全文获取类型
收费全文 | 466篇 |
免费 | 42篇 |
专业分类
508篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 12篇 |
2021年 | 12篇 |
2020年 | 6篇 |
2019年 | 7篇 |
2018年 | 12篇 |
2017年 | 10篇 |
2016年 | 11篇 |
2015年 | 32篇 |
2014年 | 23篇 |
2013年 | 31篇 |
2012年 | 49篇 |
2011年 | 32篇 |
2010年 | 28篇 |
2009年 | 25篇 |
2008年 | 32篇 |
2007年 | 21篇 |
2006年 | 18篇 |
2005年 | 21篇 |
2004年 | 12篇 |
2003年 | 18篇 |
2002年 | 11篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 16篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 5篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1969年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有508条查询结果,搜索用时 15 毫秒
1.
Antti Hervonen Lasse Kanerva Anja H. Tissari Birgit V. A. Suurhasko 《Cell and tissue research》1974,148(4):535-550
Summary The ultrastructure and protein content of the five subfractions of the crude mitochondrial fraction from the brain stem of the 1-day old and adult rat was examined. The morphological composition of the subfractions after fixation in glutaraldehyde and osmiumtetroxide in the adult rat brain stem resembled that previously reported for the whole brain; synaptosomes sedimented in a sucrose gradient in subfractions C and D. In the 1-day old rat, mature synaptosomes were found in subfractions A, B, C and D; E contained mainly free mitochondria. 80–95% of the processes in the adult and 10–30% in the 1-day old rat contained synaptic vesicles which were of four types: (1) small agranular vesicles (2) large dense core vesicles (3) large agranular vesicles (4) coated vesicles. Pre- and postsynaptic membrane thickenings were demonstrated in many nerve-ending particles. In the subfractions of the 1-day old rat the protein content was one half and the distribution resembled that in the adult. Evidently nerve endings develop faster in the brain stem than in cortical areas; a serotoninor adrenergic origin of the early synaptosomes is suggested.This study was supported by a grant from the Paulo Foundation. 相似文献
2.
3.
Bacterial Oxidation of Sulfide Minerals in Column Leaching Experiments at Suboptimal Temperatures 总被引:4,自引:2,他引:2
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 purpose of the work was to quantitatively characterize temperature effects on the bacterial leaching of sulfide ore material containing several sulfide minerals. The leaching was tested at eight different temperatures in the range of 4 to 37°C. The experimental technique was based on column leaching of a coarsely ground (particle diameter, 0.59 to 5 mm) ore sample. The experimental data were used for kinetic analysis of chalcopyrite, sphalerite, and pyrrhotite oxidation. Chalcopyrite yielded the highest (73 kJ/mol) and pyrrhotite yielded the lowest (25 kJ/mol) activation energies. Especially with pyrrhotite, diffusion contributed to rate limitation. Arrhenius plots were also linear for the reciprocals of lag periods and for increases of redox potentials (dmV/dt). Mass balance analysis based on total S in leach residue was in agreement with the highest rate of leaching at 37 and 28°C. The presence of elemental S in leach residues was attributed to pyrrhotite oxidation. 相似文献
4.
Involvement of Escherichia coli DNA polymerase II in response to oxidative damage and adaptive mutation. 总被引:10,自引:1,他引:9
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)
M Escarceller J Hicks G Gudmundsson G Trump D Touati S Lovett P L Foster K McEntee M F Goodman 《Journal of bacteriology》1994,176(20):6221-6228
DNA polymerase II (Pol II) is regulated as part of the SOS response to DNA damage in Escherichia coli. We examined the participation of Pol II in the response to oxidative damage, adaptive mutation, and recombination. Cells lacking Pol II activity (polB delta 1 mutants) exhibited 5- to 10-fold-greater sensitivity to mode 1 killing by H2O2 compared with isogenic polB+ cells. Survival decreased by about 15-fold when polB mutants containing defective superoxide dismutase genes, sodA and sodB, were compared with polB+ sodA sodB mutants. Resistance to peroxide killing was restored following P1 transduction of polB cells to polB+ or by conjugation of polB cells with an F' plasmid carrying a copy of polB+. The rate at which Lac+ mutations arose in Lac- cells subjected to selection for lactose utilization, a phenomenon known as adaptive mutation, was increased threefold in polB backgrounds and returned to wild-type rates when polB cells were transduced to polB+. Following multiple passages of polB cells or prolonged starvation, a progressive loss of sensitivity to killing by peroxide was observed, suggesting that second-site suppressor mutations may be occurring with relatively high frequencies. The presence of suppressor mutations may account for the apparent lack of a mutant phenotype in earlier studies. A well-established polB strain, a dinA Mu d(Apr lac) fusion (GW1010), exhibited wild-type (Pol II+) sensitivity to killing by peroxide, consistent with the accumulation of second-site suppressor mutations. A high titer anti-Pol II polyclonal antibody was used to screen for the presence of Pol II in other bacteria and in the yeast Saccharomyces cerevisiae. Cross-reacting material was found in all gram-negative strains tested but was not detected in gram-positive strains or in S. cerevisiae. Induction of Pol II by nalidixic acid was observed in E. coli K-12, B, and C, in Shigella flexneri, and in Salmonella typhimurium. 相似文献
5.
Lasse T. Keetz Eva Lieungh Kaveh Karimi-Asli Sonya R. Geange Emiliano Gelati Hui Tang Yeliz A. Yilmaz Kjetil S. Aas Inge H. J. Althuizen Anders Bryn Stefanie Falk Rosie Fisher Anne Fouilloux Peter Horvath Sunniva Indrehus Hanna Lee Danica Lombardozzi Frans-Jan W. Parmentier Norbert Pirk Vigdis Vandvik Ane V. Vollsnes Olav Skarpaas Frode Stordal Lena M. Tallaksen 《Global Change Biology》2023,29(15):4440-4452
Dynamic Global Vegetation Models (DGVMs) provide a state-of-the-art process-based approach to study the complex interplay between vegetation and its physical environment. For example, they help to predict how terrestrial plants interact with climate, soils, disturbance and competition for resources. We argue that there is untapped potential for the use of DGVMs in ecological and ecophysiological research. One fundamental barrier to realize this potential is that many researchers with relevant expertize (ecology, plant physiology, soil science, etc.) lack access to the technical resources or awareness of the research potential of DGVMs. Here we present the Land Sites Platform (LSP): new software that facilitates single-site simulations with the Functionally Assembled Terrestrial Ecosystem Simulator, an advanced DGVM coupled with the Community Land Model. The LSP includes a Graphical User Interface and an Application Programming Interface, which improve the user experience and lower the technical thresholds for installing these model architectures and setting up model experiments. The software is distributed via version-controlled containers; researchers and students can run simulations directly on their personal computers or servers, with relatively low hardware requirements, and on different operating systems. Version 1.0 of the LSP supports site-level simulations. We provide input data for 20 established geo-ecological observation sites in Norway and workflows to add generic sites from public global datasets. The LSP makes standard model experiments with default data easily achievable (e.g., for educational or introductory purposes) while retaining flexibility for more advanced scientific uses. We further provide tools to visualize the model input and output, including simple examples to relate predictions to local observations. The LSP improves access to land surface and DGVM modelling as a building block of community cyberinfrastructure that may inspire new avenues for mechanistic ecosystem research across disciplines. 相似文献
6.
G R Thomas O Jensson G Gudmundsson L Thorsteinsson D W Cox 《American journal of human genetics》1995,56(5):1140-1146
7.
8.
To investigate the effects of acute ethanol administration on the production of proaggregatory thromboxane A2 (TxA2) and anti-aggregatory prostacyclin (PGI2), ethanol (1.5 g/kilogram body weight) was given to eight healthy nonsmoking men, and the stable metabolites thromboxane B2 (TxB2) and 6-keto-prostaglandin F1α (6-keto-PGF1α), respectively, measured by radioimmunoassay from serial blood samples before drinking and during the ensuing 18 hours. Each subject was studied as his own control on another occasion when only an equivalent volume of water was given. Serum TxB2 level decreased (p < 0.01) from 206 + 31 ng/ml (mean) ± S.E. to 1672 ± 24 and 161 ± 23 ng/ml (two and four hours after beginning of the drinking, respectively) concomitantly with the attainment of maximal blood ethanol concentrations (about 120 mg/100 ml), whereas no changes occurred in plasma 6-keto-PGF1α concentrations. Our results may provide an explanation for known effects of ethanol on platelet aggregation. They also raise speculation whether TxA2-inhibition and the antiatherogenic effect of alcohol intake are somehow related. 相似文献
9.
Lasse Ryhänen Elaine M.L. Tan Sirpa Rantala-Ryhänen Jouni Uitto 《Archives of biochemistry and biophysics》1982,215(1):230-236
Chick embryo sterna, which actively synthesize type II procollagen, were pulse-labeled with radioactive proline; protein synthesis was then inhibited by unlabeled proline and cycloheximide. After the inhibition of protein synthesis, several amino acids, polyamines, or structurally related compounds were added to the incubation medium. The conversion of procollagen, first to two intermediates, pC-collagen and pN-collagen, and then to collagen, was monitored by sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis. The addition of 50 mm β-alanine, arginine, asparagine, glutamine, hydroxylysine, lysine, or ornithine, as well as agmatine, ?-aminocaproic acid, S-2-aminoethylcysteine, cadaverine, canavanine, putrescine, or spermine clearly inhibited the removal of the carboxy-terminal extension and pC-collagen accumulated; the removal of the amino-terminal extension was not affected. The inhibition of the conversion was reversible and unaffected by fetal calf serum. The results suggest that the conversion of type II procollagen to collagen requires at least two separate proteinases for the removal of amino-terminal and carboxy-terminal extensions. The results further suggest that naturally occurring molecules may be used to modulate the rate of conversion of procollagen to collagen, and development of analogs of these compounds may provide the means to interfere with excessive deposition of collagen in diseases with tissue fibrosis. 相似文献
10.
A highly repetitive DNA element, homologous to the mariner transposon of Drosophila mauritiana was found in the intron of the gene for cecropin A, an antibacterial peptide from the Cecropia moth. The mariner-like elements (MLE) represent a homogeneous population with a copy number of about 1000/genome. Sequencing analysis showed it to be 1255 base pairs long, including 38-base pair terminal inverted repeats. The MLE contains a defective reading frame. Nevertheless, the putative product is clearly homologous to the predicted translation product encoded by mariner. In consonance is also the fact that the inverted repeats are highly conserved between the two elements and that the overall DNA homology is 48%. Since the mariner element is present in several Drosophila species closely related to Drosophila melanogaster and since MLE is present in the lepidopteran Cecropia, a route of horizontal transfer is indicated rather than vertical transmission from a common ancestor. This suggests the possible use of mariner for the construction of an interspecies vector. 相似文献