全文获取类型
收费全文 | 3224篇 |
免费 | 221篇 |
专业分类
3445篇 |
出版年
2022年 | 14篇 |
2021年 | 34篇 |
2019年 | 25篇 |
2018年 | 27篇 |
2017年 | 26篇 |
2016年 | 45篇 |
2015年 | 88篇 |
2014年 | 104篇 |
2013年 | 207篇 |
2012年 | 153篇 |
2011年 | 143篇 |
2010年 | 110篇 |
2009年 | 106篇 |
2008年 | 163篇 |
2007年 | 170篇 |
2006年 | 144篇 |
2005年 | 157篇 |
2004年 | 167篇 |
2003年 | 173篇 |
2002年 | 158篇 |
2001年 | 95篇 |
2000年 | 111篇 |
1999年 | 87篇 |
1998年 | 42篇 |
1997年 | 29篇 |
1996年 | 23篇 |
1995年 | 23篇 |
1994年 | 17篇 |
1993年 | 35篇 |
1992年 | 86篇 |
1991年 | 67篇 |
1990年 | 51篇 |
1989年 | 45篇 |
1988年 | 47篇 |
1987年 | 39篇 |
1986年 | 34篇 |
1985年 | 37篇 |
1984年 | 34篇 |
1983年 | 28篇 |
1982年 | 21篇 |
1981年 | 26篇 |
1980年 | 19篇 |
1979年 | 25篇 |
1978年 | 30篇 |
1976年 | 19篇 |
1975年 | 17篇 |
1973年 | 13篇 |
1972年 | 15篇 |
1970年 | 13篇 |
1969年 | 15篇 |
排序方式: 共有3445条查询结果,搜索用时 8 毫秒
41.
42.
Role of carbohydrate moiety of IL-5. Effect of tunicamycin on the glycosylation of IL-5 and the biologic activity of deglycosylated IL-5 总被引:4,自引:0,他引:4
A Tominaga T Takahashi Y Kikuchi S Mita S Naomi N Harada N Yamaguchi K Takatsu 《Journal of immunology (Baltimore, Md. : 1950)》1990,144(4):1345-1352
IL-5 is a T cell-derived lymphokine that induces B cell growth and differentiation in murine systems. In this study, we examined the role of carbohydrate moiety of IL-5 in the expression of biological function. IL-5 polypeptides translated in Xenopus oocytes were heterogeneous in terms of isoelectric point (pI 4.7 to 8.0) and m.w. (45,000 to 60,000 under nonreducing conditions) and yielded m.w. of 25,000 to 30,000 under reducing conditions. Treatment of rIL-5 with N-glycanase under reducing conditions yielded an IL-5 monomer of m.w. 12,000 to 14,000. Furthermore, deglycosylated rIL-5 that had been translated in the presence of tunicamycin showed very limited heterogeneity by two-dimensional gel electrophoresis (first dimension, nonequilibrium pH gradient electrophoresis; second dimension, SDS-PAGE). The m.w. was 27,000 to 28,000 under non-reducing conditions and migrated to m.w. 13,000 to 14,000 under reducing conditions. These results indicate that IL-5 is a glycoprotein carrying the N-glycosidically-linked carbohydrates. Treatment of IL-5 with sialidase caused the decrease in the heterogeneity in isoelectric point of IL-5. Deglycosylated rIL-5 that had been obtained from tunicamycin-treated oocytes could bind to IL-5-responding cells (T88-M), which express both high- and low-affinity IL-5 receptors, as efficient as intact rIL-5 under high-affinity conditions. Scatchard plot analysis of equilibrium binding of 35S-labeled rIL-5 to T88-M cells revealed that the dissociation constants (Kd) of glycosylated rIL-5 and deglycosylated rIL-5 were 127 pM and 110 pM, respectively. IL-5 activities determined by both B cell growth and differentiation assays were not affected by deglycosylation. These results indicate that N-linked glycoside moiety of IL-5 molecules may not play an essential role in the expression of its activity. 相似文献
43.
T Ohmori A Kikuchi K Yamamoto S Kim Y Takai 《The Journal of biological chemistry》1989,264(3):1877-1881
When guanosine 5'-(3-O-[35S]thio)triphosphate (GTP gamma S)-binding activity was assayed in the particulate and cytosol fractions of human platelets, most activity was found in the particulate fraction. GTP-binding proteins (G proteins) were extracted from the particulate fraction by sodium cholate and purified by several column chromatographies. At least three G proteins with Mr values of about 21,000, 22,000, and 24,000 (21K G, 22K G, and 24K G, respectively) were separated in addition to the stimulatory (Gs) and inhibitory (Gi) regulatory GTP-binding proteins of adenylate cyclase. Among them, the amount of 22K G was more than 10-fold of those of other G proteins. 22K G was purified to near homogeneity and characterized. 22K G specifically bound GTP gamma S, GTP, and GDP, with a Kd value for GTP gamma S of about 50 nM. [35S]GTP gamma S binding to 22K G was inhibited by pretreatment with N-ethylmaleimide. 22K G hydrolyzed GTP to liberate Pi, with a turnover number of 0.01 min-1. 22K G was not copurified with the beta gamma subunits of Gs and Gi and was not recognized by the antibodies against the ADP-ribosylation factor for Gs and the ras protein. The peptide map of 22K G was different from those of the smg-25A and rho proteins, which we have purified from bovine brain membranes. 21K G was identified to be the c-ras protein, but 24K G was unidentified. These results indicate that there are multiple G proteins in platelet membranes and that a novel G protein (22K G) is a major G protein in platelets. 相似文献
44.
We have analyzed the mechanisms controlling the accumulation of cytotoxic/suppressor T lymphocytes in tumor tissues. We found that tumor-infiltrating helper/inducer T cells isolated from T-9 gliosarcoma-sensitized rats between 4 and 6 days after T-9 gliosarcoma inoculation produced a lymphocyte migration factor (LMF) during in vitro culture. Four peaks of LMF activity (A through D) were detected upon fractionation of LMF by using a Mono Q anion exchange column chromatography. Peak C exhibited the strongest activity among the four peaks of LMF. The action of peak C was chemotactic, but not chemokinetic. Peak C had an isoelectric point of 8.0 and a Mr of 26,000 Da. Only cytotoxic/suppressor T cells were found to be sensitive to peak C in vitro as well as in vivo. It is thus likely that peak C is responsible for the infiltration of cytotoxic/suppressor T cells into tumor tissues. The infiltration of lymphocytes into tumor tissues might also be regulated by the expression of lymphocyte sensitivity for LMF. The target molecule for LMF at 4 days may involve an asparagine-linked oligosaccharide. 相似文献
45.
The formation of Compound I from Aspergillus niger catalase and methyl hydroperoxide (CH3OOH) has been investigated kinetically by means of rapid-scanning stopped-flow techniques. The spectral changes during the reaction showed distinct isobestic points. The second-order rate constant and the activation energy for the formation of Compound I were 6.4 x 10(3) M-1s-1 and 10.4 kcal.mol-1, respectively. After formation of Compound I, the absorbance at the Soret peak returned slowly to the level of ferric enzyme with a first-order rate constant of 1.7 x 10(-3) s-1. Spectrophotometric titration of the enzyme with CH3OOH indicates that 4 mol of peroxide react with 1 mol of enzyme to form 1 mol of Compound I. The amount of Compound I formed was proportional to the specific activity of the catalase. The irreversible inhibition of catalase by 3-amino-1,2,4-triazole (AT) was observed in the presence of CH3OOH or H2O2. The second-order rate constant of the catalase-AT formation in CH3OOH was 3.0 M-1 min-1 at 37 degrees C and pH 6.8 and the pKa value was estimated to be 6.10 from the pH profile of the rate constant of the AT-inhibition. These results indicate that A. niger catalase forms Compound I with the same properties as other catalases and peroxidases, but the velocity of the Compound I formation is lower than that of the others. 相似文献
46.
Momoko Chiba Masakazu Kikuchi Chiharu Tohyama Masataka Nishikawa 《Biological trace element research》1990,25(2):137-147
To study effects of simultaneous administration of tin (Sn) and selenium (Se) on concentrations of several essential elements, mice were injected with either SnCl2 (ip) or Na2SeO3 (sc), alone or both compounds at a daily dose of 5 mumol/kg each for 12 consecutive days. Mice were sacrificed at 20 h after the last injection and concentrations of Sn, Se, Na, Ca, Zn, P, Fe, K, and Mg in the liver, kidney, spleen, pancreas, testis, seminal vesicle, lung, femoral muscle, and femoral bone were determined. In the control mice, Sn and Se concentrations were the highest in bone (0.69 micrograms Sn and 6.93 micrograms Se/g dry wt). Administered Sn was found to accumulate in all organs except the testis. Among the essential elements determined, Na was the most affected in terms of concentration in the organs and Mg was the least affected element in these organs. Among the organs tested, each elemental concentration in the pancreas was most affected. Simultaneous injections of Sn and Se appeared to keep the correlation coefficients between elements similar to those found in the control mice. 相似文献
47.
48.
Kaoru Nakamura Takehiko Miyai Kiyoko Inoue Seiji Kawasaki Shinzaburo Oka Atsuyoshi Ohno 《Biocatalysis and Biotransformation》1990,3(1):17-24
Esters of 3-methyl-2-oxobutanoic acid are reduced with bakers' yeast by three methods: free bakers' yeast in water, immobilized bakers' yeast in water, and immobilized bakers' yeast in hexane. Although (R)-hydroxy esters are obtained in all cases, the enantiomeric excess varies from 3% (reduction of the methyl ester with free bakers' yeast in water) to 93% (reduction of the butyl ester with immobilized bakers' yeast in hexane) depending on the structure of substrate and on the reaction conditions. The mechanism of the present stereochemical control is discussed. 相似文献
49.
50.
Takeshi Kikuchi 《Journal of Protein Chemistry》1996,15(6):539-545
In a previous paper we demonstrated that the short-range compact regions in atrial natriuretic factor (-hANF) predicted by the average distance map (ADM) correspond to its active sites [Kikuchi,J. Protein Chem.11, 579–581 (1992)]. In the present paper we apply the same method to other bioactive peptides and peptidic enzyme inhibitors. We again observe that active sites in each peptide are contained in short-range compact regions predicted by the ADM for the peptide. This demonstrates that the ADM method predicts the possible location of active sites in biologically active peptides in general. The possibility of practical application of the present method to rational drug design is also discussed. 相似文献