全文获取类型
收费全文 | 612篇 |
免费 | 65篇 |
国内免费 | 3篇 |
出版年
2021年 | 9篇 |
2019年 | 5篇 |
2017年 | 6篇 |
2016年 | 13篇 |
2015年 | 15篇 |
2014年 | 21篇 |
2013年 | 24篇 |
2012年 | 22篇 |
2011年 | 27篇 |
2010年 | 18篇 |
2009年 | 20篇 |
2008年 | 29篇 |
2007年 | 29篇 |
2006年 | 16篇 |
2005年 | 22篇 |
2004年 | 18篇 |
2003年 | 26篇 |
2002年 | 24篇 |
2001年 | 16篇 |
2000年 | 21篇 |
1999年 | 23篇 |
1998年 | 13篇 |
1997年 | 18篇 |
1996年 | 8篇 |
1995年 | 9篇 |
1994年 | 13篇 |
1993年 | 12篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 17篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 17篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1971年 | 5篇 |
1970年 | 6篇 |
1969年 | 3篇 |
排序方式: 共有680条查询结果,搜索用时 15 毫秒
61.
Edrada RA Wray V Berg A Gräfe U Sudarsono Brauers G Proksch P 《Zeitschrift für Naturforschung. C, Journal of biosciences》2000,55(3-4):218-221
From the marine sponge Callyspongia aerizusa collected from the Sea of Bali, Indonesia, fungal isolates of Drechslera hawaiiensis were obtained. Culture filtrates of the fungus yielded four spiciferone derivatives which include spiciferone A (1) and B (2), and two other novel derivatives including spiciferol A (3) which is an alcohol congener of spiciferone A (1) and compound 4 which is an monocyclic spiciferone congener featuring a butoxyl side chain. The structures of the novel compounds were established on the basis of NMR spectroscopic (1H, 13C, COSY) and mass spectrometric (EIMS) data. 相似文献
62.
Role of TnrA in nitrogen source-dependent repression of Bacillus subtilis glutamate synthase gene expression
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Belitsky BR Wray LV Fisher SH Bohannon DE Sonenshein AL 《Journal of bacteriology》2000,182(21):5939-5947
Synthesis of glutamate, the cell's major donor of nitrogen groups and principal anion, occupies a significant fraction of bacterial metabolism. In Bacillus subtilis, the gltAB operon, encoding glutamate synthase, requires a specific positive regulator, GltC, for its expression. In addition, the gltAB operon was shown to be repressed by TnrA, a regulator of several other genes of nitrogen metabolism and active under conditions of ammonium (nitrogen) limitation. TnrA was found to bind directly to a site immediately downstream of the gltAB promoter. As is true for other genes, the activity of TnrA at the gltAB promoter was antagonized by glutamine synthetase under certain growth conditions. 相似文献
63.
64.
Jacobs DK Wray CG Wedeen CJ Kostriken R DeSalle R Staton JL Gates RD Lindberg DR 《Evolution & development》2000,2(6):340-347
Whether the serial features found in some molluscs are ancestral or derived is considered controversial. Here, in situ hybridization and antibody studies show iterated engrailed-gene expression in transverse rows of ectodermal cells bounding plate field development and spicule formation in the chiton, Lepidochitona cavema, as well as in cells surrounding the valves and in the early development of the shell hinge in the clam, Transennella tantilla. Ectodermal expression of engrailed is associated with skeletogenesis across a range of bilaterian phyla, suggesting a single evolutionary origin of invertebrate skeletons. The shared ancestry of bilaterian-invertebrate skeletons may help explain the sudden appearance of shelly fossils in the Cambrian. Our interpretation departs from the consideration of canonical metameres or segments as units of evolutionary analysis. In this interpretation, the shared ancestry of engrailed-gene function in the terminal/posterior addition of serially repeated elements during development explains the iterative expression of engrailed genes in a range of metazoan body plans. 相似文献
65.
66.
Shi X Wray DW Formes KJ Wang HW Hayes PM O-Yurvati AH Weiss MS Reese IP 《American journal of physiology. Heart and circulatory physiology》2000,279(4):H1548-H1554
We tested the hypothesis that hypotension occurred in older adults at the onset of orthostatic challenge as a result of vagal dysfunction. Responses of heart rate (HR) and mean arterial pressure (MAP) were compared between 10 healthy older and younger adults during onset and sustained lower body negative pressure (LBNP). A younger group was also assessed after blockade of the parasympathetic nervous system with the use of atropine or glycopyrrolate and after blockade of the beta(1)-adrenoceptor by use of metoprolol. Baseline HR (older vs. younger: 59 +/- 4 vs. 54 +/- 1 beats/min) and MAP (83 +/- 2 vs. 89 +/- 3 mmHg) were not significantly different between the groups. During -40 Torr, significant tachycardia occurred at the first HR response in the younger subjects without hypotension, whereas significant hypotension [change in MAP (DeltaMAP) -7 +/- 2 mmHg] was observed in the elderly without tachycardia. After the parasympathetic blockade, tachycardiac responses of younger subjects were diminished and associated with a significant hypotension at the onset of LBNP. However, MAP was not affected after the cardiac sympathetic blockade. We concluded that the elderly experienced orthostatic hypotension at the onset of orthostatic challenge because of a diminished HR response. However, an augmented vasoconstriction helped with the maintenance of their blood pressure during sustained LBNP. 相似文献
67.
Intraspecific Variation of Unusual Phospholipids from Corynebacterium spp. Containing a Novel Fatty Acid
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Tanja Niepel Holger Meyer Victor Wray Wolf-Rainer Abraham 《Journal of bacteriology》1998,180(17):4650-4657
The novel fatty acid trans-9-methyl-10-octadecenoic acid was isolated from the coryneform bacterial strain LMG 3820 (previously misidentified as Arthrobacter globiformis) and identified by spectroscopic methods and chemical derivatization. This fatty acid is attached to the unusual lipid acyl phosphatidylglycerol. Five different species of this lipid type were identified; their structures were elucidated by tandem mass spectrometry and are reported here for the first time. Additionally, we identified three different cardiolipins, two bearing the novel fatty acid. The characteristic 10-methyl-octadecanoic acid was present only in phosphatidylinositol. Because of the unusual fatty acid pattern of strain LMG 3820, the 16S rDNA sequence was determined and showed regions of identity to sequences of Corynebacterium variabilis DSM 20132T and DSM 20536. All three strains possessed the novel fatty acid, identifying trans-9-methyl-10-octadecenoic acid as a potential biomarker characteristic for this taxon. Surprisingly, the fatty acid and relative abundances of phospholipids of Corynebacterium sp. strain LMG 3820 were similar to those of the type strain but different from those of Corynebacterium variabilis DSM 20536, although all three strains possessed identical 16S rDNA sequences and strains DSM 20132T and DSM 20536 have 90.5% DNA-DNA homology. This is one of the rare cases wherein different organisms with identical 16S rDNA sequences have been observed to present recognizably different fatty acid and lipid compositions. Since methylation of a fatty acid considerably lowers the transition temperature of the corresponding lipid resulting in a more flexible cell membrane, the intraspecific variation in the lipid composition, coinciding with the morphological and Gram stain reaction variability of this species, probably offers an advantage for this species to inhabit different environmental niches. 相似文献
68.
K. B. Baker S. P. Wray R. Ritter S. Mason T. H. Lanthorn K.V. Savelieva 《Genes, Brain & Behavior》2010,9(6):562-574
Impaired spatial learning is a prominent deficit in fragile X syndrome (FXS). Previous studies using the Fmr1 knockout (KO) mouse model of FXS have not consistently reported a deficit in spatial learning. Fmr1 KO mice bred onto an albino C57BL/6J‐Tyrc‐Brd background showed significant deficits in several primary measures of performance during place navigation and probe trials in the Morris water maze. Fmr1 KO mice were also impaired during a serial reversal version of the water maze task. We examined fear conditioning as an additional cognitive screen. Knockout mice exhibited contextual memory deficits when trained with unsignaled shocks; however, deficits were not found in a separate group of KO mice trained with signaled shocks. No potentially confounding genotypic differences in locomotor activity were observed. A decreased anxiety‐like profile was apparent in the open field, as others have noted, and also in the platform test. Also as previously reported, startle reactivity to loud auditory stimuli was decreased, prepulse inhibition and social interaction increased in KO mice. Female Fmr1 KO mice were tested along with male KO mice in all assays, except for social interaction. The female and male KO exhibited very similar impairments indicating that sex does not generally drive the behavioral symptoms of the disorder. Our results suggest that procedural factors, such as the use of albino mice, may help to reliably detect spatial learning and memory impairments in both sexes of Fmr1 KO mice, making it more useful for understanding FXS and a platform for evaluating potential therapeutics. 相似文献
69.
Palevitch O Kight K Abraham E Wray S Zohar Y Gothilf Y 《Cell and tissue research》2007,327(2):313-322
The ontogeny of two gonadotropin-releasing-hormone (GnRH) systems, salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), was
investigated in zebrafish (Danio rerio). In situ hybridization (ISH) first detected sGnRH mRNA-expressing cells at 1 day post-fertilization (pf) anterior to the
developing olfactory organs. Subsequently, cells were seen along the ventral olfactory organs and the olfactory bulbs, reaching
the terminal nerve (TN) ganglion at 5–6 days pf. Some cells were detected passing posteriorly through the ventral telencephalon
(10–25 days pf), and by 25–30 days pf, sGnRH cells were found in the hypothalamic/preoptic area. Continuous documentation
in live zebrafish was achieved by a promoter-reporter expression system. The expression of enhanced green fluorescent protein
(EGFP) driven by the sGnRH promoter allowed the earlier detection of cells and projections and the migration of sGnRH neurons.
This expression system revealed that long leading processes, presumably axons, preceded the migration of the sGnRH neuron
somata. cGnRH-II mRNA expressing cells were initially detected (1 day pf) by ISH analysis at lateral aspects of the midbrain
and later on (starting at 5 days pf) at the midline of the midbrain tegmentum. Detection of red fluorescent protein (DsRed)
driven by the cGnRH-II promoter confirmed the midbrain expression domain and identified specific hindbrain and forebrain cGnRH-II-cells
that were not identified by ISH. The forebrain DsRed-expressing cells seemed to emerge from the same site as the sGnRH-EGFP-expressing
cells, as revealed by co-injection of both constructs. These studies indicate that zebrafish TN and hypothalamic sGnRH cell
populations share a common embryonic origin and migratory path, and that midbrain cGnRH-II cells originate within the midbrain.
This study was supported by the US-Israel Bi-national Agricultural Research and Development (BARD) Foundation (grant 3428-03). 相似文献
70.