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931.
Bedell JA Budiman MA Nunberg A Citek RW Robbins D Jones J Flick E Rholfing T Fries J Bradford K McMenamy J Smith M Holeman H Roe BA Wiley G Korf IF Rabinowicz PD Lakey N McCombie WR Jeddeloh JA Martienssen RA 《PLoS biology》2005,3(1):e13
932.
Hazkani-Covo E Wool D Graur D 《Journal of experimental zoology. Part B. Molecular and developmental evolution》2005,304(2):150-158
In 1828, Karl von Baer proposed a set of four evolutionary "laws" pertaining to embryological development. According to von Baer's third law, young embryos from different species are relatively undifferentiated and resemble one another but as development proceeds, distinguishing features of the species begin to appear and embryos of different species progressively diverge from one another. An expansion of this law, called "the hourglass model," has been proposed independently by Denis Duboule and Rudolf Raff in the 1990s. According to the hourglass model, ontogeny is characterized by a starting point at which different taxa differ markedly from one another, followed by a stage of reduced intertaxonomic variability (the phylotypic stage), and ending in a von-Baer-like progressive divergence among the taxa. A possible "translation" of the hourglass model into molecular terminology would suggest that orthologs expressed in stages described by the tapered part of the hourglass should resemble one another more than orthologs expressed in the expansive parts that precede or succeed the phylotypic stage. We tested this hypothesis using 1,585 mouse genes expressed during 26 embryonic stages, and their human orthologs. Evolutionary divergence was estimated at different embryonic stages by calculating pairwise distances between corresponding orthologous proteins from mouse and human. Two independent datasets were used. One dataset contained genes that are expressed solely in a single developmental stage; the second was made of genes expressed at different developmental stages. In the second dataset the genes were classified according to their earliest stage of expression. We fitted second order polynomials to the two datasets. The two polynomials displayed minima as expected from the hourglass model. The molecular results suggest, albeit weakly, that a phylotypic stage (or period) indeed exists. Its temporal location, sometimes between the first-somites stage and the formation of the posterior neuropore, was in approximate agreement with the morphologically defined phylotypic stage. The molecular evidence for the later parts of the hourglass model, i.e., for von Baer's third law, was stronger than that for the earlier parts. 相似文献
933.
The endangered mountain zebra (Equus zebra) is endemic to the semi-arid inhospitable mountainous escarpments of southern Africa. The species is divided taxonomically
into two geographically separated subspecies, each with differing recent population histories. In Namibia, Hartmann’s mountain
zebra (E. z. hartmannae) is common and occurs in large free-ranging populations, whereas in South Africa, prolonged hunting and habitat destruction
over the last 300 years has decimated populations of the Cape mountain zebra (E. z. zebra). In this study, we investigate the consequences of these divergent demographic histories for population genetic diversity
and structure. We also examine the phylogeographic relationship between the two taxonomic groups. Genetic information was
obtained at 15 microsatellite loci for 291 individuals from a total of 10 populations as well as 445 bp of the mitochondrial
control region sequence data from 77 individuals. Both model-based and standard analytical approaches were used to examine
the data. Both types of marker returned levels of diversity and structure that were consistent with population history. Low
genetic variation within individual Cape mountain zebra populations, the characteristic indicator of population fragmentation
and drift, was offset by moderate variation in the entire E. z. zebra sample. This implies that higher levels of diversity still exist within the Cape mountain zebra gene pool. A management strategy
that entailed the mixing of aboriginal populations is therefore advocated in order to halt the further loss of Cape mountain
zebra genetic diversity. Allele frequencies in Hartmann’s mountain zebra were relatively resilient to demographic fluctuations.
Due to the high incidence of mitochondrial haplotype sharing between populations, the hypothesis that Cape and Hartmann’s
mountain zebra mitochondrial lineages were reciprocally monophyletic was not supported. However, the presence of private alleles
at nuclear loci rendered the two subspecies genetically distinct evolutionary significant units. 相似文献
934.
Mao Y Lai C Vogtentanz G Schmidt B Day T Miller J Brandon DL Chen D 《The protein journal》2005,24(5):275-282
Monoclonal antibodies against soybean Bowman-Birk protease inhibitor (BBI) have been generated and used to detect and quantify
BBI in foods, soybean germplasm, and animal tissues and fluids. The purpose of this study was to determine the recognition
sites of two monoclonal antibodies to BBI (mAb 238 and mAb 217) in relation to the protease-inhibitory sites of BBI. The results
showed that (1) the binding of mAb 238 can be blocked by trypsin and that of mAb 217 by chymotrypsin; (2) the trypsin or chymotrypsin
inhibitory activities of BBI are blocked by mAb 238 or mAb 217, respectively; and (3) mAb 238 failed to recognize a tryptic
loop mutant BBI variant and mAb 217 was unable to bind a chymotryptic loop mutant BBI variant. These findings demonstrate
that the epitopes recognized by mAb 238 and mAb 217 reside, at least in part, in the tryptic and chymotryptic loops of BBI,
respectively. 相似文献
935.
This work concerns the cause of glycolytic oscillations in yeast. We analyse experimental data as well as models in two distinct cases: the relaxation-like oscillations seen in yeast extracts, and the sinusoidal Hopf oscillations seen in intact yeast cells. In the case of yeast extracts, we use flux-change plots and model analyses to establish that the oscillations are driven by on/off switching of phosphofructokinase. In the case of intact yeast cells, we find that the instability leading to the appearance of oscillations is caused by the stoichiometry of the ATP-ADP-AMP system and the allosteric regulation of phosphofructokinase, whereas frequency control is distributed over the reaction network. Notably, the NAD+/NADH ratio modulates the frequency of the oscillations without affecting the instability. This is important for understanding the mutual synchronization of oscillations in the individual yeast cells, as synchronization is believed to occur via acetaldehyde, which in turn affects the frequency of oscillations by changing this ratio. 相似文献
936.
Witonsky SG Gogal RM Duncan RB Norton H Ward D Lindsay DS 《International journal for parasitology》2005,35(1):113-123
Immunodeficient CD8 knockout mice were infected with Sarcocystis neurona merozoites, in order to determine the role of CD8 cells in protective immunity. Using a direct agglutination test, all infected mice seroconverted by selected time points. Infected mice developed splenomegaly and bilateral lymphadenopathy. Histological changes included marked follicular development in the spleen, endothelitis and moderate perivascular inflammation in the liver, and meningoencephalitis in the brain. Infected brains were positive for S. neurona by polymerase chain reaction. Corresponding to histopathological changes, there were decreased numbers of B-cells in the spleen. The mice did not have significant memory (CD44hi/CD4) or effector (CD45RBhi/CD4) populations present at the time of euthanasia. Flow cytometry confirmed the lack of CD8 cells. Taken together, these data support previous studies suggesting a critical role for CD8 cells in the prevention of menigoencephalitis in S. neurona-infected mice. 相似文献
937.
CR1R2OH, Ri = CH3 or H, react with the complex [CoIII(NH3)5CN]2+ to form an observable intermediate probably via bonding to the nitrogen of the cyanide. This intermediate isomerizes to form a second intermediate. The second intermediate decomposes into Co2+(aq), 5NH4+, CN− and R1R2CO. The plausible structures of the intermediates are discussed. The radicals CH3, CH2CHO, , and are considerably less reactive towards this complex, the formation of intermediates in their presence is not observed. 相似文献
938.
Plasma membrane neurotransmitter transporters rapidly traffic to and from the cell surface in neurons. This trafficking may be important in regulating neuronal signaling. Such regulation will be subject to the number of trafficking transporters and their trafficking rates. In the present study, we define an acutely recycling pool of endogenous gamma-aminobutyric acid transporters (GAT1) in cortical neurons that comprises approximately one-third of total cellular GAT1. Kinetic analysis of this pool estimates exocytosis and endocytosis time constants of 1.6 and 0.9 min, respectively, and thus approximately one-third of the recycling pool is plasma membrane resident in the basal state. Recent evidence shows that GAT1 substrates, second messengers, and interacting proteins regulate GAT1 trafficking. These triggers could act by altering trafficking rates or by changing the recycling pool size. In the present study we examine three GAT1 modulators. Calcium depletion decreases GAT1 surface expression by diminishing the recycling pool size. Sucrose increases GAT1 surface expression by blocking clathrin- and dynamin-dependent endocytosis, but it does not change the recycling pool size. Protein kinase C decreases surface GAT1 expression by increasing the endocytosis rate, but it does not change the exocytosis rate or the recycling pool size. Based upon estimates of GAT1 molecules in cortical boutons, the present data suggest that approximately 1000 transporters comprise the acutely recycling pool, of which 300 are on the surface in the basal state, and five transporters insert into the plasma membrane every second. This insertion could represent the fusion of one transporter-containing vesicle. 相似文献
939.
Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces programmed cell death through the caspase activation cascade and translocation of cleaved Bid (tBid) by the apical caspase-8 to mitochondria to induce oligomerization of multidomain Bax and Bak. However, the roles of prosurvival Bcl-2 family proteins in TRAIL apoptosis remain elusive. Here we showed that, besides the specific cleavage and activation of Bid by caspase-8 and caspase-3, TRAIL-induced apoptosis in Jurkat T cells required the specific cleavage of Mcl-1 at Asp-127 and Asp-157 by caspase-3, while other prototypic antiapoptotic factors such as Bcl-2 or Bcl-X(L) seemed not to be affected. Mutation at Asp-127 and Asp-157 of Mcl-1 led to cellular resistance to TRAIL-induced apoptosis. In sharp contrast to cycloheximide-induced Mcl-1 dilapidation, TRAIL did not activate proteasomal degradation of Mcl-1 in Jurkat cells. We further established for the first time that the C-terminal domain of Mcl-1 became proapoptotic as a result of caspase-3 cleavage, and its physical interaction and cooperation with tBid, Bak, and voltage-dependent anion-selective channel 1 promoted mitochondrial apoptosis. These results suggested that removal of N-terminal domains of Bid by caspase-8 and Mcl-1 by caspase-3 enabled the maximal mitochondrial perturbation that potentiated TRAIL-induced apoptosis. 相似文献
940.
Mishra S Mishra JP Gee K McManus DC LaCasse EC Kumar A 《The Journal of biological chemistry》2005,280(45):37536-37546
Exposure of phagocytic cells to bacterial endotoxin (lipopolysaccharide; LPS) or inflammatory cytokines confers antiapoptotic survival signals; however, in the absence of the appropriate stimulus, monocytes are programmed to undergo apoptosis. Macrophage survival may thus influence inflammatory and immune responses and susceptibility to microbial pathogens. Herein, we demonstrate that LPS and the proinflammatory cytokine, tumor necrosis factor-alpha (TNF-alpha), enhance monocytic cell survival through the induction of the antiapoptotic c-IAP2 gene in a human promonocytic THP-1 cell line. We also investigated the role of upstream signaling molecules including the mitogen-activated protein kinases, phosphatidylinositol 3-kinase, and the calcium signaling pathways in the regulation of c-IAP2 expression and eventual survival of monocytic cells. Our results suggest that LPS and TNF-alpha-induced c-IAP2 expression was regulated by calmodulin (CaM) through the activation of calmodulin-dependent protein kinase-II (CaMKII). In addition, CaM and CaMKII regulated c-IAP2 expression in LPSand TNF-alpha-stimulated cells through NF-kappaB activation. Moreover, the CaM/CaMKII pathway also regulated LPS- and TNF-alpha-mediated inhibition of apoptosis in these cells. Taken together, these results suggest that LPS- and TNF-alpha-induced c-IAP2 expression and its associated antiapoptotic survival signals in THP-1 cells are regulated selectively by CaM/CaMKII through NF-kappaB activation. 相似文献