全文获取类型
收费全文 | 28236篇 |
免费 | 2311篇 |
国内免费 | 2068篇 |
专业分类
32615篇 |
出版年
2024年 | 73篇 |
2023年 | 295篇 |
2022年 | 755篇 |
2021年 | 1221篇 |
2020年 | 858篇 |
2019年 | 1098篇 |
2018年 | 1176篇 |
2017年 | 837篇 |
2016年 | 1225篇 |
2015年 | 1706篇 |
2014年 | 1940篇 |
2013年 | 2168篇 |
2012年 | 2571篇 |
2011年 | 2342篇 |
2010年 | 1530篇 |
2009年 | 1389篇 |
2008年 | 1634篇 |
2007年 | 1445篇 |
2006年 | 1251篇 |
2005年 | 1134篇 |
2004年 | 911篇 |
2003年 | 875篇 |
2002年 | 771篇 |
2001年 | 565篇 |
2000年 | 428篇 |
1999年 | 399篇 |
1998年 | 266篇 |
1997年 | 209篇 |
1996年 | 151篇 |
1995年 | 154篇 |
1994年 | 122篇 |
1993年 | 104篇 |
1992年 | 144篇 |
1991年 | 125篇 |
1990年 | 107篇 |
1989年 | 96篇 |
1988年 | 77篇 |
1987年 | 68篇 |
1986年 | 54篇 |
1985年 | 59篇 |
1984年 | 28篇 |
1983年 | 30篇 |
1982年 | 28篇 |
1981年 | 14篇 |
1979年 | 20篇 |
1978年 | 16篇 |
1977年 | 21篇 |
1976年 | 15篇 |
1975年 | 15篇 |
1972年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
谷胱甘肽参与动植物体内的各种代谢活动,起着重要的作用。谷胱甘肽的测定方法有多种,如碘量法、纸层析法、高效液相色谱法等,但目前为止还没有一种快速、简便、准确、经济的方法。本文就谷胱甘肽的测定方法进展进行了简要概述。 相似文献
103.
Huachen Gan Guibo Wang Qin Hao Q. Jane Wang Hua Tang 《The Journal of biological chemistry》2013,288(52):37343-37354
At the interface between host and external environment, the airway epithelium serves as a major protective barrier. In the present study we show that protein kinase D (PKD) plays an important role in the formation and integrity of the airway epithelial barrier. Either inhibition of PKD activity or silencing of PKD increased transepithelial electrical resistance (TEER), resulting in a tighter epithelial barrier. Among the three PKD isoforms, PKD3 knockdown was the most efficient one to increase TEER in polarized airway epithelial monolayers. In contrast, overexpression of PKD3 wild type, but not PKD3 kinase-inactive mutant, disrupted the formation of apical intercellular junctions and their reassembly, impaired the development of TEER, and increased paracellular permeability to sodium fluorescein in airway epithelial monolayers. We further found that overexpression of PKD, in particular PKD3, markedly suppressed the mRNA and protein levels of claudin-1 but had only minor effects on the expression of other tight junctional proteins (claudin-3, claudin-4, claudin-5, occludin, and ZO-1) and adherent junctional proteins (E-cadherin and β-catenin). Immunofluorescence study revealed that claudin-1 level was markedly reduced and almost disappeared from intercellular contacts in PKD3-overexpressed epithelial monolayers and that claudin-4 was also restricted from intercellular contacts and tended to accumulate in the cell cytosolic compartments. Last, we found that claudin-1 knockdown prevented TEER elevation by PKD inhibition or silencing in airway epithelial monolayers. These novel findings indicate that PKD negatively regulates human airway epithelial barrier formation and integrity through down-regulation of claudin-1, which is a key component of tight junctions. 相似文献
104.
105.
Lee MH Han DW Woo YI Uzawa M Park JC 《Journal of microbiology and biotechnology》2008,18(7):1274-1277
The inactivating efficiency of alternating high-voltage pulsed (AHVP) current was investigated in brine (20 w/v% NaCl) and saline (0.9 w/v% NaCl) inoculated with 1x 107 cells/ml of Listeria monocytogenes. AHVP current at 12 V with 1 pulse completely inactivated L. monocytogenes in brine within 3 ms, while the bacteria in saline were fully inactivated by 10-pulsed electric treatment at 12 V within the same time. Electron microscopic observation demonstrated substantial structural damage of electrically treated L. monocytogenes in brine. These results suggest that AHVP treatment would be effective for the rapid and complete inactivation of L. monocytogenes in brine or saline solution. 相似文献
106.
Bacillus thuringiensis is a Gram‐positive aerobic bacterium that produces insecticidal crystalline inclusions during sporulation phases of the mother cell. The virulence factor, known as parasporal crystals, is composed of Cry and Cyt toxins. Most Cry toxins display a common 3‐domain topology. Cry toxins exert intoxication through toxin activation, receptor binding and pore formation in a suitable larval gut environment. The mosquitocidal toxins of Bt subsp. israelensis (Bti) were found to be highly active against mosquito larvae and are widely used for vector control. Bt subsp. jegathesan is another strain which possesses high potency against broad range of mosquito larvae. The present review summarizes characterized receptors for Cry toxins in mosquito larvae, and will also discuss the diversity and effects of 3‐D mosquitocidal Cry toxin and the ongoing research for Cry toxin mechanisms generated from investigations of lepidopteran and dipteran larvae. 相似文献
107.
Wan-Ji Lee You-jin Kim Dae-Won Kim Han Saem Lee Ho Yeon Lee Kisoon Kim 《Journal of virology》2012,86(24):13810-13811
The complete genome sequence of human respiratory syncytial virus genotype A (HRSV-A) with a 72-nucleotide duplication in the C-terminal part of the attachment protein G gene was determined and analyzed. The genome was 15,277 bp in length, and 0.46 to 6.03% variations were identified at the nucleotide level compared with the previously reported complete genome of HRSV-A. Characterization of the genome will improve understanding of the diversity of the HRSV-A major antigens and enable an in-depth analysis of its genetics. 相似文献
108.
Yanglin Hua Bao YangJian Tang Zhonghua MaQing Gao Mouming Zhao 《Carbohydrate polymers》2012,87(1):343-347
The water-soluble Dictyophora indusiata polysaccharides (DIP) were extracted from the fruiting body of D. indusiata. The structural features of purified DIPs I and II were investigated. The results indicated that DIP I was composed of glucose (Glc) and mannose (Man) with molecular weight of 2100 kDa, while DIP II comprised of xylose (Xyl), galactose (Gal), glucose (Glc) and Man with molecular weight of 18.16 kDa. The glycosidic linkage of DIP I was composed of →1)-Glc-(6→: →1)-Man-(3,6→ with the ratio of 5.6:1.0, while DIP II was composed of →1)-Glc-(6→: →1)-Man-(3,6→: →1)-Xyl-(5→: →1)-Gal-(3→: →1)-Gal-(6→: with the ratio of 4.9: 15.5: 7.8: 1.0: 5.7. DIP significantly (P < 0.05) decreased the malondialdehyde (MDA), lipofuscin levels and increased the superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) activities of mice. The strong in vivo antioxidant activity indicated DIP had great potential as functional food. 相似文献
109.
Han Fang Jonathan D. Caranto Rosalinda Mendoza Alexander B. Taylor P. John Hart Donald M. Kurtz Jr. 《Journal of biological inorganic chemistry》2012,17(8):1231-1239
Flavo-diiron proteins (FDPs) contain non-heme diiron and proximal flavin mononucleotide (FMN) active sites and function as terminal components of a nitric oxide reductase (NOR) and/or a four-electron dioxygen reductase (O2R). While most FDPs show similar structural, spectroscopic, and redox properties, O2R and NOR activities vary significantly among FDPs. A potential source of this variability is the iron ligation status of a conserved His residue that provides an iron ligand in all known FDP structures but one, where this His residue is rotated away from iron and replaced by a solvent ligand. In order to test the effect of this His ligation status, we changed this ligating His residue (H90) in Thermotoga maritima (Tm) FDP to either Asn or Ala. The wild-type Tm FDP shows significantly higher O2R than NOR activity. Single crystal X-ray crystallography revealed a remarkably conserved diiron site structure in the H90N and ?A variants, differing mainly by either Asn or solvent coordination, respectively, in place of H90. The steady-state activities were minimally affected by the H90 substitutions, remaining significantly higher for O2R versus NOR. The pre-steady-state kinetics of the fully reduced FDP with O2 were also minimally affected by the H90 substitutions. The results indicate that the coordination status of this His ligand does not significantly modulate the O2R or NOR activities, and that FDPs can retain these activities when the individual iron centers are differentiated by His ligand substitution. This differentiation may have implications for the O2R and NOR mechanisms of FDPs. 相似文献
110.
Robert‐Jan Bleichrodt G. Jerre van Veluw Brand Recter Jun‐ichi Maruyama Katsuhiko Kitamoto Han A. B. Wösten 《Molecular microbiology》2012,86(6):1334-1344
Hyphae of higher fungi are compartmentalized by septa. These septa contain a central pore that allows for inter‐compartmental and inter‐hyphal cytoplasmic streaming. The cytoplasm within the mycelium is therefore considered to be a continuous system. In this study, however, we demonstrate by laser dissection that 40% of the apical septa of exploring hyphae of Aspergillus oryzae are closed. Closure of septa correlated with the presence of a peroxisome‐derived organelle, known as Woronin body, near the septal pore. The location of Woronin bodies in the hyphae was dynamic and, as a result, plugging of the septal pore was reversible. Septal plugging was abolished in a ΔAohex1 strain that cannot form Woronin bodies. Notably, hyphal heterogeneity was also affected in the ΔAohex1 strain. Wild‐type strains of A. oryzae showed heterogeneous distribution of GFP between neighbouring hyphae at the outer part of the colony when the reporter was expressed from the promoter of the glucoamylase gene glaA or the α‐glucuronidase gene aguA. In contrast, GFP fluorescence showed a normal distribution in the case of the ΔAohex1 strain. Taken together, it is concluded that Woronin bodies maintain hyphal heterogeneity in a fungal mycelium by impeding cytoplasmic continuity. 相似文献