全文获取类型
收费全文 | 7898篇 |
免费 | 731篇 |
国内免费 | 2篇 |
专业分类
8631篇 |
出版年
2024年 | 4篇 |
2023年 | 41篇 |
2022年 | 81篇 |
2021年 | 181篇 |
2020年 | 117篇 |
2019年 | 136篇 |
2018年 | 170篇 |
2017年 | 177篇 |
2016年 | 220篇 |
2015年 | 417篇 |
2014年 | 466篇 |
2013年 | 591篇 |
2012年 | 727篇 |
2011年 | 697篇 |
2010年 | 439篇 |
2009年 | 408篇 |
2008年 | 564篇 |
2007年 | 504篇 |
2006年 | 494篇 |
2005年 | 436篇 |
2004年 | 459篇 |
2003年 | 327篇 |
2002年 | 371篇 |
2001年 | 80篇 |
2000年 | 43篇 |
1999年 | 70篇 |
1998年 | 88篇 |
1997年 | 53篇 |
1996年 | 31篇 |
1995年 | 26篇 |
1994年 | 25篇 |
1993年 | 31篇 |
1992年 | 14篇 |
1991年 | 14篇 |
1990年 | 20篇 |
1989年 | 14篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1973年 | 3篇 |
1967年 | 2篇 |
1960年 | 3篇 |
排序方式: 共有8631条查询结果,搜索用时 15 毫秒
1.
Pathogenic Neisseria use a variety of mechanisms to survive the bactericidal action of the complement system. Serum resistance is a crucial virulence factor for the development of severe meningococcal disease, meningococcal meningitis and disseminated gonococcal infection. Furthermore, local inflammation at the site of gonococcal infection exposes the bacteria to moderate concentrations of complement factors. We review current concepts of neisserial serum resistance with emphasis on porins and polysaccharides exposed on the neisserial surface and their interaction with components of normal human serum. 相似文献
2.
The CMP-N-acetylneuraminic acid (CMP-NeuNAc) synthetase gene of Neisseria meningitidis group B is located on a 2.3-kb EcoRI fragment within the cps gene cluster. Nucleotide sequence determination of the gene encoding the CMP-NeuNAc synthetase revealed a 515-bp open reading frame that can encode a 18.9-kDA protein. A computer data base scan revealed a 59.4% identity to the CMP-NeuNAc synthetase gene of E. coli K1. Enzymatic activity was confirmed in vitro and in vivo. Transformation of the CMP-NeuNAc defective E. coli K1 strain EV5 with the meningococcal CMP-NeuNAc synthetase could complement the defect in E. coli. 相似文献
3.
D Matthias E Engler L Will-Shahab H J Herrmann C H Becker 《Acta biologica et medica Germanica》1977,36(9):1279-1284
A 14-days' training of rats designed to adapt the animals to the procedure of blood-pressure measurement caused in the myocardium a decrease, in serum an increase in noradrenaline ( NA) content. The latter remained unchanged following 3 days of treatment with 2.5 mg depot angiotensin II (AII) but decreased by more than one-half in the myocardium of untreated animals, and increased in serum. Despite the considerable difference in myocardial NA content and blood-pressure behaviour, both trained and untrained rats showed the same morphological reactions following administration of A II. These myocardial alterations which largely correspond to the so-called epinephrine myocarditis should not therefore be due solely to NA action; rather, the involvement of A II should be considered also. 相似文献
4.
Matthias Kirsch Mustafa B. A. Djamgoz Hans-Joachim Wagner 《Cell and tissue research》1990,260(1):123-130
Summary A negative feedback interaction between luminosity type horizonatal cells (HCs) and green-sensitive cones generates the long-wavelength-sensitive depolarizing response in biphasic chromaticity type HCs. This interaction is suppressed in the dark and is potentiated by light adaptation of the retina. HCs are morphologically plastic; during light adaptation, their dendritic terminals within cone pedicles extend, giving rise to spinules. This paper examines whether there is a quantitative correlation between the time course of light-dependent formation of the spinules and enhancement of the feedback interaction. The strength of the feedback interaction in isolated retinac of the roach was determined as the neutral wavelength at which reversal of spectral response polarity occurred in biphasic HCs. A good correlation was found between the neutral wavelength and the spinule/ribbon ratios of retinae. Biphasic HCs were intracellularly stained with horseradish peroxidase and the correlative ultrastructure of the contacted pedicles was examined. Neutral wavelength was found to be correlated with the spinule number, weighted according to the number of synaptic contacts mediating feed-forward transmission. The latter was estimated from the total number of labelled Cb/H2 HC processes (central and lateral) at synaptic triads. A model in which spinules mediate the negative feedback interaction of HCs in the retina of cyprinid fish is presented. 相似文献
5.
Isolation and identification of granule-associated proteins relevant for poly(3-hydroxyalkanoic acid) biosynthesis in Chromatium vinosum D 总被引:1,自引:0,他引:1
Matthias Liebergesell Bernhard Schmidt Alexander Steinbüchel 《FEMS microbiology letters》1992,99(2-3):227-232
Abstract Poly(3-hydroxybutyric acid) granules, which harbored only four major granule-associated proteins as revealed by SDS polyacrylamide gel electrophoresis, were isolated from crude cellular extracts of Chromatium vinosum D by centrifugation in a linear sucrose gradient. N-Terminal amino acid sequence determination identified two proteins of M r 41 000 and M r 40 000 as the phaE Cv and phaC Cv translational products, respectively, of C. vinosum D. In a previous study it was shown that both proteins are required for the expression opf poly(3-hydroxyalkanoic acid) synthase activity. The N-terminus of the third protein ( M r 17 000) exhibited no homology to other proteins. Lysozyme, which was during purification of the granules, exhibited a strong affinity to PHB granules and was identified as the fourth protein enriched with the granules. 相似文献
6.
Cloning and Mapping of a Novel Nodulation Region from Bradyrhizobium japonicum by Genetic Complementation of a Deletion Mutant 总被引:4,自引:2,他引:2 下载免费PDF全文
The phenotypes of a set of Bradyrhizobium japonicum 110 mutants with large deletions in the region of symbiotic gene cluster I were tested. The majority of the mutants showed a delayed nodulation on soybean and, by mixed-infection experiments, were found to be strongly reduced in their competitiveness. Phenotypic comparison of mutants with different deletion endpoints allowed a preliminary localization of two genomic regions, called nod-1 and nod-2, which were required for normal nodulation on soybean. Loss of nod-1 was found to result in a Nod− phenotype on cowpea, mung bean, and siratro. A recombinant cosmid was identified which fully restored nodulation ability of a mutant lacking nod-1. Using Tn5-containing derivatives and subclones of this cosmid for complementation, we delimited the nod-1 region to a DNA segment of 3.1 to 3.5 kilobase pairs. 相似文献
7.
8.
9.
Matthias Laska 《Primates; journal of primatology》1996,37(4):457-465
The purpose of this study was to test the influence of sex, age, social rank, matriline membership, posture, and visual and
tactual motor control on manual preferences inSaimiri sciureus. A well-established social group of 12 squirrel monkeys, aged 2 to 14 yrs and consisting of two matrilines with social rank
known for each animal, was presented with four different food-reaching tasks and assessed for hand preferences with a minimum
of 100 reaches per animal.
Frequency of occurrence of hand preferences at the group level and degree of hand preferences at the individual level depended
on posture and on whether the reaching act took place under visual or tactual guidance. Sex, age, social rank, and matriline
membership were not found to determine frequency of occurrence, direction or degree of hand preferences with the exception
of one task in which a significant negative correlation between the degree of hand preference and age was found. Nine out
of 12 monkeys showed task-dependent changes in the hand they used preferentially while only three animals preferred the same
hand in all four tasks. Significant preferences for the use of right or left hand on a given task were distributed almost
equally between individuals. Thus, the results of this study suggest task-specific demands like posture and/or whether reaching
was visually or tactually guided to be the major correlates of hand preferences in food-reaching tasks in squirrel monkeys. 相似文献
10.