全文获取类型
收费全文 | 5210篇 |
免费 | 355篇 |
国内免费 | 4篇 |
专业分类
5569篇 |
出版年
2021年 | 46篇 |
2020年 | 26篇 |
2019年 | 30篇 |
2018年 | 46篇 |
2017年 | 45篇 |
2016年 | 56篇 |
2015年 | 120篇 |
2014年 | 133篇 |
2013年 | 296篇 |
2012年 | 205篇 |
2011年 | 224篇 |
2010年 | 143篇 |
2009年 | 128篇 |
2008年 | 232篇 |
2007年 | 268篇 |
2006年 | 198篇 |
2005年 | 214篇 |
2004年 | 222篇 |
2003年 | 209篇 |
2002年 | 198篇 |
2001年 | 213篇 |
2000年 | 212篇 |
1999年 | 167篇 |
1998年 | 64篇 |
1997年 | 73篇 |
1996年 | 63篇 |
1995年 | 47篇 |
1994年 | 62篇 |
1993年 | 41篇 |
1992年 | 123篇 |
1991年 | 117篇 |
1990年 | 130篇 |
1989年 | 130篇 |
1988年 | 111篇 |
1987年 | 76篇 |
1986年 | 82篇 |
1985年 | 99篇 |
1984年 | 83篇 |
1983年 | 59篇 |
1982年 | 45篇 |
1981年 | 53篇 |
1980年 | 39篇 |
1979年 | 54篇 |
1978年 | 37篇 |
1977年 | 33篇 |
1976年 | 33篇 |
1975年 | 36篇 |
1974年 | 33篇 |
1973年 | 40篇 |
1971年 | 26篇 |
排序方式: 共有5569条查询结果,搜索用时 0 毫秒
41.
Solution conformation of endothelin determined by means of 1H-NMR spectroscopy and distance geometry calculations 总被引:4,自引:0,他引:4
H Tamaoki Y Kobayashi S Nishimura T Ohkubo Y Kyogoku K Nakajima S Kumagaye T Kimura S Sakakibara 《Protein engineering》1991,4(5):509-518
The structure of endothelin-1 (ET-1), an endothelial cell-derived peptide with vasoconstricting activity, was determined in an aqueous solution by means of a combination of NMR and distance geometry calculations. The resulting structure is characterized by an alpha-helical conformation in the sequence region, Lys9-Cys15. Furthermore, an extended structure and a turn structure exist in the Cys1-Ser4 and Ser5-Asp8 regions respectively, and no preferred conformation was found for the C-terminal part of the peptide which was not uniquely constrained by the NMR data. These structural elements, the alpha-helical structure in the sequence portion, Cys-X-X-X-Cys, and the extended structure in Cys-X-Cys, are homologous to those found commonly in several neurotoxic peptides. 相似文献
42.
A sensitive method for detecting metallothioneins (MTs) by use of silver staining after sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of carboxymethylated MTs was developed. Carboxymethylation of metallothioneins is indispensable because it prevents their aggregation, thereby allowing each of them to be detected as a single band by SDS-PAGE. However, when the gel was subjected to the silver-staining method of C. R. Merril, D. Goldman, S. A. Sedman, and M. H. Ebert [(1981) Science 211, 1437-1438], the image of carboxymethylated purified MTs was totally negative. Pretreatment of the gel with 1% sodium thiosulfate just prior to the silver-staining procedure successfully reversed the negative image of carboxymethylated MTs. Further, they could be detected with a limit of nanogram levels per lane. This method can be applied to MTs in cell extracts from cultured cell lines treated with cadmium or to those from liver of cadmium-intoxicated mice. 相似文献
43.
We reported that: (i) 3Y1tsF121 cells, a temperature-sensitive (ts) mutant of rat 3Y1 fibroblasts, are reversibly arrested either in the G1 or in the G2 phase, at the nonpermissive temperature. (ii) Cells retain the ability to resume proliferation at the permissive temperature after prolonged arrest in the G1 phase (for 5 days), whereas they lose it after prolonged arrest in the G2 phase (over 24 h). (iii) The G1 arrest is overcome at the nonpermissive temperature by the addition of fresh serum (H. Zaitsu and G. Kimura (1984) J. Cell. Physiol. 119, 82; (1985) J. Cell. Physiol. 124, 177). In the present study, the G2 arrest was overcome by exposing the cells to fresh serum, at the nonpermissive temperature. The G2 arrest occurred only at a higher cell density than that of the G1 arrest. The efficiency of the overcome was higher in the case of the G2 arrest than in case of the G1 arrest. When cells synchronized at the G1/S border by aphidicolin at the permissive temperature were released from the block, they divided in the absence of serum, at the permissive temperature. Even if they had passed through the previous G2 phase in a very high concentration of fresh serum at the permissive temperature, mitotic cells did not enter the S phase in the absence of serum, even at the permissive temperature. When the cells arrested in the G1 phase (not in G0) due to the ts defect were incubated in the absence of serum at the permissive temperature, only 34% entered the S phase and only 15% divided. These results suggest that (i) the ts defect in 3Y1tsF121 limiting cellular proliferation in both the G1 and the G2 phases is probably due to a single mutational event, and is a serum-requiring event. (ii) Preparation of the serum-requiring event which is required for the G2 traverse is completed in the G1 phase, under ordinary conditions. (iii) However, cells are able to fulfill the serum-requiring event in the G2 phase as well as in the G1 phase when the preparation is below the required level. (iv) The commitment to DNA synthesis is not necessarily a commitment to cell division. (v) Cells are arrested in the G1 phase more safely and more effectively than in the G2 phase, by the serum-related mechanism. 相似文献
44.
Structure and regulation of the Escherichia coli ruv operon involved in DNA repair and recombination. 总被引:23,自引:7,他引:16
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)
H Shinagawa K Makino M Amemura S Kimura H Iwasaki A Nakata 《Journal of bacteriology》1988,170(9):4322-4329
45.
H Ueda T Hashimoto E Furuya K Tagawa K Kitagawa M Matsumoto S Yoneda K Kimura T Kamada 《Journal of biochemistry》1988,104(1):81-86
The changes in cerebral metabolism in mice in severe hypoxia were investigated by analyses of changes in the levels of energy metabolites and near-infrared spectrophotometric assessment of the states of hemoglobin and cytochrome oxidase. Under 4.4% O2, the contribution of anaerobic ATP production was at most about 20% of the demand. However, the cerebral ATP level was kept at the control level until about 1 min before death. Pentobarbital anesthesia, which reduced the cerebral rate of metabolism, prolonged the survival time, although anaerobic ATP production still did not support ATP demand. Under these conditions, deoxygenation of hemoglobin and reduction of cytochrome oxidase proceeded rapidly within 1 min. Hemoglobin reached the maximum state of deoxygenation in the middle phase of hypoxia, with no further change until death. However, cytochrome oxidase was reduced slowly with one phase of partial reoxidation due to increase of cerebral blood volume, and reached the completely reduced state at death. From these results it was concluded that the aerobic ATP synthesis, which supplied more than 80% of the cerebral demand, decreased gradually because of limitation of oxygen supply, and that the failure of oxidative phosphorylation to meet demand triggered the decrease in the cellular ATP level that led to death. 相似文献
46.
To determine whether GnRH modifies prolactin (PRL) secretion in response to thyrotrophin-releasing hormone (TRH) in normal women, a group of eleven normal women, 23 to 40 years of age, was studied in the mid-follicular phase of the menstrual cycle. The PRL response to TRH was evaluated in serum under control conditions and after GnRH infusion. GnRH administration augmented basal PRL release and amplified TRH-induced PRL release. These results suggest that GnRH may be involved in PRL release, partly by increasing the sensitivity of the lactotrophs to TRH. 相似文献
47.
N Chino K Yoshizawa-Kumagaye Y Noda T X Watanabe T Kimura S Sakakibara 《Biochemical and biophysical research communications》1986,141(2):665-672
To obtain antiparallel and parallel dimers of alpha-human atrial natriuretic peptide (alpha-hANP), two fully protected peptides I and II having the same amino acid sequence as alpha-hANP with different protective groups at the cysteinyl residues were synthesized, the former having Acm and Npys and the latter MeBzl and Acm. Equivalent amounts of peptides I and II were mixed and subjected to HF deprotection. Next, the first disulfide bond was linked between the remaining Npys group in I and the liberated SH group in II to form a monodisulfide dimer. The second disulfide bond was formed within the newly formed dimer between the remaining Acm groups by treatment with iodine, giving an antiparallel dimer. The parallel dimer of alpha-hANP was synthesized similarly starting from the protected peptide II. These dimers could be clearly segregated on HPLC. The retention time on HPLC of the antiparallel dimer was identical with that of natural beta-hANP. Both dimers showed biological activities as high as one third to one sixth of alpha-hANP in smooth muscle spasmolytic activity, and almost the same level of natriuretic activity as alpha-hANP at a high dose (10 nmol/kg) but about one fifth the activity at a low dose (1 nmol/kg). In these assay systems, the antiparallel dimer showed a slower onset and a tendency of longer duration than alpha-hANP. 相似文献
48.
Some properties of a Saccharomyces cerevisiae mutant resistant to 2-amino-4-methyl-5-beta-hydroxyethylthiazole 总被引:3,自引:0,他引:3
A mutant of Saccharomyces cerevisiae highly resistant to 2-amino-4-methyl-5-beta-hydroxyethylthiazole (2-aminohydroxyethylthiazole), an antimetabolite of 4-methyl-5-beta-hydroxyethylthiazole (hydroxyethylthiazole), has been isolated. Its resistance to 2-aminohydroxyethylthiazole was about 10(4) times that of the sensitive parent strain. The amount of thiamin synthesized in the cells of the resistant strain grown in minimal medium was less than half of that of the sensitive strain. The ability to synthesize thiamin from 2-methyl-4-amino-5-hydroxymethylpyrimidine (hydroxymethylpyrimidine) and hydroxyethylthiazole in the resistant strain was low compared with that of the sensitive strain. These results were found to be due to a deficiency of hydroxyethylthiazole kinase in the resistant strain: in sonic extracts of cells the enzyme activity was only 0.67% of that of the sensitive strain. Although the cells of the sensitive strain could accumulate exogenous hydroxyethylthiazole in the form of hydroxyethylthiazole monophosphate, no significant uptake of hydroxyethylthiazole by the cells of the resistant strain was observed. The possibilities that 2-aminohydroxyethylthiazole monophosphate may be the actual inhibitor of the growth of Saccharomyces cerevisiae, and that hydroxyethylthiazole may not be involved in the pathway of de novo synthesis of thiamin via hydroxyethylthiazole monophosphate, are discussed. 相似文献
49.
W Huang T Kimura K Mashima K Miyazaki H Masaki J Yamashita T Horio 《Journal of biochemistry》1986,100(3):687-696
We previously reported that sera from various kinds of animals contain a protein(s) capable of inhibiting the growth of the non-malignant epithelial cell line derived from Buffalo rat liver (BRL). In the present study, a similar epithelial cell-specific growth inhibitor (EGI) was purified to homogeneity from an acid-ethanol extract of human platelets. During purification, EGI was separated from the major component of type beta transforming growth factor (TGF-beta), which can stimulate the colony formation of the non-malignant fibroblastic cell line derived from rat kidney (NRK) in soft agar in the presence of epidermal growth factor (EGF). The purified EGI had an Mr of 27,000, and was composed of two subunits identical in Mr. It significantly inhibited the growth in monolayer cultures of three non-malignant epithelial cell lines, BRL, MDCK (from Madin-Darby canine kidney) and BSC-1 (from African green monkey kidney), at doses lower than 40 pg/ml in medium containing 10% fetal calf serum. Its inhibitory activity was stable against heating at 90 degrees C for 3 min, but not against treatment with 50 mM dithiothreitol. In addition, TGF-beta was also partially purified from the same extract. The purified TGF-beta did not show any inhibitory activity toward the growth of BRL, MDCK, BSC-1, or NRK. 相似文献
50.
Cross-linking site in fibrinogen for alpha 2-plasmin inhibitor 总被引:4,自引:0,他引:4
A plasma proteinase inhibitor, alpha 2-plasmin inhibitor (alpha 2PI), is cross-linked with alpha chain of fibrin(ogen) by activated coagulation Factor XIII (plasma transglutaminase). alpha 2PI serves only as a glutamine substrate (amine acceptor) for activated Factor XIII in the cross-linking reaction, and the cross-linking occurs between Gln-2 of the alpha 2PI molecule and a lysine residue (amine donor) of fibrin(ogen) alpha chain, whose position was investigated. alpha 2PI and fibrinogen were reacted by activated Factor XIII. The resulting alpha 2PI fibrinogen A alpha chain complex was separated and subjected to two cycles of Edman degradation using phenyl isothiocyanate for the first cycle and dimethylaminoazobenzene-isothiocyanate for the second cycle. The aqueous phase after the cleavage stage of the second cycle, containing dimethylaminoazobenzene-thiohydantoin-Gln cross-linked with A alpha chain, was subjected to CNBr fragmentation and tryptic digestion. Only one of the peptides was found to have the peak of absorbance at 420 nm, indicating the presence of dimethylaminoazobenzene-thiohydantoin-Gln in that peptide. The peptide was identified as corresponding to residues Asn-290-Arg-348 of A alpha chain by analyses of the NH2-terminal amino acid sequence and amino acid composition. The peptide contains a single lysine at position 303, indicating that Lys-303 of fibrinogen A alpha chain is the lysine residue that forms a cross-link with Gln-2 of alpha 2PI. 相似文献