全文获取类型
收费全文 | 2770篇 |
免费 | 206篇 |
国内免费 | 1篇 |
学科分类
生物科学 | 2977篇 |
出版年
2023年 | 31篇 |
2022年 | 51篇 |
2021年 | 72篇 |
2020年 | 56篇 |
2019年 | 74篇 |
2018年 | 113篇 |
2017年 | 90篇 |
2016年 | 117篇 |
2015年 | 142篇 |
2014年 | 140篇 |
2013年 | 192篇 |
2012年 | 227篇 |
2011年 | 218篇 |
2010年 | 147篇 |
2009年 | 102篇 |
2008年 | 153篇 |
2007年 | 156篇 |
2006年 | 157篇 |
2005年 | 116篇 |
2004年 | 97篇 |
2003年 | 99篇 |
2002年 | 80篇 |
2001年 | 46篇 |
2000年 | 19篇 |
1999年 | 18篇 |
1998年 | 17篇 |
1997年 | 9篇 |
1996年 | 13篇 |
1995年 | 13篇 |
1994年 | 18篇 |
1993年 | 11篇 |
1992年 | 7篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 14篇 |
1986年 | 7篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1979年 | 8篇 |
1975年 | 8篇 |
1974年 | 6篇 |
1973年 | 5篇 |
1972年 | 6篇 |
1970年 | 6篇 |
1969年 | 6篇 |
1968年 | 6篇 |
1964年 | 5篇 |
排序方式: 共有2977条查询结果,搜索用时 15 毫秒
1.
2.
P Petrás J Zdrazílek H Srámová L Masková 《Journal of hygiene, epidemiology, microbiology, and immunology》1988,32(1):59-69
Tests for enterotoxins A, B, C, D, E and TSST-1 production were carried out on 775 S. aureus strains isolated from various sources (50 mothers and neonates studied periodically, mothers and infants treated for various acute inflammatory conditions, members of hospital staff, environmental swabs) during the period 1981-1983 at a maternity ward chosen for a 3-year systematic study and on additional 97 isolates obtained in 1985 from another maternity ward. This had contributed to a better classification of strains within certain phage type groups. It was found that the distribution of S. aureus types in the particular sub-sets varied, depending on the source of isolates. At the maternity ward followed for 3 years there was a clear-cut trend towards the spread of phage-untypable isolates producing enterotoxin C whereas at ward examined for comparative purposes B enterotoxin producers of phage type 95 were predominant. The tests for enterotoxigenicity has also proved to be useful as the epidemiological marker characterizing the predominantly circulating S. aureus strain. It has been confirmed that the majority role in the spread of maternity-ward-staphylococci is played by the neonates and the factors of hospital environment. 相似文献
3.
4.
Résumé L'ultrastructure des lamelles branchiales et spécialement celle des chloride cells du poisson rouge (Carassius aureus) a été étudiée. Nous avons constaté que du matériel amorphe floconneux, faiblement adiélectronique était attaché aux endroits des creux apicaux. Afin de préciser la nature de ce matériel, nous avons étudié ces structures au microscope électronique avec les techniques suivantes: acide periodique méthènamine d'argent, colorations au fer colloïdal et au bleu d'alcian. Après la réaction à l'acide periodique méthènamine d'argent, de fines précipitations aux endroits des creux apicaux, correspondant au matériel floconneux visible après la fixation au glutaraldéhyde tétroxyde d'osmium, étaient visibles. La coloration au bleu d'alcian révélait des particules fortement colorées formant un film plus ou moins continu à la surface libre des lamelles, sauf aux endroits oò les chloride cells sont en contact avec la surface. Là et notamment dans les 2reux apicaux, du matériel légèrement granuleux, de faible densité, faisait une couche assez épaisse attachée à la membrane cellulaire. Tenant compte des résultats d'autres auteurs et de nos propres observations, nous considérons que la plus grande partie du matériel se trouvant à la surface des chloride cells, et particulièrement dans les creux apicaux, est de type glycoprotéique.
Dédié à Monsieur le Professeur Dr Ernst Horstmann, Hambourg, à l'occasion de son soixantième anniversaire. 相似文献
The ultrastructure of the chloride cells in the gill epithelium of the goldfish
Summary The ultrastructure of the secondary lamellae of the gills and especially that of the chloride cells of Carassius aureus was studied. We found an amorphous, flakey, slightly adielectronic material in the areas of the apical pits. In order to determine the nature of this material, we studied these structures electronmicroscopically applying the periodic acid silver methenamine, colloidal iron and alcian blue methods. The periodic acid silver methenamine reaction, resulted in finely dispersed precipitations which were deposited in the areas of the apical pits and which correspond to the flakey material seen in the ordinary electron micrographs. The alcian blue method reveales strongly stained particles which form a more or less continuous film on the free surface of the lamellae, interrupted only at the level of the chloride cells. In these areas, notably within the apical pits, a rather thick layer of finely granular low-density material is attached to the plasma membrane. In taking into account other studies performed on this subject, as well as our own observations, we consider the material found on the surface of the chloride cells and particularly within their apical pits to be predominantly of glycoproteinous nature.
Dédié à Monsieur le Professeur Dr Ernst Horstmann, Hambourg, à l'occasion de son soixantième anniversaire. 相似文献
5.
Butomus umbellatus L. is a plant species typical of littoral communities of river and stream shores. It can form continuous stands in shallow reservoirs with fluctuating water level. Their expansion is promoted by: (a) intensive vegetative reproduction of plants, (b) crowded sprouting from rhizome fragments on emerged pond bottom, (c) shallow water layer in the year following summer drainage. Expansion of B. umbellatus depends on ploidy level: two cytotypes were found in the Czech and Slovak Republics, differing in their reproductive ability. Seed production of triploids is strongly limited (they are self-incompatible within clones), while diploids can be fully fertile. Nevertheless, even in diploids, the efficiency of seed reproduction under natural conditions is low. Triploids spread by intensive vegetative reproduction, which is decisive for clonal growth of populations and their regeneration after scraping of bottom surface. During seasonal development, maximum of aboveground biomass is produced in early summer, while underground biomass increases till autumn. Growth of the plants is limited by cutting before maximum underground biomass is attained, or by duck grazing. 相似文献
6.
In 1981–1992, the breeding fauna of 153 fishponds was studies in three fishpond regions in south Bohemia (Czechoslovakia). On each pond, all water and wetland birds were censused by the Two-check method, which consists of adult birds counts during each breeding season (the first in the second part of May, and the second in the second part of June). We assessed the numbers of all species living in water and wetland habitats in the breeding season.The decline in abundances (expressed as number of individuals) of ducks (Anatinae), grebes (Podicipediformes), Coot (Fulica atra), Moorhen (Galinulla chloropus), Black-headed Gull (Larus ridibundus) were the most marked changes recorded. Marked increase in abundances was found in Cormorant (Phalacrocorax carbo) and Mute Swan (Cygnus olor) during the whole decade, whereas in Graylag Goose (Anser anser) the increase was restricted to the first half of the period under study. Numbers of charadriform and passeriform birds fluctuated in the dependence of water level variation. 相似文献
7.
Summary Ubiquinone-10 (Q10) production was measured in batch cultures of Paracoccus denitrificans grown for 8 h at increasing oxygen concentrations (0–21 % O2 in the sparging gas). Whereas the cellular level of Q10 decreased monotonically from 1.2 to 0.5 mol/g d.w., the total yield of Q10 was maximal at 2.5 % O2 and amounted to 350 nmol (0.3 mg) per L of culture. 相似文献
8.
Petr Vetrovsky Jean-Claude Stoclet Gustav Entlicher 《The international journal of biochemistry & cell biology》1996,28(12):1311-1318
It has been speculated that NG-hydroxy-l-arginine (OH-l-Arg), which is an intermediate in NO production from l-arginine, may be converted to NO by superoxide ion. However, there is still no direct evidence for this conversion. In the present study this was investigated using superoxide ion generated either in acellular or cellular systems. It was found that OH-l-Arg and hydroxylamine were converted to nitrite and nitrate apparently via NO by superoxide ion in aqueous solution. Arginine remained unaffected. These changes were observed during reaction of chemical substances as well as in a biological system (zymosan-activated macrophages in culture). Superoxide dismutase prevented this transformation. OH-l-Arg was also spontaneously hydrolysed to hydroxylamine and l-citrulline, however this occurred at pH > 9 only. Activated microsomes (containing different isoforms of cytochrome P450) were unable to replace NO-synthase in its ability to produce OH-l-Arg from l-arginine. These data support the hypothesis that a pathway alternative to the well-known synthesis of NO by NO-synthase via OH-l-Arg exists. This pathway may involve the production of OH-l-Arg by NO-synthase and decomposition of OH-l-Arg to NO by the action of superoxide ion. Alternatively, hydrolysis of OH-l-Arg to hydroxylamine may occur followed by its oxidation to NO, again by superoxide ion. 相似文献
9.
Rospars Jean-Pierre Lánský Petr Tuckwell Henry C. Vermeulen Arthur 《Journal of computational neuroscience》1996,3(1):51-72
The coding of odor intensity by an olfactory receptor neuron model was studied under steady-state stimulation. Our model neuron is an elongated cylinder consisting of the following three components: a sensory dendritic region bearing odorant receptors, a passive region consisting of proximal dendrite and cell body, and an axon. First, analytical solutions are given for the three main physiological responses: (1) odorant-dependent conductance change at the sensory dendrite based on the Michaelis-Menten model, (2) generation and spreading of the receptor potential based on a new solution of the cable equation, and (3) firing frequency based on a Lapicque model. Second, the magnitudes of these responses are analyzed as a function of odorant concentration. Their dependence on chemical, electrical, and geometrical parameters is examined. The only evident gain in magnitude results from the activation-to-conductance conversion. An optimal encoder neuron is presented that suggests that increasing the length of the sensory dendrite beyond about 0.3 space constant does not increase the magnitude of the receptor potential. Third, the sensivities of the responses are examined as functions of (1) the concentration at half-maximum response, (2) the lower and upper concentrations actually discriminated, and (3) the width of the dynamic range. The overall gain in sensitivity results entirely from the conductance-to-voltage conversion. The maximum conductance at the sensory dendrite appears to be the main tuning constant of the neuron because it determines the shift toward low concentrations and the increase in dynamic range. The dynamic range of the model cannot exceed 5.7 log units, for a sensitivity increase at low odor concentration is compensated by a sensitivity decrease at high odor concentration. 相似文献
10.
Abstract A circular restriction map of the genome of the phage L ( Salmonella typhimurium ) has been constructed with five restriction endonucleases, Eca I, Eco RI, Bam HI, Bgl I, and Pst I. The Eco RI fragments of phage-L DNA were cloned into pACYC184, and the resulting recombinant plasmids pL1, pL2,…,pL7 were introduced into Salmonella typhimurium . The genes present on the fragments cloned were identified by the marker rescue experiments with the L-phage amber mutants. A physical gene map of the L genome obtained in this way was compared with that of P22. 相似文献