全文获取类型
收费全文 | 6755篇 |
免费 | 618篇 |
国内免费 | 3篇 |
出版年
2023年 | 30篇 |
2022年 | 64篇 |
2021年 | 163篇 |
2020年 | 74篇 |
2019年 | 123篇 |
2018年 | 140篇 |
2017年 | 114篇 |
2016年 | 197篇 |
2015年 | 347篇 |
2014年 | 440篇 |
2013年 | 536篇 |
2012年 | 584篇 |
2011年 | 574篇 |
2010年 | 365篇 |
2009年 | 342篇 |
2008年 | 446篇 |
2007年 | 433篇 |
2006年 | 423篇 |
2005年 | 386篇 |
2004年 | 348篇 |
2003年 | 317篇 |
2002年 | 308篇 |
2001年 | 44篇 |
2000年 | 53篇 |
1999年 | 71篇 |
1998年 | 64篇 |
1997年 | 43篇 |
1996年 | 35篇 |
1995年 | 36篇 |
1994年 | 30篇 |
1993年 | 29篇 |
1992年 | 24篇 |
1991年 | 16篇 |
1990年 | 17篇 |
1989年 | 20篇 |
1988年 | 10篇 |
1987年 | 21篇 |
1986年 | 16篇 |
1985年 | 10篇 |
1983年 | 12篇 |
1981年 | 3篇 |
1980年 | 13篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1972年 | 3篇 |
1965年 | 2篇 |
排序方式: 共有7376条查询结果,搜索用时 31 毫秒
991.
Foley S Stolarczyk E Mouni F Brassart C Vidal O Aïssi E Bouquelet S Krzewinski F 《Archives of microbiology》2008,189(2):157-167
Bifidobacterium bifidum, in contrast to other bifidobacterial species, is auxotrophic for N-acetylglucosamine. Growth experiments revealed assimilation of radiolabelled N-acetylglucosamine in bacterial cell walls and in acetate, an end-product of central metabolism via the bifidobacterial d-fructose-6-phosphate shunt. While supplementation with fructose led to reduced N-acetylglucosamine assimilation via the d-fructose-6-phosphate shunt, no significant difference was observed in levels of radiolabelled N-acetylglucosamine incorporated into cell walls. Considering the central role played by glutamine fructose-6-phosphate transaminase
(GlmS) in linking the biosynthetic pathway for N-acetylglucosamine to hexose metabolism, the GlmS of Bifidobacterium was characterized. The genes encoding the putative GlmS of B. longum DSM20219 and B. bifidum DSM20082 were cloned and sequenced. Bioinformatic analyses of the predicted proteins revealed 43% amino acid identity with
the Escherichia coli GlmS, with conservation of key amino acids in the catalytic domain. The B. longum GlmS was over-produced as a histidine-tagged fusion protein. The purified C-terminal His-tagged GlmS possessed glutamine
fructose-6-phosphate amidotransferase activity as demonstrated by synthesis of glucosamine-6-phosphate from fructose-6-phosphate
and glutamine. It also possesses an independent glutaminase activity, converting glutamine to glutamate in the absence of
fructose-6-phosphate. This is of interest considering the apparently reduced coding potential in bifidobacteria for enzymes
associated with glutamine metabolism.
S. Foley and E. Stolarczyk contributed equally to this work 相似文献
992.
Olivier Monteuuis Sylvie Doulbeau Jean-Luc Verdeil 《Trees - Structure and Function》2008,22(6):779-784
A meristem-issued rejuvenated line was obtained in 1986 from a 100-year-old Sequoiadendron giganteum tree and has been since then micropropagated in tissue culture conditions maintaining its juvenile-like characteristics.
By contrast, grafts and rooted microcuttings from the same genotype planted in outdoor conditions for several years exhibited
mature foliage traits and the grafts started to produce cones, which are obvious indicators of physiological aging. These
three different clonal lines were compared with regard to global DNA methylation assessed by HPLC. The in vitro rejuvenated
line showed a much higher level of DNA methylation (23% as average value) than the two other outdoor origins from the same
clone which displayed similar degrees of global methylation (average values of 13.4% for the grafts and 13.8% for the cuttings).
Overall these DNA global methylation values obtained for the first time in S. giganteum are consistent with the level of methylation reported for many plants using the same HPLC protocols. The fact that shoots
exhibiting a juvenile-like leaf morphology can be characterized by higher DNA methylation than mature-like ones is discussed
in relation to physiological aging, referring to other studies on the same topic. 相似文献
993.
Variation in UV sensitivity among common frog Rana temporaria populations along an altitudinal gradient 总被引:1,自引:0,他引:1
Solar ultraviolet-B (UV-B) radiation can be harmful for developing amphibians. As the UV-B dose increases with altitude, it has been suggested that high-altitude populations may have an increased tolerance to high levels of UV-B radiation as compared to lowland populations. We tested this hypothesis with the common frog (Rana temporaria) by comparing populations from nine altitudes (from 333 to 2450m above sea level). Eggs collected in the field were used for laboratory experiments, i.e., exposed to high levels of artificial UV-B radiation. Eggs were reared at 14+/-2 degrees C and exposed to UV treatments until hatching. Embryonic developmental rates increased strongly and linearly with increasing altitude, suggesting a genetic capacity for faster development in highland than lowland eggs. Body length at hatching varied significantly with UV-B treatments, being lower when eggs developed under direct UV-B exposure. Body length at hatching also increased as the altitude of populations increased, but UV-B exposure times were shorter as altitude of population increased. However, the body length difference between exposed and non-exposed individuals in each population decreased as altitude of populations increased, suggesting a costly effect of UV exposure on growth. Type of UV exposure did not influence the mean rates of embryonic mortality and deformity, but both mortality and deformity rates increased as the altitude of populations increased (while UV-B exposure duration decreased). The effect of UV-B on body length at hatching, mortality, and deformities suggests that the sensitivity to UV-B varied among populations along the altitudinal gradient. These results are discussed in evolutionary terms, specifically the potential of R. temporaria high-altitude populations to develop local genetic adaptation to high levels of UV-B. 相似文献
994.
Sambou T Dinadayala P Stadthagen G Barilone N Bordat Y Constant P Levillain F Neyrolles O Gicquel B Lemassu A Daffé M Jackson M 《Molecular microbiology》2008,70(3):762-774
Mycobacterium tuberculosis and other pathogenic mycobacterial species produce large amounts of a glycogen-like alpha-glucan that represents the major polysaccharide of their outermost capsular layer. To determine the role of the surface-exposed glucan in the physiology and virulence of these bacteria, orthologues of the glg genes involved in the biosynthesis of glycogen in Escherichia coli were identified in M. tuberculosis H37Rv and inactivated by allelic replacement. Biochemical analyses of the mutants and complemented strains indicated that the synthesis of glucan and glycogen involves the alpha-1,4-glucosyltransferases Rv3032 and GlgA (Rv1212c), the ADP-glucose pyrophosphorylase GlgC (Rv1213) and the branching enzyme GlgB (Rv1326c). Disruption of glgC reduced by half the glucan and glycogen contents of M. tuberculosis, whereas the inactivation of glgA and Rv3032 affected the production of capsular glucan and glycogen, respectively. Attempts to disrupt Rv3032 in the glgA mutant were unsuccessful, suggesting that a functional copy of at least one of the two alpha-1,4-glucosyltransferases is required for growth. Importantly, the glgA mutant was impaired in its ability to persist in mice, suggesting a role for the capsular glucan in the persistence phase of infection. Unexpectedly, GlgB was found to be an essential enzyme. 相似文献
995.
The organization of the Escherichia coli chromosome has been defined genetically as consisting of four insulated macrodomains and two less constrained regions. Here we have examined the movement of chromosomal loci by tracking fluorescent markers in time-lapse microscopy during a complete cell cycle. Analysing the positioning, the segregation pattern and the motility of markers allowed us to show that the dynamic behaviour of loci belonging to various macrodomains and less constrained regions is radically different. In macrodomains constraints on mobility are apparent whereas in non-structured regions, markers exhibited a greater motility that may explain their ability to interact with flanking macrodomains. Following replication, duplicated markers belonging to macrodomains show a colocalization step and this landmark is not apparent in non-structured regions. Chromosome segregation occurs in three steps: first, the origin-proximal half of the chromosome consisting of the Ori macrodomain and the two non-structured region segregates concomitantly in a short period of time. Second, the Right and Left macrodomains segregate progressively following the genetic map. Third, the Ter macrodomain is rapidly segregated before division, after a significant period of colocalization. Macrodomain territories defined as cellular spaces occupied by the different macrodomains can be identified. 相似文献
996.
Kocher O Yesilaltay A Shen CH Zhang S Daniels K Pal R Chen J Krieger M 《Biochimica et biophysica acta》2008,1782(5):310-316
PDZK1 is a scaffold protein containing four PDZ protein interaction domains, which bind to the carboxy termini of a number of membrane transporter proteins, including ion channels (e.g., CFTR) and cell surface receptors. One of these, the HDL receptor, scavenger receptor class B type I (SR-BI), exhibits a striking, tissue-specific dependence on PDZK1 for its expression and activity. In PDZK1 knockout (KO) mice there is a marked reduction of SR-BI protein expression (approximately 95%) in the liver, but not in steroidogenic tissues or, as we show in this report, in bone marrow- or spleen-derived macrophages, or lung-derived endothelial cells. Because of hepatic SR-BI deficiency, PDZK1 KO mice exhibit dyslipidemia characterized by elevated plasma cholesterol carried in abnormally large HDL particles. Here, we show that inactivation of the PDZK1 gene promotes the development of aortic root atherosclerosis in apolipoprotein E (apoE) KO mice fed with a high fat/high cholesterol diet. However, unlike complete SR-BI-deficiency in SR-BI/apoE double KO mice, PDZK1 deficiency in PDZK1/apoE double knockout mice did not result in development of occlusive coronary artery disease or myocardial infarction, presumably because of their residual expression of SR-BI. These findings demonstrate that deficiency of an adaptor protein essential for normal expression of a lipoprotein receptor promotes atherosclerosis in a murine model. They also define PDZK1 as a member of the family of proteins that is instrumental in preventing cardiovascular disease by maintaining normal lipoprotein metabolism. 相似文献
997.
Ernkvist M Birot O Sinha I Veitonmaki N Nyström S Aase K Holmgren L 《Biochimica et biophysica acta》2008,1783(3):429-437
We have previously shown that angiomotin (Amot) plays an important role in growth factor-induced migration of endothelial cells in vitro. Genetic knock-down of Amot in zebrafish also results in inhibition of migration of intersegmental vessels in vivo. Amot is expressed as two different isoforms, p80-Amot and p130-Amot. Here we have analyzed the expression of the two Amot isoforms during retinal angiogenesis in vivo and demonstrate that p80-Amot is expressed during the migratory phase. In contrast, p130-Amot is expressed during the period of blood vessel stabilization and maturation. We also show that the N-terminal domain of p130-Amot serves as a targeting domain responsible for localization of p130-Amot to actin and tight junctions. We further show that the relative expression levels of p80-Amot and p130-Amot regulate a switch between a migratory and a non-migratory cell phenotype where the migratory function of p80-Amot is dominant over the stabilization and maturation function of p130-Amot. Our data indicates that homo-oligomerization of p80-Amot and hetero-oligomerization of both isoforms are critical for this regulation. 相似文献
998.
Legardinier S Hubert JF Le Bihan O Tascon C Rocher C Raguénès-Nicol C Bondon A Hardy S Le Rumeur E 《Biochimica et biophysica acta》2008,1784(4):672-682
Dystrophin is a muscle scaffolding protein that establishes a structural link between the cytoskeleton and the extracellular matrix. Despite the large body of knowledge about the dystrophin gene and its interactions, the functional importance of the large central rod domain remains highly controversial. It is composed of 24 spectrin-like repeats interrupted by four hinges that delineate three sub-domains. We express repeat 1-3 and repeat 20-24 sub-domains, delineated by hinges 1-2 and 3-4 and the single repeats 2 and 23. We determine their lipid-binding properties, thermal and urea stabilities and refolding velocities. By using intrinsic tryptophan fluorescence spectroscopy and size exclusion chromatography, we show that repeat 2 and the repeat 1-3 sub-domain strongly interact with anionic lipids. By contrast, repeat 23 and the repeat 20-24 sub-domain do not interact with lipids. In addition, the repeat 1-3 sub-domain and repeat 2 are dramatically less stable and refold faster than the repeat 20-24 sub-domain and repeat 23. The contrasting properties of the two sub-domains clearly indicate that they make up two units of the rod domain that are not structurally interchangeable, thus providing molecular evidence supporting the observations on the biological function of dystrophin. 相似文献
999.
Olivier Dangles Thomas Steinmann Dominique Pierre Fabrice Vannier Jérôme Casas 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2008,194(7):653-663
Understanding the relative contributions of the shape of a sensory organ and the arrangement of receptors to the overall performance of the organ has long been a challenge for sensory biologists. We tackled this issue using the wind-sensing system of crickets, the cerci, two conical abdominal appendages covered with arrays of filiform hairs. Scanning electron microscopy coupled with 3D reconstruction methods were used for mapping of all cercal filiform hairs. The hairs are arranged according to their diameter in a way that avoids collisions with neighbours during hair deflection: long hairs are regularly spaced, whereas short hairs are both randomly and densely distributed. Particle image velocimetry showed that the variation in diameter of the cercus along its length modifies the pattern of fluid velocities. Hairs are subject to higher air flow amplitudes at the base than at the apex of the cercus. The relative importance of interactions between receptors and the air flow around the organ may explain the performance of the cricket's cercal system: it is characterised by a high density of statistically non-interacting short hairs located at the base of the cercus where sensitivity to air currents is the highest. 相似文献
1000.
A novel procedure for genotyping of single nucleotide polymorphisms in trisomy with genomic DNA and the invader assay
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Individuals with trisomy 21 display complex phenotypes with differing degrees of severity. Numerous reliable methods have been established to diagnose the initial trisomy in these patients, but the identification and characterization of the genetic basis of the phenotypic variation in individuals with trisomy remains challenging. To date, methods that can accurately determine genotypes in trisomic DNA samples are expensive, require specialized equipment and complicated analyses. Here we report proof-of-concept results for an Invader® assay-based genotyping procedure that can determine SNP genotypes in trisomic genomic DNA samples in a simple and cost-effective manner. The procedure requires only two experimental steps: a real-time measurement of the fluorescent Invader® signal and analysis with a specifically designed clustering algorithm. The approach was tested using genomic DNA samples from 23 individuals with trisomy 21, and results were compared to genotypes previously determined with pyrosequencing. Additional assays for 15 SNPs were tested in a set of 21 DNA samples to assess assay performance. Our method successfully identified the correct SNP genotypes for the trisomic genomic DNA samples tested, and thus provides an alternative to determine SNP genotypes in trisomic DNA samples for subsequent association studies in patients with Down syndrome and other trisomies. 相似文献