全文获取类型
收费全文 | 105536篇 |
免费 | 7587篇 |
国内免费 | 131篇 |
出版年
2023年 | 567篇 |
2022年 | 814篇 |
2021年 | 1777篇 |
2020年 | 1378篇 |
2019年 | 1680篇 |
2018年 | 2770篇 |
2017年 | 2502篇 |
2016年 | 3416篇 |
2015年 | 4599篇 |
2014年 | 4806篇 |
2013年 | 6516篇 |
2012年 | 7518篇 |
2011年 | 6858篇 |
2010年 | 4531篇 |
2009年 | 3678篇 |
2008年 | 5349篇 |
2007年 | 5068篇 |
2006年 | 4809篇 |
2005年 | 4179篇 |
2004年 | 4092篇 |
2003年 | 3717篇 |
2002年 | 3549篇 |
2001年 | 2675篇 |
2000年 | 2528篇 |
1999年 | 2127篇 |
1998年 | 1032篇 |
1997年 | 874篇 |
1996年 | 795篇 |
1995年 | 758篇 |
1994年 | 594篇 |
1993年 | 610篇 |
1992年 | 1218篇 |
1991年 | 1125篇 |
1990年 | 1025篇 |
1989年 | 986篇 |
1988年 | 874篇 |
1987年 | 819篇 |
1986年 | 775篇 |
1985年 | 812篇 |
1984年 | 784篇 |
1983年 | 603篇 |
1982年 | 497篇 |
1981年 | 443篇 |
1980年 | 428篇 |
1979年 | 563篇 |
1978年 | 492篇 |
1977年 | 454篇 |
1975年 | 482篇 |
1974年 | 501篇 |
1973年 | 477篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
13.
Páraic ó Cuív Rajesh Gupta Hareshwar P. Goswami Mark Morrison 《Applied and environmental microbiology》2013,79(19):6173-6175
Clostridium thermocellum encodes a cellulosomal, modular, and thermostable serine protease inhibitor (serpin), PinA. PinA stability but not inhibitory activity is affected by the Fn(III) and Doc(I) domains, and PinA is a broad inhibitor of subtilisin-like proteases and may play a key role in protecting the cellulosome from protease attack. 相似文献
14.
Myoglobin (Mb) is the classic vertebrate oxygen-binding protein present in aerobic striated muscles. It functions principally in oxygen delivery and provides muscle with its characteristic red colour. Members of the Antarctic icefish family (Channichthyidae) are widely thought to be extraordinary for lacking cardiac Mb expression, a fact that has been attributed to their low metabolic rate and unusual evolutionary history. Here, we report that cardiac Mb deficit, associated with pale heart colour, has evolved repeatedly during teleost evolution. This trait affects both gill- and air-breathing species from temperate to tropical habitats across a full range of salinities. Cardiac Mb deficit results from total pseudogenization in three-spined stickleback and is associated with a massive reduction in mRNA level in two species that evidently retain functional Mb. The results suggest that near or complete absence of Mb-assisted oxygen delivery to heart muscle is a common facet of teleost biodiversity, even affecting lineages with notable oxygen demands. We suggest that Mb deficit may affect how different teleost species deal with increased tissue oxygen demands arising under climate change. 相似文献
15.
16.
Sergio Cardoso Laura Valverde Miguel A. Alfonso-Sánchez Leire Palencia-Madrid Xabier Elcoroaristizabal Jaime Algorta Susana Catarino David Arteta Rene J. Herrera María Teresa Zarrabeitia José A. Pe?a Marian M. de Pancorbo 《PloS one》2013,8(7)
The European genetic landscape has been shaped by several human migrations occurred since Paleolithic times. The accumulation of archaeological records and the concordance of different lines of genetic evidence during the last two decades have triggered an interesting debate concerning the role of ancient settlers from the Franco-Cantabrian region in the postglacial resettlement of Europe. Among the Franco-Cantabrian populations, Basques are regarded as one of the oldest and more intriguing human groups of Europe. Recent data on complete mitochondrial DNA genomes focused on macrohaplogroup R0 revealed that Basques harbor some autochthonous lineages, suggesting a genetic continuity since pre-Neolithic times. However, excluding haplogroup H, the most representative lineage of macrohaplogroup R0, the majority of maternal lineages of this area remains virtually unexplored, so that further refinement of the mtDNA phylogeny based on analyses at the highest level of resolution is crucial for a better understanding of the European prehistory. We thus explored the maternal ancestry of 548 autochthonous individuals from various Franco-Cantabrian populations and sequenced 76 mitogenomes of the most representative lineages. Interestingly, we identified three mtDNA haplogroups, U5b1f, J1c5c1 and V22, that proved to be representative of Franco-Cantabria, notably of the Basque population. The seclusion and diversity of these female genetic lineages support a local origin in the Franco-Cantabrian area during the Mesolithic of southwestern Europe, ∼10,000 years before present (YBP), with signals of expansions at ∼3,500 YBP. These findings provide robust evidence of a partial genetic continuity between contemporary autochthonous populations from the Franco-Cantabrian region, specifically the Basques, and Paleolithic/Mesolithic hunter-gatherer groups. Furthermore, our results raise the current proportion (≈15%) of the Franco-Cantabrian maternal gene pool with a putative pre-Neolithic origin to ≈35%, further supporting the notion of a predominant Paleolithic genetic substrate in extant European populations. 相似文献
17.
18.
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
19.
20.
E. Molina Grima J. A. Sánchez Pérez F. García Camacho F. G. Acién Fernández J. M. Fernández Sevilla F. Valdés Sanz 《Biotechnology letters》1994,16(10):1035-1040
Summary Eicosapentaenoic acid (EPA) volumetric productivity from an outdoor chemostat culture ofPhaeodactylum tricornutum UTEX 640 in a 50-l tubular photobioreactor varies with dilution rate, reaching a maximum of 47.8 mg l–1 d–1 at D=0.36 d–1. Continuous culture at high dilution rates' is proposed as the most adequate operating mode to maximize polyunsaturated fatty acid production. 相似文献