全文获取类型
收费全文 | 2464篇 |
免费 | 211篇 |
专业分类
2675篇 |
出版年
2023年 | 5篇 |
2022年 | 19篇 |
2021年 | 49篇 |
2020年 | 17篇 |
2019年 | 21篇 |
2018年 | 33篇 |
2017年 | 35篇 |
2016年 | 77篇 |
2015年 | 116篇 |
2014年 | 130篇 |
2013年 | 145篇 |
2012年 | 218篇 |
2011年 | 206篇 |
2010年 | 151篇 |
2009年 | 132篇 |
2008年 | 143篇 |
2007年 | 156篇 |
2006年 | 137篇 |
2005年 | 125篇 |
2004年 | 148篇 |
2003年 | 124篇 |
2002年 | 128篇 |
2001年 | 30篇 |
2000年 | 20篇 |
1999年 | 31篇 |
1998年 | 39篇 |
1997年 | 23篇 |
1996年 | 19篇 |
1995年 | 20篇 |
1994年 | 20篇 |
1993年 | 22篇 |
1992年 | 18篇 |
1991年 | 12篇 |
1990年 | 11篇 |
1989年 | 16篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 9篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
排序方式: 共有2675条查询结果,搜索用时 0 毫秒
921.
922.
923.
Increased ethanol resistance and consumption in Eps8 knockout mice correlates with altered actin dynamics 总被引:5,自引:0,他引:5
Offenhäuser N Castelletti D Mapelli L Soppo BE Regondi MC Rossi P D'Angelo E Frassoni C Amadeo A Tocchetti A Pozzi B Disanza A Guarnieri D Betsholtz C Scita G Heberlein U Di Fiore PP 《Cell》2006,127(1):213-226
Dynamic modulation of the actin cytoskeleton is critical for synaptic plasticity, abnormalities of which are thought to contribute to mental illness and addiction. Here we report that mice lacking Eps8, a regulator of actin dynamics, are resistant to some acute intoxicating effects of ethanol and show increased ethanol consumption. In the brain, the N-methyl-D-aspartate (NMDA) receptor is a major target of ethanol. We show that Eps8 is localized to postsynaptic structures and is part of the NMDA receptor complex. Moreover, in Eps8 null mice, NMDA receptor currents and their sensitivity to inhibition by ethanol are abnormal. In addition, Eps8 null neurons are resistant to the actin-remodeling activities of NMDA and ethanol. We propose that proper regulation of the actin cytoskeleton is a key determinant of cellular and behavioral responses to ethanol. 相似文献
924.
Bauer U Bohn HF Federle W 《Proceedings. Biological sciences / The Royal Society》2008,275(1632):259-265
The leaves of Nepenthes pitcher plants are specialized pitfall traps which capture and digest arthropod prey. In many species, insects become trapped by 'aquaplaning' on the wet pitcher rim (peristome). Here we investigate the ecological implications of this capture mechanism in Nepenthes rafflesiana var. typica. We combine meteorological data and continuous field measurements of peristome wetness using electrical conductance with experimental assessments of the pitchers' capture efficiency. Our results demonstrate that pitchers can be highly effective traps with capture rates as high as 80% but completely ineffective at other times. These dramatic changes are due to the wetting condition of the peristome. Variation of peristome wetness and capture efficiency was perfectly synchronous, and caused by rain, condensation and nectar secreted from peristome nectaries. The presence of nectar on the peristome increased surface wetness mainly indirectly by its hygroscopic properties. Experiments confirmed that pitchers with removed peristome nectaries remained generally drier and captured prey less efficiently than untreated controls. This role of nectar in prey capture represents a novel function of plant nectar. We propose that the intermittent and unpredictable activation of Nepenthes pitcher traps facilitates ant recruitment and constitutes a strategy to maximize prey capture. 相似文献
925.
926.
927.
Schneider K Kuznetzov VK Sanzharova NI Kanter U Telikh KM Khlopuk MS 《Radiation and environmental biophysics》2008,47(2):241-252
Field-grown maize hybrids were assessed for variability in 137Cs accumulation in vegetative parts of young and mature maize shoots and grains during 2 years with contrasting climatic conditions.
Trials were carried out at different sites in the Tula region of Russia, which is characterized by a highly homogenous soil
classified as Luvic Chernozem according to FAO/UNESCO, and average contamination levels of about 509–564 Bq 137Cs kg−1 soil. In the first year, 19 hybrids were tested. The two hybrids with the highest and the two with the lowest 137Cs concentration ratios (C
r) were also tested in the second year, together with another 11 hybrids. All samples were additionally assessed for their
potassium content. In both investigation periods 137Cs accumulation in vegetative shoots and grains was found to vary up to more than twofold between hybrids. However, C
r values of those hybrids that showed a relatively low 137Cs accumulation in the first year were not necessarily low in the second year, and the ratio between the 137Cs C
r of low- and high-accumulating hybrids was much smaller than in the year before. In both vegetative shoots and grains the
variance caused by the different years was larger than the genotypic variance, thus indicating the limits of genotype selection
for this trait. Significant correlations were determined between the 40K and 137Cs C
r values in the same tissue, but for one hybrid indications for uncoupling of the two traits were found. Average Cs/K ratios
in young shoots, mature shoots and grains were 0.06, 0.05 and 0.02, respectively, indicating tissue- and stage-specific regulation
of accumulation within each plant. The findings are discussed with respect to new approaches towards a better understanding
of 137Cs accumulation and its potential reduction in plants.
Katharina Schneider was deceased. 相似文献
928.
929.
Markert A Steffan N Ploss K Hellwig S Steiner U Drewke C Li SM Boland W Leistner E 《Plant physiology》2008,147(1):296-305
Ergoline alkaloids occur in taxonomically unrelated taxa, such as fungi, belonging to the phylum Ascomycetes and higher plants of the family Convolvulaceae. The disjointed occurrence can be explained by the observation that plant-associated epibiotic clavicipitalean fungi capable of synthesizing ergoline alkaloids colonize the adaxial leaf surface of certain Convolvulaceae plant species. The fungi are seed transmitted. Their capacity to synthesize ergoline alkaloids depends on the presence of an intact differentiated host plant (e.g. Ipomoea asarifolia or Turbina corymbosa [Convolvulaceae]). Here, we present independent proof that these fungi are equipped with genetic material responsible for ergoline alkaloid biosynthesis. The gene (dmaW) for the determinant step in ergoline alkaloid biosynthesis was shown to be part of a cluster involved in ergoline alkaloid formation. The dmaW gene was overexpressed in Saccharomyces cerevisiae, the encoded DmaW protein purified to homogeneity, and characterized. Neither the gene nor the biosynthetic capacity, however, was detectable in the intact I. asarifolia or the taxonomically related T. corymbosa host plants. Both plants, however, contained the ergoline alkaloids almost exclusively, whereas alkaloids are not detectable in the associated epibiotic fungi. This indicates that a transport system may exist translocating the alkaloids from the epibiotic fungus into the plant. The association between the fungus and the plant very likely is a symbiotum in which ergoline alkaloids play an essential role. 相似文献
930.