全文获取类型
收费全文 | 355534篇 |
免费 | 22775篇 |
国内免费 | 1070篇 |
专业分类
379379篇 |
出版年
2018年 | 15844篇 |
2017年 | 14807篇 |
2016年 | 11772篇 |
2015年 | 4315篇 |
2014年 | 4881篇 |
2013年 | 6849篇 |
2012年 | 12096篇 |
2011年 | 22630篇 |
2010年 | 19116篇 |
2009年 | 14768篇 |
2008年 | 18507篇 |
2007年 | 20887篇 |
2006年 | 7012篇 |
2005年 | 7628篇 |
2004年 | 7595篇 |
2003年 | 7689篇 |
2002年 | 7269篇 |
2001年 | 12319篇 |
2000年 | 12232篇 |
1999年 | 9167篇 |
1998年 | 2676篇 |
1997年 | 2764篇 |
1996年 | 2714篇 |
1995年 | 2476篇 |
1994年 | 2427篇 |
1993年 | 2350篇 |
1992年 | 7198篇 |
1991年 | 7034篇 |
1990年 | 7065篇 |
1989年 | 6857篇 |
1988年 | 6372篇 |
1987年 | 6028篇 |
1986年 | 5353篇 |
1985年 | 5661篇 |
1984年 | 4473篇 |
1983年 | 3885篇 |
1982年 | 2684篇 |
1981年 | 2494篇 |
1980年 | 2304篇 |
1979年 | 4107篇 |
1978年 | 3134篇 |
1977年 | 2881篇 |
1976年 | 2826篇 |
1975年 | 3280篇 |
1974年 | 3497篇 |
1973年 | 3524篇 |
1972年 | 3729篇 |
1971年 | 3473篇 |
1970年 | 2538篇 |
1969年 | 2299篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
N V Guliaeva O L Levina I P Levina 《Biulleten' eksperimental'no? biologii i meditsiny》1985,100(8):204-206
Male albino rats were exposed to daily emotional painful stress (EPS) for 4 weeks. The arterial blood pressure of the stressed animals increased and the dynamics of the heart rate changed after functional loading (hypokinesis during one or two hours) as compared with the control group. The increase of the heart weight and activation of cytochrome oxidase activity in the cerebral cortex and hippocampus of rats exposed to EPS were also demonstrated. The use of 20% ethyl alcohol instead of drinking water during EPS partially prevented vegetative disturbances and activation of hippocampal cytochrome oxidase and fully prevented the heart hypertrophy and activation of the enzyme in the cortex. Alcoholization resulted in the increased weight of the spleen and brown adipose tissue and thymus involution. A possible mechanism of the antistress action of alcohol linked with normalization of intensified lipid peroxidation under stress is discussed. 相似文献
994.
E N Wardle 《BMJ (Clinical research ed.)》1980,281(6250):1285-1286
995.
Alkaliphilic anaerobic community at pH 10 总被引:7,自引:0,他引:7
Relict or ancient microbial communities in extreme environment might be analogous to the centers of origin of bacterial diversity. A bacterial community of an alkaline lake was investigated, and the diversity of bacteria found there indicates that both conditions of autonomy and phylogenetic variety are fulfilled for anaerobic bacteria developing at pH 10±0.2. Major functional groups in the trophic network were present. Representatives of proteolytic, bacteriolytic, cellulolytic, saccharolytic, dissipotrophic, acetogenic, sulfate-reducing, methanogenic bacteria were isolated. 相似文献
996.
To ascertain the health risks that may be posed by the land application of sewage sludges, a scheme was devised to determine the types and numbers of pathogenic and potentially pathogenic bacteria present in sludges. A processing treatment was adapted to sludge to give a homogenate which yielded the greatest numbers of viable bacteria. Conventional methods were successful in enumerating Klebsiella, Staphylococcus, gram-negative enteric bacteria, and commonly used indicator organisms. Modifications of conventional methods improved the enumeration of Salmonella, Mycobacterium sp., fluorescent Pseudomonas sp., and Clostridium perfringens. However, Shigella methodology yielded only one isolate. Utilizing the proposed scheme, the population densities of these organisms were estimated in three domestic wastewater sludges. In light of these results, the potential impact of land application of sewage sludges is discussed. 相似文献
997.
B. Pernet-Coudrier G. Varrault M. Saad J. P. Croue M.-F. Dignac J.-M. Mouchel 《Biogeochemistry》2011,106(1):89-106
Understanding the nature of organic matter is a necessary first step in assessing contaminant bioavailability and allowing
water supply managers to optimise the treatment train in the aim of providing safe and inexpensive drinking water. This study
provides further insight into the composition, structure and functional groups of dissolved organic matter (DOM) (both hydrophobic
and hydrophilic) from urban aquatic systems by means of various analytical techniques (DAX-8/XAD-4 fractionation, elemental
analysis, UV and FTIR spectroscopies, 13C and 15N isotopic analysis, size exclusion chromatography and Pyrolysis-GC-MS). The analytical range chosen for this study constitutes
a powerful tool in the characterisation of DOM in urban water. The inclusion of information from one technique to the next
might not only serve as a support to each one, but also as a complement. The DOM fraction from treated effluent and, more
generally, DOM from urban water (i.e. receiving treated effluent) display a strong hydrophilic characteristic [i.e. low humic
substance (HS) content, low SUVA], along with a high distribution in molecular weights observed by SEC and low average molecular
weight. Due to the origin of this DOM, proteinaceous structures constitute the main compounds, as observed by FTIR and Py-GC-MS.
Such characteristics (i.e. heterogeneity, low average molecular weight and diverse functional groups, which make up a total
of N) could explain that DOM from treated effluent displayed a strong reactive potential metals pollutants as previously demonstrated. 相似文献
998.
Six polymorphic dinucleotide microsatellite loci were isolated and characterized from the White‐chinned Petrel Procellaria aequinoctialis, using a degenerate primer and PCR‐based technique to construct and screen an enriched genomic library. Preliminary data on three populations show heterozygosity levels ranging from 0.22 to 0.67 and allele numbers from three to nine. Preliminary data also suggest genetic distance between these three populations (FST 0.088). Cross‐species amplification of these six microsatellite loci and one further locus were tested in six other procellariiform species of the genus Procellaria, Macronectes, Thalassarche and Diomedea. 相似文献
999.
1000.