全文获取类型
收费全文 | 8870篇 |
免费 | 640篇 |
国内免费 | 460篇 |
出版年
2024年 | 8篇 |
2023年 | 72篇 |
2022年 | 80篇 |
2021年 | 321篇 |
2020年 | 230篇 |
2019年 | 265篇 |
2018年 | 282篇 |
2017年 | 231篇 |
2016年 | 320篇 |
2015年 | 461篇 |
2014年 | 578篇 |
2013年 | 638篇 |
2012年 | 739篇 |
2011年 | 703篇 |
2010年 | 413篇 |
2009年 | 371篇 |
2008年 | 424篇 |
2007年 | 416篇 |
2006年 | 367篇 |
2005年 | 359篇 |
2004年 | 292篇 |
2003年 | 299篇 |
2002年 | 241篇 |
2001年 | 195篇 |
2000年 | 193篇 |
1999年 | 162篇 |
1998年 | 108篇 |
1997年 | 102篇 |
1996年 | 104篇 |
1995年 | 101篇 |
1994年 | 78篇 |
1993年 | 78篇 |
1992年 | 127篇 |
1991年 | 101篇 |
1990年 | 72篇 |
1989年 | 72篇 |
1988年 | 66篇 |
1987年 | 49篇 |
1986年 | 41篇 |
1985年 | 53篇 |
1984年 | 33篇 |
1983年 | 24篇 |
1982年 | 19篇 |
1981年 | 10篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1971年 | 7篇 |
1970年 | 7篇 |
1966年 | 7篇 |
排序方式: 共有9970条查询结果,搜索用时 156 毫秒
991.
Previously, we reported that Phe105 in transmembrane domain 2 of the mouse dopamine transporter (DAT) is crucial for high-affinity cocaine binding. In the current study, we investigated whether other residues surrounding Phe105 also affect the potency of cocaine inhibition. After three rounds of sequential random mutagenesis at these residues, we found a triple mutant (L104V, F105C and A109V) of mouse DAT that retained over 50% uptake activity and was 69-fold less sensitive to cocaine inhibition when compared with the wild-type mouse DAT. The triple mutation also resulted in a 47-fold decrease in sensitivity to methylphenidate inhibition, suggesting that the binding sites for cocaine and methylphenidate may overlap. In contrast, the inhibition of dopamine uptake by amphetamine or methamphetamine was not significantly changed by the mutations, suggesting that the binding sites for the amphetamines differ from those for cocaine and methylphenidate. Such functional but cocaine-insensitive DAT mutants can be used to generate a knock-in mouse line to study the role of DAT in cocaine addiction. 相似文献
992.
Ji Q Lu J Chao Q Gu M Xu M 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2005,111(8):1495-1503
Wide-compatibility (WC) is one of the most important traits in rice, which can overcome the fertility barrier in the indica/japonica hybrids, and hence to make it possible to utilize the higher yield potential of inter-subspecific hybrids. The S
5
n
gene located on chromosome 6 has been previously reported to be responsible for the wide-compatibility in rice. Here we report
the precise location of the S
5
n
gene. In the first-pass mapping, the S
5
n
gene was restricted within a 200 kb region by using a population of 242 isogenic lines in combination with high-density markers
developed in the S
5 region. In the fine mapping, the S
5 region was further saturated with newly developed markers and more isogenic lines (549 in total) were investigated. Eventually,
the S
5
n
gene was mapped within a 50 kb region delimited by the left marker J13 and the right marker J17. One BAC clone screened from
the BAC library of the WC rice variety 02428 covered the whole S
5 region. Sequence analysis of the 50 kb region revealed two candidate genes, coding an aspartyl protease and a hypothetical
protein. This result would greatly accelerate both cloning and marker-assisted selection of this important S
5
n
gene.
Qing Ji and Jufei Lu have contributed equally to this paper. 相似文献
993.
Lerceteau-Köhler E Guérin G Denoyes-Rothan B 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2005,111(5):862-870
Bulked segregant analysis combined with AFLPs was used to identify molecular markers linked to the Rca2 gene conferring resistance to Colletotrichum acutatum pathogenicity group 2 which causes anthracnose in the octoploid strawberry Fragaria × ananassa. DNA bulks originating from a cross between the resistant cultivar ‘Capitola’ and the susceptible cultivar ‘Pajaro’ were
screened with 110 EcoRI/MseI AFLP combinations. Four AFLP markers were found linked in coupling phase to Rca2 with recombination percentages between 0% and 17.7%. Among the four markers linked to the resistance gene, two were converted
into SCAR markers (STS-Rca2_417 and STS-Rca2_240) and screened in a large segregating population including 179 genotypes.
The Rca2 resistance gene was estimated to be 0.6 cM from STS-Rca2_417 and 2.8 cM from STS-Rca2_240. The presence/absence of the two
SCAR markers was further studied in 43 cultivars of F. × ananassa, including 14 susceptible, 28 resistant, and one intermediate genotype. Results showed that 81.4% and 62.8% of the resistant/susceptible
genotypes were correctly predicted by using STS-Rca2_417 and STS-Rca2_240, respectively. The 14 susceptible genotypes showed
no amplification for either SCARs. These developed SCARs constitute new tools for indirect selection criteria of anthracnose
resistance genotypes in strawberry breeding programs. 相似文献
994.
Removal of a selectable marker gene from genetically modified (GM) crops alleviates the risk of its release into the environment and hastens the public acceptance of GM crops. Here we report the production of marker-free transgenic rice by using a chemically regulated, Cre/loxP-mediated site-specific DNA recombination in a single transformation. Among 86 independent transgenic lines, ten were found to be marker-free in the T0 generation and an additional 17 lines segregated marker-free transgenic plants in the T1 generation. Molecular and genetic analyses indicated that the DNA recombination and excision in transgenic rice were precise and the marker-free recombinant T-DNA was stable and heritable.The first two authors contributed equally to the work 相似文献
995.
In this paper, several different procedures for constructing confidence regions for the true evolutionary tree are evaluated both in terms of coverage and size without considering model misspecification. The regions are constructed on the basis of tests of hypothesis using six existing tests: Shimodaira Hasegawa (SH), SOWH, star form of SOWH (SSOWH), approximately unbiased (AU), likelihood weight (LW), generalized least squares, plus two new tests proposed in this paper: single distribution nonparametric bootstrap (SDNB) and single distribution parametric bootstrap (SDPB). The procedures are evaluated on simulated trees both with small and large number of taxa. Overall, the SH, SSOWH, AU, and LW tests led to regions with higher coverage than the nominal level at the price of including large numbers of trees. Under the specified model, the SOWH test gives accurate coverage and relatively small regions. The SDNB and SDPB tests led to the small regions with occasional undercoverage. These two procedures have a substantial computational advantage over the SOWH test. Finally, the cutoff levels for the SDNB test are shown to be more variable than those for the SDPB test. 相似文献
996.
A cDNA of 417 bp encoding an S-RNase gene, named PA S3, was isolated from apricot, Prunus aremeniaca. Nine S-alleles, S1–S9, were recognized by S-allele-specific PCR and confirmed by Southern blot analysis using PA S3 as probe. The S-genotypes of the six cultivars were determined and the results of self- and cross-pollination tests among the six cultivars were consistent with the predicted S-haplotypes by PCR analysis. 相似文献
997.
Ahn NS Hu H Park JS Park JS Kim JS An S Kong G Aruoma OI Lee YS Kang KS 《Mutation research》2005,579(1-2):189-199
Although 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has a variety of carcinogenic and noncarcinogenic effects in experimental animals, its role in human carcinogenicity remain controversial. A simian virus 40-immortalized cell line from normal human breast epithelial cells with stem cells and luminal characteristics (M13SV1) was used to study whether TCDD can induce AIG positive colony formation and cause increased cell numbers in a inverted U-shaped dose–response manner. TCDD activated Akt, ERK2, and increased the expression of CYP1A1, PAI-2, IL-lb mRNA, and ERK2 protein levels. TCDD was able to increased phosphorylation and expression of ERK2 in same dose–response manner as AIG positive colony formation. Thus, TCDD induced tumorigenicity in M13SV1, possibly through the phosphorylation of ERK2 and/or Akt. Further, cDNA microarray with 7448 sequence-verified clones was used to profile various gene expression patterns after treatment of TCDD. Three clear patterns could be delineated: genes that were dose-dependently up-regulated, genes expressed in either U-shape and/or inverted U-shape. The fact that these genes are intrinsically related to breast epithelial cell proliferation and survival clearly suggests that they may be involved in the TCDD-induced breast tumorigenesis. 相似文献
998.
Analysis of the plant architecture via tree-structured statistical models: the hidden Markov tree models 总被引:1,自引:0,他引:1
Plant architecture is the result of repetitions that occur through growth and branching processes. During plant ontogeny, changes in the morphological characteristics of plant entities are interpreted as the indirect translation of different physiological states of the meristems. Thus connected entities can exhibit either similar or very contrasted characteristics. We propose a statistical model to reveal and characterize homogeneous zones and transitions between zones within tree-structured data: the hidden Markov tree (HMT) model. This model leads to a clustering of the entities into classes sharing the same 'hidden state'. The application of the HMT model to two plant sets (apple trees and bush willows), measured at annual shoot scale, highlights ordered states defined by different morphological characteristics. The model provides a synthetic overview of state locations, pointing out homogeneous zones or ruptures. It also illustrates where within branching structures, and when during plant ontogeny, morphological changes occur. However, the labelling exhibits some patterns that cannot be described by the model parameters. Some of these limitations are addressed by two alternative HMT families. 相似文献
999.
Headspace volatiles from apple-bearing twigs were collected in the field with a Radiello sampler during three different diurnal periods over the complete fruit growing season. Analyses by thermal desorption-GC-MS identified a total of 62 compounds in changing quantities, including the terpenoids alpha-pinene, camphene, beta-pinene, limonene, beta-caryophyllene and (E,E)-alpha-farnesene, the aldehydes (E)-2-hexenal, benzaldehyde and nonanal, and the alcohol (Z)-3-hexen-1-ol. The variations in emission of these plant odours were statistically related to temperature, humidity and rainfall in the field. Remarkably, rainfall had a significant positive influence on changes in volatile release during all three diurnal periods, and further factors of significance were temperature and relative humidity around noon, relative humidity in the late afternoon, and temperature and relative humidity during the night. Rainfall was associated consistently with an increase in the late afternoon in terpene and aldehyde volatiles with a known repellent effect on the codling moth, one of the key pests of apple fruit. During the summer of 2003, a season characterized by below-average rainfall, some postulated effects of drought on trees were tested by establishing correlations with rainfall. Emissions of the wood terpenes alpha-pinene, beta-pinene and limonene were negatively correlated with rainfall. Another monoterpene, camphene, was only detected in this summer but not in the previous years, and its emissions were negatively correlated with rainfall, further supporting the theory that drought can result in higher formation of secondary metabolites. Finally, the two green leaf volatiles (E)-2-hexenal and (Z)-3-hexen-1-ol were negatively correlated with rainfall, coinciding well with the expectation that water deficit stress increases activity of lipoxygenase. To our knowledge, this work represents the first empirical study concerning the influence of abiotic factors on volatile emissions from apple trees in situ. 相似文献
1000.
INTRODUCTIONCytokinesis is a very complicated and carefully orches-trated process. During the last step of this process, anintercellular bridge is formed between the two daughtercells. A number of studies suggest that this intercellularbridge is not merel… 相似文献