全文获取类型
收费全文 | 308篇 |
免费 | 37篇 |
出版年
2021年 | 3篇 |
2018年 | 2篇 |
2016年 | 5篇 |
2015年 | 6篇 |
2014年 | 7篇 |
2013年 | 13篇 |
2012年 | 8篇 |
2011年 | 14篇 |
2010年 | 6篇 |
2009年 | 6篇 |
2008年 | 13篇 |
2007年 | 13篇 |
2006年 | 10篇 |
2005年 | 8篇 |
2004年 | 14篇 |
2003年 | 8篇 |
2002年 | 13篇 |
2001年 | 7篇 |
2000年 | 14篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 10篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 3篇 |
1980年 | 9篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1968年 | 3篇 |
1965年 | 5篇 |
1963年 | 2篇 |
1962年 | 2篇 |
排序方式: 共有345条查询结果,搜索用时 187 毫秒
61.
Uggla A. Beskow P. Schwan O. Bergquist N. R. Waller T. 《Acta veterinaria Scandinavica》1983,24(1):113-119
Sera from 155 ewes representing 21 different sheep flocks from the central parts of Sweden were examined for the presence of antibodies to Toxoplasma gondii by the indirect fluorescent-antibody test. Seropositive animals were found in 14 flocks, which corresponded to 55 % of the tested sera. Animals from the same flock were with few exceptions either all positive or all negative. Some ewes with a history of abortion a few months before blood sampling showed high titers indicating causative correlation with toxoplasmosis. These are the first verified cases of ovine toxoplasmal abortions in Sweden. 相似文献
62.
Vanillic acid metabolism was studied in wild-type Sporotrichum pulverulentum and three different mutants. Vanillic acid was found to be oxidatively decarboxylated to methoxyhydroquinone (MHQ) and simultaneously reduced to vanillin and vanillyl alcohol to different degrees depending upon the cultivation conditions. The reducing pathway cannot be utilized unless the fungus has access to an easily metabolized carbon source such as glucose or cellobiose, while decarboxylation takes place in cultures with only vanillic acid present. Polymerization reactions also occurred in the culture solutions. Some evidence for reoxidation of vanillin and vanillyl alcohol was obtained in vivo, and in vitro experiments using horseradish peroxidase.Using vanillic acids labelled in the carboxyl, methoxyl and the aromatic ring it was shown that decarboxylation occures before ring-cleavage, which in turn takes place earlier than the release of 14CO2 from O14CH3-vanillate. The 14CO2 evolution from the methoxyl group is repressed by 1% cellobiose as compared to 0.25% cellobiose, but is stimulated by 26 mM nitrogen (as asparagine plus NH4NO3) compared to 2.6 mM nitrogen. Since S. pulverulentum appears to require three hydroxyl groups attached to the benzene ring before ring-cleavage can occur, preparation for ring-cleavage is apparently achieved by hydroxylation rather than by demethylation.A scheme for metabolism of vanillic acid by S. pulverulentum based upon these results is proposed.Non-Standard Abbreviations WT
wild type Sporotrichum pulverulentum
- MHQ
methoxyhydroquinone
- MQ
methoxyquinone
- NKM
Norkrans medium
- DMS
dimethylsuccinate
- DHP
dehydropolymer of coniferyl alcohol 相似文献
63.
Temperature-sensitive mutations affecting the replication of F-prime factors in Escherichia coli K 12 总被引:9,自引:0,他引:9
Summary More temperature-sensitive mutants affecting the replication of the F-gal+ episome of Escherichia coli K12 have been isolated. Eight of the mutations were located on F itself and three were located on the chromosome.The temperature sensitive F-gal+'s have been integrated into the chromosome to produce Hfr strains. These Hfr strains have transfer origins similar to Hfr Cavalli, and all show aberrant excision and transfer of elongated segments of the chromosome including the integrated F-gal to generate long merodiploids.The chromosomal mutations that govern the replication of F have been termed seg (for segregation). Wild-type F-gal+ can be integrated into seg cells at 42° C to give Hfrs, in a process analogous to integrative suppression in the formation of Hfrs from cells carrying mutations that are temperature-sensitive for chromosomal DNA replication (dnaA). A curious feature of an Hfr derived from a seg strain is that it also shows F-genote enlargement as well as normal transfer of chromosomal genetic marker. Preliminary transductional mapping data show that the mutation seg-2 is linked to the threonine locus (minute 0). 相似文献
64.
Low-molecular-weight T4 phage-specific RNA 总被引:1,自引:0,他引:1
65.
66.
Efraim Lavie David L. Hirschberg George Schreiber K. Thor Lucas Hill Ingegerd Hellstrom Karl-Erik Hellstrom 《Cancer immunology, immunotherapy : CII》1991,33(4):223-230
Summary Measurements in cancer patients showed that the pH of tumors averages 0.8 unit lower than that of the surrounding normal tissues, confirming published work. Based on this, the anti-carcinoma monoclonal antibody (mAb) L6 was used to prepare immunoconjugates with daunomycin (DM), the drug being released at the acidic pH of the tumor. A direct linking of the aconitic derivative of DM (AcoDM) to mAb L6 led to conjugates that either had a low drug/antibody ratio (<5:1) or precipitated in vitro. In order to increase the drug load and avoid precipitation, several biopolymers were tested as spacers between the drug and the L6. To attach the polymer derivative to the mAb, the former was maleimidized and the mAb was thiolated. The AcoM/mAb ratio obtained was 20, and the mAb retained its highly specific binding to tumor cells. At pH 6 the AcoDM-L6 conjugate was toxic to cultured C-3347 carcinoma cells with an inhibitory concentration (IC50) of 5 µg/ml. The conjugate was less effective than the free DM with an IC50 of 0.2 µg/ml. The L6 alone was not toxic. At a tumor pH of 6.5, 15% of the AcoDM was released. The amount of released drug reached a maximum 24–48 h after exposure to the acidic medium.In vivo localization studies demonstrated a similar tumor uptake of the conjugate and mAb L6 with 18% of the injected dose/g tumor and a maximum uptake in tumor 48 h after injection. Our data indicate that it is possible to construct conjugates based on a pH-sensitive linker that can be targeted successfully to a tumor with release of a portion of the drug at the tumor site, but testing is needed to establish whether such release has anti-tumor activity in vivo and offers an advantage over treatment with unconjugated drug. 相似文献
67.
RepFIC, a basic replicon of IncFI plasmids that has homology with a basic replicon of IncFII plasmids 总被引:5,自引:0,他引:5
It was found that a DNA segment containing genes for autonomous replication and its control (basic replicon) present in the IncFI plasmid P307 has homology with RepA, a basic replicon present in IncFII plasmids. The basic replicon in P307 is referred to as RepFIC and the homologous basic replicon in IncFII plasmids is referred to as RepFIIA. In 11 other IncFI plasmids studied a region that has homology with RepFIC and RepFIIA was demonstrated. Thus, of the several basic replicons present in IncFI plasmids, RepFIC is evolutionarily related to a basic replicon of IncFII plasmids. 相似文献
68.
Nucleotide sequence and replication characteristics of RepFIB, a basic replicon of IncF plasmids. 总被引:14,自引:8,他引:6
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
D Saul A J Spiers J McAnulty M G Gibbs P L Bergquist D F Hill 《Journal of bacteriology》1989,171(5):2697-2707
A second autonomous replicon of P307, RepFIB, has been isolated that has significant homology with other replicons in IncFI group plasmids. Eleven homologous repeats of 21 base pairs are present on the sequence and flank an open reading frame capable of coding for a protein of about Mr = 40,000. This protein was identified by maxicell analysis of cloned RepFIB. A series of deletion mutations of RepFIB were inserted into a DNA polymerase I-dependent vector and examined for their replication proficiency in a polA1 strain. These experiments defined a minimal replication region of 1.6 kilobases which includes the three repeats immediately upstream and downstream of the open reading frame. Deletion of a second set of repeats further downstream doubled the copy number of a chimeric plasmid replicating under RepFIB control. It was concluded that these repeats control the copy number of the replicon. Incompatibility tests showed that all three sets of repeats could express incompatibility with a resident RepFIB plasmid. 相似文献
69.
70.