全文获取类型
收费全文 | 929篇 |
免费 | 107篇 |
国内免费 | 2篇 |
专业分类
1038篇 |
出版年
2022年 | 9篇 |
2021年 | 13篇 |
2019年 | 10篇 |
2018年 | 15篇 |
2017年 | 11篇 |
2016年 | 16篇 |
2015年 | 38篇 |
2014年 | 36篇 |
2013年 | 46篇 |
2012年 | 37篇 |
2011年 | 39篇 |
2010年 | 30篇 |
2009年 | 24篇 |
2008年 | 36篇 |
2007年 | 41篇 |
2006年 | 36篇 |
2005年 | 30篇 |
2004年 | 32篇 |
2003年 | 21篇 |
2002年 | 25篇 |
2001年 | 18篇 |
2000年 | 24篇 |
1999年 | 22篇 |
1998年 | 21篇 |
1997年 | 14篇 |
1996年 | 15篇 |
1995年 | 17篇 |
1994年 | 9篇 |
1993年 | 14篇 |
1992年 | 19篇 |
1991年 | 11篇 |
1990年 | 13篇 |
1989年 | 16篇 |
1988年 | 16篇 |
1987年 | 21篇 |
1986年 | 10篇 |
1985年 | 18篇 |
1984年 | 13篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 16篇 |
1976年 | 13篇 |
1975年 | 9篇 |
1974年 | 11篇 |
1969年 | 7篇 |
1968年 | 7篇 |
1960年 | 7篇 |
排序方式: 共有1038条查询结果,搜索用时 15 毫秒
1.
A strain of Methylomonas albus BG8WM, a type 1 obligate methanotroph, which had been maintained for 2 ycars by serial passage on solid medium containing methanol as a carbon source was found to mutate at a frequency of 10-5-10-6 to resistance to dichloromethane (DCMR), the parental strain BG8 did not give rise to DCMR colonies. DCMR strains were no longer capable of growth on methane as a carbon cource and exhibited greatly reduced or undetectable methane mono-oxygenase activity. The mutants fell into three groups on the basis of SDS-PAGE analysis of the polypeptide profiles of the particulate fraction of cell extracts. One or more of four polypeptides of Mr 70,000, 50,000, 25,000 and 23,000 were implicated as being components of the methane mono-oxygenase. Spontaneous reversion to growth on methane and sensitivity to dichloromethane occurred at a frequency of about 10-8. The loss of methane mono-oxygenase activity was not associated with loss of the resident 55 kb plasmid.Abbreviations DCMR
dichloromethane-resistant
- SDS-PAGE
sodium dodecyl sulphate polyacrylamide gel electrophoresis
- NMS
nitrate minimal salts medium 相似文献
2.
Schistosoma mansoni polypeptides immunogenic in mice vaccinated with radiation-attenuated cercariae 总被引:2,自引:0,他引:2
We compared the humoral immune response of mice protected against Schistosoma mansoni by vaccination with radiation-attenuated cercariae to that of patently infected mice, and we identified antigens that elicit a greater, or unique, immune response in the vaccinated mice. These comparisons were based upon radioimmunoprecipitations and immunodepletion of [35S]methionine-labeled schistosomular and adult worm polypeptides, followed by one- and two-dimensional polyacrylamide gel analyses. The humoral responses of patently infected mice and of mice vaccinated once were remarkably similar and were directed against schistosome glycoproteins ranging in molecular size from greater than 300 to less than 10 kDa. Exposing mice to a second vaccination resulted in a marked change in the immune response, to one predominantly directed toward high molecular size glycoproteins. Sequential immunodepletion techniques identified five schistosomular and seven adult worm antigens that showed a greater or unique immunogenicity in vaccinated mice as compared with patently infected mice. These adult worm antigens were purified by preparative sequential immunoaffinity chromatography and used to prepare a polyclonal antiserum, anti-irradiated vaccine. This antiserum bound to the surface of live newly transformed and lung-stage schistosomula, as assessed by immunofluorescence assays, and was reactive with a number of 125I-labeled schistosomular surface polypeptides, including a doublet of 150 kDa that was also recognized by sera of vaccinated mice but not by sera of patently infected mice. 相似文献
3.
4.
Summary Cucumber seedlings were grown in a Portsmouth soil-sand system to study how varying soil clay and organic matter content might
modify cucumber seedling response to ferulic acid, a reported allelopathic agent. Leaf area expansion of cucumber seedlings,
soil respiration, and soil solution concentrations of ferulic acid were monitored. Leaf area, mean absolute rates of leaf
expansion, and shoot dry weight of cucumber seedlings were significantly reduced by ferulic acid concentrations ranging from
10 to 70 μg/g dry soil. Ferulic acid was applied every other day, since it rapidly disappeared from soil solution as a result
of retention by soil particles, utilization by microbes and/or uptake by roots. The amount of ferulic acid retained (i.e., adsorbed, polymerized,etc.) by soil particles appeared to be secondary to microbial utilization and/or uptake by roots. Varying clay (5.3 to 9.8 g/cup)
and organic matter (2.0 to 0.04g/cup) contents of the soil appeared to have little impact on the disappearance of ferulic
acid from soil solution under “ideal” growth conditions for cucumber seedlings unless larger amounts of ferulic acid were
added to the soil; in this case 200 μg/g. The addition of ferulic acid to the soil materials substantially increased the activity
of the soil microbes. This latter conclusion is based on recovery of ferulic acid from soil solution and soil respiration
measurements.
Paper No. 10347 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, N C 27695-7601. The use
of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of the product
named, nor criticism of similar ones not mentioned. 相似文献
5.
6.
S Dalton 《The EMBO journal》1992,11(5):1797-1804
7.
Methods for computing the standard errors of branching points in an evolutionary tree and their application to molecular data from humans and apes 总被引:23,自引:2,他引:21
Statistical methods for computing the standard errors of the branching
points of an evolutionary tree are developed. These methods are for the
unweighted pair-group method-determined (UPGMA) trees reconstructed from
molecular data such as amino acid sequences, nucleotide sequences,
restriction-sites data, and electrophoretic distances. They were applied to
data for the human, chimpanzee, gorilla, orangutan, and gibbon species.
Among the four different sets of data used, DNA sequences for an
895-nucleotide segment of mitochondrial DNA (Brown et al. 1982) gave the
most reliable tree, whereas electrophoretic data (Bruce and Ayala 1979)
gave the least reliable one. The DNA sequence data suggested that the
chimpanzee is the closest and that the gorilla is the next closest to the
human species. The orangutan and gibbon are more distantly related to man
than is the gorilla. This topology of the tree is in agreement with that
for the tree obtained from chromosomal studies and DNA-hybridization
experiments. However, the difference between the branching point for the
human and the chimpanzee species and that for the gorilla species and the
human-chimpanzee group is not statistically significant. In addition to
this analysis, various factors that affect the accuracy of an estimated
tree are discussed.
相似文献
8.
A S Robertson P S Burge A Hedge J Sims F S Gill M Finnegan C A Pickering G Dalton 《BMJ (Clinical research ed.)》1985,291(6492):373
A cross sectional survey investigating "building sickness" was carried out in two buildings with similar populations of office workers but differing ventilation systems, one being fully air conditioned with humidification and the other naturally ventilated. The prevalence of symptoms related to work was assessed by a questionnaire administered by a doctor. A stratified, randomly selected sample of workers was seen (84% response). Building sickness includes several distinct syndromes related to work, most of which were significantly more common in the air conditioned building than the naturally ventilated building--namely, rhinitis (28% v 5%), nasal blockage and dry throat (35% v 9%), lethargy (36% v 13%), and headache (31% v 15%). The prevalence of work related asthma and humidifier fever was low and did not differ significantly between the two buildings. An environmental assessment of the offices was performed to attempt to identify possible factors responsible for the differences in the prevalence of disease. Globe temperature, dry bulb temperature, relative humidity, moisture content, air velocity, positive and negative ions, and carbon monoxide, ozone, and formaldehyde concentrations were all measured. None of these factors differed between the buildings, suggesting that building sickness is caused by other factors. 相似文献
9.
Growth and physiology of Azotobacter chroococcum in continuous culture 总被引:22,自引:0,他引:22
10.
ESR studies of copper(II) complex ions 总被引:1,自引:0,他引:1