全文获取类型
收费全文 | 17117篇 |
免费 | 1473篇 |
国内免费 | 2篇 |
出版年
2023年 | 69篇 |
2022年 | 97篇 |
2021年 | 383篇 |
2020年 | 245篇 |
2019年 | 330篇 |
2018年 | 398篇 |
2017年 | 340篇 |
2016年 | 538篇 |
2015年 | 826篇 |
2014年 | 935篇 |
2013年 | 1042篇 |
2012年 | 1299篇 |
2011年 | 1190篇 |
2010年 | 754篇 |
2009年 | 693篇 |
2008年 | 1001篇 |
2007年 | 907篇 |
2006年 | 818篇 |
2005年 | 822篇 |
2004年 | 773篇 |
2003年 | 739篇 |
2002年 | 650篇 |
2001年 | 248篇 |
2000年 | 199篇 |
1999年 | 202篇 |
1998年 | 217篇 |
1997年 | 167篇 |
1996年 | 145篇 |
1995年 | 138篇 |
1994年 | 131篇 |
1993年 | 99篇 |
1992年 | 143篇 |
1991年 | 136篇 |
1990年 | 128篇 |
1989年 | 102篇 |
1988年 | 113篇 |
1987年 | 88篇 |
1986年 | 118篇 |
1985年 | 104篇 |
1984年 | 116篇 |
1983年 | 88篇 |
1982年 | 89篇 |
1981年 | 96篇 |
1980年 | 76篇 |
1979年 | 73篇 |
1978年 | 81篇 |
1977年 | 73篇 |
1975年 | 59篇 |
1974年 | 61篇 |
1973年 | 59篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Protein Kinase PKR Mediates the Apoptosis Induction and Growth Restriction Phenotypes of C Protein-Deficient Measles Virus 总被引:1,自引:0,他引:1 下载免费PDF全文
Ann M. Toth Patricia Devaux Roberto Cattaneo Charles E. Samuel 《Journal of virology》2009,83(2):961-968
The measles virus (MV) accessory proteins V and C play important roles in MV replication and pathogenesis. Infection with recombinant MV lacking either V or C causes more cell death than infection with the parental vaccine-equivalent virus (MVvac), and C-deficient virus grows poorly relative to the parental virus. Here, we show that a major effector of the C phenotype is the RNA-dependent protein kinase PKR. Using human HeLa cells stably deficient in PKR as a result of RNA interference-mediated knockdown (PKRkd cells), we demonstrated that a reduction in PKR partially rescued the growth defect of C knockout (Cko) virus but had no effect on the growth of either wild-type (WT) or V knockout (Vko) virus. Increased growth of the Cko virus in PKRkd cells correlated with increased viral protein expression, while defective growth and decreased protein expression in PKR-sufficient cells correlated with increased phosphorylation of PKR and the α subunit of eukaryotic initiation factor 2. Furthermore, infection with WT, Vko, or especially Cko virus caused significantly less apoptosis in PKRkd cells than in PKR-sufficient cells. Although apoptosis induced by Cko virus infection in PKR-sufficient cells was blocked by a caspase antagonist, the growth of Cko virus was not restored to the WT level by treatment with this pharmacologic inhibitor. Taken together, these results indicate that PKR plays an important antiviral role during MV infection but that the virus growth restriction by PKR is not dependent upon the induction of apoptosis. Furthermore, the results establish that a principal function of the MV C protein is to antagonize the proapoptotic and antiviral activities of PKR. 相似文献
2.
3.
4.
W Y Mok R C Luiz?o M do S Barreto da Silva 《Applied and environmental microbiology》1982,44(3):570-575
A total of 2,886 bats captured in the Amazon Basin of Brazil were processed for the isolation of fungi. From the livers, spleens, and lungs of 155 bats (5.4%), 186 fungal isolates of the genera Candida (123 isolates), Trichosporon (26 isolates), Torulopsis (25 isolates), Kluyveromyces (11 isolates), and Geotrichum (1 isolate) were recovered. Seven known pathogenic species were present: Candida parapsilosis, C. guilliermondii, C. albicans, C. stellatoidea, C. pseudotropicalis, Trichosporon beigelii, and Torulopsis glabrata. Twenty-three culture-positive bats showed identical fungal colonization in multiple organs or mixed colonization in a single organ. The fungal isolation rates for individual bat species varied from 1 fungus per 87 bats to 3 fungi per 13 bats, and the mycoflora diversity for members of an individual fungus-bearing bat species varied from 16 fungi per 40 bats to 7 fungi per 6 bats. Of the 38 fungal species isolated, 36 had not been previously described as in vivo bat isolates. Of the 27 culture-positive bat species, 21 had not been previously described as mammalian hosts for medically or nonmedically important fungi. 相似文献
5.
Maturity Onset Diabetes of the Young (MODY) is a heterogeneous group of genetic diseases characterized by a primary defect in insulin secretion and hyperglycemia, non-ketotic disease, monogenic autosomal dominant mode of inheritance, age at onset less than 25 years, and lack of auto-antibodies. It accounts for 2–5% of all cases of non-type 1 diabetes. MODY subtype 2 is caused by mutations in the glucokinase (GCK) gene. In this study, we sequenced the GCK gene of two volunteers with clinical diagnosis for MODY2 and we were able to identify four mutations including one for a premature stop codon (c.76C>T). Based on these results, we have developed a specific PCR-RFLP assay to detect this mutation and tested 122 related volunteers from the same family. This mutation in the GCK gene was detected in 21 additional subjects who also had the clinical features of this genetic disease. In conclusion, we identified new GCK gene mutations in a Brazilian family of Italian descendance, with one due to a premature stop codon located in the second exon of the gene. We also developed a specific assay that is fast, cheap and reliable to detect this mutation. Finally, we built a molecular ancestry model based on our results for the migration of individuals carrying this genetic mutation from Northern Italy to Brazil. 相似文献
6.
A review of in vitro mutagenesis assessment of metal compounds in mammalian and nonmammalian test systems has been compiled.
Prokaryotic assays are ineffective or inconsistent in their detection of most metals as mutagens, with the notable exception
of hexavalent chromium. Mammalian assay systems appear to be similarly inappropriate for the screening of metal compounds
based upon the limited number of studies that have employed those compounds having known carcinogenic activity. Although of
limited value as screening tests for the detection of potentially carcinogenic metal compounds, the well-characterized in
vitro mutagenesis systems may prove to be of significant value as a means to elucidate mechanisms of metal genotoxicity. 相似文献
7.
8.
Accumulation of the labdane diterpene Marrubiin in glandular trichome cells along the ontogeny of Marrubium vulgare plants 总被引:1,自引:0,他引:1
The content of the diterpene Marrubiin was assessed by GC-FID in leaves of Marrubium vulgare plants along their ontogeny. Maximum accumulation occurred just before flowering time and in fully expanded leaves. After
feeding the plants with radio labeled [3H]-geranyl geranyl diphosphate, up to 70% of the radioactivity was recovered in HPLC-Rt coincidental with authentic Marrubiin,
which was also characterized by GC-EIMS, thus confirming that the biosynthesis of Marrubiin proceeds through the 1-deoxy-D-xylulose-5-phosphate
pathway. The major accumulation of radioactivity occurred in glandular trichome cells, and the product remained stable throughout. 相似文献
9.
10.
A simple modification of nuclear staining after acid hydrolysis has been made which provides easy identification of quail nuclear markings in a chick-quail chimera. This method also improves the histologic detail normally seen with hematoxylin and eosin when compared to the more commonly used Feulgen reaction. Embryonic tissues can be fixed in Zenker's or Helly's solution and the sections obtained are hydrolyzed in acid (3.5 N HCl at 37 C for 40-50 min). After acid hydrolysis the sections are stained with hematoxylin and eosin rather than Schiff reagent and fast green. The interphase nuclei of chick cells show homogeneous or mottled purplish blue staining, while quail nuclei contain a dark blue spot. This staining corresponds to the reddish purple staining of the quail's heterochromatin seen adjacent to the nucleolus in the standard Feulgen stain. This new technique facilitates identification of quail cell types in the chick host and provides superior histology of the chick tissues by demonstrating cytoplasmic detail. 相似文献