全文获取类型
收费全文 | 14589篇 |
免费 | 1416篇 |
国内免费 | 5篇 |
专业分类
16010篇 |
出版年
2023年 | 53篇 |
2022年 | 194篇 |
2021年 | 350篇 |
2020年 | 192篇 |
2019年 | 243篇 |
2018年 | 306篇 |
2017年 | 252篇 |
2016年 | 437篇 |
2015年 | 766篇 |
2014年 | 783篇 |
2013年 | 888篇 |
2012年 | 1187篇 |
2011年 | 1146篇 |
2010年 | 705篇 |
2009年 | 613篇 |
2008年 | 866篇 |
2007年 | 848篇 |
2006年 | 827篇 |
2005年 | 741篇 |
2004年 | 698篇 |
2003年 | 682篇 |
2002年 | 592篇 |
2001年 | 114篇 |
2000年 | 69篇 |
1999年 | 134篇 |
1998年 | 201篇 |
1997年 | 114篇 |
1996年 | 117篇 |
1995年 | 108篇 |
1994年 | 96篇 |
1993年 | 113篇 |
1992年 | 93篇 |
1991年 | 71篇 |
1990年 | 76篇 |
1989年 | 62篇 |
1988年 | 72篇 |
1987年 | 53篇 |
1986年 | 50篇 |
1985年 | 54篇 |
1984年 | 64篇 |
1983年 | 74篇 |
1982年 | 66篇 |
1981年 | 61篇 |
1980年 | 64篇 |
1979年 | 42篇 |
1978年 | 43篇 |
1977年 | 41篇 |
1976年 | 43篇 |
1975年 | 40篇 |
1974年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Three forms of glutamate dehydrogenase have been isolated from developing soybean seed. Their intracellular locations could not be determined directly because organelles and marker enzymes showed abnormal distribution on sucrose density gradient fractionation. By analogy with enzymes from other parts of the plant, glutamate dehydrogenase 2 was shown to be located in chloroplasts and glutamate dehydrogenase 3 in mitochondria. Glutamate dehydrogenase 1 could not be located in this way because it is found only in the seed. The three enzymes are similar in pH optima, molecular weight and substrate specificity with respect to 2-oxoglutarate and l-glutamate. The mitochondrial enzyme is specific for NAD+. The chloroplast enzyme shows low activity with NADP+ relative to NAD+ but uses NADPH readily in the aminating direction. Glutamate dehydrogenase 1 is active with both nucleotides and is the only form to show substantial deaminating activity with NADP+. Glutamate dehydrogenases 1 and 2 are activated and stabilized by glutathione and 2-mercaptoethanol whereas enzyme 3 is unaffected. No significant metabolic control of any of the enzymes could be detected. Malate, citrate, adenine nucleotides and long-chain fatty acyl CoA derivatives gave slight inhibition at high concentrations. Amino acids had no effect on activity. A possible role for the enzyme characteristic of the developing seed is discussed in relation to nutrient supply during the accumulation of reserve materials in the seed. 相似文献
52.
Elizabeth Penry 《BMJ (Clinical research ed.)》1982,284(6321):1043-1044
53.
John L. Sternick Elizabeth M. Allen Linda M. Ripani Denis J. Schrier Vernon L. Moore 《Cellular immunology》1981,65(2):211-220
When C57BL/6 mice were injected iv with BCG in an oil-in-saline emulsion, they developed intense pulmonary granulomatous inflammation (PGI) and splenomegaly as well as chemotactic activity for macrophages and angiotensin-converting enzyme (ACE) in their lung fluids. PGI, splenomegaly, and levels of chemotactic activity and ACE were markedly reduced in T-cell-deficient “B” mice. The capacity to develop PGI was fully restored and splenomegaly was partially restored in “B” mice by the provision of syngeneic thymocytes, spleen cells, or purified T cells. These results indicate that the full expression of BCG-induced PGI is dependent upon thymus-derived cells and is associated with high levels of chemotactic activity for macrophages and ACE in the lung lavage fluid. Although BCG-induced splenomegaly appears to be T cell dependent, it did not reach its full magnitude in reconstituted “B” mice. 相似文献
54.
The sensitivities of 26 starch gel electrophoretic enzyme assays have been compared using HeLa human cells and A9 mouse cells grown in vitro.This research was supported by National Institutes of Health Grant No. USPHS GM 09966. 相似文献
55.
56.
57.
A several-fold greater counting efficiency is observed for protein labeled with [3H]leucine than for free [3H]leucine using a conventional filter disk assay. A similar, though less marked, effect is noted for 14C-labeled molecules. These results are comparable to those reported by others for counting efficiencies of labeled DNA and deoxynucleotides and illustrate the generality of this effect with regard to macromolecules and their low-molecular weight precursors. This phenomenon, presumably due to differences in the distribution of large and small molecules within filters, gives rise to errors in the quantitation of macromolecule synthesis if a counting efficiency identical to that of the precursor is assumed to apply. A convenient method for determining counting efficiencies of various molecules bound to filters is presented which eliminates this problem. 相似文献
58.
The relative proportions of carbonyl, O-acetyl, and O-(methylthio)methylsugars resulting from the partial oxidation of methyl α-D-glucopyranoside with methyl sulphoxide and acetic anhydride have been investigated@ the preparation of the 2- and 6-(methylthio)methyl ethers of methyl α-D-glucopyranoside is described. 相似文献
59.
The extracellular mucilage from Beijerinckia mobilis, a member of the Azotobacteriaceae, after removal of contaminating protein, was separated into a neutral polysaccharide (N-2, 10%); a neutral, dialysable fraction (N-1, 5%), consisting of glucose and oligosaccharides containing glucose, arabinose, and rhamnose; and an acidic polysaccharide (85%). N-2 (mol. wt, 1900) was highly branched and comprised glucopyranose, mannopyranose, and arabinofuranose residues (1:1:1). The various linkages were determined. The acid fraction was a polymer of high molecular weight composed of L-guluronic acid (65%), D-glucose (15%), and D-glycero-D-mannoheptose (20%), together with acetic and pyruvic acids. From the results of methylation, periodate oxidation, and partial hydrolysis, a branched molecule with a backbone of guluronic acid and heptose, and side chains of glucose and guluronic acid is proposed. Pyruvic acid was found to be acetal-linked to 2?5% of the heptose residues. The similarities between this polysaccharide and that from the related species Azotobacter indicum are discussed. 相似文献
60.
Using an electrophoretic variant for glutathione reductase, we have been able to map the structural gene for this enzyme to chromosome 8 in Mus musculus. 相似文献