全文获取类型
收费全文 | 3744篇 |
免费 | 253篇 |
国内免费 | 4篇 |
专业分类
4001篇 |
出版年
2023年 | 22篇 |
2022年 | 68篇 |
2021年 | 137篇 |
2020年 | 51篇 |
2019年 | 64篇 |
2018年 | 92篇 |
2017年 | 69篇 |
2016年 | 109篇 |
2015年 | 157篇 |
2014年 | 181篇 |
2013年 | 247篇 |
2012年 | 277篇 |
2011年 | 311篇 |
2010年 | 180篇 |
2009年 | 122篇 |
2008年 | 179篇 |
2007年 | 165篇 |
2006年 | 145篇 |
2005年 | 120篇 |
2004年 | 126篇 |
2003年 | 104篇 |
2002年 | 87篇 |
2001年 | 84篇 |
2000年 | 62篇 |
1999年 | 72篇 |
1998年 | 26篇 |
1997年 | 18篇 |
1995年 | 25篇 |
1994年 | 17篇 |
1993年 | 23篇 |
1992年 | 37篇 |
1991年 | 49篇 |
1990年 | 29篇 |
1989年 | 38篇 |
1988年 | 29篇 |
1987年 | 33篇 |
1986年 | 28篇 |
1985年 | 23篇 |
1984年 | 23篇 |
1983年 | 24篇 |
1982年 | 22篇 |
1980年 | 18篇 |
1979年 | 38篇 |
1978年 | 18篇 |
1977年 | 23篇 |
1974年 | 22篇 |
1973年 | 22篇 |
1972年 | 20篇 |
1969年 | 16篇 |
1967年 | 16篇 |
排序方式: 共有4001条查询结果,搜索用时 15 毫秒
21.
Site-related differences in the localization of the monoclonal antibody OX7 in SL2 and SL1 lymphomas
Howard Sands Peter L. Jones William P. Neacy Sudhir A. Shah Brian M. Gallagher 《Cancer immunology, immunotherapy : CII》1986,22(3):169-175
Summary The uptake of a monoclonal antibody (OX7) by murine lymphomas (SL1, SL2) growing in two sites in the mouse were compared. SL2 tumors grown in the subrenal site showed greater specific antibody uptake than did the same tumor grown in the subcutaneous site. Major differences in membrane bound antibody, in vitro antibody binding patterns, and gamma scintillation camera imaging were also observed between the two sites. These differences may be due to the greater blood flow measured in tumors growing in the subrenal capsule than those growing at the subcutaneous site. The differences observed in antibody uptake of the same tumor growing in two different sites raises questions concerning the choice of animal model systems that can be used to predict clinical utility. 相似文献
22.
Various Bacteroides spp. were examined by physiological tests, presence of specific enzymes, antibiotic sensitivity, menaquinone composition and a few miscellaneous tests. The data matrix containing 58 strains and 55 unit characters was examined using Gower's similarity coefficients (SG) and included matching negative character states and multistate characters. The highly saccharolytic strains were separated from the less saccharolytic and non-fermentative strains at the 55% similarity level; while at the slightly higher level of 63% strains of Capnocytophaga (formerly Bact. ochraceus) were recovered as a compact phenon distinct from other saccharolytic species. The phenogram was divided into 6 clusters at 72% similarity level. Most of the 'Bact. fragilis group' of species clustered in one phenon while Bact. melaninogenicus ssp. melaninogenicus, Bact. bivius and a new species, Bact. denticola, formed another group. Another phenon comprised the saccharolytic non-pigmented species closely related to Bact. oralis such as Bact. buccalis and Bact. pentosaceus. The less saccharolytic strains of Bact. melaninogenicus ssp. intemedius and Bact. disiens were recovered in a distinct phenon. The low affinity (less than 55% similarity) between the two subspecies of Bact. melaninogenicus emphasised the need for reclassifying these taxa into separate species. The non-fermentative and very weakly saccharolytic strains formed good taxospecies. The separation of this cluster into three subclusters is in excellent agreement with chemotaxonomic data now available. 相似文献
23.
Genus Bacteroides. A chemotaxonomical perspective 总被引:3,自引:0,他引:3
24.
25.
26.
27.
Abstract— The reduction of desmosterol by cell-free preparations from developing rat brain was established and the age-dependent alterations in reductase activity were correlated with levels of desmosterol in brain. An increase in enzymic activity followed closely the sharp increase in levels of desmosterol that was observed at about 5 days of age and that reached a maximum at 8-11 days of postnatal age. Furthermore, the abrupt decrease in the desmosterol content of brain at 13-15 days of age was associated with a decrease in enzymic activity. We suggest that the enzyme may be substrate-induced and that this attribute may be of significance with respect to the ontogenesis of myelin. Cerebral desmosterol reductase exhibited a specific requirement for NADPH and was primarily a particulate enzyme. 相似文献
28.
Chemical composition of hyphal walls of dermatophytes 总被引:3,自引:0,他引:3
29.
30.
Coleoptile and root tips ofTriticum aestivum cv. Arnej 624 and those ofAvena sativa cv. Victory (Svalöf) as well as dry excised embryos ofTriticum aestivum cv. Rival (Svalöf) and those ofArachis hypogaea cv. 34 3A. H. were cultivated in media containing various concentrations of sucrose and growth regulators, like ascorbic acid, indole-3-acetic acid and gibberellin. Growth, differentiation and water uptake of the various explants were determined at regular time intervals. Further, the concentration of the endogenous ascorbic acid in mg./g. fresh weight, as well as the amount of this growth regulator utilized as per cent of the total were determined. Although all the three growth regulators promote growth in the explants, their effect is best felt when sucrose of a higher concentration (1.0 per cent) is added to the medium. In fact, the response to 1.0 per cent sucrose is sometimes as good as a combination of a growth regulator with sucrose, especially in the case of root explants. The results clearly indicate that the biosynthesis of ascorbic acid in the explants is catalyzed by the addition of indole-3-acetic acid as well as gibberellin. Simultaneously, the utilization of ascorbic acid is also appreciably increased by the presence of these growth regulators. Addition of 1.0 per cent sucrose to the medium containing the above mentioned growth regulators augments to a considerable extent not only the concentration of ascorbic acid, but also steps up its utilization. Enhancement of ascorbic acid as well as its increased utilization are correlated with rapid imbibition of water, growth and differentiation. The role of ascorbic acid in growth is discussed; and on the basis of the data presented here it is postulated that: (1) auxin and gibberellin function in the growth process by catalyzing the biosynthesis of ascorbic acid; and (2) that ascorbic acid not only participates in activation of various enzyme systems, but also stimulates the production of adenosine triphosphate by acting as an electron donor in photosynthetic phosphorylation as well as oxidative phosphorylation; (3) that the above action of ascorbic acid creates a favourable redox balance for synthesis of nucleic acids, proteins, enzymeproteins, and cell-wall constituents, thus enabling the processes of cell division and enlargement to proceed at a fast rate; and (4) that the relative rates of cell division and cell enlargement as well as “ageing” will determine the pattern of plant development. 相似文献