全文获取类型
收费全文 | 17350篇 |
免费 | 1341篇 |
国内免费 | 4篇 |
出版年
2023年 | 83篇 |
2022年 | 245篇 |
2021年 | 400篇 |
2020年 | 235篇 |
2019年 | 355篇 |
2018年 | 435篇 |
2017年 | 370篇 |
2016年 | 559篇 |
2015年 | 852篇 |
2014年 | 985篇 |
2013年 | 1256篇 |
2012年 | 1486篇 |
2011年 | 1386篇 |
2010年 | 909篇 |
2009年 | 760篇 |
2008年 | 1066篇 |
2007年 | 1084篇 |
2006年 | 969篇 |
2005年 | 854篇 |
2004年 | 851篇 |
2003年 | 724篇 |
2002年 | 677篇 |
2001年 | 190篇 |
2000年 | 155篇 |
1999年 | 166篇 |
1998年 | 151篇 |
1997年 | 125篇 |
1996年 | 123篇 |
1995年 | 98篇 |
1994年 | 69篇 |
1993年 | 93篇 |
1992年 | 102篇 |
1991年 | 88篇 |
1990年 | 71篇 |
1989年 | 58篇 |
1988年 | 60篇 |
1987年 | 40篇 |
1986年 | 42篇 |
1985年 | 53篇 |
1984年 | 35篇 |
1983年 | 46篇 |
1982年 | 44篇 |
1981年 | 38篇 |
1980年 | 37篇 |
1979年 | 30篇 |
1978年 | 19篇 |
1977年 | 27篇 |
1976年 | 23篇 |
1975年 | 28篇 |
1974年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
Favorable and unfavorable HLA class I alleles and haplotypes in Zambians predominantly infected with clade C human immunodeficiency virus type 1
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Tang J Tang S Lobashevsky E Myracle AD Fideli U Aldrovandi G Allen S Musonda R Kaslow RA;Zambia-UAB HIV Research Project 《Journal of virology》2002,76(16):8276-8284
The setpoint of viral RNA concentration (viral load [VL]) during chronic human immunodeficiency virus type 1 (HIV-1) infection reflects a virus-host equilibration closely related to CD8(+) cytotoxic T-lymphocyte (CTL) responses, which rely heavily on antigen presentation by the human major histocompatibility complex (MHC) (i.e., HLA) class I molecules. Differences in HIV-1 VL among 259 mostly clade C virus-infected individuals (137 females and 122 males) in the Zambia-UAB HIV Research Project (ZUHRP) were associated with several HLA class I alleles and haplotypes. In particular, general linear model analyses revealed lower log(10) VL among those with HLA allele B*57 (P = 0.002 [without correction]) previously implicated in favorable response and in those with HLA B*39 and A*30-Cw*03 (P = 0.002 to 0.016); the same analyses also demonstrated higher log(10) VL among individuals with A*02-Cw*16, A*23-B*14, and A*23-Cw*07 (P = 0.010 to 0.033). These HLA effects remained strong (P = 0.0002 to 0.075) after adjustment for age, gender, and duration of infection and persisted across three orders of VL categories (P = 0.001 to 0.084). In contrast, neither B*35 (n = 15) nor B*53 (n = 53) showed a clear disadvantage such as that reported elsewhere for these closely related alleles. Other HLA associations with unusually high (A*68, B*41, B*45, and Cw*16) or low (B*13, Cw*12, and Cw*18) VL were either unstable or reflected their tight linkage respecting disequilibria with other class I variants. The three consistently favorable HLA class I variants retained in multivariable models and in alternative analyses were present in 30.9% of subjects with the lowest (<10,000 copies per ml) and 3.1% of those with the highest (>100,000) VL. Clear differential distribution of HLA profiles according to level of viremia suggests important host genetic contribution to the pattern of immune control and escape during HIV-1 infection. 相似文献
932.
Intramolecular complementing mutations in tobacco mosaic virus movement protein confirm a role for microtubule association in viral RNA transport 总被引:5,自引:0,他引:5
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Boyko V Ashby JA Suslova E Ferralli J Sterthaus O Deom CM Heinlein M 《Journal of virology》2002,76(8):3974-3980
The movement protein (MP) of Tobacco mosaic virus (TMV) facilitates the cell-to-cell transport of the viral RNA genome through plasmodesmata (Pd). A previous report described the functional reversion of a dysfunctional mutation in MP (Pro81Ser) by two additional amino acid substitution mutations (Thr104Ile and Arg167Lys). To further explore the mechanism underlying this intramolecular complementation event, the mutations were introduced into a virus derivative expressing the MP as a fusion to green fluorescent protein (GFP). Microscopic analysis of infected protoplasts and of infection sites in leaves of MP-transgenic Nicotiana benthamiana indicates that MP(P81S)-GFP and MP(P81S;T104I;R167K)-GFP differ in subcellular distribution. MP(P81S)-GFP lacks specific sites of accumulation in protoplasts and, in epidermal cells, exclusively localizes to Pd. MP(P81S;T104I;R167K)-GFP, in contrast, in addition localizes to inclusion bodies and microtubules and thus exhibits a subcellular localization pattern that is similar, if not identical, to the pattern reported for wild-type MP-GFP. Since accumulation of MP to inclusion bodies is not required for function, these observations confirm a role for microtubules in TMV RNA cell-to-cell transport. 相似文献
933.
Long-term circulation of vaccine-derived poliovirus that causes paralytic disease 总被引:8,自引:0,他引:8
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Cherkasova EA Korotkova EA Yakovenko ML Ivanova OE Eremeeva TP Chumakov KM Agol VI 《Journal of virology》2002,76(13):6791-6799
Successful implementation of the global poliomyelitis eradication program raises the problem of vaccination against poliomyelitis in the posteradication era. One of the options under consideration envisions completely stopping worldwide the use of the Sabin vaccine. This strategy is based on the assumption that the natural circulation of attenuated strains and their derivatives is strictly limited. Here, we report the characterization of a highly evolved derivative of the Sabin vaccine strain isolated in a case of paralytic poliomyelitis from a 7-month-old immunocompetent baby in an apparently adequately immunized population. Analysis of the genome of this isolate showed that it is a double (type 1-type 2-type 1) vaccine-derived recombinant. The number of mutations accumulated in both the type 1-derived and type 2-derived portions of the recombinant genome suggests that both had diverged from their vaccine predecessors approximately 2 years before the onset of the illness. This fact, along with other recent observations, points to the possibility of long-term circulation of Sabin vaccine strain derivatives associated with an increase in their neurovirulence. Comparison of genomic sequences of this and other evolved vaccine-derived isolates reveals some general features of natural poliovirus evolution. They include a very high preponderance and nonrandom distribution of synonymous substitutions, conservation of secondary structures of important cis-acting elements of the genome, and an apparently adaptive character of most of the amino acid mutations, with only a few of them occurring in the antigenic determinants. Another interesting feature is a frequent occurrence of tripartite intertypic recombinants with either type 1 or type 3 homotypic genomic ends. 相似文献
934.
Differential requirements for COPI coats in formation of replication complexes among three genera of Picornaviridae
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Picornavirus RNA replication requires the formation of replication complexes (RCs) consisting of virus-induced vesicles associated with viral nonstructural proteins and RNA. Brefeldin A (BFA) has been shown to strongly inhibit RNA replication of poliovirus but not of encephalomyocarditis virus (EMCV). Here, we demonstrate that the replication of parechovirus 1 (ParV1) is partly resistant to BFA, whereas echovirus 11 (EV11) replication is strongly inhibited. Since BFA inhibits COPI-dependent steps in endoplasmic reticulum (ER)-Golgi transport, we tested a hypothesis that different picornaviruses may have differential requirements for COPI in the formation of their RCs. Using immunofluorescence and cryo-immunoelectron microscopy we examined the association of a COPI component, beta-COP, with the RCs of EMCV, ParV1, and EV11. EMCV RCs did not contain beta-COP. In contrast, beta-COP appeared to be specifically distributed to the RCs of EV11. In ParV1-infected cells beta-COP was largely dispersed throughout the cytoplasm, with some being present in the RCs. These results suggest that there are differences in the involvement of COPI in the formation of the RCs of various picornaviruses, corresponding to their differential sensitivity to BFA. EMCV RCs are likely to be formed immediately after vesicle budding from the ER, prior to COPI association with membranes. ParV1 RCs are formed from COPI-containing membranes but COPI is unlikely to be directly involved in their formation, whereas formation of EV11 RCs appears to be dependent on COPI association with membranes. 相似文献
935.
Infection of human epithelial cells with adenoviruses induces an apoptosis paradigm that is efficiently suppressed by the expression of viral E1B-19K protein, which is a functional homolog of the cellular antiapoptosis protein BCL-2. The mechanisms of adenovirus (Ad)-induced apoptosis appear to involve the cellular BCL-2 family proapoptotic proteins. Recent genetic studies with fibroblasts derived from mutant mouse embryos indicate that a class of the BCL-2 family proapoptotic proteins (designated BH-123 or multidomain proteins) such as BAX and BAK constitutes an essential component of the core apoptosis machinery in animal cells. We have examined the role of BAX in Ad-induced apoptosis in human epithelial cells using two colon cancer cell lines, HCT116Bax (Bax(+/-)) and HCT116BaxKO (Bax(-/-)) (L. Zhang, J. Yu, B. H. Park, K. W. Kinzler, and B. Vogelstein, Science 290:989-992, 2000). Infection of Bax(+/-) cells with an Ad type 2 mutant (dl250) defective in expression of the E1B-19K protein resulted in enhanced cytopathic effect, large plaques on cell monolayers, fragmentation of cellular DNA, and enhanced cell death. These mutant phenotypes were not efficiently expressed in Bax(-/-) cells, suggesting that BAX is essential for Ad-induced apoptosis. Infection of Bax(+/-) cells with dl250 induced increased levels of an N-terminally processed form of BAX. Cells infected with the 19K mutant also contained enhanced levels of truncated BAX in membrane-inserted form. Our results suggest that at least a part of the mechanism utilized by E1B-19K to suppress apoptosis during Ad infection may involve modulation of the activities of BAX. 相似文献
936.
Two new coumarin glycosides (1 and 2) along with two known coumarin glucosides, daphnin (3) and daphnetin glucoside (4) were isolated from the aerial parts of Cruciata taurica. The structures of the new compounds were elucidated by spectral methods and chemical means as 7-O-(6' -acetoxy-beta-D-glucopyranosyl)-8-hydroxycoumarin (1) and 7-O-[6 '-O-(3',4'-dihydroxycinnamoyl)-beta-D-glucopyranosyl]-8-hydroxycoumarin (2). The phylogenetic significance of coumarins in C. taurica was discussed. 相似文献
937.
938.
Solinís MA de la Cruz Y Calvo B Hernández RM Gascón AR Goñi I Gurruchaga MD Pedraz JL 《Chirality》2002,14(10):806-813
We studied the release of salbutamol and ketoprofen enantiomers from HPMC K100M matrices containing two types of cellulose derivatives: cellulose tris (3,5-dimethylphenylcarbamate) and cellulose tris (2,3-dichlorophenylcarbamate), chiral excipients used as stationary phases for liquid chromatography. These matrices provided an extended release of both drugs. Ketoprofen release from formulations elaborated with cellulose tris (2,3-dichlorophenylcarbamate) was by anomalous transport, because the value of n (release exponent of the diffusion equation) ranged between 0.60-0.68, whereas for all other formulations the value of exponent n ranged from 0.50-0.54. The drug thus diffuses through the matrix and is released following a quasi-Fickian diffusion mechanism (stereoselective process). The matrices preferentially retained R-salbutamol and S-ketoprofen and cellulose tris (3,5-dimethylphenylcarbamate) showed more capacity of chiral discrimination for both drugs than cellulose tris (2,3-dichlorophenylcarbamate). Moreover, we observed that stereoselectivity is dependent on the amount of chiral excipient in the formulation. Diffusion tests confirmed the chiral interaction between drugs and cellulose derivatives observed in the dissolution assays except for matrices elaborated with ketoprofen and cellulose tris (2,3-dichlorophenylcarbamate), where the low stereoselectivity observed with the matrices is due to the presence of HPMC K100M. We conclude that the inclusion of these cellulose derivatives in HPMC matrices does not result in a relevant stereoselectivity with respect to the two drugs studied. 相似文献
939.
Mustakerova E Todorova M Tsankova E 《Zeitschrift für Naturforschung. C, Journal of biosciences》2002,57(7-8):568-570
Aerial parts of Achillea collina afforded, in addition to five known sesquiterpene lactones two new germacranolides and one new eudesmanolide, the structures of which were elucidated by spectroscopic methods. 相似文献
940.
Delporte C Muñoz O Rojas J Ferrándiz M Payá M Erazo S Negrete R Maldonado S San FA Backhouse N 《Zeitschrift für Naturforschung. C, Journal of biosciences》2002,57(1-2):100-108
The probable antipyretic, antiinflammatory, analgesic and antioxidant properties of Kageneckia oblonga, Rosaceae, were investigated and the major compounds of its active extracts were isolated. The study comprised the acute toxicity of the extracts of global methanol, hexane, dichloromethane and methanol. The cytotoxicity of global methanol extract was studied in three tumoral cell lines. All the extracts exhibited the pharmacological activities under study. Methanol and dichloromethane were the most toxic extracts. From the global methanol extract, isolations were performed of prunasin, 23,24- dihydro-cucurbitacin F, and a new cucurbitacin, 3beta-(beta-D-glucosyloxy)-16alpha,23alpha-epoxycucurbita-5,24-diene-11-one. The cytotoxicity of both cucurbitacins on human neutrophils at the assayed concentrations was not statistically significant. In-vitro assays showed that both cucurbitacins can be partly responsible for the analgesic, antipyretic, and anti-inflammatory activities. Evaluation was done of the cytotoxicity of global methanol extract, 23, 24-dihydrocucurbitacin F, aqueous extracts and prunasin against P-388 murine leukaemia, A-549 human lung carcinoma and HT-29 colon carcinoma. Since global methanol extract presented a strong cytotoxicity against P-388 murine leukaemia, A-549 human lung carcinoma, and HT-29 cell lines, it is highly probable that this extract contain one or more cytotoxic compounds that could be investigated for their potential use as an agent against cancer. 相似文献