全文获取类型
收费全文 | 2327篇 |
免费 | 117篇 |
国内免费 | 8篇 |
专业分类
2452篇 |
出版年
2024年 | 4篇 |
2023年 | 28篇 |
2022年 | 56篇 |
2021年 | 115篇 |
2020年 | 68篇 |
2019年 | 58篇 |
2018年 | 106篇 |
2017年 | 79篇 |
2016年 | 99篇 |
2015年 | 147篇 |
2014年 | 175篇 |
2013年 | 209篇 |
2012年 | 194篇 |
2011年 | 175篇 |
2010年 | 108篇 |
2009年 | 106篇 |
2008年 | 112篇 |
2007年 | 107篇 |
2006年 | 102篇 |
2005年 | 64篇 |
2004年 | 53篇 |
2003年 | 44篇 |
2002年 | 34篇 |
2001年 | 10篇 |
2000年 | 9篇 |
1999年 | 11篇 |
1998年 | 14篇 |
1997年 | 15篇 |
1996年 | 12篇 |
1995年 | 5篇 |
1994年 | 8篇 |
1993年 | 12篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 8篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 4篇 |
1972年 | 4篇 |
1971年 | 7篇 |
1969年 | 3篇 |
排序方式: 共有2452条查询结果,搜索用时 15 毫秒
121.
Ana Milstein Mohammed Ekram Azim Mohammed Abdul Wahab Marc Charles Jean Verdegem 《Environmental Biology of Fishes》2003,68(3):247-260
The potential of periphyton-based aquaculture in South Asia is under investigation in an extensive research program. This paper is a further analysis of data from four experiments carried out in that framework, to explore periphyton, fish and fertilizer dose effects on water quality. Factor analysis and ANOVA models applied to a data matrix of water quality parameters in ponds with and without artificial substrates (bamboo poles and kanchi sticks), with and without fish (filter feeders catla and rohu, with and without bottom feeder kalbaush), and with a standard or 50% increased fertilizer dose, allowed us to identify the underlying ecological processes governing this novel periphyton-based pond system, and construct conceptual graphic models of the periphyton–environment relationships observed. We clearly established that the phosphorus flow is mainly linked to phytoplankton activity in the water column and decomposition on the pond bottom, while nitrogen flow is mainly linked to autotrophic (photosynthesis) and heterotrophic (decomposition and nitrification) processes that take place in the periphyton in addition to the water column and pond bottom. Consequently, disruption of the pond bottom by bottom feeding fish primarily promoted phosphate cycling and phytoplankton, while periphyton development on the supplied substrates and fertilization mainly improved oxygen balance and nitrogen related processes developing in the water column. The use of bamboo poles led to better results than kanchi sticks, related to the greater autotrophic periphyton development on bamboo and to the larger surface of bamboo poles that facilitate fish grazing and periphyton dislodgment that in turn have a renewal effect on periphyton. Stocking bottom feeding fish produces a fertilizing effect through the food web that benefits the filter-feeding fish and that makes it unnecessary to increase the dose of inorganic and organic fertilizers applied to the ponds. Thus, the output of this analysis will help the fish farmers in resource constrained countries to improve their production in periphyton-based ponds just by choosing bamboo substrates, stocking a bottom feeder fish together with the filter feeders, and saving money on fertilizers. 相似文献
122.
123.
124.
Ji?í ?míd Ji?í Moravec Luká? Kratochvíl Václav Gvo?dík Abdul Karim Nasher Salem M. Busais Thomas Wilms Mohammed Y. Shobrak Salvador Carranza 《ZooKeys》2013,(355):79-107
A recent molecular phylogeny of the Arid clade of the genus Hemidactylus revealed that the recently described H. saba and two unnamed Hemidactylus species from Sinai, Saudi Arabia and Yemen form a well-supported monophyletic group within the Arabian radiation of the genus. The name ‘Hemidactylus saba species group’ is suggested for this clade. According to the results of morphological comparisons and the molecular analyses using two mitochondrial (12S and cytb) and four nuclear (cmos, mc1r, rag1, rag2) genes, the name Hemidactylus granosus Heyden, 1827 is resurrected from the synonymy of H. turcicus for the Sinai and Saudi Arabian species. The third species of this group from Yemen is described formally as a new species H. ulii
sp. n. The phylogenetic relationships of the members of ‘Hemidactylus saba species group’ are evaluated and the distribution and ecology of individual species are discussed. 相似文献
125.
Maria J. Gomez-Lamarca Julia Falo-Sanjuan Robert Stojnic Sohaib Abdul Rehman Leila Muresan Matthew L. Jones Zoe Pillidge Gustavo Cerda-Moya Zhenyu Yuan Sarah Baloul Phillippe Valenti Kerstin Bystricky Francois Payre Kevin OHolleran Rhett Kovall Sarah J. Bray 《Developmental cell》2018,44(5):611-623.e7
126.
Cluster Computing - HPC or super-computing clusters are designed for executing computationally intensive operations that typically involve large scale I/O operations. This most commonly involves... 相似文献
127.
Neutrophil elastase and myeloperoxidase regulate the formation of neutrophil extracellular traps 总被引:1,自引:0,他引:1
Neutrophils release decondensed chromatin termed neutrophil extracellular traps (NETs) to trap and kill pathogens extracellularly. Reactive oxygen species are required to initiate NET formation but the downstream molecular mechanism is unknown. We show that upon activation, neutrophil elastase (NE) escapes from azurophilic granules and translocates to the nucleus, where it partially degrades specific histones, promoting chromatin decondensation. Subsequently, myeloperoxidase synergizes with NE in driving chromatin decondensation independent of its enzymatic activity. Accordingly, NE knockout mice do not form NETs in a pulmonary model of Klebsiella pneumoniae infection, which suggests that this defect may contribute to the immune deficiency of these mice. This mechanism provides for a novel function for serine proteases and highly charged granular proteins in the regulation of chromatin density, and reveals that the oxidative burst induces a selective release of granular proteins into the cytoplasm through an unknown mechanism. 相似文献
128.
Wada K Takeuchi A Saiki K Sutomo R Van Rostenberghe H Yusoff NM Laosombat V Sadewa AH Talib NA Yusoff S Lee MJ Ayaki H Nakamura H Matsuo M Nishio H 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2006,838(1):9-14
Mutations in the gene encoding UDP-glucuronosyltransferase 1A1 (UGT1A1) may reduce the glucuronidation of estradiol, bilirubin, etc. In the present study, we used a liquid chromatography-tandem mass spectrometry (LC/MS/MS) method to assay the activities of recombinant mutated UGT1A1 toward 17beta-estradiol (E2), by determining its glucuronide (E2G) content. Direct evidence for glucuronide formation was provided by E2G-specific ion peaks. The UGT1A1 activities of G71R (exon 1), F83L (exon 1), I322V (exon 2) and G493R (exon 5) mutants were 24, 30, 18 and 0.6% of the normal UGT1A1 activity, respectively. In conclusion, our study showed that LC/MS/MS enabled accurate evaluation of the effects of mutations on recombinant UGT1A1 activity towards E2. 相似文献
129.
Molecular phylogeny and divergence time estimation of Cosmodela (Coleoptera: Carabidae: Cicindelinae) tiger beetle species from Southeast Asia 下载免费PDF全文
Cosmodela Rivalier, 1961, represents a genus of tiger beetles that currently contains 13 described species widely distributed across Southeast Asia. A phylogenetic analysis based on the mitochondrial DNA fragments 16S and COI and the nuclear marker wingless and a phylogeographic analysis using a COI fragment were carried out on two subspecies of Cosmodela aurulenta (C. a. juxtata and C. a. aurulenta). The results support the hypothesis that these two subspecies are significantly different to be considered as separate species that diverged during the Pleistocene. TAXONDNA analysis was used to investigate the capability of the COI region as a marker for discriminating both entities and to quantify intra‐ and intertaxa genetic variation. The minimum distance between C. aurulenta and C. juxtata was 2.7837%, and no overlap of intra‐ and intertaxa genetic divergence was observed. Both taxa, here considered as valid species, occur in sympatry in the Malay Peninsula, with C. aurulenta most probably originating from the area and C. juxtata a secondary colonizer that expanded southwards from the Asian mainland. Our data infer a continental origin of the Indonesian samples of C. aurulenta, and they most likely dispersed across the land bridges that emerged during glacial maxima to form Sundaland. 相似文献
130.
Nurlisa Yusuf Ammar Zakaria Mohammad Iqbal Omar Ali Yeon Md Shakaff Maz Jamilah Masnan Latifah Munirah Kamarudin Norasmadi Abdul Rahim Nur Zawatil Isqi Zakaria Azian Azamimi Abdullah Amizah Othman Mohd Sadek Yasin 《BMC bioinformatics》2015,16(1)