全文获取类型
收费全文 | 250987篇 |
免费 | 17253篇 |
国内免费 | 166篇 |
专业分类
268406篇 |
出版年
2021年 | 2152篇 |
2019年 | 2025篇 |
2018年 | 3572篇 |
2017年 | 3383篇 |
2016年 | 4220篇 |
2015年 | 4088篇 |
2014年 | 5406篇 |
2013年 | 7705篇 |
2012年 | 9045篇 |
2011年 | 9454篇 |
2010年 | 6754篇 |
2009年 | 5696篇 |
2008年 | 8407篇 |
2007年 | 8603篇 |
2006年 | 8282篇 |
2005年 | 7703篇 |
2004年 | 7873篇 |
2003年 | 7522篇 |
2002年 | 7537篇 |
2001年 | 10130篇 |
2000年 | 9723篇 |
1999年 | 7674篇 |
1998年 | 2475篇 |
1997年 | 2311篇 |
1996年 | 2106篇 |
1995年 | 1931篇 |
1992年 | 5955篇 |
1991年 | 6136篇 |
1990年 | 6071篇 |
1989年 | 5999篇 |
1988年 | 5522篇 |
1987年 | 5175篇 |
1986年 | 4739篇 |
1985年 | 5011篇 |
1984年 | 4015篇 |
1983年 | 3312篇 |
1982年 | 2220篇 |
1981年 | 1938篇 |
1979年 | 3598篇 |
1978年 | 2803篇 |
1977年 | 2626篇 |
1976年 | 2574篇 |
1975年 | 3053篇 |
1974年 | 3345篇 |
1973年 | 3301篇 |
1972年 | 2917篇 |
1971年 | 2776篇 |
1970年 | 2364篇 |
1969年 | 2309篇 |
1968年 | 2207篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
73.
74.
75.
76.
The fully enclosed Taiaro lagoon is hypersaline (42.5 psu) and non-tidal; constant salinity and water level result from strong
evaporation balanced by low percolation through the lagoon floor. Seawater can flow over the atoll rim during exceptionally
high seas and may then replenish lagoonal communities with propagules of oceanic origin. The distinctive water chemistry of
the lagoon suggests a possible way of identifying these immigrants. We established this potential by analysing stable isotopes
of carbon and oxygen in the recent growth layers of otoliths of two adult reef fishes, Chaetodon ulietensis and Acanthurus triostegus, collected from both sides of the atoll rim. Fish from the two locations were discriminated by their isotopic signatures,
suggesting that analysis of the microchemical signatures deposited during the larval development could be used in future work
to determine which individuals and species complete their life-cycles in this unusual lagoon.
Accepted: 28 August 1997 相似文献
77.
Application of 1% methol, which, along with cold, activates specific thermosensitive ionic channels, changes the number of functioning cold receptors on the skin of the forearm similarly to the cold exposure test; however, it does not affect the number of heat receptors and does not significantly change the threshold of cold sensation. Group variants of responses to menthol that indicate individual differences in the sensitivity of skin receptors to the effects of methol and cold have been found. The results obtained give grounds to suggest that, from the variant of response to menthol (a decrease, increase, or absence of changes in the number of functioning cold receptors 5 min after menthol application), it is possible to predict specific features of response to cold. 相似文献
78.
Maria V. Sergeeva Vadim V. Mozhaev Joseph O. Rich Yuri L. Khmelnitsky 《Biotechnology letters》2000,22(17):1419-1422
A novel biocatalytic reaction of transamidation of non-activated amides with amines is reported. Among 45 different lipolytic and proteolytic enzymes tested, only the lipase from Candida antarcticawas able to catalyze this reaction. The reaction proceeded with up to ca. 80% conversion in anhydrous methyl tert-butyl ether and worked with both N-substituted and unsubstituted amides. The biocatalytic transamidation is an equilibrium process and, therefore, higher conversions to the desired amide were achieved by using increased concentrations of the amine nucleophile. 相似文献
79.
80.
D. Pangallo K. Chovanov H. Drahovska F. De Leo C. Urzì 《International biodeterioration & biodegradation》2009,63(7):868-872
The aim of this work was the evaluation of fluorescence ITS-PCR (f-ITS) as a molecular tool to analyze the microbial community involved in the biodeterioration of cultural heritage surfaces. As a case study we analyzed by f-ITS ninety-two bacterial strains isolated from a medieval fresco and the surrounding air environment. The internal transcribed spacer between the 16S and 23S rRNA genes was amplified, and then the fluorescently labeled PCR products were separated by capillary electrophoresis. Bacterial strains were identified by 16S rDNA sequencing. The f-ITS electropherograms showed different profiles coherent with the affiliation of the strains at the genus and species levels. Among the isolates obtained from the fresco surface, those belonging to the genus Bacillus were the most prevailing exhibiting 8 different f-ITS profiles. The airborne bacilli exhibited only 2 of these 8 profiles. Staphylococcus were mostly isolated from air and produced 4 different profiles. Pseudomonas isolates presented 3 different profiles, and one of them was typical of Pseudomonas putida. Members of the other genera produced their distinctive profiles. Our results show that f-ITS is a promising molecular tool for the rapid selection and clustering of strains isolated from different sources. 相似文献