全文获取类型
收费全文 | 8788篇 |
免费 | 517篇 |
国内免费 | 2篇 |
出版年
2023年 | 20篇 |
2022年 | 43篇 |
2021年 | 120篇 |
2020年 | 77篇 |
2019年 | 79篇 |
2018年 | 134篇 |
2017年 | 113篇 |
2016年 | 198篇 |
2015年 | 277篇 |
2014年 | 324篇 |
2013年 | 568篇 |
2012年 | 536篇 |
2011年 | 559篇 |
2010年 | 343篇 |
2009年 | 349篇 |
2008年 | 588篇 |
2007年 | 544篇 |
2006年 | 544篇 |
2005年 | 553篇 |
2004年 | 550篇 |
2003年 | 489篇 |
2002年 | 453篇 |
2001年 | 157篇 |
2000年 | 146篇 |
1999年 | 137篇 |
1998年 | 116篇 |
1997年 | 109篇 |
1996年 | 61篇 |
1995年 | 66篇 |
1994年 | 71篇 |
1993年 | 55篇 |
1992年 | 99篇 |
1991年 | 70篇 |
1990年 | 70篇 |
1989年 | 70篇 |
1988年 | 86篇 |
1987年 | 59篇 |
1986年 | 46篇 |
1985年 | 36篇 |
1984年 | 44篇 |
1983年 | 33篇 |
1982年 | 42篇 |
1981年 | 30篇 |
1980年 | 25篇 |
1979年 | 33篇 |
1978年 | 29篇 |
1977年 | 18篇 |
1975年 | 20篇 |
1974年 | 18篇 |
1973年 | 21篇 |
排序方式: 共有9307条查询结果,搜索用时 15 毫秒
71.
72.
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
73.
Accessibility of phosphatidylethanolamine in bacteriophage PM2 and in its gram-negative host.
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The reaction of trinitrobenzenesulfonic acid with phosphatidylethanolamine in the cytoplasmic membrane of Alteromonas espejiana suggests that 50% of this lipid occupies the outer lamella. In PM2, similar analysis suggests that 56% of this lipid populates the outer lamella of the membrane, the surface of which accounts for 60% of the membrane area. 相似文献
74.
When investigating the effects of divalent cations (Mg2+, Ca2+, Sr2+, Ba2+, Mn2+ and Ni2+) on 3H-baclofen binding to rat cerebellar synaptic membranes, we found that the specific binding of 3H-baclofen was not only dependent on divalent cations, but was increased dose-dependently in the presence of these cations. The effects were in the following order of potency: Mn2+ congruent to Ni2+ greater than Mg2+ greater than Ca2+ greater than Sr2+ greater than Ba2+. Scatchard analysis of the binding data revealed a single component of the binding sites in the presence of 2.5 mM MgCl2, 2.5 mM CaCl2 or 0.3 mM MnCl2 whereas two components appeared in the presence of 2.5 mM MnCl2 or 1 mM NiCl2. In the former, divalent cations altered the apparent affinity (Kd) without affecting density of the binding sites (Bmax). In the latter, the high-affinity sites showed a higher affinity and lower density of the binding sites than did the single component of the former. As the maximal effects of four cations (Mg2+, Ca2+, Mn2+ and Ni2+) were not additive, there are probably common sites of action of these divalent cations. Among the ligands for GABAB sites, the affinity for (-), (+) and (+/-) baclofen, GABA and beta-phenyl GABA increased 2-6 fold in the presence of 2.5 mM MnCl2, in comparison with that in HEPES-buffered Krebs solution (containing 2.5 mM CaCl2 and 1.2 mM MgSO4), whereas that for muscimol was decreased to one-fifth. Thus, the affinity of GABAB sites for its ligands is probably regulated by divalent cations, through common sites of action. 相似文献
75.
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
76.
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
77.
78.
Chemical modification of tyrosyl residues of stem bromelain 总被引:1,自引:0,他引:1
79.
80.