全文获取类型
收费全文 | 67211篇 |
免费 | 5436篇 |
国内免费 | 5607篇 |
出版年
2024年 | 116篇 |
2023年 | 706篇 |
2022年 | 1796篇 |
2021年 | 3305篇 |
2020年 | 2209篇 |
2019年 | 2754篇 |
2018年 | 2690篇 |
2017年 | 2030篇 |
2016年 | 2740篇 |
2015年 | 4098篇 |
2014年 | 4884篇 |
2013年 | 5360篇 |
2012年 | 6201篇 |
2011年 | 5667篇 |
2010年 | 3568篇 |
2009年 | 3083篇 |
2008年 | 3815篇 |
2007年 | 3278篇 |
2006年 | 2904篇 |
2005年 | 2408篇 |
2004年 | 2196篇 |
2003年 | 1973篇 |
2002年 | 1773篇 |
2001年 | 1202篇 |
2000年 | 1017篇 |
1999年 | 943篇 |
1998年 | 623篇 |
1997年 | 557篇 |
1996年 | 548篇 |
1995年 | 514篇 |
1994年 | 438篇 |
1993年 | 327篇 |
1992年 | 462篇 |
1991年 | 326篇 |
1990年 | 270篇 |
1989年 | 282篇 |
1988年 | 175篇 |
1987年 | 178篇 |
1986年 | 138篇 |
1985年 | 142篇 |
1984年 | 72篇 |
1983年 | 65篇 |
1982年 | 63篇 |
1981年 | 33篇 |
1980年 | 35篇 |
1979年 | 38篇 |
1978年 | 20篇 |
1977年 | 26篇 |
1975年 | 20篇 |
1973年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 671 毫秒
51.
52.
Hanhan Liu Qiangqiang Jia Gianluca Tettamanti Sheng Li 《Insect biochemistry and molecular biology》2013,43(11):1068-1078
In the fruitfly, Drosophila melanogaster, autophagy and caspase activity function in parallel in the salivary gland during metamorphosis and in a common regulatory hierarchy during oogenesis. Both autophagy and caspase activity progressively increase in the remodeling fat body, and they are induced by a pulse of the molting hormone (20-hydroxyecdysone, 20E) during the larval-prepupal transition. Inhibition of autophagy and/or caspase activity in the remodeling fat body results in 25–40% pupal lethality, depending on the genotypes. Interestingly, a balancing crosstalk occurs between autophagy and caspase activity in this tissue: the inhibition of autophagy induces caspase activity and the inhibition of caspases induces autophagy. The Drosophila remodeling fat body provides an in vivo model for understanding the molecular mechanism of the balancing crosstalk between autophagy and caspase activity, which oppose with each other and are induced by the common stimulus 20E, and blockage of either path reinforces the other path. 相似文献
53.
54.
55.
Mingcheng Qian Xinyu Jiang Mingting Zhang Lijuan Hu Huimin Liu Shuai Zhao Xiaoying Zhou Xin Chen 《化学与生物多样性》2021,18(4):e2000979
In this article, we designed and synthesized two series of matrine analogs with ring-opening in the lactam portion of the molecule. Our in vitro cytotoxicity study showed that analog N-(3-bromophenyl)-4-[(1R,3aS,10aR,10bS)-decahydro-1H,4H-pyrido[3,2,1-ij][1,6]naphthyridin-1-yl]butanamide ( B11 ) with a meta-bromide on the phenyl ring displayed the best antiproliferative activity. Moreover, B11 induced cell cycle arrest in G1 phase and cell apoptosis in a dose-dependent manner in A549 cells. Molecular modeling revealed that B11 achieved a higher docking score compared to its precursor tert-butyl (1R,3aS,10aR,10bS)-1-[4-(3-bromoanilino)-4-oxobutyl]octahydro-1H,4H-pyrido[3,2,1-ij][1,6]naphthyridine-2(3H)-carboxylate ( A11 , an analog of B11 with a Boc group) and parent compound matrine, possibly because B11 formed a hydrogen bond with SER91 and a halogen bond with GLN320 on the binding site of annexin A2. Overall, we discovered the potential anticancer lead compound B11 , which can be used for further study both in vitro and in vivo. 相似文献
56.
This study was conducted to investigate the prevalence of cognitive impairment, depression, and comorbidity of the two conditions and related factors in subjects aged in early 60s. This cross-sectional study included 3,174 inhabitants aged 60–64 years old in a rural area of Korea. Cognitive function was evaluated by the Korean version of the Mini-Mental State Examination (MMSE-K), and depression was measured using the short form of the Geriatric Depression Scale (GDS-15). The overall prevalence of cognitive impairment (MMSE-K≤24) was 17.4%, that of depression was 26.0% (GDS-15≥8), and the co-morbidity was 7.1%. Female gender, living with one housemate, and high GDS-15 score were significantly associated with increased cognitive impairment. Employment status and more years of schooling were associated with a decreased probability of cognitive impairment. Increased depression was significantly associated with bereavement and receiving benefits from the Medical Aid Program. Employed status, more years of schooling, and higher MMSE-K scores were significantly associated with decreased depression. The risk of comorbidity was associated with bereavement and receipt of Medical Aid benefits (odds ratio[OR], 1.85; 95% confidence interval[CI], 1.26–2.71; OR, 5.02; 95% CI, 2.37–10.63; respectively). Employment and more years of schooling were associated with a lower risk of comorbidity (OR, 0.46; 95% CI, 0.34–0.62, P-trend <0.01). The correlated factors for cognitive impairment, depression, and comorbidity of the two conditions were similar, and employment status and years of schooling were associated with all three conditions. 相似文献
57.
58.
To overcome the high energy-consuming process of microalgae drying, a two-step lipase catalysis technique for the preparation of biodiesel from microalgae lipid of Chlorella spp. was developed. In the first step, free fatty acids (FAAs) and triacylglycerols (TAGs) are released after cell disruption and extracted, while the TAGs were hydrolysed by free lipase in aqueous phase. In the second step, FAAs were esterified with ethanol in the catalysis of free suspended lipase. The maximum rate of hydrolysis and esterification was 93.6% and 91.3%, respectively. The effects of reaction parameters, such as reaction time, enzyme amount, water content and molar ratio of lipid to ethanol on hydrolysis or esterification, were investigated. The results indicated that two-step reaction process (hydrolyse esterify) for biodiesel production were feasible. 相似文献
59.
60.