全文获取类型
收费全文 | 685篇 |
免费 | 24篇 |
出版年
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 25篇 |
2020年 | 16篇 |
2019年 | 16篇 |
2018年 | 17篇 |
2017年 | 13篇 |
2016年 | 16篇 |
2015年 | 24篇 |
2014年 | 31篇 |
2013年 | 42篇 |
2012年 | 42篇 |
2011年 | 69篇 |
2010年 | 37篇 |
2009年 | 28篇 |
2008年 | 51篇 |
2007年 | 47篇 |
2006年 | 47篇 |
2005年 | 37篇 |
2004年 | 40篇 |
2003年 | 27篇 |
2002年 | 23篇 |
2001年 | 18篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 1篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1994年 | 1篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1972年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1964年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有709条查询结果,搜索用时 109 毫秒
701.
Judith M. Klatt Gonzalo V. Gomez-Saez Steffi Meyer Petra Pop Ristova Pelin Yilmaz Michael S. Granitsiotis Jennifer L. Macalady Gaute Lavik Lubos Polerecky Solveig I. Bühring 《The ISME journal》2020,14(12):3024
Cyanobacterial mats were hotspots of biogeochemical cycling during the Precambrian. However, mechanisms that controlled O2 release by these ecosystems are poorly understood. In an analog to Proterozoic coastal ecosystems, the Frasassi sulfidic springs mats, we studied the regulation of oxygenic and sulfide-driven anoxygenic photosynthesis (OP and AP) in versatile cyanobacteria, and interactions with sulfur reducing bacteria (SRB). Using microsensors and stable isotope probing we found that dissolved organic carbon (DOC) released by OP fuels sulfide production, likely by a specialized SRB population. Increased sulfide fluxes were only stimulated after the cyanobacteria switched from AP to OP. O2 production triggered migration of large sulfur-oxidizing bacteria from the surface to underneath the cyanobacterial layer. The resultant sulfide shield tempered AP and allowed OP to occur for a longer duration over a diel cycle. The lack of cyanobacterial DOC supply to SRB during AP therefore maximized O2 export. This mechanism is unique to benthic ecosystems because transitions between metabolisms occur on the same time scale as solute transport to functionally distinct layers, with the rearrangement of the system by migration of microorganisms exaggerating the effect. Overall, cyanobacterial versatility disrupts the synergistic relationship between sulfide production and AP, and thus enhances diel O2 production.Subject terms: Microbial ecology, Biogeochemistry, Water microbiology 相似文献
702.
703.
Cakmak Nuray Yilmaz Emin Gemcioglu Salih Baser Sükran Erten Ozcan Erel 《Journal of Medical Biochemistry》2021,40(3):270
BackgroundPrimary Sjögren''s syndrome (pSS) is a disease associated with the overexpression of proinflammatory cytokines, and oxidative stress is one of the factors responsible for its etiopathogenesis. This study aimed to investigate the thiol/disulphide homeostasis in pSS patients.MethodsThe study included 68 pSS patients and 69 healthy controls. Thiol/disulphide homeostasis (total thiol, native thiol, and disulphide levels) was measured using the automatic spectrophotometric method developed by Erel and Neselioglu, and the results of the 2 groups were compared.ResultsThe gender and age distributions of the pSS and control groups were similar (P = 0.988 and P = 0.065). Total thiol and native thiol levels were lower in the pSS group than in the control group (470.08 ± 33.65 µmol/L vs. 528.21 ± 44.99 µmol/L, P < 0.001, and 439.14 ± 30.67 µmol/L vs. 497.56 ± 46.70 µmol/L, P < 0.001, respectively). There were no differences in disulphide levels between groups [17.00 (range 0.70-217.0) µmol/L vs. 14.95 (range 2.10-40.10) µmol/L, P = 0.195].ConclusionsIt was concluded that the thiol/disulphide balance shifted towards disulphide in patients with pSS. 相似文献
704.
Neriman Rückert-Ülkümen 《Pal?ontologische Zeitschrift》1994,68(3-4):463-472
Two bony fishes from Late Tertiary sediments of Edirne-Süloçlu (Thrakia, Turkey) are described. They belong to the generaKnightia andCtenopharyngodon, both of which are not known from Europe till now:Knightia sp. from finely laminated marl of Sarmatian-Pannonian age at Eskikadin Köyü near Süloçlu andCtenopharyngodon hermi n.sp. from the Pannonian Congeria limestone near Edirne. Knightia has been described only from Paleocene and Eocene deposits of North America, whileCtenopharyngodon was known only from the Recent of Eastern Asia (China). 相似文献
705.
A juvenile cup, disarticulated arm plates, and columnals of the crinoid Arachnocrinus sarizensis n. sp. are described from the Eastern Taurus Mountains of central Turkey. This is the first Paleozoic crinoid based on a cup and arm plates reported from Turkey. Suggested revision of the Gasterocomidae includes transfer of Arachnocrinus and Ancyrocrinus to the family and rejection of Kopficrinus from the family. The stratigraphic range of Arachnocrinus is extended upward into the Middle Devonian from the Early Devonian. The Devonian of Turkey is of special interest because it includes Laurasian and Gondwanan components on different tectonic blocks. The paleogeographic range of Arachnocrinus is extended from the North American plate onto the Anatolian block, which would have been located on the southern edge of the Paleotethys Sea in the Middle Devonian in a shelf basin off the northern coast of Gondwana at approximately 42° south latitude. 相似文献
706.
Judith M. Klatt Mohammad A. A. Al-Najjar Pelin Yilmaz Gaute Lavik Dirk de Beer Lubos Polerecky 《Applied and environmental microbiology》2015,81(6):2025-2031
Before the Earth''s complete oxygenation (0.58 to 0.55 billion years [Ga] ago), the photic zone of the Proterozoic oceans was probably redox stratified, with a slightly aerobic, nutrient-limited upper layer above a light-limited layer that tended toward euxinia. In such oceans, cyanobacteria capable of both oxygenic and sulfide-driven anoxygenic photosynthesis played a fundamental role in the global carbon, oxygen, and sulfur cycle. We have isolated a cyanobacterium, Pseudanabaena strain FS39, in which this versatility is still conserved, and we show that the transition between the two photosynthetic modes follows a surprisingly simple kinetic regulation controlled by this organism''s affinity for H2S. Specifically, oxygenic photosynthesis is performed in addition to anoxygenic photosynthesis only when H2S becomes limiting and its concentration decreases below a threshold that increases predictably with the available ambient light. The carbon-based growth rates during oxygenic and anoxygenic photosynthesis were similar. However, Pseudanabaena FS39 additionally assimilated NO3− during anoxygenic photosynthesis. Thus, the transition between anoxygenic and oxygenic photosynthesis was accompanied by a shift of the C/N ratio of the total bulk biomass. These mechanisms offer new insights into the way in which, despite nutrient limitation in the oxic photic zone in the mid-Proterozoic oceans, versatile cyanobacteria might have promoted oxygenic photosynthesis and total primary productivity, a key step that enabled the complete oxygenation of our planet and the subsequent diversification of life. 相似文献
707.
The principle that the small subunit ribosomal RNA (ssu rRNA) is generally accessible to oligonucleotide probes designed to have high thermodynamic affinity was tested with Stenotrophomonas maltophilia, Rhodobacter sphaeroides, Bacillus subtilis, and Saccharomyces cerevisiae. Fluorescein-labeled probes, designed to have ΔGoverall° = −14 ± 1 and to avoid the potential of nucleobase-specific quenching, were used to target 20 randomly selected sites in each organism. A site was considered accessible if probe brightness was at least 10 times the background signal. With 30-h hybridizations, 71 out of 80 target sites passed the accessibility criterion. Three additional sites were demonstrated to be accessible with either longer hybridizations, which seemed to have a negative effect on some probes, or the addition of formamide to the hybridization buffer. The remaining 6 sites were demonstrated to be accessible by changing the fluorophore to Cy5, slightly modifying probe lengths, using dual-labeled fluorescein probes, or a combination of these approaches. Probe elongations were only needed in 4 probes, indicating a 95% success in correctly predicting ΔGoverall°, the key parameter for the design of high affinity probes. In addition, 94% of the fluorescein labeled probes yielded bright signals, demonstrating that nucleobase-specific quenching of fluorescein is an important factor affecting probe brightness that can be predicted during probe design. Overall, the results support the principle that with a rational design of probes, it is possible to make most target sites in the ssu rRNA accessible. 相似文献
708.
709.
To obtain regenerable magnetic nanoparticles, triethoxy(3-isocyanatopropyl)silane and iminodiacetic acid (IZ) were used as the starting material and immobilized on Fe3O4 nanoparticles. Copper ions (Cu2+ ions) were loaded on the Fe-IZ nanoparticles and used for cellulase immobilization. The support was characterized by spectroscopic methods (FTIR, NMR) and thermogravimetric analysis, transmission electron microscopy, scanning electron microscope, X-ray diffraction, energy dispersive X-ray analysis, and vibrating sample magnetometer techniques. As a result of experiments, the amount of protein bound to immobilized cellulase (Fe-IZ-Cu-E) and cellulase activity was found to be 33.1 mg/g and 154 U/g at pH 5, 50°C, for 3 h. The results indicated that the free cellulase had kept only 50% of its activity after 2 h, while the Fe-IZ-Cu-E was observed to be around 77%, at 60°C. It was found that the immobilized cellulase maintained 93% of its initial catalytic activity after its sixth use. Furthermore, the Fe-IZ-Cu-E retained about 75% of its initial activity after 28 days of storage. To reuse the support material (Fe-IZ-Cu), it was regenerated by thorough washing with ammonia or imidazole. 相似文献