全文获取类型
收费全文 | 795篇 |
免费 | 57篇 |
国内免费 | 1篇 |
出版年
2023年 | 8篇 |
2022年 | 4篇 |
2021年 | 11篇 |
2020年 | 9篇 |
2019年 | 13篇 |
2018年 | 15篇 |
2017年 | 15篇 |
2016年 | 18篇 |
2015年 | 30篇 |
2014年 | 35篇 |
2013年 | 64篇 |
2012年 | 49篇 |
2011年 | 41篇 |
2010年 | 30篇 |
2009年 | 18篇 |
2008年 | 33篇 |
2007年 | 40篇 |
2006年 | 36篇 |
2005年 | 44篇 |
2004年 | 47篇 |
2003年 | 36篇 |
2002年 | 26篇 |
2001年 | 19篇 |
2000年 | 21篇 |
1999年 | 14篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 15篇 |
1991年 | 11篇 |
1990年 | 14篇 |
1989年 | 14篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1978年 | 3篇 |
1977年 | 7篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1973年 | 2篇 |
1971年 | 3篇 |
1967年 | 2篇 |
排序方式: 共有853条查询结果,搜索用时 15 毫秒
1.
2.
Rapid immunofluorescent determination of cells in the S phase in pea root meristems: An alternative to autoradiography 总被引:2,自引:0,他引:2
Photosystem II (PS II) activity and the localization of ribulose-l,5-bisphosphate (RuBP) carboxylase (EC 4.1.1.39) were studied in primary leaves of young maize plants ( Zea mays L. cv. Fronica) by tetra-nitro-blue-tetrazoliumchloride reduction and immunolocalization, respectively. In tissue of 3-day-old plants all chloroplasts were structurally identical. From day 4 they developed into their typical appearance of mesophyll and bundle sheath chloroplasts. First PS II-activity was present in both types of chloroplasts. From day 4 it disappeared in bundle sheath chloroplasts concomitant with the loss of grana. RuBP carboxylase on the other hand was only present in bundle sheath chloroplasts at all stages of development. Thus, the control of the development of the photosystems and the Calvin cycle enzymes seem to differ. 相似文献
3.
Properties of carboxymethylated cross-linked hemoglobin A 总被引:2,自引:0,他引:2
The selective carboxymethylation of the N-terminal amino groups of hemoglobin A with glyoxylic acid and sodium cyanoborohydride has been studied as a function of the state of ligation of hemoglobin. The N-terminal residues have been established as the primary sites of reaction by peptide mapping of the tryptic digest of each chain and subsequent amino acid analysis of the modified peptides. With oxyhemoglobin, the desired derivatives with a carboxymethyl group at the N-terminal of either or both chains amounted to 55% [Di Donato, A., Fantl, W. J., Acharya, A. S., & Manning, J. M. (1983) J. Biol. Chem. 258, 11890-11895]. In the present study it is shown that with deoxyhemoglobin the amount of the desired derivative is increased to 75%. The oxygen equilibrium curve of hemoglobin A carboxymethylated on its four N-terminal residues [0.5 mM as tetramer in 50 mM [bis(2-hydroxyethyl)amino]tris(hydroxymethyl)methane (Bis-Tris), pH 7.5, 37 degrees C] had a P50 value of 30 mmHg (Hill coefficient n = 2.8, alkaline Bohr value = 0.4) compared to a P50 of 9 mmHg for unmodified hemoglobin under the same conditions (n = 2.5, alkaline Bohr value = 0.5). In carboxymethylated oxyhemoglobin A, cross-linked with the mild agent glycolaldehyde for 3.5 h, there was 85% of Mr 64,000 species and 15% of Mr 128,000 or higher species. For the former, the extent of cross-linking between two subunits was 19%. For the latter, there was 29% of two cross-linked subunits and 13% of three cross-linked subunits. Termination of cross-linking, which may be desirable in some circumstances, can be successfully achieved with isonicotinic acid hydrazide.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
4.
Identification of S-100 proteins and S-100-binding proteins in a detergent-resistant EDTA/KCl-extractable fraction from bovine brain membranes 总被引:1,自引:0,他引:1
The Triton X-100-resistant residue of brain membranes contains appreciable amounts of S-100 proteins. This fraction of S-100 can be solubilized by high concentrations of EDTA plus or minus high concentrations of KCl. Whereas KCl (0.6 M) extracts the detergent-resistant S-100, NaCl (1 M) does not. Endogenous Ca2+ is required and is sufficient for S-100 to remain associated with the detergent-resistant residue. However, 0.6 M KCl extracts a further fraction of Triton X-100-resistant S-100. In contrast, the Triton X-100-extractable fraction of S-100 resists the action of EDTA. These data suggest that Ca2+ regulates the extent of association of S-100 with Triton X-100-resistant components in brain membranes, whereas the association of S-100 with the lipid bilayer of brain membranes and/or with some intrinsic membrane proteins is less Ca2+-regulated. Several S-100-binding proteins are identified in the detergent-resistant residue of brain membranes by an overlay procedure. 相似文献
5.
The interaction of S-100b protein with cardiolipin (CL) vesicles has been studied by electron spin resonance, pyrene fluorescence, and circular dichroism. Electron spin resonance and pyrene fluorescence data indicate that S-100b binds to the polar surface of vesicles Ca2+-independently. In the presence of Ca2+, S-100b potentiates the Ca2+-induced clustering of the polar headgroups of CL molecules and causes a further reduction in the Ca2+-dependent decrease in the lateral mobility of the pyrene inserted into the lipid bilayer, which points to an effect of the protein on the hydrophobic core of the lipid bilayer through a larger perturbation of its polar surface. Circular dichroism analyses indicate that CL vesicles cause a decrease in the alpha-helical content of S-100b, analogous to that produced by Ca2+ and that the effects of CL vesicles and of Ca2+ on the secondary structure of the protein are supra-additive. By this technique, we found that the affinity of Ca2+ for S-100b increases substantially in the presence of CL vesicles, even in the presence of physiologic concentrations of KCl, suggesting that once S-100b had interacted with CL vesicles it assumes a new conformation in which its Ca2+-binding properties are greatly enhanced. These results are discussed in relation to binding of S-100b proteins to natural membranes, and to a possible involvement of S-100b in the regulation of membrane structural organization. 相似文献
6.
Sarah A. Jewell Donato Di Monte Plinio Richelmi Giorgio Bellomo Sten Orrenius 《Journal of biochemical and molecular toxicology》1986,1(3):13-22
Incubation of isolated rat hepatocytes with tert-butylhydroperoxide resulted in marked cytotoxicity preceded by intracellular glutathione depletion and extensive lipid peroxidation. Addition of antioxidants delayed, but did not prevent, this toxicity. A significant decrease in protein-free sulfhydryl groups also, occurred in the presence of tert-butylhydroperoxide; direct oxidation of protein thiols and mixed disulfide formation with glutathione were responsible for this decrease. The involvement of protein thiol depletion in tert-butylhydroperoxide–induced cytotoxicity is suggested by our observation that administration of dithiothreitol, which caused re-reduction of the oxidized sulfhydryl groups and mixed disulfides, efficiently protected the cells from toxicity. Moreover, depletion of intracellular glutathione by pretreatment of the hepatocytes with diethyl maleate accelerated and enhanced the depletion of protein thiols induced by tert-butylhydroperoxide and potentiated cell toxicity even in the absence of lipid peroxidation. 相似文献
7.
8.
Giovanna Zolese Ileana Giambanco Giovanna Curatola Roberto Staffolani Enrico Gratton Rosario Donato 《Cell calcium》1996,20(6):465-474
Phase-modulation fluorescence lifetime measurements were used to study the single Trp residue of the Ca2+-binding protein S-100a both in the absence and in the presence of Ca2+ and/or Mg2+. Trp fluorescence decay for the protein was satisfactorily described by Lorentzian lifetime distributions centered around two components (approximately 4 ns and 0.5 ns). Lifetime values were unchanged by 2 mM Ca2+, but the fractional intensity associated with longer lifetime increased up to 75%. In the presence of Mg2+, the Ca2+ induced increase of the fractional intensity associated with longer lifetime was only 57%. For the protein in buffer, about the 85% of the recovered anisotropy was associated to a rotational correlation time of 6.7 ns. After the addition of Ca2+, this value was increased to 16.08 ns. In the presence of Mg2+, Ca+2 increased the rotational correlation time to 33.75 ns. Similar studies were performed with S-100a interacting with egg phosphatidylcholine vesicles (SUV). Our data suggest that the conformation of the protein may be influenced by structural features of the lipidic membrane. Moreover, data obtained in the presence of Mg2+ indicate some interaction between lipids and S-100, likely mediated by this ion. 相似文献
9.
DNA topoisomerase activity is present at a very early stageof germination in nuclear extract of pea root meristems. Theactivity of this enzyme changes before the onset of replicativeDNA synthesis, thus suggesting the existence of a correlationbetween DNA topoisomerase I and events taking place during therelease of cells from a quiescent state. An antibody preparedagainst a human topoisomerase I is able to immuno-precipitatepart of the DNA topoisomerase activity present in pea nuclearextracts, and recognizes a protein with a molecular weight of45 kDa. We suggest that the 45 kDa protein is a DNA topoisomeraseI; its presence during embryogenesis and its storage in dryseeds would explain the presence of DNA topoisomerase I activityduring early stages of germination. Key words: Pisum sativum L, DNA topoisomerase, nuclei, quiescence, proliferation 相似文献
10.
Donato Torre Giulio Ferrario Giancarla Bonetta Lorenza Perversi Roberto Tambini Filippo Speranza 《FEMS immunology and medical microbiology》1994,9(3):183-188
Abstract Several studies have demonstrated that Bordetella pertussis has the ability to enter and survive intracellularly within human polymorphonuclear leukocytes (PMNL) and human monocytes/macrophages. The effects of human recombinant gamma interferon (IFN-γ) on the survival of B. pertussis in PMNL and human monocytes, and on the oxidative burst activity of PMNL and human monocytes in response to B. pertussis were assessed in this study. IFN-γ partially increased intracellular killing of phagocytosed B. pertussis in human monocytes, as determined by an orange acridine-crystal violet assay. In contrast, IFN-γ did not enhance intracellular killing of B. pertussis in PMNL. No significant increase of superoxide production was noted in human monocytes in response to B. pertussis when stimulated with various concentrations of IFN-γ. The partial increase of B. pertussis killing by IFN-γ within monocytes, together with poor production of superoxide may explain how B. pertussis can survive within human phagocytic cells, and thus cause a more prolonged course of the disease. 相似文献