全文获取类型
收费全文 | 1697篇 |
免费 | 61篇 |
国内免费 | 1篇 |
出版年
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 11篇 |
2020年 | 11篇 |
2019年 | 15篇 |
2018年 | 22篇 |
2017年 | 17篇 |
2016年 | 43篇 |
2015年 | 69篇 |
2014年 | 60篇 |
2013年 | 102篇 |
2012年 | 88篇 |
2011年 | 122篇 |
2010年 | 70篇 |
2009年 | 56篇 |
2008年 | 100篇 |
2007年 | 114篇 |
2006年 | 115篇 |
2005年 | 97篇 |
2004年 | 80篇 |
2003年 | 113篇 |
2002年 | 91篇 |
2001年 | 13篇 |
2000年 | 14篇 |
1999年 | 20篇 |
1998年 | 23篇 |
1997年 | 11篇 |
1996年 | 13篇 |
1995年 | 21篇 |
1994年 | 17篇 |
1993年 | 13篇 |
1992年 | 15篇 |
1991年 | 19篇 |
1990年 | 15篇 |
1989年 | 12篇 |
1988年 | 5篇 |
1987年 | 10篇 |
1986年 | 14篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1965年 | 3篇 |
排序方式: 共有1759条查询结果,搜索用时 15 毫秒
991.
Using minced horseradish roots and peroxides for the deodorization of swine manure: a pilot scale study 总被引:1,自引:0,他引:1
Govere EM Tonegawa M Bruns MA Wheeler EF Kephart KB Voigt JW Dec J 《Bioresource technology》2007,98(6):1191-1198
Enzymes that have proven to be capable of removing toxic compounds from water and soil may also be useful in the deodorization of animal manures. Considering that pork production in the US is a $40-billion industry with over half a million workers, odor control to protect air quality in the neighboring communities must be considered an essential part of managing livestock facilities. This pilot scale (20-120 L) study tested the use of minced horseradish (Armoracia rusticana L.) roots (1:10 roots to swine slurry ratio), with calcium peroxide (CaO(2) at 34 mM) or hydrogen peroxide (H(2)O(2) at 68 mM), to deodorize swine slurry taken from a 40,000-gallon storage pit at the Pennsylvania State University's Swine Center. Horseradish is known to contain large amounts of peroxidase, an enzyme that, in the presence of peroxides, can polymerize phenolic odorants and thus reduce the malodor. Twelve compounds commonly associated with malodor (seven volatile fatty acids or VFAs, three phenolic compounds and two indolic compounds) were used as odor indicators. Their concentration in swine slurry before and after treatment was determined by gas chromatography (GC) to assess the deodorization effect. The pilot scale testing demonstrated a complete removal of phenolic odorants (with a detection limit of 0.5 mg L(-1)) from the swine slurry, which was consistent with our previous laboratory experiments using 30-mL swine slurry samples. Horseradish could be recycled (reused) five times while retaining significant reduction in the concentration of phenolic odorants. In view of these findings, inexpensive plant materials, such as horseradish, represent a promising tool for eliminating phenolic odorants from swine slurry. 相似文献
992.
MOTIVATION: Inferring species phylogenies with a history of gene losses and duplications is a challenging and an important task in computational biology. This problem can be solved by duplication-loss models in which the primary step is to reconcile a rooted gene tree with a rooted species tree. Most modern methods of phylogenetic reconstruction (from sequences) produce unrooted gene trees. This limitation leads to the problem of transforming unrooted gene tree into a rooted tree, and then reconciling rooted trees. The main questions are 'What about biological interpretation of choosing rooting?', 'Can we find efficiently the optimal rootings?', 'Is the optimal rooting unique?'. RESULTS: In this paper we present a model of reconciling unrooted gene tree with a rooted species tree, which is based on a concept of choosing rooting which has minimal reconciliation cost. Our analysis leads to the surprising property that all the minimal rootings have identical distributions of gene duplications and gene losses in the species tree. It implies, in our opinion, that the concept of an optimal rooting is very robust, and thus biologically meaningful. Also, it has nice computational properties. We present a linear time and space algorithm for computing optimal rooting(s). This algorithm was used in two different ways to reconstruct the optimal species phylogeny of five known yeast genomes from approximately 4700 gene trees. Moreover, we determined locations (history) of all gene duplications and gene losses in the final species tree. It is interesting to notice that the top five species trees are the same for both methods. AVAILABILITY: Software and documentation are freely available from http://bioputer.mimuw.edu.pl/~gorecki/urec 相似文献
993.
Role of histone and DNA methylation in gene regulation 总被引:3,自引:0,他引:3
994.
Kobiela J Stefaniak T Krajewski J Kalinska-Blach B Zurawa-Janicka D Lachinski A Gackowski D Olinski R Nowak J Knap N Lipinska B Sledzinski Z Wozniak M 《Acta biochimica Polonica》2007,54(2):289-295
The objective of this study was to assess the dynamics of oxidative damage to cellular macromolecules such as proteins, lipids and DNA under conditions of oxidative stress triggering early stages of estrogen-dependent carcinogenesis. A rodent model of carcinogenesis was used. Syrian hamsters were sacrificed after 1, 3, 5 h and one month from the initial implantation of estradiol. Matching control groups were used. Kidneys as target organs for estradiol-mediated oxidative stress were excised and homogenized for biochemical assays. Subcellular fractions were isolated. Carbonyl groups (as a marker of protein oxidation) and lipid hydroxyperoxides were assessed. DNA was isolated and 8-oxodGuo was assessed. Electron paramagnetic resonance spectroscopy was used to confirm the results for lipid peroxidation. Exposition to estradiol in the rodent model leads to damage of macromolecules of the cell, including proteins and DNA, but not lipids. Proteins appear to be the primary target of the damage but are closely followed by DNA. It has previously been speculated that protein peroxides can increase DNA modifications. This time sequence was observed in our study. Nevertheless, the direct relation between protein and DNA damage still remains unsolved. 相似文献
995.
Robert V. Considine Mark R. Nyce Jerzy W. Kolaczynski Pei Li Zhang Joanna P. Ohannesian John H. Moore James W. Fox Jos F. Caro 《Journal of cellular biochemistry》1997,65(2):254-258
In the present study we have examined the effect of dexamethasone on ob gene mRNA expression and leptin release from isolated human subcutaneous adipocytes. Dexamethasone stimulated leptin release from cultured adipocytes in a time- and dose-dependent manner. A two-fold increase in leptin release was detectable by 36 h of treatment with 10−7 M dexamethasone. Leptin release was preceded by a significant 83±30% increase in ob mRNA after 24 h exposure to the compound. Co-incubation of cells with dexamethasone (107 M) and insulin (10−7 or 10−9 M) completely blocked the dexamethasone-stimulated increase in ob mRNA and leptin release. These data demonstrate that insulin and glucocorticoids regulate leptin synthesis and release from human adipocytes in vitro. J. Cell. Biochem. 65:254–258. © 1997 Wiley-Liss, Inc. 相似文献
996.
In angiosperms, growth of the root apex is determined by the quiescent centre. All tissues of the root proper and the root cap are derived from initial cells that surround this zone. The diversity of cell lineages originated from these initials suggests an interesting variation of the displacement velocity within the root apex. However, little is known about this variation, especially in the most apical region including the root cap. This paper shows a method of determination of velocity field for this region taking the Arabidopsis root apex as example. Assuming the symplastic growth without a rotation around the root axis, the method combines mathematical modelling and two types of empirical data: the published velocity profile along the root axis above the quiescent centre, and dimensions of cell packet originated from the initials of epidermis and lateral root cap. The velocities, calculated for points of the axial section, vary in length and direction. Their length increases with distance from the quiescent centre, in the root cap at least twice slower than in the root proper, if points at similar distance from the quiescent centre are compared. The vector orientation depends on the position of a calculation point, the widest range of angular changes, reaching almost 90°, in the lateral root cap. It is demonstrated how the velocity field is related to both distribution of growth rates and growth-resulted deformation of the cell wall system. Also changes in the field due to cell pattern asymmetry and differences in slope of the velocity profile are modelled. 相似文献
997.
998.
Csaba I. Nagy Imre Vass Gábor Rákhely István Zoltán Vass András Tóth ágnes Duzs Loredana Peca Jerzy Kruk Péter B. Kós 《Journal of bacteriology》2014,196(19):3430-3440
Although the biogeochemistry of the two environmentally hazardous compounds arsenic and sulfide has been extensively investigated, the biological interference of these two toxic but potentially energy-rich compounds has only been hypothesized and indirectly proven. Here we provide direct evidence for the first time that in the photosynthetic model organism Synechocystis sp. strain PCC6803 the two metabolic pathways are linked by coregulated genes that are involved in arsenic transport, sulfide oxidation, and probably in sulfide-based alternative photosynthesis. Although Synechocystis sp. strain PCC6803 is an obligate photoautotrophic cyanobacterium that grows via oxygenic photosynthesis, we discovered that specific genes are activated in the presence of sulfide or arsenite to exploit the energy potentials of these chemicals. These genes form an operon that we termed suoRSCT, located on a transposable element of type IS4 on the plasmid pSYSM of the cyanobacterium. suoS (sll5036) encodes a light-dependent, type I sulfide:quinone oxidoreductase. The suoR (sll5035) gene downstream of suoS encodes a regulatory protein that belongs to the ArsR-type repressors that are normally involved in arsenic resistance. We found that this repressor has dual specificity, resulting in 200-fold induction of the operon upon either arsenite or sulfide exposure. The suoT gene encodes a transmembrane protein similar to chromate transporters but in fact functioning as an arsenite importer at permissive concentrations. We propose that the proteins encoded by the suoRSCT operon might have played an important role under anaerobic, reducing conditions on primordial Earth and that the operon was acquired by the cyanobacterium via horizontal gene transfer. 相似文献
999.
Christian Gieger Ludwig Geistlinger Elisabeth Altmaier Martin Hrabé de Angelis Florian Kronenberg Thomas Meitinger Hans-Werner Mewes H.-Erich Wichmann Klaus M. Weinberger Jerzy Adamski Thomas Illig Karsten Suhre 《PLoS genetics》2008,4(11)
The rapidly evolving field of metabolomics aims at a comprehensive measurement of ideally all endogenous metabolites in a cell or body fluid. It thereby provides a functional readout of the physiological state of the human body. Genetic variants that associate with changes in the homeostasis of key lipids, carbohydrates, or amino acids are not only expected to display much larger effect sizes due to their direct involvement in metabolite conversion modification, but should also provide access to the biochemical context of such variations, in particular when enzyme coding genes are concerned. To test this hypothesis, we conducted what is, to the best of our knowledge, the first GWA study with metabolomics based on the quantitative measurement of 363 metabolites in serum of 284 male participants of the KORA study. We found associations of frequent single nucleotide polymorphisms (SNPs) with considerable differences in the metabolic homeostasis of the human body, explaining up to 12% of the observed variance. Using ratios of certain metabolite concentrations as a proxy for enzymatic activity, up to 28% of the variance can be explained (p-values 10−16 to 10−21). We identified four genetic variants in genes coding for enzymes (FADS1, LIPC, SCAD, MCAD) where the corresponding metabolic phenotype (metabotype) clearly matches the biochemical pathways in which these enzymes are active. Our results suggest that common genetic polymorphisms induce major differentiations in the metabolic make-up of the human population. This may lead to a novel approach to personalized health care based on a combination of genotyping and metabolic characterization. These genetically determined metabotypes may subscribe the risk for a certain medical phenotype, the response to a given drug treatment, or the reaction to a nutritional intervention or environmental challenge. 相似文献