全文获取类型
收费全文 | 1634篇 |
免费 | 135篇 |
国内免费 | 2篇 |
出版年
2022年 | 13篇 |
2021年 | 23篇 |
2020年 | 7篇 |
2019年 | 12篇 |
2018年 | 24篇 |
2017年 | 22篇 |
2016年 | 41篇 |
2015年 | 72篇 |
2014年 | 71篇 |
2013年 | 87篇 |
2012年 | 130篇 |
2011年 | 107篇 |
2010年 | 82篇 |
2009年 | 71篇 |
2008年 | 123篇 |
2007年 | 101篇 |
2006年 | 105篇 |
2005年 | 102篇 |
2004年 | 98篇 |
2003年 | 90篇 |
2002年 | 78篇 |
2001年 | 32篇 |
2000年 | 11篇 |
1999年 | 26篇 |
1998年 | 24篇 |
1997年 | 21篇 |
1996年 | 17篇 |
1995年 | 17篇 |
1994年 | 19篇 |
1993年 | 19篇 |
1992年 | 16篇 |
1991年 | 13篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1968年 | 4篇 |
1965年 | 2篇 |
排序方式: 共有1771条查询结果,搜索用时 15 毫秒
21.
22.
Gerhard Kopperschläger Elke Usbeck Eberhard Hofmann 《Biochemical and biophysical research communications》1976,71(1):371-378
Intracellular cross-linking of yeast phosphofructokinase with a series of diimidoesters of different chain length resulted in the appearance of tetramers as largest cross-linked product of the enzyme subunits. The native enzyme is evidently composed of eight subunits being arranged in two tetramers α4β4. In the tetramers the monomers are probably assembled in tetrahedral geometry. 相似文献
23.
Bruno Hoste Lieve Luyten Ilse Claeys Elke Clynen Mazibur M. Rahman Arnold De Loof Michael Breuer 《Entomologia Experimentalis et Applicata》2002,104(2-3):281-288
In order to unravel the physiological, endocrine, and behavioral differences between gregarious and solitarious forms of the desert locust, Schistocerca gregaria (Forsk.) (Orthoptera, Acrididae), a constant supply of rather large numbers of solitary individuals has to be guaranteed. This represents a bottleneck, mainly because of the intensity of the labor involved and limited laboratory accommodation. The method we describe here substantially reduces the space and manpower needed. The survival rate we obtained in the solitarised population was relatively high, reaching about 55%. The optimal rearing temperature proved to be 32–36 °C. Cabbage leaves and oat flakes sufficed for feeding all year round. Special racks have been designed that enable high density stacking and easy handling. The solitarisation process was monitored over ten consecutive generations. Changes in morphometrics, eye stripes, color, and behavior were recorded, of which only morphometrics, temperature related development, and mortality are discussed. A shift towards the solitarious phase was recorded, with clear differences between gregarious, 1st generation and 7th to 10th generation solitarious locusts. 相似文献
24.
Andreas B. Herrmann Martha-Lena Müller Martin F. Orth Jörg P. Müller Alma Zernecke Andreas Hochhaus Thomas Ernst Elke Butt Jochen J. Frietsch 《Journal of cellular and molecular medicine》2020,24(5):2942-2955
Chronic myeloid leukaemia (CML) is a clonal myeloproliferative stem cell disorder characterized by the constitutively active BCR-ABL tyrosine kinase. The LIM and SH3 domain protein 1 (LASP1) has recently been identified as a novel BCR-ABL substrate and is associated with proliferation, migration, tumorigenesis and chemoresistance in several cancers. Furthermore, LASP1 was shown to bind to the chemokine receptor 4 (CXCR4), thought to be involved in mechanisms of relapse. In order to identify potential LASP1-mediated pathways and related factors that may help to further eradicate minimal residual disease (MRD), the effect of LASP1 on processes involved in progression and maintenance of CML was investigated. The present data indicate that not only overexpression of CXCR4, but also knockout of LASP1 contributes to proliferation, reduced apoptosis and migration as well as increased adhesive potential of K562 CML cells. Furthermore, LASP1 depletion in K562 CML cells leads to decreased cytokine release and reduced NK cell-mediated cytotoxicity towards CML cells. Taken together, these results indicate that in CML, reduced levels of LASP1 alone and in combination with high CXCR4 expression may contribute to TKI resistance. 相似文献
25.
Aafke M. Schipper Jelle P. Hilbers Johan R. Meijer Laura H. Anto Ana Benítez‐Lpez Melinda M. J. de Jonge Luuk H. Leemans Eddy Scheper Rob Alkemade Jonathan C. Doelman Sido Mylius Elke Stehfest Detlef P. van Vuuren Willem‐Jan van Zeist Mark A. J. Huijbregts 《Global Change Biology》2020,26(2):760-771
Scenario‐based biodiversity modelling is a powerful approach to evaluate how possible future socio‐economic developments may affect biodiversity. Here, we evaluated the changes in terrestrial biodiversity intactness, expressed by the mean species abundance (MSA) metric, resulting from three of the shared socio‐economic pathways (SSPs) combined with different levels of climate change (according to representative concentration pathways [RCPs]): a future oriented towards sustainability (SSP1xRCP2.6), a future determined by a politically divided world (SSP3xRCP6.0) and a future with continued global dependency on fossil fuels (SSP5xRCP8.5). To this end, we first updated the GLOBIO model, which now runs at a spatial resolution of 10 arc‐seconds (~300 m), contains new modules for downscaling land use and for quantifying impacts of hunting in the tropics, and updated modules to quantify impacts of climate change, land use, habitat fragmentation and nitrogen pollution. We then used the updated model to project terrestrial biodiversity intactness from 2015 to 2050 as a function of land use and climate changes corresponding with the selected scenarios. We estimated a global area‐weighted mean MSA of 0.56 for 2015. Biodiversity intactness declined in all three scenarios, yet the decline was smaller in the sustainability scenario (?0.02) than the regional rivalry and fossil‐fuelled development scenarios (?0.06 and ?0.05 respectively). We further found considerable variation in projected biodiversity change among different world regions, with large future losses particularly for sub‐Saharan Africa. In some scenario‐region combinations, we projected future biodiversity recovery due to reduced demands for agricultural land, yet this recovery was counteracted by increased impacts of other pressures (notably climate change and road disturbance). Effective measures to halt or reverse the decline of terrestrial biodiversity should not only reduce land demand (e.g. by increasing agricultural productivity and dietary changes) but also focus on reducing or mitigating the impacts of other pressures. 相似文献
26.
Jonathan C. Doelman Elke Stehfest Detlef P. van Vuuren Andrzej Tabeau Andries F. Hof Maarten C. Braakhekke David E. H. J. Gernaat Maarten van den Berg Willem‐Jan van Zeist Vassilis Daioglou Hans van Meijl Paul L. Lucas 《Global Change Biology》2020,26(3):1576-1591
Afforestation is considered a cost‐effective and readily available climate change mitigation option. In recent studies afforestation is presented as a major solution to limit climate change. However, estimates of afforestation potential vary widely. Moreover, the risks in global mitigation policy and the negative trade‐offs with food security are often not considered. Here we present a new approach to assess the economic potential of afforestation with the IMAGE 3.0 integrated assessment model framework. In addition, we discuss the role of afforestation in mitigation pathways and the effects of afforestation on the food system under increasingly ambitious climate targets. We show that afforestation has a mitigation potential of 4.9 GtCO2/year at 200 US$/tCO2 in 2050 leading to large‐scale application in an SSP2 scenario aiming for 2°C (410 GtCO2 cumulative up to 2100). Afforestation reduces the overall costs of mitigation policy. However, it may lead to lower mitigation ambition and lock‐in situations in other sectors. Moreover, it bears risks to implementation and permanence as the negative emissions are increasingly located in regions with high investment risks and weak governance, for example in Sub‐Saharan Africa. Afforestation also requires large amounts of land (up to 1,100 Mha) leading to large reductions in agricultural land. The increased competition for land could lead to higher food prices and an increased population at risk of hunger. Our results confirm that afforestation has substantial potential for mitigation. At the same time, we highlight that major risks and trade‐offs are involved. Pathways aiming to limit climate change to 2°C or even 1.5°C need to minimize these risks and trade‐offs in order to achieve mitigation sustainably. 相似文献
27.
Alida Frankline Hasiniaina Ute Radespiel Sharon E. Kessler Mamy Rina Evasoa Solofonirina Rasoloharijaona Blanchard Randrianambinina Elke Zimmermann Sabine Schmidt Marina Scheumann 《Ecology and evolution》2020,10(8):3784-3797
Acoustic phenotypic variation is of major importance for speciation and the evolution of species diversity. Whereas selective and stochastic forces shaping the acoustic divergence of signaling systems are well studied in insects, frogs, and birds, knowledge on the processes driving acoustic phenotypic evolution in mammals is limited. We quantified the acoustic variation of a call type exchanged during agonistic encounters across eight distinct species of the smallest‐bodied nocturnal primate radiation, the Malagasy mouse lemurs. The species live in two different habitats (dry forest vs. humid forest), differ in geographic distance to each other, and belong to four distinct phylogenetic clades within the genus. Genetically defined species were discriminated reliably on the phenotypic level based on their acoustic distinctiveness in a discriminant function analysis. Acoustic variation was explained by genetic distance, whereas differences in morphology, forest type, or geographic distance had no effect. The strong impact of genetics was supported by a correlation between acoustic and genetic distance and the high agreement in branching pattern between the acoustic and molecular phylogenetic trees. In sum, stochastic factors such as genetic drift best explained acoustic diversification in a social communication call of mouse lemurs. 相似文献
28.
De Bauw Pieterjan Smolders Erik Verbeeck Mieke Senthilkumar Kalimuthu Houben Eva Vandamme Elke 《Plant and Soil》2021,463(1-2):187-204
Plant and Soil - Upland rice production is often constrained by phosphorus deficiency (P) and drought events. Methods are needed to maximize P use efficiency, while promoting deep root development... 相似文献
29.
30.