全文获取类型
收费全文 | 768273篇 |
免费 | 90604篇 |
国内免费 | 566篇 |
专业分类
859443篇 |
出版年
2016年 | 8264篇 |
2015年 | 12300篇 |
2014年 | 14061篇 |
2013年 | 20096篇 |
2012年 | 22681篇 |
2011年 | 22882篇 |
2010年 | 15170篇 |
2009年 | 14180篇 |
2008年 | 20174篇 |
2007年 | 21001篇 |
2006年 | 19437篇 |
2005年 | 19045篇 |
2004年 | 18754篇 |
2003年 | 17920篇 |
2002年 | 17452篇 |
2001年 | 34911篇 |
2000年 | 35609篇 |
1999年 | 28449篇 |
1998年 | 10117篇 |
1997年 | 10462篇 |
1996年 | 10011篇 |
1995年 | 9275篇 |
1994年 | 9258篇 |
1993年 | 9124篇 |
1992年 | 22923篇 |
1991年 | 22055篇 |
1990年 | 21527篇 |
1989年 | 21036篇 |
1988年 | 19324篇 |
1987年 | 18592篇 |
1986年 | 17426篇 |
1985年 | 17280篇 |
1984年 | 14495篇 |
1983年 | 12520篇 |
1982年 | 9962篇 |
1981年 | 9098篇 |
1980年 | 8395篇 |
1979年 | 14037篇 |
1978年 | 11063篇 |
1977年 | 10175篇 |
1976年 | 9527篇 |
1975年 | 10440篇 |
1974年 | 11406篇 |
1973年 | 11223篇 |
1972年 | 10318篇 |
1971年 | 9454篇 |
1970年 | 8070篇 |
1969年 | 7945篇 |
1968年 | 7166篇 |
1967年 | 6169篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Immersion staining of coarse fish in the Thames 总被引:1,自引:0,他引:1
C. P. Mathews 《Journal of fish biology》1970,2(1):57-58
Thirty-one vital dyes were screened for marking bleak, roach and gudgeon by total body immersion in aqueous solutions of the dye. Only six dyes stained without killing, and of these Nile blue, neutral red and Bismarck brown were used successfully in the field. This approach to estimation of population size was abandoned because (1) the toxicity of the dyes varied at different times of year, (2) the numbers needed for release were impractically high and (3) fingerlings showed extremely high mortality on handling. 相似文献
992.
993.
J C Lambert G Vallette G E Seralini R Vranckx E Nunez C Stora 《Comptes rendus de l'Académie des sciences. Série III, Sciences de la vie》1986,302(9):353-358
Data are presented which indicate a possible action of alpha-fetoprotein (AFP) on female germinal cells. The in vitro maturation of mature mice oocytes was significantly inhibited when mouse AFP replaced albumin in the culture medium. In addition, the degenerative aspect of oocytes cultured with AFP seemed to indicate that this me?otic inhibition was caused by a premature degeneration of oocytes rather than by a blockage at a specific stage of maturation. Thus AFP, perhaps through its ligands, may play a role in the reduction of germinal cells during fetal and immediate post-natal life rather than in the arrest of me?osis at the diplotene stage. 相似文献
994.
The transport of ATP out of mitochondria and uptake of ADP and Pi into the matrix are coupled to the uptake of one proton (Klingenberg, M., and Rottenberg, H. (1977) Eur. J. Biochem. 73, 125--130). According to the chemiosmotic hypothesis of oxidative phosphorylation this coupling of nucleotide and Pi transport to proton transport implies that the P/O ratio for the synthesis and transport of ATP to the external medium is less than the P/O ratio for the synthesis of ATP inside mitochondria. A survey of previous determinations of the P/O ratio of intact mitochondria showed little convincing evidence in support of the currently accepted values of 3 with NADH-linked substrates and 2 with succinate. We have measured P/O ratios in rat liver mitochondria by the ADP pulse method and by 32 Pi esterification, measuring oxygen uptake with an oxygen electrode, and find values close to 2 with beta-hydroxybutyrate as substrate and 1.3 with succinate as substrate in the presence of rotenone to inhibit NADH oxidation. These values were largely independent of pH, temperature, Mg2+ ion concentration, Pi concentration, ADP pulse size, or amount of mitochondria used. We suggest that these are the true values of the P/O ratio for ATP synthesis and transport by mitochondria, and that previously reported higher values resulted from errors in the determination of oxygen uptake and the use of substrates which lead to ATP synthesis by succinate thiokinase. 相似文献
995.
996.
997.
998.
Future uses of pollen analysis must include plant macrofossils 总被引:8,自引:0,他引:8
999.
R. Shainkin-Kestenbaum C. Caruso G. M. Berlyne 《Biological trace element research》1991,28(3):213-221
The effect of nickel on superoxide dismutase activity (SOD), as well as on rate of hydroxydopamine oxidation, was studied in vitro since lipid peroxidation has been implicated in cell damage by nickel, whose toxicity and carcinogenicity are well established. Nickel strongly inhibits SOD activity. The degree of inhibition is directly proportion to the nickel concentration (tested range 0.066 to 0.33 microgram/mL in the reaction mixture); to the substrate concentration (tested range 0.4 x 10 4M to 1.1 x 10 4M 6-hydroxydopamine); and to reaction mixture. Autoxidation of 6-hydroxydopamine was increased by nickel concentrations higher than 15 micrograms/mL. The combination of excessive oxygen free radical production and inhibition of their elimination by inhibition of SOD activity may contribute to the nickel toxicity that has been reported in industrial accidents, as well as to the high incidence of cancer occurring in nickel workers. It may also contribute to many complications in uremic patients, in whom increased serum nickel levels were reported to be in a similar range to those inhibiting SOD. 相似文献
1000.
E. R. R. Rochedo L. F. C. Conti H. G. Paretzke 《Radiation and environmental biophysics》1996,35(4):243-261
The structure and mathematical model of PARATI, a detailed computer programme developed for the assessment of the radiological
consequences of an accidental contamination of urban areas, is described with respect to the scenarios used for the estimation
of exposure fields in a village or town, the models for the initial and secondary contamination with the radionuclide 137Cs, the concepts for calculating the resulting radiation exposures and the changes with time of the contamination and radiation
fields. Kerma rates at various locations in tropical urban areas are given, and the contribution of different contaminated
surfaces to these rates after dry or wet deposition are discussed.
Received: 12 April 1996 / Accepted in revised form: 30 August 1996 相似文献