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81.
We present a simplified binocular neural network model of the primary visual cortex with separate ON/OFF-pathways and modifiable afferent as well as intracortical synaptic couplings. Random as well as natural image stimuli drive the weight adaptation which follows Hebbian learning rules stabilized with constant norm and constant sum constraints. The simulations consider the development of orientation and ocular dominance maps under different conditions concerning stimulus patterns and lateral couplings. With random input patterns realistic orientation maps with +/- 1/2-vortices mostly develop and plastic lateral couplings self-organize into mexican hat type structures on average. Using natural greyscale images as input patterns, realistic orientation maps develop as well and the lateral coupling profiles of the cortical neurons represent the two point correlations of the input image used. 相似文献
82.
83.
Juge-Aubry CE Hammar E Siegrist-Kaiser C Pernin A Takeshita A Chin WW Burger AG Meier CA 《The Journal of biological chemistry》1999,274(15):10505-10510
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85.
With a view to visualizing the ultrastructural distribution of syringyl lignins in secondary plant cell walls, a polyclonal antibody raised from a synthetic DHP polymer consisting only of syringyl propane units was prepared. To test the reactivity of the antiserum, a mini-dot-blot immunoassay reducing the amounts of substrates and antiserum was developed. A characteristic attribute of the S-antiserum appears to be its specific recognition of sequences of three or more consecutive syringyl units. On ultra-thin sections of model plants of Arabidopsis thaliana, Populus and tobacco, the antiserum allowed us to demonstrate a higher concentration of syringyl epitopes in fibres than in vessels. Variations in the distribution pattern of these epitopes between the three plants examined suggest that the synthesis of syringyl lignins in angiosperms depends on the species. 相似文献
86.
Trucco A Polishchuk RS Martella O Di Pentima A Fusella A Di Giandomenico D San Pietro E Beznoussenko GV Polishchuk EV Baldassarre M Buccione R Geerts WJ Koster AJ Burger KN Mironov AA Luini A 《Nature cell biology》2004,6(11):1071-1081
The organization of secretory traffic remains unclear, mainly because of the complex structure and dynamics of the secretory pathway. We have thus studied a simplified system, a single synchronized traffic wave crossing an individual Golgi stack, using electron tomography. Endoplasmic-reticulum-to-Golgi carriers join the stack by fusing with cis cisternae and induce the formation of intercisternal tubules, through which they redistribute their contents throughout the stack. These tubules seem to be pervious to Golgi enzymes, whereas Golgi vesicles are depleted of both enzymes and cargo. Cargo then traverses the stack without leaving the cisternal lumen. When cargo exits the stack, intercisternal connections disappear. These findings provide a new view of secretory traffic that includes dynamic intercompartment continuities as key players. 相似文献
87.
Diagnostic polymorphisms in the mitochondrial cytochrome b gene allow discrimination between cattle,sheep, goat,roe buck and deer by PCR-RFLP 总被引:3,自引:0,他引:3
Background
As an alternative to direct DNA sequencing of PCR products, random PCR-RFLP is an efficient technique to discriminate between species. The PCR-RFLP-method is an inexpensive tool in forensic science, even if the template is degraded or contains only traces of DNA from various species. 相似文献88.
Palmer G Burger D Mezin F Magne D Gabay C Dayer JM Guerne PA 《Arthritis research & therapy》2004,6(3):R181-R189
Leflunomide is an immunomodulatory agent used for the treatment of rheumatoid arthritis. In this study, we investigated the
effect of A77 1726 – the active metabolite of leflunomide – on the production of IL-1 receptor antagonist (IL-1Ra) by human
synovial fibroblasts and articular chondrocytes. Cells were incubated with A77 1726 alone or in combination with proinflammatory
cytokines. IL-1Ra production was determined by ELISA. A77 1726 alone had no effect, but in the presence of IL-1β or tumour
necrosis factor-α it markedly enhanced the secretion of IL-1Ra in synovial fibroblasts and chondrocytes. The effect of A77
1726 was greatest at 100 μmol/l. In synovial fibroblasts and de-differentiated chondrocytes, A77 1726 also increased IL-1β-induced
IL-1Ra production in cell lysates. Freshly isolated chondrocytes contained no significant amounts of intracellular IL-1Ra.
A77 1726 is a known inhibitor of pyrimidine synthesis and cyclo-oxygenase (COX)-2 activity. Addition of exogenous uridine
did not significantly modify the effect of A77 1726 on IL-1Ra production, suggesting that it was not mediated by inhibition
of pyrimidine synthesis. Indomethacin increased IL-1β-induced IL-1Ra secretion in synovial fibroblasts and de-differentiated
chondrocytes, suggesting that inhibition of COX-2 may indeed enhance IL-1β-induced IL-1Ra production. However, the stimulatory
effect of indomethacin was consistently less effective than that of A77 1726. A77 1726 increases IL-1Ra production by synovial
fibroblasts and chondrocytes in the presence of proinflammatory cytokines, and thus it may possess chondroprotective effects.
The effect of A77 1726 may be partially mediated by inhibition of COX-2, but other mechanisms likely concur to stimulate IL-1Ra
production. 相似文献
89.
Root : shoot ratios, optimization and nitrogen productivity 总被引:5,自引:0,他引:5
90.
Svensson M Fast J Mossberg AK Düringer C Gustafsson L Hallgren O Brooks CL Berliner L Linse S Svanborg C 《Protein science : a publication of the Protein Society》2003,12(12):2794-2804
HAMLET (human alpha-lactalbumin made lethal to tumor cells) is a complex of human alpha-lactalbumin and oleic acid (C18:1:9 cis) that kills tumor cells by an apoptosis-like mechanism. Previous studies have shown that a conformational change is required to form HAMLET from alpha-lactalbumin, and that a partially unfolded conformation is maintained in the HAMLET complex. This study examined if unfolding of alpha-lactalbumin is sufficient to induce cell death. We used the bovine alpha-lactalbumin Ca(2+) site mutant D87A, which is unable to bind Ca(2+), and thus remains partially unfolded regardless of solvent conditions. The D87A mutant protein was found to be inactive in the apoptosis assay, but could readily be converted to a HAMLET-like complex in the presence of oleic acid. BAMLET (bovine alpha-lactalbumin made lethal to tumor cells) and D87A-BAMLET complexes were both able to kill tumor cells. This activity was independent of the Ca(2+)site, as HAMLET maintained a high affinity for Ca(2+) but D87A-BAMLET was active with no Ca(2+) bound. We conclude that partial unfolding of alpha-lactalbumin is necessary but not sufficient to trigger cell death, and that the activity of HAMLET is defined both by the protein and the lipid cofactor. Furthermore, a functional Ca(2+)-binding site is not required for conversion of alpha-lactalbumin to the active complex or to cause cell death. This suggests that the lipid cofactor stabilizes the altered fold without interfering with the Ca(2+)site. 相似文献