全文获取类型
收费全文 | 3289篇 |
免费 | 138篇 |
国内免费 | 323篇 |
出版年
2024年 | 5篇 |
2023年 | 32篇 |
2022年 | 45篇 |
2021年 | 68篇 |
2020年 | 72篇 |
2019年 | 80篇 |
2018年 | 61篇 |
2017年 | 68篇 |
2016年 | 69篇 |
2015年 | 83篇 |
2014年 | 113篇 |
2013年 | 328篇 |
2012年 | 119篇 |
2011年 | 137篇 |
2010年 | 101篇 |
2009年 | 217篇 |
2008年 | 196篇 |
2007年 | 193篇 |
2006年 | 142篇 |
2005年 | 145篇 |
2004年 | 125篇 |
2003年 | 128篇 |
2002年 | 101篇 |
2001年 | 103篇 |
2000年 | 87篇 |
1999年 | 85篇 |
1998年 | 88篇 |
1997年 | 80篇 |
1996年 | 60篇 |
1995年 | 68篇 |
1994年 | 82篇 |
1993年 | 69篇 |
1992年 | 65篇 |
1991年 | 45篇 |
1990年 | 44篇 |
1989年 | 41篇 |
1988年 | 33篇 |
1987年 | 30篇 |
1986年 | 29篇 |
1985年 | 19篇 |
1984年 | 23篇 |
1983年 | 3篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 9篇 |
1976年 | 9篇 |
排序方式: 共有3750条查询结果,搜索用时 62 毫秒
961.
Bryn Duffy Chad Schwietert Alex France Niti Mann Krista Culbertson Benjamin Harmon John P. McCue 《Biological trace element research》1998,64(1-3):197-213
An alternative approach to the development of clinically useful protease inhibitors was investigated. The approach utilized
coordination chemistry of transition metal ions rather than substrate analogs to block active sites of these enzymes. In the
case of serine proteases it was found that aqueous Ti(IV) is a potent inhibitor of the trypsin subclass, but not the chymotrypsin
subclass. The direct binding of Ti(IV) to trypsin was made possible by the presence of a free carboxyl group at the bottom
of the substrate binding pocket of the enzyme, and the five-coordinate geometry of TiO(SO4)(H2O). Although initial binding of Ti(IV) was reversible, it was followed in time by irreversible inhibition. Direct binding
of octahedral or tetrahedral metal ion complexes was prevented by the inability of the enzyme active sites to promote formation
of a five-coordinate transition state of the metal ion required for reaction. These studies demonstrate the ability of direct
metal ion binding as a way to enhance blocking of enzyme active sites as compared with that of traditional organic inhibitors.
Application of these findings was investigated by measuring the affect Ti(IV) had on growth ofEscherichia coli, Salmonella typhimurium, andPseudotnonas aeruginosa. Five-coordinate titanyl sulfate completely inhibited the growth of these organisms. This suggests that five-coordinate titanyl
sulfate, which is easier and less expensive to manufacture than conventional antibiotics, may be useful in controlling endemic
infections ofE. coli andS. typhimurium. 相似文献
962.
F. Hartung R. Werner H.-P. Mühlbach C. Büttner 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1998,96(6-7):797-802
Using a PCR-based assay with highly specific primers, we were able to clearly identify all of 28 different Pseudomonas solanacearum strains, whereas none of the other bacteria tested gave a cross reaction. The PCR sensitivity in standard dilution experiments
of pure strains was in the range of 10 to 100 cells. The assay was also investigated for its suitability in routine diagnosis
of potato tubers and tomato plants inoculated with various amounts of P. solanacearum; it reached a sensitivity of 103 cells per specimen. The region between primers PS96H and PS96I was sequenced for the first time and aligned. A total of 17
P. solanacearum strains have been sequenced, resulting in six different sequence groups. When the variable sequence was analyzed, a high
correlation between point mutations and geographical origin of the P. solanacearum strains was revealed. The PCR assay described in this study combined with automatical sequencing of the amplificated region
provides a powerful tool for the epidemiology of P. solanacearum.
Received: 1 September 1997 / Accepted: 15 October 1997 相似文献
963.
R. Batchvarova V. Nikolaeva S. Slavov S. Bossolova V. Valkov S. Atanassova S. Guelemerov A. Atanassov H. Anzai 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1998,97(5-6):986-989
Six oriental cultivars of tobacco (Nicotiana tabacum L.) were evaluated for transformation and foreign gene expression. Leaf-disc explant tissue was transformed with Agrobacterium tumefaciens strain LBA4404 carrying the plasmid pARK21, which contains NPTII gene and ttr (tabtoxin resistance) gene conferring the resistance to Pseudomonas syringae pv. tabaci. The disease resistance of regenerated plants and segregation of this trait up to R7 progeny were investigated in a greenhouse and under field conditions. Our results indicated that the resistance to Pseudomonas syringae pv. tabaci introduced by transformation is heritable.
Received: 10 June 1997 / Accepted: 31 March 1998 相似文献
964.
SORAYA C M LEAL-BERTIOLI ALETÉIA V PASCOAL PATRÍCIA M GUIMARÃES MARIA F GROSSI DE SÁ REJANE L GUIMARÃES DAMARES C MONTE DAVID J BERTIOLI 《The Annals of applied biology》2003,143(3):349-357
The protein Tarin 1, from Colocasia esculenta, was expressed in Nicotiana tabacum. Bioassays were done on plants expressing Tarin 1 at different levels using Spodoptera frugiperda larvae, various bacteria and fungi and the root‐knot nematode Meloidogyne javanica. It was found that S. frugiperda larvae fed on transformed plants had retarded and lower pupation, lower accumulated biomass and higher mortality rate than larvae fed on control plants. Also, Tarin 1 was found to inhibit the growth in vitro of Pseudomonas syringae pv. tomato. For Meloidogyne javanica, both relative replication and root damage were greater in control plants than in transformed plants, but the results were not statistically significant. This work illustrates the effects of plants expressing Tarin 1, on the growth and development of insects and bacteria, and shows its potential for pest management. 相似文献
965.
Pseudomonas fluorescensstrainPf7–14 was evaluated for biological control of rice blast in field experiments. StrainPf7–14 was formulated in methylcellulose:talc (1:4) and applied to IR50 rice (Oryza sativa) seeds as a seed treatment and as foliar sprays in seedbed and field experiments. When applied as a seed treatment followed by three foliar applications, the strain provided a 68.5% suppression of rice blast in the seedbed experiment and a 59.6% suppression in the field experiment. The persistence and migration ofPf7–14 on the rice plant was studied with the aid oflacZYgenes inserted into the bacterium. In greenhouse experiments,Pf7–14gal was detected on rice roots at 106to 105cfu/g of root tissue for 110 days, the duration of the rice crop. Migration of the strain from the seeds to the leaves occurred only until the seedlings were 16 days old. WhenPf7–14 was applied to the rice plants by foliar sprays, 104cfu of the bacterium per gram of leaf tissue was detected for the next 40 days. The limited migration of the bacterial biocontrol agent emphasizes the need for multiple foliar applications of the bacterium to sustain the bacterial population for effective suppression of rice blast. 相似文献
966.
Development of ELISA for the detection of Ralstonia solanacearum in tomato: its application in seed health testing 总被引:3,自引:0,他引:3
N. Rajeshwari M.D. Shylaja M. Krishnappa H.S. Shetty C.N. Mortensen S.B. Mathur 《World journal of microbiology & biotechnology》1998,14(5):697-704
Bacterial wilt caused by Ralstonia (formerly Pseudomonas) solanacearum is worldwide in distribution. It is one of the most destructive bacterial diseases of economically important crops. The serological assays so far developed for the detection of R. solanacearum were able to provide information as to the presence or absence of the pathogen in soil and plant materials. However, they could not discriminate between virulent and avirulent strains of the pathogen and were not specific to strains and races. In the present investigation, virulent bacterial cells (encapsulated with mucin) from tomato seeds were used as antigen and polyclonal antisera were developed in rabbit using a classical immunization protocol. Antisera thus developed were examined for the antibody titre, sensitivity, specificity, rapidity and the efficacy of the antibody in identifying the virulent and avirulent strains of the pathogen and the potential for application of this assay to the screening of infected plant materials and seeds. Our results indicate that the anti-tomato R. solanacearum: (i) has a good antibody titre of 1:10,000; (ii) can detect as few as 100 bacterial cells/ml; (iii) is tomato-specific (it reacted with tomato R. solanacearum, and not with isolates from chilli or eggplant); (iv) is reactive to all isolates of R. solanacearum from tomato; (v) is not cross-reactive with non-pseudomonads; (vi) is virulent strain-specific as it recognizes the virulent exopolysaccharide component as an antigenic determinant; (vii) reactivity could be correlated well with the degree of infection in tomato seeds and plant materials. The enzyme linked immunosorbent assay developed is sensitive, specific and rapid, therefore suitable for the detection of R. solanacearum isolates from tomato seeds during routine assays. 相似文献
967.
The aim of this study was to determine the impact of wild-type along with functionally and nonfunctionally modified Pseudomonas fluorescens strains in the rhizosphere. The wild-type F113 strain carried a gene encoding the production of the antibiotic 2,4-diacetylphloroglucinol (DAPG) useful in plant disease control, and was marked with a lacZY gene cassette. The first modified strain was a functional modification of strain F113 with repressed production of DAPG, creating the DAPG-negative strain F113 G22. The second paired comparison was a nonfunctional modification of wild-type (unmarked) strain SBW25, constructed to carry marker genes only, creating strain SBW25 EeZY-6KX. Significant perturbations were found in the indigenous bacterial population structure, with the F113 (DAPG+) strain causing a shift towards slower growing colonies (K strategists) compared with the nonantibiotic-producing derivative (F113 G22) and the SBW25 strains. The DAPG+ strain also significantly reduced, in comparison with the other inocula, the total Pseudomonas populations but did not affect the total microbial populations. The survival of F113 and F113 G22 were an order of magnitude lower than the SBW 25 strains. The DAPG+ strain caused a significant decrease in the shoot-to-root ratio in comparison to the control and other inoculants, indicating plant stress. F113 increased soil alkaline phosphatase, phosphodiesterase and aryl sulphatase activities compared to the other inocula, which themselves reduced the same enzyme activities compared to the control. In contrast to this, the β-glucosidase, β-galactosidase and N -acetyl glucosaminidase activities decreased with the inoculation of the DAPG+ strain. These results indicate that soil enzymes are sensitive to the impact of inoculation with genetically modified microorganisms (GMMs). 相似文献
968.
Shigeaki Harayama 《Journal of molecular evolution》1994,38(4):328-335
TOL plasmid pWW0 of Pseudomonas putida encodes a set of enzymes responsible for the degradation of toluene. The structural genes for these catobolic enzymes are clustered into two operons—namely, the xylCMAB and xylXYZLTEGFJQKIH operons. We examined the codon usage patterns of these catabolic genes by measuring the codon-usage distances between pairs of these catabolic genes. The codon-usage distance, d, between gene 1 and gene 2 was defined as d = [(p
j
– q
j
)2]1/2, where p
j
> and q
j
are the frequencies of the j-th codon in gene 1 and 2, respectively, j being any one of the 64 possible codons. We found that the genes in the same operon exhibit similar codon-usage patterns while genes in the different operons exhibit different codon bias. This observation suggests that genes in the same operon have coevolved, and that the ancestors of the xylCMAB and xylXYZLTEGFJQKIH operons evolved in different organisms.
Correspondence to: S. Harayama 相似文献
969.
《FEBS letters》1994,350(2-3):207-212
The interactions of catechol (substrate), 2-hydroxy-pyridine-N-oxide (substrate analogue) and 2-bromophenol (inhibitor) with the extradiol cleaving catechol-2,3-dioxygenase from Pseudomonas putida mt-2 have been monitored through X-ray absorption spectroscopy (XAS). The analysis of the data provides details about the mode of coordination of the substrate and of the inhibitors to the active site of the enzyme. 相似文献
970.
A novel type of oxygenolytic ring cleavage: 2,4-oxygenation and decarbonylation of 1H-3-hydroxy-4-oxoquinaldine and 1H-3-hydroxy-4-oxoquinoline 总被引:1,自引:0,他引:1
Iris Bauer ré de Beyer Barbara Tshisuaka Susanne Fetzner Franz Lingens 《FEMS microbiology letters》1994,117(3):299-304
Abstract The utilization of quinaldine (2-methylquinoline) by Arthrobacter sp. Rü61a proceeds via 1 H -4-oxoquinaldine, 1 H -3-hydroxy-4-oxoquinaldine, and N -acetyl-anthranilic acid. By analogy, 1 H -4-oxoquinoline is degraded by Pseudomonas putida 33/1 via 1 H -3-hydroxy-4-oxoquinoline and N -formylanthranilic acid. Using the purified enzymes from both organisms, the mode of N -heterocyclic ring cleavage was investigated. The conversions of 1 H -3-hydroxy-4-oxoquinaldine and 1 H -3-hydroxy-4-oxoquinoline to N -acetyl- and N -formylanthranilic acid, respectively, were both accompanied by the release of carbon monoxide. The enzyme-catalysed transformations were performed in an [18 O]O2 atmosphere and resulted in the incorporation of two oxygen atoms into the respective products, N -acetyl- and N -formylanthranilic acid, indicating an oxygenolytic attack at C-2 and C-4 of both 1 H -3-hydroxy-4-oxoquinaldine and 1 H -3-hydroxy-4-oxoquinolone. 相似文献