全文获取类型
收费全文 | 2093篇 |
免费 | 100篇 |
国内免费 | 1篇 |
专业分类
2194篇 |
出版年
2023年 | 6篇 |
2022年 | 13篇 |
2021年 | 22篇 |
2020年 | 15篇 |
2019年 | 21篇 |
2018年 | 37篇 |
2017年 | 37篇 |
2016年 | 61篇 |
2015年 | 86篇 |
2014年 | 85篇 |
2013年 | 172篇 |
2012年 | 153篇 |
2011年 | 141篇 |
2010年 | 111篇 |
2009年 | 93篇 |
2008年 | 144篇 |
2007年 | 153篇 |
2006年 | 140篇 |
2005年 | 141篇 |
2004年 | 95篇 |
2003年 | 103篇 |
2002年 | 87篇 |
2001年 | 13篇 |
2000年 | 19篇 |
1999年 | 21篇 |
1998年 | 23篇 |
1997年 | 16篇 |
1996年 | 22篇 |
1995年 | 20篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 12篇 |
1981年 | 4篇 |
1980年 | 9篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 6篇 |
1973年 | 3篇 |
排序方式: 共有2194条查询结果,搜索用时 0 毫秒
991.
Keiji Watanabe Nobuyuki Komatsu Yuichi Ishii & Masami Negishi 《FEMS microbiology ecology》2009,67(1):57-68
Effective isolation of freshwater bacterioplankton belonging to genus Polynucleobacter from a shallow eutrophic lake and its tributary was achieved by size-selective filtration with a 0.7-μm pore filter and cultivation on R2A agar medium. Partial 16S rRNA gene analysis showed that over 80% of all the strains were highly similar to the Polynucleobacter cluster. Essential medium components for effective cultivation are pyruvate, yeast extract and peptone, whereas soluble starch and glucose are not necessary. Isolate KF001 (affiliated with Polynucleobacter subcluster D) has a strict requirement for organic acids as carbon sources, and we hypothesize that the Polynucleobacter cluster of bacteria could utilize compounds formed via photochemically dissolved organic matter (DOM) degradation for growth. Because organic acids form from solar radiation of DOM in aquatic environments, carbon sources that are typical products of DOM photochemical degradation were added to the medium. These compounds were readily utilized by KF001 in this study. Finally, we observed the stimulation of strain KF001 activity by photochemical degradation of natural lake water. Our findings suggest a carbon flow of DOM photoproducts to Polynucleobacter in the freshwater microbial loop. 相似文献
992.
Satoru Kawai Makoto Hirai Kosuke Haruki Kazuyuki Tanabe Yuichi Chigusa 《Parasitology international》2009,58(3):300-302
Plasmodium knowlesi has a relatively broad host range extending to humans, in whom it causes zoonotic malaria. Recent studies have shown that human infection with P. knowlesi is widely distributed in forested areas of Southeast Asia. In the present study, we evaluated commercial rapid diagnostic tests (RDTs) for human malaria to assess their reactivity and sensitivity in detecting P. knowlesi parasites using blood samples obtained from infected monkeys. The blood samples were assayed using two commercial RDTs based on immunochromatographic assays: (i) the OptiMAL-IT, designed to detect parasite lactate dehydrogenase (pLDH) of both P. falciparum and other plasmodia, and (ii) the Entebe Malaria Cassette (MC), designed to detect P. falciparum-specific histidine-rich protein 2 (PfHRP2) and P. vivax-specific pLDH. Interestingly, when the P. knowlesi-infected blood samples were examined with the RDTs, OptiMAL test results were interpreted as falciparum malaria-positive, while Entebe MC test results were interpreted as vivax malaria-positive. The sensitivities of both tests in detecting P. knowlesi parasite were similar to those for P. falciparum and higher than P. vivax. Thus, commercial RDTs based on detection of pLDH should be used with great caution, and should not replace conventional microscopy in the diagnosis of suspected cases of P. knowlesi malaria. 相似文献
993.
The introduction of the snail-eating flatworm Platydemus manokwari (Tricladida: Rhynchodemidae) has been considered a cause of the extinction of native land snails on several Pacific islands.
Although P. manokwari is known to attack land snails on the ground, whether P. manokwari attacks snails on trees remains unclear. To clarify the effect of P. manokwari on arboreal snails, we examined survival rates of land snails experimentally placed on tree trunks (0.5–2.0 m above the ground)
in a forest on Chichijima, Ogasawara (Bonin) Islands, in the northwestern Pacific Ocean. The survival of snails experimentally
placed on tree trunks with artificially created snail scent trails rapidly decreased for 7 days, and the mortality was caused
by P. manokwari predation. However, snails placed on tree trunks without snail scent trails were not attacked by P. manokwari. Therefore, P. manokwari climbed tree trunks, likely tracking the snail scent. We found that over 40% of the snails placed on tree trunks with snail
scent trails were eaten by P. manokwari within 7 days. This experiment supports the hypothesis that P. manokwari predation is an important cause of the rapid decline or extinction of native arboreal snails on Pacific islands. 相似文献
994.
Tohru Kobayashi Kohsuke Uchimura Masayuki Miyazaki Yuichi Nogi Koki Horikoshi 《Extremophiles : life under extreme conditions》2009,13(1):121-129
A high-alkaline, salt-activated alginate lyase is produced by Agarivorans sp. JAM-A1m from a deep-sea sediment off Cape Nomamisaki on Kyushu Island, Japan. Purified to homogeneity, as judged by SDS-PAGE,
the enzyme (A1m) had a molecular mass of approximately 31 kDa. The optimal pH was around 10 in glycine–NaOH buffer, and the
activity was increased to 1.8 times by adding 0.2 M NaCl. However, when the optimal pH in the presence of 0.2 M NaCl was shifted
to pH 9.0, the activity was more than 10 times compared with that at pH 9 in the absence of NaCl. A1m showed the optimal temperature
at around 30°C and was stable to incubation between pH 6 and 9. The enzyme degraded favorably mannuronate–guluronate and guluronate-rich
fragments in alginate. Shotgun cloning and sequencing of the gene for A1m revealed a 930-bp open reading frame, which encoded
a mature enzyme of 289 amino acids (32,295 Da) belonging to polysaccharide lyase family 7. The deduced amino acid sequence
showed the highest similarity to that of a Klebsiella enzyme, with only 54% identity. 相似文献
995.
Background
The microbial community in the gut of termites is responsible for the efficient decomposition of recalcitrant lignocellulose. Prominent features of this community are its complexity and the associations of prokaryotes with the cells of cellulolytic flagellated protists. Bacteria in the order Bacteroidales are involved in associations with a wide variety of gut protist species as either intracellular endosymbionts or surface-attached ectosymbionts. In particular, ectosymbionts exhibit distinct morphological patterns of the associations. Therefore, these Bacteroidales symbionts provide an opportunity to investigate not only the coevolutionary relationships with the host protists and their morphological evolution but also how symbiotic associations between prokaryotes and eukaryotes occur and evolve within a complex symbiotic community. 相似文献996.
Eriko Sasamori Mieko Kato Yuichi Tagawa 《Archives of biochemistry and biophysics》2010,501(2):232-238
The anti-prion protein (PrP) monoclonal antibody T2 has previously been prepared using PrP-knockout mice immunized with mouse recombinant PrP residues 121-231, however its interaction mechanism to PrP antigen has not been cleared. Here we identified and characterized the epitope of T2 antibody. The competitive ELISA with 20-mer synthetic peptides derived from PrP121-231 showed that T2 antibody had no affinity for these peptides. The analysis with deletion mutants of PrP revealed that 10 amino acids in the N terminus and 66 amino acids in the C terminus of PrP121-231 were necessary for reactivity with T2. Two far regions are necessary for complete affinity of the T2 antibody for PrP; either region alone is not sufficient to retain the affinity. The epitope recognized by T2 antibody is discontinuous and conformational. We examined the effect of disulfide bond and salt bridges. Alkylation of cysteine residues in C terminus of PrP121-231, which breaks a disulfide bond and disrupts the structure, had diminished the reactivity. Mutations induced in the PrP121-231 to break the disulfide bond or salt bridges, markedly had reduced the reactivity with T2 antibody. It suggests that T2 antibody recognized the structure maintained by the disulfide bond and salt bridges. 相似文献
997.
Yokoyama T Masujin K Schmerr MJ Shu Y Okada H Iwamaru Y Imamura M Matsuura Y Murayama Y Mohri S 《PloS one》2010,5(11):e15450
Background
Sheep scrapie is caused by multiple prion strains, which have been classified on the basis of their biological characteristics in inbred mice. The heterogeneity of natural scrapie prions in individual sheep and in sheep flocks has not been clearly defined.Methodology/Principal Findings
In this study, we intravenously injected 2 sheep (Suffolk and Corriedale) with material from a natural case of sheep scrapie (Suffolk breed). These 3 sheep had identical prion protein (PrP) genotypes. The protease-resistant core of PrP (PrPres) in the experimental Suffolk sheep was similar to that in the original Suffolk sheep. In contrast, PrPres in the Corriedale sheep differed from the original PrPres but resembled the unusual scrapie isolate, CH1641. This unusual PrPres was not detected in the original sheep. The PrPres distributions in the brain and peripheral tissues differed between the 2 breeds of challenged sheep. A transmission study in wild-type and TgBoPrP mice, which overexpressing bovine PrP, led to the selection of different prion strains. The pathological features of prion diseases are thought to depend on the dominantly propagated strain.Conclusions/Significance
Our results indicate that prion strain selection occurs after both inter- and intraspecies transmission. The unusual scrapie prion was a hidden or an unexpressed component in typical sheep scrapie. 相似文献998.
Yuichi Iida Jung-Hyun Kim Yasuhiro Kazuki Hidetoshi Hoshiya Masato Takiguchi Masahiro Hayashi Indri Erliandri Hee-Sheung Lee Alex Samoshkin Hiroshi Masumoto William C. Earnshaw Natalay Kouprina Vladimir Larionov Mitsuo Oshimura 《DNA research》2010,17(5):293-301
Human artificial chromosomes (HACs), which carry a fully functional centromere and are maintained as a single-copy episome, are not associated with random mutagenesis and offer greater control over expression of ectopic genes on the HAC. Recently, we generated a HAC with a conditional centromere, which includes the tetracycline operator (tet-O) sequence embedded in the alphoid DNA array. This conditional centromere can be inactivated, loss of the alphoidtet-O (tet-O HAC) by expression of tet-repressor fusion proteins. In this report, we describe adaptation of the tet-O HAC vector for gene delivery and gene expression in human cells. A loxP cassette was inserted into the tet-O HAC by homologous recombination in chicken DT40 cells following a microcell-mediated chromosome transfer (MMCT). The tet-O HAC with the loxP cassette was then transferred into Chinese hamster ovary cells, and EGFP transgene was efficiently and accurately incorporated into the tet-O HAC vector. The EGFP transgene was stably expressed in human cells after transfer via MMCT. Because the transgenes inserted on the tet-O HAC can be eliminated from cells by HAC loss due to centromere inactivation, this HAC vector system provides important novel features and has potential applications for gene expression studies and gene therapy. 相似文献
999.
Yuichi Sakamoto 《Mycoscience》2010,51(3):163-169
Formation of the Flammulina velutipes fruiting body can be induced by lowering the ambient temperature (first treatment) in complete darkness. Fruiting bodies formed under these conditions elongate without pileus formation (pinhead fruiting body), suggesting that they cannot mature in complete darkness. However, after light treatment of the pinhead fruiting body (second treatment), a pileus develops immediately, and the stipe also thickens and becomes increasingly pigmented. The apical region swells as a result of cell division starting 2 days after light treatment, the pileus–stipe junction fracture and hymenium primordia form on day 4, and gills appear at day 6. Pf1 and Pf3 are specifically expressed after exposure to low temperature without light. The cell wall-associated protein [pileus-specific hydrophobin-like protein (PSH)] is specifically induced in the pileus, but not in the stipe, following the second light treatment to the pinhead fruiting body. These results suggest that Pf1 and Pf3 would be involved in fruiting body induction and that PSH would be involved in pileus formation. These phenomena will aid further histological and molecular biological investigations into the mechanisms behind fruiting body development in F. velutipes. 相似文献
1000.
Yuichi Kano Yôichi Kawaguchi Tomomi Yamashita Yukihiro Shimatani 《Ichthyological Research》2010,57(2):180-188
The distribution of the oriental weatherloach, Misgurnus anguillicaudatus, together with related environmental factors were surveyed at 185 paddy field locations on Sado Island in Japan. This was
associated with the reintroduction of the Japanese crested ibis, Nipponia nippon, which prefers to feed on the loach. Loach were found to be present at 90 locations (49%). Analysis with GIS, GLM and AIC
revealed that positive factors for the loach distribution included the presence of an earth ditch, the connections at outlets
and the proportion of paddy field area within an 800 m radius. Conversely, pumping-up water irrigation and flow irrigation
affected loach distribution negatively. In an interview survey that was conducted concurrently, older farmers in the area
recalled that the loach had once been distributed over almost the entire island (89/96, 93%) about half a century ago. The
farmers also suggested that the impact of agricultural chemicals was one of the main reasons for loach reduction or local
extinction. A map of the current potential loach distribution was made using the best fit model from GIS variables. The loach
was expected to be distributed in the Kuninaka region with high probability (60–100%) and in patches in the Osado and Kosado
regions with low–medium probability (10–50%). As a feasible scenario for the conservation of the loach, another predictive
map of the loach distributions was made using a model fit based on the GIS variables and outlet connection, in which the all
of the outlets were presumed to be connected to the ditches without gaps. In this case, the loach were expected to be distributed
almost throughout the paddy fields with medium–high probability (40–100%). In another scenario that presumed the complete
land consolidation of all the paddy fields, the probability of loach occurrence was low (0–30%) throughout the island with
the exception of the island’s center in the Kuninaka region. 相似文献