全文获取类型
收费全文 | 10863篇 |
免费 | 852篇 |
国内免费 | 6篇 |
专业分类
11721篇 |
出版年
2023年 | 72篇 |
2022年 | 186篇 |
2021年 | 280篇 |
2020年 | 155篇 |
2019年 | 282篇 |
2018年 | 310篇 |
2017年 | 276篇 |
2016年 | 399篇 |
2015年 | 623篇 |
2014年 | 633篇 |
2013年 | 822篇 |
2012年 | 954篇 |
2011年 | 899篇 |
2010年 | 556篇 |
2009年 | 538篇 |
2008年 | 649篇 |
2007年 | 660篇 |
2006年 | 558篇 |
2005年 | 501篇 |
2004年 | 444篇 |
2003年 | 400篇 |
2002年 | 368篇 |
2001年 | 94篇 |
2000年 | 60篇 |
1999年 | 82篇 |
1998年 | 93篇 |
1997年 | 67篇 |
1996年 | 61篇 |
1995年 | 67篇 |
1994年 | 62篇 |
1993年 | 42篇 |
1992年 | 55篇 |
1991年 | 41篇 |
1990年 | 28篇 |
1989年 | 42篇 |
1988年 | 24篇 |
1987年 | 27篇 |
1986年 | 27篇 |
1985年 | 31篇 |
1984年 | 19篇 |
1983年 | 27篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 18篇 |
1979年 | 23篇 |
1978年 | 15篇 |
1977年 | 15篇 |
1974年 | 15篇 |
1972年 | 11篇 |
1968年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Juan M. Bello-López Cristina A. Domínguez-Mendoza Arit S. de León-Lorenzana Laura Delgado-Balbuena Yendi E. Navarro-Noya Selene Gómez-Acata Analine Rodríguez-Valentín Victor M. Ruíz-Valdiviezo Marco Luna-Guido Nele Verhulst Bram Govaerts Luc Dendooven 《Extremophiles : life under extreme conditions》2014,18(4):733-743
After chloroform fumigating an arable soil, the relative abundance of phylotypes belonging to only two phyla (Actinobacteria and Firmicutes) and two orders [Actinomycetales and Bacillales (mostly Bacillus)] increased in a subsequent aerobic incubation, while it decreased for a wide range of bacterial groups. It remained to be seen if similar bacterial groups were affected when an extreme alkaline saline soil was fumigated. Soil with electrolytic conductivity between 139 and 157 dS m?1, and pH 10.0 and 10.3 was fumigated and the bacterial community structure determined after 0, 1, 5 and 10 days by analysis of the 16S rRNA gene, while an unfumigated soil served as control. The relative abundance of the Firmicutes increased in the fumigated soil (52.8 %) compared to the unfumigated soil (34.2 %), while that of the Bacteroidetes decreased from 16.2 % in the unfumigated soil to 8.8 % in the fumigated soil. Fumigation increased the relative abundance of the genus Bacillus from 14.7 % in the unfumigated soil to 25.7 %. It was found that phylotypes belonging to the Firmicutes, mostly of the genus Bacillus, were dominant in colonizing the fumigated alkaline saline as found in the arable soil, while the relative abundance of a wide range of bacterial groups decreased. 相似文献
52.
Leishmania major, like all the other kinetoplastid protozoa, are unable to synthesize purines and rely on purine nucleobase and nucleoside acquisition across the parasite plasma membrane by specific permeases. Although, several genes have been cloned that encode nucleoside transporters in Leishmania and Trypanosoma brucei, much less progress has been made on nucleobase transporters, especially at the molecular level. The studies reported here have cloned and expressed the first gene for a L. major nucleobase transporter, designated LmaNT3. The LmaNT3 permease shows 33% identity to L. donovani nucleoside transporter 1.1 (LdNT1.1) and is, thus, a member of the equilibrative nucleoside transporter (ENT) family. ENT family members identified to date are nucleoside transporters, some of which also transport one or several nucleobases. Functional expression studies in Xenopus laevis oocytes revealed that LmaNT3 mediates high levels of uptake of hypoxanthine, xanthine, adenine and guanine. Moreover, LmaNT3 is an high affinity transporter with K(m) values for hypoxanthine, xanthine, adenine and guanine of 16.5 +/- 1.5, 8.5 +/- 0.6, 8.5 +/- 1.1, and 8.8 +/- 4.0 microM, respectively. LmaNT3 is, thus, the first member of the ENT family identified in any organism that functions as a nucleobase rather than nucleoside or nucleoside/nucleobase transporter. 相似文献
53.
Marco Schmidt Holger Kreft Adjima Thiombiano Georg Zizka 《Diversity & distributions》2005,11(6):509-516
A map of plant species diversity in Burkina Faso is presented based on field observations and specimen data from the Ouagadougou University Herbarium (OUA) and the Herbarium Senckenbergianum (FR). A map of collecting intensity and field observations illustrates centres of botanical research activities in Burkina Faso. To overcome problems associated with biased sampling intensity, distributions of species have been modelled and extrapolated to maps of vascular plant diversity, life forms and diversity of four selected families (Poaceae, Cyperaceae, Dioscoreaceae and Rubiaceae). The area of most intensive collection and observation is around Gorom‐Gorom and Fada N’Gourma. Modelled diversity generally increases towards the south, as does the proportion of phanerophytes, lianas and hemicryptophytes, while the opposite trend is observed for therophytes. Poaceae diversity is highly correlated with total vascular plant diversity, making the family especially suitable as an indicator for overall plant diversity. Cyperaceae are rather evenly distributed throughout the country, Dioscoreaceae are restricted to the Sudanian Zone. Rubiaceae have their highest diversities in the very south. Our approach can be transferred to areas with a similar database, certainly to other areas within West Africa. Future research should focus on distribution data for rare species, enabling our approach to evaluate the West African system of protected areas. 相似文献
54.
Elena Bassi Emanuela Donaggio Andrea Marcon Massimo Scandura Marco Apollonio 《Mammalian Biology》2012,77(5):369-376
Red fox (Vulpes vulpes) and wolf (Canis lupus) are two widespread opportunistic predators living in simpatry in many areas. Nonetheless, scarce information are available on their trophic interactions. We investigated food habits of these two carnivores in a mountain area in Italy and assessed the extent of their trophic niche overlap, focusing on the consumption of wild ungulates. Thereby we analyzed the content of 669 red fox scats and 253 wolf scats collected between May 2008 and April 2009. Red foxes resulted to have a more than three times higher niche breadth than wolves. Vegetables, small mammals, wild ungulates, and invertebrates were major items (altogether 92% of volume) of the red fox annual diet. On the contrary wolf annual diet relied on wild ungulates (94% of volume) with wild boar (Sus scrofa) being the main food item. The degree of trophic niche overlap between the two species was found to be low (Pianka's O = 0.356). Diet variation between the warm and the cold seasons was limited in both species, and higher in red fox than in wolf. The two canids appeared to use wild ungulates unevenly being the former more selective for younger preys, smaller in size (newborn piglets and roe deer Capreolus capreolus fawns), whereas the latter exhibited a preference for medium-sized and large ungulates (10–35 kg wild boar and adult roe deer). Even if wild ungulates represent the main shared food category, the different use of age/weight classes by the two predators, together with their possible consumption as carrions by red fox, suggests a very limited trophic competition between wolf and red fox.This study represents a contribution to the knowledge of trophic interaction in predator–prey systems where sympatric carnivores are present. 相似文献
55.
Barucca M Biscotti MA Olmo E Canapa A 《Journal of experimental zoology. Part B. Molecular and developmental evolution》2006,306(2):164-167
The ParaHox gene cluster contains three homeobox genes, Gsx, Xlox and Cdx and has been demonstrated to be an evolutionary sister of the Hox gene cluster. Among deuterostomes the three genes are found in the majority of taxa, whereas among protostomes they have so far been isolated only in the phylum Sipuncula.We report the partial sequences of all three ParaHox genes in the polyplacophoran Nuttallochiton mirandus, the first species of the phylum Mollusca where all ParaHox genes have been isolated. This finding has phylogenetic implications for the phylum Mollusca and for its relationships with the other lophotrochozoan taxa. 相似文献
56.
57.
Giulio Poli Ivana Barravecchia Gian Carlo Demontis Andrea Sodi Alessandro Saba Stanislao Rizzo Marco Macchia Tiziano Tuccinardi 《Journal of enzyme inhibition and medicinal chemistry》2022,37(1):1765
The human retinal pigment epithelium-specific 65-kDa protein (hRPE65) plays a crucial role within the retinoid visual cycle and several mutations affecting either its expression level or its enzymatic function are associated with inherited retinal diseases such as Retinitis Pigmentosa. The gene therapy product voretigene neparvovec (Luxturna) has been recently approved for treating hereditary retinal dystrophies; however, the treatment is currently accessible only to patients presenting confirmed biallelic mutations that severely impair hRPE65 function, and many reported hRPE65 missense mutations lack sufficient evidences for proving their pathogenicity. In this context, we developed a computational approach aimed at evaluating the potential pathogenic effect of hRPE65 missense variants located on the dimerisation domain of the protein. The protocol evaluates how mutations may affect folding and conformation stability of this protein region, potentially helping clinicians to evaluate the eligibility for gene therapy of patients diagnosed with this type of hRPE65 variant of uncertain significance. 相似文献
58.
We describe a chemo-enzymatic synthesis of 3'- and 6'-O-sialyllactose, two trisaccharides occurring in the 'acidic fraction' of the human milk oligosaccharides and endowed with potential antiadhesive activity. The key step is the highly regioselective 6'-O-acylation of benzyllactoside, which gave access to suitably protected lactose building blocks to be used as acceptors in the sialylation reaction. Moreover, the synthesis of the carboxymethyl and sulfo analogues of the title compounds is reported. 相似文献
59.
Coccetti P Zinzalla V Tedeschi G Russo GL Fantinato S Marin O Pinna LA Vanoni M Alberghina L 《Biochemical and biophysical research communications》2006,346(3):786-793
We have previously identified Ser201 of Sic1, a yeast cyclin-dependent kinase inhibitor, as an in vitro target of protein kinase CK2. Here we present new evidence, by using specific anti-P-Ser201 antibodies and 2-D gel electrophoresis coupled to MALDI mass spectrometry analysis, that Sic1 is phosphorylated in vivo on Ser201 shortly after its de novo synthesis, during late anaphase in glucose-grown cells. This phosphorylation is also detected in Sic1 immunopurified from G1 cells. In agreement with these data we also show that the catalytic alpha' subunit of CK2, whose function is required for cell cycle progression, is detected in Sic1 immunopurified complexes, and that phosphorylation on Ser201 is reduced after CK2 inactivation at the non-permissive temperature in a cka1delta cka2(ts) yeast strain. These data strongly support the notion that CK2 phosphorylates Sic1 in vivo. 相似文献
60.