全文获取类型
收费全文 | 1067篇 |
免费 | 69篇 |
国内免费 | 1篇 |
专业分类
1137篇 |
出版年
2022年 | 13篇 |
2021年 | 29篇 |
2020年 | 11篇 |
2019年 | 9篇 |
2018年 | 15篇 |
2017年 | 18篇 |
2016年 | 30篇 |
2015年 | 43篇 |
2014年 | 37篇 |
2013年 | 66篇 |
2012年 | 68篇 |
2011年 | 89篇 |
2010年 | 48篇 |
2009年 | 40篇 |
2008年 | 62篇 |
2007年 | 40篇 |
2006年 | 38篇 |
2005年 | 46篇 |
2004年 | 50篇 |
2003年 | 23篇 |
2002年 | 30篇 |
2001年 | 19篇 |
2000年 | 15篇 |
1999年 | 11篇 |
1998年 | 7篇 |
1997年 | 13篇 |
1996年 | 8篇 |
1992年 | 9篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 13篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 6篇 |
1981年 | 15篇 |
1980年 | 15篇 |
1979年 | 7篇 |
1978年 | 14篇 |
1977年 | 10篇 |
1976年 | 13篇 |
1975年 | 11篇 |
1974年 | 7篇 |
1973年 | 10篇 |
1971年 | 8篇 |
1970年 | 8篇 |
1968年 | 7篇 |
1966年 | 7篇 |
排序方式: 共有1137条查询结果,搜索用时 15 毫秒
1.
2.
Role of neuraminic acid in the heterogeneity of alkaline phosphatase in sheep brain 总被引:2,自引:2,他引:0 下载免费PDF全文
1. Comparative studies of the polyuridylic acid-directed phenylalanine-incorporating activity of cell-free systems derived from rat and chicken livers demonstrated markedly lower activity in the chicken liver system. 2. The chicken liver cell sap contained the factor(s) responsible for this lower activity. Ribosomes from chicken and rat performed equally well in the presence of rat liver cell sap. Chicken liver cell sap, when mixed with rat liver cell sap, caused an inhibition of incorporation of phenylalanine into acid-insoluble material. 3. Though ribosomal preparations and cell sap from both rat and chicken liver degraded polyuridylic acid to some extent, the chicken liver cell sap contained the largest amount of activity. 4. Rat liver cell sap inhibited the nuclease activities of ribosomal preparations, but no such nuclease inhibition could be demonstrated with chicken liver cell sap. 相似文献
3.
The purpose of this study was to investigate the distribution of protein-polysaccharides in the glomerular and non-glomerular
regions of the nephron. The techniques used include the digestion of kidney slices with specific polysaccharidases: neuraminidase,
hyaluronidase, chondroitinase ABC, and collagenase followed by several cytochemical techniques to identify the glycosaminoglycans
and glycoproteins at the light and electron microscope levels. Differential staining of hyaluronic acid and sulphated glycosaminoglycans
was accomplished with Alcian Blue at pH 2.5 and pH 0.5, respectively. Sialoproteins were stained with Alcian Blue at pH 2.5.
The periodic acid Schiff’s reaction technique was employed for the visualization of collagen. At the electron microscope level
the polysaccharides were identified with the periodic acid-chromic acid-silver methenamine reaction. Our results indicated
that the major polysaccharide components of the glomerular basement membrane were sialoproteins and collagen, with smaller
amounts of hyaluronic acid and various sulphated glycosaminoglycans. Hyaluronidase digestion resulted in partial detachment
of epithelial processes from the glomerular basement membrane indicating the hyaluronic acid may have a role in the stability
of the attachment of these processes. Tubular basement membranes also contain sialoproteins and sulphated glycosaminoglycans
but in considerably lower concentrations than the glomerular basement membrane. Bowman’s capsule appears to contain mostly
sulphated glycosaminoglycans and has a lower concentration of sialoproteins and hyaluronic acid. 相似文献
4.
The movement of Ca2+ across the basolateral plasma membrane was determined in purified preparations of this membrane isolated from rabbit proximal and distal convoluted tubules. The ATP-dependent Ca2+ uptake was present in basolateral membranes from both these tubular segments, but the activity was higher in the distal tubules. A very active Na+/Ca2+ exchange system was also demonstrated in the distal-tubular membranes, but in proximal-tubular membranes this exchange system was not demonstrable. The presence of Na+ outside the vesicles gradually inhibited the ATP-dependent Ca2+ uptake in the distal-tubular-membrane preparations, but remained without effect in those from the proximal tubules. The activity of the Na+/Ca2+ exchange system in the distal-tubular membranes was a function of the imposed Na+ gradient. These results suggest that the major differences in the characteristics of Ca2+ transport in the proximal and in the distal tubules are due to the high activity of a Na+/Ca2+ exchange system in the distal tubule and its virtual absence in the proximal tubule. 相似文献
5.
D Sahal J Ramachandran Y Fujita-Yamaguchi 《Archives of biochemistry and biophysics》1988,260(1):416-426
The receptors for insulin and insulin-like growth factor (IGF) I are structurally similar transmembrane proteins. Ligand binding to the extracellular domain of the receptor stimulates its cytoplasmic tyrosine protein kinase which phosphorylates its own beta subunit as well as exogenous substrates. It is believed, from several lines of evidence, that tyrosine-specific protein kinases are mediating some or all of the actions of insulin (or IGF-I). In order to gain insights into the substrate specificity of the structurally related insulin and IGF-I receptor kinases, we have studied the action of highly purified receptors isolated from human placental membranes. Present studies using selected tyrosine-containing polymers have revealed: (i) Polymers such as (Y,A,E)n and (Y-A-E)n inhibit beta subunit autophosphorylation and exogenous substrate phosphorylation by autophosphorylated receptors. (ii) Insulin receptor kinase is at least 10 times more sensitive to these inhibitors than IGF-I receptor kinase. (iii) (Y-A-E)n is approximately 8 times more potent an inhibitor than (Y,A,E)n toward both receptors. (iv) While (E4,Y1)n and (E6,A3,Y1)n are good substrates for both receptor kinases, the ratio of phosphate incorporation into the former to the latter is characteristically high (approximately 4) for the IGF-I receptor and low (approximately 1) for the insulin receptor. These results imply that the substrate specificity and enzymatic action of these two receptor kinases are distinct. 相似文献
6.
We have cloned a cDNA coding for the smallest rat neurofilament protein. The cDNA is 861 nucleotides long coding for 287 amino acids from the internal alpha-helical region and the carboxy-terminal tail domain of the neurofilament protein. Comparison of the porcine, mouse and rat neurofilament protein sequences shows that the protein is highly conserved (greater than 93% identity). Blot analysis indicates that the cDNA is derived from a single neurofilament gene that codes for two different poly(A)+ mRNA species. 相似文献
7.
A square matrix of spots (A) was presented in rapid alternation with an uncorrelated matrix (B). If the square arrays are superimposed spatially one sees random incoherent motion. However, incoherent motion was seen only if the outer edges were exactly aligned. If the outline of matrix A is shifted horizontally by 1 degree in relation to B, then the edges are seen to oscillate to and fro. Surprisingly, all the dots in the matrix were seen to 'adhere' to the edges and to move horizontally (Ramachandran, 1981). We then aligned the edges again to produce incoherent motion and superimposed a sine-wave grating on the pattern. If the grating was moved horizontally then all the spots 'adhered' to it and moved horizontally as well. This illusion ('motion capture') was optimal (a) at a 90 degrees spatial phase shift of the grating; (b) at low spatial frequencies (less than 0.5 cycles); and (c) when the grating was alternated in step with the dot patterns. Density modulated gratings were just as effective. We conclude that the unambiguous motion signal derived from the grating is applied spontaneously to the dots as well. 相似文献
8.
9.
If the collagen triple helix is so built as to have one set of NH ? O hydrogen bonds of the type N3H3(A) ? O2(B), then it is possible to have a linkage between N1H1(B) and O1(A) through the intermediary of a water molecule with an oxygen O leading to the formation of the hydrogen bonds N1(B) ? O and O (A). In the same configuration, another water molecule with an oxygen O can link two earbonyl oxygens of chains A and B forming the hydrogen bonds O O1(A) and O O0 (B). The two water oxygens also become receptors at the same time for CH ? O hydrogen bonds. Thus, the neighboring chains in the triple helix are held together by secondary valence bond linkages occurring regularly sit intervals of about 3 Å along the length of the protofibril. The additional water molecules occur on the periphery of the proto-fibril and will contribute their full share towards stabilizing the structure in the solid state. In solution, they will be disturbed by the medium unless they are protected by long side groups. It appears that this type of two-bonded structure, in which one NH ? O bond is to a water molecule, can explain several observations on the stability and hydrogen exchange properties of collagen itself and related synthetic polypeptides. The nature of the water bonds and their strength are found to be better in the one-bonded structure proposed from Madras than in the one having the coordinates of Rich and Crick. 相似文献
10.