全文获取类型
收费全文 | 497篇 |
免费 | 45篇 |
国内免费 | 1篇 |
专业分类
543篇 |
出版年
2022年 | 8篇 |
2021年 | 5篇 |
2019年 | 4篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 24篇 |
2014年 | 26篇 |
2013年 | 35篇 |
2012年 | 32篇 |
2011年 | 43篇 |
2010年 | 17篇 |
2009年 | 20篇 |
2008年 | 22篇 |
2007年 | 13篇 |
2006年 | 12篇 |
2005年 | 12篇 |
2004年 | 16篇 |
2003年 | 9篇 |
2002年 | 16篇 |
2001年 | 19篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 14篇 |
1997年 | 16篇 |
1996年 | 11篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 13篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1988年 | 3篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 6篇 |
1971年 | 2篇 |
1970年 | 3篇 |
排序方式: 共有543条查询结果,搜索用时 0 毫秒
1.
Ca2+ is an important intracellular messenger affecting many diverse processes. In eukaryotic cells, Ca2+ storage is achieved within specific intracellular organelles, especially the endoplasmic/sarcoplasmic reticulum, in which Ca2+ is buffered by specific proteins known as Ca2+ buffers. Ca2+ buffers are a diverse group of proteins, varying in their affinities and capacities for Ca2+, but they typically also carry out other functions within the cell. The wide range of organelles containing Ca2+ and the evidence supporting cross-talk between these organelles suggest the existence of a dynamic network of organellar Ca2+ signaling, mediated by a variety of organellar Ca2+ buffers. 相似文献
2.
Light-Induced Polar pH Changes in Leaves of Elodea canadensis: I. Effects of Carbon Concentration and Light Intensity 总被引:2,自引:2,他引:0 下载免费PDF全文
Leaves of the submerged aquatic Elodea canadensis Michx. exhibit a light induced polar pH reaction. In this study, the effects of light intensity and dissolved inorganic carbon concentration on this polar reaction were examined. At a light intensity of 100 watts per square meter the leaf showed a polar pH response when the dissolved inorganic carbon concentration was less than about 1 millimolar. The polar reaction was suppressed at a higher dissolved inorganic carbon concentration. This suppression was not due to the buffering capacity of bicarbonate. Because another weak acid, acetate, did not inhibit the polarity, but even had a small stimulatory effect, the effect of bicarbonate is also not due to acidification of the cytoplasm. The suppression of the polar reaction by CO2/HCO3− was relieved when the light intensity was increased. Apparently there is competition for product(s) of the photosynthetic light reactions between processes generating the polar reaction and the carbon fixation reactions. The possibility that the redox state of the cell regulates the generation of the polar reaction is discussed. 相似文献
3.
Thermophiles: A life at elevated temperatures 总被引:1,自引:0,他引:1
Interest in the ecology, physiology and evolution of microorganisms adapted to growth at relatively high temperatures (up to 110°C) has increased enormously during the past two decades. This interest was stimulated by the discovery of marine hydrothermal vent ecosystems, and also by awareness of the potential of thermophilic microbes in biotechnological processes. Subsequent attempts to isolate new thermophilic organisms have been very successful. Moreover, these results, in combination with much-improved techniques for studying the phylogeny of microorganisms, have renewed interest in the evolution of microbes and the early development of life. 相似文献
4.
Plasmid pUCD607 was mobilized into the biocontrol agent Enterobacter cloacae strain E6 by conjugation and the resultant strain, E6(pUCD607), was bioluminescent. Biocontrol of Pythium ultimum by E6(pUCD607) was similar to that of the parent strain, E6. The location of E6(pUCD607) in the soil and in the rhizosphere
of lettuce was readily determined by pressing agar medium against plant roots in a root box, allowing the bacteria to grow
overnight on the medium, and detecting the presence of bioluminescence by autophotography. There was a positive, linear correlation
between population sizes determined by dilution plating and the quantity of light emitted due to bioluminescence. However,
both the intercept and slope of this line varied among experiments possibly due to the differing physiological states of cells
recovered from soils. The amount of light emitted by the bioluminescent strain E6(pUCD607) was not quantitative. This technique
is useful for qualitative determinations of populations and for photographically locating bacteria. 相似文献
5.
Patch clamp studies on root cell vacuoles of a salt-tolerant and a salt-sensitive plantago species : regulation of channel activity by salt stress 总被引:5,自引:2,他引:3 下载免费PDF全文
Plantago media L. and Plantago maritima L. differ in their strategy toward salt stress, a major difference being the uptake and distribution of ions. Patch clamp techniques were applied to root cell vacuoles to study the tonoplast channel characteristics. In both species the major channel found was a 60 to 70 picosiemens channel with a low ion selectivity. The conductance of this channel for Na+ was the same as for K+, PK+/PNa+ = 1, whereas the cation/anion selectivity (PK+/Pc1−) was about 5. Gating characteristics were voltage and calcium dependent. An additional smaller channel of 25 picosiemens was present in P. maritima. In the whole vacuole configuration, the summation of the single channel currents resulted in slowly activated inward currents (t½ = 1.2 second). Inwardly directed, ATP-dependent currents could be measured against a ΔpH gradient of 1.5 units over the tonoplast. This observation strongly indicated the physiological intactness of the used vacuoles. The open probability of the tonoplast channels dramatically decreased when plants were grown on NaCl, although single channel conductance and selectivity were not altered. 相似文献
6.
Frans A. Prins Ronnie van Diemen-Steenvoorde Jan Bonnet Ingrid Cornelese-ten Velde 《Histochemistry and cell biology》1993,99(6):417-425
Reflection contrast microscopy (RCM) of ultrathin sections was recently introduced as a sensitive technique for visualization with enhanced definition in immunogold histochemistry. Experience of using RCM as a major tool in immunocytochemical research in different fields is summarized, e.g. oncology, nephrology and embryology. The sensitive visualization of immunocytochemical labels, gold particles or peroxidase-diaminobenzidine deposits in or on ultrathin sections, by RCM instead of electron microscopy is demonstrated. RCM of ultrathin sections is an adequate light microscopical alternative for immunoelectron microscopy, since an overview of both label and tissue is obtained with a high image definition and high contrast of label. In the studies presented, RCM is shown to provide a better gradation in staining intensity and staining pattern than other light microscopical methods. Moreover, a precise localization of multiple labels is obtained with this method. Besides the applications shown, ultrathin section visualization by RCM is very useful for correlative light- and electron microscopical studies of fine structures. Commercially available fluorescence microscopes can be adapted for proper RCM functioning; an adaptation scheme and list of microscopes tested is provided. 相似文献
7.
H. H. T. Prins 《Ethology : formerly Zeitschrift fur Tierpsychologie》1989,81(1):47-71
The African buffalo Syncerus caffer was studied in Lake Manyara National Park, Tanzania. Emphasis was placed on the study of (individual) buffalo cows, which live in mixed herds. Buffalo herds are discrete social units and females were never observed in another herd than their own. The herd showed a structure with respect to the distribution of sex-age classes. Individual cows generally kept the same location within the herd. The location in the herd appeared to be coupled to food intake and was strongly related to physical condition. The best location (highest intake and best condition) was between the front and the centre of the herd, the worst location was the rear of the herd (when moving or grazing). Females with calves appeared to have the highest position in the hierarchy as determined from the rate of displacement over food; adult bulls did not interact with cows. Few births were observed during the late dry season and it appears that there is a calving peak at the end of the long rains. Conception rate increased when cows increased in condition and dropped when cows lost condition. Cows showed a strong seasonality in condition but bulls on average hardly changed in condition, except for a loss in condition during the inferred conception peak. Buffalo herds in Manyara showed a fusion-fission pattern independent of season but strongly influenced by the size of the herd: large herds split more often than smaller ones. In large herds, buffalo grazed closer together than in small herds and it appeared likely that competition was more severe in large herds. Animals in the rear of a large herd lost condition faster during the dry season than animals in the best location in the herd, and especially cows in the rear split off most frequently from the herd to graze in a smaller fragment. From the literature on cattle, it is inferred that the reproductive success of cows in the rear of the herd will be lower than of cows in the best location, and this differential is confirmed by the behaviour of adult bulls. It is as yet unclear what the advantage is for adult cows in the rear of a large herd to stay in that herd but the sharing of information with more successful individuals seems a good candidate. 相似文献
8.
C. J. Lord S. K. Bohlander E. A. Hopes C. T. Montague N. J. Hill J. -B. Prins R. J. Renjilian L. B. Peterson L. S. Wicker J. A. Todd P. Denny 《Mammalian genome》1995,6(9):563-570
Development of novel congenic mouse strains has allowed us to better define the location of the diabetogenic locus, Idd3, on Chromosome (Chr) 3. Congenic strains were identified by use of published and newly developed microsatellite markers, their genomes fingerprinted by a rapid, fluorescence-based approach, and their susceptibility to type 1 diabetes evaluated. The maximum interval containing Idd3 is now approximately 4 cM. 相似文献
9.
A number of kinetic parameters of the lactate dehydrogenases of three rumen bacterial species (Peptostreptococcus productus, Propionibacterium acnes and Actinomyces viscosus), the rumen ciliate Isotricha prostoma and mixed rumen microorganisms (MRM) with respect to NADH, pyruvate, fructose-1,6-diphosphate (FDP) as well as the effects of several nucleotide phosphates were studied.Partially purified LDH of Peptostr. productus had the same kinetic parameters as in crude cell free extracts. Values for Km, determined by Michaelis-Menten kinetics with pyruvate as the substrate, were in the same range for all lactate dehydrogenases. After feeding a cow, changes in the apparent Km and Vmax values for NADH of the total LDH activity in MRM were followed.It is suggested that of the factors studied the ratio NADH/NAD(H) and ATP are the most important regulatory factors for the lactate dehydrogenases of mixed rumen microorganisms.The investigation were supported by the Foundation for Fundamental Biological Research (BION), which is subsidized by the Netherlands Organization for the Advancement of Pure Research (ZWO) 相似文献
10.
Synthesis of acetate from CO2 in the cecum of some rodents 总被引:3,自引:0,他引:3