全文获取类型
收费全文 | 11634篇 |
免费 | 1102篇 |
国内免费 | 1750篇 |
出版年
2024年 | 29篇 |
2023年 | 188篇 |
2022年 | 361篇 |
2021年 | 614篇 |
2020年 | 457篇 |
2019年 | 550篇 |
2018年 | 543篇 |
2017年 | 418篇 |
2016年 | 524篇 |
2015年 | 746篇 |
2014年 | 955篇 |
2013年 | 962篇 |
2012年 | 1153篇 |
2011年 | 1041篇 |
2010年 | 653篇 |
2009年 | 599篇 |
2008年 | 691篇 |
2007年 | 592篇 |
2006年 | 593篇 |
2005年 | 424篇 |
2004年 | 373篇 |
2003年 | 323篇 |
2002年 | 243篇 |
2001年 | 122篇 |
2000年 | 123篇 |
1999年 | 91篇 |
1998年 | 102篇 |
1997年 | 69篇 |
1996年 | 69篇 |
1995年 | 56篇 |
1994年 | 56篇 |
1993年 | 40篇 |
1992年 | 62篇 |
1991年 | 45篇 |
1990年 | 54篇 |
1989年 | 44篇 |
1988年 | 34篇 |
1987年 | 29篇 |
1986年 | 29篇 |
1985年 | 33篇 |
1984年 | 46篇 |
1983年 | 30篇 |
1982年 | 34篇 |
1981年 | 42篇 |
1980年 | 24篇 |
1979年 | 24篇 |
1978年 | 20篇 |
1977年 | 23篇 |
1975年 | 23篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
995.
Yanting Dong Xiuwei Wang Jianlin Zhang Zhen Guan Lin Xu Jianhua Wang Ting Zhang Bo Niu 《Molecular and cellular biochemistry》2015,398(1-2):223-231
The causal metabolic pathway and the underlying mechanism between folate deficiency and neural tube defects (NTDs) remain obscure. Thymidylate (dTMP) is catalyzed by thymidylate synthase (TS) using the folate-derived one-carbon unit as the sole methyl donor. This study aims to examine the role of dTMP biosynthesis in the development of neural tube in mice by inhibition of TS via a specific inhibitor, raltitrexed (RTX). Pregnant mice were intraperitoneally injected with various doses of RTX on gestational day 7.5, and embryos were examined for the presence of NTDs on gestational day 11.5. TS activity and changes of dUMP and dTMP levels were measured following RTX treatment at the optimal dose. DNA damage was determined by detection of phosphorylated replication protein A2 (RPA2) and γ-H2AX in embryos with NTDs induced by RTX. Besides, apoptosis and proliferation were also analyzed in RTX-treated embryos with NTDs. We found that NTDs were highly occurred by the treatment of RTX at the optimal dose of 11.5 mg/kg b/w. RTX treatment significantly inhibited TS activity. Meanwhile, dTMP was decreased associated with the accumulation of dUMP in RTX-treated embryos. Phosphorylated RPA2 and γ-H2AX were significantly increased in RTX-treated embryos with NTDs compared to control. More apoptosis and decreased proliferation were also found in embryos with NTDs induced by RTX. These results indicate that impairment of dTMP biosynthesis caused by RTX led to the development of NTDs in mice. DNA damage and imbalance between apoptosis and proliferation may be potential mechanisms. 相似文献
996.
Min-Te Chou Bo W. Han Chiung-Po Hsiao Phillip D. Zamore Zhiping Weng Jui-Hung Hung 《Nucleic acids research》2015,43(17):e109
Small silencing RNAs, including microRNAs, endogenous small interfering RNAs (endo-siRNAs) and Piwi-interacting RNAs (piRNAs), have been shown to play important roles in fine-tuning gene expression, defending virus and controlling transposons. Loss of small silencing RNAs or components in their pathways often leads to severe developmental defects, including lethality and sterility. Recently, non-templated addition of nucleotides to the 3′ end, namely tailing, was found to associate with the processing and stability of small silencing RNAs. Next Generation Sequencing has made it possible to detect such modifications at nucleotide resolution in an unprecedented throughput. Unfortunately, detecting such events from millions of short reads confounded by sequencing errors and RNA editing is still a tricky problem. Here, we developed a computational framework, Tailor, driven by an efficient and accurate aligner specifically designed for capturing the tailing events directly from the alignments without extensive post-processing. The performance of Tailor was fully tested and compared favorably with other general-purpose aligners using both simulated and real datasets for tailing analysis. Moreover, to show the broad utility of Tailor, we used Tailor to reanalyze published datasets and revealed novel findings worth further experimental validation. The source code and the executable binaries are freely available at https://github.com/jhhung/Tailor. 相似文献
997.
998.
999.
Based on field investigations, as well as investigation of relevant specimens, Pimpinella rhomboidea var. tenuiloba is shown to be conspecific with Melanosciadium bipinnatum. The distribution and habitat of M. bipinnatum is redescribed and notes on the taxonomy of the species are presented. 相似文献
1000.
Wenhao?Chen Dianfeng?ZhengEmail author Naijie?Feng Tao?Liu Yang?Liu Shen?Gong Hongqiu?Cui Hongtao?Xiang 《Acta Physiologiae Plantarum》2015,37(1):1723
Application of plant growth regulators (PGRs) to soybean plants is known to induce changes in nitrogenase activity in root nodules, and this led us to hypothesize that PGRs would affect nitrogenase activity in free-living rhizobia cultures. Little is known about the molecular basis of the effects of PGRs on nitrogenase activity in free-living rhizobia cultures. Therefore, a comparative study was conducted on the effects of gibberellins (GA3) and mepiquat chloride (PIX), which regulate plant growth, on the nitrogenase activity of the nitrogen-fixing bacterium Bradyrhizobium japonicum. Fix and nif gene regulation and protein expression in free-living cultures of B. japonicum were investigated using real-time PCR and two-dimensional electrophoresis after treatment with GA3 or PIX. GA3 treatment decreased nitrogenase activity and the relative expression of nifA, nifH, and fixA genes, but these effects were reversed by PIX treatment. As expected, several proteins involved in nitrogenase synthesis were down-regulated in the GA3-treated group. Conversely, several proteins involved in nitrogenase synthesis were up-regulated in the PIX-treated group, including bifunctional ornithine acetyltransferase/N-acetylglutamate synthase, transaldolase, ubiquinol-cytochrome C reductase iron-sulfur subunit, electron transfer flavoprotein subunit beta, and acyl-CoA dehydrogenase. Two-pot experiments were conducted to evaluate the effects of GA3 and PIX on nodulation and nitrogenase activity in Rhizobium-treated legumes. Interestingly, GA3 treatment increased nodulation and depressed nitrogenase activity, but PIX treatment decreased nodulation and enhanced nitrogenase activity. Our data show that the nif and fix genes, as well as several proteins involved in nitrogenase synthesis, are up-regulated by PIX and down-regulated by GA3, respectively, in B. japonicum. 相似文献