全文获取类型
收费全文 | 9374篇 |
免费 | 675篇 |
国内免费 | 2篇 |
出版年
2024年 | 4篇 |
2023年 | 50篇 |
2022年 | 123篇 |
2021年 | 222篇 |
2020年 | 134篇 |
2019年 | 173篇 |
2018年 | 228篇 |
2017年 | 189篇 |
2016年 | 314篇 |
2015年 | 504篇 |
2014年 | 587篇 |
2013年 | 691篇 |
2012年 | 825篇 |
2011年 | 848篇 |
2010年 | 555篇 |
2009年 | 432篇 |
2008年 | 561篇 |
2007年 | 564篇 |
2006年 | 488篇 |
2005年 | 505篇 |
2004年 | 429篇 |
2003年 | 404篇 |
2002年 | 356篇 |
2001年 | 84篇 |
2000年 | 60篇 |
1999年 | 83篇 |
1998年 | 90篇 |
1997年 | 66篇 |
1996年 | 58篇 |
1995年 | 57篇 |
1994年 | 45篇 |
1993年 | 44篇 |
1992年 | 25篇 |
1991年 | 27篇 |
1990年 | 30篇 |
1989年 | 20篇 |
1988年 | 17篇 |
1987年 | 14篇 |
1986年 | 17篇 |
1985年 | 13篇 |
1984年 | 14篇 |
1983年 | 15篇 |
1982年 | 16篇 |
1981年 | 13篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1967年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
61.
62.
63.
Palynomorph assemblages have been recovered from deposits believed to straddle the Ordovician/Silurian boundary, from the upper member of the Salar del Rincón Formation, in the Puna region of north-west Argentina. The palynomorph assemblages are dominated by terrestrial cryptospores, but also contain marine elements (acritarchs, prasinophycean algae and chitinozoans). The cryptospore assemblages are similar in composition to those described from coeval deposits worldwide, suggesting that the producers were cosmopolitan and tolerated a wide range of climatic conditions. They are correlated with the Imperfectotriletes spp. Interval Biozone (sub-biozone α) of the Imperfectotriletes spp.- Laevolancis divellomedia Assemblage Biozone, indicating a Hirnantian (latest Ordovician) age. Acritarchs include late Ordovician species such as Eupoikilosusa striata and Villosacapsula cf. setosapellicula , that coexist with the Llandovery species Dactylofusa estillis. Based on lithological and palynological evidence, an early Llandovery, or a late Hirnantian (post-glacial) age is proposed for the basal part of the upper member of the Salar del Rincón Formation. 相似文献
64.
Francesca Gherardi Federica Tarducci Marco Vannini 《Ethology : formerly Zeitschrift fur Tierpsychologie》1988,77(4):300-316
Locomotor activity in a field population of the freshwater crab, Potamon fluviatile, was studied during the breeding season by means of radio-telemetry and by direct counts of active animals along a transect of the stream. The basic pattern of crabs' locomotor activity can be described as a sequence of short distance movements around the shelters (foraging movements), followed by rarer long distance displacements (wandering movements). Whilst direct counting showed that the crabs exhibit a broadly nocturnal rhythm in foraging movements, no daily periodicity in wandering activity was revealed by telemetry. There is sexual difference in these latter excursions: females move farther along the stream and into the surrounding terrestrial habitat than do males. This behaviour is in contrast to observations made during the non-breeding season and is probably related to the stage of female reproduction. 相似文献
65.
Beatriz M. Brena Claudia Pazos Laura Franco-Fraguas Francisco Batista-Viera 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1996,684(1-2)
This review surveys recent developments in chromatographic methods for the separation of amylases from complex extracts, including the separation of isozymes. It contains two tables with the properties and molecular characteristics of α- and β-amylases from different sources as well as an updated review of methods for the determination of amylase activity. The main subject of this review is a detailed evaluation of the application of newly developed chromatographic methods for the purification of amylases. 相似文献
66.
L. Vannini R. Lanciotti F. Gardini M. E. Guerzoni 《World journal of microbiology & biotechnology》1996,12(1):85-90
Chemical changes in the medium, induced by the fermentative species Lactobacillus plantarum and Lactobacillus brevis and by the enzymatic action of a proteolytic, spoilage species, Yarrowia lipolytica, were analysed using Fourier-transform i.r. spectroscopy (FTIR). Changes in the absorbance data over time could be modelled using one of the more current predictive, mathematical models of microbial growth, such as the Gompertz equation. Moreover, a linear correlation between FTIR data (expressed as absorbance of some selected peaks) and viability data (expressed as log10 c.f.u./g or ml) was observed during the fermentation process, both for L. plantarum and L. brevis. 相似文献
67.
68.
Claudia Crestini Alessandro D'Annibale Giovanni Giovannozzi-Sermanni 《Biotechnology Techniques》1996,10(4):243-248
Summary Total and specific activities of extra-cellular laccases from Lentinus edodes were enhanced by adding corn straw and chestnut juice to the liquid growth medium. The aqueous extracts were chemically characterized and revealed the presence of several phenolic and non-phenolic compounds. Extensive extraction of these components from the tested extracts completely annulled their stimulating properties on laccase production, suggesting that these compounds can act at micromole levels. 相似文献
69.
This article presents for the first time a modified protocol for RNase protection analysis that allows the substitution of32P with33P without loss of the high sensitivity of this method achieved with32P. With this protocol, we were able to detect at least 1 pg of specific mRNA. In the RNase protection analysis33P labeled riboprobes are more advantageous with regard to an easier handling and better resolution. 相似文献
70.
Rapeseed (Brassica napus) is a crop relatively tolerant to salt and sodium. Our objective was to study the interactions between Na, K and Ca and their relationship with its yield under the isolated effects of soil salinity or sodicity.Two experiments were carried out using pots filled with the Ah horizon of a Typic Natraquoll. There were three salinity levels (2.3 dS m-1; 6.0 dS m-1 and 10.0 dS m-1) and three sodicity levels, expressed as sodium adsorption ratios (SAR: 12; 27 and 44). The soil was kept near field capacity.As soil salinity increased, the K/Na and Ca/Na ratios in the tissues decreased markedly but yields and aerial biomass production were not affected. As soil SAR value increased, the K/Na and Ca/Na ratios in plants and K-Na and Ca-Na selectivities decreased. Plants could not maintain their Ca concentration in soil with a high SAR. The grain yield and biomass production diminished significantly in the highest SAR treatment. Our results are consistent with those showing detrimental osmotic effects of salts in Brassica napus. Conversely, under sodicity, the K/Na and Ca/Na ratios in plant tissues decreased considerably, in accordance with grain and biomass production. These results show that the effects of sodicity are different from those of salinity. 相似文献