全文获取类型
收费全文 | 218篇 |
免费 | 12篇 |
出版年
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 5篇 |
2017年 | 6篇 |
2016年 | 3篇 |
2015年 | 13篇 |
2014年 | 8篇 |
2013年 | 12篇 |
2012年 | 20篇 |
2011年 | 13篇 |
2010年 | 6篇 |
2009年 | 6篇 |
2008年 | 10篇 |
2007年 | 6篇 |
2006年 | 5篇 |
2005年 | 5篇 |
2004年 | 9篇 |
2003年 | 8篇 |
2002年 | 4篇 |
2001年 | 7篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1965年 | 2篇 |
1960年 | 1篇 |
1959年 | 2篇 |
排序方式: 共有230条查询结果,搜索用时 15 毫秒
1.
Barbara Grzelakowska-Sztabert Małgorzata Balińska 《Biochimica et Biophysica Acta (BBA)/General Subjects》1980,632(2):164-172
Betaine when present in the culture medium could induce the activity of betaine: homocysteine methyltransferase (EC 2.1.1.5) in mouse L-cells, and leukemic L1210 cells, as well as in mouse embryo fibroblasts grown in vitro. We found this process to be time- and concentration-dependent. A persisting contact of the cells with betaine was indispensible for expressing and maintaining the enzyme activity. The treatment of cells with cycloheximide or actinomycin D abolished the process of induction. Methionine as well as homocysteine, when present either in the culture medium or in the reaction mixture, strongly depressed the activity of this enzyme. The L-cells with the induced betaine: homocysteine methyltransferase survived but did not multiply in the methionine-deficient medium, therefore, they did not become prototrophs with respect to methionine. 相似文献
2.
Singh Awtar Bali Aradhana Kumar Ashwani Yadav Rajender Kumar Minhas Paramjit Singh 《Journal of Plant Growth Regulation》2022,41(5):1989-1998
Journal of Plant Growth Regulation - Exogenous applications of plant growth regulators (PGRs) were evaluated for their effects on growth, physiological attributes, and yield of sodicity stressed... 相似文献
3.
4.
Soyeon Goo Purva Joshi Greg Sands Dane Gerneke Andrew Taberner Qaasim Dollie Ian LeGrice Denis Loiselle 《The Journal of general physiology》2009,134(4):339-350
Trabeculae carneae are the smallest naturally arising collections of linearly arranged myocytes in the heart. They are the preparation of choice for studies of function of intact myocardium in vitro. In vivo, trabeculae are unique in receiving oxygen from two independent sources: the coronary circulation and the surrounding ventricular blood. Because oxygen partial pressure (PO2) in the coronary arterioles is identical in specimens from both ventricles, whereas that of ventricular blood is 2.5-fold higher in the left ventricle than in the right ventricle, trabeculae represent a “natural laboratory” in which to examine the influence of “extravascular” PO2 on the extent of capillarization of myocardial tissue. We exploit this advantage to test four hypotheses. (1) In trabeculae from either ventricle, a peripheral annulus of cells is devoid of capillaries. (2) Hence, sufficiently small trabeculae from either ventricle are totally devoid of capillaries. (3) The capillary-to-myocyte ratios in specimens from either ventricle are identical to those of their respective walls. (4) Capillary-to-myocyte ratios are comparable in specimens from either ventricle, reflecting equivalent energy demands in vivo, driven by identical contractile frequencies and comparable wall stresses. We applied confocal fluorescent imaging to trabeculae in cross section, subsequently using semi-automated segmentation techniques to distinguish capillaries from myocytes. We quantified the capillary-to-myocyte ratios of trabeculae from both ventricles and compared them to those determined for the ventricular free walls and septum. Quantitative interpretation was furthered by mathematical modeling, using both the classical solution to the diffusion equation for elliptical cross sections, and a novel approach applicable to cross sections of arbitrary shape containing arbitrary disposition of capillaries and non-respiring collagen cords. 相似文献
5.
Gerta Fleissner Kirsten Schuchardt Dietrich Neumann Geetha Bali Gerald Falkenberg Guenther Fleissner 《Chronobiology international》2013,30(1):17-30
Living in the tidal zones of the sea requires synchronization with the dominant environmental influences of tidal, solar, and lunar periodicity. Endogenous clocks anticipate those geoclimatic changes and control the respective rhythms of vital functions. But the underlying mechanisms are only partly understood. While the circadian clocks in animals are investigated employing neurobiological, molecular, and genetic approaches, clocks with a lunar periodicity have been studied with reference to development and behavior only. Sites of their pacemakers, zeitgeber receptors, and coupled endocrine components are unknown. Here, a lunar‐rhythmic change of shielding pigment transparency in the larval ocelli of the intertidal midge Clunio marinus is demonstrated for the first time as a possible access to the neurobiology of lunar timing mechanisms. We studied third instar larvae (Vigo strain) throughout the lunar cycle by light‐ and electron-microscopy as well as by x‐ray fluorescence analysis for the identification of the pigment. Moonlight detection is a prerequisite for photic synchronization of the lunar clock. The larval ocelli of Clunio putatively may function as moonlight receptors and are also controlled by the circalunar clock itself, hence being primary candidates for tracing input and output pathways of the lunar pacemaker. Additionally, the demonstration of a reversible optical change of shielding pigment transparency in Clunio is a novel finding, not reported so far in any other animal species, and reveals a mechanism to enhance photosensitivity under the condition of very dim light. It represents a remarkable change of a sense organ from an imaging device to a radiometer. Its restriction to the developmental stage susceptible to lunar timing elucidates a unique sensory strategy evolved at the level of sensory input. It also raises basic questions about the biochemistry of optically active pigments, like melanin, and their intracellular control. 相似文献
6.
Yingjie Li Shilpa Bali Sarah Borg Emanuel Katzmann Stuart J. Ferguson Dirk Schüler 《Journal of bacteriology》2013,195(18):4297-4309
The alphaproteobacterium Magnetospirillum gryphiswaldense synthesizes magnetosomes, which are membrane-enveloped crystals of magnetite. Here we show that nitrite reduction is involved in redox control during anaerobic biomineralization of the mixed-valence iron oxide magnetite. The cytochrome cd1-type nitrite reductase NirS shares conspicuous sequence similarity with NirN, which is also encoded within a larger nir cluster. Deletion of any one of these two nir genes resulted in impaired growth and smaller, fewer, and aberrantly shaped magnetite crystals during nitrate reduction. However, whereas nitrite reduction was completely abolished in the ΔnirS mutant, attenuated but significant nitrite reduction occurred in the ΔnirN mutant, indicating that only NirS is a nitrite reductase in M. gryphiswaldense. However, the ΔnirN mutant produced a different form of periplasmic d1 heme that was not noncovalently bound to NirS, indicating that NirN is required for full reductase activity by maintaining a proper form of d1 heme for holo-cytochrome cd1 assembly. In conclusion, we assign for the first time a physiological function to NirN and demonstrate that effective nitrite reduction is required for biomineralization of wild-type crystals, probably by contributing to oxidation of ferrous iron under oxygen-limited conditions. 相似文献
7.
Ira Espuny-Camacho Kimmo A. Michelsen David Gall Daniele Linaro Anja Hasche Jérôme Bonnefont Camilia Bali David Orduz Angéline Bilheu Adèle Herpoel Nelle Lambert Nicolas Gaspard Sophie Péron Serge N. Schiffmann Michele Giugliano Afsaneh Gaillard Pierre Vanderhaeghen 《Neuron》2013,77(3):440-456
Download : Download video (68MB) 相似文献
8.
9.
Shilpa Bali Sarah Rollauer Pietro Roversi Evelyne Raux‐Deery Susan M. Lea Martin J. Warren Stuart J. Ferguson 《Molecular microbiology》2014,92(1):153-163
It has recently been shown that the biosynthetic route for both the d1‐haem cofactor of dissimilatory cd1 nitrite reductases and haem, via the novel alternative‐haem‐synthesis pathway, involves siroheme as an intermediate, which was previously thought to occur only as a cofactor in assimilatory sulphite/nitrite reductases. In many denitrifiers (which require d1‐haem), the pathway to make siroheme remained to be identified. Here we identify and characterize a sirohydrochlorin–ferrochelatase from Paracoccus pantotrophus that catalyses the last step of siroheme synthesis. It is encoded by a gene annotated as cbiX that was previously assumed to be encoding a cobaltochelatase, acting on sirohydrochlorin. Expressing this chelatase from a plasmid restored the wild‐type phenotype of an Escherichia coli mutant‐strain lacking sirohydrochlorin–ferrochelatase activity, showing that this chelatase can act in the in vivo siroheme synthesis. A ΔcbiX mutant in P. denitrificans was unable to respire anaerobically on nitrate, proving the role of siroheme as a precursor to another cofactor. We report the 1.9 Å crystal structure of this ferrochelatase. In vivo analysis of single amino acid variants of this chelatase suggests that two histidines, His127 and His187, are essential for siroheme synthesis. This CbiX can generally be identified in α‐proteobacteria as the terminal enzyme of siroheme biosynthesis. 相似文献
10.
A fossil of a colonial organism with pyritized soft tissues of elongated fusiform zooids, found in the middle part of the early Floian Fenxiang Formation in Hubei Province of China, probably represents the oldest reliable record of a hydroid cnidarian. The preservation of the fossil is sufficiently different from that of associated carbonized skeletons of graptolites to exclude affinities with this group. The fossil is unlikely to be a bryozoan because of the mode of budding from proximal, not distal, parts of parent zooids, which is typical rather of hydroids. Although no thecae are preserved, the fossil, named Sinobryon elongatum gen. et sp. nov., is suggested to be a thecate hydroid, possibly related to the Haleciidae. The apparent presence of an advanced member of the thecaphoran Macrocolonia clade in strata 470 Ma old means that much of the hydroid (and cnidarian) diversification preceded the Middle Ordovician. 相似文献