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71.
72.
Bax/Bak-mediated mitochondrial outer membrane permeabilization (MOMP) is essential for “intrinsic” apoptotic cell death. Published studies used synthetic liposomes to reveal an intrinsic pore-forming activity of Bax, but it is unclear how other mitochondrial outer membrane (MOM) proteins might facilitate this function. We carefully analyzed the kinetics of Bax-mediated pore formation in isolated MOMs, with some unexpected results. Native MOMs were more sensitive than liposomes to added Bax, and MOMs displayed a lag phase not observed with liposomes. Heat-labile MOM proteins were required for this enhanced response. A two-tiered mathematical model closely fit the kinetic data: first, Bax activation promotes the assembly of a multimeric complex, which then catalyzes the second reaction, Bax-dependent pore formation. Bax insertion occurred immediately upon Bax addition, prior to the end of the lag phase. Permeabilization kinetics were affected in a reciprocal manner by [cBid] and [Bax], confirming the “hit-and-run” hypothesis of cBid-induced direct Bax activation. Surprisingly, MOMP rate constants were linearly related to [Bax], implying that Bax acts non-cooperatively. Thus, the oligomeric catalyst is distinct from Bax. Moreover, contrary to common assumption, pore formation kinetics depend on Bax monomers, not oligomers. Catalyst formation exhibited a sharp transition in activation energy at ∼28°C, suggesting a role for membrane lipid packing. Furthermore, catalyst formation was strongly inhibited by chemical antagonists of the yeast mitochondrial fission protein, Dnm1. However, the mammalian ortholog, Drp1, was undetectable in mitochondrial outer membranes. Moreover, ATP and GTP were dispensable for MOMP. Thus, the data argue that oligomerization of a catalyst protein, distinct from Bax and Drp1, facilitates MOMP, possibly through a membrane-remodeling event. 相似文献
73.
Recombinant human progastrin6–80 binds two ferric ions with an apparent dissociation constant of 2.2 ± 0.1 μM [Baldwin (2004) Protein J 23:65–70]. The aims of the present study were to express fragments of recombinant procholecystokinin and to determine whether or not
they bound ferric ions. Recombinant rat and human procholecystokinin57–95 were expressed as glutathione S-transferase fusion proteins in E. coli. The fusion proteins were bound to glutathione-agarose, cleaved with thrombin, and purified by reverse phase HPLC. Recombinant
procholecystokinin57–95 did not bind to either the CCK1 or CCK2 receptor with high affinity. No change in absorption spectrum was observed on addition
of ferric ions, and analysis of the quenching of tryptophan fluorescence observed in the presence of ferric ions indicated
that binding to procholecystokinin57–95 was at least 40–fold weaker than the binding of ferric ions to progastrin6–80. 相似文献
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Kalie E Jaitin DA Podoplelova Y Piehler J Schreiber G 《The Journal of biological chemistry》2008,283(47):32925-32936
Type I interferons (IFNs) signal for their diverse biological effects by binding a common receptor on target cells, composed of the two transmembrane IFNAR1 and IFNAR2 proteins. We have previously differentially enhanced the antiproliferative activity of IFN by increasing the weak binding affinity of IFN to IFNAR1. In this study, we further explored the affinity interdependencies between the two receptor subunits and the role of IFNAR1 in differential IFN activity. For this purpose, we generated a panel of mutations targeting the IFNAR2 binding site on the background of the IFNalpha2 YNS mutant, which increases the affinity to IFNAR1 by 60-fold, resulting in IFNAR2-to-IFNAR1 binding affinity ratios ranging from 1000:1 to 1:1000. Both the antiproliferative and antiviral potencies of the interferon mutants clearly correlated to the in situ binding IC(50) values, independently of the relative contributions of the individual receptors, thus relating to the integral lifetime of the complex. However, the antiproliferative potency correlated throughout the entire range of affinities, as well as with prolonged IFNAR1 receptor down-regulation, whereas the antiviral potency reached a maximum at binding affinities equivalent to that of wild-type IFNalpha2. Our data suggest that (i) the specific activity of interferon is related to the ternary complex binding affinity and not to affinity toward individual receptor components and (ii) although the antiviral pathway is strongly dependent on pSTAT1 activity, the cytostatic effect requires additional mechanisms that may involve IFNAR1 down-regulation. This differential interferon response is ultimately mediated through distinct gene expression profiling. 相似文献
76.
Investigations into the metabolism of drugs used in aquatic animal therapy are useful for understanding the mechanisms of xenobiotic transformation systems and can aid the development of dosing regimens. This study investigated the metabolism of the synthetic anthelmintic praziquantel, which has application in helminthiasis treatment for several fish species including kingfish Seriola lalandi, a commercial aquaculture finfish species. At least 7 mono- or dihydroxylated derivatives of the parent compound were identified in kingfish after administration of a 150 mg kg(-1) oral praziquantel dose, paralleling findings in mammals. The structure of one representative mono-hydroxylated species that was prominent in the skin, muscle, liver, kidney and plasma of kingfish was investigated using fragmentation experiments; this revealed that hydroxylation of the parent molecule occurred in the tetrahydroisoquinoline region of praziquantel, analogous with mammalian metabolites, but different to that of the active mammalian metabolite (trans-4-OH-praziquantel). The implications of these findings with regard to biotransformation systems for this drug in mammals and fish are discussed. 相似文献
77.
The voltage dependent anion channel (VDAC), located in the outer mitochondrial membrane, functions as a major channel allowing
passage of small molecules and ions between the mitochondrial inter-membrane space and cytoplasm. Together with the adenine
nucleotide translocator (ANT), which is located in the inner mitochondrial membrane, the VDAC is considered to form the core
of a mitochondrial multiprotein complex, named the mitochondrial permeability transition pore (MPTP). Both VDAC and ANT appear
to take part in activation of the mitochondrial apoptosis pathway. Other proteins also appear to be associated with the MPTP,
for example, the 18 kDa mitochondrial Translocator Protein (TSPO), Bcl-2, hexokinase, cyclophylin D, and others. Interactions
between VDAC and TSPO are considered to play a role in apoptotic cell death. As a consequence, due to its apoptotic functions,
the TSPO has become a target for drug development directed to find treatments for neurodegenerative diseases and cancer. In
this context, TSPO appears to be involved in the generation of reactive oxygen species (ROS). This generation of ROS may provide
a link between activation of TSPO and of VDAC, to induce activation of the mitochondrial apoptosis pathway. ROS are known
to be able to release cytochrome c from cardiolipins located at the inner mitochondrial membrane. In addition, ROS appear to be able to activate VDAC and allow
VDAC mediated release of cytochrome c into the cytosol. Release of cytochrome c from the mitochondria forms the initiating
step for activation of the mitochondrial apoptosis pathway. These data provide an understanding regarding the mechanisms whereby
VDAC and TSPO may serve as targets to modulate apoptotic rates. This has implications for drug design to treat diseases such
as neurodegeneration and cancer. 相似文献
78.
Mischa R. Müller Kenneth Saunders Christopher Grace Macy Jin Nicole Piche-Nicholas John Steven Ronan O’Dwyer Leeying Wu Lam Khetemenee Yulia Vugmeyster Timothy P. Hickling Lioudmila Tchistiakova Stephane Olland Davinder Gill Allan Jensen Caroline J. Barelle 《MABS-AUSTIN》2012,4(6):673-685
Advances in recombinant antibody technology and protein engineering have provided the opportunity to reduce antibodies to their smallest binding domain components and have concomitantly driven the requirement for devising strategies to increase serum half-life to optimise drug exposure, thereby increasing therapeutic efficacy. In this study, we adopted an immunization route to raise picomolar affinity shark immunoglobulin new antigen receptors (IgNARs) to target human serum albumin (HSA). From our model shark species, Squalus acanthias, a phage display library encompassing the variable binding domain of IgNAR (VNAR) was constructed, screened against target, and positive clones were characterized for affinity and specificity. N-terminal and C-terminal molecular fusions of our lead hit in complex with a naïve VNAR domain were expressed, purified and exhibited the retention of high affinity binding to HSA, but also cross-selectivity to mouse, rat and monkey serum albumin both in vitro and in vivo. Furthermore, the naïve VNAR had enhanced pharmacokinetic (PK) characteristics in both N- and C-terminal orientations and when tested as a three domain construct with naïve VNAR flanking the HSA binding domain at both the N and C termini. Molecules derived from this platform technology also demonstrated the potential for clinical utility by being available via the subcutaneous route of delivery. This study thus demonstrates the first in vivo functional efficacy of a VNAR binding domain with the ability to enhance PK properties and support delivery of multifunctional therapies. 相似文献
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80.