全文获取类型
收费全文 | 1356037篇 |
免费 | 122510篇 |
国内免费 | 1517篇 |
出版年
2021年 | 17790篇 |
2019年 | 16160篇 |
2018年 | 17366篇 |
2017年 | 16166篇 |
2016年 | 27875篇 |
2015年 | 42389篇 |
2014年 | 50558篇 |
2013年 | 76777篇 |
2012年 | 35656篇 |
2011年 | 23547篇 |
2010年 | 42876篇 |
2009年 | 44466篇 |
2008年 | 22629篇 |
2007年 | 20595篇 |
2006年 | 26297篇 |
2005年 | 27250篇 |
2004年 | 26620篇 |
2003年 | 24232篇 |
2002年 | 22562篇 |
2001年 | 35106篇 |
2000年 | 32703篇 |
1999年 | 32378篇 |
1998年 | 25519篇 |
1997年 | 25313篇 |
1996年 | 24798篇 |
1995年 | 23007篇 |
1994年 | 22817篇 |
1993年 | 21909篇 |
1992年 | 27840篇 |
1991年 | 25967篇 |
1990年 | 24594篇 |
1989年 | 25378篇 |
1988年 | 23340篇 |
1987年 | 22083篇 |
1986年 | 21232篇 |
1985年 | 23144篇 |
1984年 | 22792篇 |
1983年 | 20033篇 |
1982年 | 20753篇 |
1981年 | 19974篇 |
1980年 | 18574篇 |
1979年 | 19017篇 |
1978年 | 18028篇 |
1977年 | 17284篇 |
1976年 | 16452篇 |
1975年 | 16089篇 |
1974年 | 16786篇 |
1973年 | 17105篇 |
1972年 | 14669篇 |
1971年 | 13408篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
261.
Energy storage in arthropods has important implications for survival and reproduction. The lipid content of 276 species of adult arthropods with wet mass in the range 0.2–6.13 g is determined to assess how lipid mass scales with body mass. The relative contribution of lipids to total body mass is investigated with respect to phylogeny, ontogeny and sex. The lipid content of adult insects, arachnids, and arthropods in general shows an isometric scaling relationship with respect to body mass (M) (Marthropod lipid = ?1.09 ×Mdry1.01 and Marthropod lipid = ?1.00 ×Mlean0.98). However, lipid allocation varies between arthropod taxa, as well as with sex and developmental stage within arthropod taxa. Female insects and arachnids generally have higher lipid contents than males, and larval holometabolous insects and juvenile arachnids have higher lipid contents than adults. 相似文献
262.
263.
264.
265.
Mycotoxin production by various toxigenic fungi, growing on a bread analogue, was investigated at various water activities (aw ) and pH combinations. Citrinin, ochratoxin A and sterigmatocystin could be detected at aw > 0·80, while patulin was only observed at aw = 0·95. These results show that some toxins may be produced at lower water activities than have been reported on synthetic media and suggest that, where possible, natural substrates should be used to investigate factors affect-ing mycotoxin production in foodstuffs. 相似文献
266.
267.
268.
269.
Neurospora grows vegetatively as a syncytium in which multiple nuclei exist within a connected cytoplasm. Because of the ability of separate and distinct mycelia to fuse, the possibility exists of generating heterocaryotic cultures in which the nuclei and cytoplasms of two different strains are comingled into the same syncytium. We have used such heterocaryons, in which the component parts differed with respect to their circadian clock phase, to examine whether or not clock-dominant phases exist in the circadian cycle. To this end, the phase subsequent to the formation of heterocaryons by pairs of mycelial discs that are initially at different circadian phases was examined in Neurospora crassa. The resulting phase was an average of the parent phases in many cases, but was sometimes observed to correspond more closely to just one of the original parental phases. In these cases, we did not observe any dominant phases in the circadian cycle; the phase of a particular parent disc was more dominant in the heterocaryon when the proportion of the nuclei from that parent was greater in the heterocaryon. In some instances, which occurred mostly when the difference in phase of the parental discs was large, the resultant phase could not be related in a simple way to the parental phases. An interpretation based on a limit cycle model of the circadian oscillation is possible. 相似文献
270.
The selective action of the antibiotics chloramphenicol and cycloheximide on the synthesis of ferredoxin in liquid cultures of Chlamydomonas reinhardii was studied. Highly specific antibodies raised against Chlamydomonas ferredoxin were used to determine the in vivo synthesis of apoferredoxin and conversion into native protein. The results indicate that 80S ribosomes are involved in the synthesis. Chlamydomonas cells growing in the absence of iron did not synthesize immunologically detectable amounts of ferredoxin. We suggest that this is based upon feed-back inhibition of apoferredoxin synthesis at the translational level.Abbreviations CAP
chloramphenicol
- CHI
cycloheximide
- IgG
Immunoglobulin G
- PBS
140.4 mM NaCl. 9 mM Na2HPO4, 1.3 mM NaH2PO4 (pH 74)
- SDS
sodium dodecvl sulphate
- Fd
Ferredoxin
- apoFd
Apoferredoxin
- CM-Fd
Scarboxymethylated Fd
- TCA-Fd
Fd treated with trichloroacetic acid 相似文献