全文获取类型
收费全文 | 3808篇 |
免费 | 341篇 |
国内免费 | 325篇 |
专业分类
4474篇 |
出版年
2024年 | 7篇 |
2023年 | 45篇 |
2022年 | 110篇 |
2021年 | 201篇 |
2020年 | 131篇 |
2019年 | 165篇 |
2018年 | 155篇 |
2017年 | 123篇 |
2016年 | 185篇 |
2015年 | 226篇 |
2014年 | 249篇 |
2013年 | 282篇 |
2012年 | 319篇 |
2011年 | 293篇 |
2010年 | 185篇 |
2009年 | 166篇 |
2008年 | 208篇 |
2007年 | 154篇 |
2006年 | 167篇 |
2005年 | 146篇 |
2004年 | 137篇 |
2003年 | 107篇 |
2002年 | 115篇 |
2001年 | 97篇 |
2000年 | 85篇 |
1999年 | 79篇 |
1998年 | 46篇 |
1997年 | 44篇 |
1996年 | 38篇 |
1995年 | 34篇 |
1994年 | 28篇 |
1993年 | 21篇 |
1992年 | 19篇 |
1991年 | 23篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 10篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有4474条查询结果,搜索用时 15 毫秒
51.
Xiaomin Tang Weidong Bao Wenli Zhang Zhukuan Cheng 《植物学报(英文版)》2007,49(6):953-960
To develop reliable techniques for chromosome identification is critical for cytogenetic research, especially for genomes with a large number and smaller-sized chromosomes. An efficient approach using bacterial artificial chromosome (BAC) clones as molecular cytological markers has been developed for many organisms. Herein, we present a set of chromosomal arm-specific molecular cytological markers derived from the gene-enriched regions of the sequenced rice genome. All these markers are able to generate very strong signals on the pachytene chromosomes of Oryza sativa L. (AA genome) when used as fluorescence in situ hybridization (FISH) probes. We further probed those markers to the pachytene chromosomes of O. punctata (BB genome) and O. officinalis (CC genome) and also got very strong signals on the relevant pachytene chromosomes. The signal position of each marker on the related chromosomes from the three different rice genomes was pretty much stable, which enabled us to identify different chromosomes among various rice genomes. We also constructed the karyotype for both O. punctata and O. officinalis with the BB and CC genomes, respectively, by analysis of 10 pachytene cells anchored by these chromosomal arm-specific markers. 相似文献
52.
53.
Ming‐Hui Qian Qiong‐Bo Hu Shun‐Xiang Ren Nasser S. Mandour Bao‐Li Qiu P. A. Stansly 《Insect Science》2012,19(3):403-411
Abstract Effects of sublethal piperonyl butoxide (PB) on parasitization of Bemisia tabaci (Gennadius ) (Hemiptera: Aleyrodidae) by Encarsia bimaculata Heraty et Polaszek (Hymenoptera: Aphelinidae) were evaluated both in cage and greenhouse experiments. When first, second and third instar B. tabaci nymphs were treated with PB, all but the first instar were significantly prolonged. Data indicated that sublethal PB could improve E. bimaculata parasitism rates without influencing parasitoid eclosion rates. Prolonged development increased rates of parasitism by E. bimaculata, from 17.6% to 24.7% in cages, presumably by increasing the duration of host exposure. Sublethal PB combined with E. bimaculata as an integrated approach to control B. tabaci was evaluated using life table parameters under greenhouse conditions. Indices of population trend (I) calculated from life tables were estimated at 4.6 for B. tabaci exposed to PB and parasitoids compared to 14.1 with parasitoids alone and 23.5 in untreated controls. The results showed that after PB was sprayed and parasitoids introduced, development of B. tabaci was delayed and the peak of each stage was postponed. The older nymphal stage had highest mortality, primarily due to mortality caused by parasitism by E. bimaculata. 相似文献
54.
[目的] 解析郫县豆瓣及其酿造半成品-蚕豆醅与辣椒醅微生物多样性和来源,探究郫县豆瓣酿造过程风味化合物特征。[方法] 采用高通量测序法测定蚕豆醅、辣椒醅与混合醅(蚕豆醅-辣椒醅混合物,发酵成熟形成郫县豆瓣)在酿造过程中的微生物群落结构;利用高效气相质谱与高效液相色谱高通量检测蚕豆醅及辣椒醅中基础理化指标及挥发性、非挥发性风味化合物浓度;利用多种生物信息学分析方法对混合醅酿造微生物及风味化合物进行溯源。[结果] 微生物方面:44%–59%的混合醅细菌来源于辣椒醅,5%–22%的混合醅细菌来源于蚕豆醅,其他混合醅细菌来源未知。同时,42%–77%的混合醅真菌来源于辣椒醅,2%–18%的混合醅真菌来源于蚕豆醅,其他混合醅真菌来源未知。另外,16个细菌属由辣椒醅特异性贡献;2个细菌属及2个真菌属由蚕豆醅特异性贡献。化合物方面:1-辛烯-3醇(1-octen-3-ol)、苯乙醛(phenylacetaldehyde)、异丁醛(isobutyraldehyde)、苹果酸(malic acid)与糠醛(furfural)仅由蚕豆醅贡献。辣椒素(capsaicin)、3-甲基-1-丁醇(3-methyl-1-butanol)、已醇(hexanol)与异丁醇(isobutanol)仅由辣椒醅贡献。[结论] 郫县豆瓣发酵中大部分微生物来源于辣椒醅,大部分发酵底物(氨基酸及葡萄糖)来源于蚕豆醅。两种发酵半成品均特异性贡献微生物及风味化合物,形成郫县豆瓣的独特风味密码。 相似文献
55.
Alzheimer''s disease (AD) is associated with abnormal functioning of the default mode network (DMN). Functional connectivity (FC) changes to the DMN have been found in patients with amnestic mild cognitive impairment (aMCI), which is the prodromal stage of AD. However, whether or not aMCI also alters the effective connectivity (EC) of the DMN remains unknown. We employed a combined group independent component analysis (ICA) and Bayesian network (BN) learning approach to resting-state functional MRI (fMRI) data from 17 aMCI patients and 17 controls, in order to establish the EC pattern of DMN, and to evaluate changes occurring in aMCI. BN analysis demonstrated heterogeneous regional convergence degree across DMN regions, which were organized into two closely interacting subsystems. Compared to controls, the aMCI group showed altered directed connectivity weights between DMN regions in the fronto-parietal, temporo-frontal, and temporo-parietal pathways. The aMCI group also exhibited altered regional convergence degree in the right inferior parietal lobule. Moreover, we found EC changes in DMN regions in aMCI were correlated with regional FC levels, and the connectivity metrics were associated with patients'' cognitive performance. This study provides novel sights into our understanding of the functional architecture of the DMN and adds to a growing body of work demonstrating the importance of the DMN as a mechanism of aMCI. 相似文献
56.
Zhang J Bao S Furumai R Kucera KS Ali A Dean NM Wang XF 《Molecular and cellular biology》2005,25(22):9910-9919
In response to DNA damage or replication stress, the protein kinase ATR is activated and subsequently transduces genotoxic signals to cell cycle control and DNA repair machinery through phosphorylation of a number of downstream substrates. Very little is known about the molecular mechanism by which ATR is activated in response to genotoxic insults. In this report, we demonstrate that protein phosphatase 5 (PP5) is required for the ATR-mediated checkpoint activation. PP5 forms a complex with ATR in a genotoxic stress-inducible manner. Interference with the expression or the activity of PP5 leads to impairment of the ATR-mediated phosphorylation of hRad17 and Chk1 after UV or hydroxyurea treatment. Similar results are obtained in ATM-deficient cells, suggesting that the observed defect in checkpoint signaling is the consequence of impaired functional interaction between ATR and PP5. In cells exposed to UV irradiation, PP5 is required to elicit an appropriate S-phase checkpoint response. In addition, loss of PP5 leads to premature mitosis after hydroxyurea treatment. Interestingly, reduced PP5 activity exerts differential effects on the formation of intranuclear foci by ATR and replication protein A, implicating a functional role for PP5 in a specific stage of the checkpoint signaling pathway. Taken together, our results suggest that PP5 plays a critical role in the ATR-mediated checkpoint activation. 相似文献
57.
58.
59.
Wei Cao Li Zhang David B Rosen Laura Bover Gokuran Watanabe Musheng Bao Lewis L Lanier Yong-Jun Liu 《PLoS biology》2007,5(10)
Dendritic cells are equipped with lectin receptors to sense the extracellular environment and modulate cellular responses. Human plasmacytoid dendritic cells (pDCs) uniquely express blood dendritic cell antigen 2 (BDCA2) protein, a C-type lectin lacking an identifiable signaling motif. We demonstrate here that BDCA2 forms a complex with the transmembrane adapter FcɛRIγ. Through pathway analysis, we identified a comprehensive signaling machinery in human pDCs, similar to that which operates downstream of the B cell receptor (BCR), which is distinct from the system involved in T cell receptor (TCR) signaling. BDCA2 crosslinking resulted in the activation of the BCR-like cascade, which potently suppressed the ability of pDCs to produce type I interferon and other cytokines in response to Toll-like receptor ligands. Therefore, by associating with FcɛRIγ, BDCA2 activates a novel BCR-like signaling pathway to regulate the immune functions of pDCs. 相似文献
60.
野大豆叶绿体在低温(77K)时出现三条荧光发射谱带,它们来源于不同的色素蛋白复合体。 在纳秒脉冲激光激发下,捕光天线色素的相对荧光量子产额,随激光强度的增加有明显下降现象。用激子理论和动力学方程讨论和计算了激子扩散参量。指出激子转移是随机的,非相干的。 相似文献