全文获取类型
收费全文 | 370篇 |
免费 | 15篇 |
出版年
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 9篇 |
2017年 | 4篇 |
2016年 | 12篇 |
2015年 | 11篇 |
2014年 | 14篇 |
2013年 | 11篇 |
2012年 | 23篇 |
2011年 | 32篇 |
2010年 | 17篇 |
2009年 | 8篇 |
2008年 | 21篇 |
2007年 | 36篇 |
2006年 | 12篇 |
2005年 | 19篇 |
2004年 | 17篇 |
2003年 | 12篇 |
2002年 | 17篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1970年 | 3篇 |
1965年 | 1篇 |
1963年 | 1篇 |
1952年 | 1篇 |
排序方式: 共有385条查询结果,搜索用时 15 毫秒
71.
We investigated the host suitability of the Mediterranean flour moth Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) for a polyphagous koinobiont endoparasitoid Meteorus pulchricornis (Wesmael) (Hymenoptera: Braconidae), a common natural enemy of various pest lepidopteran larvae. The estimated probability of adult wasp emergence was 80% or higher when eggs were laid in nearly fully grown larvae of E. kuehniella (fresh weight, >?20.0 mg). The body size of emerged adult wasps increased with the initial weight of the host larvae at oviposition. The fresh weight of adult wasps reared on E. kuehniella was approximately 60% of that when reared on a natural host Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae), and the lifetime fecundity of wasps reared on E. kuehniella was approximately half of that when reared on S. litura. Ephestia kuehniella was shown to be a positive host candidate for the mass rearing of M. pulchricornis, but further investigation is needed to increase the body size of wasps for more practical use of this species as a biocontrol agent. 相似文献
72.
Tünde Szmatona-Túri Gábor Magos Diána Vona-Túri Blanka Gál András Weiperth 《Biologia》2018,73(5):523-529
The main objective of this paper is to report habitat occupancy, naturalness status and phenology of Urocoras longispinus (Chyzer and Kulczyński 1897), a little-known spider species. Sampling was conducted in Natura 2000 habitats of the Mátra Mountains, and four disturbed mainroad verges in Hungary between 2012 and 2015. We recorded 356 adult specimens active throughout the year, but abundance was highest in autumn. In the Mátra Mountains shrub removal negatively affected the abundance of U. lonsgspinus: the species preferred shaded habitats. The intensity of mowing maintenance caused changes in the species’ abundance in mainroad verges: the number of individual spiders increased as a result of both without maintenance and enhanced maintenance. We conclude that U. longispinus is a stenochronous spider species which lives in both human-disturbed and undisturbed habitats. However, the nature of the disturbance influenced the abundance of this species to varying degrees. 相似文献
73.
Janusz Czerepko Andrzej Boczoń Michał Wróbel Radosław Gawryś Karol Sokołowski 《Wetlands Ecology and Management》2018,26(4):689-702
Raised bogs dominated by the vegetation association Ledo-Sphagnetum magellanici Sukopp 1959 em. Neuhäusl 1969 are a valuable and ecologically important plant community that occurs in Central Europe. They develop in impervious depressions with precipitation as the only water source, and are particularly sensitive to drainage, climate change, eutrophication and overgrowing by trees and shrubs. The high pressure of threat justifies taking protective measures. This research focused on the effects of the removal of birch from two bogs, which were dominated by two birch species (Betula pubescens, B. pendula) and also included stands of Scots pine (Pinus sylvestris); the bogs are located in northeastern Poland and showed signs of drying. The trees were removed in early spring 2008. To capture the response to tree cutting, vegetation monitoring was performed for 7 years. The results were compared to pre-cutting environmental conditions (precipitation, temperature, air transpiration). At the first site, which was drained at the beginning of the twentieth century, the ground water level initially decreased; then, from 2010 onwards, the level stabilised and exhibited a negative correlation with the average annual air temperature. While the second site exhibited no significant differences in the ground water table, a correlation with the average annual rainfall was found. At both sites, there was an increase in the coverage of species appropriate for raised bogs, Oxycocco-Sphagnatea Br.-Bl. et R. Tx. 1943, whereas only the second site had significant coverage of these species. These actions improved the habitat conditions and initiated the process of raised bog restoration at that site because Oxycocco-Sphagnatea species cover and frequency increased. 相似文献
74.
Matthew C. P. Glyn Michaela Egertová Blanka Gazdova Aleš Kovarik Milan Bezdek Andrew R. Leitch 《Chromosoma》1997,106(8):485-492
This paper describes the effects of 5-azacytidine on the condensation state of rye (Secale cereale L.) chromatin introduced into the wheat genome (Triticum aestivum L. cv. Beaver). The wheat cultivar Beaver carries a translocation between the short arm of rye chromosome 1R (1RS) and the
long arm of wheat chromosome 1B (1BL/1RS). 1RS can be detected using genomic in situ hybridisation and carries a ribosomal
DNA (rDNA) locus that can be simultaneously detected using multiple labelling strategies. The rDNA locus divides 1RS into
a distal region that is gene rich and a proximal region that is gene poor and highly methylated. 1RS also carries a large
block of subtelomeric heterochromatin. The drug, which acts to inhibit DNA methylation in plants, has three pronounced effects
on interphase nuclei. (1) It induces aberrant condensation of the rye subtelomeric heterochromatin and in many cases induces
sister chromatid separation in the subtelomeric heterochromatin of G2 nuclei. (2) Nuclei trisomic for 1RS are observed at
low frequency in treated material and are probably a consequence of aberrant sister chromatid separation or condensation.
(3) The drug alters normal condensation of 1RS euchromatin. However, contrary to expectation the effect is not simply to induce
decondensation. The proximal region of the arm actually condenses at low levels of drug administration while the distal region
remains unaltered or increases its decondensation state. Increasing the concentration of 5-azacytidine induces a biphasic
response and at the highest concentration used all regions of the arm show signs of decondensation. Thus the influence of
the drug on chromatin condensation depends on the genomic structure.
Received: 14 July 1997; in revised form: 26 August 1997 / Accepted: 27 August 1997 相似文献
75.
Zdeněk Wimmer Richard Tykva Blanka Bennettová Věra Vlasáková Tomáš Elbert 《Invertebrate neuroscience : IN》1997,3(2-3):193-197
A synthetic insect juvenile hormone analog (a juvenoid), ethylN-[2-[4-[[2,2-(ethylenedioxy)cyclohexyl]methyl]phenox]ethyl]carbamate, which has displayed high biological activity against
different insect species and high stability under field conditions, was selected as a biologically active model compound for
a study of a juvenile hormone analog degradation. The biologically active compound itself and its three diversely radiolabeled
derivatives were applied to the flesh fly (Sarcophaga bullata) or the tsetse fly (Glossina palpalis), respectively. Monitoring of a fate of the applied juvenile hormone analog was carried out using a detection method of the
radioactivity microdistribution within the whole insect body in combination with a radio high performance liquid chromatography
(radio-HPLC), both of whole-body extracts made in different, but in advance scheduled, time intervals, and of extracts of
insect excreta accumulated over an eight-day experiment. 相似文献
76.
Conservation tool or threatening process? management implications of interactions of cattle with vegetation and land at the Vale of Belvoir reserve
下载免费PDF全文
![点击此处可从《Ecological Management & Restoration》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Blanka Tengia Matthew Taylor Jamie Kirkpatrick 《Ecological Management & Restoration》2016,17(2):147-151
A recently purchased private reserve of high conservation value has been grazed in summer by cattle since the early nineteenth century. We ask whether the cattle are causing continuing damage and whether they are necessary to maintain any conservation values. We used five‐year‐old exclosures to determine the effects of cattle on wetland vegetation, mapped damage to soils and landforms and mapped cattle dung deposition in relation to the distributions of rare and threatened plant species. Cattle impacts on wetland plants were minor. Cattle damage to landforms by pugging and bank collapse was frequent near unfenced water bodies. Rare and threatened species were largely on well‐drained ground, while cattle dung was concentrated in wetlands and near water bodies. We conclude that cattle grazing is impacting some conservation values and is not necessary for conservation purposes. Destocking should be accompanied by careful monitoring of threatened plant populations. If necessary, alternative planned disturbances can provide regeneration niches for rare and threatened plants. 相似文献
77.
78.
79.
Status of Savi's pipistrelle Hypsugo savii (Chiroptera) and range expansion in Central and south‐eastern Europe: a review
下载免费PDF全文
![点击此处可从《Mammal Review》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Marcel Uhrin Ulrich Hüttmeir Marina Kipson Péter Estók Konrad Sachanowicz Szilárd Bücs Branko Karapandža Milan Paunović Primož Presetnik Andriy‐Taras Bashta Edita Maxinová Blanka Lehotská Roman Lehotský Levente Barti István Csösz Farkas Szodoray‐Paradi Imre Dombi Tamás Görföl Sándor A. Boldogh Csaba Jére Irina Pocora Petr Benda 《Mammal Review》2016,46(1):1-16
- 相似文献
80.
Characterization of Infectious Deoxyribonucleic Acid from Temperate Bacillus subtilis Bacteriophage φ 105
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Phenol-extracted, infectious deoxyribonucleic acid (DNA) species from phi105 phage particles, from phi105 lysogenic bacteria, and from induced phi105 lysogenic bacteria were sedimented in sucrose gradients. Infectious DNA from phi105 particles sedimented like the bulk of mature phage DNA in neutral sucrose. Infectivity of prophage DNA was associated with fast-sedimenting material of heterogenous size. Infectious vegetative phage DNA sedimented somewhat faster than mature phage DNA; it was rapidly converted to a poorly infectious form during the infection. 相似文献