全文获取类型
收费全文 | 3035篇 |
免费 | 198篇 |
出版年
2020年 | 19篇 |
2019年 | 18篇 |
2018年 | 32篇 |
2017年 | 29篇 |
2016年 | 45篇 |
2015年 | 84篇 |
2014年 | 110篇 |
2013年 | 155篇 |
2012年 | 149篇 |
2011年 | 160篇 |
2010年 | 93篇 |
2009年 | 81篇 |
2008年 | 140篇 |
2007年 | 187篇 |
2006年 | 173篇 |
2005年 | 157篇 |
2004年 | 154篇 |
2003年 | 139篇 |
2002年 | 132篇 |
2001年 | 28篇 |
2000年 | 20篇 |
1999年 | 36篇 |
1998年 | 33篇 |
1997年 | 34篇 |
1996年 | 31篇 |
1995年 | 37篇 |
1994年 | 27篇 |
1993年 | 41篇 |
1992年 | 19篇 |
1991年 | 21篇 |
1990年 | 27篇 |
1989年 | 29篇 |
1988年 | 36篇 |
1987年 | 30篇 |
1985年 | 31篇 |
1984年 | 27篇 |
1983年 | 40篇 |
1982年 | 37篇 |
1981年 | 36篇 |
1980年 | 40篇 |
1979年 | 30篇 |
1978年 | 33篇 |
1977年 | 28篇 |
1976年 | 23篇 |
1975年 | 24篇 |
1973年 | 25篇 |
1972年 | 18篇 |
1971年 | 18篇 |
1970年 | 21篇 |
1967年 | 18篇 |
排序方式: 共有3233条查询结果,搜索用时 15 毫秒
101.
The effects of pressure, temperature and some organic solvents on the recovery of various lipid classes from plant and animal tissues can be assessed by fractional extraction with dense carbon dioxide and consecutive analysis by thin-layer chromatography. 相似文献
102.
Zusammenfassung Es wurde die Röntgenstrahleninaktivierung von Laktatdehydrogenase in Rattenleber und Invertase in Hefe untersucht. Die Inaktivierung war in den feuchten lebenden Zellen und in den getrockneten Zellen praktisch gleich, obwohl ein Beitrag der indirekten Strahlenwirkung in den feuchten Zellen zu erwarten war.Auszugsweise vorgetragen auf dem XI. Internationalen Kongreß für Radiologie, Rom, September 1965 相似文献
103.
Zusammenfassung Durch Äthylen wird die radiale Polarität im Sproß vonVicia faba gestört. Es treten 2 Endodermen, eine davon zwischen den Gefäßbündeln und dem inneren Teil des Marks, auf. Auch ein zweites, Seitenwurzeln bildendes Perizykelgewebe entsteht. Die Kutinisierung der Membranen im Bereich der Endodermen kann infolge der gestörten radialen Polarität völlig diffus werden und sich sogar auf Markzellen ausdehnen. Die auch sonst allgemein mit Polaritätsverlust verbundene Embryonalisierung äußert sich in dichten Zellwucherungen im Mark.Mit 6 Textabbildungen. 相似文献
104.
105.
The paratabulate calcareous cyst of Calciodinellum operosum Deflandre was recorded in a sediment trap sample collected in the Bay of Naples (Tyrrhenian Sea, Italy). The germination of this resting stage produced a phototrophic vegetative cell that had the typical plate pattern of a Scrippsiella species. The cyst morphotypes, observed in a clonal culture of this species, ranged from cysts with well-developed paratabulation to cysts in which the paratabulation was barely visible, to cysts covered by irregularly shaped crystals. The analysis of thin sections of the calcareous cysts using the polarized light microscope equipped with crossed nicols and a gypsum plate showed that the optical orientation of the calcite crystals was tangential in all the morphotypes examined. We suggest that the crystallographic method we describe might provide insights for calcareous cyst taxonomy and phylogeny . 相似文献
106.
Ariana M. Chao Thomas A. Wadden Robert I. Berkowitz George Blackburn Paula Bolin Jeanne M. Clark Mace Coday Jeffrey M. Curtis Linda M. Delahanty Gareth R. Dutton Mary Evans Linda J. Ewing John P. Foreyt Linda J. Gay Edward W. Gregg Helen P. Hazuda James O. Hill Edward S. Horton Denise K. Houston John M. Jakicic Robert W. Jeffery Karen C. Johnson Steven E. Kahn William C. Knowler Anne Kure Katherine L. Michalski Maria G. Montez Rebecca H. Neiberg Jennifer Patricio Anne Peters Xavier Pi‐Sunyer Henry Pownall David Reboussin Bruce Redmon W. Jack Rejeski Helmut Steinburg Martha Walker Donald A. Williamson Rena R. Wing Holly Wyatt Susan Z. Yanovski Ping Zhang 《Obesity (Silver Spring, Md.)》2020,28(5):893-901
107.
Alexandra Magro Emilie Lecompte Jean-Louis Hemptinne Antonio O. Soares Anne-Marie Dutrillaux Jérôme Murienne Helmut Fürsch Bernard Dutrillaux 《Journal of Zoological Systematics and Evolutionary Research》2020,58(1):194-208
Parthenogenesis, the development of unfertilized eggs resulting in the exclusive production of female offspring, is rare in animals relative to sexual reproduction and is mainly reported in invertebrates. It has been hypothesized that polyploidy, hybridization and endosymbiont infections are its major causal events but the mechanisms triggering asexual reproduction remain unclear. Here, we study the proximate causes at the origin of parthenogenesis in the first reported case of asexuality in the Coccinellidae (Coleoptera). The asexual populations were found in the Azores and the Mascarene archipelagos, and were identified as Nephus voeltzkowi Weise, a bisexual species widespread in sub-Saharan Africa. The specimens from both populations are diploid but present different karyotypes and heterozygosities that evoke hybrid origins, commonly associated with parthenogenesis in Coleoptera. However, the close proximity of their genomes (99.8% homology for the complete mitochondrial genome and 99.9% for the complete nuclear ribosomal cluster) together with the congruence between the mtDNA tree and the nuclear tree, and the low heterozygosity levels, suggests that the two populations are not hybrid. We propose that they belong to a single chromosomally polymorphic species undergoing Robertsonian fusions. Furthermore, specimens from both populations are infected with Wolbachia (supergroup B strain), contrary to sympatric bisexual species of the same genus. Although Wolbachia has been shown to induce parthenogenesis in haplodiploid organisms, it has been recently suggested that it could also induce parthenogenesis in hosts with other sex determination systems. Whether chromosome rearrangements and/or Wolbachia infections are post-parthenogenetic events or are at the origin of parthenogenesis still needs to be determined. 相似文献
108.
109.
Kirleis Wiebke Kroll Helmut Reiser Tanja Schmid Clemens Schmütz Kay 《Vegetation History and Archaeobotany》2021,30(1):171-174
Vegetation History and Archaeobotany - The online Archaeobotanical Literature Database (ArchbotLit) is an important tool for getting targeted access to archaeobotanical publications. It offers the... 相似文献
110.
Axonal connections are widely regarded as faithful transmitters of neuronal signals with fixed delays. The reasoning behind this is that extracellular potentials caused by spikes travelling along axons are too small to have an effect on other axons. Here we devise a computational framework that allows us to study the effect of extracellular potentials generated by spike volleys in axonal fibre bundles on axonal transmission delays. We demonstrate that, although the extracellular potentials generated by single spikes are of the order of microvolts, the collective extracellular potential generated by spike volleys can reach several millivolts. As a consequence, the resulting depolarisation of the axonal membranes increases the velocity of spikes, and therefore reduces axonal delays between brain areas. Driving a neural mass model with such spike volleys, we further demonstrate that only ephaptic coupling can explain the reduction of stimulus latencies with increased stimulus intensities, as observed in many psychological experiments. 相似文献