全文获取类型
收费全文 | 100234篇 |
免费 | 788篇 |
国内免费 | 816篇 |
出版年
2023年 | 41篇 |
2022年 | 93篇 |
2021年 | 158篇 |
2020年 | 85篇 |
2019年 | 130篇 |
2018年 | 11950篇 |
2017年 | 10772篇 |
2016年 | 7660篇 |
2015年 | 931篇 |
2014年 | 666篇 |
2013年 | 793篇 |
2012年 | 4767篇 |
2011年 | 13333篇 |
2010年 | 12346篇 |
2009年 | 8504篇 |
2008年 | 10180篇 |
2007年 | 11726篇 |
2006年 | 709篇 |
2005年 | 887篇 |
2004年 | 1341篇 |
2003年 | 1356篇 |
2002年 | 1089篇 |
2001年 | 330篇 |
2000年 | 207篇 |
1999年 | 97篇 |
1998年 | 83篇 |
1997年 | 105篇 |
1996年 | 69篇 |
1995年 | 40篇 |
1994年 | 57篇 |
1993年 | 68篇 |
1992年 | 55篇 |
1991年 | 69篇 |
1990年 | 39篇 |
1989年 | 39篇 |
1988年 | 46篇 |
1987年 | 38篇 |
1986年 | 22篇 |
1985年 | 31篇 |
1984年 | 37篇 |
1983年 | 42篇 |
1982年 | 38篇 |
1981年 | 30篇 |
1980年 | 27篇 |
1975年 | 18篇 |
1973年 | 18篇 |
1972年 | 253篇 |
1971年 | 280篇 |
1965年 | 18篇 |
1962年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Shay O’Farrell Brian E. Luckhurst Stephen J. Box Peter J. Mumby 《Coral reefs (Online)》2016,35(2):421-425
Parrotfishes are an ecologically and commercially important teleost group whose grazing contributes to maintaining coral-dominated states on hermatypic reefs. However, overfishing has skewed sex ratios of Atlantic parrotfishes because fishing has disproportionate impacts on larger individuals, and males are generally larger than females. Whether protection from fishing may allow sex ratios to return to equilibrium is unknown, as fishing can induce irreversible ecological and/or evolutionary shifts. Bermuda banned trap fishing in 1990, creating a unique opportunity to analyse long-term responses of Atlantic parrotfishes to release from fishing. We found that sex ratios of four common parrotfishes were initially skewed, with male proportions ranging from 0.04 to 0.18. However, male proportions rebounded within 3–4 yr, equilibrating at values ranging from 0.36 to 0.54, similar to those reported at unfished sites in the region. Our results are encouraging for regional efforts to recover lost grazing function by restoring overfished herbivore populations. 相似文献
992.
Gregg M. Recer 《Aerobiologia》2004,20(4):179-190
Exposure to fungal allergens is an important contributor to allergic respiratory disease, but information on the efficacy of residential fungal allergen-avoidance in allergic-disease management is lacking. Using vacuum cleaners with high-efficiency exhaust filtration is one method recommended for reducing residential allergen exposure levels, but their use to reduce fungal-spore exposure levels has not been evaluated. To evaluate the effectiveness of high-efficiency vacuuming to control airborne fungal-spore levels, fungal bioaerosols were repeatedly assessed over the course of 10 months in homes randomly assigned to groups using either conventionally filtered (control) or high-efficiency-filtered vacuum cleaners for routine vacuum cleaning. Air samples were analyzed for three fungal-spore categories representing taxa with predominantly outdoor sources and one representing taxa that commonly have indoor sources. In a two-way analysis of variance, sampling period had a significant effect on mean levels of all fungal-spore categories. Vacuum cleaner type had a marginally significant effect on the indoor spore category, with one high-efficiency vacuum group mean (of three) significantly lower than one control mean. No effect was observed of vacuum cleaner type on outdoor spore categories. Including home-environment variables in analysis of covariance models strengthened the effect of the vacuum-type treatment on the indoor spore category, with no effect on the three outdoor spore categories. Decreased indoor spore levels vs. controls were only observed in high-efficiency vacuum groups during the last sampling period, at the end of the heating season. The results suggest that using a vacuum with high-efficiency filtered exhaust could have some modest effectiveness in controlling airborne fungal-spore exposure in homes when infiltration of outdoor air is very limited. 相似文献
993.
994.
Romeu Cardoso Guimarães 《Origins of life and evolution of the biosphere》2011,41(4):357-371
An investigation of the biosynthesis pathways producing glycine and serine was necessary to clarify an apparent inconsistency
between the self-referential model (SRM) for the formation of the genetic code and the model of coevolution of encodings and
of amino acid biosynthesis routes. According to the SRM proposal, glycine was the first amino acid encoded, followed by serine.
The coevolution model does not state precisely which the first encodings were, only presenting a list of about ten early assignments
including the derivation of glycine from serine—this being derived from the glycolysis intermediate glycerate, which reverses
the order proposed by the self-referential model. Our search identified the glycine-serine pathway of syntheses based on one-carbon
sources, involving activities of the glycine decarboxylase complex and its associated serine hydroxymethyltransferase, which
is consistent with the order proposed by the self-referential model and supports its rationale for the origin of the genetic
code: protein synthesis was developed inside an early metabolic system, serving the function of a sink of amino acids; the
first peptides were glycine-rich and fit for the function of building the early ribonucleoproteins; glycine consumption in
proteins drove the fixation of the glycine-serine pathway. 相似文献
995.
996.
997.
This review focuses on utilization of plant lectins as medical diagnostic reagents and tools. The lectin-related diagnostic
is aimed at detection of several diseases connected to alteration of the glycosylation profiles of cells and at identification
of microbial and viral agents in clinical microbiology. Certain lectins, proposed for or used as diagnostic tools could even
recognize those cellular determinants, which are not detected by available antibodies. Broad information is presented on the
lectinomics field, illustrating that lectin diagnostics might become practical alternative to antibody-based diagnostic products.
In addition, the rising trend of lectin utilization in biomedical diagnostics might initiate a development of innovative methods
based on better analytical technologies. Lectin microarray, a rapid and simple methodology, can be viewed as an example for
such initiative. This technology could provide simple and efficient screening tools for analysis of glycosylation patterns
in biological samples (cellular extracts, tissues and the whole cells), allowing thus personalized detection of changes associated
with carbohydrate-related diseases. 相似文献
998.
Stephen A. Matlin M.Amelia Prazeres Magalis Bittner Mario Silva 《Phytochemistry》1984,23(12):2863-2866
Rimuene and nubigenol have been identified in Podocarpus saligna for the first time, and the structures of three new norditerpene dilactones, salignones K, L and M, isolated from this species have been elucidated. 相似文献
999.
1000.
Xylose anaerobic conversion by open-mixed cultures 总被引:1,自引:0,他引:1
Margarida F. Temudo Tania Mato Robbert Kleerebezem Mark C. M. van Loosdrecht 《Applied microbiology and biotechnology》2009,82(2):231-239
Xylose is, after glucose, the dominant sugar in agricultural wastes. In anaerobic environments, carbohydrates are converted
into volatile fatty acids and alcohols. These can be used as building blocks in biotechnological or chemical processes, e.g.,
to produce bioplastics. In this study, xylose fermentation by mixed microbial cultures was investigated and compared with
glucose under the same conditions. The product spectrum obtained with both substrates was comparable. It was observed that,
in the case of xylose, a higher fraction of the carbon was converted into catabolic products (butyrate, acetate, and ethanol)
and the biomass yield was approximately 20% lower than on glucose, 0.16 versus 0.21 Cmol X/Cmol S. This lower yield is likely
related to the need of an extra ATP during xylose uptake. When submitted to a pulse of glucose, the population cultivated
on xylose could instantaneously convert the glucose. No substrate preference was observed when glucose and xylose were fed
simultaneously to the continuously operated bioreactor. 相似文献