全文获取类型
收费全文 | 3696篇 |
免费 | 192篇 |
专业分类
3888篇 |
出版年
2021年 | 30篇 |
2020年 | 22篇 |
2019年 | 35篇 |
2018年 | 72篇 |
2017年 | 65篇 |
2016年 | 81篇 |
2015年 | 85篇 |
2014年 | 98篇 |
2013年 | 141篇 |
2012年 | 212篇 |
2011年 | 219篇 |
2010年 | 140篇 |
2009年 | 85篇 |
2008年 | 203篇 |
2007年 | 175篇 |
2006年 | 214篇 |
2005年 | 167篇 |
2004年 | 150篇 |
2003年 | 153篇 |
2002年 | 154篇 |
2001年 | 91篇 |
2000年 | 80篇 |
1999年 | 60篇 |
1998年 | 32篇 |
1997年 | 25篇 |
1996年 | 33篇 |
1995年 | 25篇 |
1994年 | 31篇 |
1993年 | 30篇 |
1992年 | 27篇 |
1991年 | 27篇 |
1990年 | 29篇 |
1989年 | 24篇 |
1988年 | 23篇 |
1987年 | 21篇 |
1986年 | 24篇 |
1985年 | 26篇 |
1984年 | 36篇 |
1983年 | 27篇 |
1982年 | 49篇 |
1981年 | 31篇 |
1979年 | 26篇 |
1978年 | 28篇 |
1977年 | 22篇 |
1976年 | 27篇 |
1975年 | 30篇 |
1974年 | 45篇 |
1973年 | 31篇 |
1972年 | 26篇 |
1968年 | 22篇 |
排序方式: 共有3888条查询结果,搜索用时 0 毫秒
41.
Martina Kyselková Jiří Janata Markéta Ságová-Marečková Jan Kopecký 《Archives of microbiology》2010,192(3):195-200
In acetohydroxy acid synthase from Streptomyces cinnamonensis mutants affected in valine regulation, the impact of mutations on interactions between the catalytic and the regulatory subunits
was examined using yeast two-hybrid system. Mutations in the catalytic and the regulatory subunits were projected into homology
models of the respective proteins. Two changes in the catalytic subunit, E139A (α domain) and ΔQ217 (β domain), both located
on the surface of the catalytic subunit dimer, lowered the interaction with the regulatory subunit. Three consecutive changes
in the N-terminal part of the regulatory subunit were examined. Changes G16D and V17D in a loop and adjacent α-helix of ACT
domain affected the interaction considerably, indicating that this region might be in contact with the catalytic subunit during
allosteric regulation. In contrast, the adjacent mutation L18F did not influence the interaction at all. Thus, L18 might participate
in valine binding or conformational change transfer within the regulatory subunits. Shortening of the regulatory subunit to
107 residues reduced the interaction essentially, suggesting that the C-terminal part of the regulatory subunit is also important
for the catalytic subunit binding. 相似文献
42.
43.
Snábel V D'Amelio S Mathiopoulos K Turceková L Dubinský P 《Journal of helminthology》2000,74(2):177-181
Variability in Echinococcus granulosus is very important epidemiologically since strain characteristics may influence local patterns of transmission of hydatid disease. To classify the genotype presented in pig protoscoleces of the Slovak territory, a DNA-based approach has been used. Nucleotide sequences for a 471 bp region of the mitochondrial NADH dehydrogenase 1 (ND1) gene revealed a substantial affinity of isolates examined to the G7 genotype. Only a 0.9-3.4% sequence variation was recorded for E. granulosus samples compared with the reference G7 variant. To distinguish between G7 and G9 genotypes not differing in ND1 sequences, isolates were additionally examined by PCR-RFLP analysis of the nuclear ITS1 region. The resulting two-banded pattern is characteristic for the G7 strain. The data presented thus provides the first explicit evidence of the G7 genotype in the Slovak region. 相似文献
44.
Irena Kolouchová Olga Schreiberová Jan Masák Karel Sigler Tomá? ?ezanka 《Folia microbiologica》2012,57(6):473-483
We used reversed phase liquid chromatography?Celectrospray ionization tandem mass spectrometry for direct analysis of mycolic acids (MAs) from four different cultivations of Rhodococcus erythropolis. This technique enabled us to identify and quantify the specific molecular species of MAs directly from lipid extracts of the bacterium, including the determination of their basic characteristics such as retention time and mass spectra. We identified a total of 60 molecular species of MAs by means of LC/MS. In collision-induced dissociation tandem mass spectrometry, the [M-H]? ions eliminated two residues, i.e., meroaldehyde and carboxylate anions containing ??-alkyl chains. The structural information from these fragment ions affords structural assignment of the mycolic acids, including the lengths and number of double bond(s). Two strains, i.e., R. erythropolis CCM 2595 and genetically modified strain CCM 2595 pSRK 21 phe were cultivated on two different substrates (phenol and phenol with addition of humic acids as a sole carbon source). The addition of humic acids showed that there is a marked increase of unsaturated mycolic acids, mostly in the range of 20?C100?%. This effect is more pronounced in the R. erythropolis CCM 2595 strain. 相似文献
45.
46.
47.
Zdenka Otýpková Milan Chytrý Lubomír Tichý Vilém Pechanec Jan W. Jongepier Ondřej Hájek 《Biologia》2011,66(2):266-274
The flora of the White Carpathians, a mountain range in the south-east of the Czech Republic, is documented by about 485,000
records of vascular plant occurrences collected since the mid-19th century. A total of 1299 species recorded in 93 grid cells of 2.8 × 3.1 km were used for an analysis of spatial patterns
of floristic diversity in the White Carpathians. Multivariate statistical techniques such as ordination and classification
were used to reveal the main gradients in floristic composition and species richness, and measured environmental data and
Ellenberg indicator values were used to assess underlying environmental factors. There is a striking floristic contrast between
the western and eastern part of the study area, which is associated with differences in climate, mean altitude, topographic
heterogeneity measured as altitudinal range, and land use. The western part is characterised by thermophilous, continental
and calcicolous species of open habitats. In contrast, the more forested eastern part along the state border with Slovakia
and the north-eastern part of the area are characterised by acidophilous species with higher moisture requirements. This pattern
is consistent with the established phytogeographical division of the Czech Republic into the phytogeographical regions of
Thermophyticum and Mesophyticum. The further division of the area into four regions, based on classified grid data, is also
similar to the current division into phytogeographical districts, except for the Javorníky district. There are two distinct
hot spots of species richness, in the western and the extreme north-eastern part. A poorer flora was found in landscapes with
intensive agriculture. Species richness is associated with different environmental factors than species composition, namely
with soil types and land-use categories. Alien species are more common in areas with a higher incidence of arable land and
built-up areas, and less common in areas dominated by grasslands and forests. 相似文献
48.
49.
Serological data identify a single major histocompatibility complex (MHC) class I locus in cattle. Molecular data, however, demonstrate the presence of at least two cattle MHC (BoLA) class I loci. To investigate the number of transcribed BoLA class I genes, we amplified cattle cDNA by using a single MHC class I-specific primer that hybridized to a conserved region of exon 4 and a non-specific 3 primer. Six BoLA class I cDNAs have been cloned and sequenced from a Bos taurus bull heterozygous for BoLA class I serological antigens, demonstrating the presence of a minimum of three loci. Sequence comparisons suggested that one of these cDNAs may be an unexpressed allele or the product of a nonclassical locus.The nucleotide sequence data reported in this paper have been submitted to the GenBank nucleotide sequence database and have been assigned the accession numbers U01186 and U01187. 相似文献
50.
Luis?Sánchez-PulidoEmail author Ana?M?Rojas Karel?H?van Wely Carlos?Martinez-A Alfonso?Valencia 《BMC bioinformatics》2004,5(1):91