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61.
Jens‐Peter David Martin N. Andersen Søren‐Peter Olesen Hanne B. Rasmussen Nicole Schmitt 《Traffic (Copenhagen, Denmark)》2013,14(4):399-411
The voltage‐gated potassium channel KV7.1 is regulated by non‐pore forming regulatory KCNE β‐subunits. Together with KCNE1, it forms the slowly activating delayed rectifier potassium current IKs. However, where the subunits assemble and which of the subunits determines localization of the IKs‐complex has not been unequivocally resolved yet. We employed trafficking‐deficient KV7.1 and KCNE1 mutants to investigate IKs trafficking using the polarized Madin‐Darby Canine Kidney cell line. We find that the assembly happens early in the secretory pathway but provide three lines of evidence that it takes place in a post‐endoplasmic reticulum compartment. We demonstrate that KV7.1 targets the IKs‐complex to the basolateral membrane, but that KCNE1 can redirect the complex to the apical membrane upon mutation of critical KV7.1 basolateral targeting signals. Our data provide a possible explanation to the fact that KV7.1 can be localized apically or basolaterally in different epithelial tissues and offer a solution to divergent literature results regarding the effect of KCNE subunits on the subcellular localization of KV7.1/KCNE complexes . 相似文献
62.
Mechanism of force generation of a viral DNA packaging motor 总被引:6,自引:0,他引:6
Chemla YR Aathavan K Michaelis J Grimes S Jardine PJ Anderson DL Bustamante C 《Cell》2005,122(5):683-692
A large family of multimeric ATPases are involved in such diverse tasks as cell division, chromosome segregation, DNA recombination, strand separation, conjugation, and viral genome packaging. One such system is the Bacillus subtilis phage phi 29 DNA packaging motor, which generates large forces to compact its genome into a small protein capsid. Here we use optical tweezers to study, at the single-molecule level, the mechanism of force generation in this motor. We determine the kinetic parameters of the packaging motor and their dependence on external load to show that DNA translocation does not occur during ATP binding but is likely triggered by phosphate release. We also show that the motor subunits act in a coordinated, successive fashion with high processivity. Finally, we propose a minimal mechanochemical cycle of this DNA-translocating ATPase that rationalizes all of our findings. 相似文献
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66.
Rhipsalis (Cactaceae): loss and gain of floral rewards is mirrored in range sizes and distribution patterns of species 下载免费PDF全文
Bernadette Grosse‐Veldmann Stefan Abrahamczyk Jens Mutke Wilhelm Barthlott Maximilian Weigend 《Botanical journal of the Linnean Society. Linnean Society of London》2016,180(4):491-503
Autogamous species are usually distinguishable from xenogamous relatives by smaller flowers, fewer or even no floral rewards and lower pollen–ovule (P/O) ratios. Many Rhipsalis spp. are small flowered, selfing and include the most widespread species in Cactaceae. However, Rhipsalis also includes a large number of narrowly endemic species and is most diverse in the Atlantic rainforests of Brazil. To investigate the evolution of floral function and the correlation between floral function and range size, we analysed display size, floral reward and P/O ratios of Rhipsalis and its closest relatives, reconstructed ancestral traits and related these patterns to the distributions and range sizes of the species. Display size and sugar amount are reduced in subgenera Goniorhipsalis and Rhipsalis and secondarily increased in Phyllarthrorhipsalis, whereas the P/O ratio is decreased in subgenera Rhipsalis and Phyllarthrorhipsalis. We interpret this pattern as a switch from a predominantly xenogamous to an autogamous reproductive system, followed by a return to a predominantly xenogamous system. None of the floral parameters shows significant correlations with range size, except for display size. Nevertheless, those species with the smallest flowers, lowest sugar amounts per flower and lowest P/O ratios occur either outside southeastern Brazil and/or have comparatively large distribution ranges. Almost all Rhipsalis spp. occurring outside the Atlantic rainforests are restricted to the clade formed by subgenera Rhipsalis and Phyllarthrorhipsalis. Thus, we believe that the evolution of an autogamous reproduction system enabled this lineage of Rhipsalis to diversify and spread in the Atlantic rainforests, in the rest of the Neotropics and even spread to the Old World, where it is the only member of the family. 相似文献
67.
Walter J Loach DM Alqumber M Rockel C Hermann C Pfitzenmaier M Tannock GW 《Environmental microbiology》2007,9(7):1750-1760
The dlt operon of Gram-positive bacteria encodes proteins required for the incorporation of D-alanine esters into cell wall-associated teichoic acids (TA). D-alanylation of TA has been shown to be important for acid tolerance, resistance to antimicrobial peptides, adhesion, biofilm formation, and virulence of a variety of pathogenic organisms. The aim of this study was to determine the importance of D-alanylation for colonization of the gastrointestinal tract by Lactobacillus reuteri 100-23. Insertional inactivation of the dltA gene resulted in complete depletion of D-alanine substitution of lipoteichoic acids. The dlt mutant had similar growth characteristics as the wild type under standard in vitro conditions, but formed lower population sizes in the gastrointestinal tract of ex-Lactobacillus-free mice, and was almost eliminated from the habitat in competition experiments with the parental strain. In contrast to the wild type, the dlt mutant was unable to form a biofilm on the forestomach epithelium during gut colonization. Transmission electron microscope observations showed evidence of cell wall damage of mutant bacteria present in the forestomach. The dlt mutant had impaired growth under acidic culture conditions and increased susceptibility to the cationic peptide nisin relative to the wild type. Ex vivo adherence of the dlt mutant to the forestomach epithelium was not impaired. This study showed that D-alanylation is an important cell function of L. reuteri that seems to protect this commensal organism against the hostile conditions prevailing in the murine forestomach. 相似文献
68.
Population Structure of Rat-Derived Pneumocystis carinii in Danish Wild Rats 总被引:1,自引:0,他引:1 下载免费PDF全文
Robert J. Palmer Osvald P. Settnes Jens Lodal Ann E. Wakefield 《Applied microbiology》2000,66(11):4954-4961
The rat model of Pneumocystis carinii pneumonia is frequently used to study human P. carinii infection, but there are many differences between the rat and human infections. We studied naturally acquired P. carinii in wild rats to examine the relevance of the rat model for human infection. P. carinii DNA was detected in 47 of 51 wild rats and in 10 of 12 nonimmunosuppressed laboratory rats. Evidence for three novel formae speciales of rat-derived P. carinii was found, and these were provisionally named Pneumocystis carinii f. sp. rattus-secundi, Pneumocystis carinii f. sp. rattus-tertii, and Pneumocystis carinii f. sp. rattus-quarti. Our data suggest that low-level carriage of P. carinii in wild rats and nonimmunosuppressed laboratory rats is common and that wild rats are frequently coinfected with more than one forma specialis of P. carinii. We also examined the diversity in the internally transcribed spacer (ITS) regions of the nuclear rRNA operon of Pneumocystis carinii f. sp. carinii by using samples from wild rats and laboratory rats and spore trap samples. We report a lack of variation in the ITS1 and ITS2 regions that is consistent with an evolutionary bottleneck in the P. carinii f. sp. carinii population. This study shows that human- and rat-derived P. carinii organisms are very different, not only in genetic composition but also in population structure and natural history. 相似文献
69.
Lake-Ee Quek Christoph Wittmann Lars K Nielsen Jens O Krömer 《Microbial cell factories》2009,8(1):25-15
Background
The quantitative analysis of metabolic fluxes, i.e., in vivo activities of intracellular enzymes and pathways, provides key information on biological systems in systems biology and metabolic engineering. It is based on a comprehensive approach combining (i) tracer cultivation on 13C substrates, (ii) 13C labelling analysis by mass spectrometry and (iii) mathematical modelling for experimental design, data processing, flux calculation and statistics. Whereas the cultivation and the analytical part is fairly advanced, a lack of appropriate modelling software solutions for all modelling aspects in flux studies is limiting the application of metabolic flux analysis. 相似文献70.
Wolf-Dietrich Hard Jens M. Warnecke Roland K. Hartmann 《Molecular biology reports》1995,22(2-3):161-169
Modification interference is a powerful method to identify important functional groups in RNA molecules. We review here recent developments of techniques to screen for chemical modifications that interfere with (i) binding of(pre-)tRNA to bacterial RNase P RNA or (ii) pre-tRNA cleavage by this ribozyme. For example, two studies have analyzed positions at which a substitution of sulfur for thepro-Rp oxygen affects tRNA binding [1] or catalysis [2]. The results emphasize the functional key role of a central core element present in all known RNase P RNA subunits. The four sulfur substitutions identified in one study [2] to inhibit the catalytic step also interfered with binding of tRNA toE. coli RNase P RNA [1]. This suggests that losses in binding energy due to the modification at these positions affect the enzyme-substrate and the enzyme-transition state complex. In addition, the two studies have revealed, for the first time, sites of direct metal ion coordination in RNase P RNA. The potentials, limitations and interpretational ambiguities of modification interference experiments as well as factors influencing their outcome are discussed.Abbreviations nt
nucleotide(s)
- PAGE
polyacrylamide gel electrophoresis 相似文献