全文获取类型
收费全文 | 5085篇 |
免费 | 404篇 |
国内免费 | 172篇 |
出版年
2023年 | 45篇 |
2022年 | 55篇 |
2021年 | 92篇 |
2020年 | 129篇 |
2019年 | 162篇 |
2018年 | 193篇 |
2017年 | 134篇 |
2016年 | 131篇 |
2015年 | 167篇 |
2014年 | 293篇 |
2013年 | 338篇 |
2012年 | 243篇 |
2011年 | 283篇 |
2010年 | 253篇 |
2009年 | 282篇 |
2008年 | 301篇 |
2007年 | 263篇 |
2006年 | 235篇 |
2005年 | 221篇 |
2004年 | 156篇 |
2003年 | 185篇 |
2002年 | 142篇 |
2001年 | 111篇 |
2000年 | 90篇 |
1999年 | 72篇 |
1998年 | 89篇 |
1997年 | 48篇 |
1996年 | 60篇 |
1995年 | 51篇 |
1994年 | 56篇 |
1993年 | 55篇 |
1992年 | 57篇 |
1991年 | 44篇 |
1990年 | 28篇 |
1989年 | 37篇 |
1988年 | 50篇 |
1987年 | 41篇 |
1986年 | 35篇 |
1985年 | 43篇 |
1984年 | 94篇 |
1983年 | 60篇 |
1982年 | 50篇 |
1981年 | 46篇 |
1980年 | 41篇 |
1979年 | 43篇 |
1978年 | 12篇 |
1977年 | 12篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1974年 | 6篇 |
排序方式: 共有5661条查询结果,搜索用时 31 毫秒
1.
C. J. Gray 《Biocatalysis and Biotransformation》1988,1(3):187-196
The polypeptide chain of an enzyme is folded so that the necessary functional groups are brought together in the active site. Conformational changes may disrupt this arrangement and cause loss of enzymic activity. The effect of soluble additives on the unfolding process is discussed. Additives may be classified as substrates and similar ligands, small uncharged organic molecules, specific and non-specific ionic species, and polymers. 相似文献
2.
3.
RegB is involved in the control of the phage T4 life cycle. It inactivates the phage early mRNAs when their translation is
no more required. We determined its structure and identified residues involved in substrate binding. For this, all backbone
and 90% of side-chain resonance frequencies were assigned. 相似文献
4.
5.
Low rates of iridoid glycoside hydrolysis in two Longitarsus leaf beetles with different feeding specialization confer tolerance to iridoid glycoside containing host plants 下载免费PDF全文
Susanne Dobler 《Physiological Entomology》2015,40(1):18-29
Iridoid glycosides are plant defence compounds that are deterrent and/or toxic for unadapted herbivores but are readily sequestered by dietary specialists of different insect orders. Hydrolysis of iridoid glycosides by β‐glucosidase leads to protein denaturation. Insect digestive β‐glucosidases thus have the potential to mediate plant–insect interactions. In the present study, mechanisms associated with iridoid glycoside tolerance are investigated in two closely‐related leaf beetle species (Coleoptera: Chrysomelidae) that feed on iridoid glycoside containing host plants. The polyphagous Longitarsus luridus Scopoli does not sequester iridoid glycosides, whereas the specialist Longitarsus tabidus Fabricius sequesters these compounds from its host plants. To study whether the biochemical properties of their β‐glucosidases correspond to the differences in feeding specialization, the number of β‐glucosidase isoforms and their kinetic properties are compared between the two beetle species. To examine the impact of iridoid glycosides on the β‐glucosidase activity of the generalist, L. luridus beetles are kept on host plants with or without iridoid glycosides. Furthermore, β‐glucosidase activities of both species are examined using an artificial β‐glucosidase substrate and the iridoid glycoside aucubin present in their host plants. Both species have one or two β‐glucosidases with different substrate affinities. Interestingly, host plant use does not influence the specific β‐glucosidase activities of the generalist. Both species hydrolyse aucubin with a much lower affinity than the standard substrate. The neutral pH reduces the β‐glucosidase activity of the specialist beetles by approximately 60% relative to its pH optimum. These low rates of aucubin hydrolysis suggest that the ability to sequester iridoid glycosides has evolved as a key to potentially preventing iridoid glycoside hydrolysis by plant‐derived β‐glucosidases. 相似文献
6.
7.
Piotr Politański Elźbieta Rajkowska Marcin Brodecki Andrzej Bednarek Marek Zmyślony 《Bioelectromagnetics》2013,34(4):333-336
The aim of this study was to investigate the effect of static magnetic fields (SMF) on reactive oxygen species induced by X‐ray radiation. The experiments were performed on lymphocytes from male albino Wistar rats. After exposure to 3 Gy X‐ray radiation (with a dose rate of 560 mGy/min) the measurement of intracellular reactive oxygen species in lymphocytes, using a fluorescent probe, was done before exposure to the SMF, and after 15 min, 1 and 2 h of exposure to the SMF or a corresponding incubation time. For SMF exposure, 0 mT (50 µT magnetic field induction opposite to the geomagnetic field) and 5 mT fields were chosen. The trend of SMF effects for 0 mT was always opposite that of 5 mT. The first one decreased the rate of fluorescence change, while the latter one increased it. Bioelectromagnetics 34:333–336, 2013. © 2012 Wiley Periodicals, Inc. 相似文献
8.
9.
10.
《Bioorganic & medicinal chemistry》2014,22(13):3316-3324
Desymmetrization of the pseudochiral (2r)-configured cyclohexane-1,2,3-triamines 8 with dimethyl oxalate led to racemic aminoquinoxaline-2,3-diones 9. Selective introduction of the κ pharmacophoric structural elements pyrrolidine and 3,4-dichlorophenylacetamide with a two-carbon distance afforded conformationally restricted κ agonists 13–15 based on the quinoxaline ring system. In competitive radioligand receptor binding studies the benzylamine 13b, the secondary amine 14b, and the carbamate 15 displayed high κ receptor affinity. The Ki value of the lead compound derived methoxycarbonyl derivative 15 is 9.7 nM. However, the κ affinity of 15 is exceeded by 13b and 14b with a basic functional group instead of the methoxycarbonyl group in 1-position of the quinoxaline system. The chlorine atoms of the dichlorophenylacetyl residue are essential, since the corresponding phenylacetyl analogs show considerably reduced κ affinity. The potent κ ligands 13b, 14b and 15 are selective over the related μ- and δ-opioid receptors, σ1, σ2 and NMDA receptors. In the [35S]GTPγS-binding assay 13b behaved as partial agonist with lower activity than U-69,593. 相似文献