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21.
22.
The relation between the size of a fly and the number of ovarioles in its ovary was investigated in Phormia regina and Sarcophaga bullata. Small flies of varying size were produced by taking larvae prematurely off the food. The smallest flies thus obtained were derived from larvae only of the weight of a normal larva. The number of ovarioles in an ovary is directly proportional to the size of the fly and, in the extreme case, is about the normal number in Sarcophaga and about in Phormia. Larvae prematurely taken off the food, but fed again after starving for several days, grow to normal or almost normal size and develop ovaries with about the normal number of ovarioles. Small or re-fed Sarcophaga do not show any changes in the anatomy of individual ovarioles but in Phormia disorders in ovariole development and a consequent reduction of fertility are frequent. The number of ovarioles remains identical from the early pupal stage all through the development of the pharate fly and then through ovarian development in the adult fly: it is determined by the size of the larva when it was taken off the food. This shows that it is not lack of space in a small adult fly abdomen which determines the number nor the occurrence of degenerative processes during ovarian development. 相似文献
23.
Pokorna B Mandl M Borilova S Ceskova P Markova R Janiczek O 《Applied and environmental microbiology》2007,73(11):3752-3754
Wide ranges of growth yields on sulfur (from 2.4 x 10(10) to 8.1 x 10(11) cells g(-1)) and maximum sulfur oxidation rates (from 0.068 to 1.30 mmol liter(-1) h(-1)) of an Acidithiobacillus ferrooxidans strain (CCM 4253) were observed in 73 batch cultures. No significant correlation between the constants was observed. Changes of the Michaelis constant for sulfur (from 0.46 to 15.5 mM) in resting cells were also noted. 相似文献
24.
Singh R Kaur B Kalina I Popov TA Georgieva T Garte S Binkova B Sram RJ Taioli E Farmer PB 《Mutation research》2007,620(1-2):71-82
Epidemiological studies conducted in metropolitan areas have demonstrated that exposure to environmental air pollution is associated with increases in mortality. Carcinogenic polycyclic aromatic hydrocarbons (c-PAHs) are the major source of genotoxic activities of organic mixtures associated with respirable particulate matter, which is a constituent of environmental air pollution. In this study,we wanted to evaluate the relationship between exposure to these genotoxic compounds present in the air and endogenous oxidative DNA damage in three different human populations exposed to varying levels of environmental air pollution. As measures of oxidative DNA damage we have determined 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG) by liquid chromatography–tandem mass spectrometry (LC–MS/MS) and cyclic pyrimidopurinone N-1,N2 malondialdehyde-2′-deoxyguanosine (M1dG) by the immunoslot blot assay from lymphocyte DNA of participating individuals. The level of endogenous oxidative DNA damage was significantly increased in individuals exposed to environmental air pollution compared to unexposed individuals from Kosice (8-oxodG adducts) and Sofia (M1dG adducts). However, there was no significant difference in the level of endogenous oxidative DNA and exposure to environmental air pollution in individuals from Prague (8-oxodG and M1dG adducts) and Kosice (M1dG adducts). The average level of M1dG adducts was significantly lower in unexposed and exposed individuals from Kosice compared to those from Prague and Sofia. The average level of 8-oxodG adducts was significantly higher in unexposed and exposed individuals from Kosice compared to those from Prague. A significant increasing trend according to the interaction of c-PAHs exposure and smoking status was observed in levels of 8-oxodG adducts in individuals from Kosice. However, no other relationship was observed for M1dG and 8-oxodG adduct levels with regard to the smoking status and c-PAH exposure status of the individuals. The conclusion that can be made from this study is that environmental air pollution may alter the endogenous oxidative DNA damage levels in humans but the effect appears to be related to the country where the individuals reside. Genetic polymorphisms of the genes involved in metabolism and detoxification and also differences in the DNA repair capacity and antioxidant status of the individuals could be possible explanations for the variation observed in the level of endogenous oxidative DNA damage for the different populations. 相似文献
25.
26.
Sequence and length recognition of the C-terminal turnover element of LpxC, a soluble substrate of the membrane-bound FtsH protease 总被引:1,自引:0,他引:1
Führer F Müller A Baumann H Langklotz S Kutscher B Narberhaus F 《Journal of molecular biology》2007,372(2):485-496
The membrane-anchored FtsH protease is essential in Escherichia coli as it adjusts the cellular amount of LpxC, the key enzyme in lipopolysaccharide (LPS) biosynthesis. Both accumulation and depletion of LpxC are toxic to E. coli. By continuous proteolysis of LpxC, FtsH maintains a low concentration of LpxC and, hence, the proper equilibrium between LPS and phospholipids. The C terminus of LpxC is required for turnover. By adding this tail to glutathione-S-transferase (GST) we show that it is necessary but not sufficient for FtsH-mediated degradation. A detailed mutational analysis revealed six non-polar residues in the C terminus of LpxC that are critical for degradation. Alteration of the C-terminal AVLA motif towards the SsrA-like sequence ALAA directed LpxC to other cellular proteases reinforcing the importance of the C-terminal tail for targeting to FtsH. Short C-terminal truncations stabilized LpxC. Most mutations in the C terminus of LpxC left its enzymatic activity intact as was shown by growth assays, microscopy and 2-keto-3-deoxyoctonate (KDO) determination. The critical length of the turnover element was defined by internal deletions. A C-terminal tail of about 20 amino acids length is required for proteolysis of LpxC by FtsH. 相似文献
27.
Radka B?ízová Lucie Vaní?ková Mária Fa?arová Sunday Ekesi Michal Hoskovec Blanka Kalinová 《ZooKeys》2015,(540):385-404
Ceratitis
fasciventris, Ceratitis
anonae and Ceratitis
rosa are polyphagous agricultural pests originating from the African continent. The taxonomy of this group (the so-called Ceratitis FAR complex) is unclear. To clarify the taxonomic relationships, male and female-produced volatiles presumably involved in pre-mating communication were studied using comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GC×GC-TOFMS) followed by multivariate analysis, and gas chromatography combined with electroantennographic detection (GC-EAD). GC×GC-TOFMS analyses revealed sex specific differences in produced volatiles. Male volatiles are complex mixtures that differ both qualitatively and quantitatively but share some common compounds. GC-EAD analyses of male volatiles revealed that the antennal sensitivities of females significantly differ in the studied species. No female volatiles elicited antennal responses in males. The results show clear species-specific differences in volatile production and provide complementary information for the distinct delimitation of the putative species by chemotaxonomic markers. 相似文献
28.
Imramovsky A Pesko M Ferriz JM Kralova K Vinsova J Jampilek J 《Bioorganic & medicinal chemistry letters》2011,21(15):4564-4567
A series of photosynthetic electron transport (PET) inhibitors from the group of salicylanilide alkylcarbamates was investigated. The compounds were analyzed using RP-HPLC to determine lipophilicity, and their PET inhibition was determined in spinach (Spinacia oleracea L.) chloroplasts. The site of action of the studied compounds is situated at the donor site of photosystem 2 (PS 2). Compounds substituted by chlorine in C′-3 and C′-4 of the aniline ring and the optimal length of the alkyl chain pentyl-heptyl in the carbamate moiety provided the most active PET inhibitors (IC50 inhibition <10 μmol/L). Disubstitution in C′-3,4 by chlorine caused significant PET inhibiting activity decrease. Nevertheless, for all three series of C′-3, C′-4, C′-3,4 compounds, the dependence of PET activity on lipophilicity showed to be quasi-parabolic. 相似文献
29.
Plants often combine multiple strategies to achieve pollen transfer. The dioecious Clusia nemorosa (Clusiaceae) produces floral resin, a specialized reward for resin-collecting bees. It also exhibits floral automimicry with
female flowers mimicking male flowers in order to attract pollen-collecting insects. We observed the hourly visitation frequency
and behaviour of bee visitors on two rock savanna sites in French Guiana. The major strategy in pollen transfer and the variation
in visitation rates among visitor species were examined. We hypothesized that the visitation rate will vary between the floral
sexes and degree of this variation will differ between the two-reward systems. We found no evidence for visits being exclusively
related to resin collection, which we expected to be the principal strategy in pollen transfer. Deceit pollination appeared
to have minor importance and seemed to be locally associated with the site, where demand for pollen was greater. Flower visits
that probably facilitated most pollen transfer, combined resin and pollen. The pollinators involved in this system collected
pollen from male flowers and resin from female flowers. The fruit set was not particularly low (44.19%) so offering different
rewards by different flower genders has not constrained reproductive success in this system. Pronounced variation in visitation
rates between sexes was not related to the pollination mechanisms but to the demand for the two rewards. Overall demand for
pollen was greater than demand for resin. Female flowers were visited much less frequently than male flowers. Peak pollen
collection occurred in the morning, i.e., as soon as the resource was available, while resin was collected throughout the
day. There was a local variability in demand for the two resources because both the visitation rate and the behaviour of foraging
bees varied between the two observation sites. 相似文献
30.