全文获取类型
收费全文 | 8377篇 |
免费 | 386篇 |
国内免费 | 727篇 |
出版年
2023年 | 95篇 |
2022年 | 171篇 |
2021年 | 231篇 |
2020年 | 235篇 |
2019年 | 344篇 |
2018年 | 351篇 |
2017年 | 255篇 |
2016年 | 222篇 |
2015年 | 226篇 |
2014年 | 540篇 |
2013年 | 651篇 |
2012年 | 464篇 |
2011年 | 514篇 |
2010年 | 414篇 |
2009年 | 378篇 |
2008年 | 357篇 |
2007年 | 332篇 |
2006年 | 256篇 |
2005年 | 253篇 |
2004年 | 244篇 |
2003年 | 177篇 |
2002年 | 232篇 |
2001年 | 170篇 |
2000年 | 179篇 |
1999年 | 141篇 |
1998年 | 125篇 |
1997年 | 116篇 |
1996年 | 97篇 |
1995年 | 85篇 |
1994年 | 95篇 |
1993年 | 107篇 |
1992年 | 96篇 |
1991年 | 84篇 |
1990年 | 62篇 |
1989年 | 34篇 |
1988年 | 41篇 |
1987年 | 40篇 |
1985年 | 75篇 |
1984年 | 120篇 |
1983年 | 108篇 |
1982年 | 116篇 |
1981年 | 104篇 |
1980年 | 98篇 |
1979年 | 79篇 |
1978年 | 71篇 |
1977年 | 71篇 |
1976年 | 72篇 |
1975年 | 47篇 |
1974年 | 35篇 |
1973年 | 33篇 |
排序方式: 共有9490条查询结果,搜索用时 31 毫秒
1.
Classification and ordination of plant communities along an altitudinal gradient on the Presidential Range,New Hampshire,USA 总被引:1,自引:0,他引:1
An analysis of vegetation along an altitudinal gradient on the Presidential Range, New Hampshire, USA, using the Braun–Blanquet approach followed by multivariate data analysis is presented. Twelve main plant communities have been distinguished. Floristic information is presented in twelve tables and one appendix. The relationships of the communities to complex environmental gradients are analyzed using Correspondence Analysis. Floristic composition and community structure are controlled primarily by the altitudinal gradient (temperature, precipitation), and by mesotopographic conditions (snow accumulation, exposure and cryoturbation, slope position, and soil moisture). 相似文献
2.
As part of systematic studies of the genus Porphyrain New Zealand, constituent sugar analyses of cell wall polysaccharidesin situ in dry thalli were found to yield data that weretaxonomically informative. Variation in constituent sugar levels betweenspecieswas sufficient in some cases to be useful in species differentiation. Thereproductive state of thallus regions had a significant impact on the levels ofconstituent sugars, whereas storage of dried thalli for eight months had noeffect. Three epiphytic taxa currently classified as species ofPorphyra appear to be incorrectly placed within the genus,as their constituent sugars and the levels of these sugars differed markedlyfrom those of all other species examined. 相似文献
3.
Field observations of two sympatric pitheciine species reveal that the positional repertoire of the white-faced saki, Pithecia pithecia, is dominated by leaping behaviors, whereas the bearded saki, Chiropotes satanas, is predominantly quadrupedal. Examination and comparison of the postcranial skeletal morphologies and limb proportions of these species display numerous features associated with their respective locomotor behaviors. These observations accord with associations found in other primate and mammalian groups and with predictions based on theoretical and experimental biomechanics. Preliminary observations of the skeletal morphology of Cacajao calvus demonstrate a marked similarity to that of Chiropotes. The fossil platyrrhine Cebupithecia sarmientoi displays greater similarity to Pithecia, suggesting that its positional repertoire also included significant leaping and clinging behaviors. 相似文献
4.
5.
《Nucleosides, nucleotides & nucleic acids》2013,32(5-8):837-839
Abstract Some diacid biodegradable synthesis of aziduthymidine (AZT) were synthesized and applied to production of about 60 different derivatives. 相似文献
6.
7.
8.
9.
Ruth Duncan Pavla Rejmanova Jindrich Kopeček John B. Lloyd 《Biochimica et Biophysica Acta (BBA)/General Subjects》1981,678(1):143-150
Synthetic 125I-labelled N-(2-hydroxypropyl)methacrylamide copolymers containing four different, potentially degradable peptidyl side chains were incubated with rat visceral yolk sacs cultured in vitro. All copolymers were captured by fluid-phase pinocytosis and three of the side chains were susceptible to lysosomal hydrolysis, resulting in release of [125I]iodotyrosine back into the culture medium. Uptake and degradation was completely inhibited by 2,4-dinitrophenol. The thiol-proteinase inhibitor leupeptin did not affect the rate of pinocytosis, but caused different degrees of inhibition of hydrolysis depending on side chain composition. 相似文献
10.
Benjamin S. Johnson Lexie Chafin Daniela Farkas Jessica Adair Ajit Elhance Laszlo Farkas Joseph S. Bednash James D. Londino 《Molecular & cellular proteomics : MCP》2022,21(7):100256
Identifying protein–protein and other proximal interactions is central to dissecting signaling and regulatory processes in cells. BioID is a proximity-dependent biotinylation method that uses an “abortive” biotin ligase to detect proximal interactions in cells in a highly reproducible manner. Recent advancements in proximity-dependent biotinylation tools have improved efficiency and timing of labeling, allowing for measurement of interactions on a cellular timescale. However, issues of size, stability, and background labeling of these constructs persist. Here we modified the structure of BioID2, derived from Aquifex aeolicus BirA, to create a smaller, highly active, biotin ligase that we named MicroID2. Truncation of the C terrminus of BioID2 and addition of mutations to alleviate blockage of biotin/ATP binding at the active site of BioID2 resulted in a smaller and highly active construct with lower background labeling. Several additional point mutations improved the function of our modified MicroID2 construct compared with BioID2 and other biotin ligases, including TurboID and miniTurbo. MicroID2 is the smallest biotin ligase reported so far (180 amino acids [AAs] for MicroID2 versus 257 AAs for miniTurbo and 338 AAs for TurboID), yet it demonstrates only slightly less labeling activity than TurboID and outperforms miniTurbo. MicroID2 also had lower background labeling than TurboID. For experiments where precise temporal control of labeling is essential, we in addition developed a MicroID2 mutant, termed lbMicroID2 (low background MicroID2), that has lower labeling efficiency but significantly reduced biotin scavenging compared with BioID2. Finally, we demonstrate utility of MicroID2 in mass spectrometry experiments by localizing MicroID2 constructs to subcellular organelles and measuring proximal interactions. 相似文献