全文获取类型
收费全文 | 1783篇 |
免费 | 93篇 |
出版年
2023年 | 12篇 |
2022年 | 14篇 |
2021年 | 47篇 |
2020年 | 26篇 |
2019年 | 35篇 |
2018年 | 41篇 |
2017年 | 31篇 |
2016年 | 42篇 |
2015年 | 69篇 |
2014年 | 87篇 |
2013年 | 112篇 |
2012年 | 159篇 |
2011年 | 134篇 |
2010年 | 111篇 |
2009年 | 78篇 |
2008年 | 101篇 |
2007年 | 99篇 |
2006年 | 76篇 |
2005年 | 94篇 |
2004年 | 75篇 |
2003年 | 61篇 |
2002年 | 60篇 |
2001年 | 23篇 |
2000年 | 11篇 |
1999年 | 22篇 |
1998年 | 9篇 |
1997年 | 11篇 |
1996年 | 10篇 |
1995年 | 8篇 |
1994年 | 14篇 |
1993年 | 6篇 |
1992年 | 21篇 |
1991年 | 16篇 |
1990年 | 21篇 |
1989年 | 21篇 |
1988年 | 13篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1983年 | 8篇 |
1982年 | 12篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 11篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1973年 | 4篇 |
1970年 | 4篇 |
1968年 | 5篇 |
排序方式: 共有1876条查询结果,搜索用时 18 毫秒
21.
Bahman Tabaraie Bal Krishan Sharma Praveen Rishi nee Sharma Rakesh Sehgal Nirmal Kumar Ganguly 《Microbiology and immunology》1994,38(7):553-559
Porins were prepared from smooth strain of Salmonella typhi 0–901 and chemotype of rough mutant of S. typhimurium Ra-30. Mice were immunized with both the porin preparations in different groups and challenged with S. typhimurium LT2–71 and S. enteritidis SH-1269. Porin immunized mice showed significant protection (P <0.01) against challenge with homologous as well as heterologous strains. Hence, the use of porins may be attempted in future to protect against salmonellosis. 相似文献
22.
Martina Ferraguti Sergio Magallanes Jéssica Jiménez-Peñuela Josué Martínez-de la Puente Luz Garcia-Longoria Jordi Figuerola Jaime Muriel Tamer Albayrak Staffan Bensch Camille Bonneaud Rohan H. Clarke Gábor Á. Czirják Dimitar Dimitrov Kathya Espinoza John G. Ewen Farah Ishtiaq Wendy Flores-Saavedra László Zsolt Garamszegi Olof Hellgren Dita Horakova Kathryn P. Huyvaert Henrik Jensen Asta Križanauskienė Marcos R. Lima Charlene Lujan-Vega Eyðfinn Magnussen Lynn B. Martin Kevin D. Matson Anders Pape Møller Pavel Munclinger Vaidas Palinauskas Péter L. Pap Javier Pérez-Tris Swen C. Renner Robert Ricklefs Sergio Scebba Ravinder N. M. Sehgal Manuel Soler Eszter Szöllősi Gediminas Valkiūnas Helena Westerdahl Pavel Zehtindjiev Alfonso Marzal 《Global Ecology and Biogeography》2023,32(5):809-823
Aim
The increasing spread of vector-borne diseases has resulted in severe health concerns for humans, domestic animals and wildlife, with changes in land use and the introduction of invasive species being among the main possible causes for this increase. We explored several ecological drivers potentially affecting the local prevalence and richness of avian malaria parasite lineages in native and introduced house sparrows (Passer domesticus) populations.Location
Global.Time period
2002–2019.Major taxa studied
Avian Plasmodium parasites in house sparrows.Methods
We analysed data from 2,220 samples from 69 localities across all continents, except Antarctica. The influence of environment (urbanization index and human density), geography (altitude, latitude, hemisphere) and time (bird breeding season and years since introduction) were analysed using generalized additive mixed models (GAMMs) and random forests.Results
Overall, 670 sparrows (30.2%) were infected with 22 Plasmodium lineages. In native populations, parasite prevalence was positively related to urbanization index, with the highest prevalence values in areas with intermediate urbanization levels. Likewise, in introduced populations, prevalence was positively associated with urbanization index; however, higher infection occurred in areas with either extreme high or low levels of urbanization. In introduced populations, the number of parasite lineages increased with altitude and with the years elapsed since the establishment of sparrows in a new locality. Here, after a decline in the number of parasite lineages in the first 30 years, an increase from 40 years onwards was detected.Main conclusions
Urbanization was related to parasite prevalence in both native and introduced bird populations. In invaded areas, altitude and time since bird introduction were related to the number of Plasmodium lineages found to be infecting sparrows. 相似文献23.
Enzymatic 3-O-sulfation of terminal ß-Gal residueswas investigated by screening sulfotransferase activity presentin 37 human tissue specimens toward the following synthesizedacceptor moieties: Galß1,3GalNAc-O-Al, Galß1,4GlcNAcß-O-Al,Galß1,3GlcNAcß-O-Al, and mucin-type Galß1,4GlcNAcß1,6(Galß1,3)GalNAc-O-Bnstructures containing a C-3 methyl substituent on either Gal.Two distinct types of Gal: 3-O-sulfotransferases were revealed.One (Group A) was specific for the Galß1, 3GalNAc-linkage and the other (Group B) was directed toward the Galß1,4GlcNAcbranch ß1,6 linked to the blood group T hapten. Enzymeactivities found in breast tissues were unique in showing astrict specificity for the T-hapten. Galß-O-allylor benzyl did not serve as acceptors for Group A but were veryactive with Group B. An exainination of activity present insix human sera revealed a specificity of the serum enzyme towardß1,3 linked Gal, particularly, the T-hapten withoutß1,6 branching. Group A was highly active toward T-haptenlacrylamidecopolymer, anti-freeze glycoprotein, and fetuin O-glycosidicasialo glycopeptide; less active toward fetuin triantennaryasialo glycopeptide; and least active toward bovine IgG diantennaryglycopeptide. Group B was moderately and highly active, respectively,with the latter two glycopeptides noted and least active withthe first two. Competition experiments performed with Galß1,3GaLNAc-O-Aland Galß1,4GlcNAcß1,6(Galß1,3)GalNAc-O-Bnhaving a C-3 substituent (methyl or sulfate) on either Gal reinforcedearlier findings on the specificity characteristics of GroupA and Group B. Group A displayed a wider range of optimal activity(pH 6.07.4), whereas Group B possessed a peak of activityat pH 7.2. Mg2+ stimulated Group A 55% and Group B 150%, whereasMn+2 stimulated Group B 130% but inhibited Group A 75%. Ca2+stimulated Group B 100% but inhibited Group A 35%. Group A andGroup B enzymes appeared to be of the same molecular size (<100,000Da) as observed by Sephacryl S-100 HR column chromatography.The following effects upon Gal: 3-O- sulfotransferase activitiesby fucose, sulfate, and other substituents on the carbohydratechains were noted. (1) A methyl or GlcNAc substituent on C-6of GalNAc diminished the ability of Galß1,3GalNAc-O-Alto act as an acceptor for Group A. (2) An 1,3-fucosyl residueon the ß1,6 branch in the mucin core structure didnot affect the activity of Group A toward Gal linked ß1,3to GalNAc-. (3) Lewis x and Lewis a terminals did not serveas acceptors for either Group A or B enzymes. (4) Eliminationof Group B activity on Gal in the ß1,6 branch owingto the presence of a 3-fucosyl or 6-sulfo group on GlcNAc didnot hinder any action toward Gal linked ß1,3 to GalNAc.(5) Group A activity on Gal linked ß1,3 to GalNAcremained imaffected by 3'-sulfation of the ß1,6 branch.The reverse was true for Group B. (6) The acceptor activityof the T-hapten was increased somewhat upon C-6 sulfation ofGalNAc, whereas, C-6 slalylation resulted in an 85% loss ofactivity. (7) A novel finding was that Galß1,4GlcNAcß-O-Aland Galß1,3GlcNAcß-O-M, upon C-6 sulfationof the GlcNAc moiety, became 100% inactive and 5- to 7-foldactive, respectively, in their ability to serve as acceptorsfor Group B. human tissues glycoprotein galactose:sulfotransferase specificities kinetic properties 相似文献
24.
Caffeine causes severe retardation of growth and development and high mortality of larvae Telmatoscopus albipunctatus. In general, sensitivity to caffeine is inversely proportional to the age of the treated larvae. Adults originating from treated larvae show lower fertility. Treatment of pupae results in elongated abdomens, abnormal wings and reduced fertility in adults. Caffeine also affects adversely polytenization of chromosomes. It is suggested that effects on larval growth and polytenization of chromosomes are due to retardation of DNA synthesis. Other possible mechanisms of action of caffeine are discussed.
Zusammenfassung Koffein verursacht starke Verzögerung von Wachstum und Entwicklung sowie hohe Mortalität der Larven von Telmatoscopus albipunctatus. Im allgemeinen ist die Empfindlichkeit genenüber Koffein umgekehrt proportional zum Alter der behandelten Larven. Adulte, die als Larven damit behandelt wurden, zeigen verminderte Fertilität. Behandlung von Puppen ergibt Adulte mit verlängertem Abdomen, anormalen Flügeln und verminderter Fertilität. Koffein beeinflußt auch die Polytänisierung der Chromosomen ungünstig. Es wird angenommen, daß die Beeinflussung des Larvenwachstums und der Polytänisierung der Chromosomen zurückzuführen ist auf verzögerte DNS-Synthese. Es werden sodann andere mögliche Mechanismen der Wirkung des Koffeins diskutiert.相似文献
25.
Ethanolic extract of the leaves of Vitex negundo yielded a new iridoid named 2′-p-hydroxybenzoyl mussaenosidic acid. The structure was established on the basis of chemical and spectral data. 相似文献
26.
Activities of Phosphorylase, glyceraldehyde-3 -phosphate dehydrogenase, lactate dehydrogenase, malate dehydrogenase and succinate
dehydrogenase in the rat endometrial tissue are significantly inhibited by an intrauterine copper device, while it stimulated
glucose-6-phosphate dehydrogenase activity. The copper device decreased the lactate/pyruvate ratio in the tissue; pyruvate
utilizationin vitro by the rat endometrium is also blocked by copper. These findings suggested that the normal carbohydrate metabolism of the
tissue may be affected in presence of copper, thus resulting in a change of the endometrial function, which may be one of
the factors responsible for the contraceptive and pharmacological action of an intrauterine copper device. 相似文献
27.
Sera from 129 squirrel monkeys, Saimiri sciureus, were analyzed for 15 chemical constituents. The values obtained were then analyzed for statistical significance causing the following sets of variables: (1) colony-bred versus noncolony-bred, (2) karyotype (3) vendor, (4) sex and (5) dietary iodine supplementation versus nonsupplementation. Calcium, inorganic phosphorous, albumin, uric acid, blood urea nitrogen, glucose, alkaline phosphatase and potassium were high in colony-bred animals. Cholesterol, total protein and chloride were lower in colony-bred animals than in noncolony-bred animals. No differences were seen in total bilirubin, lactic dehydrogenase, serum glutamic oxaloacetic transaminase and sodium. When the noncolony-bred animals were separated by karyotype, total protein was higher and chloride was lower between animals from Peru versus from Guyana. Colombian animals had total protein values lower than Peruvian and lactic dehydrogenase values higher than Peruvian. Colony-bred Peruvian monkeys had serum glutamic oxaloacetic transaminase values higher than colony-bred Colombian monkeys. No differences were observed between monkeys from different vendors. Chemical constituents higher between noncolony-bred males and females were calcium and alkaline phosphatase. There were no differences observed for colony-bred males and females. Dietary iodine supplementation appeared to increase both total bilirubin and calcium. 相似文献
28.
Nirupama Banerjee Rakesh Bhatnagar L. Viswanathan 《Applied microbiology and biotechnology》1981,11(4):226-228
Summary Furfural, a Maillard reaction product, was found to inhibit growth and alcohol production by Saccharomyces cerevisiae. Furfural concentrations above 1 mg ml–1 significantly decreased CO2 evolution by resuspended yeast cells. Important glycolytic enzymes such as hexokinase, phosphofructokinase, triosephosphate dehydrogenase, aldolase and alcohol dehydrogenase were assayed in presence of furfural. Dehydrogenases appeared to be the most sensitive enzymes and are probably responsible for the observed inhibition of alcohol production and growth. 相似文献
29.
30.
S. S. Marwaha R. P. Sethi J. F. Kennedy Rakesh Kumar 《Enzyme and microbial technology》1983,5(6):449-453
Vitamin B12 production in fermentation of Propionibacterium shermanii and Propionibacterium arl AKU 1251 in whey permeate medium has been studied. The observed results and simulated expected values obtained by fitting statistical equations to the recorded data showed that 24 h old inoculum, 5 mg iron l?1 and 4% whey lactose were optimal for vitamin B12 biosynthesis in both strains when fermentation was carried out under anerobic (84 h) and aerobic (84 h) conditions at 30°C. The supplementation of whey medium with 0.5% (NH4)2HPO4 enhanced further the metabolite yield; however, the preference for a mixed carbon source (lactose + d-glucose or lactose + d-fructose) at different levels varied in the strains under study. P. shermanii, under optimal cultural conditions, was found to be a better strain than Propionibacterium arl AKU, 1251 in fermenting whey lactose for product (vitamin B12) formation. 相似文献