全文获取类型
收费全文 | 6375篇 |
免费 | 357篇 |
国内免费 | 1篇 |
出版年
2023年 | 23篇 |
2022年 | 48篇 |
2021年 | 89篇 |
2020年 | 57篇 |
2019年 | 75篇 |
2018年 | 95篇 |
2017年 | 91篇 |
2016年 | 142篇 |
2015年 | 215篇 |
2014年 | 260篇 |
2013年 | 428篇 |
2012年 | 404篇 |
2011年 | 423篇 |
2010年 | 247篇 |
2009年 | 224篇 |
2008年 | 395篇 |
2007年 | 362篇 |
2006年 | 362篇 |
2005年 | 324篇 |
2004年 | 298篇 |
2003年 | 302篇 |
2002年 | 272篇 |
2001年 | 133篇 |
2000年 | 136篇 |
1999年 | 141篇 |
1998年 | 56篇 |
1997年 | 55篇 |
1996年 | 41篇 |
1995年 | 39篇 |
1994年 | 35篇 |
1993年 | 36篇 |
1992年 | 85篇 |
1991年 | 82篇 |
1990年 | 65篇 |
1989年 | 78篇 |
1988年 | 62篇 |
1987年 | 42篇 |
1986年 | 43篇 |
1985年 | 50篇 |
1984年 | 41篇 |
1983年 | 49篇 |
1982年 | 21篇 |
1981年 | 20篇 |
1980年 | 20篇 |
1979年 | 39篇 |
1978年 | 22篇 |
1977年 | 18篇 |
1976年 | 22篇 |
1975年 | 19篇 |
1973年 | 18篇 |
排序方式: 共有6733条查询结果,搜索用时 19 毫秒
131.
When thiamine concentration in subculture medium was rapidlylowered to nil, soybean cells in suspension became necroticand stopped growing entirely. When it was gradually lowered,cell growth was vigorous until the concentration was reducedto 7.8?103 mg/liter. The cells at this level of thiamineceased growing for a time, but prolonged culture in the samemedium resulted in the appearance of fresh white cells whichcould be easily distinguished from the old brown, necrotic cellsin the aggregates. These new cell lines could be subculturedwith further reduction in the thiamine supply, growing as largeraggregates of about 4 mm in diameter. New cell lines were similarly obtained by prolonged culturesin media containing a thiamine precursor; three lines appearedto be habituated to the pyrimidine moiety and one to the thiazolemoiety. The latter cell line could be subcultured without thiamineand its precursors for at least eight passages. These habituatedcells were characterized by the increase of the dry to freshweight ratio and by their growth in large aggregates.
1Present address: Section of Phytochemical Research, Eisai Co.,Ltd., Kawashima, Gifu 483, Japan. (Received December 15, 1978; ) 相似文献
132.
Chlorella vulgaris 11h cells grown in air enriched with 4% CO2(high-CO2 cells) had carbonic anhydrase (CA) activity whichwas 20 to 90 times lower than that of algal cells grown in ordinaryair (containing 0.04% CO2, low-CO2 cells). The CO2 concentrationduring growth did not affect either ribulose 1,5-bisphosphate(RuBP) carboxylase activity or its Km for CO2. When high-CO2 cells were transferred to low CO2 conditions,CA activity increased without a lag period, and this increasewas accompanied by an increase in the rate of photosynthetic14CO2 fixation under 14CO2-limiting conditions. On the otherhand, CA activity as well as the rate of photosynthetic 14CO2fixation at low 14CO2 concentrations decreased when low-CO2cells were transferred to high CO2 conditions. Diamox, an inhibitor of CA, at 0.1 mM did not affect photosynthesisof low-CO2 cells at high CO2 concentration (0.5%). Diamox inhibitedphotosynthesis only under low CO2 concentrations, and the lowerthe CO2 concentration, the greater was the inhibition. Consequently,the CO2 concentration at which the rate of photosynthesis attainedone-half its maximum rate (Km) greatly increased in the presenceof this inhibitor. When CO2 concentration was higher than 1%, the photosyntheticrate in low-CO2 cells decreased, while that in high-CO2 cellsincreased. Fractionation of the low-CO2 cells in non-aqueous medium bydensity showed that CA was fractionated in a manner similarto the distribution of chlorophyll and RuBP carboxylase. These observations indicate that CA enhances photosynthesisunder CO2-limiting conditions, but inhibits it at CO2 concentrationshigher than a certain level. The mechanism underlying the aboveregulatory functions of CA is discussed.
1This work was reported at the International Symposium on PhotosyntheticCO2-Assimilation and Photorespiration, Sofia, August, 1977 (18).Requests for reprints should be addressed to S. Miyachi, RadioisotopeCentre, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan. (Received December 11, 1978; ) 相似文献
133.
H Takeuchi H Tamura A Kumagai M Ikeda 《Comptes rendus des séances de la Société de biologie et de ses filiales》1979,173(5):980-988
The influences of two water soluble contrast media, meglumine iothalamate and meglumine iocarmate, on the neuronal excitability and on the neuronal sensitivity to putative transmitters were examined in comparison with those of sucrose using two identifiable giant neurones of Achatina fulica Férussac (the TAN and the PON). A relatively low increase of osmotic pressure of the extracellular fluid, produced by the application of contrast media, reversed the Cl- dependent inhibition caused by a putative transmitter. The same increase of this osmotic pressure, however, did not influence the Cl- independent inhibition and the excitation of the neurone examined. The hyperpolarization of neuromembrane was caused by an increase of osmotic pressure of the extracellular fluid. Its relatively high increase was necessary to make spontaneous spike discharges disappear totally. All effects of the two contrast media, observed in this study, were due to the increase of osmotic pressure of the extracellular fluid ; no specific effect of the contrast media containing the iodine on the indicators used was observed. 相似文献
134.
Summary The role of the recA gene product of Escherichia coli in genetic recombination was examined in a system where recombination takes place in the absence of protein synthesis. recA200 bacteria were infected with two mutant strains of phage lambda in the presence of chloramphenicol and rifampin, and the resulting recombinant DNA molecules were measured by in vitro packaging. When recA200 bacteria grown at a temperature that is permissive for RecA phenotype were transferred to a temperature that is restrictive for RecA phenotype in the presence of the inhibitors, recombination of the infecting phages was severely blocked. This result shows that the recombination activity of the recA200 cells is inactivated by the change of temperature even in the absence of protein synthesis. The most likely explanation of this result is that the recA protein is directly involved in the recombination detected in the presence of chloramphenicol and rifampin. 相似文献
135.
Ubiquinone (UQ) formation in BY-2 tobacco cells was especially promoted by a high concentration of 2,4-D. 2,4,5-T, MCP and NAA also promoted UQ formation in these cells. The UQ content in the cells cultured at high concentrations of 2,4-D was higher than that of controls throughout the culture period. The addition of 2,4-D at an early period in cell growth was very effective in promoting UQ formation, but addition at the stationary phase was ineffective. Cell growth was improved by adding phosphate to the medium but UQ content was decreased. UQ content decreased slowly during subculturing, whereas cell growth recovered gradually. 相似文献
136.
Koenig J. H. Ikeda Kazuo 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1983,151(3):295-310
Journal of Comparative Physiology A - Intracellular recordings were made from the motor neurons which innervate the dorsal longitudinal flight muscle (DLM) inDrosophila, while a normal-appearing... 相似文献
137.
138.
The mechanism for the generation of the Ca2+/calmodulin (CaM)-independent activity of calmodulin-dependent protein kinase II (CaM-kinase II) by autophosphorylation was studied by characterizing the autothiophosphorylated enzyme, which is resistant to hydrolysis. When CaM-kinase II was incubated with adenosine 5'-O-(thiotriphosphate) at 5 degrees C, the incorporation of thiophosphate into the enzyme occurred rapidly, reaching a maximum level within a few minutes, in parallel with increase in Ca2+/CaM-independent activity. The maximum level was 1 mol of thiophosphate per mol of subunit of the enzyme, and the thiophosphorylation occurred exclusively at Thr286 in the alpha subunit and Thr287 in the other subunits of the enzyme. These results, taken together, indicate that the autothiophosphorylation of Thr286/Thr287 of each subunit is involved in the generation of the Ca2+/CaM-independent activity. The activity of the autothiophosphorylated enzyme, when assayed in the presence of Ca2+/CaM, showed the same kinetic properties as did the Ca2+/CaM-dependent activity of the original non-phosphorylated enzyme, but when assayed in the absence of Ca2+/CaM, it showed the same Vmax as the Ca2+/CaM-dependent activity but higher Km values for protein substrates. Thus, the phosphorylation of Thr286/Thr287 of the subunit of the enzyme by autophosphorylation appears to not only enhance the affinity of its substrate-binding site for the protein substrate, although it is lower than that of the enzyme activated by the binding of CaM, but also convert the active site to the fully active state. 相似文献
139.
Isocitrate dehydrogenase kinase/phosphatase: identification of mutations which selectively inhibit phosphatase activity.
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Mutations in aceK, the gene encoding isocitrate dehydrogenase kinase/phosphatase, which selectively inhibit phosphatase activity have been isolated. These mutations yield amino acid substitutions within a 113-residue region of this 578-residue protein. These mutations may define a regulatory domain of this protein. 相似文献
140.
M Nakazato S Ikeda K Shiomi S Matsukura K Yoshida H Shimizu T Atsumi K Kangawa H Matsuo 《FEBS letters》1992,306(2-3):206-208
A novel variant transthyretin which contains a leucine-for-valine substitution at position 30 was isolated and identified in the serum of a patient with familial amyloidotic polyneuropathy (FAP). The amino acid substitution was proven to result from a guanine-to-cytosine change at the first base of codon 30 located in exon 2 in the mutated transthyretin gene by restriction fragment length analysis on the amplified transthyretin gene using Cfr13 I. The study indicates that the point mutation of the transthyretin gene is a cause of the disorder. 相似文献