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941.
Serganov A Keiper S Malinina L Tereshko V Skripkin E Höbartner C Polonskaia A Phan AT Wombacher R Micura R Dauter Z Jäschke A Patel DJ 《Nature structural & molecular biology》2005,12(3):218-224
The majority of structural efforts addressing RNA's catalytic function have focused on natural ribozymes, which catalyze phosphodiester transfer reactions. By contrast, little is known about how RNA catalyzes other types of chemical reactions. We report here the crystal structures of a ribozyme that catalyzes enantioselective carbon-carbon bond formation by the Diels-Alder reaction in the unbound state and in complex with a reaction product. The RNA adopts a lambda-shaped nested pseudoknot architecture whose preformed hydrophobic pocket is precisely complementary in shape to the reaction product. RNA folding and product binding are dictated by extensive stacking and hydrogen bonding, whereas stereoselection is governed by the shape of the catalytic pocket. Catalysis is apparently achieved by a combination of proximity, complementarity and electronic effects. We observe structural parallels in the independently evolved catalytic pocket architectures for ribozyme- and antibody-catalyzed Diels-Alder carbon-carbon bond-forming reactions. 相似文献
942.
Conference Report
Ninth Oxford Conference Organised by the Oxford International Biomedical Centre (OIBC) 相似文献943.
A series of events organized at Mansfield College and Magdalen College School by Oxford International Biomedical Centre from March 29th to April 1st 2004, is reported. There were more than 60 active participants (speakers, moderators and discussants) plus the general audience. A special programme for the group of five youngsters from developing and restructuring countries, for the first time in the 10 years history of OIBC conferences, was also run. 相似文献
944.
Zachara BA Włodarczyk Z Masztalerz M Adamowicz A Gromadzinska J Wasowicz W 《Biological trace element research》2004,97(1):1-13
In animals and humans, the highest level of selenium (Se) occurs in the kidney. This organ is also the major site of the synthesis
of the selenoenzyme glutathione peroxidase (GSH-Px). Decreased Se levels and GSH-Px activities in blood are common symptoms
in the advanced stage of chronic renal failure (CRF). Blood samples for Se levels and GSH-Px activities measurements from
patients were collected just before transplantation and 3, 7, 14, 30, and 90 d posttransplant. The Se levels in whole blood
and plasma of patients before transplantation (79.5 and 64.5 ng/mL, respectively) were lower by 23% and 21%, respectively,
as compared with controls (p<0.0001), and 7 d after operation, it further decreased in both components (p<0.01). Fourteen days after surgery, the levels reached the initial values and increased slowly in the later period. Red blood
cell GSH-Px activity in patients in the entire period of the study did not differ from the control group. Plasma GSH-Px of
patients before the surgery was extremely low (76 U/L) as compared with controls (243 U/L; p<0.0001) but increased rapidly to 115 U/L after 3 d, to 164 U/L after 14 d, and to 208 U/L after 3 mo posttransplant. In CRF
patients, after kidney transplantation, plasma GSH-Px activity increased rapidly, approaching, after 3 mo, the values that
were close to the normal levels. A negative correlation between creatinine level and plasma GSH-Px activity is observed in
patients after kidney transplantation. Monitoring of plasma GSH-Px activity may be a useful additional marker of the transplanted
kidney function. 相似文献
945.
Three-dimensional biofilm structure quantification 总被引:7,自引:0,他引:7
Quantitative parameters describing biofilm physical structure have been extracted from three-dimensional confocal laser scanning microscopy images and used to compare biofilm structures, monitor biofilm development, and quantify environmental factors affecting biofilm structure. Researchers have previously used biovolume, volume to surface ratio, roughness coefficient, and mean and maximum thicknesses to compare biofilm structures. The selection of these parameters is dependent on the availability of software to perform calculations. We believe it is necessary to develop more comprehensive parameters to describe heterogeneous biofilm morphology in three dimensions. This research presents parameters describing three-dimensional biofilm heterogeneity, size, and morphology of biomass calculated from confocal laser scanning microscopy images. This study extends previous work which extracted quantitative parameters regarding morphological features from two-dimensional biofilm images to three-dimensional biofilm images. We describe two types of parameters: (1) textural parameters showing microscale heterogeneity of biofilms and (2) volumetric parameters describing size and morphology of biomass. The three-dimensional features presented are average (ADD) and maximum diffusion distances (MDD), fractal dimension, average run lengths (in X, Y and Z directions), aspect ratio, textural entropy, energy and homogeneity. We discuss the meaning of each parameter and present the calculations in detail. The developed algorithms, including automatic thresholding, are implemented in software as MATLAB programs which will be available at site prior to publication of the paper. 相似文献
946.
Beyenal H Yakymyshyn C Hyungnak J Davis CC Lewandowski Z 《Journal of microbiological methods》2004,58(3):367-374
We have developed an optical microsensor to quantify fluorescent light intensity distribution in biofilms. The optical system consisted of a beam splitter, light couplers, filters and a spectrophotometer able to accept the fiberoptic cable to measure fluorescent light intensity. The emitted light, fluorescence from the biofilm, was collected at the tip of the optical microsensor and was transferred to a spectrophotometer via a fiberoptic cable. The total fluorescent light intensity was evaluated from the emission spectrum by numerical integration. The newly developed fiberoptic microsensor was tested using a Staphylococcus aureus strain producing yellow fluorescent protein (YFP) grown as biofilm. We used a 405-nm violet laser diode for excitation, and measured the emission intensity between 480 nm and 540 nm. The optical microsensor that quantifies fluorescent light intensity is a promising tool in biofilm research which often requires detection and quantification of fluorescent light intensity distribution generated by various fluorescent proteins. 相似文献
947.
948.
Krasowska M Grzywna ZJ Mycielska ME Djamgoz MB 《European biophysics journal : EBJ》2004,33(6):535-542
Fractal methods were used to analyze quantitative differences in secretory membrane activities of two rat prostate cancer cell lines (Mat-LyLu and AT-2) of strong and weak metastatic potential, respectively. Each cells endocytic activity was determined by horseradish peroxidase uptake. Digital images of the patterns of vesicular staining were evaluated by multifractal analyses: generalized fractal dimension (Dq) and its Legendre transform f(), as well as partitioned iterated function system – semifractal (PIFS-SF) analysis. These approaches revealed consistently that, under control conditions, all multifractal parameters and PIFS-SF codes determined had values greater for Mat-LyLu compared with AT-2 cells. This would agree generally with the endocytic/vesicular activity of the strongly metastatic Mat-LyLu cells being more developed than the corresponding weakly metastatic AT-2 cells. All the parameters studied were sensitive to tetrodotoxin (TTX) pre-treatment of the cells, which blocked voltage-gated Na+ channels (VGSCs). Some of the parameters had a simple dependence on VGSC activity, whereby pre-treatment with TTX reduced the values for the MAT-LyLu cells and eliminated the differences between the two cell lines. For other parameters, however, there was a complex dependence on VGSC activity. The possible physical/physiological meaning of the mathematical parameters studied and the nature of involvement of VGSC activity in control of endocytosis/secretion are discussed. 相似文献
949.
Augustynowicz A Dziecioł J Barwijuk-Machała M Dadan J Puchalski Z Sulkowski S 《Folia histochemica et cytobiologica / Polish Academy of Sciences, Polish Histochemical and Cytochemical Society》2004,42(3):165-168
We have undertaken an attempt to compare the application efficacy of the proliferative activity markers in differential diagnosis of thyroid Hürthle cell tumors (HCT) using the PCNA and Ki-67 labeling and AgNOR visualisation techniques. The present work is a retrospective analysis of 78 Hürthle cell tumors: 20 Hürthle cell carcinomas (HCC), 32 Hürthle cell adenomas (HCA) and 26 hyperplastic nodules with Hurthle cell metaplasia (HCM). Five microm sections were stained according to AgNOR technique and labeled with antibodies against PCNA and Ki-67. AgNOR dot count in the nucleus and proliferative index (PI - percentage of cells expressing PCNA and Ki-67) in randomly chosen nuclei (100 in case of AgNOR and over 1000 in case of PI) were evaluated in each slide. The mean values of AgNOR dot count, PI-PCNA and PI-Ki-67 in HCC, HCA and HCM were respectively: 5.1, 61.3 and 54.9; 3.4, 42.4 and 38.6 and 2.5, 39.3 and 34.3. Statistically significant difference was found in all the proliferative activity markers between malignant and benign tumors: HCC:HCA (p<0.01) and HCC:HCM (p<0.001). There was no statistically significant difference between HCA and HCM. 相似文献
950.
Sroka Z Kuta I Cisowski W Dryś A 《Zeitschrift für Naturforschung. C, Journal of biosciences》2004,59(5-6):363-367
A methanol extract was obtained from defatted (petroleum ether) inflorescence of Helichrysum arenarium (L.) Moench (perennial herb native to Middle and Southeast Europe). The extract was evaporated under reduced pressure and the dry residue was dissolved in hot water. The aqueous solution was stored for 6 d at 4 degrees C and the precipitate discarded. The remaining solution was divided into three aliquots a, b and c. Part a was extracted with ethyl acetate to obtain extract (A), part b was extracted with diethyl ether to obtain extract (B) and part c was subjected to alkaline hydrolysis and then extracted with diethyl ether to obtain extract (C). Extracts (A), (B) and (C) were evaporated under reduced pressure to obtain the dry residues A, B and C which were further investigated for phenolic compound content by TLC and HPLC and for antiradical activity with 2,2-diphenyl-1-picrylhydrazyl radical (DPPH*) as a substrate. Residue C exhibited stronger antiradical properties than non-hydrolysed residues A and B. HPLC analysis showed a great increase of caffeic acid in residue C. We concluded that the hydrolysis process led to a significant increase of free caffeic acid (strong antioxidant) concentration resulting in increased antiradical activity of residue C. 相似文献