全文获取类型
收费全文 | 1711篇 |
免费 | 90篇 |
专业分类
1801篇 |
出版年
2023年 | 4篇 |
2022年 | 16篇 |
2021年 | 23篇 |
2020年 | 19篇 |
2019年 | 18篇 |
2018年 | 37篇 |
2017年 | 22篇 |
2016年 | 45篇 |
2015年 | 81篇 |
2014年 | 76篇 |
2013年 | 141篇 |
2012年 | 122篇 |
2011年 | 152篇 |
2010年 | 79篇 |
2009年 | 61篇 |
2008年 | 131篇 |
2007年 | 126篇 |
2006年 | 124篇 |
2005年 | 114篇 |
2004年 | 99篇 |
2003年 | 100篇 |
2002年 | 65篇 |
2001年 | 11篇 |
2000年 | 12篇 |
1999年 | 13篇 |
1998年 | 15篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 9篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 10篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 2篇 |
排序方式: 共有1801条查询结果,搜索用时 4 毫秒
51.
Goncalo L. Silva Jacek Plewka Helga Lichtenegger Ana C. Dias-Cabral Alois Jungbauer Rupert Tscheließnig 《Biotechnology and bioengineering》2019,116(1):76-86
Staphylococcal protein A chromatography is an established core technology for monoclonal antibody purification and capture in the downstream processing. MabSelect SuRe involves a tetrameric chain of a recombinant form of the B domain of staphylococcal protein A, called the Z-domain. Little is known about the stoichiometry, binding orientation, or preferred binding. We analyzed small-angle X-ray scattering data of the antibody–protein A complex immobilized in an industrial highly relevant chromatographic resin at different antibody concentrations. From scattering data, we computed the normalized radial density distributions. We designed three-dimensional (3D) models with protein data bank crystallographic structures of an IgG1 (the isoform of trastuzumab, used here; Protein Data Bank: 1HZH) and the staphylococcal protein A B domain (the native form of the recombinant structure contained in MabSelect SuRe resin; Protein Data Bank: 1BDD). We computed different binding conformations for different antibody to protein A stoichiometries (1:1, 2:1, and 3:1) and compared the normalized radial density distributions computed from 3D models with those obtained from the experimental data. In the linear range of the isotherm we favor a 1:1 ratio, with the antibody binding to the outer domains in the protein A chain at very low and high concentrations. In the saturation region, a 2:1 ratio is more likely to occur. A 3:1 stoichiometry is excluded because of steric effects. 相似文献
52.
53.
Correction to Escalada F, Marco E, Duarte E, Muniesa JM, Boza R, Tejero M, Cáceres E. Assessment of angle velocity in girls with adolescent idiopathic scoliosis. Scoliosis 2009; 4:20. 相似文献
54.
Zebrowski J 《Planta》1999,207(3):410-417
The mechanical response of cereal plant shoots to loads caused by wind and gravity in the field is swaying in flexure around
the vertical or near vertical transient equilibrium position determined by the stationary component of the wind pressure.
The aim of this work was to characterise the kinematic and dynamic attributes and their interrelations in freely swaying inflorescence-bearing
stems of wheat (Triticum aestivum L.) and Triticale. The fundamental natural frequency of the stems appeared to be considerably lower than predicted from the theory of vibration
using the model of a cantilever beam oscillator and assuming the spring constant to be equal to the force-deflection ratio.
Because of the rate of deformation and visco-elastic behaviour of the plant material, a discrepancy of about 10% was found
between the dynamic and static stem bending resistance. The presence of the tip inflorescence caused vibrating vertical stems
to behave as compressed columns in which the effective spring constant was strongly biased by the apical load due to the weight
of the inflorescence. At the late milk stage, in the freely swaying stems of wheat and Triticale, the resistance to dynamic lateral loads was reduced by about 30% as a result of compression exerted by the inflorescence.
So the prominent effect of the tip inflorescence on the dynamic behaviour (the effective spring constant and the natural frequency)
of the stem is attributed to the non-negligible magnitude of the inflorescence weight relative to the critical load producing
elastic buckling in slender vertical structures. Stem softening as a consequence of increasing inflorescence weight is assumed
to be one of the essential factors reducing the lodging resistance in cereal crops at the late milk stage. The feasibility
of the compressed-column approach for predicting the dynamic bending performance of slender vertical plant organs is discussed.
Received: 4 March 1998 / Accepted: 20 July 1998 相似文献
55.
Wesierska-Gadek J Gueorguieva M Wojciechowski J Tudzarova-Trajkovska S 《Journal of cellular biochemistry》2004,93(4):774-787
We reported previously that treatment of rats with the hepatocarcinogen N-nitrosomorpholine (NNM) caused severe hepatotoxicity associated with apoptosis of hepatocytes beginning 12 h after administration of NNM. We observed that poly(ADP-ribose) polymerase 1 (PARP-1), one of the major nuclear targets for caspases, was proteolytically degraded generating primarily 64 and 54 kDa fragments. Interestingly, at 20, 30, and 40 h post-treatment a 85 kDa cleavage product of PARP-1 resembling that generated by caspase-3 appeared additionally in hepatocytes. More detailed analysis performed in the present study revealed that the 85 kDa fragment of PARP-1 was generated in the liver in 10 of 17 (60%) animals examined between 20 and 40 h after NNM administration. The caspase-3 generated 85 kDa fragment was detected solely in hepatocytes undergoing apoptosis as evidenced by immunostaining performed with the antibody recognizing exclusively PARP-1 cleaved at position 214/215. The appearance of the 85 kDa fragment of PARP-1 in the liver nuclei coincided temporally with an significant increase of caspase-3 activity in hepatocytes. In contrast, in testis samples obtained from the same animals, no changes characteristic for apoptosis such as induction of caspases activity or degradation of nuclear PARP-1 could be detected. Our results evidence unequivocally that PARP-1 in liver is not resistant to caspases and can be processed in vivo by activated caspase-3 producing the p85 kDa fragment. Moreover, the caspase-3 induced PARP-1 fragmentation coinciding with the increase of caspase-3 activity was detected solely in the target organ and exclusively in hepatocytes undergoing apoptosis. Considering the fact that the caspase-3 mediated PARP-1 cleavage occurred only in 60% of animals tested between 20 and 40 h, it becomes obvious that the cellular response in vivo to the same trigger(s) strongly varies and may depend on a variety of intrinsic factors. It remains to elucidate which additional factors may be involved in the modulation of cellular response to the strong insults thereby activating different pathways and generating distinct outcomes. 相似文献
56.
57.
de Los Ríos A Ascaso C Wierzchos J Fernández-Valiente E Quesada A 《Applied and environmental microbiology》2004,70(1):569-580
The three-dimensional structures of two types of cyanobacterium-dominated microbial mats from meltwater ponds on the McMurdo Ice Shelf were as determined by using a broad suite of complementary techniques, including optical and fluorescence microscopy, confocal scanning laser microscopy, scanning electron microscopy with back-scattered electron-imaging mode, low-temperature scanning electron microscopy, and microanalyitical X-ray energy dispersive spectroscopy. By using a combination of the different in situ microscopic techniques, the Antarctic microbial mats were found to be structures with vertical stratification of groups of cyanobacteria and mineral sediments, high contents of extracellular polymeric substances, and large void spaces occupied by water. In cyanobacterium-rich layers, heterocystous nostocalean and nonheterocystous oscillatorialean taxa were the most abundant taxa and appeared to be intermixed with fine-size deposits of epicellular silica and calcium carbonate. Most of the cyanobacterial filaments had similar orientations in zones without sediment particles, but thin filaments were tangled among thicker filaments. The combination of the microscopic techniques used showed the relative positions of biological and mineral entities within the microbial mats and enabled some speculation about their interactions. 相似文献
58.
Łodyga-Chruścińska E Ołdziej S Micera G Sanna D Chruściński L Olczak J Zabrocki J 《Journal of inorganic biochemistry》2004,98(3):447-458
Complex formation between Cu(II) and three tetrazole analogues of opioid peptide-deltorphin I has been investigated. In potentiometric and spectroscopic (UV-Vis, CD and EPR) studies have been established the thermodynamic stability, speciation and structure of Cu(II) complexes with Tyr-D-Ala-Phe-Asp-Val-Val-Gly-NH2 (L1), Tyr-Psi(CN4)-Gly-Phe-Asp-Val-Val-Gly-NH2 (L2), Tyr-Gly-Psi(CN4)-Phe-Asp-Val-Val-Gly-NH2 (L3) and Tyr-D-Ala-Psi(CN4)-Phe-Asp-Val-Val-Gly-NH2 (L4). The site of the insertion of tetrazole moiety Psi(CN4) into the peptide sequences has critical impact on their co-ordination ability. Comparison of the binding ability of the tetrazole analogues reveals that around physiological pH region the L3 and L4 are more effective ligands for copper(II) than L(1) and L(2). The peptide conformation changes achieved by Cu(II) co-ordination may be essential for binding of the tetrazole deltorphins at the opiate receptors. 相似文献
59.
Zachara BA Koterska D Manitius J Sadowski L Dziedziczko A Salak A Wasowicz W 《Biological trace element research》2004,97(1):15-30
Patients with chronic renal failure (CRF) usually have a lower than healthy level of selenium (Se) in whole blood and plasma.
Plasma glutathione peroxidase (GSH-Px) is synthesized mostly in the kidney. In CRF patients, activity of this enzyme is significantly
reduced and its reduction increases with the progress of the disease. The aim of the study was to evaluate the effect of Se
supplementation to CRF patients at various stages of the disease on Se concentration in blood components and on plasma GSH-Px
activity.
The study group comprised 53 CRF patients at various stages of the disease supplemented with Se (200 μg/d for 3 mo as Se-enriched
yeast, containing about 70% l-selenomethionine [SeMet]). The control group consisted of 20 healthy subjects. The Se concentration in blood components was
measured spectrofluorometrically with 2,3-diaminonaphthalene as a complexing reagent. GSH-Px activity in red cell hemolysates
and plasma was assayed by the coupled method with tert-butyl hydroperoxide as a substrate.
The Se concentration in whole blood and plasma of CRF patients is significantly lower as compared with healthy subjects, but
similar at all stages of the disease. In the patients’ plasma, total protein and albumin levels are also significantly lower
than in healthy subjects. Plasma GSH-Px activity in patients is extremely low, and contrary to Se concentration, it decreases
linearly with the increasing stage of the illness. Se-supplied patients show an increased Se concentration in all blood components
and at all disease stages, whereas plasma GSH-Px activity is enhanced only at the incipient stage of the disease. Se supply
has no effect on plasma GSH-Px activity in uremic patients at the end stage of the disease. Total plasma protein and albumin
levels did not change after Se supplementation. Our data seem to show that in patients with CRF lower total protein and albumin
levels in plasma may be the chief cause of the low blood and plasma Se concentrations. GSH-Px activity decreases along with
the kidney impairment. At the end stage of the disease, Se supplementation in the form of Se-enriched yeast has no effect
on the increase in plasma GSH-Px activity. 相似文献
60.
Flensburg J Haid D Blomberg J Bielawski J Ivansson D 《Journal of biochemical and biophysical methods》2004,60(3):391-334
A new matrix-assisted laser desorption/ionization time of flight mass spectrometer (MALDI-ToF MS), developed specifically for the identification and characterization of proteins and peptides in proteomic investigations, is described. The mass spectrometer which can be integrated with the 2-D gel electrophoresis workflow is a bench-top instrument, enabling rapid, reliable and unattended protein identification in low-, as well as high-throughput proteomics applications. To obtain precise information on peptide sequences, the instrument utilizes a timed ion gate and a unique quadratic field reflectron (Z2 technology), allowing single-run, post-source decay (PSD) of selected peptides. In this study, the performance of the instrument in reflectron, PSD and linear mode, respectively, was investigated. The results showed that the limit of detection for a single peptide in reflectron mode was 125 amol with a signal to noise ratio exceeding 20. Average mass resolution for peptides larger than 2000 u was around 13,000 full width, half maximum (FWHM). The limit for protein identification during peptide mass fingerprinting (PMF) was 500 amol with a sequence coverage of 18%. Mass error during PMF analysis was less than 15 ppm for 17 out of 25 (68%) identified peptides. In PSD mode, a complete series of y-ions of a CAF-derivatized peptide could be obtained from 3.75 fmol of material. The average mass error of PSD-generated fragments was less than 0.14 u. Finally, in linear mode, intact proteins with molecular masses greater than 300,000 u were detected with mass errors below 0.2%. 相似文献