USEPA priority-controlled list by GC-MS.The compound-specific stable carbon isotopes of the individual PAHs were also analyzed by GC-C-IRMS.The sources of PAHs in the SPMs and surface sediments in the Yangtze estuarine and nearby coastal... 相似文献
184.
185.
In this paper, we present a new method for seismic stratigraphic absorption compensation based on the adaptive molecular decomposition.
Using this method, we can remove most of the effects resulting from wavelets truncation and interference which usually exist
in the common time-frequency absorption compensation method. Based on the assumption that the amplitude spectrum of the source
wavelet is smooth, we first construct a set of adaptive Gabor frames based on the time-variant properties of the seismic signal
to transform the signal into the time-frequency domain and then extract the slowly varying component (the wavelet’s time-varying
amplitude spectrum) in each window in the time-frequency domain. Then we invert the absorption compensation filter parameters
with an objective function defined using the correlation coefficients in each window to get the corresponding compensation
filters. Finally, we use these filters to compensate the time-frequency spectrum in each window and then transform the time-frequency
spectrum to the time domain to obtain the absorption-compensated signal. By using adaptive molecular decomposition, this method
can adapt to isolated and overlapped seismic signals from the complex layers in the inhomogeneous viscoelastic medium. The
viability of the method is verified by synthetic and real data sets. 相似文献
186.
西安地铁施工诱发地表沉降及对城墙的影响 总被引:1,自引:0,他引:1
以西安地铁2号线为背景,利用3种预测公式对实测地表沉降值进行拟合,得到了沉降槽形态参数。利用拟合参数,借鉴“刚度修正法”原理对地铁下穿城墙施工诱发其基础的沉降进行预测,并建立城墙的三维有限元模型,对城墙所能承受的极限变形能力和承载力进行量化分析,分析结果表明:Peck公式能较好地描述地表沉降特征;考虑后期蠕变和固结作用,盾构施工所诱发的城墙基础最大沉降量不得超过20 mm,期望对后期地铁施工引起地表沉降及其对建筑物的响应提供科学参考。 相似文献
187.
Climate variability recorded by n-alkanes of paleolake sediment in Qaidam Basin on the northeast Tibetan Plateau in late MIS3 总被引:1,自引:0,他引:1
PU Yang ZHANG HuCai LEI GuoLiang CHANG FengQin YANG MingSheng ZHANG WenXiang LEI YanBin YANG LunQing & PANG YouZhi State Key Laboratory of Lake Science Environment Nanjing Institute of Geography Limnology Chinese Academy of Sciences Nanjing China Graduate University of Chinese Academy of Sciences Beijing Key Laboratory of Boyang Lake MOE School of Environmental Chemical Engineering Nanchang University Nanchang 《中国科学:地球科学(英文版)》2010,(6)
Here we combine n-alkanes preserved in a shell bar section from Qarhan paleolake, Qaidam Basin with the other sedimentary proxies to elucidate the lake evolution process during the period 39.7 to 17.5 14C ka BP (calibrated age ranges from 43.5 to 22.4 cal. ka BP). In different stages, the n-alkane homologues exhibited different distribution modes indicative of variations in the surrounding vegetation and the hydrologic condition of the lake. The n-alkanes proxies (CPIh, ACLh, Paq) have the same trends as th... 相似文献
188.
Evaluation of the response modification coefficient and collapse potential of special concentrically braced frames 总被引:1,自引:0,他引:1
Special concentrically braced frames (SCBFs) are commonly used for seismic design of buildings. Their large elastic stiffness and strength efficiently sustains the seismic demands during smaller, more frequent earthquakes. During large, infrequent earthquakes, SCBFs exhibit highly nonlinear behavior due to brace buckling and yielding and the inelastic behavior induced by secondary deformation of the framing system. These response modes reduce the system demands relative to an elastic system without supplemental damping using a response modification coefficient, commonly termed the R factor. More recently, procedures put forth in FEMAP695 have been made to quantify the R factor through a formalized procedure that accounts for collapse potential. The primary objective of the research in this paper was to evaluate the approach for SCBFs. An improved model for SCBFs that permits simulation of brace fracture was used to conduct response history analyses. A series of three‐story, nine‐story and 20‐story SCBFs were designed and evaluated. Initially, the FEMAP695 method was conducted to estimate collapse and the corresponding R factor. An alternate procedure for scaling the multiple acceleration records to the seismic design hazard was also evaluated. The results show significant variation between the two methods. Of the three variations of buildings studied, the largest vulnerability was identified for the three‐story building. To achieve a consistent margin of safety against collapse, a significantly lower R factor is required for the low‐rise SCBFs (three‐story), whereas the mid‐rise and high‐rise SCBFs (nine‐story and 20‐story) may continue to use the current value of 6, as provided in ASCE‐07. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
189.
Luwen WANG Jiwen GE Liang FENG Yaoyao LIU Yu LI Jiumei WANG Xiang XIAO Zhiqi ZHANG 《大气科学进展》2022,39(8):1375-1385
Wetland ecosystems are the most important natural methane (CH4) sources, whose fluxes periodically fluctuate. Methanogens (methane producers) and methanotrophs (methane consumers) are considered key factors affecting CH4 fluxes in wetlands. However, the symbiotic relationship between methanogens and methanotrophs remains unclear. To help close this research gap, we collected and analyzed samples from four soil depths in the Dajiuhu subalpine peatland in January, April, July, and October 2019 and acquired seasonal methane flux data from an eddy covariance (EC) system, and investigated relationships. A phylogenetic molecular ecological networks (pMENs) analysis was used to identify keystone species and the seasonal variations of the co-occurrence patterns of methanogenic and methanotrophic communities. The results indicate that the seasonal variations of the interactions between methanogenic and methanotrophic communities contributed to CH4 emissions in wetlands. The keystone species discerned by the network analysis also showed their importance in mediating CH4 fluxes. Methane (CH4) emissions in wetlands were lowest in spring; during this period, the most complex interactions between microbes were observed, with intense competition among methanogens while methanotrophs demonstrated better cooperation. Reverse patterns manifested themselves in summer when the highest CH4 flux was observed. Methanoregula formicica was negatively correlated with CH4 fluxes and occupied the largest ecological niches in the spring network. In contrast, both Methanocella arvoryzae and Methylocystaceae demonstrated positive correlations with CH4 fluxes and were better adapted to the microbial community in the summer. In addition, soil temperature and nitrogen were regarded as significant environmental factors to CH4 fluxes. This study was successful in explaining the seasonal patterns and microbial driving mechanisms of CH4 emissions in wetlands. 相似文献
190.