全文获取类型
收费全文 | 666篇 |
免费 | 46篇 |
出版年
2023年 | 13篇 |
2022年 | 32篇 |
2021年 | 41篇 |
2020年 | 24篇 |
2019年 | 30篇 |
2018年 | 23篇 |
2017年 | 26篇 |
2016年 | 21篇 |
2015年 | 26篇 |
2014年 | 27篇 |
2013年 | 55篇 |
2012年 | 36篇 |
2011年 | 40篇 |
2010年 | 32篇 |
2009年 | 26篇 |
2008年 | 28篇 |
2007年 | 26篇 |
2006年 | 17篇 |
2005年 | 13篇 |
2004年 | 13篇 |
2003年 | 16篇 |
2002年 | 17篇 |
2001年 | 5篇 |
2000年 | 14篇 |
1999年 | 8篇 |
1998年 | 8篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1978年 | 11篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1971年 | 4篇 |
1966年 | 1篇 |
1964年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有712条查询结果,搜索用时 15 毫秒
51.
Simultaneous and continuous measurements of extracellular pH, potassium (K(+)), and lactate (L(-)) in ischemic rabbit papillary muscle are presented for the first time. Potentiometric pH and K(+) sensors and an amperometric lactate biosensor were used. These miniature electrodes were previously developed and individually tested for this purpose. The pH sensor was based on an iridium oxide layer electrodeposited on a planar platinum electrode fabricated on a flexible substrate. The potentiometric K(+) sensor was based on a polymeric membrane and valinomycin ionophore. The L(-) biosensor was based on lactate oxidase and an organic conducting salt polarized at 0.15V vs Ag/AgCl reference electrode. The utility of this novel analytical system to cardiovascular research was demonstrated by using the system to study the interrelationship of cellular K(+) and lactate loss in ischemic myocardium, and the role of extracellular pH and buffer capacity on this relationship. The results indicated: (i) sequential brief episodes of ischemia produced reproducible trends of L(-), pH, and K(+) changes during the first three episodes, (ii) extracellular L(-) increased with increasing buffer capacity of extracellular compartment, (iii) the patterns of extracellular L(-) and K(+) changes were not related directly, and (iv) L(-) transport and lactic acid diffusion were not the primary cause of extracellular acidosis during ischemia. 相似文献
52.
Background
Existing cut-offs for fasting plasma glucose (FPG) and post-load glucose (2hPG) criteria are not equivalent in the diagnosis of diabetes and glucose intolerance. Adjusting cut-offs of single measurements have not helped so we undertook this project to see if they could be complementary. 相似文献53.
Abdel-Rahman AA Abdel-Megied AE Goda AE Zeid IF El Ashry el SH 《Nucleosides, nucleotides & nucleic acids》2003,22(11):2027-2038
Reverse nucleoside derivatives of 2-(methylsulfanyl)uracils 6a-d were prepared by treating of the sodium salt of 2-(methylsulfanyl)uracils (5a-d) with methyl 2,3-O-isopropylidene-5-O-p-toluenesulfonyl-beta-D-ribofuranoside (2). The alkylation of 2-thiouracils 4a-d with methyl 5-deoxy-5-iodo-2,3-O-isopropylidene-D-ribofuranoside (3) afforded the corresponding S-ribofuranoside derivatives 8a-d. Deisopropylidenation of 6a-d and 8a-d afforded the corresponding deprotected derivatives 7a-d and 9a-d, respectively. The Anti-HBV activity of selected compounds was studied. 相似文献
54.
Escherichia coli cells contain potential division sites at midcell and adjacent to the cell poles. Selection of the correct division site at midcell is controlled by three proteins: MinC, MinD, and MinE. It has previously been shown (D. Raskin and P. de Boer, Cell 91:685-694, 1997) that MinE-Gfp localizes to the midcell site in an MinD-dependent manner. We use here Gfp-MinD to show that MinD associates with the membrane around the entire periphery of the cell in the absence of the other Min proteins and that MinE is capable of altering the membrane distribution pattern of Gfp-MinD. Studies with the isolated N-terminal and C-terminal MinE domains indicated different roles for the two MinE domains in the redistribution of membrane-associated MinD. 相似文献
55.
Growth of three Frankia strains associated with roots of Casuarina tree, treated with different concentrations of metal ions, was measured as total protein content. One strain was highly resistant to different aluminum ion concentrations up to 10 mmol/L. The other two strains were more sensitive to the higher aluminum concentrations (1.25-10 mmol/L). Growth inhibition by cobalt and lead concentrations varied, depending on the tested strain. Stimulation occurred only at cobalt concentrations of 0.33 and 0.65 mmol/L for one strain. 相似文献
56.
Blundell TL Burke DF Chirgadze D Dhanaraj V Hyvönen M Innis CA Parisini E Pellegrini L Sayed M Sibanda BL 《Biological chemistry》2000,381(9-10):955-959
We review here signalling complexes that we have defined using X-ray analysis in our laboratory. They include growth factors and their receptors: nerve growth factor (NGF) and its hetero-hexameric 7S NGF storage complex, hepatocyte growth factor/scatter factor (HGF/SF) NK1 dimers and fibroblast growth factor (FGF1) in complex with its receptor (FGFR2) ectodomain and heparin. We also review our recent structural studies on intracellular signalling complexes, focusing on phosducin transducin GPry, CK2 protein kinase and its complexes, and the cyclin D-dependent kinase, Cdk6, bound to the cell cycle inhibitor p19INK4d. Comparing the structures of these complexes with others we show that the surface area buried in signalling interactions does not always give a good indication of the strength of the interactions. We show that conformational changes are often important in complexes with intermediate buried surface areas of 1500 to 2000 A2, such as Cdk6INK4 interactions. Some interactions involve recognition of continuous epitopes, where there is no necessity for a tertiary structure and very often the binding conformation is induced during the process of interaction, for example phosducin binding to the betagamma subunits (Gtbetagamma) of the heterotrimeric G protein transducin. 相似文献
57.
A hydrophobic lock-and-key intersubunit motif involving a phenylalanine is a major structural feature conserved at the dimer interface of classes alpha, mu and pi glutathione transferases. In order to determine the contribution of this subunit interaction towards the function and stability of human class alpha GSTA1-1, the interaction was truncated by replacing the phenylalanine 'key' Phe-51 with serine. The F51S mutant protein is dimeric with a native-like core structure indicating that Phe-51 is not essential for dimerization. The mutation impacts on catalytic and ligandin function suggesting that tertiary structural changes have occurred at/near the active and non-substrate ligand-binding sites. The active site appears to be disrupted mainly at the glutathione-binding region that is adjacent to the lock-and-key intersubunit motif. The F51S mutant displays enhanced exposure of hydrophobic surface and ligandin function. The lock-and-key motif stabilizes the quaternary structure of hGSTA1-1 at the dimer interface and the protein concentration dependence of stability indicates that the dissociation and unfolding processes of the mutant protein remain closely coupled. 相似文献
58.
Out of Africa and back again: nested cladistic analysis of human Y chromosome variation 总被引:18,自引:3,他引:15
Hammer MF; Karafet T; Rasanayagam A; Wood ET; Altheide TK; Jenkins T; Griffiths RC; Templeton AR; Zegura SL 《Molecular biology and evolution》1998,15(4):427-441
We surveyed nine diallelic polymorphic sites on the Y chromosomes of 1,544
individuals from Africa, Asia, Europe, Oceania, and the New World.
Phylogenetic analyses of these nine sites resulted in a tree for 10
distinct Y haplotypes with a coalescence time of approximately 150,000
years. The 10 haplotypes were unevenly distributed among human populations:
5 were restricted to a particular continent, 2 were shared between Africa
and Europe, 1 was present only in the Old World, and 2 were found in all
geographic regions surveyed. The ancestral haplotype was limited to African
populations. Random permutation procedures revealed statistically
significant patterns of geographical structuring of this paternal genetic
variation. The results of a nested cladistic analysis indicated that these
geographical associations arose through a combination of processes,
including restricted, recurrent gene flow (isolation by distance) and range
expansions. We inferred that one of the oldest events in the nested
cladistic analysis was a range expansion out of Africa which resulted in
the complete replacement of Y chromosomes throughout the Old World, a
finding consistent with many versions of the Out of Africa Replacement
Model. A second and more recent range expansion brought Asian Y chromosomes
back to Africa without replacing the indigenous African male gene pool.
Thus, the previously observed high levels of Y chromosomal genetic
diversity in Africa may be due in part to bidirectional population
movements. Finally, a comparison of our results with those from nested
cladistic analyses of human mtDNA and beta-globin data revealed different
patterns of inferences for males and females concerning the relative roles
of population history (range expansions) and population structure
(recurrent gene flow), thereby adding a new sex-specific component to
models of human evolution.
相似文献
59.
Anwar MM Mahfouz HA Sayed AS 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》1998,119(2):493-501
Myelosuppression is the most serious, dose limiting, toxicity of cytotoxic drugs. Efforts to protect the bone marrow have been only variably successful, and no agreement exists on how to approach this problem. Melatonin, the major hormonal product of the pineal gland, is supposed to have both chemoprotective and myelostimulatory effects. This experimental study was carried out to test these two effects on the bone marrow of rats, daily intraperitoneally injected with 100 microg melatonin. Injection of 10 mg aracytin for 10 days produced a significant (P < 0.01) decrease in red blood cells count (RBCs), total leucocytic count, as well as platelets count. When melatonin was injected along with aracytin, it would significantly increase (P < 0.05) RBC count and (P < 0.01) blood platelet count. Injection of melatonin after aracytin treatment would significantly increase (P < 0.01) RBC, total leucocytic and platelet counts in comparison with rats treated with aracytin only. The effects of melatonin were more clear in rats treated with it after aracytin injection than those treated with melatonin and aracytin at the same time. Furthermore, it was found that aracytin produced a significant (P < 0.01) decrease in serum total proteins, albumin, and significantly increased the (P < 0.01) albumin/globulin ratio. Melatonin injection would significantly increase (P < 0.01) total protein, globulin, and significantly decrease (P < 0.01) the albumin/glubulin ratio when injected either with aracytin or after aracytin treatment. These results indicate that melatonin protects bone marrow, lymphoid tissues from damaging effect of cytotoxic drugs, as well as stimulating the suppressed bone marrow. 相似文献
60.
The packed‐bed adsorption and elution of aqueous solutions of whey concentrate powders were investigated at pH 3.7 using a 5‐mL SP Sepharose FF column to separate and isolate two major proteins namely, α‐lactalbumin (ALA) and β‐lactoglobulin (BLG) from these solutions. ALA displaced and eluted BLG from the column in a pure form. Pure ALA could then be eluted with good recovery. A novel consecutive two‐stage separation process was developed to separate ALA and BLG from whey concentrate mixtures. Almost all of the BLG in the feed was recovered, with 78% being recovered at 95% purity and a further 20% at 86% purity. In addition, 67% of ALA was recovered, 48% at 54% purity and 19% at 60% purity. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 相似文献