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41.
The Effects of Cytokinin and Light on Hypocotyl Elongation in Arabidopsis Seedlings Are Independent and Additive 总被引:10,自引:2,他引:8 下载免费PDF全文
Cytokinin has been reported to mimic some of the effects of light on de-etiolation responses in dark-grown Arabidopsis seedlings. The interaction between cytokinin and light was examined by analyzing cytokinin dose and light fluence effects on hypocotyl elongation in wild-type and mutant Arabidopsis seedlings with defects in light or hormone responses. It was found that (a) cytokinin and light-response systems have independent and additive effects on the inhibition of hypocotyl elongation and (b) either cytokinin or light can saturate the morphogenic responses. As a consequence, cytokinin has no effect on hypocotyl elongation under normal growth conditions because light levels saturate the hypocotyl inhibition response. To determine whether a functional light-response pathway is required for cytokinin responses, light-insensitive long hypocotyl (hy) mutants were tested for cytokinin responses. The hy mutants (hy1 to hy6) had normal cytokinin responses, except phyB-1 (hy3-1), in which hypocotyl elongation was insensitive to cytokinin. Cytokinin insensitivity in phyB-1 was attributed to an indirect effect of the mutation on cytokinin responses. The effects of cytokinin on the inhibition of hypocotyl elongation are largely mediated by ethylene, and blocking the ethylene-response pathway through the action of a cytokinin-resistant, ethylene-insensitive mutant (ckr1/ein2) had no effect on the light inhibition of hypocotyl elongation. These results do not support the idea that cytokinin mediates the action of light on hypocotyl elongation. 相似文献
42.
Cloning and characterization of the katB gene of Pseudomonas aeruginosa encoding a hydrogen peroxide-inducible catalase: purification of KatB, cellular localization, and demonstration that it is essential for optimal resistance to hydrogen peroxide. 下载免费PDF全文
S M Brown M L Howell M L Vasil A J Anderson D J Hassett 《Journal of bacteriology》1995,177(22):6536-6544
Pseudomonas aeruginosa is an obligate aerobe that is virtually ubiquitous in the environment. During aerobic respiration, the metabolism of dioxygen can lead to the production of reactive oxygen intermediates, one of which includes hydrogen peroxide. To counteract the potentially toxic effects of this compound, P. aeruginosa possesses two heme-containing catalases which detoxify hydrogen peroxide. In this study, we have cloned katB, encoding one catalase gene of P. aeruginosa. The gene was cloned on a 5.4-kb EcoRI fragment and is composed of 1,539 bp, encoding 513 amino acids. The amino acid sequence of the P. aeruginosa katB was approximately 65% identical to that of a catalase from a related species, Pseudomonas syringae. The katB gene was mapped to the 71- to 75-min region of the P. aeruginosa chromosome, the identical region which harbors both sodA and sodB genes encoding both manganese and iron superoxide dismutases. When cloned into a catalase-deficient mutant of Escherichia coli (UM255), the recombinant P. aeruginosa KatB was expressed (229 U/mg) and afforded this strain resistance to hydrogen peroxide nearly equivalent to that of the wild-type E. coli strain (HB101). The KatB protein was purified to homogeneity and determined to be a tetramer of approximately 228 kDa, which was in good agreement with the predicted protein size derived from the translated katB gene. Interestingly, KatB was not produced during the normal P. aeruginosa growth cycle, and catalase activity was greater in nonmucoid than in mucoid, alginate-producing organisms. When exposed to hydrogen peroxide and, to a greater extent, paraquat, total catalase activity was elevated 7- to 16-fold, respectively. In addition, an increase in KatB activity caused a marked increase in resistance to hydrogen peroxide. KatB was localized to the cytoplasm, while KatA, the "housekeeping" enzyme, was detected in both cytoplasmic and periplasmic extracts. A P. aeruginosa katB mutant demonstrated 50% greater sensitivity to hydrogen peroxide than wild-type bacteria, suggesting that KatB is essential for optimal resistance of P. aeroginosa to exogenous hydrogen peroxide. 相似文献
43.
Structure and evolution of teleost mitochondrial control regions 总被引:50,自引:0,他引:50
Woo-Jai Lee Janet Conroy W. Huntting Howell Thomas D. Kocher 《Journal of molecular evolution》1995,41(1):54-66
We amplified and sequenced the mitochondrial control region from 23 species representing six families of teleost fish. The length of this segment is highly variable among even closely related species due to the presence of tandemly repeated sequences and large insertions. The position of the repetitive sequences suggests that they arise during replication both near the origin of replication and at the site of termination of the D-loop strand. Many of the conserved sequence blocks (CSBs) observed in mammals are also found among fish. In particular, the mammalian CSB-D is present in all of the fish species studied. Study of potential secondary structures of RNAs from the conserved regions provides little insight into the functional constraints on these regions. The variable structure of these control regions suggests that particular care should be taken to identify the most appropriate segment for studies of intraspecific variation.
Correspondence to: T.D. Kocher 相似文献
44.
The breeding season was 157, 154, <126, 210 and 217 days for Rambouillet, Columbia, Suffolk, Rambouillet x Finnish Landrace and Columbia x Finnish Landrace ewes respectively. Treatment of cyclic ewes with pregnant mare serum gonadotropin (PMSG) (500 IU), following a 12-day treatment with progestin-containing intravaginal sponges, did not affect fertility, but did decrease the time from sponge removal to estrus, (control 48.0 +/- 3.1 hr; PMSG 39.4 +/- 1.8 hr) to the preovulatory surge of LH (control 52.7 +/- 2.8 hr; PMSG 39.0 +/- 1.7 hr) and FSH (control 52.3 +/- 2.9 hr; PMSG 42.8 +/- 1.6 hr) and caused an elevation of serum LH levels prior to the preovulatory surge (control 1.25 +/- 0.18 ng/ml; PMSG 2.31 +/- 0.22 ng/ml). Exposure of the purebred ewes to 18 hours of daylight in January, decreasing by 30 minutes a week subsequently, counteracted the seasonal reduction in the number of ewes lambing following induced breeding under natural daylight in May. Prolificacy was greatest in crossbred ewes and their fertility was not affected by season. Gestation period was longer for fall-bred ewes and varied with breed. 相似文献
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46.
Summary Pulse-chase experiments utilising(3H)leucine have been used to study the effects of colchicine and vinblastine on intracellular transport and secretion of newly synthesised growth hormone from rat anterior pituitary fragments. Growth hormone was isolated from medium and fragments by polyacrylamide gel electrophoresis. When colchicine or vinblastine, which disrupt microtubules, were added immediately after pulse labelling, inhibition of the subsequent secretion of newly synthesised growth hormone was detected throughout the succeeding 5 h. Similar inhibition was seen if the drugs were added after a 1 h delay. However, if colchicine or vinblastine were added only after a 2 h chase incubation, then no significant effect on subsequent release of labelled growth hormone was seen. The results suggest that these agents may inhibit the transport of newly formed growth hormone storage granules from the Golgi complex to the cytoplasmic pool. Microtubules do not appear to be involved in the mechanism of the final secretion of newly synthesised hormone by exocytosis.These studies were supported by grants from the Medical Research Council and British Diabetic Association 相似文献
47.
Circular dichroic, infrared and other studies on the protein component of pig brain thromboplastin. 总被引:1,自引:0,他引:1 下载免费PDF全文
1. A four-step procedure used to isolate the protein component (apoprotein III) of pig brain thromboplastin yielded approximately 25 mg from 500g of brain. 2. In the absence of detergent, apoprotein III had an apparent mol.wt. of 360 000 by gel-filtration, and, after electrophoresis on polyacrylamide gels in the presence of sodium docecyl sulphate, it appeared as a major protein band of mol.wt.59 000, suggesting the existence of polymeric and monomeric forms. 3. Chemical analyses of apoprotein III revealed that hydrophilic and hydrophobic amino acids were present in a ratio of 3:2, together with approx, 9% (w/w) of carbohydrate. 4. The far-u.v.c.d. and i.r. spectral data indicated that, like other membrane proteins, apoprotein III has a high percentage of unordered structure with lesser amounts of alpha and beta-forms. 5. Relipidation of apoprotein III to restore clotting activity caused no extensive alteration in the c.d. and i.r. spectra, indicating that the phospholipid associates with a comparatively small hydrophobic segment. The constrained unordered conformation, which makes the major contribution to the c.d. spectrum, probably forms a separate domain in the aqueous phase. The absence of any increase in the amplitude of both negative c.d. extrema, following relipidation, contrasted with the substantial increase observed in a helix-forming solvent and raises the possibility that the more stable polymeric form of apoprotein III is retained as the active form in the lipid phase. 6. We suggest that as a consequence of cell membrane damage, the recognition and activation of factor VII may involve minor changes of conformation that are dependent upon the flexibility inherent in an unordered secondary structure. 相似文献
48.
Identification and Properties of the Messenger RNA Activity in Chlamydomonas reinhardi Coding for the Large Subunit of d-ribulose-1,5-bisphosphate Carboxylase 总被引:3,自引:2,他引:1 下载免费PDF全文
Properties of the mRNA coding for the large subunit of ribulose-1,5-bisphosphate carboxylase from Chlamydomonas reinhardi were determined. Large subunit synthesis, directed by RNA from partially purified whole cell extracts, was detected by specific immunoprecipitation of polypeptide products synthesized in a heterologous translation system derived from Escherichia coli. Large subunit synthesis showed sharp RNA concentration dependence in an E. coli translation system, and at optimal RNA concentrations, immunoprecipitable large subunit synthesis accounted for 2% of the total incorporation. Large subunit messenger activity sedimented at 12 to 14S on nondenaturing sucrose gradients and did not bind to oligo(dT)-cellulose suggesting the mRNA is not polyadenylated. The immunoprecipitable products translated in vitro are not complete polypeptide chains, but are smaller peptides identifiable as large subunit fragments by tryptic fingerprint analysis. No immunoprecipitable product was obtained when similar RNA fractions were tested in a wheat germ translation system. 相似文献
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