全文获取类型
收费全文 | 2342篇 |
免费 | 174篇 |
国内免费 | 2篇 |
出版年
2023年 | 6篇 |
2022年 | 28篇 |
2021年 | 46篇 |
2020年 | 41篇 |
2019年 | 61篇 |
2018年 | 58篇 |
2017年 | 56篇 |
2016年 | 84篇 |
2015年 | 116篇 |
2014年 | 157篇 |
2013年 | 189篇 |
2012年 | 211篇 |
2011年 | 203篇 |
2010年 | 118篇 |
2009年 | 97篇 |
2008年 | 140篇 |
2007年 | 160篇 |
2006年 | 120篇 |
2005年 | 97篇 |
2004年 | 101篇 |
2003年 | 124篇 |
2002年 | 79篇 |
2001年 | 12篇 |
2000年 | 16篇 |
1999年 | 15篇 |
1998年 | 16篇 |
1997年 | 12篇 |
1996年 | 20篇 |
1995年 | 13篇 |
1994年 | 14篇 |
1993年 | 15篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1969年 | 3篇 |
1962年 | 2篇 |
排序方式: 共有2518条查询结果,搜索用时 708 毫秒
191.
Overexpression, purification and characterization of the Trichoderma atroviride endochitinase, Ech42, in Pichia pastoris 总被引:1,自引:0,他引:1
Pérez-Martínez AS De León-Rodríguez A Harris LJ Herrera-Estrella A Barba de la Rosa AP 《Protein expression and purification》2007,55(1):183-188
The endochitinase gene ech42 from Trichoderma atroviride was cloned and expressed in Pichia pastoris using a constitutive expression system. Over 98% of the recombinant protein was secreted into the culture medium as glycoprotein. A high endochitinase concentration, 186 mg/L with a specific enzyme activity of 14,128 Umg(-1) was produced. The optimal enzyme kinetic parameters for the recombinant protein were identical to those reported for the enzyme isolated from T. atroviride. The recombinant endochitinase possesses suitable features for biotechnological applications, such as activity at acidic pH and thermostability. 相似文献
192.
A hypocaloric diet enriched in legumes specifically mitigates lipid peroxidation in obese subjects 总被引:2,自引:0,他引:2
Legume intake could specifically protect against lipid peroxidation in addition to the effects associated to weight loss when included in hypocaloric diets. Thus, 30 obese subjects (age: 36 +/- 8 years and BMI: 32.0 +/- 5.3 kg/m(2)) were nutritionally treated by a 8-week energy restriction ( - 30% energy expenditure) with a legume enriched diet (4 days/week servings, [image omitted] ) or without legumes (control diet (CD), [image omitted] ). Body weight, circulating cholesterol, oxidized LDL (ox-LDL), malondialdehyde (MDA) and urinary 8-isoprostane F(2alpha) (8-iso-PGF(2alpha)) were measured at baseline and at endpoint. After the nutritional intervention, all obese subjects lost weight, specially those individuals who followed the legumes-enriched diet as compared to the CD ( - 7.7 +/- 3 vs. - 5.3 +/- 2.7%; p = 0.023), which was accompanied by marked decreases in total cholesterol levels (p < 0.001) and statistically significant diet-related reductions on plasma ox-LDL, plasma MDA and urinary 8-iso-PGF(2alpha) output. Therefore, a balanced diet with moderate caloric restriction including 4 day/week legume servings empowered the oxidative stress improvement related to weight loss through a reduction in lipid peroxidation as compared to a control hypocaloric diet. 相似文献
193.
Sureda A Ferrer MD Tauler P Maestre I Aguiló A Córdova A Tur JA Roche E Pons A 《Free radical research》2007,41(8):874-883
We studied the effects of intense exercise on the neutrophil antioxidant enzyme activities and gene expression. Blood samples were taken from seven cyclists in basal conditions and 3 h after two competition stages of 165 km. Serum creatine kinase (CK) activity, plasma carbonyl derivatives and uric acid levels increased after exercise. The cycling stage induced neutrophilia and increased myeloperoxidase (MPO) activity and reactive oxygen species (ROS) production. Antioxidant enzyme activities (catalase, glutathione peroxidase and superoxide dismutase) decreased after exercise, although gene expression increased. Immunocytochemistry showed catalase (CAT) enzyme equally distributed between the cytoplasm and organelles before exercise, and after exercise the cytoplasmic CAT levels were reduced and were absent in the compartments. After in vitro stimulation with opsonized zymosan (OZ) the extracellular CAT levels increased. This suggests a CAT secretion in order to avoid neutrophil-induced oxidative damage at a local level or to regulate the function of ROS as extracellular signalling molecules. 相似文献
194.
Cortés-Rojo C Calderón-Cortés E Clemente-Guerrero M Manzo-Avalos S Uribe S Boldogh I Saavedra-Molina A 《Free radical research》2007,41(11):1212-1223
The deleterious effects of H2O2 on the electron transport chain of yeast mitochondria and on mitochondrial lipid peroxidation were evaluated. Exposure to H2O2 resulted in inhibition of the oxygen consumption in the uncoupled and phosphorylating states to 69% and 65%, respectively. The effect of H2O2 on the respiratory rate was associated with an inhibition of succinate-ubiquinone and succinate-DCIP oxidoreductase activities. Inhibitory effect of H2O2 on respiratory complexes was almost completely recovered by β-mercaptoethanol treatment. H2O2 treatment resulted in full resistance to QO site inhibitor myxothiazol and thus it is suggested that the quinol oxidase site (QO) of complex III is the target for H2O2. H2O2 did not modify basal levels of lipid peroxidation in yeast mitochondria. However, H2O2 addition to rat brain and liver mitochondria induced an increase in lipid peroxidation. These results are discussed in terms of the known physiological differences between mammalian and yeast mitochondria. 相似文献
195.
Vittorini S Storti S Parri MS Cerillo AG Clerico A 《Molecular medicine (Cambridge, Mass.)》2007,13(1-2):105-111
In animal models of conotruncal heart defects, an abnormal calcium sensitivity of the contractile apparatus and a depressed L-type calcium current have been described. Sarcoplasmic reticulum (SR) Ca(2+) ATPase (SERCA) is a membrane protein that catalyzes the ATP-dependent transport of Ca(2+) from the cytosol to the SR. The activity of SERCA is inhibited by phospholamban (PLN) and sarcolipin (SLN), and all these proteins participate in maintaining the normal intracellular calcium handling. Ryanodine receptors (RyRs) are the major SR calcium-release channels required for excitation-contraction coupling in skeletal and cardiac muscle. Our objective was to evaluate SERCA2a (i.e., the SERCA cardiac isoform), PLN, SLN, and RyR2 (i.e., the RyR isoform enriched in the heart) gene expression in myocardial tissue of patients affected by tetralogy of Fallot (TOF), a conotruncal heart defect. The gene expression of target genes was assessed semiquantitatively by RT-PCR using the calsequestrin (CASQ, a housekeeping gene) RNA as internal standard in the atrial myocardium of 23 pediatric patients undergoing surgical correction of TOF, in 10 age-matched patients with ventricular septal defect (VSD) and in 13 age-matched children with atrial septal defect (ASD). We observed a significantly lower expression of PLN and SLN in TOF patients, while there was no difference between the expression of SERCA2a and RyR2 in TOF and VSD. These data suggest a complex mechanism aimed to enhance the intracellular Ca(2+) reserve in children affected by tetralogy of Fallot. 相似文献
196.
Optimisation of biocide dose as a function of residual biocide in a heat exchanger pilot plant effluent 总被引:1,自引:0,他引:1
Biofouling is one of the most serious problems facing numerous industrial processes. In the case of a heat exchanger unit, biological deposits adhering to the inside surface of its tubes reduce heat transfer and, thus, the thermal performance of the cycle. Control of this phenomenon is proving fundamental for both land and marine equipment to operate in optimum working conditions. Hence, it is necessary to apply antifouling methods capable of keeping surfaces free of any kind of biofouling. This paper reports on the behaviour resulting from use of the flow inversion method vs that obtained by using various chemical treatments. The study compares the effectiveness of certain chemical treatments (Na hypochlorite, peracetic acid and a compound formed by Na bromide + Na hypochlorite) for removing a biofouling film that has already formed on the inside surfaces of tubes in a heat exchanger pilot plant. The paper also addresses the issue of optimising the concentration of biocide dose as a function of the residual biocide in order minimise the environmental impact caused by effluent from industrial plants. The results indicate that it is possible to eliminate a biofilm formed on the inside surfaces of tubes by the use of intermittent doses of chemical treatments at low concentrations and over long application times. Furthermore, once the stabilisation phase is reached 6 d after starting the treatment, it is possible to maintain the conditions achieved using only 20% of the initial dosage. 相似文献
197.
198.
Santi I Scarselli M Mariani M Pezzicoli A Masignani V Taddei A Grandi G Telford JL Soriani M 《Molecular microbiology》2007,63(3):754-767
By the analysis of the recently sequenced genomes of Group B Streptococcus (GBS) we have identified a novel immunogenic adhesin with anti-phagocytic activity, named BibA. The bibA gene is present in 100% of the 24 GBS strains analysed. BibA-specific IgG were found in human sera from normal healthy donors. The putative protein product is a polypeptide of 630 amino acids containing a helix-rich N-terminal domain, a proline-rich region and a canonical LPXTG cell wall-anchoring domain. BibA is expressed on the surface of several GBS strains, but is also recovered in GBS culture supernatants. BibA specifically binds to human C4-binding protein, a regulator of the classic complement pathway. Deletion of the bibA gene severely reduced the capacity of GBS to survive in human blood and to resist opsonophagocytic killing by human neutrophils. In addition, BibA expression increased the virulence of GBS in a mouse infection model. The role of BibA in GBS adhesion was demonstrated by the impaired ability of a bibA knockout mutant strain to adhere to both human cervical and lung epithelial cells. Furthermore, we calculated that recombinant BibA bound to human epithelial cells of distinct origin with an affinity constant of approximately 10(-8) M for cervical epithelial cells. Hence BibA is a novel multifunctional protein involved in both resistance to phagocytic killing and adhesion to host cells. The identification of this potential new virulence factor represents an important step in the development of strategies to combat GBS-associated infections. 相似文献
199.
Flores N Leal L Sigala JC de Anda R Escalante A Martínez A Ramírez OT Gosset G Bolivar F 《Journal of molecular microbiology and biotechnology》2007,13(1-3):105-116
In Escherichia coli the phosphotransferase system (PTS) consumes one molecule of phosphoenolpyruvate (PEP) to phosphorylate each molecule of internalized glucose. PEP bioavailability into the aromatic pathway can be increased by inactivating the PTS. However, the lack of the PTS results in decreased glucose transport and growth rates. To overcome such drawbacks in a PTS(-) strain and reconstitute rapid growth on glucose phenotype (Glc(+)), the glk and galP genes were cloned into a plasmid and the arcA gene was inactivated. Simultaneous overexpression of glk and galP increased the growth rate and regenerated a Glc(+) phenotype. However, the highest growth rate was obtained when glk and galP were overexpressed in the arcA(-) background. These results indicated that the arcA mutation enhanced glycolytic and respiratory capacities of the engineered strain. 相似文献
200.
Tornés Elisabet Alández-Rodríguez Juan Corrochano Alfredo Nolla-Querol Pepita Trapote Maria Carmen Sabater Sergi 《Hydrobiologia》2022,849(8):1821-1837
Hydrobiologia - Consequences of anthropogenic climate change directly affect freshwater ecosystems and their aquatic biological communities. Diatoms are amongst the most sensitive organisms to... 相似文献