全文获取类型
收费全文 | 2746篇 |
免费 | 29篇 |
国内免费 | 27篇 |
出版年
2023年 | 15篇 |
2022年 | 20篇 |
2021年 | 20篇 |
2020年 | 34篇 |
2019年 | 40篇 |
2018年 | 45篇 |
2017年 | 25篇 |
2016年 | 24篇 |
2015年 | 22篇 |
2014年 | 192篇 |
2013年 | 233篇 |
2012年 | 123篇 |
2011年 | 244篇 |
2010年 | 213篇 |
2009年 | 158篇 |
2008年 | 184篇 |
2007年 | 189篇 |
2006年 | 201篇 |
2005年 | 158篇 |
2004年 | 141篇 |
2003年 | 102篇 |
2002年 | 119篇 |
2001年 | 11篇 |
2000年 | 16篇 |
1999年 | 16篇 |
1998年 | 25篇 |
1997年 | 10篇 |
1996年 | 22篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1985年 | 13篇 |
1984年 | 20篇 |
1983年 | 13篇 |
1982年 | 14篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1975年 | 10篇 |
1974年 | 5篇 |
1972年 | 10篇 |
1971年 | 3篇 |
排序方式: 共有2802条查询结果,搜索用时 15 毫秒
1.
We present a single-step procedure for the specific mass labeling of unblocked protein N termini. We show that the dye fluorescamine, which is commonly assumed to require mildly alkaline conditions for undergoing a nonspecific reaction with α- and ε-amino groups associated with amino acids, in fact shows a specific reaction only with α-amino groups present at protein N termini when mildly acidic conditions are used. We use this finding to label, identify, and sequence the trypsinolysis-derived N-terminal peptide of lysozyme, using only mass spectrometry, to illustrate how this method could be used with other proteins. 相似文献
2.
Pedro J. I. Salas Dora E. Vega-Salas Enrique Rodriguez-Boulan 《The Journal of membrane biology》1987,98(3):223-236
Summary Madin-Darby canine kidney (MDCK) cells kept in suspension culture for 12–15 hr displayed high-affinity binding sites for125I-lathyritic (soluble) collagen (120,000/cell,K
D
=30nm) and preferred collagens types I and IV over laminin or fibronectin as substrates during the first hour of attachment. On the other hand, after 4 hr, attachment to all four substrates was equally efficient. Upon challenge with a collagen substrate, the high-affinity sites were rapidly recruited on it (T1/2=6 min). Their occupancy by soluble collagen triggered the exocytosis of a second large population of low-affinity collagen binding sites that included laminin and seems to be involved in a second cell-attachment mechanism. These results are compatible with a twostep model of MDCK cell attachment to the substrate: first, via high-affinity collagen binding sites, and second, via laminin of cellular origin. 相似文献
3.
Cataract is the major reason for human blindness worldwide. α-Crystallin, as a key chaperone of eye lenses, keeps the lenticular tissues in its transparent state over time. In this study, cataract-causing familial mutations, P20R and A171T, were introduced in CRYАB gene. After successful expression in Escherichia coli and subsequent purification, the recombinant proteins were subjected to extensive structural and functional analyses using various spectroscopic techniques, gel electrophoresis, and electron microscopy. The results of fluorescence and Raman assessments suggest important but discreet conformational changes in human αB-Cry upon these cataractogenic mutations. Furthermore, the mutant proteins exhibited significant secondary structural alteration as revealed by FTIR and Raman spectroscopy. An increase in conformational stability was seen in the human αB-Cry bearing these congenital cataractogenic mutations. The oligomeric size distribution and chaperone-like activity of human αB-Cry were significantly altered by these mutations. The P20R mutant protein was observed to loose most of the chaperone-like activity. Finally, these cataractogenic mutant proteins exhibited an increased propensity to form the amyloid fibrils when incubated under environmental stress. Overall, the structural and functional changes in mutated human αB-Cry proteins can shed light on the pathogenic development of congenital cataracts. 相似文献
4.
Characterization of B and H blood-group active glycosphingolipids from human B erythrocyte membranes
Peter Hanfland 《Chemistry and physics of lipids》1975,15(2):105-124
Two blood group B active glycosphingolipids (B-I and B-II) previously isolated and highly purified from human B erythrocytes [21] were analysed first by degradation with α-D-galactosidase from coffee beans, α-L-fucosidase from bovine kidney and with 0,1 N trichloracetic acid; the native B-glycolipids as well as their degradation products were then investigated by methylation analysis with combined gas chromatography-mass spectrometry, by thin layer chromatography, twodimensional immunodiffusion and by the hemagglutination inhibition technique. Together with the results obtained by mass spectrometry of permethylated glycolipids [26] the following structures were elucidated: α-D-galactopyranosyl-(1 → 3)-[α-L-fucopyranosyl-(1 → 2)]-D-galactopyranosyl-(1 → 4)-N-acetyl-D-glucosaminosyl-(1 → 3)-D-galactopyranosyl-(1 → 4)-D-glucopyranosyl-(1 → 1)-ceramide for the B-I glycosphingolipid and α-D-galactopyranosyl-(1 → 3)-[α-L-fucopyranosyl-(1 → 2)]-D-galactopyranosyl-(1 → 4)-N-acetyl-D-glucosaminosyl-(1 → 3)-D-galactopyranosyl-(1 → 4)-N-acetyl-D-glucosaminosyl-(1 → 3)-D-galactopyranosyl-(1 → 4)-D-glucopyranosyl-(1 → 1)-ceramide for the B-II glycosphingolipid. A H active glycolipid fraction from B erythrocytes further purified by thin layer chromatography was also investigated by methylation analysis. The pattern of its partially methylated alditol acetates was essentially the same as that of the α-galactosidase treated and permethylated B-I glycolipid. It also exhibited strongly precipitating and hemagglutination inhibiting H properties as well as the two α-galactosidase treated B-I and B-II glycosphingolipids. Based upon these data the following tentative structure was proposed: α-L-fucopyranosyl-(1 → 2)-D-galactopyranosyl-(1 → 4)-N-acetyl-D-glucosaminosyl-(1 → 3)-D-galactopyranosyl-(1 → 4)-D-glucopyranosyl-(1 → 1)-ceramide. Gas chromatographic analysis revealed sphingosine and lignoceric, nervonic and behenic acids to be the main components of the ceramide residues of the three glycosphingolipids. From the data presented the H active substance very probably can be regarded as the immediate precursor of the B-I glycosphingolipid from human B erythrocyte membranes. 相似文献
5.
Extracellular matrix (ECM) modulates the EGF-induced migration of liver epithelial cells in serum-free,hormone-supplemented medium 总被引:2,自引:0,他引:2
Summary The influence of the extracellular matrix (ECM) glycoproteins collagen, IV laminin (LN), and fibronectin (FN) on the in vitro
migration of epithelial cells was studied using the ECM migration track method (4) with preparations immunostained for LN
and FN. The locomotion of rat liver epithelial cells stimulated to migrate in serum-free medium by epidermal growth factor
(EGF) in the presence of the protein per cm2. Neither LN nor collagen IV decreased the number of migrating cells, indicating that the inhibition is a specific effect
of fibronectin. The data also indicate that the FN-mediated inhibition of migration is an additional and not alternative mechanism
to the well-established contact inhibition of locomotion (1) which also occurs in liver epithelial cell cultures. The system
is being used for a further analysis of the factors that influence migration of normal and neoplastic epithelial cells and
the biochemical mechanisms underlying the migration reaction.
Editor’s Statement This paper describes new and heretofore neglected aspects of EGF and fibronectin action on the migratory
behavior of cultured cells. Gordon H. Sato 相似文献
6.
V P Torchilin A L Klibanov N N Ivanov M A Gluckhova V E Koteliansky H K Kleinman G R Martin 《Journal of cellular biochemistry》1985,28(1):23-29
We have incorporated antibodies against fibronectin or laminin into liposomes and studied their interaction with insoluble forms of these antigens. The antibodies, after modification by palmitoylchloride, were incorporated into the lipid bilayer by the cholate dialysis method. The antibodies in the liposomes recognized their specific antigen with little reaction to the alternative attachment protein or to albumin (less than 2%). The binding of antibody-containing liposomes to insoluble antigen was inhibited by soluble antibodies to the respective antigens but not by antibodies to other antigens. The affinity constant of the liposome-antibody complex with the antigen was estimated at 1-10 X 10(-9) M liposomes. Thus, antibodies in liposomes retain their reactivity and specificity, and the reaction constant is comparable to that observed for immune complexes. 相似文献
7.
Neurotransmitter-caused increase in [3H]inositol incorporation into phosphatidylinositol de novo synthesis vs exchange 总被引:1,自引:0,他引:1
[3H]inositol and 32Pi were simultaneously incorporated into rat parotid phosphatidylinositol. The ratio of [3H]/32Pi incorporation dropped dramatically following stimulation with muscarinic or alpha-adrenergic agonists and returned to control values following the addition of appropriate antagonists. The drop in [3H]/32Pi ratio can be explained by a rapid increase in de- novo synthesis of phosphatidylinositol following its receptor-mediated breakdown. The change in this ratio also provided evidence for the existence of CDP-DG + inositol in equilibrium phosphatidylinositol exchange reaction in the intact tissue. 相似文献
8.
- 1.
- 1. The net uptake of α-aminoisobutyric acid (AIB) in Ehrlich ascites tumor cells has been studied under a variety of transmembrane concentration gradients of Na+, K+ and AIB itself. 相似文献
9.
Bruno Mhul Michle Aubery Hans-Georg Mannherz Patrice Codogno 《Journal of cellular biochemistry》1993,52(3):266-274
The myoblast cell surface activity of ecto-5′-nucleotidase was stimulated by a laminin substrate, whereas fibronectin and gelatin did not increase the AMPase activity of ecto-5′-nucleotidase. This increase was related to a higher expression of ecto-5′-nucleotidase on the surface of cells seeded on a laminin substrate, but without the mobilization of an intracellular pool of enzyme. Furthermore, laminin and its fragments E′1 and E8 modified the AMPase activity of the ecto-5′-nucleotidase purified from chicken striated muscle and reconstituted in liposomes. Over the range of concentrations used, intact laminin and its fragment E8, consisting of the distal half of the long arm, stimulated the AMPase activity of ecto-5′-nucleotidase. By contrast, the large fragment derived from the short arms, designated E′1, inhibited the AMPase activity. Furthermore, the monoclonal anti-ecto-5′-nucleotidase antibody, CG37, abolished the stimulatory effect of fragment E8 on the AMPase activity of ecto-5′-nucleotidase but did not reverse the inhibitory effect of fragment E′1. In conclusion, laminin stimulates the AMPase activity of ecto-5′-nucleotidase by two mechanisms: inducing the expression of ecto-5′-nucleotidase to the cell surface and direct modulation of the enzymatic activity. 相似文献
10.
Fatemeh Sabet Sarvestani Ali-Mohammad Tamaddon Ramin Yaghoobi Bita Geramizadeh Negar Azarpira 《Engineering in Life Science》2023,23(7):2200140
Angiogenesis is a vital step in tissue regeneration. Hence, the current study aimed to prepare oxidized dextran (Odex)/collagen (Col)-hydrogels with laminin (LMN), as an angiogenic extracellular matrix (ECM) component, for promoting human umbilical vein endothelial cell (HUVEC) proliferation and function. Odex/Col scaffolds were constructed at various concentrations and temperatures. Using oscillatory rheometry, scanning electron microscopy (SEM), and cell viability testing, the scaffolds were characterized, and then HUVEC proliferation and function was compared with or without LMN. The gelation time could be modified by altering the Odex/Col mass ratio as well as the temperature. SEM showed that Odex/Col hydrogels had a more regular three-dimensional (3D) porous structure than the Col hydrogels. Moreover, HUVECs grew faster in the Col scaffold (12 mg/mL), whereas the Odex (30 mg/mL)/Col (6 mg/mL) scaffold exhibited the lowest apoptosis index. Furthermore, the expression level of vascular endothelial growth factor (VEGF) mRNA in the group without LMN was higher than that with LMN, and the Odex (30 mg/mL)/Col (6 mg/mL) scaffold without LMN had the highest VEGF protein secretion, allowing the cells to survive and function effectively. Odex/Col scaffolds, with or without LMN, are proposed as a tissue engineering construct to improve HUVEC survival and function for angiogenesis. 相似文献