全文获取类型
收费全文 | 6468篇 |
免费 | 476篇 |
国内免费 | 1篇 |
出版年
2023年 | 23篇 |
2022年 | 72篇 |
2021年 | 130篇 |
2020年 | 80篇 |
2019年 | 139篇 |
2018年 | 182篇 |
2017年 | 145篇 |
2016年 | 225篇 |
2015年 | 292篇 |
2014年 | 381篇 |
2013年 | 456篇 |
2012年 | 498篇 |
2011年 | 470篇 |
2010年 | 311篇 |
2009年 | 256篇 |
2008年 | 388篇 |
2007年 | 349篇 |
2006年 | 292篇 |
2005年 | 297篇 |
2004年 | 304篇 |
2003年 | 269篇 |
2002年 | 247篇 |
2001年 | 105篇 |
2000年 | 80篇 |
1999年 | 76篇 |
1998年 | 53篇 |
1997年 | 40篇 |
1996年 | 60篇 |
1995年 | 32篇 |
1994年 | 33篇 |
1993年 | 33篇 |
1992年 | 57篇 |
1991年 | 49篇 |
1990年 | 43篇 |
1989年 | 35篇 |
1988年 | 39篇 |
1987年 | 29篇 |
1986年 | 31篇 |
1985年 | 31篇 |
1984年 | 19篇 |
1983年 | 31篇 |
1982年 | 27篇 |
1981年 | 24篇 |
1980年 | 23篇 |
1979年 | 19篇 |
1977年 | 21篇 |
1976年 | 15篇 |
1975年 | 19篇 |
1974年 | 17篇 |
1972年 | 15篇 |
排序方式: 共有6945条查询结果,搜索用时 15 毫秒
991.
Guadalupe Medina-de la Rosa Moisés Graciano Carcaño-Montiel Jesús Francisco López-Olguín Miguel Ángel Hernández-Espinosa José Antonio Rivera-Tapia 《Archives Of Phytopathology And Plant Protection》2016,49(11-12):310-321
The chitinase enzyme was identified in isolated bacteria of maize rhizosphere as well as its potential for the biological control of fungi associated at seeds of the same plant. The production of chitinase enzyme was found in the genera identified as Acinetobacter, Bacterium, Burkholderia, Paenibacillus, Pseudomonas, Rhizobium, Shewanella, Sphingomonas and Stenotrophomonas. Bacterial isolates with ability to degrade fungal mycelium from maize fungi as Fusarium and Alternaria among others, were detected. Bacterial chitinase activity and the presence of the chiA gene were determined. The inoculation of chitinolytic bacteria showed a positive effect in the control of fungi in maize seeds. The results support the potential use of chitinase enzyme producing bacteria on the control of phytopathogenic fungi. 相似文献
992.
Ronivaldo Rodrigues da Silva Tatiane Beltramini Souto Tássio Brito de Oliveira Lilian Caroline Gonçalves de Oliveira Daniel Karcher Maria Aparecida Juliano Luiz Juliano Arthur H. C. de Oliveira André Rodrigues Jose C. Rosa Hamilton Cabral 《Journal of industrial microbiology & biotechnology》2016,43(8):1059-1069
In this study, we detail the specificity of an aspartic peptidase from Rhizomucor miehei and evaluate the effects of this peptidase on clotting milk using the peptide sequence of k-casein (Abz-LSFMAIQ-EDDnp) and milk powder. Molecular mass of the peptidase was estimated at 37 kDa, and optimum activity was achieved at pH 5.5 and 55 °C. The peptidase was stable at pH values ranging from 3 to 5 and temperatures of up 45 °C for 60 min. Dramatic reductions in proteolytic activity were observed with exposure to sodium dodecyl sulfate, and aluminum and copper (II) chloride. Peptidase was inhibited by pepstatin A, and mass spectrometry analysis identified four peptide fragments (TWSISYGDGSSASGILAK, ASNGGGGEYIFGGYDSTK, GSLTTVPIDNSR, and GWWGITVDRA), similar to rhizopuspepsin. The analysis of catalytic specificity showed that the coagulant activity of the peptidase was higher than the proteolytic activity and that there was a preference for aromatic, basic, and nonpolar amino acids, particularly methionine, with specific cleavage of the peptide bond between phenylalanine and methionine. Thus, this peptidase may function as an important alternative enzyme in milk clotting during the preparation of cheese. 相似文献
993.
Valenti D Vacca RA de Pinto MC De Gara L Marra E Passarella S 《Biochimica et biophysica acta》2007,1767(1):66-78
To investigate whether and how mitochondria can change in plant programmed cell death (PCD), we used the non-photosynthetic Tobacco Bright Yellow 2 (TBY-2) cells. These can be synchronized to high levels, stand out in terms of growth rate and homogeneity and undergo PCD as a result of heat shock. Using these cells we investigated the activity of certain mitochondrial proteins that have a role in providing ATP and/or other nucleoside triphosphates (NTPs). We show that, already after 2 h from the heat shock, when cell viability remains unaffected, the rate of ADP/ATP exchange due to adenine nucleotide translocator (ANT) activity, and the rate of the reactions catalysed by adenylate kinase (ADK; EC 2.7.4.3) and nucleoside diphosphate kinase (NDPK; EC 2.7.4.6) are inhibited in a non-competitive-like manner. In all cases, externally added ascorbate partially prevented the inhibition. These effects occurred in spite of minor (for ANT) or no changes in the mitochondrial protein levels as immunologically investigated. Interestingly, a decrease of both the steady state level of the ascorbate pool and of the activity of l-galactono-gamma-lactone dehydrogenase (GLDH) (EC 1.3.2.3), the mitochondrial enzyme catalysing the last step of ascorbate biosynthesis, were also found. 相似文献
994.
Lupo G Anfuso CD Ragusa N Tirolo C Marchetti B Gili E La Rosa C Vancheri C 《Biochimica et biophysica acta》2007,1771(4):522-532
In cell cultures of human lung fibroblasts, we found that oxidized LDL (oxLDL), after 24-h treatment, stimulated arachidonic acid release. A putative role for phospholipases A(2) and MAPK activities in this process was postulated. Consequently, we studied the contribution of either Ca(2+)-dependent, cytosolic phospholipase A(2) (cPLA(2)) or Ca(2+)-independent phospholipase A(2) (iPLA(2)), and the role of the MAP kinase family in oxLDL toxicity to fibroblastic cells in vitro. Activation of extracellular signal-regulated kinases ERK1/2, p38 and c-Jun NH(2)-terminal kinase (JNK) was also assessed with Western blotting. Compared with cellular samples untreated or treated with native LDL, treatment with oxLDL (50-100 microM hydroperoxides) for 24 h significantly increased the levels of either cPLA(2) protein expression or constitutively phosphorylated cPLA(2) protein; in addition we observed enzyme translocation to membranes. iPLA(2) activity was not stimulated by oxLDL. Arachidonic acid release appeared to be associated with phosphorylation of ERK1/2 which was significantly enhanced in a dose-dependent manner whereas no activation of p38 and JNKs was found, indicating that these MAPKs are not involved in mediating the maximal oxLDL response. Western blotting on subcellular fractions and confocal microscopy analyses confirmed an increase in 15-lipoxygenase (15-LO) protein expression and translocation upon activation. A significant increase of cyclooxygenase-2 expression into membrane fraction was also found. Collectively, the data presented link the stimulation of ERK-cPLA(2)-15-LO pathway by oxLDL to the prooxidant mechanism of the lipoprotein complex. It may initially stimulate the fibroblast reaction against the oxidation challenge as well as metabolic repair, such as during lung inflammation and pulmonary fibrosis. 相似文献
995.
De Simone F Guzzi R Sportelli L Marsh D Bartucci R 《Biochimica et biophysica acta》2007,1768(6):1541-1549
Human serum albumin (HSA) is an abundant plasma protein that transports fatty acids and also binds a wide variety of hydrophobic pharmacores. Echo-detected (ED) EPR spectra and D(2)O-electron spin echo envelope modulation (ESEEM) Fourier-transform spectra of spin-labelled free fatty acids and phospholipids were used jointly to investigate the binding of stearic acid to HSA and the adsorption of the protein on dipalmitoyl phosphatidylcholine (DPPC) membranes. In membranes, torsional librations are detected in the ED-spectra, the intensity of which depends on chain position at low temperature. Water penetration into the membrane is seen in the D(2)O-ESEEM spectra, the intensity of which decreases greatly at the middle of the membrane. Both the chain librational motion and the water penetration are only little affected by adsorption of serum albumin at the DPPC membrane surface. In contrast, both the librational motion and the accessibility of the chains to water are very different in the hydrophobic fatty acid binding sites of HSA from those in membranes. Indeed, the librational motion of bound fatty acids is suppressed at low temperature, and is similar for the different chain positions, at all temperatures. Correspondingly, all segments of the bound chains are accessible to water, to rather similar extents. 相似文献
996.
De Rosa MC Carelli Alinovi C Schininà ME Clementi ME Amato A Cappabianca MP Pezzotti M Giardina B 《Biochimica et biophysica acta》2007,1774(10):1299-1306
This study examines the functional and structural effects of amino acid substitution at alpha(1)beta(2) interface of Hb Santa Clara (beta 97His-->Asn). We have characterized the variation by a combination of electrospray ionisation mass spectrometry and DNA sequence analysis followed by oxygen-binding experiments. Functional studies outlined an increased oxygen affinity, reduced effect of organic phosphates and a reduced Bohr effect with respect to HbA. In view of the primary role of this interface in the cooperative quaternary transition from the T to R conformational state, a theoretical three-dimensional model of Hb Santa Clara was generated. Structural investigations suggest that replacement of Asn for His beta 97 results in a significant stabilization of the high affinity R-state of the haemoglobin molecule with respect to the low affinity T-state. The role of beta FG4 position has been further examined by computational models of known beta FG4 variants, namely Hb Malm? (beta 97His-->Gln), Hb Wood (beta 97His-->Leu), Hb Nagoya (beta 97His-->Pro) and Hb Moriguchi (beta 97His-->Tyr). These findings demonstrate that, among the various residues at the alpha(1)beta(2) (and alpha(2)beta(1)) intersubunit interface, His beta FG4 contributes significantly to the quaternary constraints that are responsible for the low oxygen affinity of human deoxyhaemoglobin. 相似文献
997.
998.
Giner RM Mancini L Kamal AM Perretti M 《Biochemical and biophysical research communications》2007,354(2):414-419
We tested whether glucocorticoids modulated osteoblast expression of the annexin 1 system, including the ligand and two G-coupled receptors termed formyl-peptide receptor (FPR) and FPR-like-1 (FPRL-1). In Saos-2 cells, rapid up-regulation of FPR mRNA upon cell incubation with dexamethasone (0.01-1 microM) was observed, with significant changes as early as 2h and a more marked response at 24h; annexin 1 and FPRL-1 mRNA changes were more subtle. At the protein level, dexamethasone provoked a rapid externalization of annexin 1 (maximal at 2h) followed by delayed time-dependent changes in the cell cytosol. Saos-2 cell surface expression of FPR or FPRL-1 could not be detected, even when dexamethasone was added with the bone modelling cytokines interleukin-6 or interleukin-1. The uneven modulation of the annexin 1 system (mediator and its putative receptors) in osteoblasts might lead to a better understanding of how these complex biochemical pathways become operative in bone. 相似文献
999.
The production of benzophenanthridine alkaloids (sanguinarine, chelerythrine and macarpine) in cells of Eschscholtzia californica is enhanced by sodium alginate and by entrapment in Ca2+-alginate. Tyrosine decarboxylase, a key enzyme of alkaloid biosynthesis, is induced by the treatments. Alginate- entrapped cells are elicited over an extended period of time which leads to increased alkaloid biosynthesis (up to 800-fold enhancement). A major portion of alkaloids produced are released into the growth medium. 相似文献
1000.
U Raab P Lastres M A Arévalo J M López-Novoa C Caba?as E J de la Rosa C Bernabéu 《FEBS letters》1999,459(2):249-254
Endoglin is a component of the transforming growth factor beta (TGF-beta) receptor complex, highly expressed by endothelial cells. Mutations in the endoglin gene are responsible for hereditary hemorrhagic telangiectasia type 1 (HHT1), an autosomal dominant vascular disorder caused by a haploinsufficiency mechanism. Vascular lesions (telangiectasia and arteriovenous malformations) in HHT1 are associated with loss of the capillary network, suggesting the involvement of endoglin in vascular repair processes. Using the chick chorioallantoic membrane (CAM) as an angiogenic model, we have analyzed the expression and function of chicken endoglin. A pan-specific polyclonal antibody (pAb) recognized chicken endoglin as demonstrated by immunostaining and Western blot analysis. In ovo treatment of chicken embryos with this pAb resulted in a significantly increased area of CAM. This effect was likely mediated by modulation of the ligand binding to endoglin as this pAb was able to inhibit TGF-beta1 binding. These results support the involvement of endoglin in the angiogenic process. 相似文献