全文获取类型
收费全文 | 478篇 |
免费 | 64篇 |
专业分类
542篇 |
出版年
2019年 | 5篇 |
2018年 | 10篇 |
2015年 | 4篇 |
2014年 | 13篇 |
2013年 | 10篇 |
2012年 | 21篇 |
2011年 | 17篇 |
2010年 | 9篇 |
2009年 | 6篇 |
2008年 | 13篇 |
2007年 | 12篇 |
2006年 | 13篇 |
2005年 | 21篇 |
2004年 | 15篇 |
2003年 | 18篇 |
2002年 | 18篇 |
2001年 | 21篇 |
2000年 | 13篇 |
1999年 | 13篇 |
1998年 | 10篇 |
1997年 | 10篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 16篇 |
1991年 | 14篇 |
1990年 | 19篇 |
1989年 | 14篇 |
1988年 | 9篇 |
1987年 | 9篇 |
1986年 | 12篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 11篇 |
1978年 | 6篇 |
1977年 | 11篇 |
1976年 | 6篇 |
1975年 | 16篇 |
1974年 | 8篇 |
1973年 | 7篇 |
1972年 | 6篇 |
1971年 | 5篇 |
1970年 | 4篇 |
1969年 | 4篇 |
1967年 | 6篇 |
排序方式: 共有542条查询结果,搜索用时 0 毫秒
21.
a-Factor from Saccharomyces cerevisiae: partial characterization of a mating hormone produced by cells of mating type a. 总被引:11,自引:3,他引:8
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Conjugation between haploid cells of Saccharomyces cerevisiae is mediated through the action of diffusible mating hormones, two of which have been designated as a-factor and alpha-factor. Partially purified fractions exhibiting a-factor activity have been obtained from culture filtrates of a cells by ultrafiltration, ion-exchange chromatography, and gel filtration. The a-factor preparations specifically caused both G1 arrest and morphological alterations in cells of alpha-mating type, whereas a cells, a/alpha diploids, and nonmating alpha mutants were not affected. The a-factor activity was found in the culture filtrates of all a strains tested, but not in filtrates of alpha or a/alpha cell cultures. The hormone is sensitive to various proteases, showing that it is associated with a peptide or protein. Gel filtration studies suggest an apparent molecular weight greater than 600,000; however, this result may be due to aggregation with carbohydrate present in the preparations. Although the biological activities of a-factor are analogous to those described previously for alpha-factor, the chemical properties of these two hormones appear to be quite different. 相似文献
22.
W H?rtel J W Betz G von Sengbusch P Bader 《The journal of histochemistry and cytochemistry》1979,27(1):311-314
As a method for the preselection of alarms in gynecological cell samples, the Battelle Cytophotometry Research Group uses the slit-scan technique to obtain various cell parameters, such as the N/C ratio and the relative DNA content, from fluorescently stained cells, which are aligned one-dimensionally in the tape system designed at Battelle. The system developed at Battelle Institute analyzes all signals that exceed the background noise. As the first step in processing the slit-scan data, several threshold levels permit the separation of various artifacts. In subsequent steps, the nuclear peak is recognized, the nuclear boundaries are calculated, and seven cell parameters are determined. For the alarm detection at present only one parameter, DNA fluorescence, is used for these determinations. Visual assignment of these data to definite objects on the tape makes it possible to obtain frequency distributions of: (a) all recorded objects within the sample on the tape; (b) all signals that are classified as cells; and (c) all types of objects that preferentially cause alarms. 相似文献
23.
Mechanistic studies on thrombin catalysis 总被引:1,自引:0,他引:1
The kinetic mechanism of the cleavage of four p-nitroanilide (pNA) substrates by human alpha-thrombin has been investigated by using a number of steady-state kinetic techniques. Solvent isotope and viscosity effects were used to determine the stickiness of the substrates at the pH optimum of the reaction; a sticky substrate is defined as one that undergoes catalysis faster than it dissociates from the Michaelis complex. Whereas benzoyl-Arg-pNA could be classified as a nonsticky substrate, D-Phe-pipecolyl-Arg-pNA was very sticky. The other two substrates (tosyl-Gly-Pro-Arg-pNA and acetyl-D-Phe-pipecolyl-Arg-pNA) were slightly sticky. The pH profiles of kcat/Km were bell-shaped for all substrates. The pKa values determined from the pH dependence of kcat/Km for benzoyl-Arg-pNA were about 7.5 and 9.1. Similar pKa values were determined from the pH profiles of kcat/Km for tosyl-Gly-Pro-Arg-pNA and acetyl-D-Phe-pipecolyl-Arg-pNA and for the binding of the competitive inhibitor N alpha-dansyl-L-arginine-4-methylpiperidine amide. The groups responsible for the observed pKa values were proposed to be His57 and the alpha-amino group of Ile16. The temperature dependence of the pKa values was consistent with this assignment. The pKa values of 6.7 and 8.6 observed in the pH profile of kcat/Km for D-Phe-pipecolyl-Arg-pNA were displaced to lower values than those observed for the other substrates. The displacement of the acidic pKa value could be attributed to the stickiness of this substrate.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
24.
Neuraxin corresponds to a C-terminal fragment of microtubule-associated protein 5 (MAP5) 总被引:1,自引:0,他引:1
From cloned DNA, neuraxin has been identified as a tubulin binding protein of predicted molecular weight of 94 kDa. The deduced sequence of the rat protein exhibits high homology to the C-terminal region of mouse microtubule-associated protein 5 (MAP5). Here, we show that different neuraxin antibodies recognize MAP5, but fail to detect a protein of 94 kDa, in subcellular and microtubular fractions of the rat central nervous system. Furthermore, tubulin binding by neuraxin was found to be dependent on taxol. These data are consistent with neuraxin corresponding to a C-terminal fragment of MAP5 that contains a low-affinity tubulin binding site. 相似文献
25.
Primary culture of capillary endothelium from rat brain 总被引:11,自引:0,他引:11
P D Bowman A L Betz D Ar J S Wolinsky J B Penney R R Shivers G W Goldstein 《In vitro》1981,17(4):353-362
To provide an in vitro system for studies of brain capillary function we developed a method for culture of brain capillary endothelial cells. Capillaries were isolated from rat brain and enzymatically treated to remove the basement membrane and contaminating pericytes. Subsequent Percoll gradient centrifugation resulted in a homogeneous population of capillary endothelial cells that attached to a collagen substrate and incorporated [3H]thymidine. Evidence for the endothelial nature of these cells was provided by the presence of Factor VIII antigen and angiotensin converting enzyme activity and by the failure of platelets to adhere to the cell surface. In addition, the cells were joined together by tight junctions. Thus, primary cultures of these cells retained both endothelial and blood-brain barrier features. 相似文献
26.
27.
28.
29.
The inhibitory glycine receptor (GlyR) is a ligand-gated chloride channel protein which displays developmental heterogeneity in the mammalian central nervous system. Here we describe 2 novel cDNA variants of the rat GlyR alpha 2 subunit and demonstrate that alternative splicing generates these 2 isoforms. The deduced protein sequences (alpha 2A and alpha 2B) exhibit 99% identity with the previously characterized human alpha 2 subunit. In situ hybridization revealed expression of both alpha 2A and alpha 2B mRNAs in the prenatal rat brain, suggesting that these variant proteins may have a role in synaptogenesis. Heterologous expression in Xenopus oocytes showed that the more abundantly expressed alpha 2A subunit forms strychnine-sensitive ion channels which resemble human alpha 2 subunit GlyRs in their electrophysiological properties. 相似文献
30.
Gel shift assays were used to examine the binding of the lactose (lac) repressor to polyoperator DNA molecules. Specific binding was differentiated from nonspecific DNA association by (i) equilibrating repressor-operator complexes below the nonspecific association constant and (ii) demonstrating the effects of the inducer isopropyl beta-D-thiogalactoside (IPTG) on the formation of repressor-operator complexes. With the linear polyoperator molecules, all eight operator sites could be simultaneously bound by distinct repressors. However, with circular molecules, the eight operator sites were saturable by repressor only in the nicked circular state and not in the covalently closed circular form. Under the experimental conditions used, there was no evidence of bifunctional repressor binding or loop formation. The results suggest that the conformational perturbation of DNA that occurs upon specific repressor binding was retained in topologically closed molecules and could modify other operator sites so as to make them unavailable for specific binding. 相似文献