全文获取类型
收费全文 | 2044篇 |
免费 | 140篇 |
国内免费 | 1篇 |
出版年
2023年 | 8篇 |
2022年 | 26篇 |
2021年 | 35篇 |
2020年 | 33篇 |
2019年 | 39篇 |
2018年 | 59篇 |
2017年 | 39篇 |
2016年 | 67篇 |
2015年 | 97篇 |
2014年 | 116篇 |
2013年 | 134篇 |
2012年 | 177篇 |
2011年 | 144篇 |
2010年 | 99篇 |
2009年 | 88篇 |
2008年 | 120篇 |
2007年 | 130篇 |
2006年 | 121篇 |
2005年 | 104篇 |
2004年 | 83篇 |
2003年 | 66篇 |
2002年 | 67篇 |
2001年 | 20篇 |
2000年 | 14篇 |
1999年 | 24篇 |
1998年 | 21篇 |
1997年 | 17篇 |
1996年 | 17篇 |
1995年 | 12篇 |
1994年 | 14篇 |
1993年 | 10篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 7篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 12篇 |
1985年 | 13篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1975年 | 6篇 |
1970年 | 5篇 |
1968年 | 6篇 |
1967年 | 6篇 |
排序方式: 共有2185条查询结果,搜索用时 15 毫秒
31.
Luciano Rodríguez-Solórzano JoséC. Rodríguez JoséM. Ortiz Antolín Mellado 《FEMS microbiology letters》1984,23(2-3):329-331
Abstract The Yersinia enterocolitica strain MS201 (serotype O:3) was transformed by pBR322 DNA extracted from an Escherichia coli strain. The pBR322 DNA extracted from an Escherichia coli strain. The pBR322 DNA extracted from the transformed Y. enterocolitica is able to transform plasmid-free MS201 at a significantly higher frequency, suggesting the existence of a restriction-modification system in MS201. 相似文献
32.
The penetration of bovine kidney cells by infectious bovine rhinotracheitis virus, a member of the herpesvirus group, was
investigated using the direct immunoferritin labeling technique. Electron microscopic examination of infected cells after
10 min at 37°C revealed fusion between viral envelope and cell membrane; the former reacted with the ferritin particles conjugated
with antiviral antibody. However, shortly after penetration of the nucleocapsid, viral-specific antigenic sites on the plasma
membrane were not detected by the immunoferritin technique. Antigenically reactive structures in a disorganized array were
frequently detected extracellularly, situated above the penetration sites as indicated by the internalized nucleocapsids. 相似文献
33.
Giancarlo Bianchi Roberto Fiocchi Alessandra Tavani Luciano Manara 《Life sciences》1982,30(22):1875-1883
Single doses of naloxone (0.025 to 0.5 mg/kg) or of one of four quaternary narcotic antagonists (i.e. nalorphine allobromide, nalorphine methobromide, naloxone methobromide or naltrexone methobromide, 1 to 60 mg/kg) were given s.c. to rats before morphine, 5 mg/kg i.v. In the absence of antagonists morphine reduced G.I. transit of a charcoal meal to about 15% of drug-free controls and consistently delayed nociceptive reactions (55°C hot plate) in all animals. Doses of antagonists slightly reducing morphine antinociception (centrally effective = A) and restoring G.I. transit to about 50% of drug-free rats (peripherally effective = B) were estimated. The A:B ratio, indicating peripheral selectivity, was at least 8 for any of the quaternary antagonists given 10 min before morphine, but prolonging this interval may have resulted in a lower figure (i.e. less peripheral selectivity) because of reduced A and increased B. This was definitely so for naltrexone methobromide (A:B, > 60 at 10 min, about 1 at 80 min) and was not apparent for nalorphine methobromide according to available data, which for nalorphine allobromide and to a lesser extent for naloxone methobromide showed only an increase in B at intervals longer than 10 min. Both morphine-induced antinociception and inhibition of G.I. transit were reduced by naloxone at the lower doses tested and were fully prevented at the higher. These findings indicate that, unlike naloxone, the investigated quaternary narcotic antagonists are interesting prototype drugs for selective blockade of opiate receptors outside the CNS, although certain critical aspects, possibly biological N-dealkylation to the corresponding tertiary antagonists, condition peripheral selectivity. 相似文献
34.
Naltrexone, an opiate antagonist, was administered to young obese (ob/ob) and lean mice for five weeks. Animals had continuous access to food and received 10 mg/kg SC twice daily with equivalent volumes of saline given to controls. The effects on body weight, and pituitary and plasma levels of β-endorphin-like material were measured. Naltrexone-injected obese animals gained weight more slowly over the first three weeks while the weight gain of lean animals was not affected by naltrexone. Plasma levels of β-endorphin were shown to be significantly higher in untreated ob/ob mice and this difference increased with age (4–20 weeks). With naltrexone treatment, plasma levels in +/? mice rose and exceeded those in ob/ob. Saline treatment appeared to be a stress, and pituitary β-endorphins rose 4–6 fold in ob/ob compared with +/?. While naltrexone reduced the levels in ob/ob pituitary towards normal, no effect on β-endorphin levels in pituitary of lean mice was obtained. In vitro studies of effects of the opiate antagonists, naloxone, on insulin secretion by isolated islets provided additional evidence of resistance of lean mice to naloxone relative to ob/ob. (IRI secretion fell only in naloxone treated ob/ob islets.) These observations support the contention that this form of genetic obesity is characterized by elevated endogenous opiate levels and an increased sensitivity to opiate antagonists such as naltrexone or naloxone. 相似文献
35.
Summary The growth of two strains of the petitenegative yeast Kluyveromyces lactis is inhibited by Tetracycline in different ways under the same culture conditions. Tetracycline resistant mutants of one strain have been isolated which can tolerate doses as high as 3000 g/ml of antibiotic.The segregation pattern of this character obtained by random spore analysis of the ascospores derived from the cross of the two strains strongly suggests that the resistance to tetracycline is under mitochondrial control. 相似文献
36.
Chronic treatment with haloperidol is associated with complete tolerance to the decreasing effect of the neuroleptic on cerebellar cGMP content, vice versa chronic haloperidol causes hypersensitivity to the enhancing effect of apomorphine on cerebellar cGMP. Thus, the administration of 0.5 mg/Kg of haloperidol decreases cerebellar cGMP by 80% in control rats but fails to alter this nucleotide in rats chronically treated with haloperidol (0.5 mg/Kg twice daily for 20 days). A dose of 0.5 mg/Kg of apomorphine enhances cGMP by approximately 25 and 60 percent in control rats and in rats chronically treated with haloperidol, respectively. The results suggest that: a) There is a functional link between striatum and cerebellum; b) Cerebellar cGMP is a sensitive index of the state of activation of striatal dopamine receptors. 相似文献
37.
38.
Dr. Laura Curatolo Christine Chaponnier Maria Benedetta Donati Luciano Morasca Giulio Gabbiani 《Cell and tissue research》1982,223(3):665-673
Summary It is known that human and animal fibroblasts are able to induce the retraction of a fibrin clot. In the present study the correlation between (i) fibrinclot retractile (FCR) activity, (ii) the number of actin stress-lines in mouse fibroblasts during growth in culture, and (iii) the sensitivity of actin stress-lines to a powerful actin-depolymerizing factor (ADF), present in plasma and serum of humans and laboratory animals was investigated. Fibroblasts at early passages (2–4) were tested for these parameters at various intervals after seeding (24, 96, and 168 h). The number of actin stress-lines was progressively higher, while the sensitivity to ADF action was progressively lower in cells cultured from 24 to 168 h; the FCR capacity was significantly decreased at 168 h. These data suggest that cells containing weakly polymerized and/or stabilized actin are more active than those containing highly polymerized and/or stabilized actin in triggering fibroblast contraction. 相似文献
39.
40.
Salvatore Andini Ettore Benedetti Luciano Ferrara Livio Paolillo Piero Andrea Temussi 《Origins of life and evolution of the biosphere》1975,6(1-2):147-153
Several polypeptides prepared by means of pyrocondensation have been the subject of structural investigations. Attention has been focused on the constitutional characterization of homo-and co-polymers containing Asp and Glu residues, whose role is essential for the formation of the so-called proteinoids. Contrary to the literature data based on chemical degradation, nmr studies show conclusively that in thermal poly-aspartic acid only β-peptide linkages are present. This result casts serious doubt on the role thermal condensation might have played in prebiotic polypeptide syntheses. 相似文献