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排序方式: 共有345条查询结果,搜索用时 78 毫秒
41.
42.
Julie E. Croft Donald R. Love Peter L. Bergquist 《Molecular & general genetics : MGG》1987,210(3):490-497
Summary The organisation of the leucine genes in Thermus thermophilus HB8 was analysed by examining the ability of recombinant DNAs to complement Escherichia coli mutations. The arrangement of the genes is different from that in the mesophilic bacteria E. coli and Salmonella typhimurium. The promoter responsible for the expression of the leuB, leuC and leuD genes of Thermus HB8 in E. coli was identified. The sequence of Thermus DNA containing this promoter revealed structural similarities to the promoter and attenuator regions of the E. coli leucine operon. 相似文献
43.
Abstract Lamellibrachia luymesi is a long‐lived vestimentiferan polychaete that produces biogenic habitat at hydrocarbon seeps on the upper Louisiana slope of the Gulf of Mexico. Lamellibrachia luymesi relies on endosymbiotic, chemoautotrophic bacteria for nutrition which are supplied with hydrogen sulphide acquired from seep sediments by the tube worms. In this study, an individual‐based model is developed for L. luymesi aggregations. The results show that aggregations can persist for centuries because of extremely low mortality rates. Recruitment patterns reflect intraspecific competition for settlement space, with the recruitment period estimated between 11 and 68 years. Substantial hydrogen sulphide requirements are estimated for large aggregations of L. luymesi, exceeding 30 mmol h?1. In addition to modifying habitat through physical structure, L. luymesi may be considered to be an ecosystem engineer because of its profound effect on the chemical environment at hydrocarbon seep sites. 相似文献
44.
Abstract: The pivotal role for voltage-sensitive calcium channels in initiating synaptic transmitter release is undisputed, but it is only partly known to what extent the different subtypes contribute in vivo. Their importance for the dendritic release of dopamine has not been investigated in vivo previously. To evaluate comprehensively the relative importance of different voltage-sensitive calcium channel subtypes for striatal dopamine release, and to further investigate the mechanism of dendritic dopamine release in the reticulate part of substantia nigra, dopamine was measured by in vivo microdialysis in the striatum or substantia nigra of awake rats. The calcium channel blockers nimodipine, ω-conotoxin-GVIA, ω-agatoxin-IVA, and neomycin were administered locally through the dialysis probes and compared with calcium-free perfusion. Results indicate that dopamine release in the striatum is mainly dependent on N- and P/Q-type channels, but the dendritic dopamine release in the substantia nigra is mediated mainly by some other calcium-dependent mechanism, for example, calcium mobilization through T-, O-, or R-type calcium channels. A portion of the dendritic release is calcium independent but can be inhibited partially by neomycin, which might suggest a role for inositol 4,5-bisphosphate breakdown products. 相似文献
45.
The morphology of cilia in sponge larvae 总被引:1,自引:0,他引:1
Patricia R. Bergquist Colin R. Green Mary E. Sinclair Heather Silyn Roberts 《Tissue & cell》1977,9(1):179-184
Sponge larvae possess cilia with unusual terminal expansions which are curled or biconcave in shape externally, as seen by scanning electron microscopy. Thin sections, passing through the point where the ciliary shaft enters the expanded area reveal the ciliary axoneme to be surrounded by many membranous folds, some of which are vesicular. The ‘club footed’ cilia occur in disparate groups of Demospongiae and most frequently, all larval cilia are of this type. There is no immediately obvious correlation between the type of movement displayed by the larvae and the occurrence of terminally expanded cilia. 相似文献
46.
Moreland D. Gibbs Rosalind A. Reeves David Mandelman Qingli Mi Jun Lee Peter L. Bergquist 《Extremophiles : life under extreme conditions》2009,13(5):817-826
Thermus aquaticus DNA polymerase (Taq polymerase) made the polymerase chain reaction feasible and led to a paradigm shift in genomic analysis. Other Thermus polymerases were reported to have comparable performance in PCR and there was an analysis of their properties in the 1990s.
We re-evaluated our earlier phylogeny of Thermus species on the basis of 16S rDNA sequences and concluded that the genus could be divided into eight clades. We examined 22
representative isolates and isolated their DNA polymerase I genes. The eight most diverse polymerase genes were selected to
represent the eight clades and cloned into an expression vector coding for a His-tag. Six of the eight polymerases were expressed
so that there was sufficient protein for purification. The proteins were purified to homogeneity and examination of the biochemical
characteristics showed that although they were competent to perform PCR, none was as thermostable as commercially available
Taq polymerase; all had similar error-frequencies to Taq polymerase and all showed the expected 5′–3′ exonuclease activity. We conclude that the initial selection of T. aquaticus for DNA polymerase purification was a far-reaching and fortuitous choice but simple mutagenesis procedures on other Thermus-derived polymerases should provide comparable thermostability for the PCR reaction. 相似文献
47.
48.
Hara-Kaonga B Gao YA Havrda M Harrington A Bergquist I Liaw L 《Transgenic research》2006,15(1):101-106
Cre recombinase has become a ubiquitous tool in transgenic strategies for regulation of transgene expression in a tissue-specific
manner. We report analysis of two SM22αCre lines and their ability to mediate genomic recombination in five independent Cre-responsive transgenic lines. One of the
SM22αCre lines developed was a tet-on system based on the reverse tetracycline transactivator. Our goal was to use this strategy
to inhibit the Notch signaling pathway specifically in smooth muscle cells. Our responder transgenes contained a constitutively
expressed marker gene (chloramphenicol acetyltransferase, CAT), flanked by loxP sites in direct orientation, upstream of Notch-related transgenes. We developed two dominant negative Notch transgenic responder
lines activated by Cre-mediated DNA recombination. The first is the extracellular domain of human Jagged1, and the second
is the extracellular domain of the human Notch2 receptor. Despite high expression of the marker gene in all responder lines,
we found that Cre-mediated genomic recombination between these five lines was highly variable, ranging from 46 to 93% of individuals
using an SM22αCre activating strain, or 8–58% of individuals using an inducible SM22αrtTACre. In all cases examined, detection of recombination by PCR correlated with expression of the transgene as determined
by Western blot analysis. Our studies reflect the variability in recombination success based on the responder strain, presumably
due to inaccessibility of the locus of integration of the responder allele. 相似文献
49.
Bergquist AJ Clair JM Collins DF 《Journal of applied physiology (Bethesda, Md. : 1985)》2011,110(3):627-637
Neuromuscular electrical stimulation (NMES) can be delivered over a nerve trunk or muscle belly and can generate contractions by activating motor (peripheral pathway) and sensory (central pathway) axons. In the present experiments, we compared the peripheral and central contributions to plantar flexion contractions evoked by stimulation over the tibial nerve vs. the triceps surae muscles. Generating contractions through central pathways follows Henneman's size principle, whereby low-threshold motor units are activated first, and this may have advantages for rehabilitation. Statistical analyses were performed on data from trials in which NMES was delivered to evoke 10-30% maximum voluntary torque 2-3 s into the stimulation (Time(1)). Two patterns of stimulation were delivered: 1) 20 Hz for 8 s; and 2) 20-100-20 Hz for 3-2-3 s. Torque and soleus electromyography were quantified at the beginning (Time(1)) and end (Time(2); 6-7 s into the stimulation) of each stimulation train. H reflexes (central pathway) and M waves (peripheral pathway) were quantified. Motor unit activity that was not time-locked to each stimulation pulse as an M wave or H reflex ("asynchronous" activity) was also quantified as a second measure of central recruitment. Torque was not different for stimulation over the nerve or the muscle. In contrast, M waves were approximately five to six times smaller, and H reflexes were approximately two to three times larger during NMES over the nerve vs. the muscle. Asynchronous activity increased by 50% over time, regardless of the stimulation location or pattern, and was largest during NMES over the muscle belly. Compared with NMES over the triceps surae muscles, NMES over the tibial nerve produced contractions with a relatively greater central contribution, and this may help reduce muscle atrophy and fatigue when NMES is used for rehabilitation. 相似文献
50.
Sigrid N?ss Benedicte A. Lie Espen Melum Marita Olsson Johannes R. Hov Peter J. P. Croucher Jochen Hampe Erik Thorsby Annika Bergquist James A. Traherne Erik Schrumpf Kirsten Muri Boberg Stefan Schreiber Andre Franke Tom H. Karlsen 《PloS one》2014,9(12)