全文获取类型
收费全文 | 560篇 |
免费 | 47篇 |
出版年
2024年 | 1篇 |
2023年 | 23篇 |
2022年 | 17篇 |
2021年 | 21篇 |
2020年 | 21篇 |
2019年 | 18篇 |
2018年 | 31篇 |
2017年 | 41篇 |
2016年 | 35篇 |
2015年 | 24篇 |
2014年 | 33篇 |
2013年 | 64篇 |
2012年 | 28篇 |
2011年 | 24篇 |
2010年 | 32篇 |
2009年 | 26篇 |
2008年 | 27篇 |
2007年 | 30篇 |
2006年 | 20篇 |
2005年 | 20篇 |
2004年 | 6篇 |
2003年 | 12篇 |
2002年 | 5篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1964年 | 1篇 |
1950年 | 1篇 |
1947年 | 1篇 |
排序方式: 共有607条查询结果,搜索用时 734 毫秒
101.
Change of multidrug resistance and sensitivity of leukemic cells to oxidative stress in large tumors
V. V. Shaposhnikova A. F. Korystova M. O. Emel’yanov M. Kh. Levitman Yu. A. Kim Yu. N. Korystov 《Biochemistry (Moscow) Supplemental Series A: Membrane and Cell Biology》2010,4(3):286-292
The possibility of modification of vincristine-resistant strain of leukemic cells upon long-term tumor transplantation was
studied. DBA2 mice were inoculated with cells P388VR, a vincristine-resistant strain of leukemic cells P388 either from small
5-day-old tumors or from large 7 to 8-day-old tumors. Multidrug resistance (MDR) of the cells was evaluated by cell sensitivity
to vincristine and from the transport of calcein ester out of cells. Sensitivity of cells to oxidative stress was determined
by cell viability and the production of reactive oxygen species in cells, by dichlorofluorescein assay. It has been shown
that properties of the P388VR strain did not change in mice inoculated with the cells from small tumors. However, if the cells
from large tumors were used for inoculation, the strain underwent the following modifications: tumors became contaminated
with erythrocytes; resistance to vincristine increased; transport of calcein ester into and out of the cells accelerated,
and sensitivity to oxidative stress raised. These changes in the properties of the P388VR strain persisted upon consequent
propagation of the tumor and could be caused by a constitutive activation of the HIF system. The possibility of the alterations
of the leukemic cells upon tumor transplantation from large tumors has to be taken into account in the experimental work with
tumor cell lines. 相似文献
102.
This investigation was concerned with the dimensions of the facial skeleton and the incidence of underbite in colobine monkeys. Standard craniofacial dimensions and the notation of the presence or absence of underbite were recorded for skulls of 308 adult, wild-caught colobines belonging to 10 species. Underbite was noted in all species examined, ranging in frequency from 10% in Colobus polykomos to 100% in 2 species of Presbytis. Univariate statistics indicate that species with high frequencies of underbite tend to have shorter, broader maxillary dental arches, shorter faces and rostrums, and longer mandibular dental arches. A multivariate discriminant analysis supported the univariate statistics. Interspecific allometric analysis of facial measurements against a constructed size variable indicated that maxillary dimensions scale in a strongly positive manner in relation to size. However, mandibular dimensions tend to scale isometrically. This pattern of facial scaling indicates that the tendency toward underbite should increase as overall size decreases. This would explain why smaller species have higher frequencies of underbite than larger species and why females often have a higher incidence of underbite than conspecific males. Zingeser has suggested that the high incidence of underbite in colobine and some cebid monkeys is an adaptation to folivory. The results of this study support an alternative hypothesis that the high incidence of underbite in colobine monkeys is related to the pattern of facial scaling with size in combination with relaxed selection on the anterior dentition. 相似文献
103.
The effect of astaxanthin and cadmium on rat erythrocyte G6PD, 6PGD,GR, and TrxR enzymes activities in vivo and on rat erythrocyte 6PGD enzyme activity in vitro
下载免费PDF全文
![点击此处可从《Journal of biochemical and molecular toxicology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Mahire Bayramoğlu Akkoyun A. Şükrü Bengü Yusuf Temel H. Turan Akkoyun Suat Ekin Mehmet Ciftci 《Journal of biochemical and molecular toxicology》2018,32(8)
In this study, the effects of astaxanthin (AST) that belongs to carotenoid family and cadmium (Cd), which is an important heavy metal, on rat erythrocyte G6PD, 6PGD, GR, and TrxR enzyme activities in vivo and on rat erythrocyte 6PGD enzyme activity in vitro were studied. In in vitro studies, 6PGD enzyme was purified from rat erythrocytes with 2′,5′‐ADP Sepharose4B affinity chromatography. Results showed inhibition of enzyme by Cd at IC50; 346.5 μM value and increase of 6PGD enzyme activity by AST. In vivo studies showed an increase in G6PD, 6PGD, and GR enzyme activities (P ? 0.05) and no chance in TrxR enzyme activity by AST. Cd ion inhibited G6PD, 6PGD, and GR enzyme activities (P ? 0.05) and also decreased TrxR enzyme activity (P ? 0.05). AST + Cd group G6PD enzyme activity was statistically low compared with control group (P ? 0.05). 6PGD and TrxR enzyme activities decreased without statistical significance (P ? 0.05); however, GR enzyme activity increased statistically significantly (P ? 0.05). 相似文献
104.
105.
Ştefan Ţălu Ilya A. Morozov Dinara Sobola Pavel Škarvada 《Bulletin of mathematical biology》2018,80(11):2856-2870
A lot of insect families have physical structures created by evolution for coloration. These structures are a source of ideas for new bio-inspired materials. The aim of this study was to quantitatively characterize the micromorphology of butterfly wings scales using atomic force microscopy and multifractal analysis. Two types of butterflies, Euploea mulciber (“striped blue crow”) and Morpho didius (“giant blue morpho”), were studied. The three-dimensional (3D) surface texture of the butterfly wings scales was investigated focusing on two areas: where the perceived colors strongly depend on and where they do not depend on the viewing angle. The results highlight a correlation between the surface coloration and 3D surface microtexture of butterfly wings scales. 相似文献
106.
Tisza A. S. Bell Emel Sen-Kilic Tamás Felföldi Gabor Vasas Matthew W. Fields Brent M. Peyton 《Antonie van Leeuwenhoek》2018,111(12):2425-2440
The Carpathian Basin is a lowland plain located mainly in Hungary. Due to the nature of the bedrock, alluvial deposits, and a bowl shape, many lakes and ponds of the area are characterized by high alkalinity. In this study, we characterized temporal changes in eukaryal and bacterial community dynamics with high throughput sequencing and relate the changes to environmental conditions in Lake Velence located in Fejér county, Hungary. The sampled Lake Velence microbial populations (algal and bacterial) were analyzed to identify potential correlations with other community members and environmental parameters at six timepoints over 6 weeks in the Spring of 2012. Correlations between community members suggest a positive relationship between certain algal and bacterial populations (e.g. Chlamydomondaceae with Actinobacteria and Acidobacteria), while other correlations allude to changes in these relationships over time. During the study, high nitrogen availability may have favored non-nitrogen fixing cyanobacteria, such as the toxin-producing Microcystis aeruginosa, and the eutrophic effect may have been exacerbated by high phosphorus availability as well as the high calcium and magnesium content of the Carpathian Basin bedrock, potentially fostering exopolymer production and cell aggregation. Cyanobacterial bloom formation could have a negative environmental impact on other community members and potentially affect overall water quality as well as recreational activities. To our knowledge, this is the first prediction for relationships between photoautotrophic eukaryotes and bacteria from an alkaline, Hungarian lake. 相似文献
107.
Production of (R)‐1‐(1,3‐benzodioxol‐5‐yl)ethanol in high enantiomeric purity by Lactobacillus paracasei BD101
下载免费PDF全文
![点击此处可从《Chirality》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Engin Şahin 《Chirality》2018,30(2):189-194
Piperonyl ring is found in a number of naturally occurring compounds and possesses enormous biological activities. There are many studies in the literature with compounds containing a piperonyl ring, but there are very few studies on the synthesis of chiral piperonyl carbinol. The objective of this study was to determine the microbial reduction ability of bacterial strains and to reveal the effects of different physicochemical parameters on this reduction ability. A total of 15 bacterial isolates were screened for their ability to reduce 1‐(benzo[d][1,3]dioxol‐5‐yl) ethanone 1 to its corresponding alcohol. Among these isolates Lactobacillus paracasei BD101 was found to be the most successful biocatalyst to reduce the ketone containing piperonyl ring to the corresponding alcohol. The reaction conditions were systematically optimized for the reducing agent L paracasei BD101, which showed high enantioselectivity and conversion for the bioreduction. The preparative scale study was performed, and a total of 3.72 g of (R)‐1‐(1,3‐benzodioxol‐5‐yl) ethanol in high enantiomeric form (>99% enantiomeric excess) was produced in a mild, cheap, and environment‐friendly process. This study demonstrates that L paracasei BD101 can be used as a biocatalyst to obtain chiral carbinol with excellent yield and selectivity. 相似文献
108.
Identifying critical migratory bottlenecks and high‐use areas for an endangered migratory soaring bird across three continents
下载免费PDF全文
![点击此处可从《Journal of avian biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Evan R. Buechley Steffen Oppel William S. Beatty Stoyan C. Nikolov Vladimir Dobrev Volen Arkumarev Victoria Saravia Clementine Bougain Anastasios Bounas Elzbieta Kret Theodora Skartsi Lale Aktay Karen Aghababyan Ethan Frehner Çağan H. Şekercioğlu 《Journal of avian biology》2018,49(7)
Migrant birds face a number of threats throughout their annual cycle, including persecution, collision with energy infrastructure, and habitat and climate change. A key challenge for the conservation of migrants is the identification of important habitat, including migratory concentration areas, because species survival rates may be determined by events in geographically very limited areas. Remote‐tracking technology is facilitating the identification of such critical habitat, although the strategic identification of important sites and incorporation of such knowledge in conservation planning remains limited. We tracked 45 individuals of an endangered, soaring migrant (Egyptian vulture Neophron percnopterus), over 75 complete migrations that traversed three continents along the Red Sea Flyway. We summarize and contextualize migration statistics by season and age class, including migration start, midpoint, and end dates, as well as linear and cumulative migration distance, migration duration and speed, and route straightness. Then, using dynamic Brownian bridge movement models, we quantified space use to identify the most important migratory bottlenecks and high‐use areas on the flyway. These areas each accounted for < 5% of the overall movement range of the tracked birds, yet > 20% of all tracks passed through bottlenecks, and > 50% of the overall vulture time spent on migration fell within high‐use areas. The most important sites were located at the southeastern Red Sea coast and Bab‐el‐Mandeb Strait (Saudi Arabia, Yemen, Djibouti), the Suez Canal zone (Egypt), and the Gulf of Iskenderun (Turkey). Discouragingly however, none of the area within the major migratory bottlenecks was protected and < 13% of the high‐use areas were protected. This demonstrates a very concerning gap in the protected area network for migratory soaring birds along the Red Sea Flyway. Because reducing threats at migratory concentrations can be a very efficient approach to protect populations, our work provides clear guidelines where conservation investment is urgently needed to benefit as many as 35 migratory soaring‐bird species that regularly use the Red Sea Flyway. 相似文献
109.
An integrative anatomical,morphological, micromorphological and molecular approach to Turkish epidendroid and orchidoid species (Orchidaceae)
下载免费PDF全文
![点击此处可从《Nordic Journal of Botany》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Gülcan Şenel Şenay Süngü Şeker Mustafa Kemal Akbulut Öznur Ergen Akçin 《Nordic Journal of Botany》2018,36(7)
We aimed to describe and analyse the morphological, anatomical and micromorphological traits of 36 Turkish orchids representing 12 genera (e.g. Anacamptis, Cephalanthera, Dactylorhiza, Orchis, Serapias) in detail and analyse their usability for solving phylogenetic and taxonomic issues. We applied UPGMA cluster analysis to anatomical, morphological and micromorphological characters such as root tubers, leaf and flower structures, pit, sclerenchymatic sheath, vascular bundle shape, crystal and starch, exodermis and endodermis structure, stomata type, bulliform cells in roots, shoots and leaves, surface structures like papillae, hairs and ornamentation on flower parts, leaves, fruits and seeds. Furthermore, in a phylogenetic framework, we analysed nuclear ribosomal ITS diversity in the same orchid species belonging, and in a combined Bayesian phylogenetic analysis based on anatomical, morphological, micromorphogical and ITS data we confirmed the usefulness of multiple data sets for effectively assessing taxonomically critical orchids. In the combined analysis, all genera were resolved as monophyletic with topologies congruent with recently published more thorough molecular phylogenetic reconstructions, while the trees obtained by seprately analysing the ITS and the anatomical, morphological, micromorphogical data were less resolved and partly inconclusive. 相似文献
110.
Selami Demirci Ayşegül Doğan Hüseyin Apdik Emre Can Tuysuz Sukru Gulluoglu Omer Faruk Bayrak Fikrettin Şahin 《Molecular and cellular biochemistry》2018,437(1-2):133-142
Cell proliferation and migration are crucial in many physiological processes including development, cancer, tissue repair, and wound healing. Cell migration is regulated by several signaling molecules. Identification of genes related to cell migration is required to understand molecular mechanism of non-healing chronic wounds which is a major concern in clinics. In the current study, the role of cytoglobin (CYGB) gene in f?broblast cell migration and proliferation was described. L929 mouse fibroblast cells were transduced with lentiviral particles for CYGB and GFP, and analyzed for cell proliferation and migration ability. Fibroblast cells overexpressing CYGB displayed decreased cell proliferation, colony formation capacity, and cell migration. Phosphorylation levels of mTOR and two downstream effectors S6 and 4E-BP1 which take part in PI3K/AKT/mTOR signaling declined in CYGB-overexpressing cells. Microarray analysis indicated that CYGB overexpression leads to downregulation of cell proliferation, migration, and tumor growth associated genes in L929 cell line. This study demonstrated the role of CYGB in fibroblast cell motility and proliferation. CYGB could be a promising candidate for further studies as a potential target for diseases related to cell migration such as cancer and chronic wound treatment. 相似文献