全文获取类型
收费全文 | 33680篇 |
免费 | 2555篇 |
国内免费 | 2426篇 |
专业分类
38661篇 |
出版年
2024年 | 73篇 |
2023年 | 410篇 |
2022年 | 964篇 |
2021年 | 1613篇 |
2020年 | 1133篇 |
2019年 | 1390篇 |
2018年 | 1351篇 |
2017年 | 965篇 |
2016年 | 1424篇 |
2015年 | 2157篇 |
2014年 | 2469篇 |
2013年 | 2632篇 |
2012年 | 3055篇 |
2011年 | 2747篇 |
2010年 | 1747篇 |
2009年 | 1484篇 |
2008年 | 1824篇 |
2007年 | 1600篇 |
2006年 | 1423篇 |
2005年 | 1161篇 |
2004年 | 963篇 |
2003年 | 868篇 |
2002年 | 684篇 |
2001年 | 575篇 |
2000年 | 465篇 |
1999年 | 484篇 |
1998年 | 304篇 |
1997年 | 306篇 |
1996年 | 289篇 |
1995年 | 230篇 |
1994年 | 246篇 |
1993年 | 165篇 |
1992年 | 236篇 |
1991年 | 196篇 |
1990年 | 137篇 |
1989年 | 112篇 |
1988年 | 85篇 |
1987年 | 120篇 |
1986年 | 87篇 |
1985年 | 71篇 |
1984年 | 57篇 |
1983年 | 38篇 |
1982年 | 37篇 |
1981年 | 27篇 |
1980年 | 26篇 |
1979年 | 26篇 |
1978年 | 21篇 |
1975年 | 22篇 |
1974年 | 22篇 |
1972年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Tohru Takata Sun Nyunt Wai Akemi Takade Yoshiro Sawae Junko Ono Kazunobu Amako 《Microbiology and immunology》1995,39(9):639-645
From plate cultures of Campylobacter jejuni grown in room air a particulate protein of 62 kDa was isolated by ion-exchange chromatography. The protein had a square shape from the side view but when viewed from the top it had a star-shaped structure. The molecular size of the whole particle determined by gel filtration was 850 kDa which suggested the presence of 14 subunits of 62 kDa in each particle. The N-terminal 37 amino residues showed more than 80% homology with the sequence of these heat shock protein (HSP) 60 homologs of Chlamydia trachomatis, Helicobacter pylori, and Escherichia coli (GroEL). This protein is immunologically cross-reactive with the antiserum for the 60-kDa HSP of Yersinia enterocolitica. Production of the 62-kDa protein increased under heat stress and growth in an aerobic atmospheric environment. From these observations we concluded that the 62-kDa protein is a Campylobacter stress protein (Cj62) which belongs to the HSP 60 family. 相似文献
82.
在96孔板中进行抗脂质过氧化的微量测定 总被引:8,自引:0,他引:8
以Fe2+/半胱氨酸诱导大鼠肝微粒体为基本模型,根据硫代巴比妥酸(TBA)反应原理,优化不同反应条件,建立了一种在96孔板上进行抗脂质过氧化测定的一步反应方法,该方法的灵敏度不低于传统的试管法,而且还具有微量、快速、简便等优点,特别适用于大规模筛选和研究抗氧化剂.此外,也可用于其它系统诱导的抗脂质过氧化的测定. 相似文献
83.
84.
85.
A study of the oxidation of prostacyclin and some of its analogs by three 15-hydroxyprostaglandin dehydrogenases was undertaken to determine the structural features of these compounds which might influence their rate of enzymatic inactivation. The effect of some structural changes seemed to be determined by the substrate specificity of individual enzymes. Other changes influenced the rate of oxidation by all three enzymes similarily. Among this latter group it was noted that a 15S hydroxyl group is necessary for oxidation to occur and that steric changes in the carboxy side chain and structural changes in the epoxy ring have a greater effect on the affinity of the substrate for the enzyme than on its maximum rate of oxidation. Certain analogs of prostacyclin are not substrates for one or more of the enzymes tested. Of these, (5S)-9-deoxy-5,9 alpha-epoxy-PGF1 and its methyl ester are potent inhibitors of only the placental enzyme---an interesting case of apparent selective metabolic regulation. 相似文献
86.
Transplasma membrane electron transport, as assayed by external ferricyanide reduction, has been related to control of growth and hormone response of cells. Elicitor-stimulated transmembrane NADPH oxidase is important for bacteriocidal superoxide production by neutrophils. Since adriamycin is myelosuppressive and can stimulate superoxide production, its effects on the two redox systems of porcine neutrophil plasma membranes were compared. Adriamycin inhibits transplasma membrane ferricyanide and stimulates superoxide production activated by phorbol myristate acetate (PMA). Ferricyanide reduction in PMA-treated cells becomes resistant to inhibition by adriamycin. These results provide evidence for an independent effect of adriamycin on transmembrane ferricyanide reduction and on superoxide generation. 相似文献
87.
88.
A M Sun G M Healy I Vacek H G Macmorine 《Biochemical and biophysical research communications》1977,79(1):185-189
Monolayer cultures have been derived from bovine embryonic pancreatic cells grown in medium CMRL-1969 supplemented with foetal calf serum. The isolate has been subcultivated up to 10 population doublings. Insulin secretion from the cells into the culture medium declined with increasing passages. Of several insulin secretagogues, glucagon was found to be effective in potentiating insulin release from the cultivated cells into the medium. Insulin secretion rose to approximately 600 μU/culture/day in the presence of glucagon as compared to an average of 10 μU/culture/day in the control. This may be the first demonstration of a beta cell line developed from bovine embryonic pancreas. 相似文献
89.
Dynamic light scattering has been used to study the temperature dependence of Ca2+-induced fusion of phosphatidylserine vesicles and mixed vesicles containing phosphatidylserine and different phosphatidylcholines. The final vesicle size after Ca2+ and EDTA incubation serves as a measure of the extent of fusion. With phosphatidylserine vesicles, the extent of fusion shows a sharp maximum at an incubation temperature which depends on the Ca2+ concentration between 0.8 and 2 mM. The shift in the fusion peak temperature with Ca2+ concentration is similar to the typical shift in the phase transition temperature with divalent cation concentration in acidic phospholipids. The results suggest a direct correlation between the fusion peak temperature and the phase transition temperature in the presence of Ca2+ prior to fusion. With mixed vesicles containing up to 33% of a phosphatidylcholine in at least 2 mM Ca2+, the extent of fusion as a function of incubation temperature also shows a maximum. The fusion peak temperature is essentially independent of the quantity and type of phosphatidylcholine and the Ca2+ concentration, and identical to that with pure phosphatidylserine in excess Ca2+. The results imply that Ca2+-induced molecular segregation occurs first, and fusion subsequently takes place between pure phosphatidylserine domains. 相似文献
90.
(p-Amidinophenyl)methanesulfonyl fluoride, an irreversible inhibitor of serine proteases 总被引:4,自引:0,他引:4
p-(Amidinophenyl)methanesulfonyl fluoride (p-APMSF) has been synthesized and shown to be a specific, irreversible inhibitor of the class of plasma serine proteases which demonstrate substrate specificity for the positively charged side chains of the amino acid lysine or arginine. In equimolar concentration, this compound causes immediate and complete irreversible inhibition of bovine trypsin and human thrombin. A 5-10-fold molar excess of reagent over enzyme is required to achieve complete irreversible inhibition of bovine Factor Xa, human plasmin, human C1-r, and human C1-s. the Ki of p-APMSF for all of the above-mentioned proteases is between 1 and 2 microM. In contrast, p-APMSF in large molar excess does not inactivate chymotrypsin or acetylcholinesterase. The unique reactivity of p-APMSF has been further shown in comparison with the related compound p-nitrophenyl (p-amidinophenyl)methanesulfonate which is an active-site titrant for thrombin but reacts poorly with Factor Xa, C1-r, and C1-s and is not hydrolyzed by bovine trypsin or human plasmin. Similarly, (p-amidinophenyl)methanesulfonate has a Ki of 30 microM for thrombin but is a poor inhibitor of trypsin, Factor Xa, C1-r, C1-s, and plasmin. Studies with bovine trypsin have demonstrated that the inhibitory activity of p-APMSF is the result of its interaction with the diisopropyl fluorophosphate reactive site. The unique reactivity of this inhibitor classifies it as one of the most effective active site directed reagents for this class of serine proteases. Collectively, these results suggest that the primary substrate binding site of these enzymes, which share a high degree of structural homology, do in fact significantly differ from each other in their ability to interact with low molecular weight inhibitors and synthetic substrates. 相似文献