全文获取类型
收费全文 | 722篇 |
免费 | 103篇 |
出版年
2023年 | 4篇 |
2022年 | 6篇 |
2021年 | 14篇 |
2020年 | 10篇 |
2019年 | 10篇 |
2018年 | 20篇 |
2017年 | 10篇 |
2016年 | 29篇 |
2015年 | 36篇 |
2014年 | 41篇 |
2013年 | 51篇 |
2012年 | 46篇 |
2011年 | 58篇 |
2010年 | 27篇 |
2009年 | 27篇 |
2008年 | 32篇 |
2007年 | 31篇 |
2006年 | 21篇 |
2005年 | 29篇 |
2004年 | 22篇 |
2003年 | 25篇 |
2002年 | 31篇 |
2001年 | 19篇 |
2000年 | 21篇 |
1999年 | 16篇 |
1998年 | 14篇 |
1997年 | 10篇 |
1996年 | 11篇 |
1995年 | 14篇 |
1994年 | 10篇 |
1993年 | 8篇 |
1992年 | 16篇 |
1991年 | 7篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 15篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1970年 | 2篇 |
1965年 | 2篇 |
1964年 | 2篇 |
排序方式: 共有825条查询结果,搜索用时 46 毫秒
121.
Several pentahalophenylplatinate complexes with Pt-Sn metal-metal bonds have been synthesized by facile insertion of SnCl2 into Pt-Cl bonds of the starting platinum substrates. The complexes have been characterized spectroscopically and, in the case of (NBu4)2[trans-Pt(SnCl3)2(C6F5)2] and (NBu4)2[trans-Pt2(μ-Cl)2(SnCl3)2(C6F5)2], the structures have been analyzed by X-ray diffraction. The reactivity of these derivatives towards neutral ligands has been explored. The electronic spectra of some selected derivatives have also been examined. 相似文献
122.
Herpes simplex virus type 1 and 2 (HSV-1 and HSV-2, respectively) are prevalent human pathogens of clinical relevance that establish long-life latency in the nervous system. They have been considered, along with the Herpesviridae family, to exhibit a low level of genetic diversity during viral replication. However, the high ability shown by these viruses to rapidly evolve under different selective pressures does not correlates with that presumed genetic stability. High-throughput sequencing has revealed that heterogeneous or plaque-purified populations of both serotypes contain a broad range of genetic diversity, in terms of number and frequency of minor genetic variants, both in vivo and in vitro. This is reminiscent of the quasispecies phenomenon traditionally associated with RNA viruses. Here, by plaque-purification of two selected viral clones of each viral subtype, we reduced the high level of genetic variability found in the original viral stocks, to more genetically homogeneous populations. After having deeply characterized the genetic diversity present in the purified viral clones as a high confidence baseline, we examined the generation of de novo genetic diversity under culture conditions. We found that both serotypes gradually increased the number of de novo minor variants, as well as their frequency, in two different cell types after just five and ten passages. Remarkably, HSV-2 populations displayed a much higher raise of nonconservative de novo minor variants than the HSV-1 counterparts. Most of these minor variants exhibited a very low frequency in the population, increasing their frequency over sequential passages. These new appeared minor variants largely impacted the coding diversity of HSV-2, and we found some genes more prone to harbor higher variability. These data show that herpesviruses generate de novo genetic diversity differentially under equal in vitro culture conditions. This might have contributed to the evolutionary divergence of HSV-1 and HSV-2 adapting to different anatomical niche, boosted by selective pressures found at each epithelial and neuronal tissue. 相似文献
123.
Jalel Mahouachi Domingo J. Iglesias Manuel Agustí Manuel Talon 《Plant Growth Regulation》2009,58(1):15-23
Current evidence in citrus indicates that gibberellins (GAs) are main determinants of early fruit set while subsequent growth
of developing fruits is mostly dependent upon carbohydrate availability. In this work, branch girdling performed at anthesis
in Satsuma mandarin (Citrus unshiu (Mak.) Marc.) cv. Okitsu transitorily reduced early abscission rates (12–32 days after anthesis, DAA) delaying initially
the process of natural fruitlet drop. The effects of girdling on growth, gibberellin (GA) and carbohydrate concentrations
in developing ovaries and fruitlets were assessed during this initial growth stage (0–69 DAA). In girdled branches, abscission
rate reduction was preceded by elevated concentrations of carbohydrate and GA in developing ovaries and fruitlets. Girdling
at anthesis stimulated higher hexose (21 DAA) and starch (6–20 DAA) concentrations and also higher GA1 (6 DAA), GA19 (13–20 DAA) and GA20 (6–20 DAA). The results established a relationship between the reduction of early abscission rates and higher concentrations
of carbohydrates and GAs induced by girdling in developing fruitlets. These findings revealed that girdling certainly increased
GA concentration and strongly suggested that its effect on early fruitlet abscission delay is likely mediated by both GA and
carbohydrates. 相似文献
124.
125.
The aim of this study was to investigate the environmental impact and the human health risks associated with metals exposure in the Catalan stretch of the Ebro River, Spain. The concentrations of the following elements were determined in soils and tap water: As, Cd, Cr, Cu, Hg, Mn, Ni, and Pb. Carcinogenic and non-carcinogenic risks were separately assessed for adults and children. Relatively low metal concentrations in tap water were found. It indicates that water intake is not a relevant source of metals for human health impact in the area under evaluation. In turn, the levels of metals in soils were similar or less than those found in a number of recent worldwide surveys. The presence of industrial facilities located upstream the Ebro River, including a chloralkali plant, should not mean additional non-carcinogenic risks for the population living in the area. The results of the current study allow us to establish that the concentrations of most carcinogenic elements (with the exception of As) should not mean potential health risks for the local population. However, because of the relatively high levels of geological origin found for As, a continued monitoring of these elements would be desirable. 相似文献
126.
127.
128.
Background
Lethal mutagenesis, or virus extinction promoted by mutagen-induced elevation of mutation rates of viruses, may meet with the problem of selection of mutagen-resistant variants, as extensively documented for standard, non-mutagenic antiviral inhibitors. Previously, we characterized a mutant of foot-and-mouth disease virus that included in its RNA-dependent RNA polymerase replacement M296I that decreased the sensitivity of the virus to the mutagenic nucleoside analogue ribavirin.Methodology and Principal Findings
Replacement M296I in the viral polymerase impedes the extinction of the mutant foot-and-mouth disease virus by elevated concentrations of ribavirin. In contrast, wild type virus was extinguished by the same ribavirin treatment and, interestingly, no mutants resistant to ribavirin were selected from the wild type populations. Decreases of infectivity and viral load of the ribavirin-resistant M296I mutant were attained with a combination of the mutagen 5-fluorouracil and the non-mutagenic inhibitor guanidine hydrocloride. However, extinction was achieved with a sequential treatment, first with ribavirin, and then with a minimal dose of 5-fluorouracil in combination with guanidine hydrochloride. Both, wild type and ribavirin-resistant mutant M296I exhibited equal sensitivity to this combination, indicating that replacement M296I in the polymerase did not confer a significant cross-resistance to 5-fluorouracil. We discuss these results in relation to antiviral designs based on lethal mutagenesis.Conclusions
(i) When dominant in the population, a mutation that confers partial resistance to a mutagenic agent can jeopardize virus extinction by elevated doses of the same mutagen. (ii) A wild type virus, subjected to identical high mutagenic treatment, need not select a mutagen-resistant variant, and the population can be extinguished. (iii) Extinction of the mutagen-resistant variant can be achieved by a sequential treatment of a high dose of the same mutagen, followed by a combination of another mutagen with an antiviral inhibitor. 相似文献129.
María Victoria Alarcón Alberto Lloret-Salamanca Pedro Gaspar Lloret Domingo José Iglesias Manuel Talón Julio Salguero 《Plant signaling & behavior》2009,4(12):1154-1156
During the first days of development, maize roots showed considerable variation in the production of ethylene and the rate of elongation. As endogenous ethylene increases, root elongation decreases. When these roots are treated with the precursor of ethylene aminocyclopropane- 1-carboxylic acid (ACC), or inhibitors of ethylene biosynthesis 2-aminoethoxyvinyl glycine (AVG) or cobalt ions, the root elongation is also inhibited. Because of root growth diminishes at high or reduced endogenous ethylene concentrations, it appears that this phytohormone must be maintained in a range of concentrations to support normal root growth. In spite of its known role as inhibitor of ethylene action, silver thiosulphate (STS) does not change significantly the root elongation rate. This suggests that the action of ethylene on root elongation should occur, at least partially, by interaction with other growth regulators.Key words: 2-aminoethoxyvinyl glycine, cobalt, ethylene, root elongation, silver thiosulphate, Zea mays 相似文献
130.
Antonio V. Bordería Ramon Lorenzo-Redondo Maria Pernas Concepción Casado Tamara Alvaro Esteban Domingo Cecilio Lopez-Galindez 《PloS one》2010,5(4)