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43.
Chest wall motion during epidural anesthesia in dogs 总被引:3,自引:0,他引:3
To determine the relative contribution of rib cage and abdominal muscles to expiratory muscle activity during quiet breathing, we used lumbar epidural anesthesia in six pentobarbital sodium-anesthetized dogs lying supine to paralyze the abdominal muscles while leaving rib cage muscle motor function substantially intact. A high-speed X-ray scanner (Dynamic Spatial Reconstructor) provided three-dimensional images of the thorax. The contribution of expiratory muscle activity to tidal breathing was assessed by a comparison of chest wall configuration during relaxed apnea with that at end expiration. We found that expiratory muscle activity was responsible for approximately half of the changes in thoracic volume during inspiration. Paralysis of the abdominal muscles had little effect on the pattern of breathing, including the contribution of expiratory muscle activity to tidal breathing, in most dogs. We conclude that, although there is consistent phasic expiratory electrical activity in both the rib cage and the abdominal muscles of pentobarbital-anesthetized dogs lying supine, the muscles of the rib cage are mechanically the most important expiratory muscles during quiet breathing. 相似文献
44.
A human muscle adenine nucleotide translocator gene has four exons, is located on chromosome 4, and is differentially expressed 总被引:8,自引:0,他引:8
K Li C K Warner J A Hodge S Minoshima J Kudoh R Fukuyama M Maekawa Y Shimizu N Shimizu D C Wallace 《The Journal of biological chemistry》1989,264(24):13998-14004
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46.
Jeff Alexander J. Alan Payne Brian Shigekawa Jeffrey A. Frelinger Peter Cresswell 《Immunogenetics》1990,31(3):169-178
The transport of human-mouse hybrid class I histocompatibility antigens has been studied in a mutant human cell line, 174 × CEM.T2 (T2). T2, a somatic cell hybrid of human B- and T-lymphoblastoid cell lines (B-LCL and T-LCL, respectively), synthesizes HLA-A2 and HLA-B5 glycoproteins, but expresses only low levels of A2 and undetectable levels of B5 at the cell surface. We have previously shown that the products of human class I genes introduced into T2 by transfection behave like the endogenous HLA-B5 glycoproteins, while the products of mouse class I alleles similarly introduced are transported normally to the cell surface. We have now determined that the surface expression of class I glycoproteins in T2 depends on the origin of the 1 and 2 domains. Human (HLA-B7) and mouse (H-2D
p
) hybrid class I genes, encoding the leader, 1, and 2 sequences of one species fused to the 3, transmembrane, and cytoplasmic domains of the other, were transfected into T2. Normal surface expression of the hybrid class I molecule was observed in T2 only when the leader, 1, and 2-encoding exons were derived from the mouse gene. The reciprocal construct, encoding human leader, 1, and 2 domains fused to the mouse 3, transmembrane, and cytoplasmic regions, resulted in biosynthesis of a hybrid glycoprotein which was not transported to the cell surface. The products of both constructs were expressed normally in control cells. The effects of glycosylation on class I antigen transport were also studied using mutant class I constructs with altered glycosylation sites. Two mutant B7 genes encoding either an extra glycosylation site at position 176 or no glycosylation sites were transfected into T2. These mutant products were expressed at the cell surface in control cells, but were synthesized and not surface-expressed in T2. These data demonstrate that the HLA/H-2 transport dichotomy in T2 is a function of the origin of the 1 and/or 2 domains of the class I glycoprotein, and is not a reflection of glycosylation differences between the human and mouse molecules.
Offprint requests to: P. Cresswell. 相似文献
47.
The green alga Chlamydomonas reinhardtii is a facultative heterotroph and, when cultured in the presence of acetate, will synthesize chlorophyll (Chl) and photosystem (PS) components in the dark. Analysis of the thylakoid membrane composition and function in dark grown C. reinhardtii revealed that photochemically competent PS II complexes were synthesized and assembled in the thylakoid membrane. These PS II centers were impaired in the electron-transport reaction from the primary-quinone electron acceptor, QA, to the secondary-quinone electron acceptor, QB (QB-nonreducing centers). Both complements of the PS II Chl a–b light harvesting antenna (LHC II-inner and LHC II-peripheral) were synthesized and assembled in the thylakoid membrane of dark grown C. reinhardtii cells. However, the LHC II-peripheral was energetically uncoupled from the PS II reaction center. Thus, PS II units in dark grown cells had a -type Chl antenna size with only 130 Chl (a and b) molecules (by definition, PS II units lack LHC II-peripheral). Illumination of dark grown C. reinhardtii caused pronounced changes in the organization and function of PS II. With a half-time of about 30 min, PS II centers were converted froma QB-nonreducing form in the dark, to a QB-reducing form in the light. Concomitant with this change, PS II units were energetically coupled with the LHC II-peripheral complement in the thylakoid membrane and were converted to a PS II form. The functional antenna of the latter contained more than 250 Chl(a+b) molecules. The results are discussed in terms of a light-dependent activation of the QA-QB electron-transfer reaction which is followed by association of the PS II unit with a LHC II-peripheral antenna and by inclusion of the mature form of PS II (PS II) in the membrane of the grana partition region.Abbreviations Chl
chlorophyll
- PS
photosystem
- QA
primary quinone electron acceptor of PS II
- QB
secondary quinone electron acceptor of PS II
- LHC
light harvesting complex
- F0
non-variable fluorescence yield
- Fplf
intermediate fluorescence yield plateau leyel
- Fmax
maximum fluorescence yield
- Fi
initial fluorescence yield increase from F0 to Fpl (Fpl–F0)
- Fv
total variable fluorescence yield (Fm–F0)
- DCMU
dichlorophenyl-dimethylurea 相似文献
48.
Jeff Reeve Lorraine H. Kligman Robert Anderson 《Applied microbiology and biotechnology》1990,33(2):161-166
Summary Isolated lipids from Deinococcus radiodurans were reconstituted at final concentrations of 1 mg/ml into dioleoyl phosphatidyl choline (DOPC) vesicles and assayed for the ability to protect cells of Escherichia coli against killing by UV light (254 nm). Values of D37 (UV dose required to reduce the number of surviving cells to 37% of the original number) were calculated from killing curves. E. coli was afforded the greatest protection with an individual lipid, identified as vitamin MK8 (D37=310 J//m2, compared to D37=67 J/m2 for E. coli irradiated in the presence of DOPC alone). Liposome-mediated protection was dependent on UV254 absorbance and not on turbidity-related light-scattering. BOth vitamin MK8 from D. radiodurans and vitamin K1, which is available commercially, showed a similar degree of UV254-protection for E. coli. The UV-protective properties of vitamin K1 were also investigated on mammalian cells in comparison with other natural lipids and known sunscreens. Survival curves were obtained for mouse fibroblast (L) cells irradiated at UV254 in the absence or presence of DOPC liposomes into which were incorporated various natural lipids or standard sunscreen ingredients, all at final concentrations of 1 mg/ml. Experimentally determined values of D37 were as follows: Vitamin K1, 73 J/m2; \-carotene, 44 J/m2; -tocopherol, 20 J/m2; sulisobenzone, 156 J/m2; p-aminobenzoic acid (PABA), 113 J/m2; benzophenone, 80 J/m2; oxybenzone, 61 J/m2 and DOPC alone. 23 J/m2. Vitamin K1, the most protective lipid tested, was also compared with PABA and oxybenzone (all at concentrations of 20 mg/ml; applied topicall) for its ability to protec Skh-hairless mice from UV254-induced erythema, yielding a UV254 protection factor of 3.5. In addition, vitamin K1 (at 100 mg/ml) was able to provide hairless mice with a small degree of UVB protection, as indicated by an experimentally determined Solar Protection Factor of 1.5–2.0. Although it is concluded that vitamin K is not likely to account for the extraordinarily high degree of UV-resistance of D. radiodurans, vitamin K does show characteristics worthy of its consideration as a UV-screening agent.
Offprint requests to: R. Anderson 相似文献
49.
Summary Carpophores were developed on defined medium from explants of stipes produced in the dark using an expansionless mutant (no. 190) ofCoprinus cinereus. Explants taken from stipes within 24 h of formation developed multiple fruit within 3–12 days without formation of mycelia. Fruiting levels were affected by stipe age (24 h), medium composition, explant size, and polarity of the explant on fruiting medium. This method offers a new tool for developmental studies and may also be of use to commercial mushroom growers. 相似文献
50.
Isolation and characterization of a mutation that alters the substrate specificity of the Escherichia coli glucose permease.
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G S Begley K A Warner J C Arents P W Postma G R Jacobson 《Journal of bacteriology》1996,178(3):940-942
We isolated 10 mannitol-positive mutants from a mannitol-negative Escherichia coli strain. These mutations mapped within ptsG, encoding the glucose permease (EIIGlc), and resulted in a G-320-to-V substitution that allows EIIGlc to transport mannitol. Gly-320 lies within a putative transmembrane helix of EIIGlc that may be involved in substrate recognition. 相似文献