全文获取类型
收费全文 | 975篇 |
免费 | 73篇 |
出版年
2023年 | 7篇 |
2022年 | 10篇 |
2021年 | 25篇 |
2020年 | 14篇 |
2019年 | 12篇 |
2018年 | 18篇 |
2017年 | 20篇 |
2016年 | 26篇 |
2015年 | 31篇 |
2014年 | 47篇 |
2013年 | 55篇 |
2012年 | 84篇 |
2011年 | 73篇 |
2010年 | 44篇 |
2009年 | 28篇 |
2008年 | 52篇 |
2007年 | 38篇 |
2006年 | 60篇 |
2005年 | 45篇 |
2004年 | 36篇 |
2003年 | 37篇 |
2002年 | 42篇 |
2001年 | 16篇 |
2000年 | 19篇 |
1999年 | 13篇 |
1998年 | 8篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 13篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 13篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1981年 | 4篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1976年 | 7篇 |
1974年 | 7篇 |
1972年 | 3篇 |
1970年 | 4篇 |
1968年 | 4篇 |
1967年 | 8篇 |
排序方式: 共有1048条查询结果,搜索用时 15 毫秒
11.
The examination of the state of conservation of works of art in stone includes the assessment of the presence of microbiological agents on the surface of the decayed monuments. These microorganisms can accelerate, via their metabolic activity, the decay process of the stone surface. At present this assessment is made with the traditional techniques for the microbiological examination of the soil, provides results only after a delay of 30 days. A bioluminescent ATP assay should provide rapid quantitation of actively growing organisms on the surface of a stone monument, and the applicability of this technique was verified on some samples of sandstone (Pietraforte) collected from a historic building (the Strozzi Palace) in Florence. These samples were evaluated for the amount of the ATP and the total number of microorganisms. The results obtained suggest that the bioluminescent assay could be suitable for detecting and quantitating the presence of microorganisms in a sample of stone. 相似文献
12.
C Orlando J d'Alayer G Baillat F Castets O Jeannequin J C Mazié A Monneron 《Biochemistry》1992,31(12):3215-3222
A brain adenylyl cyclase was shown to contain an epitope closely related to that specified by a conserved sequence containing a nucleotide-binding consensus sequence GXXXXGKS and located in the catalytic sites of bacterial, calmodulin-dependent adenylyl cyclases [Goyard, S., Orlando, C., Sabatier, J.-M., Labruyere, E., d'Alayer, J., Fontan, G., van Rietschoten, J., Mock, M., Danchin, A., Ullmann, A., & Monneron, A. (1989) Biochemistry 28, 1964-1967]. A monoclonal antibody, mab 164, produced against a peptide corresponding to this conserved sequence specifically inhibited the Bordetella pertussis adenylyl cyclase. It also specifically inhibited rat and rabbit brain synaptosomal adenylyl cyclases. The extent of inhibition depended upon the type of enzyme purification, reaching 90% for the calmodulin-sensitive species of enzyme and 20-35% for the forskolin-agarose-retained species. The extent of inhibition in a given fraction also depended upon the effector present. mab 164 reacted on Western blots of forskolin-agarose-retained fractions with a 175-kDa component and did not recognize the Gs alpha stimulatory subunit. Consequently, the 175-kDa protein was considered as a good candidate for an adenylyl cyclase catalyst. The adenylyl cyclase activity contained in forskolin-agarose-retained fractions was further purified on calmodulin-Sepharose. On Western blots of such fractions, mab 164 reacted with a 140-kDa protein, a component that appeared to derive from the 175-kDa protein enriched in the previous step. The kcat of this 140-kDa presumptive adenylyl cyclase was estimated to be of the order of 600 s-1.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
13.
Defenses against oxidative stress in the Antarctic scallop Adamussium colbecki and effects of acute exposure to metals 总被引:5,自引:0,他引:5
Since a general pathway of toxicity induced bypollutants is the enhancement of reactive oxygenspecies, biochemical responses associated withvariations in the antioxidant cellular system havebeen often proposed as biomarkers ofpollutant-mediated toxicity associated with oxidativestress. Antarctic organisms live in an extremeenvironment characterized by low water temperature,high level of dissolved oxygen, presence of ice andstrong seasonal changes in light intensity andavailability of food, conditions which could influenceboth the formation of reactive oxygen species and themechanisms for their removal. In this respect andconsidering the utility of this as a key species formonitoring marine Antarctic environment it was ofinterest to investigate the antioxidant defense systemof the scallop Adamussium colbecki.The parameters examined in the digestive gland of thescallop were the concentration of glutathione and theactivity of several glutathione dependent andantioxidant enzymes (glyoxalase I and II, glutathioneS-transferases, glutathione peroxidases, glutathionereductase, catalase, superoxide dismutase). Very highlevels of catalase suggest a possible adaptation toAntarctic extreme conditions, while the highactivities of glutathione S-transferases are moreprobably related to the feeding behavior of Pectinids.Enzymes from Adamussium colbecki generallyappeared to be active at low temperatures but, with afew exceptions, their activities increased with risingtemperature. Exposure of A. colbecki tosublethal concentrations of Cu or Hg resulted in asignificant reduction in the levels of totalglutathione and in the activity of catalase andglutathione S-transferases. Antioxidant responses ofA. colbecki could represent a useful tool inassessing the biological impact of environmentalpollutants in the Antarctic ecosystems. 相似文献
14.
L Okolicsányi M Venuti M Strazzabosco R M Iemmolo G Nassuato R Orlando F Lirussi 《Acta physiologica Hungarica》1984,64(3-4):393-400
The bioavailability of oral and intravenous cimetidine and ranitidine was studied in patients with compensated liver cirrhosis. Single doses of 200 and 400 mg cimetidine were used for both administration routes, while ranitidine was administered in doses of 150 mg orally or 50 mg i.v. Plasma concentrations and urinary recovery were determined by the HPLC method. The pharmacokinetics of both of these drugs in the cirrhotic patients did not differ from those found in normal subjects. The two doses of cimetidine given i.v. gave rise to the same plasma concentrations, while after oral administration, 400 mg produced higher plasma concentrations than 200 mg. As to the pharmacokinetic parameters, neither cimetidine nor ranitidine administered i.v. offered any further advantages compared to the oral route. The urinary recovery of both cimetidine and ranitidine was higher after intravenous than after oral administration. It is concluded therefore that the pharmacokinetics of cimetidine and ranitidine is not altered in compensated liver cirrhosis. 相似文献
15.
Antonio Baldini Dorothy A. Miller Viji Shridhar Mariano Rocchi Orlando J. Miller David C. Ward 《Chromosoma》1991,101(2):109-114
We have isolated an alpha satellite DNA clone, pG3.9, from gorilla DNA. Fluorescence in situ hybridization on banded chromosomes under high stringency conditions revealed that pG3.9 identifies homologous sequences at the centromeric region of ten gorilla chromosomes, and, with few exceptions, also recognizes the homologous chromosomes in human. A pG3.9-like alphoid DNA is present on a larger number of orangutan chromosomes, but, in contrast, is present on only tow chromosomes in the chimpanzee. These results show that the chromosomal subsets of related alpha satellite DNA sequences may undergo different patterns of evolution.by J.B. Rattner 相似文献
16.
Louise R. Romanow Orlando M. B. Ponti Chris Mollema 《Entomologia Experimentalis et Applicata》1991,60(3):247-259
Life history parameters including longevity, developmental time, and reproduction were determined for whiteflies, Trialeurodes vaporariorum (Westwood), kept in clip-on cages on susceptible parent, Lycopersicon esculentum, resistant parent, L. hirsutum glabratum, and intermediate breeding lines of tomato. Using the Lewontin triangular reproductive function, the intrinsic rate of increase (rm) was calculated for each genotype. This is an elegant tool for detecting resistance, as it incorporates all salient factors of life history. Comparing rm to the other parameters measured, selection criteria were chosen. Developmental time is not a suitable selection criterion as it varies very little even between the most susceptible and the most resistant genotypes. Additionally, developmental time of T. vaporariorum offspring was found to be highly significantly correlated to parental age on all tomato genotypes except L. hirsutum glabratum. Total reproduction, truncated population counts, and longevity appear good criteria for selection. This test, focusing on antibiotic factors, shows large differences between the resistant and susceptible parent genotypes, but much smaller differences between the breeding lines and the susceptible parent. Earlier screenings relying on a variety of tests appear to have maintained antixenotic rather than antibiotic properties in the breeding lines. 相似文献
17.
Mario Maggi Guido Fantoni Alessandro Peri Stefano Giannini Maria Luisa Brandi Claudio Orlando Mario Serio 《The Journal of steroid biochemistry and molecular biology》1991,40(4-6):481-491
Oxytocin (OT) and V1 vasopressin (VP) receptors are present simultaneously in several tissues, including the uterus. In myometrium these receptors mediate contractility, while in endometrium they mediate the release of other uterotonic substances as endothelin (ET). In rabbit myometrium, estrogens increase, while progesterone blunts neurohypophysial hormone receptors. However, the action of sex steroids on OT and V1 VP receptors differs in terms of the ED50 and maximal effect. Therefore, at parturition, only OT receptors show a dramatic rise, while V1 VP receptors do not change, suggesting a major role for OT in labor. ET is a potent stimulator of uterine activity acting through specific receptors present on myometrial cells. These receptors as well as the endometrial localization of ET are modulated by sex steroids, indicating that ET might represent a paracrine regulator of uterine activity. In humans, OT but not V1 VP receptors increase as pregnancy progresses, confirming the primary relevance of OT in timing delivery. 相似文献
18.
Stephen S. Wachtel Gloria C. Koo Albert de la Chapelle Hanna Kallio Joseph M. Heyman Orlando J. Miller 《Human genetics》1980,54(1):25-30
Summary Presence of H-Y antigen has been correlated with testicular differentiation, and absence of H-Y with failure of testicular differentiation, in a variety of mammalian species. To determine more precisely the relationship between expression of H-Y antigen and development of the testis, we studied the cells of phenotypic females with the 46,XY male karyotype. Blood leukocytes were typed H-Y+ in five XY females with gonadal dysgenesis, although in other studies blood leukocytes from XY females with gonadal dysgenesis were typed H-Y-. Thus mere presence of H-Y antigen is not sufficient to guarantee normal differentiation of the testis. In the present paper we review evidence for an additional factor in gonadal organogenesis, the H-Y antigen receptor. We infer that testicular development requires engagement of H-Y and its receptor. It follows that XY gonadal dysgenesis is the consequence of functional absence of the H-Y testis inducer as in the following conditions: failure of synthesis of H-Y or failure of specific binding of H-Y. 相似文献
19.
Jacqueline S. Lipszyc Stephanie Gordon Phillips Orlando J. Miller 《Experimental cell research》1981,133(2)
Autoradiographic analysis of [3H]uridine incorporation 48 h after polyethylene glycol-mediated cell fusion indicates that nucleolar RNA synthesis persists in both human and mouse nuclei in interspecific heterokaryons. The absence of nucleolar dominance in heterokaryons has been confirmed by zinc-dithizone nucleolus-specific staining, and is true even when there are considerably more nuclei of one species than of the other in the heterokaryon. Studies of actinomycin D-induced nucleolar segregation indicate that the zinc-binding proteins responsible for zinc-dithizone staining are located in a different nucleolar component than the protein responsible for silver staining. 相似文献
20.
Schubert M Ginolhac A Lindgreen S Thompson JF Al-Rasheid KA Willerslev E Krogh A Orlando L 《BMC genomics》2012,13(1):178
ABSTRACT: BACKGROUND: Next-Generation Sequencing has revolutionized our approach to ancient DNA (aDNA) research, by providing complete genomic sequences of ancient individuals and extinct species. However, the recovery of genetic material from long-dead organisms is still complicated by a number of issues, including post-mortem DNA damage and high levels of environmental contamination. Together with error profiles specific to the type of sequencing platforms used, these specificities could limit our ability to map sequencing reads against modern reference genomes and therefore limit our ability to identify endogenous ancient reads, reducing the efficiency of shotgun sequencing aDNA. RESULTS: In this study, we compare different computational methods for improving the accuracy and sensitivity of aDNA sequence identification, based on shotgun sequencing reads recovered from Pleistocene horse extracts using Illumina GAIIx and Helicos Heliscope platforms. We show that the performance of the Burrows Wheeler Aligner (BWA), that has been developed for mapping of undamaged sequencing reads using platforms with low rates of indel-types of sequencing errors, can be employed at acceptable run-times by modifying default parameters in a platform-specific manner. We also examine if trimming likely damaged positions at read ends can increase the recovery of genuine aDNA fragments and if accurate identification of human contamination can be achieved using a strategy previously suggested based on best hit filtering. We show that combining our different mapping and filtering approaches can increase the number of high-quality endogenous hits recovered by up to 33%. CONCLUSIONS: We have shown that Illumina and Helicos sequences recovered from aDNA extracts could not be aligned to modern reference genomes with the same efficiency unless mapping parameters are optimized for the specific types of errors generated by these platforms and by post-mortem DNA damage. Our findings have important implications for future aDNA research, as we define mapping guidelines that improve our ability to identify genuine aDNA sequences, which in turn could improve the genotyping accuracy of ancient specimens. Our framework provides a significant improvement to the standard procedures used for characterizing ancient genomes, which is challenged by contamination and often low amounts of DNA material. 相似文献