全文获取类型
收费全文 | 1031篇 |
免费 | 91篇 |
国内免费 | 1篇 |
专业分类
1123篇 |
出版年
2023年 | 4篇 |
2022年 | 8篇 |
2021年 | 16篇 |
2020年 | 13篇 |
2019年 | 4篇 |
2018年 | 10篇 |
2016年 | 17篇 |
2015年 | 25篇 |
2014年 | 37篇 |
2013年 | 45篇 |
2012年 | 58篇 |
2011年 | 60篇 |
2010年 | 36篇 |
2009年 | 34篇 |
2008年 | 56篇 |
2007年 | 47篇 |
2006年 | 66篇 |
2005年 | 53篇 |
2004年 | 64篇 |
2003年 | 56篇 |
2002年 | 49篇 |
2001年 | 10篇 |
2000年 | 18篇 |
1999年 | 24篇 |
1998年 | 14篇 |
1997年 | 32篇 |
1996年 | 10篇 |
1995年 | 17篇 |
1994年 | 11篇 |
1993年 | 8篇 |
1992年 | 12篇 |
1991年 | 11篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 13篇 |
1984年 | 5篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 17篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1974年 | 7篇 |
1973年 | 4篇 |
1969年 | 4篇 |
1965年 | 4篇 |
1964年 | 6篇 |
排序方式: 共有1123条查询结果,搜索用时 15 毫秒
91.
Van Damme EJ Charels D Menu-Bouaouiche L Proost P Barre A Rougé P Peumans WJ 《Planta》2002,214(6):853-862
Thaumatin-like proteins (TLPs) were isolated and characterized from fruits and leaves of elderberry (Sambucus nigra) and their corresponding genes cloned. In addition, the developmental regulation and induction of the different TLPs was followed in some detail. Ripening berries accumulated a fruit-specific TLP during the final stages of maturation. This fruit-specific TLP had no antifungal activity and was devoid of beta-glucanase activity. Leaves constitutively expressed a TLP that closely resembled the fruit-specific homologue. Treatment with jasmonate methyl ester induced two additional TLPs in leaves but did not induce or enhance the expression of TLPs in immature berries. In contrast to jasmonate methyl ester, both ethephon and garlic extract induced the expression of a TLP in unripe berries that normally do not express any TLP. Sequence analysis and molecular modeling indicated that all elderberry thaumatin-like proteins share a high sequence similarity with group-5 pathogenesis-related proteins. However, the proteins encoded by the different sequences differed from each other in isoelectric point and the distribution of the charges on the surface of the molecule. 相似文献
92.
93.
Barbot W Wasowicz M Dupressoir A Versaux-Botteri C Heidmann T 《Biochimica et biophysica acta》2002,1576(1-2):81-91
We have previously identified in some mouse strains (e.g. BALB/c, DBA/2) a murine Intracisternal A-particle (IAP) transposable element specifically expressed in the liver. This IAP sequence is inserted within a gene, mCCR4/m. nocturnin, the sequence of which is related to the circadian Xenopus nocturnin gene. Here we show, using real-time quantitative RT-PCR, that both the IAP sequence and the m. nocturnin gene display strong circadian expression in the liver, with peak abundance after dusk. Circadian oscillations of m. nocturnin RNA are maintained in mice without the IAP insertion (e.g. CBA/J, 129/sv), are free-running under constant light and dark conditions, and persist upon food and water privation, demonstrating that m. nocturnin is a circadian gene. In situ hybridization analyses (in 129/sv mice) further show circadian expression of m. nocturnin also in the retina, precisely at the level of the photoreceptors, a result consistent with the previously described circadian expression of the Xenopus gene. These results strengthen the strong conservation of the nocturnin gene with the identification of a functional mouse ortholog of the Xenopus gene, and demonstrate the reciprocal influence of nearby genes on the expression of transposable elements via "position effects". 相似文献
94.
Yao X Nguyen V Wriggers W Rubenstein PA 《The Journal of biological chemistry》2002,277(25):22875-22882
His(73) participates in the regulation of the nucleotide binding cleft conformation in yeast actin. Earlier molecular dynamics studies suggested that Asp(184) interacts with His(73) thereby stabilizing a "closed-cleft" G-actin. However, beta-actin in the open-cleft state shows a closer interaction of His(73) with Asp(179) than with Asp(184). We have thus assessed the relative importance of Asp(184) and Asp(179) on yeast actin stability and function. Neutral substitutions at 184 or 179 alone had little adverse effect on the monomer and polymerization behavior of actin. Arg or His at 184 in H73E actin partially rescued the monomeric properties of H73E actin, as demonstrated by near-normal thermostability and wild-type (WT)-like protease digestion patterns. ATP exchange was still considerably faster than with WT-actin although slower than that of H73E alone. However, polymerization of H73E/D184R and H73E/D184H is worse than with H73E alone. Conversely, D179R rescued all monomeric properties of H73E to near WT values and largely restored polymerization rate and filament thermostability. These results and new simulations of G-actin in the "open" state underscore the importance of the His(73)-Asp(179) interaction and suggest that the open and not the closed state of yeast actin may be favored in the absence of the methyl group of His(73). 相似文献
95.
Hammes F Boon N de Villiers J Verstraete W Siciliano SD 《Applied and environmental microbiology》2003,69(8):4901-4909
During a study of ureolytic microbial calcium carbonate (CaCO(3)) precipitation by bacterial isolates collected from different environmental samples, morphological differences were observed in the large CaCO(3) crystal aggregates precipitated within bacterial colonies grown on agar. Based on these differences, 12 isolates were selected for further study. We hypothesized that the striking differences in crystal morphology were the result of different microbial species or, alternatively, differences in the functional attributes of the isolates selected. Sequencing of 16S rRNA genes showed that all of the isolates were phylogenetically closely related to the Bacillus sphaericus group. Urease gene diversity among the isolates was examined by using a novel application of PCR-denaturing gradient gel electrophoresis (DGGE). This approach revealed significant differences between the isolates. Moreover, for several isolates, multiple bands appeared on the DGGE gels, suggesting the apparent presence of different urease genes in these isolates. The substrate affinities (K(m)) and maximum hydrolysis rates (V(max)) of crude enzyme extracts differed considerably for the different strains. For certain isolates, the urease activity increased up to 10-fold in the presence of 30 mM calcium, and apparently this contributed to the characteristic crystal formation by these isolates. We show that strain-specific calcification occurred during ureolytic microbial carbonate precipitation. The specificity was mainly due to differences in urease expression and the response to calcium. 相似文献
96.
Binz PA Abdi F Affolter M Allard L Barblan J Bhardwaj S Bienvenut WV Bulet P Burgess J Carrette O Corthals G Delalande F Diemer H Favreau P Giuliano E Gueguen Y Guillaume E Hahner S Man P Michalet S Neri D Noukakis D Palagi P Paroutaud P Pimenta DC Quadroni M Resemann A Richert S Rybak J Sanchez JC Scherl A Scheurer S Schweiger Hufnagel U Siethoff C Suckau D van Dorsselaer A Wagner Redeker W Walter N Stöcklin R 《Proteomics》2003,3(8):1562-1566
After the success of the mass spectrometry (MS) round table that was held at the first Swiss Proteomics Society congress (SPS'01) in Geneva, the SPS has organized a proteomics application exercise and allocated a full session at the SPS'02 congress. The main objective was to encourage the exchange of expertise in protein identification, with a focus on the use of mass spectrometry, and to create a bridge between the users' questions and the instrument providers' solutions. Two samples were sent to fifteen interested labs, including academic groups and MS hardware providers. Participants were asked to identify and partially characterize the samples. They consisted of a complex mixture of peptide/proteins (sample A) and an almost pure recombinant peptide carrying post-translational modifications (sample B). Sample A was an extract of snake venom from the species Bothrops jararaca. Sample B was a recombinant and modified peptide derived from the shrimp Penaeus vannamei penaeidin 3a. The eight labs that returned results reported the use of a wide range of MS instrumentation and techniques. They mentioned a variety of time and manpower allocations. The origin of sample A was generally identified together with a number of database protein entries. The difficulty of the sample identification lay in the incomplete knowledge of the Bothrops species genome sequence and is discussed. Sample B was generally and correctly identified as penaeidin. However, only one group reported the full primary structure. Interestingly, the approaches were again varied and are discussed in the text. 相似文献
97.
De Vos A Sermon K Van de Velde H Joris H Vandervorst M Lissens W De Paepe A Liebaers I Van Steirteghem A 《Human genetics》2000,106(6):605-613
Osteogenesis imperfecta (OI) is an autosomal dominant genetic disorder characterized by the presence of brittle bones and decreased bone mass (osteopenia), as a result of mutations in the genes that encode the chains of type I collagen, the major protein of bone. The clinical features of the disease range from death in the perinatal period to normal life span with minimal increase in fractures. The present report describes two polymerase chain reaction (PCR)-based assays allowing preimplantation genetic diagnosis (PGD) on the one hand for OI type I, the mildest form, and on the other hand for OI type IV, which is intermediate in severity between OI type I and OI type III. In the couple referred for PGD for OI type I, the female partner carried a 1-bp deletion in exon 43 of the COL1A1 gene, resulting in a premature stop codon in exon 46. The synthesis of too little type I procollagen results from such a non-functional or COL1A1 null allele. In the other couple, referred for PGD for OI type IV, the male partner carried a G to A substitution in exon 19 of the COL1A2 gene, which results in an abnormal gene product due to an alphaGly247 (GGT) to Ser (AGT) substitution (G247S). Both mutations result in the loss of a specific restriction enzyme recognition site and can therefore be detected by PCR amplification followed by restriction fragment analysis. PCR amplification of genomic DNA of the parents-to-be with one of the two primers fluorescently labelled, followed by automated laser fluorescence (ALF) gel electrophoresis of the amplified and restricted fragments, allowed a distinction between the healthy and affected genotypes. PCR on single Epstein-Barr-virus (EBV)-transformed lymphoblasts resulted in acceptable amplification efficiencies (87% and 85% for OI type I and OI type IV respectively) and the allele drop-out (ADO) rate was assessed at 11.5% and 11.1% for OI type I and OI type IV respectively. With research blastomeres, 100% amplification rates were obtained and no contamination was observed in the blank controls, which validated the tests for clinical application. Embryos obtained after intracytoplasmic sperm injection (ICSI) were evaluated for the presence of the normal genotype of the non-affected parent. For OI type I, two frozen-thawed ICSI-PGD cycles and two fresh ICSI-PGD cycles were carried out for the same couple. The transfer of two unaffected embryos in the last cycle resulted in a twin pregnancy. A twin pregnancy was also achieved in one clinical ICSI-PGD cycle for OI type IV. 相似文献
98.
Elisa Vescovi Brigitta Ammann Cesare Ravazzi Willy Tinner 《Vegetation History and Archaeobotany》2010,19(3):219-233
Detailed Late-glacial and Holocene palaeoenvironmental records from the northern Apennines with a robust chronology are still
rare, though the region has been regarded as a main area of potential refugia of important trees such as Picea abies and Abies alba. We present a new high-resolution pollen and stomata record from Lago del Greppo (1,442 m a.s.l., Pistoia, northern Apennines)
that has been dated relying on 12 terrestrial plant macrofossils. Late-glacial woodlands became established before 13000 cal
b.p. and were dominated by Pinus and Betula, although more thermophilous taxa such as Quercus, Tilia and Ulmus were already present in the Greppo area, probably at lower altitudes. Abies and Picea expanded locally at the onset of the Holocene at ca. 11500 cal b.p. Fagus sylvatica was the last important tree to expand at ca. 6500 cal b.p., following the decline of Abies. Human impact was generally low throughout the Holocene, and the local woods remained rather closed until the most recent
time, ca. a.d. 1700–1800. The vegetational history of Lago del Greppo appears consistent with that of previous investigations in the study
region. Late-glacial and Holocene vegetation dynamics in the northern Apennines are very similar to those in the Insubrian
southern Alps bordering Switzerland and Italy, across the Po Plain. Similarities between the two areas include the Late-glacial
presence of Abies alba, its strong dominance during the Holocene across different vegetation belts from the lowlands to high elevations, as well
as its final fire and human-triggered reduction during the mid Holocene. Our new data suggest that isolated and minor Picea abies populations survived the Late-glacial in the foothills of the northern Apennines and that at the onset of the Holocene they
moved upwards, reaching the site of Lago del Greppo. Today stands of Picea abies occur only in two small areas in the highest part of the northern Apennines, and they have become extinct elsewhere. Given
the forecast global warming, these relict Picea abies stands of the northern Apennines, which have a history of at least 13,000 years, appear severely endangered. 相似文献
99.
Chloroplast glutathione reductase: Purification and properties 总被引:4,自引:0,他引:4
Glutathione reductase was partially purified from isolated pea chloroplasts ( Pisum sativum L. cv. Progress #9). A 1600-fold purification was obtained and the purified enzyme had a specific activity of 26 μmol NADPH oxidized (mg protein)−1 min−1 . The enzyme had a native molecular weight of approximately 156 kdalton and consisted of two each of two subunits of about 41 and 42 kdalton. The Km for oxidized glutathione was 11 μ M and the Km for NADPH was 1.7 μ M . Enzyme activity was affected by the ionic strength of the assay medium, and maximum activity was observed at an ionic strength of between 60 and 100 m M . The enzyme was inactivated by sulfhydryl modifying reagents and the presence of either oxidized glutathione or NADPH affected the extent of inactivation. Chloroplast glutathione reductase probably serves in the removal of photosynthetically derived H2 O2 by reducing dehydroascorbate for ascorbate-linked reduction of H2 O2 . Intermediates of this reaction sequence, dehydroascorbate, ascorbate, reduced glutathione, and NADPH had no effect on enzymic activity. 相似文献
100.