全文获取类型
收费全文 | 663篇 |
免费 | 57篇 |
国内免费 | 2篇 |
专业分类
722篇 |
出版年
2021年 | 10篇 |
2019年 | 4篇 |
2018年 | 10篇 |
2017年 | 5篇 |
2016年 | 10篇 |
2015年 | 9篇 |
2014年 | 16篇 |
2013年 | 24篇 |
2012年 | 33篇 |
2011年 | 38篇 |
2010年 | 23篇 |
2009年 | 13篇 |
2008年 | 24篇 |
2007年 | 30篇 |
2006年 | 27篇 |
2005年 | 18篇 |
2004年 | 35篇 |
2003年 | 25篇 |
2002年 | 14篇 |
2001年 | 22篇 |
2000年 | 14篇 |
1999年 | 35篇 |
1998年 | 9篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 6篇 |
1992年 | 14篇 |
1991年 | 16篇 |
1990年 | 21篇 |
1989年 | 20篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1975年 | 7篇 |
1974年 | 13篇 |
1973年 | 10篇 |
1972年 | 5篇 |
1971年 | 6篇 |
1970年 | 4篇 |
1969年 | 6篇 |
1968年 | 4篇 |
排序方式: 共有722条查询结果,搜索用时 15 毫秒
1.
2.
3.
B J Marsden F D Sauer B A Blackwell J K Kramer 《Biochemical and biophysical research communications》1989,159(3):1404-1410
The methylcoenzyme M methylreductase reaction has an absolute requirement for 7-mercaptoheptanoylthreonine phosphate or component B, which is the active component of the intact molecule previously referred to as cytoplasmic cofactor. A hydrolytic fragment of cytoplasmic cofactor has been purified and identified as uridine 5'-(O-2-acetamido-2-deoxy-beta-manno-pyranuronosyl acid (1----4)-2-acetamido-2-deoxy-alpha-glucopyranosyl diphosphate) by high resolution NMR and fast atom bombardment mass spectro-metry. It is postulated that UDP-disaccharide may function to anchor 7-mercaptoheptanoyl threonine phosphate at the active site of the methyl-reductase enzyme complex. 相似文献
4.
Transmission and scanning EM-immunogold labeling of Leishmania major lipophosphoglycan in the sandfly Phlebotomus papatasi 总被引:1,自引:0,他引:1
T Lang A Warburg D L Sacks S L Croft R P Lane J M Blackwell 《European journal of cell biology》1991,55(2):362-372
Previous studies using immunostaining and light microscopy demonstrated expression of Leishmania major lipophosphoglycan (LPG) on parasites developing in the sandfly gut from 2 days post infection. By days 4 to 7 post infection, there appeared to be large amounts of parasite-free LPG deposited on/in the microvilli and epithelial cells lining the thoracic midgut, while forward migration of parasites and the morphological changes which accompany metacyclogenesis were associated with developmental modification of the LPG molecules. Studies presented here examine this process with much greater precision using electron microscopy and immunogold labeling techniques to study the different developmental forms (nectomonads, haptomonads, paramastigotes, and metacyclics) of promastigotes in the sandfly gut. Results obtained using LPG-specific monoclonal antibodies (WIC79.3, 45D3 and the metacyclic-specific 3F12) show (1) gold labeling over the cell surface, within the flagellar pocket, and extending along the entire length of the flagellum of electron-dense nectomonads observed in the abdominal and thoracic midgut regions on days 4 and 7 post infection, and of electron-lucid haptomonads in the foregut, (2) dense labeling around the flagellar tips, by which nectomonad forms bind to the midgut microvilli, but not on the microvilli themselves or within the epithelial cells lining the midgut, (3) significant metacyclic-specific (3F12) labeling on nectomonad forms in the lumen of the midgut and attached to the microvilli, and (4) dense labeling on the cell surface of electron-lucid paramastigotes in the esophagus and in the filamentous matrix surrounding paramastigote and metacyclic forms in the esophagus and pharynx. These results are discussed in the light of the proposed roles for LPG in parasite attachment to, and survival in, the sandfly gut. 相似文献
5.
Alison Blackwell 《Entomologia Experimentalis et Applicata》1988,48(2):149-156
Larvae of the large cabbage white butterfly, Pieris brassicae L. are important pests of cruciferous crops. Third and fifth instars were treated topically with sublethal doses of the formamidine pesticide chlordimeform. A number of excitable actions were induced but they did not persist beyond 24 hours. Following the initial period, however, subsequent development was delayed and mortality increased, particularly when third instars were treated. Dosing fifth-instar larvae caused few further deaths. A link is suggested between these results and the nutritional status of the insects, and they are discussed in terms of how they might contribute towards control.
Résumé Les chenilles de troisième et cinquième stades de P. brassicae L. ont reçu une application superficielle de chlordiméforme, insecticide à la formamidine. Les doses inférieures à 335 g/g ont été sublétales, provoquant plusieurs formes d'excitation. Bien que leur comportement soit redevenu normal en 24 heures, les troisièmes stades traités ont eu leur développement retardé et une mortalité accrue. Le traitement des chenilles plus âgées a eu moins d'effets. Une relation est suggérée entre ces observations et le régime alimentaire de cet insecte; une réduction de l'alimentation, plus importante chez les chenilles de troisième que de cinquième stade de P. brassicae, accompagne le début des altérations du comportement provoquées par le chlordiméforme. La discussion porte sur le mécanisme de contrôle sublétal du chlordiméforme, impliquant des effects immédiats et retardés.相似文献
6.
Stimulation and inhibition of secretion by phorbol myristate acetate in different cell types 总被引:1,自引:0,他引:1
G J Blackwell R W Bonser J Dawson L G Garland 《Biochemical and biophysical research communications》1985,127(3):950-955
In washed human platelets and in HL60 granulocytes phorbol myristate acetate (PMA, 1-2000nM) synergised with threshold concentrations of secretogogues to induce a sustained maximum secretory response. Likewise, superoxide production from HL60 cells maintained a maximal response at PMA concentrations between 30-300nM. At concentrations up to 10nM PMA also augmented calcium ionophore, A23187, stimulated histamine release from rat peritoneal mast cells. However, in the mast cell PMA concentrations above 10nM reduced maximum histamine release in a dose-dependent manner. 相似文献
7.
Interactions of an intact proteoglycan and its fragments with basic homopolypeptides in dilute aqueous solution
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The interactions between a proteoglycan and cationic polypeptides have been investigated by the use of circular-dichroism spectroscopy. The interaction produces an induced conformational change for poly(l-arginine) and poly(l-lysine), similar to the effects previously reported for mucopolysaccharide-polypeptide mixtures. For bovine nasal septum proteoglycan, the interactions are similar to those for chondroitin 4-sulphate, which comprises approximately 63% of the total polysaccharide. The results also suggest that the interactions produce a conformational change in the protein core. Similar studies for the Smith-degradation product show that the protein core can adopt a substantial alpha-helical content and is capable of interactions with poly-(l-arginine). The interactions for chondroitin sulphate ;doublets' are significantly different from those for the separated chains, indicating that the arrangement of the polysaccharide side chains in pairs (and larger groups) along the protein backbone contributes to the interaction properties of the intact proteoglycan. 相似文献
8.
9.
The interactions between chondroitin-6-sulfate and poly-L -arginine in aqueous salt solution have been investigated by circular dichroism techniques. In the presence of chondroitin-6-sulfate, at neutral pH, poly-L -arginine adopts the α-helical conformation rather than “charged coil” form observed in the absence of mucopolysaccharide. This interaction is at a maximum when the ratio of arginine to disaccharide residues is 2:1. Elevation of the temperature leads to a sharp melting transition at 76.0 ± 1.0°C. This behavior is in marked contrast to that for poly-L -lysine-chondroitin-6-sulfate interactions, which are at a maximum at a 1:1 residue ratio and have a melting transition at 47.0 ± 1.0°C. These results indicate a stronger interaction for poly-L -arginine than for poly-L -lysine. The positive arginine side chains appear to interact with both the negative sulfate and carboxyl residues, while those of the lysines are involved only with the sulfates. Poly-L -ornithine at neutral pH shows no conformation directing interaction with chondroitin-6-sulfate, although a small proportion of α-helix is formed on dilution of the mixture with methanol. The extent of the interaction of cationic polypeptides with chondroitin-6-sulfate increases in the order poly-L -ornithine, poly-L -lysine, poly-L -arginine, i.e., in the order of increasing side-chain length. 相似文献
10.
Structure of beta-chitin or parallel chain systems of poly-beta-(1-4)-N-acetyl-D-glucosamine 总被引:2,自引:0,他引:2
J Blackwell 《Biopolymers》1969,7(3):281-298
The structure of β-chitin has been reexamined in an X -ray diffraction study of the highly crystalline material available from pogonophore tubes. Oriented specimens were prepared by suspending the dispersed deproteinized tube in a fibrin clot which was then stretched into an oriented fiber. The X -ray diffraction patterns of pogonophore β-chitin were explained by proposing that this material consists of a mixture of two structural phases which have been named β-chitins A and B. This view was confirmed by the preparation of specimens which gave only the diffraction pattern of the A phase by treating the tubes with diaphanol. Both A and B phases gave rise to a series of hydrate structures. The lowest hydrate of β-chitin A has been studied in detail and shown to consist of an anhydrous system of parallel chitin chains. For this form, the unit cell was monoclinic with dimensions a = 4.85 Å, b = 10.38 Å (fiber axis), c = 9.26 Å, and β = 97.5°, and space group P21. Reasonable agreement was obtained between the observed X -ray intensities and those calculated for such a structure. Examination of the β-chitin of Loligo pen and diatom spines showed that these materials also consist of these A and B phases. 相似文献