全文获取类型
收费全文 | 2680篇 |
免费 | 370篇 |
国内免费 | 2篇 |
专业分类
3052篇 |
出版年
2022年 | 27篇 |
2021年 | 37篇 |
2019年 | 23篇 |
2018年 | 27篇 |
2017年 | 32篇 |
2016年 | 50篇 |
2015年 | 87篇 |
2014年 | 90篇 |
2013年 | 113篇 |
2012年 | 127篇 |
2011年 | 129篇 |
2010年 | 84篇 |
2009年 | 81篇 |
2008年 | 117篇 |
2007年 | 109篇 |
2006年 | 92篇 |
2005年 | 103篇 |
2004年 | 103篇 |
2003年 | 109篇 |
2002年 | 101篇 |
2001年 | 80篇 |
2000年 | 96篇 |
1999年 | 71篇 |
1998年 | 47篇 |
1997年 | 51篇 |
1996年 | 40篇 |
1995年 | 37篇 |
1994年 | 22篇 |
1993年 | 39篇 |
1992年 | 55篇 |
1991年 | 46篇 |
1990年 | 42篇 |
1989年 | 55篇 |
1988年 | 30篇 |
1987年 | 26篇 |
1986年 | 37篇 |
1985年 | 37篇 |
1984年 | 51篇 |
1983年 | 27篇 |
1982年 | 31篇 |
1981年 | 26篇 |
1980年 | 32篇 |
1979年 | 28篇 |
1977年 | 36篇 |
1976年 | 23篇 |
1975年 | 23篇 |
1974年 | 24篇 |
1973年 | 27篇 |
1972年 | 26篇 |
1970年 | 31篇 |
排序方式: 共有3052条查询结果,搜索用时 15 毫秒
61.
Assembly of vaccinia virus: effects of rifampin on the intracellular distribution of viral protein p65. 总被引:21,自引:19,他引:2
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)
The cytoplasmic assembly of vaccinia virus is reversibly blocked by the antibiotic rifampin, leading to the accumulation of partially membrane-delineated rifampin bodies in infected cells. Rifampin-resistant vaccinia virus mutants have point mutations in the D13L gene, which is controlled by a late promoter and expresses a 65-kDa protein, designated p65. To further characterize the mechanism of rifampin inhibition and the function of p65 in virus assembly, we raised antibodies to this protein. Immunoreactive p65 was expressed at late times of infection, and neither its expression nor its turnover was affected by rifampin. Virus-associated p65 could be extracted only with denaturing detergents from purified virions, suggesting that it is an integral viral component. Immunofluorescence studies showed that p65 is localized to the sites of virus assembly. Also, immunoelectron microscopy showed p65 to be associated with viral crescents as well as spherical, immature virions, in both cases predominantly on the inner or concave surface. In the presence of rifampin, p65 was found in large, cytoplasmic inclusion bodies that were distinct from rifampin bodies. The rifampin bodies themselves were labeled with p65 antibodies only after reversal of the rifampin block, predominantly on the viral crescents which rapidly formed following removal of the drug. We propose that p65 functions as an internal scaffold in the formation of viral crescents and immature virions, analogously to the matrix proteins of other viruses. 相似文献
62.
The decline and disappearance of Littorella uniflora from oligotrophic waters which have become eutrophic has been associated with shading or reduced CO2 supply. However NO
inf3
sup–
concentrations can reach very high levels (100–2000 mmol m–3 compared with <1–3 in oligotrophic habitats). To investigate the impact of NO
inf3
sup–
loading alone, plants were grown under three NO
inf3
sup–
regimes (very low, near-natural and high). The interactive effects of NO
inf3
sup–
and photon flux density (low and high regimes) on N assimilation and accumulation, CO2 concentrating mechanisms, C3 photosynthesis and growth were also examined. The results were unexpected. Increased NO
inf3
sup–
supply had very little effect on photosynthetic capacity, crassulacean acid metabolism (CAM) or lacunal CO2 concentrations ([CO2]i), although there was considerable plasticity with respect to light regime. In contrast, increased NO
inf3
sup–
supply resulted in a marked accumulation of NO
inf3
sup–
, free amino acids and soluble protein in shoots and roots (up to 25 mol m–3, 30 mol m–3 and 9 mg g–1 fresh weight respectively in roots), while fresh weight and relative growth rate were reduced. Total N content even under the very low NO
inf3
sup–
regime (1.6–2.3%) was mid-range for aquatic and terrestrial species (and 3.1–4.3% under the high NO
inf3
sup–
regime). These findings, together with field data, suggest that L. uniflora is not growth limited by low NO
inf3
sup–
supply in natural oligotophic habitats, due not to an efficient photosynthetic nitrogen use but to a slow growth rate, a low N requirement and to the use of storage to avoid N stress. However the increased NO
inf3
sup–
concentrations in eutrophic environments seem likely have detrimental effects on the long-term survival of L. uniflora, possibly as a consequence of N accumulation. 相似文献
63.
B. S. Griffiths 《Plant and Soil》1994,164(1):25-33
Food web studies from a range of ecosystems have demonstrated that the fauna contributes about 30% of total net nitrogen mineralization.
This results mainly from the activities of microbial-feeding microfauna (nematodes and protozoa). Microbial and microfaunal
activity is concentrated at spatially discrete and heterogeneously distributed organic substrates, including the rhizosphere.
The dynamics of microfauna and their effect on nutrient cycling and microbial processes at these sites is reviewed. The potential
manipulation of microfauna, either as an experimental tool to further understand soil microbial ecology or as a practical
means of managing nutrient flows in agroecosystems, is discussed. 相似文献
64.
Artificial destratification of a small tropical reservoir: effects upon the phytoplankton 总被引:3,自引:3,他引:0
Seasonal changes in the phytoplankton community of a small tropical reservoir were monitored over a four year period comprising
of an initial two seasonal cycles during which the water column stratified strongly for extended periods each year, and two
further seasonal cycles after installation of a mechanical aeration system to induce artificial destratification.
In the unmanaged reservoir, the concentration of chlorophyll a at 0.5 m reached maximum values (on one occasion > 90 mg m−3) when the water column was stratified and the epilimnion was very shallow (ca 2 m depth). The hypolimnion at this time was anoxic (less than 2% oxygen saturation) and had a high concentration of bacteriochlorophyll
(100–200 mg m−3).
The phytoplankton community of the unmanaged reservoir was generally dominated by cyanobacteria (Cylindrospermopsis raciborskii, Anabaena tenericaulis) during the warmer months of the year (November–March) (but replaced by chlorophyta, dinophyceae and euglenophyceae after
periods of intense rain) and by bacillariophyceae (Synedra ulna var. chaseana, S. tenera) during the cooler, dry months.
In the artificially destratified reservoir (8 h aeration day−1), the phytoplankton community was largely dominated by diatoms except after depletion of the silica content of the water
column which caused diatoms to be replaced by cyanobacteria (dominated by A. tenericaulis) and a range of chlorophytes.
The changing pattern of stratification and circulation of the water column in the unmanaged reservoir caused repeated disruption
of the established phytoplankton assemblage with peaks of high biomass associated with transient cyanobacterial blooms. Continuous
aeration and the consequent increase in the ratio mixed: euphotic depth provided conditions suitable for dominance of the
phytoplankton by diatoms, as long as silica was available, and resulted in average chlorophyll levels higher than in the unmanaged
reservoir (120 ± 10 v. 64 ± 9 mg m−2).
Hierarchical fusion analysis based on the biomass of species differentiated the phytoplankton samples into cluster groups
that could be related primarily to stratification or mixing of the water column. 相似文献
65.
Enzymological and mutational analysis of a complex primary hyperoxaluria type 1 phenotype involving alanine:Glyoxylate aminotransferase peroxisome-to-mitochondrion mistargeting and intraperoxisomal aggregation 总被引:6,自引:1,他引:5
下载免费PDF全文
![点击此处可从《American journal of human genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
C. J. Danpure P. E. Purdue P. Fryer S. Griffiths J. Allsop M. J. Lumb K. M. Guttridge P. R. Jennings J. I. Scheinman S. M. Mauer N. O. Davidson 《American journal of human genetics》1993,53(2):417-432
Primary hyperoxaluria type 1 (PH1) is a rare autosomal recessive disease caused by a deficiency of the liver-specific peroxisomal enzyme alanine:glyoxylate aminotransferase (AGT). Three unrelated PH1 patients, who possess a novel complex phenotype, are described. At the enzymological level, this phenotype is characterized by a complete, or nearly complete, absence of AGT catalytic activity and reduced AGT immunoreactivity. Unlike normal individuals in whom the AGT is confined to the peroxisomal matrix, the immunoreactive AGT in these three patients was distributed approximately equally between the peroxisomes and mitochondria. The peroxisomal AGT appeared to be aggregated into amorphous core-like structures in which no other peroxisomal enzymes could be identified. Mutational analysis of the AGT gene showed that two of the three patients were compound heterozygotes for two previously unrecognized point mutations which caused Gly41→Arg and Phe152→Iso amino acid substitutions. The third patient was shown to be a compound heterozygote for the Gly41→Arg mutation and a previously recognized Gly170→Arg mutation. All three patients were homozygous for the Pro11→Leu polymorphism that had been found previously with a high allelic frequency in normal populations. It is suggested that the Phe152→Iso and Gly170→Arg substitutions, which are only eighteen residues apart and located in the same highly conserved internal region of 58 amino acids, might be involved in the inhibition of peroxisomal targeting and/or import of AGT and, in combination with the Pro11→Leu polymorphism, be responsible for its aberrant mitochondrial compartmentalization. On the other hand, the Gly41→Arg substitution, either in combination with the Pro11→Leu polymorphism or by itself, is predicted to be responsible for the intraperoxisomal aggregation of the AGT protein. 相似文献
66.
We have discovered that, in certain crosses of natural isolates of Neurospora intermedia, linear and circular mitochondrial plasmids of the maternal parent are not transmitted to the progeny. This contrasts with the maternal transmission of organellar genetic elements generally observed in crosses between laboratory strains and between other natural isolates. Formally, failure of plasmid transmission is a type of plasmid suppression. The present cases represent the first report of plasmid suppressors in natural populations of fungi. Strains used as female parents can transmit or not transmit plasmids depending on the strain used as male parent. Males that act to suppress in one cross fail to suppress in others. Therefore, the suppression of plasmids depends on a strain-specific interaction and is not determined exclusively by the males. Since suppression is a specific interaction we inferred that it must be genetically based and tested this hypothesis by seeking segregation of suppressed and nonsuppressed phenotypes in octads. Segregation of the original full suppression of all plasmids was indeed observed in each of the three sets of testcrosses examined. The interaction type of suppression must be initiated in ascogenous tissue during the sexual cycle. It is a nonautonomous type of suppression, affecting all descendent cells. In any one case of suppression, either one, several, or all plasmids can be lost. Both linear and circular plasmids can be eliminated by the same suppressor genotype. In addition, several strains were found to contain suppressors that act after ascospore delineation. This autonomous type of suppression has been observed previously in laboratory strains, but not in natural isolates. All the cases of plasmid suppression identified in this study involved a range of apparently neutral circular and linear plasmids. Using one senescent Kalilo strain of N. intermedia, we did not detect any case of suppression of the senescence-determining linear plasmid kalDNA. 相似文献
67.
Polyphenols histochemically detected in fresh uninfected roots of Quercus, Castanopsis and Lithocarpus growing in Hong Kong and shown to be condensed tannins were found mainly as intracellular material in the cells of the root cap, the epidermal layer and the endodermis. The cell walls of the outer cortex and the endodermis also contained suberin. Following invasion by compatible ectomycorrhizal symbionts, condensed tannins disappeared from cells of the root cap and the epidermal layer but hyphae were prevented from colonizing the cortex presumably due to suberin barriers. In vitro experiments indicated that a number of broad-host ectomycorrhizal fungi could utilise various polyphenolic compounds, including tannins found in the root exudates of the host trees, with different degrees of efficiency. 相似文献
68.
To be able to understand cellular mechanisms, we require fully integrated data sets combining information about gene expression, protein expression, post-translational modification states, sub-cellular location and complex formation. Proteomics is a very powerful technique that can be applied to interrogate changes at the protein level. Studying this effectively requires specialised facilities within research institutes. Here, we describe the setting up and operation of such a facility, providing a resource for the Arabidopsis and Drosophila research communities. 相似文献
69.
70.
Griffiths GM 《Trends in cell biology》1996,6(9):329-332
The secretory granules o f cells derived from the haemopoietic lineage are 'secretory lysosomes' containing both lysosomal hydrolases and secretory proteins. Studies on cytotoxic T lymphocytes (CTLs) have elucidated several of the mechanisms that regulate protein sorting to, and secretion from, this unusual secretory organelle. In particular, recent findings from a CTL mutant have led to the hypothesis that CTLs, and other cells of the haemopoietic lineage, use specialized sorting and secretory mechanisms in which the lysosome functions as a regulated secretory granule. 相似文献