全文获取类型
收费全文 | 8053篇 |
免费 | 344篇 |
国内免费 | 310篇 |
专业分类
8707篇 |
出版年
2024年 | 11篇 |
2023年 | 81篇 |
2022年 | 156篇 |
2021年 | 167篇 |
2020年 | 232篇 |
2019年 | 330篇 |
2018年 | 334篇 |
2017年 | 225篇 |
2016年 | 220篇 |
2015年 | 192篇 |
2014年 | 466篇 |
2013年 | 751篇 |
2012年 | 241篇 |
2011年 | 493篇 |
2010年 | 284篇 |
2009年 | 341篇 |
2008年 | 367篇 |
2007年 | 388篇 |
2006年 | 340篇 |
2005年 | 337篇 |
2004年 | 300篇 |
2003年 | 286篇 |
2002年 | 230篇 |
2001年 | 144篇 |
2000年 | 128篇 |
1999年 | 121篇 |
1998年 | 125篇 |
1997年 | 138篇 |
1996年 | 149篇 |
1995年 | 133篇 |
1994年 | 97篇 |
1993年 | 84篇 |
1992年 | 91篇 |
1991年 | 70篇 |
1990年 | 52篇 |
1989年 | 58篇 |
1988年 | 40篇 |
1987年 | 37篇 |
1986年 | 44篇 |
1985年 | 40篇 |
1984年 | 87篇 |
1983年 | 50篇 |
1982年 | 67篇 |
1981年 | 40篇 |
1980年 | 33篇 |
1979年 | 33篇 |
1978年 | 12篇 |
1977年 | 20篇 |
1976年 | 15篇 |
1974年 | 14篇 |
排序方式: 共有8707条查询结果,搜索用时 15 毫秒
81.
Uri S. Ladror Gary T. Wang William L. Klein Thomas F. Holzman Grant A. Krafft 《Journal of Protein Chemistry》1994,13(4):357-366
Fluorogenic peptide substrates designed to encompass the reported-secretory and amyloidogenic cleavage sites of the amyloid- precursor protein (PP) were used to analyze proteinase activities in brain extracts from control patients and those with Alzheimer's disease (AD). Activity against the secretory substrate atpH 7.5 in control and AD brains produced a major endopeptidase cleavage at the Lys687-Leu688 bond (PP770 numbering), consistent with thePP secretase cleavage. Activity in control brains against the amyloidogenic substrate atpH 7.5 produced one cleavage at the Ala673-Glu674 bond, two residues C-terminal to the amyloidogenic Met-Asp site. However, in three of four AD brains, the major cleavage was at the Asp-Ala bond, one residue from the amyloidogenic site. Both endopeptidase and carboxypeptidase activities in AD brains were lower than in control brains. Proteinase activities against the secretory substrate had a major optimum atpH 3.0–4.0 and another atpH 6.0–7.5. Proteinase activities against the amyloidogenic substrate had a major optimum at or belowpH 3.0 and another atpH 6.0. Using both substrates, activities at lowpH were higher in AD brains than in controls, while atpH above 6.5, activities in control brains were higher than in AD. These results indicate that the levels of proteolytic enzymes in AD brains are altered relative to controls.Abbreviations A
Amyloid-
- ACN
acetonitrile
- AD
Alzheimer's disease
- PP
amyloid- precursor protein
- DABCYL
4-(4-dimethylaminophenylazo)-benzoic acid
- EDANS
5-{(2-aminoethyl)amino}napthalene-1-sulfonic acid
- MES
morpholinoethane sulfonic acid
- MOPS
morpholino-propane sulfonic acid
- RP-HPLC
reverse-phase high-performance liquid chromatography
- SDS-PAGE
sodium do-decyl sulfate-polyacrylamide gel electrophoresis
- TFA
tri-fluoroacetic acid
- Tris
tris(hydroxyethyl)aminomethane 相似文献
82.
ADP-ribosylation reaction, that is the transfer of the ADP-ribose moiety of NAD+ to acceptor protein, is catalyzed by two classes of ADP-ribosyltransferases,i.e., poly(ADP-ribose) synthetase and mono (ADP-ribosyl)transferases. These two types differ not only in the number of transferring ADP-ribose units but also in the acceptor amino acid(s) and protein. Their in hibitors, particularly those of poly(ADP-ribose) synthetase, have been successfully employed in studies on biological functions of the enzymes and other related fields of research. Recently, we found many potent and specific inhibitors of poly-(ADP-ribose) synthetase, and broadened their chemical as well as biochemical variety. More recently, we found several potent inhibitors of arginine-specific mono(ADP-ribosyl)transferases and activators of poly(ADP-ribose) synthetase. 相似文献
83.
Summary Proteasomes, also known as multicatalytic proteinase complexes, were localized in suspension cells of potato (Solanum tuberosum) by direct immunofluorescence using polyclonal antibodies labelled with fluorescein isothiocyanate. The method used allows an estimate of relative amounts of proteasomal antigens in different cell components. Proteasomes are present in the nuclei and the cytoplasm. The nucleoplasm contains small areas of weak fluorescence. The peripheral cytoplasm and possibly elements of the cytoskeleton show higher fluorescence than other parts of the cytoplasm. This indicates a localization of proteasomes similar to that known from animal cells.Abbreviations DMSO
dimethylsulfoxide
- EGTA
ethyleneglycol-bis-(-aminoethylether)-N,N,N,N-tetra acetic acid
- FITC
fluorescein isothiocyanate
- PBS
phosphate buffered saline
- PIPES
piperazine-1,4-bis-(2-ethanesulfonic acid) 相似文献
84.
G. García-Casado R. Sánchez-Monge C. Lopez-Otín G. Salcedo 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1994,89(1):60-63
A new inhibitor of insect -amylase, designated RDAI-1, has been purified from rye (Secale cereale L.) endosperm. RDAI-1 is homologous to wheat homodimeric inhibitors. This homology is supported by their similar N-terminal amino-acid sequences, inhibitory activities towards amylases from Tenebrio molitor (Coleoptera) and human saliva, and aggregative properties in gel-filtration chromatography. The gene encoding RDAI-1, IdhaR1, is located on the short arm of chromosome 3R, which is homoeologous with wheat chromosome arms 3BS and 3DS, where the genes for homodimeric inhibitors have been previously mapped. 相似文献
85.
Cysteine proteinase forms in sprouting potato tuber 总被引:1,自引:0,他引:1
Dominique Michaud Binh Nguyen-Quoc Nathalie Bernier-Vadnais Loïc Faye Serge Yelle 《Physiologia plantarum》1994,90(3):497-503
Transformation of plants with exogenous proteinase inhibitor genes represents an attractive strategy for the biological control of insect pests. However, such a strategy necessitates a thorough characterization of endogenous proteinases. which represent potential target enzymes for the exogenous inhibitors produced. In the present study. changes in general endoproteolytic activity were monitored during sprouting of potato ( Solanum tuberosum L. cv. Kennebec) tuber. Quantitative data obtained using standard procedures showed that an increase in cysteine proteinase (EC 3.4.22) activity occurs during sprouting. This increased activity results from the gradual appearance of new cysteine proteinase forms, as demonstrated by the use of class-specific proteinase activity gels. While only one cysteine proteinase form was present during early sprouting, at least six new active forms of the same class were shown to appear gradually after the mature tuber was sown, suggesting the involvement of a complex cysteine proteolytic system in the last stages of tuber protein breakdown. Interestingly, oryzacystatins I and II. two cysteine proleinase inhibitors potentially useful for insect control, had no effect on any tuber proteinase delected. Similar results were obtained with leaf, stem and stolon proteinases. This apparent absence of direct interference supports the potential of oryzacystatin genes for production of insect-tolerant transgenie potato plants. 相似文献
86.
Wounding of plants by insects is often mimicked in the laboratory by mechanical means such as cutting or crushing, and has not been compared directly with other forms of biotic stress such as virus infection. To compare the response of plants to these types of biotic and abiotic stress, trypsin inhibitor (TI) activity induced locally and systemically in mature tobacco (Nicotiana tabacum L.) and tomato (Lycopersicon esculentum L.) plants was followed for 12 days. In tobacco, cutting, crushing and insect feeding all induced comparable levels of TI activity of approx. 5 nmol·(mg leaf protein)?1 in wounded leaves, while tobacco mosaic virus (TMV) infection of tobacco induced 10-fold lower amounts in the infected leaves. In tomato, feeding by insects also led to the induction of a level of TI activity of 5 nmol·(mg leaf protein)?1. In contrast, both cutting and crushing of tomato leaves induced 10-fold higher amounts. These data show that biotic stress, in the form of insect feeding and TMV infection, and abiotic stress, in the form of wounding, have different effects on local levels of induced TI activity in mature tobacco and tomato plants. Irrespective of the type of wounding, in neither tobacco nor tomato could systemic induction of TI activity be observed in nearby unwounded leaves, which suggests that systemic induction of TI activity in mature tobacco and tomato plants is different from systemic TI induction in seedlings. Wounding of tobacco leaves, however, did increase the responsiveness to wounding elsewhere in the plant, as measured by an increased induction of TI activity. 相似文献
87.
D. B. Goodnough G. B. Baker D. D. Mousseau A. J. Greenshaw W. G. Dewhurst 《Neurochemical research》1994,19(1):5-8
Chronic studies were initiated in rats to determine the effects of high- and low-dose tranylcypromine (TCP) on [3H]tryptamine (3H-T) binding sites. Male Sprague-Dawley rats were administered TCP (0.5 or 2.5 mg/kg/day) or vehicle (distilled water) for 4, 10 or 28 days via Alzet minipumps. After decapitation, the hippocampus and striatum were used to prepare membrane fragments for single point3H-T binding. Hippocampal3H-T binding was reduced after 10 and 28 days with the low dose and after 4, 10 and 28 days with the high dose. Striatal3H-T binding was reduced by both doses at all time intervals. The high dose resulted in a significantly greater reduction in striatal3H-T binding than did the low-dose after 4, 10, and 28 days. These results suggest that a more rapid reduction of3H-T binding in the hippocampus and/or a greater reduction of3H-T binding in the striatum by high-dose TCP than by low-dose TCP may be contributing factors in the reported efficacy of the former in refractory depression. 相似文献
88.
John T. Christeller Ngaire P. Markwick Elisabeth P. J. Burgess 《Archives of insect biochemistry and physiology》1994,25(2):159-173
The midgut proteinase activities were characterized from the keratinolytic larvae of two lepidopterans, Hofmannophila pseudospretella (Stainton) (Oecophoridae) and Tineola bisselliella (Hummel) (Tineidae), and one coleopteran, Anthrenocerus australis (Hope) (Dermestidae). The major endopeptidase activities, characterized using specific enzyme inhibitors, were serine proteinases with hydrolytic activity against N-benzoyl-DL-arginine-p-nitroanilide and against N-succinyl-L-alanyl-L-alanyl-L-prolyl-L-leucine-p-nitroanilide. No significant levels of metalloendopeptidase or cysteine endopeptidase activities were detected. Aminopeptidase activity was present in all larvae. The enzyme levels and properties of the two moth larvae were similar to each other and to those of phytophagous lepidopteran larvae but different from those of the beetle larva. Whereas only a limited number of serine proteinase inhibitors inhibited the midgut proteolysis of the lepidopteran larvae, most inhibitors inhibited the midgut proteolysis of the beetle larva. © 1994 Wiley-Liss, Inc. 相似文献
89.
The influence of chromium concentration on ethylene production in bean plants ( Phaseolus vulgaris L. cv. Contender) was investigated. A Cr ion-induced inhibition of ethylene synthesis from endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) was observed within both leaf discs floated on 2 m M CrO2− 4 or Cr3+ and leaf discs from plants cultured in nutrient solutions containing 10, 20 or 40 μ M CrO2− 4 . However, Cr ions supplied either to plants with the nutrient solution or to discs with the incubation medium rather increased the conversion of exogenous ACC to ethylene. Primary leaves of plants exposed to CrO2− 4 -containing nutrient solutions showed a statistically insignificant decrease of ACC-synthase activity. In the trifoliolate leaves of plants exposed to 10 μ M CrO2− 4 , in which a significant decrease of ethylene production from endogenous ACC was observed, a substantial increase of ACC synthase was found. These results indicate that Cr ion-induced inhibition of ethylene production is not due to a breakdown of membrane integrity, which is necessary for ethylene forming enzyme activity, but caused by metabolic alterations leading to decreased ACC availability. Chromium ions may act by inhibiting ACC synthase activity or by diverting a metabolic step prior to the ACC synthase catalyzed reaction. 相似文献
90.
WIP1, a wound-inducible gene from maize with homology to Bowman-Birk proteinase inhibitors 总被引:6,自引:0,他引:6
We have cloned and sequenced a wound-inducible cDNA clone designated WIP1 (for wound-induced protein) from maize coleoptiles. It was isolated by differential screening of a cDNA library prepared from excised maize coleoptile segments. The deduced amino acid sequence predicts a secretory, cysteine-rich protein of 102 residues with a calculated molecular mass of 11 kDa and a typical N-terminal signal sequence. The protein has about 30% identity with various Bowman-Birk type proteinase inhibitors. Most interestingly, it is novel in that it is double-headed with exclusive specificity for chymotrypsin. WIP1 is strongly wound-induced in contrast to other members of the Bowman-Birk proteinase inhibitor family, which occur in seeds and are regulated during development. The response is fast, similar to defenceinduced genes, and measurable as early as 30 min after wounding. Induction can also be evoked in the intact coleoptiles and the signal is systemically transmitted in the coleoptile to adjacent regions of the wounded area. Isolation and analysis of the corresponding genomic clone reveals that WIP1 contains an intron of 90 nucleotides. 相似文献