全文获取类型
收费全文 | 345篇 |
免费 | 28篇 |
国内免费 | 1篇 |
出版年
2024年 | 2篇 |
2021年 | 4篇 |
2020年 | 6篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 5篇 |
2015年 | 14篇 |
2014年 | 16篇 |
2013年 | 14篇 |
2012年 | 21篇 |
2011年 | 22篇 |
2010年 | 25篇 |
2009年 | 10篇 |
2008年 | 18篇 |
2007年 | 21篇 |
2006年 | 20篇 |
2005年 | 16篇 |
2004年 | 17篇 |
2003年 | 16篇 |
2002年 | 25篇 |
2001年 | 4篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1987年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1968年 | 3篇 |
1966年 | 1篇 |
1965年 | 2篇 |
1963年 | 1篇 |
1962年 | 1篇 |
1959年 | 4篇 |
1957年 | 1篇 |
1954年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有374条查询结果,搜索用时 250 毫秒
101.
Lactoris fernandeziana, endemic to the island of Masatierra in the Juan Fernandez Archipelago, is the only living member of the primitive angiosperm family, Lactoridaceae. The species was surveyed for ribosomal DNA (rDNA) and RAPD (Random Amplified Polymorphic DNA) variation. Previous analyses of allozymes had revealed no variation within the species. Variation was found for length in the intergenic spacer and for restriction sites in the 18S–25S genes of rDNA, and for the presence of amplified bands using 16 primers. Different rDNA repeat lengths and restriction site variants were detected within individuals as well as within and among populations. The level of variation in RAPDs is low relative to other Juan Fernandez endemic species surveyed, and nearly all variants were restricted to single populations. The rDNA length variants were distributed throughout the island, whereas the rDNA restriction site variants and RAPD markers indicated minor genetic differences among the populations. 相似文献
102.
This study reports the first results on telemetry of caudal differential pressure during spontaneous swimming activity in cod Gadus morhua and demonstrates that tail-beat pressure may be used as a predictor of activity and swimming costs of free-swimming cod. Tail-beat pressure was monitored using a differential pressure sensor on the caudal peduncle of cod and spontaneous swimming activity was quantified using a customized video-computer tracking programme. Tail-beat pressure was found to correlate with (1) swimming speed ( U ) and oxygen consumption during forced swimming and (2) mean U during spontaneous activity. Based on the relationship between and the integrated pressure performed by the tail during forced swimming, it should be possible to predict during spontaneous activity. To gain precise measures of activity and thus predictions of for free-swimming fish, however, individual calibrations are necessary. 相似文献
103.
Laccase-catalyzed polymerization of tyrosine-containing peptides 总被引:1,自引:0,他引:1
Mattinen ML Kruus K Buchert J Nielsen JH Andersen HJ Steffensen CL 《The FEBS journal》2005,272(14):3640-3650
Laccase-catalyzed polymerization of tyrosine and tyrosine-containing peptides was studied in the presence and absence of ferulic acid (FA). Advanced spectroscopic methods such as MALDI-TOF MS, EPR, FTIR microscopy and HPLC-fluorescence, as well as more conventional analytical tools: oxygen consumption measurements and SDS/PAGE were used in the reaction mechanism studies. Laccase was found to oxidize tyrosine and tyrosine-containing peptides, with consequent polymerization of the compounds. The covalent linkage connecting the compounds was found to be an ether bond. Only small amounts of dityrosine bonds were detected in the polymers. When FA was added to the reaction mixtures, it was found to be incorporated into the polymer structure. Thus, in addition to homopolymers, different heteropolymers containing two or four FA residues were formed in the reactions. 相似文献
104.
105.
Human topoisomerase IIalpha: targeting to subchromosomal sites of activity during interphase and mitosis 下载免费PDF全文
Agostinho M Rino J Braga J Ferreira F Steffensen S Ferreira J 《Molecular biology of the cell》2004,15(5):2388-2400
Mammalian topoisomerase IIalpha (topo IIalpha) plays a vital role in the removal of topological complexities left on DNA during S phase. Here, we developed a new assay to selectively identify sites of catalytic activity of topo IIalpha with subcellular resolution. We show that topo IIalpha activity concentrates at replicating heterochromatin in late S in a replication-dependent manner and at centric heterochromatin during G2 and M phases. Inhibitor studies indicate that this cell cycle-dependent concentration over heterochromatin is sensitive to chromatin structure. We further show that catalytically active topo IIalpha concentrates along the longitudinal axis of mitotic chromosomes. Finally, we found that catalytically inert forms of the enzyme localize predominantly to splicing speckles in a dynamic manner and that this pool is differentially sensitive to changes in the activities of topo IIalpha itself and RNA polymerase II. Together, our data implicate several previously unsuspected activities in the partitioning of the enzyme between sites of activity and putative depots. 相似文献
106.
107.
A proposed design for the cryopreservation of intact and adherent human embryonic stem cell colonies 总被引:2,自引:0,他引:2
Heng BC Bested SM Chan SH Cao T 《In vitro cellular & developmental biology. Animal》2005,41(3-4):77-79
Summary Recently, it was demonstrated that the application of slow-cooling cryopreservation protocols to adherent human embryonic
stem (hES) cell colonies, cultured on matrigel or murine embryonic fibroblast feeder layers, resulted in marked improvement
in postthaw viability and reduction in cell differentiation. However, the use of commercially available culture plates for
this purpose presents several limitations. Most obviously, these plates are not designed for cryopreservation or to withstand
the low temperatures encountered during liquid nitrogen cryopreservation, or both. The physical storage of cryopreserved plates
is another consideration, in addition to difficulty in maintaining sterile conditions in liquid nitrogen storage and during
the thaw phase in a water bath. Hence, a redesign of the cell culture plate for the cryopreservation of adherent hES cell
colonies is proposed. In this model, a culture plate made of synthetic materials resistant to storage at −196° C of liquid
nitrogen is designed, with readily attachable screw-cap culture wells that function as a replacement for cryovial storage.
The detachable wells facilitate storage and after thawing can easily be reattached to a specially designed holding plate.
Currently, there are no commercially available cell culture plates using this design concept. The proposed design is envisioned
to facilitate the cryopreservation of intact adherent hES cell colonies that could assist the development of automated systems
for handling bulk quantities of cells. 相似文献
108.
Wang J Chuang K Ahluwalia M Patel S Umblas N Mirel D Higuchi R Germer S 《BioTechniques》2005,39(6):885-893
Despite many recent advances in high-throughput single nucleotide polymorphism (SNP) genotyping technologies, there is still a great need for inexpensive and flexible methods with a reasonable throughput. Here we report substantial modifications and improvements to an existing homogenous allele-specific PCR-based SNP genotyping method, making it an attractive new option for researchers engaging in candidate gene studies or following up on genome-wide scans. In this advanced version of the melting temperature (Tm)-shift SNP genotyping method, we attach two GC-rich tails of different lengths to allele-specific PCR primers, such that SNP alleles in genomic DNA samples can be discriminated by the Tms of the PCR products. We have validated 306 SNP assays using this method and achieved a success rate in assay development of greater than 83% under uniform PCR conditions. We have developed a standalone software application to automatically assign genotypes directly from melting curve data. To demonstrate the accuracy of this method, we typed 592 individuals for 6 SNPs and showed a high call rate (>98%) and high accuracy (>99.9%). With this method, 6-10,000 samples can be genotyped per day using a single 384-well real-time thermal cycler with 2-4 standard 384-well PCR instruments. 相似文献
109.
Importance of arginine 20 of the swine vesicular disease virus 2A protease for activity and virulence 总被引:1,自引:0,他引:1 下载免费PDF全文
Inoue T Alexandersen S Clark AT Murphy C Quan M Reid SM Sakoda Y Johns HL Belsham GJ 《Journal of virology》2005,79(1):428-440
A major virulence determinant of swine vesicular disease virus (SVDV), an Enterovirus that causes an acute vesicular disease, has been mapped to residue 20 of the 2A protease. The SVDV 2A protease cleaves the 1D-2A junction in the viral polyprotein, induces cleavage of translation initiation factor eIF4GI, and stimulates the activity of enterovirus internal ribosome entry sites (IRESs). The 2A protease from an attenuated strain of SVDV (Ile at residue 20) is significantly defective at inducing cleavage of eIF4GI and the activation of IRES-dependent translation compared to the 2A protease from a pathogenic strain (J1/73, Arg at residue 20), but the two proteases have similar 1D-2A cleavage activities (Y. Sakoda, N. Ross-Smith, T. Inoue, and G. J. Belsham, J. Virol. 75:10643-10650, 2001). Residue 20 has now been modified to every possible amino acid, and the activities of each mutant 2A protease has been analyzed. Selected mutants were reconstructed into full-length SVDV cDNA, and viruses were rescued. The rate of virus growth in cultured swine kidney cells reflected the efficiency of 2A protease activity. In experimentally infected pigs, all four of the mutant viruses tested displayed much-reduced virulence compared to the J1/73 virus but a significant, albeit reduced, level of viral replication and excretion was detected. Direct sequencing of cDNA derived from samples taken early and late in infection indicated that a gradual selection-reversion to a more efficient protease occurred. The data indicated that extensive sequence change and selection may introduce a severe bottleneck in virus replication, leading to a decreased viral load and reduced or no clinical disease. 相似文献
110.
Steffensen S Coelho PA Cobbe N Vass S Costa M Hassan B Prokopenko SN Bellen H Heck MM Sunkel CE 《Current biology : CB》2001,11(5):295-307
BACKGROUND: Faithful segregation of the genome during mitosis requires interphase chromatin to be condensed into well-defined chromosomes. Chromosome condensation involves a multiprotein complex known as condensin that associates with chromatin early in prophase. Until now, genetic analysis of SMC subunits of the condensin complex in higher eukaryotic cells has not been performed, and consequently the detailed contribution of different subunits to the formation of mitotic chromosome morphology is poorly understood. RESULTS: We show that the SMC4 subunit of condensin is encoded by the essential gluon locus in Drosophila. DmSMC4 contains all the conserved domains present in other members of the structural-maintenance-of-chromosomes protein family. DmSMC4 is both nuclear and cytoplasmic during interphase, concentrates on chromatin during prophase, and localizes to the axial chromosome core at metaphase and anaphase. During decondensation in telophase, most of the DmSMC4 leaves the chromosomes. An examination of gluon mutations indicates that SMC4 is required for chromosome condensation and segregation during different developmental stages. A detailed analysis of mitotic chromosome structure in mutant cells indicates that although the longitudinal axis can be shortened normally, sister chromatid resolution is strikingly disrupted. This phenotype then leads to severe chromosome segregation defects, chromosome breakage, and apoptosis. CONCLUSIONS: Our results demonstrate that SMC4 is critically important for the resolution of sister chromatids during mitosis prior to anaphase onset. 相似文献