全文获取类型
收费全文 | 771775篇 |
免费 | 91074篇 |
国内免费 | 357篇 |
出版年
2018年 | 6805篇 |
2016年 | 9117篇 |
2015年 | 12493篇 |
2014年 | 14629篇 |
2013年 | 20773篇 |
2012年 | 23202篇 |
2011年 | 23923篇 |
2010年 | 16292篇 |
2009年 | 15178篇 |
2008年 | 21440篇 |
2007年 | 22298篇 |
2006年 | 20797篇 |
2005年 | 20025篇 |
2004年 | 19724篇 |
2003年 | 19152篇 |
2002年 | 18641篇 |
2001年 | 32886篇 |
2000年 | 33036篇 |
1999年 | 26330篇 |
1998年 | 9692篇 |
1997年 | 10300篇 |
1996年 | 9652篇 |
1995年 | 9101篇 |
1994年 | 8918篇 |
1993年 | 9069篇 |
1992年 | 22437篇 |
1991年 | 22135篇 |
1990年 | 21402篇 |
1989年 | 20933篇 |
1988年 | 19519篇 |
1987年 | 18897篇 |
1986年 | 17633篇 |
1985年 | 17622篇 |
1984年 | 14803篇 |
1983年 | 12762篇 |
1982年 | 9933篇 |
1981年 | 8938篇 |
1980年 | 8607篇 |
1979年 | 14161篇 |
1978年 | 11281篇 |
1977年 | 10347篇 |
1976年 | 9866篇 |
1975年 | 10707篇 |
1974年 | 11575篇 |
1973年 | 11386篇 |
1972年 | 10494篇 |
1971年 | 9545篇 |
1970年 | 8299篇 |
1969年 | 8091篇 |
1968年 | 7582篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
G E Tranter 《Bio Systems》1987,20(1):37-48
The violation of parity by the weak interactions ensures that enantiomeric chiral molecules have inequivalent energies, one being inherently stabilized with respect to the other. These parity-violating energy differences have been calculated for a number of fundamental biomolecules including a series of alpha-amino acids, polypeptide structures, and a representative of the sugar series together with its variation over a possible prebiotic reaction path leading to alpha-amino acids. In each case the natural enantiomer found in terrestrial biochemistry was shown to be intrinsically stabilized and preferred over its unnatural enantiomer. The significance of these results in accounting for the prebiotic origins of the terrestrial biomolecular homochirality is discussed and the possible consequences of parity-violating energy differences in mineral catalysts during the prebiotic era considered. 相似文献
992.
993.
994.
ROBIN M. OVERSTREET WILLIAM E. HAWKINS JOHN W. FOURNIE 《The Journal of eukaryotic microbiology》1984,31(2):332-339
Calyptospora n. g. was erected for Eimeria funduli because the sporocyst of that species lacks Stieda and sub-Stieda bodies, has a veil supported by sporopodia, and has an anterior apical opening. A suture may be present, but it does not completely divide the sporocyst into two valves. Because C. funduli has an obligatory invertebrate intermediate host, we established Calyptosporidae n. fam. to accommodate Calyptospora and tentatively to accept Goussia. A new subgenus, Plagula, is erected for species of Goussia with a sporocystic veil not supported by sporopodia. We consider the family more primitive than Eimeriidae, Sarcocystidae, and possibly Lankesterellidae. 相似文献
995.
Naturally occurring strains of Salmonella paratyphi B unable to form adhesive (type-1) fimbriae 总被引:1,自引:0,他引:1
D C Old 《Genetical research》1982,40(3):305-313
996.
997.
The finger and palmar prints of 60 women with breast carcinoma were studied. The results were compared with two groups of
healthy women, the first consisted of old women and the second of young women. The dermatoglyphics seem to be of little use
in the diagnosis of cancers of ectodermic origin.
Supported by M.P.I. 60%, 1983 相似文献
998.
D. Higuet 《Genetica》1986,69(2):107-110
Under the hypothesis that heterosis may be due to a greater flexibility of heterozygotes, we have measured in a Drosophila melanogaster strain, polymorphic at the sepia locus, female productivity of the homozygotes and heterozygotes for this locus, in constant as well as in fluctuating temperature conditions. It was expected that the heterozygotes, being more flexible, would be better adapted to a fluctuating temperature than to a constant one. At none of the three temperature regimes (18°C; 28°C; 18–28°C) heterosis or rather overdominance was evident. However, fluctuating temperature results reveal a greater performance of all genotypes than constant-temperature ones do. 相似文献
999.
Robert C. Tait Byron E. Froman Debbie L. Laudencia-Chingcuanco Leslie D. Gottlieb 《Plant molecular biology》1988,11(4):381-388
Nuclear genes that appear to encode both cytosolic and plastid isozymes of phosphoglucose isomerase (PGI), an essential glycolytic enzyme, have been isolated from three diploid species of the annual wild flower genus Clarkia (Onagraceae). The genes do not contain introns and are expressed to varying degrees in Escherichia coli when cloned in either Charon 35 phage or pUC plasmid vectors. The PGI proteins synthesized in E. coli form dimers, are catalytically active, and their electrophoretic mobilities are similar to those of appropriate Clarkia PGIs. The nucleotide sequence of a gene encoding a plastid isozyme of C. unguiculata is described. 相似文献
1000.
The rogue tomato differs from the normal plant in that it exhibitsa lesser degree of apical dominance. Grafting techniques andmeasurements of the endogenous levels of growth substances inthe two types have been used in order to establish whether thisdifference is due to an altered hormonal balance in the roguetype. The results suggest that root-produced cytokinins play no rolein the control of apical dominance in the tomato plant, andthat lateral bud out-growth is influenced by a balance betweenapically-produced auxin, abscisic acid produced at the sitesof bud development and cytokinins synthesized within the budsthemselves. Lycopersicon esculentum L., tomato, apical dominance, abscisic acid, auxins, cytokinins, growth regulation 相似文献