全文获取类型
收费全文 | 1214篇 |
免费 | 64篇 |
国内免费 | 1篇 |
出版年
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2017年 | 17篇 |
2016年 | 22篇 |
2015年 | 23篇 |
2014年 | 25篇 |
2013年 | 65篇 |
2012年 | 53篇 |
2011年 | 37篇 |
2010年 | 25篇 |
2009年 | 30篇 |
2008年 | 44篇 |
2007年 | 39篇 |
2006年 | 39篇 |
2005年 | 53篇 |
2004年 | 46篇 |
2003年 | 54篇 |
2002年 | 47篇 |
2001年 | 44篇 |
2000年 | 56篇 |
1999年 | 31篇 |
1998年 | 20篇 |
1997年 | 14篇 |
1996年 | 13篇 |
1995年 | 12篇 |
1994年 | 15篇 |
1993年 | 12篇 |
1992年 | 26篇 |
1991年 | 19篇 |
1990年 | 32篇 |
1989年 | 22篇 |
1988年 | 24篇 |
1987年 | 17篇 |
1986年 | 21篇 |
1985年 | 28篇 |
1984年 | 26篇 |
1983年 | 20篇 |
1982年 | 18篇 |
1981年 | 8篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 13篇 |
1975年 | 10篇 |
1974年 | 17篇 |
1973年 | 8篇 |
1972年 | 11篇 |
1970年 | 8篇 |
1967年 | 10篇 |
排序方式: 共有1279条查询结果,搜索用时 15 毫秒
1.
Kuniko Murakami Chieko Wakeshima Kyuichiro Okuda 《Biochemical and biophysical research communications》1980,94(4):1098-1105
Taurodeoxycholate 7α-monooxygenase was partially purified from rat liver microsomes. The enzyme was solubilized with cholate, fractionated with polyethylene glycol and chromatographed on a Sepharose 4B column with cholate as ligand. The enzyme activity was eluted from the column into the fraction eluted with 50 mM phosphate buffer containing cholate and KCl, whereas the benzphetamine demethylase activity was eluted in the non-bound fraction. Thus it was established that both enzymes are different entities. The taurodeoxycholate 7α-monooxygenase activity was reconstituted from the partially purified cytochrome P-450, highly purified NADPH-cytochrome P-450 reductase, dilauroylglyceryl-3-phosphorylcholine and NADPH. 相似文献
2.
Abstract. Diploid rat 3Y1 fibroblasts proliferate to a saturation density, where they are arrested with a 2N DNA content. After treatment to induce ploidy conversion, the conversion rate can be estimated by determining the fraction of cells with a 4N DNA content in the confluent culture using flow cytometry. Using this method it was found that during mitotic inhibition with colcemid, 3Y1 cells were converted to tetraploids with a high efficiency (above 80%); the optimum colcemid concentration and exposure period were 40 ng/ml and 8 hr, respectively. When metaphase cells were reseeded with 40 ng/ml of colcemid, they delayed anchorage to a dish; 6 hr was required for complete adhesion (in the absence of colcemid only 1 hr was required). When reseeded metaphase cells were exposed to 40 ng/ml of colcemid for 5 hr followed by its removal, a greater fraction of the cells anchored to the substratum were converted to tetraploids, whereas most of the floating cells were not. A greater fraction of the anchored cells had formed nuclei, whereas most of the floating cells preserved condensed metaphase chromosomes. These results indicate that the cells which have formed nuclear structure without chromosome separation during mitotic inhibition are irreversibly committed to ploidy conversion, with restoration of anchorage. 相似文献
3.
Ishida Takuya Uehara Yoshitoshi Ikeya Tohru Haraguchi Takashi F. Asano Satoshi Ogino Yohei Okuda Noboru 《Limnology》2020,21(3):403-413
Limnology - Controlling phosphorous (P) loads from rice fields is important for the conservation of aquatic ecosystems, in part because P is relatively concentrated at its sources. Recently, winter... 相似文献
4.
In several vascular inflammatory reactions (i.e. immunity and thrombosis) inflammatory mediators lead to the activation of vascular endothelial cells (EC). To date, a number
of functional molecules induced on the surface of activated-EC have been identified. We report here that Globotetraosylceramide
(Gb4), a glycosphingolipid expressed in EC, is a novel inducible molecule on EC activated by TNF-α. The cell surface expression
of Gb4 is increased in a time-dependent manner under TNF-α stimulation, which shows distinct expression kinetics of major
proteins induced by TNF-α on EC. MALDI-TOF-MS analysis revealed that the enhanced Gb4 predominantly contains C24:0 fatty acid
in the ceramide moiety. Isolated caveolae/lipid raft-enriched detergent insoluble membrane domains in activated-EC predominantly
contain this molecular species of Gb4. Gb4 containing C16:0 fatty acid in the ceramide moiety, which is known to constitute
the major species of Gb4 in plasma, is also found as a major molecular species in EC. These observations indicate that Gb4,
especially with very long fatty acid, is enhanced in EC during its inflammatory reaction, and suggest the potential utility
of Gb4 as a biomarker for monitoring inflammation status of EC involving its related diseases. 相似文献
5.
In temperate waters of southern Japan, mouthbrooding males of the cardinal fish Apogon doederleini sometimes ate their entire brood within a day of spawning. In spite of annual variation in age structure and length of the breeding season, however, the annual cannibalism rate (broods cannibalized to total broods spawned) was nearly constant, 12–16%. Fish 1 year old frequently cannibalized early broods of the season, especially the first brood, whereas the cannibalism rate by 2 year-old fish did not vary within the season. In contrast, the cannibalism by older males increased late in the season. This tendency was attributed to their different allocation patterns to growth and reproduction. For 1 year-old fish, which can enhance future reproductive success by growth and cannibalizing on early broods instead of mouthbrooding (at relatively low temperatures), this may be a tactic for investing energy in growth. For fish 3 years, which have more breeding cycles and grow little, cannibalizing late broods may be energetic compensation for their poor somatic condition. No seasonal variation of cannibalism by 2 year-old fish can be explained by their intermediate nature of growth and reproduction. Multiple mate availability is one factor facilitating the cannibalism by 2 and 3 + year-old fish whose operational sex ratio is female-biased. 相似文献
6.
Modification in Cell Shape Unrelated to Cellulose Microfibril Orientation in Growing Thallus Cells of Chaetomorpha moniligera 总被引:1,自引:0,他引:1
Cellulose microfibril orientation patterns in thallus cellsof Chaetomorpha moniligera were studied, and the relationshipbetween the microfibril and the peripheral microtubule arrangementsduring cell-shape modification by colchicine was examined. Inthe cuttings from growing thalli, linearly arranged cylindricalcells developed into cask-shaped cells during 46 daysof culture at 27?C. In the cylindrical cells, microfibrils formingthe innermost portion of the wall were arranged alternatelyin longitudinal and transverse directions, but peripheral microtubuleswere always arranged only in a longitudinal direction. Thesefeatures were also noted in the cask-shaped cells. Colchicineat 103M and 3?103M accelerated both cell expansionand wall thickening with matrix deposition, but the directionsin which both microfibrils and microtubules were arranged werethe same as those of the cylindrical cells. These results indicatethat (1) the microfibril and microtubule arrangements of Chaetomorphaare not necessarily correlated, (2) changes in cell shape ofChaetomorpha are not necessarily accompanied by changes in thearrangement of cell-wall microfibrils, and (3) colchicine playsa role in the loosening and thickening of cell walls by enhancingmatrix deposition. (Received June 2, 1986; Accepted February 13, 1987) 相似文献
7.
Purification and characterization of cholesterol 7 alpha-hydroxylase from rat liver microsomes 总被引:2,自引:0,他引:2
Cholesterol 7 alpha-hydroxylase (cholesterol, NADPH: oxygen oxidoreductase, 7 alpha-hydroxylating, EC 1.14.13.17) was purified from liver microsomes of cholestryramine-fed male rats by using high-performance ion-exchange chromatography. The purified enzyme showed a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (Mr = 52,000), and its dithionite-reduced CO complex exhibited an absorption maximum at 450 nm. The specific content of the enzyme was 9 nmol of cytochrome P-450/mg of protein. Upon reconstitution with NADPH-cytochrome P-450 reductase, the enzyme showed a high activity of cholesterol 7 alpha-hydroxylation with the turnover number of 50 min-1 at 37 degrees C. The reaction was inhibited neither by aminoglutethimide nor by metyrapone, but inhibited markedly by iodoacetamide and disulfiram. The reaction was also inhibited significantly by CO. The enzyme catalyzed hydroxylation of cholesterol with strict regio- and stereoselectivity and was inert toward other sterols which are intermediates in the conversion of cholesterol to bile acids, i.e. 7 alpha-hydroxy-4-cholesten-3-one (12 alpha-hydroxylation), 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol (25-hydroxylation), and taurodeoxycholate (7 alpha-hydroxylation). Unlike other cytochromes P-450 isolated from rat liver microsomes, the enzyme showed no activity toward testosterone and xenobiotics such as 7-ethoxycoumarin and benzo[a] pyrene. The NH2-terminal amino acid sequence of the enzyme was Met-Phe-Glu-Val(Ile)-Ser-Leu-, which was distinct from those of any other cytochromes P-450 of rat liver microsomes hitherto reported. These results indicate that the enzyme is a novel species of cytochrome P-450 so far not isolated from liver microsomes. 相似文献
8.
Anomeric specificity of glucose effect on cAMP, fructose 1,6-bisphosphatase, and trehalase in yeast 总被引:1,自引:0,他引:1
Y Toyoda H Fujii I Miwa J Okuda J Sy 《Biochemical and biophysical research communications》1987,143(1):212-217
The addition of beta-D-glucose (final concentration, 50 mM) to a cell suspension of Saccharomyces cerevisiae in stationary phase caused a rapid 4-fold increase in the concentration of cAMP, while a 2-fold increase of cAMP was observed by the addition of alpha-D-glucose. beta -D-Glucose was also more effective than alpha-D-glucose in the inactivation of fructose 1,6-bisphosphatase and the activation of trehalase. These results, taken together with the previous report that alpha-D-glucose is transported more rapidly than beta-D-glucose in Saccharomyces cerevisiae, do not support the view currently proposed by some investigators that cotransport of D-glucose with protons causes the depolarization of the cell membrane, resulting in the activation of adenylate cyclase. The present data, however, provides supporting evidence for the view that cAMP-dependent protein kinase is implicated in the inactivation of fructose 1,6-bisphosphatase and the activation of trehalase. 相似文献
9.
The anomeric preference in the influx and efflux of D-glucose across the human erythrocyte membrane was studied. beta-D-Glucose was transported 1.5 times faster than alpha-D-glucose into the cells, when washed cells were incubated at 20 degrees C in medium containing either alpha- or beta-D-glucose (100 mM). On the other hand, no difference between half-times of efflux of the two anomers was distinguishable. The result demonstrates the presence of influx-efflux asymmetry in anomeric preference in D-glucose transport across the human erythrocyte membrane, and is consistent with the view (Barnett et al., Biochem. J. 145, 417-429, 1975) that the C-1 hydroxyl group of D-glucose interacts with the D-glucose transport protein only in the influx, but not in the efflux. 相似文献
10.
Adherence of streptococci to surface-modified glass 总被引:2,自引:0,他引:2
Four types of surface-modified glass were prepared. Aminopropyl glass was prepared by alkylsilylation of glass slides with gamma-aminopropyltriethoxysilane. This glass carries primary amino groups which may be protonated at pH 7.2. Owing to the presence of both positively charged ions and hydrophobic ethoxyl groups, the glass is considered to be amphipathic. Three other types of surface-modified glass slides were prepared from aminopropyl glass by forming Schiff's bases with three aldehydes: glucose, glyoxylic acid and hexanal. The aldehyde-treated slides were subsequently reduced using sodium borohydride. Thus, the surface of the glass was rendered hydrophilic, ampholytic or hydrophobic, respectively. The adherence of two Streptococcus sanguis strains and two Streptococcus mutans strains to the surface-modified glass slides was studied. Different strains showed differences in adherence to these slides depending on their physico-chemical surface properties. For S. sanguis ATCC 10556, hydrophobic bonds seemed to be most important, while in S. mutans OMZ 176, ionic interactions made the highest contribution to adhesion. Hydrogen bonds seemed to contribute least to adherence. 相似文献