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11.
Wheeler AL Long RM Ketchum RE Rithner CD Williams RM Croteau R 《Archives of biochemistry and biophysics》2001,390(2):265-278
The biosynthesis of the diterpenoid antineoplastic drug Taxol in Taxus species involves the cyclization of the ubiquitous isoprenoid intermediate geranylgeranyl diphosphate to taxa-4(5),11(12)-diene followed by cytochrome P450-mediated hydroxylation (with allylic rearrangement) of this olefin precursor to taxa-4(20),11(12)-dien-5 alpha-ol, and further oxygenation and acylation reactions. Based on the abundances of naturally occurring taxoids, the subsequent order of oxygenation of the taxane core is considered to occur at C10, then C2 and C9, followed by C13, and finally C7 and C1. Circumstantial evidence suggests that the acetylation of taxadien-5 alpha-ol may constitute the third specific step of Taxol biosynthesis. To determine whether taxadienol or the corresponding acetate ester serves as the direct precursor of subsequent oxygenation reactions, microsomal preparations isolated from induced Taxus cells and optimized for cytochrome P450 catalysis were incubated with each potential substrate. Both taxadienol and taxadienyl acetate were oxygenated to the level of a diol and to higher polyols at comparable rates by cytochrome P450 enzymes of the microsomal preparation. Preparative-scale incubation allowed the isolation of sufficient quantities of the diol derived from taxadienol to permit the NMR-based structural elucidation of this metabolite as taxa-4(20),11(12)-dien-5 alpha,13 alpha-diol, which may represent an alternate route of taxoid metabolism in induced cells. GC-MS-based structural definition of the diol monoacetate derived in microsomes from taxadienyl acetate confirmed this metabolite as taxa-4(20),11(12)-dien-5 alpha-acetoxy-10 beta-ol, thereby indicating that acetylation at C5 of taxadienol precedes the cytochrome P450-mediated insertion of the C10-beta-hydroxyl group of Taxol. 相似文献
12.
The large number of ESTs generated for Arabidopsis and rice in recent years now act as an important complement to whole genome sequencing projects. The Arabidopsis Genome Initiative has begun a coordinated effort to sequence the entire genome and, as a result, increasing numbers of large sequence entries can be found in the public databases. In addition, the mitochondrial genome of Arabidopsis has been completely sequenced. Genome sequencing studies and the public sequence databases have begun to influence the direction of diverse areas of research from physiology to evolution. 相似文献
13.
Sang‐Sup SO Tae‐Hwan HWANG Waseem AKRAM Jhong‐Kyung CHOI Jong‐Jin LEE 《Entomological Research》2012,42(3):158-162
The present study relates to a methanol extract of the seed coat of Ginkgo biloba, and tested particularly on the third instar larvae of Spodoptera exigua. The extract was found to have an inhibitory effect on the growth of the larvae besides bringing a change in the nutrient reserves in the body of the insect. Topical application of five different doses of the methanol extract resulted in a mortal effect to third instar larvae of S. exigua that is very much dependent on the dose as well as duration of exposure. Lower doses revealed lower mortality after 24 h of application. At doses of 1.00, 2.00, 4.00, 8.00 and 16.00 ng/larva, mortalities were 9.25, 26.07, 50.32, 56.28 and 92.44%, respectively. The dose for 50% mortality (LD50) of methanol extracts by applied by a topical method with 1 µL of acetone solution was 1.92 ng/larva. Nutrient reserves like protein, glycogen and lipid are known to regulate pupation and adult emergence. These reserves have been found to be lower in treated larvae, indicating the insecticidal role of methanol extracts from G. biloba against third instar larvae of S. exigua. 相似文献
14.
Hypertrophic scars and keloids. A collective review 总被引:10,自引:0,他引:10
15.
Abstract. 1. Larval rearing densities of Hemipyrellia ligurriens (Wiedemann) (Diptera: Calliphoridae) in standardized carrion were manipulated in order to investigate changes in life-history parameters in response to larval competition for food.
2. Competition was of the typical scramble type. Survivorship remained high at densities up to 32 larvae g liver-1 but decreased rapidly as larval density increased further.
3. Emergent adults were undersized with reduced fecundity and longevity. Variations in adult body size apparently reduced the effects of competition on larval mortality.
4. Females of dry weight corresponding to only 10.4% of the potential maximum emerged at the highest rearing densities of 128 larvae g liver-1. However, these females had a nearly four-fold increase in reproductive investment (per unit weight) when compared to the largest individuals.
5. The duration of larval development declined when competition was intense (i.e. at high larval densities).
6. The short adult life of H.ligurriens, combined with the unpredictability of larval habitat availability, may reduce the value of long-range dispersal so that females 'do better' by maintaining reproductive investment despite a concomitant decline in dispersal ability. 相似文献
2. Competition was of the typical scramble type. Survivorship remained high at densities up to 32 larvae g liver
3. Emergent adults were undersized with reduced fecundity and longevity. Variations in adult body size apparently reduced the effects of competition on larval mortality.
4. Females of dry weight corresponding to only 10.4% of the potential maximum emerged at the highest rearing densities of 128 larvae g liver-1. However, these females had a nearly four-fold increase in reproductive investment (per unit weight) when compared to the largest individuals.
5. The duration of larval development declined when competition was intense (i.e. at high larval densities).
6. The short adult life of H.ligurriens, combined with the unpredictability of larval habitat availability, may reduce the value of long-range dispersal so that females 'do better' by maintaining reproductive investment despite a concomitant decline in dispersal ability. 相似文献
16.
In vitro formation of assimilatory nitrate reductase: presence of the constitutive component in bacteria 总被引:9,自引:0,他引:9
Cell-free extracts of a selected group of bacteria which are capable of metabolyzing dinitrogen and/or nitrate contain a soluble form of the constitutive component which is active in the formation of NADPH-nitrate reductase when mixed with extracts of . The constitutive component in these extracts is dialyzable and is insensitive to trypsin and protease. The constitutive component which substitutes for the absence of the formation of NADPH-nitrate reductase is postulated to be a low molecular weight cofactor or polypeptide and is shown to be present in a number of unrelated bacteria. 相似文献
17.
Marc AquinoBaleyt Vianey LeosBarajas Timo Adam Mauricio HoyosPadilla Omar SantanaMorales Felipe GalvnMagaa Rogelio GonzlezArmas Christopher G. Lowe James T. Ketchum Hctor Villalobos 《Ecology and evolution》2021,11(21):14932
- Fine‐scale movement patterns are driven by both biotic (hunting, physiological needs) and abiotic (environmental conditions) factors. The energy balance governs all movement‐related strategic decisions.
- Marine environments can be better understood by considering the vertical component. From 24 acoustic trackings of 10 white sharks in Guadalupe Island, this study linked, for the first time, horizontal and vertical movement data and inferred six different behavioral states along with movement states, through the use of hidden Markov models, which allowed to draw a comprehensive picture of white shark behavior.
- Traveling was the most frequent state of behavior for white sharks, carried out mainly at night and twilight. In contrast, area‐restricted searching was the least used, occurring primarily in daylight hours.
- Time of day, distance to shore, total shark length, and, to a lesser extent, tide phase affected behavioral states. Chumming activity reversed, in the short term and in a nonpermanent way, the behavioral pattern to a general diel vertical pattern.
18.
Gerald J. Wilmink Caleb L. Roth Bennett L. Ibey Norma Ketchum Joshua Bernhard Cesario Z. Cerna William P. Roach 《Cell stress & chaperones》2010,15(6):1027-1038
MicroRNAs (miRNAs) are a class of small RNAs that play a critical role in the coordination of fundamental cellular processes.
Recent studies suggest that miRNAs participate in the cellular stress response (CSR), but their specific involvement remains
unclear. In this study, we identify a group of thermally regulated miRNAs (TRMs) that are associated with the CSR. Using miRNA
microarrays, we show that dermal fibroblasts differentially express 123 miRNAs when exposed to hyperthermia. Interestingly,
only 27 of these miRNAs are annotated in the current Sanger registry. We validated the expression of the annotated miRNAs
using qPCR techniques, and we found that the qPCR and microarray data was in well agreement. Computational target-prediction
studies revealed that putative targets for the TRMs are heat shock proteins and Argonaute-2—the core functional unit of RNA
silencing. These results indicate that cells express a specific group of miRNAs when exposed to hyperthermia, and these miRNAs
may function in the regulation of the CSR. Future studies will be conducted to determine if other cells lines differentially
express these miRNAs when exposed to hyperthermia. 相似文献
19.
The cystic fibrosis transmembrane conductance regulator (CFTR) functions in vivo as a cAMP-activated chloride channel. A member of the ATP-binding cassette superfamily of membrane transporters, CFTR contains two transmembrane domains (TMDs), two nucleotide-binding domains (NBDs), and a regulatory (R) domain. It is presumed that CFTR couples ATP hydrolysis to channel gating, and as a first step in addressing this issue directly, we have established conditions for purification of biochemical quantities of human CFTR expressed in Sf9 insect cells. Use of an 8-azido[alpha-(32)P]ATP-binding and vanadate-trapping assay allowed us to devise conditions to preserve CFTR function during purification of a C-terminal His(10)-tagged variant after solubilization with lysophosphatidylglycerol (1%) and diheptanoylphosphatidylcholine (0.3%) in the presence of excess phospholipid. Study of purified and reconstituted CFTR showed that it binds nucleotide with an efficiency comparable to that of P-glycoprotein and that it hydrolyzes ATP at rates sufficient to account for presumed in vivo activity [V(max) of 58 +/- 5 nmol min(-1) (mg of protein)(-1), K(M)(MgATP) of 0.15 mM]. In further work, we found that neither nucleotide binding nor ATPase activity was altered by phosphorylation (using protein kinase A) or dephosphorylation (with protein phosphatase 2B); we also observed inhibition (approximately 40%) of ATP hydrolysis by reduced glutathione but not by DTT. To evaluate CFTR function as an anion channel, we introduced an in vitro macroscopic assay based on the equilibrium exchange of proteoliposome-entrapped radioactive tracers. This revealed a CFTR-dependent transport of (125)I that could be inhibited by known chloride channel blockers; no significant CFTR-dependent transport of [alpha-(32)P]ATP was observed. We conclude that heterologous expression of CFTR in Sf9 cells can support manufacture and purification of fully functional CFTR. This should aid in further biochemical characterization of this important molecule. 相似文献
20.
Lisa M. Woodard Anthony R. Bielkie John F. Eisses Paul A. Ketchum 《Applied microbiology》1990,56(12):3766-3771
Fifteen of 23 ATCC strains and 2 of 9 clinical isolates of Xanthomonas maltophilia, all of which grew aerobically on ammonia, but not nitrate, as a sole nitrogen source, reduced nitrate to nitrite. X. maltophilia failed to grow anaerobically on complex medium with or without nitrate, so it is considered an obligate aerobe. Nitrate-reducing strains contained reduced methyl viologen nitrate reductase (MVH-NR) with specific activities ranging from 49.2 to 192 U mg of protein−1. Strain ATCC 17666 doubled its cell mass after 3 h of growth on nitrate broth under low aeration, possessed maximal MVH-NR activity, and converted the added nitrate to nitrite, which accumulated. Dissolved oxygen above 15% saturation greatly suppressed nitrite formation. All strains, except ATCC 14535, possessed between 0.25 and 5.05 pmol of molybdopterin mg of protein−1 as measured by the Neurospora crassa nit-1 assay. The molybdopterin activity in the soluble fraction sedimented as a single symmetrical peak with an s20,w of 5.1. Studies identified MVH-NR in selected strains as a membrane-bound protein. The deoxycholate-solubilized MVH-NR sedimented as a single peak in sucrose density gradients with an s20,w of 8.8. The MVH-NR of X. maltophilia has the physical characteristics of a respiratory nitrate reductase and may enable cells to use nitrate as an electron sink under semiaerobic conditions. 相似文献