全文获取类型
收费全文 | 971篇 |
免费 | 137篇 |
出版年
2021年 | 9篇 |
2020年 | 5篇 |
2019年 | 8篇 |
2018年 | 7篇 |
2016年 | 13篇 |
2015年 | 19篇 |
2014年 | 28篇 |
2013年 | 33篇 |
2012年 | 44篇 |
2011年 | 46篇 |
2010年 | 24篇 |
2009年 | 32篇 |
2008年 | 44篇 |
2007年 | 32篇 |
2006年 | 32篇 |
2005年 | 36篇 |
2004年 | 34篇 |
2003年 | 43篇 |
2002年 | 34篇 |
2001年 | 31篇 |
2000年 | 36篇 |
1999年 | 28篇 |
1998年 | 19篇 |
1997年 | 16篇 |
1996年 | 13篇 |
1995年 | 15篇 |
1994年 | 11篇 |
1993年 | 21篇 |
1992年 | 19篇 |
1991年 | 25篇 |
1990年 | 18篇 |
1989年 | 36篇 |
1988年 | 24篇 |
1987年 | 19篇 |
1986年 | 19篇 |
1985年 | 24篇 |
1984年 | 24篇 |
1983年 | 20篇 |
1982年 | 23篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 20篇 |
1978年 | 17篇 |
1977年 | 10篇 |
1976年 | 10篇 |
1975年 | 14篇 |
1974年 | 19篇 |
1973年 | 9篇 |
1972年 | 6篇 |
1968年 | 7篇 |
排序方式: 共有1108条查询结果,搜索用时 31 毫秒
41.
Rapid colorimetric detection of in vitro amplified DNA sequences 总被引:4,自引:0,他引:4
A colorimetric assay to detect immobilized amplified nucleic acids has been designed. This approach provides a rapid assay, suitable for clinical diagnosis, to analyze DNA sequences amplified by the polymerase chain reaction. The specific DNA sequences are captured on a solid support by the use of a recombinant fusion protein consisting of the Escherichia coli lac repressor and staphylococcal protein A. The biotin streptavidin system is used to detect the immobilized material. Positive samples can be analyzed by direct solid-phase sequencing. Here, we show that this nonradioactive concept can be used for analysis of Staphylococci and Streptococci and for specific detection of the protozoa Plasmodium falciparum in clinical samples. 相似文献
42.
The genomes of the animal papillomaviruses European elk papillomavirus, deer papillomavirus, and reindeer papillomavirus contain a novel transforming gene (E9) near the early polyadenylation site.
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We report that the genomes of reindeer papillomavirus (RPV), European elk papillomavirus (EEPV), and deer papillomavirus (DPV) contain a short conserved translational open reading frame (ORF), E9, which is located between the E5 ORF and the early polyadenylation site. In RPV, DPV, and EEPV, E9 ORFs have the potential to encode extremely hydrophobic polypeptides of approximately 40 amino acids. In mouse C127 cells transformed by EEPV and RPV, there exists a unique, abundant mRNA species of approximately 700 nucleotides which has the capacity to encode an E9 polypeptide. This mRNA is transcribed from a previously unrecognized promoter at position 4030 in the EEPV genome. The EEPV E9 ORF exhibits weak transforming activity in C127 cells and primary rat embryo fibroblasts. We also show that EEPV E5 is the major oncogene in the EEPV genome when assayed in C127 cells, although it is less efficient in transformation than the E5 genes of bovine papillomavirus type 1, DPV, and RPV. 相似文献
43.
Denys-Drash syndrome (DDS) is characterized by early onset nephropathy, pseudohermaphroditism in males and a high risk for developing Wilms' tumour (WT). The exact cause of DDS is unknown but germline mutations in the Wilms' tumour suppressor gene (WT1) have recently been described in the majority of DDS patients studied. These mutations occur de novo and are clustered around the zinc finger (ZF) coding exons of the WT1 gene. Analysis of exons 2–10 of the WT1 gene in constitutional DNA from five patients with DDS was carried out using the polymerase chain reaction (PCR) and direct DNA sequencing. In four out of the five patients, heterozygous germline mutations were found: a novel point mutation in exon 8 (ZF2) at codon 377 altering the wild-type histidine to arginine, and three previously described point mutations in exon 9 (ZF3) in the codons corresponding to amino acids 394Arg and 396Asp. In one patient, no mutations could be demonstrated. In three patients where parental DNA was available, the mutations were shown to have occurred de novo. Furthermore, since tumour DNA in two of these cases had lost the wild-type allele, polymorphic markers from the short arm of chromosome 11 were used to determine the parental origin of the mutant chromosome. In both cases, the mutant chromosome was shown to be of paternal origin. Since the majority of published WT1 mutations in DDS patients alter a RsrII restriction site in exon 9, we were able to perform PCR-based diagnosis in a female patient with early renal insufficiency and normal external genitalia. 相似文献
44.
A study was performed to investigate possible interactions by magnetic fields (MF) with the processes of initiation and promotion of chemically induced preneoplastic lesions in rat liver. Male Sprague-Dawley rats were subjected to a 70% partial hepatectomy followed after 24 h by i.p. injection of diethylnitrosamine (DENA) as a tumour initiator. Starting one week after the DENA-treatment phenobarbital (PB) was given to promote growth of enzymatically altered foci of liver cells. MF was applied immediately after the partial hepatectomy and continued until sacrifice after 12 weeks of PB exposure. Homogenous horizontal AC magnetic fields with a frequency of 50 Hz and flux densities of 0.5 μT or 0.5 mT were used. The rats coexposed with MF and DENA plus PB did not gain weight as much as the rats exposed to the chemical agents only. The MF-exposure also resulted in a slight reduction in size and numbers of the focal lesions. The results suggest an interaction of MF with the processes of chemical carcinogenesis either as a result of stress or depending on effects on the proliferation of preneoplastic cells. © 1993 Wiley-Liss, Inc. 相似文献
45.
Agneta Nordenskjöld Fredrik Hedborg Holger Luthman Magnus Nordenskjöld 《Human genetics》1993,92(3):296-298
The Beckwith-Wiedemann syndrome (BWS) is characterized by somatic overgrowth, developmental anomalies, and proneness to embryonic tumor development. The majority of cases are sporadic, but several families with an autosomal dominant mode of inheritance with variable expression and reduced penetrance have been described. In three such families, BWS has been linked to DNA markers for the insulin gene (INS) and H-ras on chromosome band 11p15. Two additional families with inherited BWS are described here. Linkage analysis has been performed with a highly informative marker for the tyrosine hydroxylase (TH) locus within the INS-IGF2 (insulin-like growth factor II)-TH gene cluser and confirms the previous observed linkage to this region (lod score 2.16 at = 0). Linkage analysis to TH provides a basis for informed genetic counselling and carrier detection in the hereditary form of the syndrome. Based on the hypothesis that IGF2 may be a candidate gene for BWS, we screened for mutations in the coding exons 7 and 9, but found no abnormalities in 5 unrelated BWS cases. 相似文献
46.
Lage Pettersson 《Molecular Engineering》1993,3(1-3):29-42
In most aqueous polyoxometalate systems, numerous, often highly negatively charged species, are formed. To establish the speciation in such complex polyanion systems, many experimental methods and techniques must be used. Moreover, it is of vital importance that the experimental data are of the highest accuracy and that the data collected from different methods are treated simultaneously with an appropriate computer program. In systems containing one or more sensitive NMR nuclei, a combined EMF-NMR method has been shown to be extremely powerful.This article firstly gives some general comments on equilibria in aqueous polyoxometalate systems including ionic medium effects, and then describes an equilibrium EMF-NMR (31P and51V) study of the five component system H+-Mo(VI)-V(V)-P(V)-e–. The study has been focused on so-called Keggin ratio solutions, Mo+V):P=12:1, since these are commonly used in selective oxidation processes. Special attention has been given to Mo10V2P and Mo9V3P solutions, where positional isomers occur. We have been able to identify and characterize all the five possible isomers of -Mo10V2PO
40
5–
at 25 and 90 °C. Besides the results from the five component system, some interesting findings from the binary, ternary and quarternary sybsystems are also reported. 相似文献
47.
Evolutionary relationships among members of the genus Chlamydia based on 16S ribosomal DNA analysis. 总被引:2,自引:0,他引:2
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)
B Pettersson A Andersson T Leitner O Olsvik M Uhln C Storey C M Black 《Journal of bacteriology》1997,179(13):4195-4205
Nucleotide sequences from strains of the four species currently in the genus Chlamydia, C. pecorum, C. pneumoniae, C. psittaci, and C. trachomatis were investigated. In vitro-amplified RNA genes of the ribosomal small subunit from 30 strains of C. pneumoniae and C. pecorum were subjected to solid-phase DNA sequencing of both strands. The human isolates of C. pneumoniae differed in only one position in the 16S rRNA gene, indicating genetic homogeneity among these strains. Interestingly, horse isolate N16 of C. pneumoniae was found to be closely related to the human isolates of this species, with a 98.9% nucleotide similarity between their 16S rRNA sequences. The type strain and koala isolates of C. pecorum were also found to be very similar to each other, possessing two different 16S rRNA sequences with only one-nucleotide difference. Furthermore, the C. pecorum strains truncated the 16S rRNA molecule by one nucleotide compared to the molecules of the other chlamydial species. This truncation was found to result in loss of a unilaterally bulged nucleotide, an attribute present in all other eubacteria. The phylogenetic structure of the genus Chlamydia was determined by analysis of 16S rRNA sequences. All phylogenetic trees revealed a distinct line of descent of the family Chlamydiaceae built of two main clusters which we denote the C. pneumoniae cluster and the C. psittaci cluster. The clusters were verified by bootstrap analysis of the trees and signature nucleotide analysis. The former cluster contained the human isolates of C. pneumoniae and equine strain N16. The latter cluster consisted of C. psittaci, C. pecorum, and C. trachomatis. The members of the C. pneumoniae cluster showed tight clustering and strain N16 is likely to be a subspecies of C. pneumoniae since these strains also share some antigenic cross-reactivity and clustering of major outer membrane protein gene sequences. C. psittaci and strain N16 branched early out of the respective cluster, and interestingly, their inclusion bodies do not stain with iodine. Furthermore, they also share less reliable features like normal elementary body morphology and plasmid content. Therefore, the branching order presented here is very likely a true reflection of evolution, with strain N16 of the species C. pneumoniae and C. psittaci forming early branches of their respective cluster and with C. trachomatis being the more recently evolved species within the genus Chlamydia. 相似文献
48.
A direct chiral chromatographic reversed phase method for the determination of the enantiomers of felodipine is described. The influence of charged and uncharged modifiers as well as the effect of the mobile phase pH on the enantiomeric resolution is discussed. A high mobile phase pH and the addition of 2-propanol as organic modifier gave the highest separation factor (α = 1.3). The high mobile phase pH (pH = 7.6) is outside the recommended pH limit of silica based columns but was necessary to achieve baseline resolution of (R)- and (S)-felodipine. Improvement of column efficiency by increasing column temperature was utilized for optimization of the enantiomeric resolution (Rs = 1.7). The enantiomers of felodipine and three related compounds were separated within 15 min. The enantiomeric purity of (R)- and (S)-felodipine in injections and (R)-felodipine in bulk substance was higher than 99.5% and no racemization was observed after storage at accelerated conditions. A poor Chiral-AGP® column used for a long period was restored using a simple wash step together with repacking the top of the chromatographic column. © 1995 Wiley-Liss, Inc. 相似文献
49.
Metabolism of aflatoxin, ochratoxin, zearalenone, and three trichothecenes by intact rumen fluid, rumen protozoa, and rumen bacteria 总被引:3,自引:0,他引:3
K H Kiessling H Pettersson K Sandholm M Olsen 《Applied and environmental microbiology》1984,47(5):1070-1073
The effect of rumen microbes on six mycotoxins (aflatoxin B1, ochratoxin A, zearalenone, T-2 toxin, diacetoxyscirpenol, and deoxynivalenol ) considered to be health risks for domestic animals was investigated. The mycotoxins were incubated with intact rumen fluid or fractions of rumen protozoa and bacteria from sheep and cattle in the presence or absence of milled feed. Rumen fluid had no effect on aflatoxin B1 and deoxynivalenol . The remaining four mycotoxins were all metabolized, and protozoa were more active than bacteria. Metabolism of ochratoxin A, zearalenone, and diacetoxyscirpenol was moderately or slightly inhibited by addition of milled feed in vitro. The capacity of rumen fluid to degrade ochratoxin A decreased after feeding, but this activity was gradually restored by the next feeding time. Ochratoxin A was cleaved to ochratoxin alpha and phenylalanine; zearalenone was reduced to alpha-zearalenol and to a lesser degree to beta-zearalenol; diacetoxyscirpenol and T-2 toxin were deacetylated to monoacetoxyscirpenol and HT-2 toxin, respectively. Feeding of 5 ppm (5 mg/kg) of ochratoxin A to sheep revealed 14 ppb (14 ng/ml) of ochratoxin A and ochratoxin alpha in rumen fluid after 1 h, but neither was detected in the blood. Whether such conversions in the rumen fluid may be considered as a first line of defense against toxic compounds present in the diet is briefly discussed. 相似文献
50.
Metabolism of aflatoxin, ochratoxin, zearalenone, and three trichothecenes by intact rumen fluid, rumen protozoa, and rumen bacteria. 总被引:5,自引:4,他引:1
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The effect of rumen microbes on six mycotoxins (aflatoxin B1, ochratoxin A, zearalenone, T-2 toxin, diacetoxyscirpenol, and deoxynivalenol ) considered to be health risks for domestic animals was investigated. The mycotoxins were incubated with intact rumen fluid or fractions of rumen protozoa and bacteria from sheep and cattle in the presence or absence of milled feed. Rumen fluid had no effect on aflatoxin B1 and deoxynivalenol . The remaining four mycotoxins were all metabolized, and protozoa were more active than bacteria. Metabolism of ochratoxin A, zearalenone, and diacetoxyscirpenol was moderately or slightly inhibited by addition of milled feed in vitro. The capacity of rumen fluid to degrade ochratoxin A decreased after feeding, but this activity was gradually restored by the next feeding time. Ochratoxin A was cleaved to ochratoxin alpha and phenylalanine; zearalenone was reduced to alpha-zearalenol and to a lesser degree to beta-zearalenol; diacetoxyscirpenol and T-2 toxin were deacetylated to monoacetoxyscirpenol and HT-2 toxin, respectively. Feeding of 5 ppm (5 mg/kg) of ochratoxin A to sheep revealed 14 ppb (14 ng/ml) of ochratoxin A and ochratoxin alpha in rumen fluid after 1 h, but neither was detected in the blood. Whether such conversions in the rumen fluid may be considered as a first line of defense against toxic compounds present in the diet is briefly discussed. 相似文献