全文获取类型
收费全文 | 31284篇 |
免费 | 2356篇 |
国内免费 | 2282篇 |
专业分类
35922篇 |
出版年
2024年 | 66篇 |
2023年 | 437篇 |
2022年 | 1077篇 |
2021年 | 1765篇 |
2020年 | 1161篇 |
2019年 | 1562篇 |
2018年 | 1423篇 |
2017年 | 997篇 |
2016年 | 1437篇 |
2015年 | 1981篇 |
2014年 | 2378篇 |
2013年 | 2590篇 |
2012年 | 2825篇 |
2011年 | 2554篇 |
2010年 | 1486篇 |
2009年 | 1376篇 |
2008年 | 1617篇 |
2007年 | 1424篇 |
2006年 | 1167篇 |
2005年 | 911篇 |
2004年 | 750篇 |
2003年 | 715篇 |
2002年 | 541篇 |
2001年 | 486篇 |
2000年 | 461篇 |
1999年 | 430篇 |
1998年 | 265篇 |
1997年 | 254篇 |
1996年 | 253篇 |
1995年 | 229篇 |
1994年 | 218篇 |
1993年 | 150篇 |
1992年 | 199篇 |
1991年 | 179篇 |
1990年 | 126篇 |
1989年 | 98篇 |
1988年 | 81篇 |
1987年 | 69篇 |
1986年 | 39篇 |
1985年 | 44篇 |
1984年 | 24篇 |
1983年 | 30篇 |
1982年 | 16篇 |
1981年 | 18篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1965年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
201.
DNA barcoding, as a tool for species discrimination, has been used efficiently in animals, algae and fungi, but there are still debates on which DNA region(s) can be used as the standard barcode(s) for land plants. Gymnosperms, especially conifers, are important components of forests, and there is an urgent need for them to be identified through DNA barcoding because of their high frequency of collection in the field. However, the feasibility of DNA barcoding in gymnosperms has not been examined based on a dense species sampling. Here we selected seven candidate DNA barcodes from the plastome (matK, rbcL, rpoB, rpoC1, atpF-atpH, psbA-trnH, and psbK-psbI) to evaluate their suitability in Picea (spruce). The results showed that none of them or their different combinations has sufficient resolution for spruce species, although matK+rbcL might be used as a two-locus barcode. The low efficiency of these candidate barcodes in Picea might be caused by the paternal inheritance of the chloroplast genome, long generation time, recent radiation, and frequent inter-specific hybridization aided by wind pollination. Some of these factors could also be responsible for the difficulties in barcoding other plant groups. Furthermore, the potential of the nuclear LEAFY gene as a land plant barcode was discussed. 相似文献
202.
Seema Sharma Haiyan Zheng Yuanpeng J. Huang Asli Ertekin Yoshitomo Hamuro Paolo Rossi Roberto Tejero Thomas B. Acton Rong Xiao Mei Jiang Li Zhao Li‐Chung Ma G. V. T. Swapna James M. Aramini Gaetano T. Montelione 《Proteins》2009,76(4):882-894
Disordered or unstructured regions of proteins, while often very important biologically, can pose significant challenges for resonance assignment and three‐dimensional structure determination of the ordered regions of proteins by NMR methods. In this article, we demonstrate the application of 1H/2H exchange mass spectrometry (DXMS) for the rapid identification of disordered segments of proteins and design of protein constructs that are more suitable for structural analysis by NMR. In this benchmark study, DXMS is applied to five NMR protein targets chosen from the Northeast Structural Genomics project. These data were then used to design optimized constructs for three partially disordered proteins. Truncated proteins obtained by deletion of disordered N‐ and C‐terminal tails were evaluated using 1H‐15N HSQC and 1H‐15N heteronuclear NOE NMR experiments to assess their structural integrity. These constructs provide significantly improved NMR spectra, with minimal structural perturbations to the ordered regions of the protein structure. As a representative example, we compare the solution structures of the full length and DXMS‐based truncated construct for a 77‐residue partially disordered DUF896 family protein YnzC from Bacillus subtilis, where deletion of the disordered residues (ca. 40% of the protein) does not affect the native structure. In addition, we demonstrate that throughput of the DXMS process can be increased by analyzing mixtures of up to four proteins without reducing the sequence coverage for each protein. Our results demonstrate that DXMS can serve as a central component of a process for optimizing protein constructs for NMR structure determination. Proteins 2009. © 2009 Wiley‐Liss, Inc. 相似文献
203.
204.
Study of the factors affecting the extraction of soybean protein by reverse micelles 总被引:3,自引:0,他引:3
Xihong Zhao Yanmei Li Xiaowei He Nanjing Zhong Zhenbo Xu Liansheng Yang 《Molecular biology reports》2010,37(2):669-675
In this work, the forward and back extraction of soybean protein by reverse micelles was studied. The reverse micellar systems
were formed by anionic surfactant sodium bis(2-ethyl hexyl) sulfosuccinate (AOT), isooctane and KCl solution. The effects
of AOT concentration, aqueous pH, KCl concentration and phase volume ratio on the extraction efficiency of soybean protein
were tested. Suitability of reverse micelles of AOT and Triton-X-100/AOT mixture in organic solvent toluene for soybean protein
extraction was also investigated. The experimental results lead to complete forward extraction at the AOT concentration 120 mmol l−1, aqueous pH 5.5 and KCl concentration 0.8 mol l−1. The backward extraction with aqueous phase (pH 5.5) resulted in 100% extraction of soybean protein from the organic phase. 相似文献
205.
Pectinase was immobilized on a sodium alginate support using glutaraldehyde and retained 66% activity. The optimal pH for
activity shifted from 3.0 to 3.5 after immobilization; however, the optimum temperature remained unchanged at 40°C. The immobilized
enzyme also had a higher thermal stability and reusability than the free enzyme, and retained 80% of initial activity after
11 batch reactions. 相似文献
206.
BingZhi Yu Zhe Zhang Xin Deng XiaoYan Xu Chen Feng YanXiao Li Cheng Cui WenHui Su HongMei Zhao DaHai Yu 《中国科学:生命科学英文版》2008,51(9):767-773
Recent studies have suggested that growth factors and hormones play important roles in cell prolif-eration and differentiation during early embryonic development. In the present study, we examined the expression and localization of insulin in the mouse oocytes and one-cell stage embryos by quantitative ELISA, RT-PCR, Western blot and immunofluorescence. In the mouse oocytes and one-cell stage em-bryos, expression of insulin was uniformly distributed in the cytoplasm. We also examined the expres-sion, activity and localization of mTOR (mammalian target of rapamycin) and p70S6K. The expression of mTOR and p70S6K was not significantly different at the cell cycle of mouse one-cell stage embryos. mTOR and S6K were distributed evenly in the cytoplasm at G1, G2 and M phase phase, but at S phase, the distribution of mTOR and S6K was around the pronucleus. At different phases, the activity of mTOR fluctuated. We also used the PI3K specific inhibitor-Wortmannin to investigate the cleavage rate of eggs. The result showed that the rate obviously decreased. When the mTOR specific inhibitor Rapa-mycin was used, the first mitotic division of the mouse one-cell stage embryo was delayed. These re-sults suggested that insulin was expressed both in mouse oocytes and one-cell stage embryos, and may play functional roles in regulation of mouse early embryogenesis by activating the signal pathway of PI3K/PKB/mTOR/S6K. 相似文献
207.
The present study was to test the hypothesis that 11,12-epoxyeicosatrienoic acid (11,12-EET), a metabolic product of arachidonic
acid by cytochrome P450 epoxygenase, regulates nitric oxide (NO) generation of the l-arginine/NO synthase (NOS) pathway in human platelets. Human platelets were incubated in the presence or absence of different
concentrations of 11,12-EET for 2 h at 37°C, followed by measurements of activities of the l-arginine/NOS pathway. Incubation with 11,12-EET increased the platelet NOS activity, nitrite production, cGMP content, and
the platelet uptake of l-[3H]arginine in a concentration-dependent manner. In addition, 11,12-EET attenuated intracellular free Ca2+ accumulation stimulated by collagen, which was at least partly mediated by EET-activated l-arginine/NOS pathway. It is suggested that 11,12-EET regulates platelet function through up-regulating the activity of the
l-arginine/NOS/NO pathway. 相似文献
208.
Wei Li Yuan-ying Shen Xuan-rong Zhang Lai-feng Ren Qiang Li Ru Shen Hai-ping Zhao 《中国病毒学》2008,23(1):57-62
To investigate the distribution of hepatitis B virus (HBV) genotypes and subgenotypes among the Bai nationality in Dali, a total of 100 serum samples from patients with chronic HBV-infection were collected for the detection of HBV genotypes and subgenotypes by genotype-specific primers and restriction fragment length polymorphism (RLFP), respectively. Among the 100 samples, the proportions of genotype B, C and mixed genotype (B C) were 41%, 25% and 34%, respectively. All the genotype B strains belonged to subgenotype Ba. In genotype C, 84% were Subgenotype Cs and 12% were subgenotype Ce. The distribution of genotypes B, C and B C showed no significant difference between male and female patients (P=0.182) and among the age groups of patients (P=0.812). The rates of HBeAg/HBeAg positivity were no significantly different among genotypes B, genotype C and mixed genotype (B C) (P=0.077/P=0.663). In Dali, genotypes B, B C and C existed among Bai nationality with chronic HBV-infection, and genotype B was the major genotype. Subgenotypes Ba and Cs were the predominant strains in patients with HBV genotype B/C infection. The most prominent characteristic was the higher prevalent rate of mixed genotype (B C) in patients. 相似文献
209.
He W Zhao Y Zhang C An L Hu Z Liu Y Han L Bi L Xie Z Xue P Yang F Hang H 《Nucleic acids research》2008,36(20):6406-6417
Rad9 is conserved from yeast to humans and plays roles in DNA repair (homologous recombination repair, and base-pair excision repair) and cell cycle checkpoint controls. It has not previously been reported whether Rad9 is involved in DNA mismatch repair (MMR). In this study, we have demonstrated that both human and mouse Rad9 interacts physically with the MMR protein MLH1. Disruption of the interaction by a single-point mutation in Rad9 leads to significantly reduced MMR activity. This disruption does not affect S/M checkpoint control and the first round of G2/M checkpoint control, nor does it alter cell sensitivity to UV light, gamma rays or hydroxyurea. Our data indicate that Rad9 is an important factor in MMR and carries out its MMR function specifically through interaction with MLH1. 相似文献
210.
Suppression subtractive hybridization (SSH) was preformed to investigate the differences of gene expression between the shaking culture mode and the liquid static culture mode which favors ganoderic acids production in Ganoderma lucidum. One novel gene preferentially expressed in liquid static culture was identified and analyzed. Its full length cDNA sequence and the 5′-flanking region were then obtained by rapid amplification of cDNA ends (RACE) and self-formed adaptor PCR (SEFA-PCR), respectively. Nucleotide sequence of the gene is not homologous to any of the known Ganoderma genes. The sequence analysis revealed that the open reading frame of this gene encodes a protein of 371 amino acids that has high homology with the mitogen-activated protein kinase (MAPK) of other five species-Postia (97%), Coprinopsis (91%), Neurospora (86%), Aspergillus (83%), and Saccharomyces (80%)-so that it can be defined as a G. lucidum MAPK gene (GenBank accession number: JF781125). Computer assisted analysis revealed that this new G. lucidum MAPK gene contains thirteen exons and twelve introns. The quantitative real-time RT-PCR (qRT-PCR) analysis showed that this new gene had a much higher expression level in liquid static culture than in traditional shaking culture. Results of this research established a good foundation for further study on the functions of the G. lucidum MAPK at the molecular level. 相似文献