全文获取类型
收费全文 | 38036篇 |
免费 | 3160篇 |
国内免费 | 2747篇 |
出版年
2024年 | 14篇 |
2023年 | 437篇 |
2022年 | 523篇 |
2021年 | 2031篇 |
2020年 | 1355篇 |
2019年 | 1712篇 |
2018年 | 1722篇 |
2017年 | 1175篇 |
2016年 | 1646篇 |
2015年 | 2404篇 |
2014年 | 2831篇 |
2013年 | 3072篇 |
2012年 | 3575篇 |
2011年 | 3166篇 |
2010年 | 1991篇 |
2009年 | 1618篇 |
2008年 | 1969篇 |
2007年 | 1721篇 |
2006年 | 1587篇 |
2005年 | 1288篇 |
2004年 | 1055篇 |
2003年 | 911篇 |
2002年 | 758篇 |
2001年 | 665篇 |
2000年 | 591篇 |
1999年 | 622篇 |
1998年 | 348篇 |
1997年 | 358篇 |
1996年 | 337篇 |
1995年 | 318篇 |
1994年 | 333篇 |
1993年 | 263篇 |
1992年 | 311篇 |
1991年 | 241篇 |
1990年 | 214篇 |
1989年 | 190篇 |
1988年 | 128篇 |
1987年 | 101篇 |
1986年 | 92篇 |
1985年 | 86篇 |
1984年 | 59篇 |
1983年 | 53篇 |
1982年 | 34篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 12篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1968年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Jian‐Yong Guo Yong‐Sheng Wang Tian Chen Xiao‐Xu Jiang Ping Wu Tao Geng Zhong‐Hua Pan Meng‐Ke Shang Cheng‐Xiang Hou Kun Gao Xi‐Jie Guo 《Insect Science》2020,27(3):449-462
Bombyx mori cytoplasmic polyhedrosis virus (BmCPV) is a major pathogen of the economic insect silkworm, Bombyx mori. Virus‐encoded microRNAs (miRNAs) have been proven to play important roles in host–pathogen interactions. In this study we identified a BmCPV‐derived miRNA‐like 21 nt small RNA, BmCPV‐miR‐1, from the small RNA deep sequencing of BmCPV‐infected silkworm larvae by stem‐loop quantitative real‐time PCR (qPCR) and investigated its functions with qPCR and lentiviral expression systems. Bombyx mori inhibitor of apoptosis protein (BmIAP) gene was predicted by both target prediction software miRanda and Targetscan to be one of its target genes with a binding site for BmCPV‐miR‐1 at the 5′ untranslated region. It was found that the expression of BmCPV‐miR‐1 and its target gene BmIAP were both up‐regulated in BmCPV‐infected larvae. At the same time, it was confirmed that BmCPV‐miR‐1 could up‐regulate the expression of BmIAP gene in HEK293T cells with lentiviral expression systems and in BmN cells by transfecting mimics. Furthermore, BmCPV‐miR‐1 mimics could up‐regulate the expression level of BmIAP gene in midgut and fat body in the silkworm. In the midgut of BmCPV‐infected larvae, BmCPV‐miR‐1 mimics could be further up‐regulated and inhibitors could lower the virus‐mediated expression of BmIAP gene. With the viral genomic RNA segments S1 and S10 as indicators, BmCPV‐miR‐1 mimics could up‐regulate and inhibitors down‐regulate their replication in the infected silkworm. These results implied that BmCPV‐miR‐1 could inhibit cell apoptosis in the infected silkworm through up‐regulating BmIAP expression, providing the virus with a better cell circumstance for its replication. 相似文献
52.
Identification of two clip domain serine proteases involved in the pea aphid's defense against bacterial and fungal infection 总被引:1,自引:0,他引:1
Phenoloxidases (POs) are required for the pea aphid's defense against bacterial and fungal infection. Prophenoloxidases (PPOs) are proteolytically converted to its active form PO through a clip domain serine protease cascade. In this study, we identified five clip domain serine proteases in the pea aphids. The messenger RNA levels of two of them, Ap_SPLP and Ap_VP, were upregulated by Gram‐positive bacterium Staphylococcus aureus and fungus Beauveria bassiana infections. Double‐stranded RNA‐based expression knockdown of these two genes resulted in reduced PO activity of the aphid hemolymph, higher loads of S. aureus and B. bassiana in the aphids, and lower survival rates of the aphids after infections. Our data suggest that Ap_SPLP and Ap_VP are involved in PPO activation pathway in the pea aphid. 相似文献
53.
When bone marrow cells were treated with an H2-receptor agonist (4-methylhistamine 10(-8) M) before treatment with hydroxyurea (10(-3) M), the suicide rate of spleen colony-forming units (CFU-s) as a whole rose significantly. The rabbit antimouse brain serum (RAMBS)-resistant CFU-s subpopulation was also significantly elevated. Prior treatment of bone marrow cells with cimetidine would prevent this effect of 4-methylhistamine (4-MH). These findings not only confirm that 4-MH can trigger mouse bone marrow CFU-s to enter a DNA synthetic phase of the cell cycle, but also suggest that the RAMBS-resistant CFU-s subpopulation is more sensitive to the effect of 4-MH. Furthermore, this suggests that concentrations of the histamine receptor change during the developmental process of CFU-s. 相似文献
54.
55.
56.
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
57.
Current challenges in embryonic-stem cell (ESC) research include the inability of sustaining and culturing of undifferentiated ESCs over time. Growth-arrested feeder cells are essential to the culture and sustaining of undifferentiated ESCs, and they are currently prepared using gamma-radiation and chemical inactivation. Both techniques have severe limitations. In this study, we developed a new, simple and effective technique (pulsed electric fields, PEFs) to produce viable growth-arrested cells (RTS34st) and used them as high-quality feeder cells to culture and sustain undifferentiated zebrafish ESCs over time. The cells were exposed to 25 sequential 10-ns electric pulses (10nsEPs) of 25, 40 and 150 kV/cm with 1-s pulse interval, or 2 sequential 50-μs electric pulses (50μsEPs) of 2.83, 1.78 and 0.78 kV/cm with 5-s pulse interval, respectively. We found that the cellular effects of PEFs depended directly upon the duration, number and electric field strength of the pulses, showing the feasibility of tuning them to produce various types of growth-arrested cells for culturing undifferentiated ESCs. Both 10nsEPs of 40 kV/cm produced by a 10nsEP generator and 50μsEPs of 1.78 kV/cm provided by inexpensive and widely available conventional electroporators, generated high-quality growth-arrested feeder cells for proliferation of undifferentiated ESCs over time. PEFs can therefore be used to replace radiation and chemical inactivation methods for preparation of growth-arrested feeder cells for advancing ESC research. 相似文献
58.
Octopus minor (Sasaki, 1920) is an important economic fishery resource in China. In order to explore the stock information and the phylogeographic status of O. minor, mitochondrial DNA cytochrome c oxidase subunit I (COI, 565?bp) and 16S rRNA (493?bp) genes were amplified from 11 different sampling locations. Genetic diversity evaluated by haplotypic and nucleotidic diversity implied high diversity in Lianjiang, and relatively low diversity in Rongcheng, which suggests that effective measures to protect the O. minor resource in this area are urgently required. Private haplotypes and remarkable higher pairwise ΦST in Yilan are responsible for the deep genetic divergence between Yilan and the 10 other populations. Haplotypes networks and two clusters’ topological structure also support the distinct subgroups (lineages A and lineages B), which apparently possess smaller genetic variation than mean interspecies distance. Taiwan island and its strait may act as a natural barrier that restricts the gene flow from the mainland. Deep genetic divergence between mainland and Taiwanese east coasts suggests different genetic stock, indicating that different management strategies are required. 相似文献
59.
Chong Gang-Gang Huang Xiao-Jun Di Jun-Hua Xu Dao-Zhu He Yu-Cai Pei Ya-Nan Tang Ya-Jie Ma Cui-Luan 《Bioprocess and biosystems engineering》2018,41(4):501-510
Bioprocess and Biosystems Engineering - Based on the Prussian blue spectrophotometric method, one high-throughput screening strategy for screening lignin-degrading microorganisms was built on... 相似文献
60.
Xinyao Zhu Srdjan Cirovic Aliah Shaheen Wei Xu 《Biomechanics and modeling in mechanobiology》2018,17(3):665-674
In this study, atomic force microscopy (AFM) is used to investigate the alterations of the poroelastic properties of hepatocellular carcinoma (SMMC-7721) cells treated with fullerenol. The SMMC-7721 cells were subject to AFM-based creep tests, and a corresponding poroelastic indentation model was used to determine the poroelastic parameters by curve fitting. Comparative analyses indicated that the both permeability and diffusion of fullerenol-treated cells increased significantly while their elastic modulus decreased by a small amount. From the change in the trend of the determined parameter, we verified the corresponding alternations of cytoskeleton (mainly filaments actin), which was reported by the previous study using confocal imaging method. Our investigation on SMMC-7721 cell reveals that the poroelastic properties could provide a better understanding how the cancer cells are affected by fullerenol or potentially other drugs which could find possible applications in drug efficacy test, cancer diagnosis and secure therapies. 相似文献