全文获取类型
收费全文 | 20972篇 |
免费 | 1774篇 |
国内免费 | 1961篇 |
出版年
2024年 | 54篇 |
2023年 | 309篇 |
2022年 | 686篇 |
2021年 | 1235篇 |
2020年 | 792篇 |
2019年 | 1053篇 |
2018年 | 988篇 |
2017年 | 736篇 |
2016年 | 1058篇 |
2015年 | 1383篇 |
2014年 | 1684篇 |
2013年 | 1840篇 |
2012年 | 1958篇 |
2011年 | 1802篇 |
2010年 | 1095篇 |
2009年 | 955篇 |
2008年 | 1101篇 |
2007年 | 888篇 |
2006年 | 722篇 |
2005年 | 622篇 |
2004年 | 534篇 |
2003年 | 477篇 |
2002年 | 375篇 |
2001年 | 328篇 |
2000年 | 276篇 |
1999年 | 288篇 |
1998年 | 194篇 |
1997年 | 175篇 |
1996年 | 146篇 |
1995年 | 130篇 |
1994年 | 125篇 |
1993年 | 110篇 |
1992年 | 122篇 |
1991年 | 117篇 |
1990年 | 73篇 |
1989年 | 59篇 |
1988年 | 47篇 |
1987年 | 39篇 |
1986年 | 29篇 |
1985年 | 33篇 |
1984年 | 30篇 |
1983年 | 17篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1950年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Four new labdane-type rhamnopyranosides derived from 13-epimanool, compounds 1-4, with differently acetylated sugar moieties, were isolated from A. veitchianus. Their structures and absolute configurations were elucidated by chemical transformation, spectroscopic and mass-spectrometric analyses (IR, 1D- and 2D-NMR, HR-ESI-MS), as well as by single-crystal X-ray diffraction (compound 1). The isolates 2-4 were investigated for their cytotoxic properties against cultured human hepatoma (SMMC-7721), ovarian neoplasm (HO-8910), and leukemia (HL-60) cells, and for their antibacterial activities against Escherichia coli, Bacillus subtilis, and Staphylococcus aureus. 相似文献
972.
Mallikarjuna K. Aradhya Daniel Potter Fangyou Gao Charles J. Simon 《Tree Genetics & Genomes》2007,3(4):363-378
The eastern Asian and eastern North American disjunction in Juglans offers an opportunity to estimate the time since divergence of the Eurasian and American lineages and to compare it with
paleobotanical evidence. Five chloroplast DNA noncoding spacer (NCS) sequences: trnT−trnF, psbA−trnH, atpB−rbcL, trnV-16S rRNA, and trnS-trnfM and data from earlier studies (matK, ITS, and nuclear RFLP) were used to reconstruct phylogeny and to estimate the divergence time of major lineages. Seventeen
taxa from four sections of Juglans and two outgroup taxa, Pterocarya stenoptera and Carya illinoiensis were included. NCS data was congruent only with matK data. Both maximum parsimony (MP) and maximum likelihood (ML) cladograms were concordant at the sectional level and revealed
three well-supported monophyletic clades corresponding to sections Juglans, Cardiocaryon, and Rhysocaryon in both NCS and combined analyses. The single extant American butternut, Juglans cinerea was placed within the poorly resolved, but well-supported Rhysocaryon. Placement of taxa within Rhysocaryon and Cardiocaryon were inconsistent between NCS and combined analyses. Overall, the results suggest that: (1) the NCS sequence divergence observed
within and between sections of Juglans is low and the addition of matK data only marginally improved resolution within Rhysocaryon; (2) the early divergence of section Juglans in both MP and ML analyses of NCS and combined data implies its ancient origin in contrast to fossil evidence, which suggests
the earliest divergence of sections Rhysocaryon and Cardiocaryon; and (3) the extant taxa may not hold the footprints to unravel the evolutionary history of the genus. 相似文献
973.
Fu BY Xiong JH Zhu LH Zhao XQ Xu HX Gao YM Li YS Xu JL Li ZK 《Molecular genetics and genomics : MGG》2007,278(6):599-609
Drought tolerance (DT) in rice is known to be controlled by many quantitative trait loci (QTLs) and involved differential
expression of large numbers of genes, but linking QTLs with their underlying genes remains the most challenging issue in plant
molecular biology. To shed some light on this issue, differential gene expression in response to PEG simulated drought in
3 unique genetic materials (a lowland rice, IR64 and its derived line, PD86 which has 11 introgressed DT QTLs, and a upland
rice IRAT109) was investigated using a PCR-based subtractive hybridization strategy. More than 300 unique subtracted cDNA
sequences, covering genes of diverse cellular activities and functions, were identified and confirmed by semi-quantitative
and quantitative RT-PCR. Detailed bioinformatics analyses of the data revealed two interesting results. First, the levels
and mechanisms of DT of the three rice lines were associated with the number and types of differentially expressed genes,
suggesting different DT mechanisms in rice are controlled by different sets of genes and different metabolic pathways, and
most differentially expressed genes under drought were able to contribute to DT. Second, there appeared a high correspondence
in genomic location between DT QTLs and clusters of differentially expressed genes in rice, suggesting some DT QTLs may represent
clusters of co-regulated and functionally related genes. Thus, differential gene expression analyses using genetically characterized
materials can provide additional insights into the molecular basis of QTLs and convergent evidence to shortlist the candidate
genes for target QTLs.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Bin-Ying Fu and Jian-Hua Xiong are contributed to this work equally. 相似文献
974.
小麦胚芽鞘扩展蛋白特性及对水分胁迫的响应 总被引:3,自引:0,他引:3
扩展蛋白是植物细胞壁延伸过程中的关键调节因子,在植物的生长发育以及对逆境的响应过程中起着重要作用。本文选用小麦(HF 9703)胚芽鞘为材料,采用Hepes法和SDS法分别提取小麦胚芽鞘扩展蛋白,通过改良的植物组织伸长测定仪测定其活性,并利用扩展蛋白抗体进行免疫印迹以检测其丰度,主要研究了小麦胚芽鞘扩展蛋白的特性及对水分胁迫的响应。结果表明:Hepes法提取的扩展蛋白活性较高,而SDS法的提取效率高;离体小麦胚芽鞘扩展蛋白的活性具有pH依赖性,且随缓冲液的交替更换(pH 4.5:pH 6.8)而反复逆转;扩展蛋白主要定位于细胞壁中;小麦胚芽鞘扩展蛋白和黄瓜下胚轴扩展蛋白具有交叉重组活性,但这种活性具有种属特异性。水分胁迫诱导小麦胚芽鞘扩展蛋白的活性和丰度提高,扩展蛋白活性的提高在小麦对水分胁迫的抗性方面可能具有重要作用。 相似文献
975.
The ubiquitin-like conjugation reactions, ATG8/microtubule-associated protein 1 light chain 3/MAP1LC3 (LC3) to phosphatidylethanolamine (PE) and ATG12 to ATG5, are biochemical hallmarks for autophagy, a cellular process that degrades bulk cellular proteins and organelles. The two conjugation reactions share the same E1-like enzyme ATG7 but have different E2-like enzymes, ATG3 for LC3-PE and ATG10 for ATG12-ATG5. In cells, ATG12-ATG5 conjugation appears to be required for LC3-PE conjugation. Previously, in vitro reconstitution of LC3-PE conjugation, but not the upstream ATG12-ATG5 conjugation, was reported. In this study, we describe for the first time the de novo reconstitution of mammalian ATG12-ATG5 conjugation by using purified recombinant proteins. We show that ATG7, ATG10 and ATP as an energy source are all essential for ATG12-ATG5 conjugation, and mutation of the specific lysine residue of ATG5 for ATG12 conjugation abrogates the reaction. Furthermore, a potent stimulating activity for ATG12-ATG5 conjugation was detected in mammalian cell extracts, and was surprisingly identified as ribosomes. Our detail biochemical analyses indicate that the ribonucleic acid (RNA) component of ribosomes is both necessary and sufficient for this stimulation. 相似文献
976.
Gao YY Zhang DF Li H Liu R Zhuang ZH Li QF Wang SY Peng XX 《Journal of proteome research》2007,6(11):4321-4329
Elevated creatine kinase (CK) in the circulation was generally regarded to be a passive release from muscle damage. We utilized proteomic methodologies to characterize amphioxus humoral fluid APPs in response to caudal trauma, and found several spots of CK alterations with up-regulation and pI shift. Its amount and enzyme activity showed a dynamic pattern of APP in humoral fluid accompanied with a reduction in enzyme activity of muscle, whereas there was no significant difference in CK amount of muscle and the other tissues and in CK enzyme activity of the other tissues between different time points of sample collection following caudal trauma. In addition, CK phosphorylation regulation during injury was not achieved by monoclonal antibodies separately against phosphothreonine, phosphotyrosine, and phosphoserine. These results suggested that the CK elevation of humoral fluid might be from muscle, being an active response to caudal trauma rather than a passive release from muscle damage. Therefore, CK ability in response to caudal trauma should be highly concerned. 相似文献
977.
Inhaled anesthetics bind specifically to a wide variety of proteins in the brain. This set of proteins must include those that contribute to the physiological and behavioral phenotypes of anesthesia and the related side effects. To identify the anesthetic-binding targets and functional pathways associated with these targets in human brain, halothane photolabeling and two-dimensional (2D) gel electrophoresis were used. Both membrane and soluble proteins from human temporal cortex were prepared. More than 300 membrane and 400 soluble protein spots were detected on the stained blots, of which 23 membrane and 34 soluble proteins were labeled by halothane and identified by mass spectroscopy. Their functional classification reveals five groups, including carbohydrate metabolism, protein folding, oxidative phosphorylation, nucleoside triphosphatase, and dimer/kinase activity with different correlative stringency. When network analysis of the interaction between these protein molecules is used, the weighted interaction accentuates the cellular protein components important in cell growth and proliferation, cell cycle and cell death, and cell-cell signaling and interactions, although no pathway was specific. This study provides evidence for multiple anesthetic binding targets and suggests potential pathways involved in their actions. 相似文献
978.
Although three-dimensional electron microscopy (3D-EM) permits structural characterization of macromolecular assemblies in distinct functional states, the inability to classify projections from structurally heterogeneous samples has severely limited its application. We present a maximum likelihood-based classification method that does not depend on prior knowledge about the structural variability, and demonstrate its effectiveness for two macromolecular assemblies with different types of conformational variability: the Escherichia coli ribosome and Simian virus 40 (SV40) large T-antigen. 相似文献
979.
Dandan Jiang Dandan Zhang Shengnan Li Yueting Liang Qianwei Zhang Xu Qin Jinlan Gao Jin-Long Qiu 《Molecular Plant Pathology》2022,23(4):583-594
Efficient and modular genome editing technologies that manipulate the genome of bacterial pathogens will facilitate the study of pathogenesis mechanisms. However, such methods are yet to be established for Xanthomonas oryzae pv. oryzae (Xoo), the causal agent of rice bacterial blight. We identified a single type I-C CRISPR-Cas system in the Xoo genome and leveraged this endogenous defence system for high-efficiency genome editing in Xoo. Specifically, we developed plasmid components carrying a mini-CRISPR array, donor DNA, and a phage-derived recombination system to enable the efficient and programmable genome editing of precise deletions, insertions, base substitutions, and gene replacements. Furthermore, the type I-C CRISPR-Cas system of Xoo cleaves target DNA unidirectionally, and this can be harnessed to generate large genomic deletions up to 212 kb efficiently. Therefore, the genome-editing strategy we have developed can serve as an excellent tool for functional genomics of Xoo, and should also be applicable to other CRISPR-harbouring bacterial plant pathogens. 相似文献
980.
Li Nan Shi Hangyu Hou Pengfei Gao Lu Shi Yongqiang Mi Weiyang Zhang Gang Wang Ning Dai Wei Wei Lin Jin Tianbo Shi Yongzhi Guo Shiwen 《Functional & integrative genomics》2022,22(1):27-33
Functional & Integrative Genomics - This study ascertained to explore the potential contribution of ARRDC3 polymorphisms in the risk and prognosis of glioma. One thousand sixty-one patients and... 相似文献