全文获取类型
收费全文 | 6842篇 |
免费 | 426篇 |
国内免费 | 2篇 |
出版年
2023年 | 12篇 |
2022年 | 33篇 |
2021年 | 102篇 |
2020年 | 67篇 |
2019年 | 65篇 |
2018年 | 115篇 |
2017年 | 87篇 |
2016年 | 162篇 |
2015年 | 219篇 |
2014年 | 289篇 |
2013年 | 483篇 |
2012年 | 449篇 |
2011年 | 454篇 |
2010年 | 294篇 |
2009年 | 308篇 |
2008年 | 498篇 |
2007年 | 456篇 |
2006年 | 442篇 |
2005年 | 448篇 |
2004年 | 471篇 |
2003年 | 427篇 |
2002年 | 353篇 |
2001年 | 66篇 |
2000年 | 83篇 |
1999年 | 83篇 |
1998年 | 90篇 |
1997年 | 68篇 |
1996年 | 48篇 |
1995年 | 68篇 |
1994年 | 58篇 |
1993年 | 43篇 |
1992年 | 51篇 |
1991年 | 26篇 |
1990年 | 28篇 |
1989年 | 33篇 |
1988年 | 23篇 |
1987年 | 18篇 |
1986年 | 22篇 |
1985年 | 21篇 |
1984年 | 20篇 |
1983年 | 16篇 |
1982年 | 24篇 |
1981年 | 25篇 |
1980年 | 18篇 |
1979年 | 16篇 |
1978年 | 13篇 |
1977年 | 15篇 |
1976年 | 10篇 |
1975年 | 11篇 |
1969年 | 10篇 |
排序方式: 共有7270条查询结果,搜索用时 31 毫秒
41.
42.
Binding of a fluorescent allosteric effector, beta-naphthyl triphosphate (beta-NapP3), to human adult hemoglobin (HbA) at various levels of oxygen saturation were investigated by simultaneous measurements of fluorescence, absorbance and oxygen partial pressure. Amounts of beta-NapP3 bound to HbA were easily estimated from the fluorescence intensities of HbA solutions, because it was previously proved that the fluorescence of beta-NapP3 bound to HbA is completely quenched. Exchange reactions of the above fluorescent allosteric effector with 2,3-bisphosphoglycerate (DPG) were also examined at various levels of oxygen saturation. It was found that beta-NapP3 binds to deoxyHbA tetramer in the molar ratio of 2:1, and that one of the two beta-NapP3 competes with DPG. It was also found that beta-NapP3 binds to completely oxygenated HbA tetramer in the molar ratio of 1:1, and that the bound beta-NapP3 was not released by adding DPG. The binding affinity of beta-NapP3 for the noncompetitive site of completely oxygenated HbA, to which DPG does not bind, was smaller than that for the noncompetitive site of deoxyHbA, to which DPG also does not bind. Furthermore, the correlations between oxygen bindings by HbA and the bindings of beta-NapP3 to HbA in the intermediate stages of deoxygenation were investigated. It was revealed that HbA as a tetramer exists in three conformational states rather than simple two states as Monod, Wyman, and Changeux had proposed. 相似文献
43.
Construction and Characterization of Isogenic Series of Saccharomyces cerevisiae Polyploid Strains 总被引:1,自引:1,他引:0
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Tetraploid cells of Saccharomyces cerevisiae are generated spontaneously in a homothallic MATa/MATα diploid population at low frequency (approximately 10−6 per cell) through the homozygosity of mating-type alleles by mitotic recombination followed by homothallic switching of the mating-type alleles. To isolate tetraploid clones more effectively, a selection method was developed that used a dye plate containing 40 mg each of eosin Y and amaranth in synthetic nutrient agar per liter. It was possible to isolate tetraploid clones on the dye plate at a frequency of 1 to 3% among the colonies colored dark red in contrast to the light red of the original diploid colonies. Isogenic series of haploid to tetraploid clones with homozygous or heterozygous genomic configurations were easily constructed with the tetraploid strains. No significant differences in specific growth rate or fermentative rate were observed corresponding to differences in ploidy, although the haploid clones showed a higher frequency of spontaneous respiratory-deficient cells than did the others. However, a significant increment in the fermentative rate in glucose nutrient medium was observed in the hybrid strains constructed with two independent homozygous cell lines. These observations strongly suggest that the polyploid strains favored by the brewing and baking industries perform well not because of the physical increment of the cellular volume by polyploidy but because of the genetic complexity or heterosis by heterozygosity of the genome in the hybrid polyploid cells. 相似文献
44.
Nobuyuki Sasakawa Konosuke Kumakura Satoshi Yamamoto Ryuichi Kato 《Life sciences》1983,33(20):2017-2024
Effects of N-(6-aminohexyl)-5-chloro-1-naph-thalenesulfonamide (W-7), a calmodulin antagonist, on catecholamine (CA) release and 45Ca2+ uptake were studied using cultured bovine adrenal chromaffin cells. W-7 inhibited the carbamylcholine (CCh)-evoked CA release and 45Ca2+ uptake in a concentration-dependent manner. The inhibitory effect of W-7 on CCh-evoked CA release was not overcome either by an increase in extracellular calcium or CCh concentration. Although W-7 inhibited the high K+-evoked CA release and 45Ca2+ uptake, potency of the drug was approximately 50–100 fold less than when inhibiting the CCh-evoked CA release and 45Ca2+ uptake. The inhibitory effects of W-7 were observed both in norepinephrine release and epinephrine release. Moreover, W-7 inhibited the CCh-evoked 45Ca2+ efflux. These results suggest that the inhibition of CA release by W-7 in adrenal chromaffin cells is mainly due to its inhibition of calcium uptake. W-7 may influence the linkage between acetylcholine-receptor and calcium uptake with higher potency than depolarization-dependent calcium entry. 相似文献
45.
Absorption spectra of chlorophyll a in phosphatidylcholine liposomesat different temperatures were analyzed by a curve fitting method.The absorption spectrum was found to be composed of one majorband with a peak at 670671 nm and minor bands with peaksat 650652, 662663 and 684686 nm. Upon coolingbelow the phase transition temperature of the lipid, the componentabsorbing at 670671 nm increased significantly at theexpense of the component absorbing at 662663 nm. No changein the extents of other bands was observed.
1 CIW-DPB Publication No. 795.
2On leave from the Department of Biology, Faculty of Science,Kanazawa University, Marunouchi, Kanazawa 920, Japan. (Received December 20, 1982; Accepted April 27, 1983) 相似文献
46.
Hiroshi Kagawa Toshihisa Kuwajima Hiroshi Asai 《Biochimica et Biophysica Acta (BBA)/General Subjects》1974,338(2):496-504
A fluorescent ATP analog, β-naphthyl triphosphate, was hydrolyzed to β-naphthyl diphosphate and orthophosphate by heavy meromyosin ATPase. In the process of hydrolysis the fluorescence intensity of β-naphthyl triphosphate changed remarkably. Thus, the rate of β-naphthyl triphosphate hydrolysis is evaluated directly and continuously by measuring the time course of fluorescence intensity.In the presence of Ca2+, the Michaelis constant (Km) of β-naphthyl triphosphate hydrolysis by heavy meromyosin was similar to that of ATP hydrolysis. While, in the presence of Mg2+ the Km of β-napthyl triphosphate hydrolysis was 9.0·10−6 M, much larger than the value of ATP hydrolysis, indicating that the apparent affinity of the enzyme for β-naphthyl triphosphate is less than that for ATP.The pH dependence of β-naphthyl triphosphatase activity resembled that of ATPase activity, suggesting a similarity in the mechanism of hydrolysis of the two substrates. 相似文献
47.
Summary Spectinomycin resistant (spc
r) mutants were obtained by treating the cells of E. coli K12, W3637 with nitrosoguanidine. The compositions of ribosomal proteins were analyzed for six out of eleven such spc
r-mutants with chromatography on a carboxymethyl cellulose (CMC) column. The 30s ribosomal subunit from all of the spc
r-mutants was found to contain the altered 30-4 protein component, while no difference was detected in 50s ribosomal proteins between spc
r and spc
s bacteria.Abbreviations used CMC
carboxymethyl cellulose
-
str
streptomycin
-
spc
spectinomycin 相似文献
48.
K Kopaczyk J Asai D W Allmann T Oda D E Green 《Archives of biochemistry and biophysics》1968,123(3):602-621
49.
Masami Matsumoto Yukihiro Shoyama Itsuo Nishioka Hisashi Iwai Satoshi Wakimoto 《Plant cell reports》1989,7(8):636-638
Virus free plants of Rehmannia glutinosa Libosch. var. purpurea Makino were obtained through meristem tip tissue cultures from plants infected with a mixture of tabocco mosaic virus(TMV), a member of the carlavirus group, and an unknown spherical virus. The re-infection rate of the virus free plants by TMV in the field was determined by enzyme linked immunosorbent assay(ELISA). Twenty seven percent of the plants were re-infected during the first year, 31 % by the end of second year, and 63 % by the end of the third year. The yield of root and iridoid glycoside contents gradually decreased each year. These results led to the conclusion that virus infection causes marked decrease of the yield of roots and productivity of secondary metabolites. 相似文献
50.