全文获取类型
收费全文 | 1073479篇 |
免费 | 111091篇 |
国内免费 | 431篇 |
专业分类
1185001篇 |
出版年
2018年 | 10060篇 |
2016年 | 13410篇 |
2015年 | 17418篇 |
2014年 | 20668篇 |
2013年 | 30286篇 |
2012年 | 33517篇 |
2011年 | 34479篇 |
2010年 | 23554篇 |
2009年 | 21809篇 |
2008年 | 30863篇 |
2007年 | 32224篇 |
2006年 | 30211篇 |
2005年 | 29006篇 |
2004年 | 28903篇 |
2003年 | 27914篇 |
2002年 | 27185篇 |
2001年 | 44444篇 |
2000年 | 44108篇 |
1999年 | 35604篇 |
1998年 | 13481篇 |
1997年 | 13657篇 |
1996年 | 12982篇 |
1995年 | 12098篇 |
1994年 | 11717篇 |
1993年 | 11799篇 |
1992年 | 29789篇 |
1991年 | 29272篇 |
1990年 | 28631篇 |
1989年 | 28177篇 |
1988年 | 26208篇 |
1987年 | 24974篇 |
1986年 | 23358篇 |
1985年 | 23634篇 |
1984年 | 19546篇 |
1983年 | 17010篇 |
1982年 | 13138篇 |
1981年 | 11814篇 |
1980年 | 11068篇 |
1979年 | 18585篇 |
1978年 | 14639篇 |
1977年 | 13393篇 |
1976年 | 12794篇 |
1975年 | 14127篇 |
1974年 | 15297篇 |
1973年 | 15046篇 |
1972年 | 13872篇 |
1971年 | 12510篇 |
1970年 | 10909篇 |
1969年 | 10763篇 |
1968年 | 9626篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
Five species of sand eels (Ammodytidae) are regularly found in the north-east Atlantic. Some of these species (i.e. Ammodytes tobianus L. and A. marinus Raitt) are difficult to identify by morphological criteria. The aims of the study reported were (a) to reveal unambiguous genetic traits for species classification and (b) to study possible population structure of the more common species in Norwegian waters. In total more than 900 specimens were analysed for inter- and intraspecific allozyme variation. Reference samples were obtained from Scotland and Denmark. By combining the patterns at different loci, all five species could be unambiguously defined. In Norwegian waters A. marinus was found together with minor numbers of Hyperoplus lanceolatus (Le Sauvage). As expected, Gymnammodytes semisquamatus (Jourdain) and H. immaculatus (Corbin) were not found, but not finding A. tobianus in these waters was unexpected. Distribution of alleles at three polymorphic loci did not indicate any structure of A. marinus in Norwegian waters. 相似文献
994.
995.
A. B. Martynenko 《Biology Bulletin》2009,36(2):184-192
Species groups formed in light coniferous forests prevailing in southeastern Russia are considered using the example of butterflies. Problems concerning the formation of species composition and its originality in some insects groups are discussed. A classification analysis of species checklists for twelve local faunas of Transbaikalia and the southern Far East of Russia is performed. It is shown that the faunas of areas occupied by light coniferous forests have a common background. 相似文献
996.
Fast, efficient and selective deprotection of the tert-butoxycarbonyl (Boc) group of various amino acids and peptides was achieved by using hydrogen chloride (4 m) in anhydrous dioxane solution for 30 min at room temperature. In the cases studied in our laboratory, this protocol provided superior selectivity to deprotect Nalpha-Boc groups in the presence of tert-butyl esters and tert-butyl ethers, including thio-tert-butyl ethers, but not phenolic tert-butyl ethers. 相似文献
997.
F. Kees M. Bucher G. Mair H. Grobecker 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2001,753(2):50
A high-performance liquid chromatographic method is described for the determination of opipramol in human plasma. Opipramol was extracted into tert.-butylmethyl ether, separated on a cyanopropyl silica column and detected at 254 nm. Imipramine was used as internal standard. The limit of quantitation was 250 pg/ml using 1.5 ml plasma. Precision was better than 9%, inaccuracy less than 8%. The assay is more sensitive than previously published methods, and it has been applied to the analysis of plasma samples from a pharmacokinetic study. 相似文献
998.
999.
The cost of mutualism in a fly-fungus interaction 总被引:2,自引:0,他引:2
The movement ability of individuals has become increasingly important to a variety of ecological questions. In this study,
I investigate how plant structure and changes in body size through development affect the movement ability of a predaceous
stinkbug, Podisus maculiventris, on three species of goldenrod (Solidago spp.) representing a wide range of surface complexities. I adapt existing techniques for quantifying movement in two dimensions
to the study of movement on natural plant structures in three dimensions. These experiments indicate that plant structure
and insect size are significant factors affecting the movement ability of P. maculiventris. Changes in movement ability due to factors of ontogeny and different habitat structures suggest that the scale of an individual’s
ambit or ecological sphere of influence may vary within its lifespan. Considering the influence of ontogeny and habitat structure
on movement ability may be useful to investigations of population dynamics, foraging behavior, and pest management.
Received: 14 July 1999 / Accepted: 23 March 2000 相似文献
1000.
A N Palmisano J R Winton W W Dickhoff 《Biochemical and biophysical research communications》1999,258(3):784-791
We cloned and sequenced a chinook salmon Hsp90 cDNA; sequence analysis shows it to be Hsp90alpha. Phylogenetic analysis supports the hypothesis that alpha and beta paralogs of Hsp90 arose as a result of a gene duplication event and that they diverged early in the evolution of vertebrates, before tetrapods separated from the teleost lineage. Among several differences distinguishing poikilothermic Hsp90alpha sequences from their bird and mammal orthologs, the teleost versions specifically lack a characteristic QTQDQP phosphorylation site near the N-terminus. We used the cDNA to develop an RNA (Northern) blot to quantify cellular Hsp90 mRNA levels. Chinook salmon embryonic (CHSE-214) cells responded to heat shock with a rapid rise in Hsp90 mRNA through 4 h, followed by a gradual decline over the next 20 h. Hsp90 mRNA level may be useful as a stress indicator, especially in a laboratory setting or in response to acute heat stress. 相似文献