全文获取类型
收费全文 | 4968篇 |
免费 | 463篇 |
国内免费 | 2篇 |
出版年
2023年 | 20篇 |
2022年 | 34篇 |
2021年 | 89篇 |
2020年 | 65篇 |
2019年 | 71篇 |
2018年 | 56篇 |
2017年 | 68篇 |
2016年 | 99篇 |
2015年 | 245篇 |
2014年 | 241篇 |
2013年 | 297篇 |
2012年 | 389篇 |
2011年 | 398篇 |
2010年 | 252篇 |
2009年 | 205篇 |
2008年 | 278篇 |
2007年 | 301篇 |
2006年 | 284篇 |
2005年 | 295篇 |
2004年 | 259篇 |
2003年 | 248篇 |
2002年 | 245篇 |
2001年 | 47篇 |
2000年 | 30篇 |
1999年 | 47篇 |
1998年 | 80篇 |
1997年 | 41篇 |
1996年 | 37篇 |
1995年 | 38篇 |
1994年 | 35篇 |
1993年 | 47篇 |
1992年 | 34篇 |
1991年 | 26篇 |
1990年 | 31篇 |
1989年 | 20篇 |
1988年 | 12篇 |
1987年 | 30篇 |
1986年 | 19篇 |
1985年 | 22篇 |
1984年 | 35篇 |
1983年 | 38篇 |
1982年 | 37篇 |
1981年 | 24篇 |
1980年 | 38篇 |
1979年 | 17篇 |
1978年 | 33篇 |
1977年 | 19篇 |
1976年 | 15篇 |
1974年 | 17篇 |
1973年 | 19篇 |
排序方式: 共有5433条查询结果,搜索用时 15 毫秒
1.
Kevin Karbstein Kathleen Prinz Frank Hellwig Christine Rmermann 《Ecology and evolution》2020,10(11):5015-5033
Intraspecific trait variation (ITV), based on available genetic diversity, is one of the major means plant populations can respond to environmental variability. The study of functional trait variation and diversity has become popular in ecological research, for example, as a proxy for plant performance influencing fitness. Up to now, it is unclear which aspects of intraspecific functional trait variation (iFDCV) can be attributed to the environment or genetics under natural conditions. Here, we examined 260 individuals from 13 locations of the rare (semi‐)dry calcareous grassland species Trifolium montanum L. in terms of iFDCV, within‐habitat heterogeneity, and genetic diversity. The iFDCV was assessed by measuring functional traits (releasing height, biomass, leaf area, specific leaf area, leaf dry matter content, Fv/Fm, performance index, stomatal pore surface, and stomatal pore area index). Abiotic within‐habitat heterogeneity was derived from altitude, slope exposure, slope, leaf area index, soil depth, and further soil factors. Based on microsatellites, we calculated expected heterozygosity (He) because it best‐explained, among other indices, iFDCV. We performed multiple linear regression models quantifying relationships among iFDCV, abiotic within‐habitat heterogeneity and genetic diversity, and also between separate functional traits and abiotic within‐habitat heterogeneity or genetic diversity. We found that abiotic within‐habitat heterogeneity influenced iFDCV twice as strong compared to genetic diversity. Both aspects together explained 77% of variation in iFDCV ( = .77, F2, 10 = 21.66, p < .001). The majority of functional traits (releasing height, biomass, specific leaf area, leaf dry matter content, Fv/Fm, and performance index) were related to abiotic habitat conditions indicating responses to environmental heterogeneity. In contrast, only morphology‐related functional traits (releasing height, biomass, and leaf area) were related to genetics. Our results suggest that both within‐habitat heterogeneity and genetic diversity affect iFDCV and are thus crucial to consider when aiming to understand or predict changes of plant species performance under changing environmental conditions. 相似文献
2.
Shira Weingarten-Gabbay Susan Klaeger Siranush Sarkizova Leah R. Pearlman Da-Yuan Chen Kathleen M.E. Gallagher Matthew R. Bauer Hannah B. Taylor W. Augustine Dunn Christina Tarr John Sidney Suzanna Rachimi Hasahn L. Conway Katelin Katsis Yuntong Wang Del Leistritz-Edwards Melissa R. Durkin Christopher H. Tomkins-Tinch Pardis C. Sabeti 《Cell》2021,184(15):3962-3980.e17
3.
4.
5.
Kendra I. Siler‐Marsiglio Gerry Shaw Marieta B. Heaton 《Developmental neurobiology》2004,59(3):261-271
Pycnogenol® (PYC), a patented combination of bioflavonoids extracted from the bark of French maritime pine (Pinus maritima), scavenges free radicals and promotes cellular health. The protective capacity of PYC against ethanol toxicity of neurons has not previously been explored. The present study demonstrates that in postnatal day 9 (P9) rat cerebellar granule cells the antioxidants vitamin E (VE) and PYC (1) dose dependently block cell death following 400, 800, and 1600 mg/dL ethanol exposure (2) inhibit the ethanol‐induced activation of caspase‐3 in the same model system; and (3) reduce neuronal membrane disruption as assayed by phosphatidylserine translocation to the cell surface. These results suggest that both PYC and VE have the potential to act as therapeutic agents, antagonizing the induction of neuronal cell death by ethanol exposure. © 2004 Wiley Periodicals, Inc. J Neurobiol 59: 261–271, 2004 相似文献
6.
The seasonal growth and decline of a population of Elodea canadensis Mich. growing in an irrigation drain are described, together with some characteristics of the aquatic environment (turbidity, photosynthetically-available radiation, temperature and pH). Overwintering buds (up to 5000 m?2) in the form of swollen dormant stem apices are produced in autumn with the onset of cold weather, remain in the mud, and grow out in the spring. In late summer vegetative reproduction also occurs when large numbers of the leafless stem portions which are capable of growing into independent plants are swept downstream from established populations. Results suggest that control measures should be applied in early summer when populations are approaching nuisance size, and again in late summer before fragmentation occurs and overwintering propagules are initiated. In irrigation channels in Australia, where draining and drying are not feasible, biomass in successfully reduced by widespread use of herbicides. 相似文献
7.
Kathleen Postle 《Journal of bioenergetics and biomembranes》1993,25(6):591-601
TonB protein couples cytoplasmic membrane electrochemical potential to active transport of iron-siderophore complexes and vitamin B12 through high-affinity outer membrane receptors of Gram-negative bacteria. The mechanism of energy transduction remains to be determined, but important concepts have already begun to emerge. Consistent with its function, TonB is anchored in the cytoplasmic membrane by its uncleaved amino terminus while largely occupying the periplasm. Both the connection to the cytoplasmic membrane and the amino acid sequences of the anchor are essential for activity. TonB directly associates with a number of envelope proteins, among them the outer membrane receptors and cytoplasmic membrane protein ExbB. ExbB and TonB interact through their respective transmembrane domains. ExbB is proposed to recycle TonB to an active conformation following energy transduction to the outer membrane. TonB most likely associates with the outer membrane receptors through its carboxy terminus, which is required for function. In contrast, the novel prolinerich region of TonB can be deleted without affecting function. A model that incorporates this information, as well as tempered speculation, is presented. 相似文献
8.
9.
Affinity Purification of Synenkephalin-Containing Peptides Including a Novel 23.3-Kilodalton Species 总被引:1,自引:1,他引:0
Abstract: Affinity chromatography has been used for rapid and high-yield purification of synenkephalin (proenkephalin 1 -70) containing peptides present in bovine adrenal medulla (BAM) chromaffin granular lysate. A column of CN-Br-activated Sepharose 4B coupled to synenkephalin antiserum bound synenkephalin immunoreactivity which was eluted by a stepwise gradient of 50 mM ammonium acetate containing 20% (vol/vol) acetonitrile over the pH range 7–3. Synenkephalin immunoreactivity emerged as two peaks, eluting at pH 5.5 and 4.5. Characterization of the two peaks by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting indicated that the pH 5.5 peak contained principally low-molecular-weight proenkephalin species (8.6 and 12.6 kilodaltons), whereas the pH 4.5 peak contained, in addition, high-molecular-weight proenkephalin species (18.2 and 23.3 kilodaltons). The 8.6- and 12.6- kilodalton species were isolated from the pH 5.5 peak by TSK gel filtration HPLC, whereas the pH 4.5 peak was further purified by passage over successive affinity columns coupled to antiserum against BAM 22P (proenkephalin 182–203) and [Met5 ]-enkephalin-Arg6 -Gly7 -Leu8 . The former column retains the 23.3-kilodalton species, whereas the latter column retains the 18.2-kilodalton species. The 23.3- kilodalton peptide represents a novel putative proenkephalin intermediate (proenkephalin-1–206), containing [Leu5 ]- enkephalin at the C-terminus. 相似文献
10.
Begonia (sect.Gireoudia)lyman-smithii is described and illustrated, and its relationships are discussed. 相似文献