全文获取类型
收费全文 | 376篇 |
免费 | 33篇 |
出版年
2022年 | 6篇 |
2021年 | 15篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 10篇 |
2015年 | 18篇 |
2014年 | 15篇 |
2013年 | 21篇 |
2012年 | 21篇 |
2011年 | 16篇 |
2010年 | 7篇 |
2009年 | 14篇 |
2008年 | 11篇 |
2007年 | 13篇 |
2006年 | 16篇 |
2005年 | 12篇 |
2004年 | 12篇 |
2003年 | 5篇 |
2002年 | 7篇 |
2001年 | 9篇 |
2000年 | 6篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1995年 | 4篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 8篇 |
1989年 | 14篇 |
1988年 | 4篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1970年 | 5篇 |
1969年 | 3篇 |
1948年 | 2篇 |
1943年 | 2篇 |
排序方式: 共有409条查询结果,搜索用时 31 毫秒
1.
2.
Prokaryotic and ciliate communities of healthy and aquarium White Syndrome (WS)-affected coral fragments were screened using denaturing gradient gel electrophoresis (DGGE). A significant difference (R = 0.907, p < 0.001) in 16S rRNA prokaryotic diversity was found between healthy (H), sloughed tissue (ST), WS-affected (WSU) and antibiotic treated (WST) samples. Although 3 Vibrio spp were found in WS-affected samples, two of these species were eliminated following ampicillin treatment, yet lesions continued to advance, suggesting they play a minor or secondary role in the pathogenesis. The third Vibrio sp increased slightly in relative abundance in diseased samples and was abundant in non-diseased samples. Interestingly, a Tenacibaculum sp showed the greatest increase in relative abundance between healthy and WS-affected samples, demonstrating consistently high abundance across all WS-affected and treated samples, suggesting Tenacibaculum sp could be a more likely candidate for pathogenesis in this instance. In contrast to previous studies bacterial abundance did not vary significantly (ANOVA, F2, 6 = 1.000, p = 0.422) between H, ST, WSU or WST. Antimicrobial activity (assessed on Vibrio harveyi cultures) was limited in both H and WSU samples (8.1% ±8.2 and 8.0% ±2.5, respectively) and did not differ significantly (Kruskal-Wallis, χ2 (2) = 3.842, p = 0.146). A Philaster sp, a Cohnilembus sp and a Pseudokeronopsis sp. were present in all WS-affected samples, but not in healthy samples. The exact role of ciliates in WS is yet to be determined, but it is proposed that they are at least responsible for the neat lesion boundary observed in the disease. 相似文献
3.
Extinction can be attributed broadly to environmental or genetic stress. The ability to detect such stresses before they seriously affect a population can enhance the effectiveness of conservation programs. Recent studies have shown that within-individual morphological variability may provide a valuable early indicator of environmental and genetic stress. 相似文献
4.
A model system (1) was established to analyze purine and pyrimidine metabolism. This system has been expanded to include macrosimulation of DNA synthesis and the study of its regulation by terminal deoxynucleoside triphosphates (dNTPs) via a complex set of interactions. Computer experiments reveal that our model exhibits adequate and reasonable sensitivity in terms of dNTP pool levels and rates of DNA synthesis when inputs to the system are varied. These simulation experiments reveal that in order to achieve maximum DNA synthesis (in terms of purine metabolism), a proper balance is required in guanine and adenine input into this metabolic system. Excessive inputs will become inhibitory to DNA synthesis. In addition, studies are carried out on rates of DNA synthesis when various parameters are changed quantitatively. The current system is formulated by 110 differential equations. 相似文献
5.
Summary
Pseudomonas syringae pv. glycinea Race 8 strain PgB3 is naturally resistant to trimethoprim (Tp) at concentrations up to 500 g/ml. A genomic library of total PgB3 DNA was constructed by ligating EcoRI-restricted DNA into the EcoRI site of the cosmid vector, pLAFR1, packaging the DNA in vitro into bacteriophage lambda, and transducing E. coli DH1 cells. Of 960 cosmid clones selected for resistance to tetracycline, six were resistant to trimethoprim at 500 g/ml. An insert into pLAFR1 of about 9.4 kb was shown to be consistently present in the tirmethoprim-resistant clones. Southern blot analysis using radioactively labeled insert DNA as probe indicated that the 9.4 kb fragment hybridized only with a 40 kb indigenous plasmid from PgB3 designated pPg2. 相似文献
6.
Interferon and cell division. VI. Inhibitory effect of interferon on the multiplication of mouse embryo and mouse kidney cells in primary cultures 总被引:17,自引:0,他引:17
7.
8.
Previous studies with rainbow trout (Oncorhynchus mykiss) have shown that allozymic heterozygotes have increased developmental stability, as measured by reduced fluctuating bilateral
asymmetry. In this paper, we examine the phenotypic effects of null alleles at two lactate dehydrogenase (LDH) loci. If the
association between allozymic heterozygosity and developmental stability is due largely to linked chromosomal segments, then
we would expect null allele heterozygotes to have increased developmental stability. In contrast, heterozygotes for LDH null
alleles in three populations have reduced developmental stability. This suggests that the reduction in enzyme activity at
these loci is having a deleterious effect on development that is strong enough to mask any beneficial effects that may be
associated with heterozygosity for these chromosomal segments. The LDH loci examined in this study are members of two different
paralogous pairs of duplicate genes produced by the polyploidization of the ancestral salmonid genome. The apparent deleterious
effects of these null alleles in heterozygotes could retard the possible loss of duplicate gene expression. 相似文献
9.
Genomic organization of GB viruses A and B: two new members of the Flaviviridae associated with GB agent hepatitis. 总被引:16,自引:6,他引:10 下载免费PDF全文
A S Muerhoff T P Leary J N Simons T J Pilot-Matias G J Dawson J C Erker M L Chalmers G G Schlauder S M Desai I K Mushahwar 《Journal of virology》1995,69(9):5621-5630
The genomes of two positive-strand RNA viruses have recently been cloned from the serum of a GB agent-infected tamarin by using representational difference analysis. The two agent, GB viruses A and B (GBV-A and GBV-B, respectively), have genomes of 9,493 and 9,143 nucleotides, respectively, and single large open reading frames that encode potential polyprotein precursors of 2,972 and 2,864 amino acids, respectively. The genomes of these agents are organized much like those of other pestiviruses and flaviviruses, with genes predicted to encode structural and nonstructural proteins located at the 5' and 3' ends, respectively. Amino acid sequence alignments and subsequent phylogenetic analysis of the RNA-dependent RNA polymerases (RdRps) of GBV-A and GBV-B show that they possess conserved sequence motifs associated with supergroup II RNA polymerases of positive-strand RNA viruses. On the basis of similar analyses, the GBV-A- and GBV-B-encoded helicases show significant identity with the supergroup II helicases of positive-strand RNA viruses. Within the supergroup II RNA polymerases and helicases, GBV-A and GBV-B are most closely related to the hepatitis C virus group. Across their entire open reading frames, the GB agents exhibit 27% amino sequence identity to each other, approximately 28% identity to hepatitis C virus type 1, and approximately 20% identity to either bovine viral diarrhea virus or yellow fever virus. The degree of sequence divergence between GBV-A and GBV-B and other Flaviviridae members demonstrates that the GB agents are representatives of two new genera within the Flaviviridae family. 相似文献
10.
Compressed synangia referable to the medullosan pollen organ genus Aulacotheca Halle have been discovered in Early Pennsylvanian sediments from Rock Island County, Illinois, U.S.A. Specimens were recovered from localized shales containing floral elements suggesting an upland environment. Based on synangial size, morphology, sporangial number, and prepollen type, two distinct forms, A. collicola n.sp. and Aulacotheca sp., are recognized. Synangia of A. collicola are 11–17 × 2.5 – 4.0 mm and have four to six sporangia. Free sporangial tips are acutely pointed and dehiscence is through a longitudinal slit to the inside of the synangium. Prepollen averages 181 × 129 μm and has a monolete suture with median deflection. Sexine on proximal and distal surfaces shows narrow, closely spaced, anastomosing inpockets; distal and lateral walls are separated by a deep, encircling fold. Synangia of Aulacotheca sp. are 21–33 × 3.8 – 5.5 mm and have 4–6 sporangia. Distally, free sporangial tips have a narrow extension, giving a mucronate appearance. Features of these species suggest that greater morphological diversity in synangial and pollen structure occurs in Aulacotheca and the medullosan pteridosperms than previously recognized. 相似文献