全文获取类型
收费全文 | 553971篇 |
免费 | 57563篇 |
国内免费 | 223篇 |
专业分类
611757篇 |
出版年
2018年 | 4924篇 |
2016年 | 6458篇 |
2015年 | 7929篇 |
2014年 | 9634篇 |
2013年 | 14227篇 |
2012年 | 15970篇 |
2011年 | 16561篇 |
2010年 | 11258篇 |
2009年 | 10357篇 |
2008年 | 14992篇 |
2007年 | 15381篇 |
2006年 | 14696篇 |
2005年 | 13879篇 |
2004年 | 13950篇 |
2003年 | 13510篇 |
2002年 | 13248篇 |
2001年 | 25334篇 |
2000年 | 25663篇 |
1999年 | 20307篇 |
1998年 | 6995篇 |
1997年 | 7292篇 |
1996年 | 6931篇 |
1995年 | 6321篇 |
1994年 | 6377篇 |
1993年 | 6317篇 |
1992年 | 17012篇 |
1991年 | 16635篇 |
1990年 | 16324篇 |
1989年 | 16368篇 |
1988年 | 15002篇 |
1987年 | 14257篇 |
1986年 | 13172篇 |
1985年 | 13305篇 |
1984年 | 10787篇 |
1983年 | 9356篇 |
1982年 | 6906篇 |
1981年 | 6103篇 |
1980年 | 5956篇 |
1979年 | 10359篇 |
1978年 | 8102篇 |
1977年 | 7216篇 |
1976年 | 6878篇 |
1975年 | 7711篇 |
1974年 | 8265篇 |
1973年 | 8103篇 |
1972年 | 7429篇 |
1971年 | 6703篇 |
1970年 | 5862篇 |
1969年 | 5483篇 |
1968年 | 5030篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Various 2-nitronaphthofuran derivatives (related to each other by simple structural modifications) were tested for 2 different effects in CV-1 monkey kidney cell cultures: the immediate inhibition of normal DNA synthesis and the capacity of pretreated cultures (40 h of contact) to support the replication of UV-damaged Herpes simplex virus (HSV). For all compounds tested, a fair correlation was found between their efficiencies to inhibit cellular DNA synthesis and to provoke an increase in UV-HSV production (virus reactivation). Virus reactivation was due to an increase in both the number of virus-producing cells and the amount of infectious particles produced per cell. The most efficient 2-nitronaphthofurans (particularly 2-nitro-7-methoxy-naphtho[2,1-b]furan-R 7000) were at least as potent as aflatoxin B1 in inducing virus reactivation. 相似文献
992.
993.
994.
995.
By means of radioimmunoassay a clear-cut peak of melatonin concentration was found in the pineal organ of the pigeon at the middle of the scotophase (Coisin et al. 1982a). The aim of the present study was to identify the cell type responsible for the nocturnal indole metabolism, including melatonin synthesis, in the pineal of this avian species. After a short-term incubation or organ culture in the presence of [3H]-indolic precursors, [3H]-5-hydroxytryptophan or [3H]-5-hydroxytryptamine, the relative amounts of deaminated and acetylated products occurring in the pineal organ were measured by the use of thin layer chromatography and liquid-scintillation counting. It was possible to modify the relative amounts of deaminated and acetylated indoles by the application of some inhibitors of monoamine oxidase and cyclic nucleotide phosphodiesterase. Irrespective of the experimental conditions, high-resolution autoradiography combined with the above-mentioned radiochemical experiments showed that the cells of the receptor line (modified photoreceptor cells) are responsible for indole storage and metabolism, and very probably also for melatonin biosynthesis. The other cell types of the pineal parenchyma did not display significant labeling. 相似文献
996.
Biomass, relative growth rate (RGR), organic and inorganic solute contents in control and NaCl (50–100 mM) affected roots
or calli of the wild tomato genotypeLycopersicon pennellii and theLycopersicon esculentum wilty mutantflacca were compared. Under NaCl-stress, the RGR of calli fromL. pennellii was higher than that of the mutantflacca, while the root biomass of the former was lower than that of the latter. Constant water contents were found in calli and
roots, irrespective of the genotypes and NaCl concentrations. Taking into account the solute contents of the apoplasm, Na+ accumulation was similar in the sensitive tissues (calli fromL. flacca, roots ofL. pennellii) and the tolerant ones (calli fromL. pennellii, flacca roots). Decreased K+ and Mg2+ and increased proline contents were found in both sensitive tissues. In comparison with sensitiveL. pennellii roots, salt sensitiveflacca calli showed increased total organic acid and amino acid contents. 相似文献
997.
O W Petersen P E H?yer J Hilgers P Briand B van Deurs 《Virchows Archiv. B, Cell pathology including molecular pathology》1985,50(1):27-42
Epithelial cell islets in primary monolayer cultures of human breast biopsies were characterized by combined immuno-, enzyme- and DNA cytochemistry as well as by analysis of attachment-, spread- and growth patterns. For cultivation we used explants from reduction mammoplasties, benign lesions, primary carcinomas and metastases. Milk fat globule membrane antigen (MFGM-A) was detected with a monoclonal antibody, and the tetrazolium reaction for glucose 6-phosphate dehydrogenase (G6PDH) as well as DNA content of the cultured cells were quantified. Spreading and growth of individual islets were studied by image analysis. Fibroblast-like cells did not express MFGM-A, and whereas epithelial (MFGM-A positive) cell islets of normal and benign origin showed cells with no or low G6PDH reaction, respectively, the majority of epithelial cell islets from 11 out of 21 carcinomas showed strong reaction. Cell islets with strong G6PDH reaction were sometimes hyperdiploid. Moreover, whereas cell islets with no or low reaction from both benign lesions and carcinomas readily attached and spread in a serum-free medium and showed population doubling times of 30 to 110 h, cell islets with strong reaction from carcinomas and metastatic lesions required serum for attachment and their growth rate was too low to be determined. 相似文献
998.
999.
K H?kkinen M Alén P V Komi 《European journal of applied physiology and occupational physiology》1984,53(2):97-105
Various aspects of neuromuscular, anaerobic, and aerobic performance capacity were investigated in four powerlifters, seven bodybuilders, and three wrestlers with a history of specific training for several years. The data (means +/- SD) showed that the three subject groups possessed similar values for maximal isometric force per unit bodyweight (50.7 +/- 9.6, 49.3 +/- 4.1, and 49.3 +/- 10.9 N/kg, respectively). However, significant (P less than 0.05) differences were observed in the times for isometric force production, so that e.g., times to produce a 30% force level were shorter for the wrestlers and bodybuilders (28.3 +/- 3.1 and 26.4 +/- 6.6 ms) than that (53.3 +/- 23.7 ms) for the powerlifters. Utilization of elastic energy by the wrestlers was significantly (P less than 0.05) better than that of the other two subject groups, as judged from differences between the counter-movement and squat jumps at 0, 40, and 100 kg's loads. No differences were observed between the groups in anaerobic power in a 1-min maximal test, but the values for VO2 max were higher (P less than 0.05) among the wrestlers and bodybuilders (57.8 +/- 6.6 and 50.8 +/- 6.8 ml X kg-1 X min-1) as compared to the powerlifters (41.9 +/- 7.2 ml X kg-1 X min-1). Within the limitations of the subject sample, no differences of a statistical significancy were observed between the groups in fibre distribution, fibre areas, or the area ratio of fast (FT) and slow (ST) twitch fibres in vastus lateralis.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
1000.