全文获取类型
收费全文 | 1073篇 |
免费 | 69篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 13篇 |
2020年 | 7篇 |
2019年 | 13篇 |
2018年 | 9篇 |
2017年 | 16篇 |
2016年 | 23篇 |
2015年 | 34篇 |
2014年 | 35篇 |
2013年 | 49篇 |
2012年 | 65篇 |
2011年 | 67篇 |
2010年 | 37篇 |
2009年 | 43篇 |
2008年 | 57篇 |
2007年 | 43篇 |
2006年 | 53篇 |
2005年 | 62篇 |
2004年 | 58篇 |
2003年 | 55篇 |
2002年 | 37篇 |
2001年 | 18篇 |
2000年 | 20篇 |
1999年 | 23篇 |
1998年 | 22篇 |
1997年 | 11篇 |
1996年 | 19篇 |
1995年 | 14篇 |
1994年 | 11篇 |
1993年 | 14篇 |
1992年 | 14篇 |
1991年 | 14篇 |
1990年 | 18篇 |
1989年 | 18篇 |
1988年 | 14篇 |
1987年 | 17篇 |
1986年 | 13篇 |
1985年 | 16篇 |
1984年 | 12篇 |
1983年 | 18篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1970年 | 2篇 |
1967年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有1142条查询结果,搜索用时 15 毫秒
41.
Hansen Joan H. Skov Christian Baktoft Henrik Brönmark Christer Chapman Ben B. Hulthén Kaj Hansson Lars-Anders Nilsson P. Anders Brodersen Jakob 《Ecosystems》2020,23(2):292-306
Ecosystems - Patterns of animal migration and the ecological forces that shape them have been studied for centuries. Yet ecological impacts caused by the migration, such as altered... 相似文献
42.
Andrew M. Liebhold Christer Björkman Alain Roques Ottar N. Bjørnstad Maartje J. Klapwijk 《Population Ecology》2020,62(4):372-384
We explore a common feature of insect population dynamics, interspecific synchrony, which refers to synchrony in population dynamics among sympatric populations of different species. Such synchrony can arise via several possible mechanisms, including shared environmental effects and shared trophic interactions, but distinguishing the relative importance among different mechanisms can be challenging. We analyze interannual time series of population densities of the larch budmoth, Zeiraphera griseana (Lepidoptera: Tortricidae), along with six sympatric larch-feeding folivores from a site in the European Alps 1952–1979. These species include five lepidopterans, Exapate duratella, Ptycholomoides aeriferana, Spilonota laricana, Epirrita autumnata and Teleiodes saltuum, and one hymenopteran sawfly Pristiphora laricis. We document that the highly regular oscillatory behavior (period 9–10 years) of Z. griseana populations is similarly evident in the dynamics of most of the sympatric folivores. We also find that all of the sympatric species are phase synchronized with Z. griseana populations with half of the sympatric species exhibiting nonlagged phase synchrony and three of the species exhibiting 2–5 year lags behind Z. griseana populations. We adapt a previously developed tritrophic model of Z. griseana dynamics to explore possible mechanisms responsible for observed phase synchronization. Results suggest that either shared stochastic influences (e.g., weather) or shared parasitoid impacts are likely causes of nonlagged phase synchronization. The model further indicates that observed patterns of lagged phase synchronization are most likely caused by either shared delayed induced host plant defenses or direct density-dependent effects shared with Z. griseana. 相似文献
43.
Fayetteville Green Lake (FGL) is a recognized, extensively studied present‐day model of the stratified Proterozoic ocean. Nonetheless, biomass sedimentation in FGL remains hard to explain: while virtually all sediment pigments belong to photosynthetic sulfur bacteria from a chemocline, the isotopic carbon signature of the bulk organic matter suggests its epilimnetic phytoplankton origin. To explain the epilimnetic origin of sedimented carbon, we studied the dominant Synechococci, isolated from FGL. Here, we present experimental evidence that FGL Synechococci produce copious extracellular polysaccharides (EPS) especially when availability of inorganic carbon (Ci) is high relative to availability of other macronutrients, for example phosphorus. The accumulating EPS become impregnated with calcium, magnesium, and sodium cations and are released to the environment as ballasted cell coverings. Sedimentation of these cell‐free EPS can constitute the bulk of pigment‐free organic material in FGL sediment. Because increased availability of Ci specifically stimulates production of EPS and the accumulated EPS adsorb cations and become ballasted, we propose the universal role of cyanobacterial EPS in biomass sedimentation in the high‐Ci Paleoproterozoic ocean as well as in modern aquatic systems like FGL. 相似文献
44.
Hampus Petrn Gabriele Gloder Diana Posledovich Christer Wiklund Magne Friberg 《Ecology and evolution》2021,11(1):242-251
The evolution of host range drives diversification in phytophagous insects, and understanding the female oviposition choices is pivotal for understanding host specialization. One controversial mechanism for female host choice is Hopkins’ host selection principle, where females are predicted to increase their preference for the host species they were feeding upon as larvae. A recent hypothesis posits that such larval imprinting is especially adaptive in combination with anticipatory transgenerational acclimation, so that females both allocate and adapt their offspring to their future host. We study the butterfly Pieris rapae, for which previous evidence suggests that females prefer to oviposit on host individuals of similar nitrogen content as the plant they were feeding upon as larvae, and where the offspring show higher performance on the mother's host type. We test the hypothesis that larval experience and anticipatory transgenerational effects influence female host plant acceptance (no‐choice) and preference (choice) of two host plant species (Barbarea vulgaris and Berteroa incana) of varying nitrogen content. We then test the offspring performance on these hosts. We found no evidence of larval imprinting affecting female decision‐making during oviposition, but that an adult female experience of egg laying in no‐choice trials on the less‐preferred host Be. incana slightly increased the P. rapae propensity to oviposit on Be. incana in subsequent choice trials. We found no transgenerational effects on female host acceptance or preference, but negative transgenerational effects on larval performance, because the offspring of P. rapae females that had developed on Be. incana as larvae grew slower on both hosts, and especially on Be. incana. Our results suggest that among host species, preferences are guided by hard‐wired preference hierarchies linked to species‐specific host traits and less affected by larval experience or transgenerational effects, which may be more important for females evaluating different host individuals of the same species. 相似文献
45.
Bertil Persson Anders Andersson Björn Hultberg Christer Hansson 《Free radical research》2013,47(2):151-156
Glutathione, the most abundant low-molecular weight thiol in the skin, has been shown to protect the skin from both photobiological and chemical injury. The thiols, glutathione in particular, have also been shown to be crucially involved in defence against contact allergens. Since the levels of extracellular thiol concentrations are important determinants of intracellular thiol status, we have compared the normal concentrations and the redox status of the main low-molecular weight thiol components in the extracellular fluid at the dermo-epidermal junction with the corresponding plasma levels. In their sulfhydryl form, all three thiols, i.e. glutathione, cysteine and homocysteine, were more abundant in experimental skin blister fluid than in plasma, as were the free disulfides of glutathione and homocysteine, whereas the free disulfides of cysteine were about the same in blister fluid and in plasma. Protein mixed disulfide levels were higher in plasma than in blister fluid. The present results provide information concerning the extracellular defence in the skin. 相似文献
46.
47.
Martin Olofsson Sven Jakobsson Christer Wiklund 《Biological journal of the Linnean Society. Linnean Society of London》2013,109(2):290-297
Small eyespots on butterflies have long been thought to deflect attacks, and birds are the presumptive drivers selecting for these patterns; however, evidence of this function is still ambiguous. Marginal eyespots typically consist of a UV‐reflective white pupil, surrounded by one black and one yellowish ring. We have recently shown that Cyanistes caeruleus (blue tits) attack such eyespots, but only under low light intensities with accentuated UV levels: the increased salience of the eyespots relative to the rest of the butterfly probably explains this result. Possibly the background against which the butterfly is concealed may deceive birds to make similar errors. We therefore presented speckled wood butterflies decorated with eyespots (or controls without eyespots) to C. caeruleus against two backgrounds: oak and birch bark. Our results show that: (1) eyespots, independent of background, were effective in deflecting attacks; (2) the time elapsed between a bird landing and the attack was interactively dependent on the background and whether the butterfly bore an eyespot; and (3) the speed at which a butterfly was attacked predicted the outcome, with faster birds being more prone to errors than slower birds. This underscores a speed–accuracy trade‐off in the predators, and that background plays a role in the defensive qualities of marginal eyespots. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 290–297. 相似文献
48.
49.
Origin of the S‐Shaped JV Curve and the Light‐Soaking Issue in Inverted Organic Solar Cells
下载免费PDF全文
![点击此处可从《Liver Transplantation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Anton Sundqvist Oskar J. Sandberg Mathias Nyman Jan‐Henrik Smått Ronald Österbacka 《Liver Transplantation》2016,6(6)
Inverted organic solar cells generally exhibit a strong s‐shaped kink in the current–voltage characteristics (JV curve) that may be removed by exposure to UV light (light‐soaking) leading to a drastically improved performance. Using in‐device characterization methods the origin of the light‐soaking issue in inverted solar cells employing titanium dioxide (TiO2) as an electron selective layer is clarified. An injected hole reservoir accumulated at the TiO2/organic interface of the pristine device is observed from extraction current transients; the hole reservoir increases the recombination and results in an s‐shape in the JV curve of pristine devices. The hole reservoir and the s‐shape is a result of the energetics at the selective contact in the pristine device; the effect of UV exposure is to decrease the work function of the indium tin oxide/TiO2‐contact, increasing the built‐in potential. This hinders the build‐up of the hole reservoir and the s‐shape is removed. The proposed model is in excellent agreement with drift‐diffusion simulations. 相似文献
50.
Francisco Gómez Real Laura Pérez Barrionuevo Karl Franklin Eva Lindberg Randi Jacobsen Bertelsen Bryndís Benediktsdóttir Bertil Forsberg Thorarinn Gislason Rain J?gi Ane Johannessen Ernst Omenaas Eirunn Saure Vivi Schlünssen Trude Duelien Skorge Kjell Torén Antonio Pérez Saavedra ?istein Svanes Anne Nordrehaug ?str?m Christer Janson Cecilie Svanes 《PloS one》2016,11(1)