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991.
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994.
Cristiane Elizabeth Costa de Macêdo Veronique Van Sint Jan Jean-Marie Kinet Stanley Lutts 《Acta Physiologiae Plantarum》2009,31(6):1255-1262
The effects of Al2(SO4)3·18H2O on growth of root and apical root cells were studied in seedlings of rice cultivars differing in Al resistance including
I Kong Pao and Aiwu (Al-sensitive) and IRAT 112 and IR6023-10-1-1 (Al-resistant). Inhibition of root growth was a typical
effect of Al, and the extent of the inhibition depended on both cultivar and Al concentration. Al impaired the activity of
the root meristem as indicated by reductions in its size, mitotic activity and the diameter of the meristematic cell nucleoli.
Cell size in the elongation zone of the root was also reduced by Al. The reliability of the haematoxylin staining method to
classify rice cultivars according to their Al-sensitivity failed to discriminate the Al-resistant IR6023-10-1-1 cultivar from
the two sensitive cultivars. The results are discussed in relation to the Al resistance mechanisms operating in rice. 相似文献
995.
Dónall A. Mac Dónaill 《Origins of life and evolution of the biosphere》2003,33(4-5):433-455
The question of whether the size and make-up of the natural nucleotide alphabet is a consequence of selection pressure, or simply a frozen accident, is one of the fundamental questions of biology. Nucleotide replication is essentially an information transmission phenomenon, and so it seems reasonable to explore the issue from the perspective of theoretical computer science, and of error-coding theory in particular. In this analysis it is shown that the essential recognition features of nucleotides may be naturally expressed as 4-digit binary numbers, capturing the hydrogen acceptor/donor patterns (3-bits) and the purine/pyrimidine feature (1-bit). Optimal alphabets consist of nucleotides in which the purine/pyrimidine feature is related to the acceptor/donor pattern as a parity bit. Numerically interpreted, such alphabets correspond to parity check codes, simple but effective error-resistant structures. The natural alphabet appears to be an adaptation of one of two optimal solutions, constrained to its present size and composition by a combination of chemical and coding-theory factors. 相似文献
996.
997.
The RNA world hypothesis refers to the early period on earth in which RNA was central in assuring both genetic continuity and catalysis. The end of this era coincided with the development of the genetic code and protein synthesis, symbolized by the apparition of the first non-random messenger RNA (mRNA). Modern transfer-messenger RNA (tmRNA) is a unique hybrid molecule which has the properties of both mRNA and transfer RNA (tRNA). It acts as a key molecule during trans-translation, a major quality control pathway of modern bacterial protein synthesis. tmRNA shares many common characteristics with ancestral RNA. Here, we present a model in which proto-tmRNAs were the first molecules on earth to support non-random protein synthesis, explaining the emergence of early genetic code. In this way, proto-tmRNA could be the missing link between the first mRNA and tRNA molecules and modern ribosome-mediated protein synthesis. 相似文献
998.
Marina Yolanda De La Vega-Salazar Edgar Avila-Luna Constantino Macías-Garcia 《Biodiversity and Conservation》2003,12(10):2043-2056
The Goodeidae is a family of endemic fish from central Mexico. Populations of several species are declining in the wild and two have been reported extinct; Skiffia francesae and Zoogoneticus tequila. Both species were native to just one locality in the Ameca basin. It is difficult to infer the causes of extinction, since limnological data from Teuchitlán prior to the extinction events are not available, and there are no replicate populations. As an alternative approach, we explored the potential links between key environmental variables and events of local extinction of any species in the two genera (four Skiffia spp. and two Zoogoneticus spp.). In 14 localities known to harbour populations of fish of at least one of the six focal species, we conducted limnological surveys in the rainy and in the dry season, and quantified population densities of endemic and introduced fish. In addition, we quantified the concentration of agricultural pollutants in water and mud samples taken from every locality in the dry season. We found that all the focal species face some conservation threat, but we also discovered an extremely small population of the reputedly extinct Zoogoneticus tequila; in contrast, Skiffia francesae was not found. Eutrophication and habitat fragmentation appear to be the main threats to the focal species, with habitat fragmentation exponentially reducing population size and driving populations into refuges where they face stochastic extinction. 相似文献
999.
1000.
Xiomara Pérez-Hernández Sebastián Méndez-Álvarez Teresa Delgado Antonio Moreno Jose Reyes-Darias Antonio Sierra López Jesús Villar Agustín González Antonio Martín Sánchez Manuel Macía Félix Claverie-Martín 《International microbiology》2002,5(3):117-120
Over the last decade vancomycin-resistant enterococci (VRE) have emerged as nosocomial pathogens. The aim of this study was
to determine the prevalence of VRE in clinical samples from hospitalized patients in the Canary Islands. From April to November
2000, 437 enterococci were isolated from patients hospitalized at the four main health care centers in those islands. Identification
to the species level was performed with the GPS-TA (Vitek 1) or the Wider I system. A PCR assay was used to determine the
genotype of glycopeptide resistance (vanA, vanB, vanC1, and vanC2/C3 genes). Only three (0.7%) VRE were detected: one vanA
Enterococcus faecalis, and two vanC1
Enterococcus gallinarum. To our knowledge, this is the first VRE study carried out in the Canary Islands hospitals, and the results showed a low
prevalence of VRE.
Electronic Publication 相似文献