全文获取类型
收费全文 | 2503篇 |
免费 | 73篇 |
国内免费 | 13篇 |
专业分类
2589篇 |
出版年
2013年 | 54篇 |
2012年 | 59篇 |
2011年 | 54篇 |
2010年 | 64篇 |
2009年 | 112篇 |
2008年 | 80篇 |
2007年 | 63篇 |
2006年 | 57篇 |
2005年 | 53篇 |
2004年 | 50篇 |
2003年 | 26篇 |
2002年 | 19篇 |
2001年 | 16篇 |
2000年 | 18篇 |
1999年 | 27篇 |
1998年 | 36篇 |
1997年 | 41篇 |
1996年 | 37篇 |
1995年 | 27篇 |
1994年 | 25篇 |
1993年 | 19篇 |
1992年 | 36篇 |
1991年 | 17篇 |
1990年 | 22篇 |
1989年 | 22篇 |
1988年 | 19篇 |
1987年 | 22篇 |
1986年 | 19篇 |
1985年 | 20篇 |
1984年 | 14篇 |
1983年 | 18篇 |
1981年 | 21篇 |
1980年 | 14篇 |
1979年 | 20篇 |
1977年 | 15篇 |
1976年 | 13篇 |
1972年 | 13篇 |
1971年 | 16篇 |
1959年 | 49篇 |
1958年 | 123篇 |
1957年 | 137篇 |
1956年 | 134篇 |
1955年 | 149篇 |
1954年 | 150篇 |
1953年 | 119篇 |
1952年 | 104篇 |
1951年 | 98篇 |
1950年 | 59篇 |
1949年 | 14篇 |
1948年 | 23篇 |
排序方式: 共有2589条查询结果,搜索用时 0 毫秒
91.
JOSÉ ANTONIO FERNÁNDEZ PRIETO CARLOS AGUIAR EDUARDO DIAS MARÍA DE LOS ÁNGELES FERNÁNDEZ CASADO JUAN HOMET 《Botanical journal of the Linnean Society. Linnean Society of London》2008,158(3):522-533
The taxonomy and nomenclature of the genus Huperzia Bernh. in the Azores and Madeira have been reviewed. Plants collected in the Azores and Madeira were characterized morphologically. The independence between two endemic species common to Madeira and the Azores Islands –Huperzia suberecta (Lowe) Tardieu and Huperzia dentata (Herter) Holub – is clearly shown. A clear‐cut morphological separation between these taxa and Huperzia selago (L.) Bernh. ex Schrank & Mart. of continental Europe is established. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158 , 522–533. 相似文献
92.
GUSTAVO BRUGES ADOLFO BORGES SINAI SÁNCHEZ DE VILLARROEL ITALA LIPPO DE BÉCEMBERG GISELA FRANCIS DE TOBA FABIOLA PLÁCERES 《Journal of receptor and signal transduction research》2013,33(2-3):189-216
Muscarinic activation of tracheal smooth muscle (TSM) involves a M3AChR/heterotrimeric-G protein/NPR-GC coupling mechanism. G protein activators Mastoparan (MAS) and Mastoparan-7 stimulated 4- and 10-fold the NPR-GC respectively, being insensitive to PTX and antibodies against Gαi/o subfamily. Muscarinic and MAS stimulation of NPR-GC was blocked by antibodies against C-terminal of Gαq16, whose expression was confirmed by RT-PCR. However, synthetic peptides from C-terminal of Gαq15/16 stimulated the NPR-GC. Coupling of αq16 to M3AChR is supported by MAS decreased [3H]QNB binding, being abolished after M3AChR-4-DAMP-alkylation. Anti-i3M3AChR antibodies blocked the muscarinic activation of NPR-GC, and synthetic peptide from i3M3AChR (M3P) was more potent than MAS increasing GTPγ [35S] and decreasing the [3H]QNB activities. Coupling between NPR-GC and Gαq16 was evaluated by using trypsin-solubilized-fraction from TSM membranes, which displayed a MAS-sensitive-NPR-GC activity, being immunoprecipitated with anti-Gαq16, also showing an immunoreactive heterotrimeric-G-β -subunit. These data support the existence of a novel transducing cascade, involving Gαq16β γ coupling M3AChR to NPR-GC. 相似文献
93.
94.
95.
96.
HENDRIK-JAN MEGENS RIENK DE JONG KONRAD FIEDLER 《Biological journal of the Linnean Society. Linnean Society of London》2005,84(2):225-241
The Oriental butterfly genus Arhopala is by far the most species‐rich genus within the subfamily Theclinae. We investigated whether biotic interactions with larval host plants or ants are phylogenetically constrained in the evolutionary history of Arhopala, by collating available information on the ecology of Arhopala from the literature as well as from personal observations, and analysing and interpreting these data rigorously in a phylogenetic context. Larvae of all species in the sister‐group of Arhopala and Flos feed on Fabaceae. However, the predominant feeding preference of Arhopala s.l., with the exception of a particular monophyletic and species‐rich group, called ‘Group A’, appears to be centred on Fagaceae, with additional records of Dipterocarpaceae feeding. The preference for Fagaceae has strong phylogenetic inertia, as indicated by T‐PTP tests designed to test for phylogenetic signal. Adding all available life‐history data, using the phylogeny presented before as scaffolding, further increased the phylogenetic signal in host plant data. Feeding on Fabaceae (mainly in the outgroup) and Euphorbiaceae also showed significant phylogenetic signal, but feeding on Dipterocarpaceae did not and was found scattered across the phylogeny. Except for the Dipterocarpaceae, phylogenetic signal in feeding preferences was very clear, even despite uneven taxon sampling and apparent lability in host plant use. Ant association also demonstrated historical constraint, but based on the phylogenetic hypothesis presented here it was not clear whether increased ant association intimacy emerged independently various times in Group A, as well as in several basal groups. Our finding of distinct phylogenetic patterns in the host plant and to a lesser degree in ant association data contradicts the hypothesis that life‐history traits are very labile in the Lycaenidae. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 84 , 225–241. 相似文献
97.
PAULA M. DE OMENA MÔNICA F. KERSCH‐BECKER PABLO A. P. ANTIQUEIRA TIAGO N. BERNABÉ SANDRA BENAVIDES‐GORDILLO FÁTIMA C. RECALDE CAMILA VIEIRA GUSTAVO H. MIGLIORINI GUSTAVO Q. ROMERO 《Ecological Entomology》2018,43(3):389-393
1. A key challenge in the study of mutualistic interactions is understanding sources of variation that strengthen or weaken these interactions. In spider–plant mutualisms, spiders benefit plants by improving plant nutrition and protecting plants from herbivory. Although the benefits of plants to spider growth and survival are often claimed, they are rarely demonstrated. 2. In this study, empirical evidence is provided that bromeliads (Bromelia balansae, Bromeliaceae) are essential for the resilience of the mutualistic bromeliad‐living jumping spider populations (Psecas chapoda, Salticidae) after a fire event, sheltering spiders from the heat of the flames. 3. Spider populations were compared before and after a natural fire event and it was shown that spiders of different ages survived the fire. The survival of such individuals allowed the population of P. chapoda spiders to recover rapidly, returning to pre‐fire levels in 5 months. 4. Bromeliads reduced the susceptibility of P. chapoda spiders to burning, and this mutualistic relationship contributed to the resilience of the spider population after a fire event. It is suggested that frequent fires in fire‐prone landscapes may have strengthened this spider–plant relationship, contributing to the maintenance and evolution of this association. 相似文献
98.
99.
Simple scaling of photosynthesis from leaves to canopies without the errors of big-leaf models 总被引:24,自引:0,他引:24
In big-leaf models of canopy photosynthesis, the Rubisco activity per unit ground area is taken as the sum of activities per unit leaf area within the canopy, and electron transport capacity is similarly summed. Such models overestimate rates of photosynthesis and require empirical curvature factors in the response to irradiance. We show that, with any distribution of leaf nitrogen within the canopy (including optimal), the required curvature factors are not constant but vary with canopy leaf area index and leaf nitrogen content. We further show that the underlying reason is the difference between the time-averaged and instantaneous distributions of absorbed irradiance, caused by penetration of sunflecks and the range of leaf angles in canopies. These errors are avoided in models that treat the canopy in terms of a number of layers – the multi-layer models. We present an alternative to the multi-layer model: by separately integrating the sunlit and shaded leaf fractions of the canopy, a single layered sun/shade model is obtained, which is as accurate and simpler. The model is a scaled version of a leaf model as distinct from an integrative approach. 相似文献
100.
CECILE POMPORT-CASTILLON BERNARD ROMESTAND JOHAN F. DE JONCKHEERE 《The Journal of eukaryotic microbiology》1997,44(6):540-544
ABSTRACT. The SSUrDNA and the ITS of different microsporidia from eight fishes, four insects and a shrimp were amplified and digested with restriction enzymes. The generated riboprints suggest a close evolutionary relationship between Glugea americanus and Spraguea lophii suggesting that Glugea americanus should be renamed Spraguea americanus and that the tissue infected and host origin should be considered of greater taxonomic importance for defining a genus than previously considered. Phylogenetic analysis of the riboprints demonstrates an unidentified microsporidium from a bumper fish ( Chloroscombrus chrysurus ) is related although not identical to Microgemma oviodea , a parasite from red band fish. We were also able to distinguish between Glugea anomala and Glugea atherinae and Glugea stephani but were not able to differenciate among the latter two. Insects isolates, Nosema costelytrae, N. bombycis, N. trichoplusiae, Nosema sp. and a shrimp isolate, Agmasoma penaei , are not related to the fish isolates. 相似文献