首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   151篇
  免费   4篇
林业   19篇
农学   10篇
基础科学   2篇
  60篇
综合类   4篇
农作物   10篇
水产渔业   6篇
畜牧兽医   24篇
园艺   4篇
植物保护   16篇
  2023年   1篇
  2022年   1篇
  2021年   5篇
  2020年   7篇
  2019年   3篇
  2018年   9篇
  2017年   6篇
  2016年   5篇
  2015年   2篇
  2014年   4篇
  2013年   8篇
  2012年   3篇
  2011年   12篇
  2010年   2篇
  2009年   3篇
  2008年   7篇
  2007年   5篇
  2006年   7篇
  2005年   6篇
  2004年   9篇
  2003年   8篇
  2002年   6篇
  2001年   2篇
  2000年   2篇
  1999年   4篇
  1998年   3篇
  1997年   4篇
  1996年   3篇
  1995年   1篇
  1994年   1篇
  1993年   1篇
  1992年   1篇
  1991年   1篇
  1990年   2篇
  1989年   1篇
  1988年   3篇
  1987年   1篇
  1981年   3篇
  1980年   1篇
  1977年   1篇
  1959年   1篇
排序方式: 共有155条查询结果,搜索用时 265 毫秒
51.
Potato plants (cvs. ‘Russet Burbank’, ‘Red Pontiac’, ‘Norchip’ and ‘Norgold Russet’) were grown in an artificial medium for 28 days under greenhouse conditions and were watered with solutions containing various rates of NaCl or Na2SO4 alone and in combination with CaSO4. NaCl and Na2SO4 slowed growth of young plants. On a mole basis Na2SO4 slowed growth more than NaCl. The addition of CaSO4 reduced the deleterious effect of NaCl or Na2SO4 solutions. Growth of ‘Russet Burbank’ plants was the most adversely affected by solutions of NaCl or Na2SO4. Watering with solutions of NaCl or Na2SO4 also reduced the number of ‘Russet Burbank’ plants.  相似文献   
52.
Summary The degree of inter- and intra-specific variation in the populations of allogamous and autogamousSecale L. species was estimated in support of isoenzyme markers. Totally, 11 different species ofSecale were analysed including perennial species:S. kuprijanovii Grossh.,S. chaldicum Fed.,S. montanum Guss.,S. anatolicum Boiss., and annual species:S. silvestre Host.,S. vavilovii Grossh.,S. ancestrale Zhuk.,S. dighoricum Vav.,S. afghanicum Vav.,S. segetale Roshev.; as well as the cultivated ryeS. cereale L. cv. Dakowskie Zote. Isoenzymes were analysed in the first leaf of single young seedlings grown in controlled conditions using starch-gel slab electrophoresis technique and the electrophoretic forms of two different enzyme systems were detected: nonspecific esterases (E. C. 3. 1. 1) and peroxidase (E. C. 1. 11. 1. 7). It was found that the breeding system of rye species has a distinct affect on the isoenzyme variation in their populations. The selffertile annual species,S. silvestre, was monomorphic for both enzyme systems. A very low esterases polymorphism was also found in other autogamous species,S. vavilovii, however a similar degree of polymorphism in allogamous annual species,S. segetale andS. dighoricum, was observed. Generally, the perennialSecale species were more polymorphic than the annual ones, and the isoenzyme variation in the population of cultivated ryeS. cereale was similar to some other wild annual species. It was observed that the intra-specific isoenzyme variation inSecale was bigger than the inter-specific. Esterases electrophoretic forms showed to be very sensitive markers of variation in rye species.
Isoenzym-Variation bei Wildarten der GattungSecale L.
Zusammenfassung Der Grad der inter- und intraspezifischen Variation in Populationen von allogamen und autogamen Arten der GattungSecale L. wurde mit Hilfe von Isoenzymmerkmalen geschätzt. Insgesamt wurden 11 verschiedene Arten vonSecale einschließlich der mehrjährigen Arten analysiert:S. kuprijanovii Grossh.,S. chaldicum Fed.,S. montanum Guss.,S. anatolicum Boiss. und die einjährigen Arten:S. silvestre Host.,S. vavilovii Grossh.,S. ancestrale Zhuk.,S. dighoricum Vav.,S. afghanicum Vav.,S. segetale Roshev., wie auch des KulturroggensS. cereale L. cv. Dankowskie Zote. Die Isoenzyme wurden am ersten Blatt junger Einzelsämlinge, die unter kontrollierten Bedingungen angezogen wurden, unter Anwendung der Stärkegel-Plattenelektrophorese-Technik geprüft, und die elektrophoretischen Formen von zwei verschiedenen Enzymsystemen wurden nachgewiesen: nichtspezifische Esterasen (E. C.3.1. 1.)und Peroxidase (E. C. 1. 11. 1. 7.). Es wurde gefunden, daß das Fortpflanzungssystem der Roggen-Arten eine bestimmte Wirkung auf die Isoenzymvariation in ihren Populationen hat. Die selbstfertile einjährige Art,Secale silvestris, war hinsichtlich beider Enzymsysteme monomorph. Ein sehr schwach ausgeprägter Esterasenpolymorphismus wurde in einer anderen autogamen Art,S. vavilovii, gefunden, jedoch wurde ein ähnlicher Grad von Polymorphismus in allogamen einjährigen Arten,S. segetale undS. dighoricum, beobachtet. Grundsätzlich waren die mehrjährigenSecale-Arten polymorpher als die einjährigen, und die Isoenzym-Variation der Populationen des kultivierten RoggensS. cereale war ähnlich der einiger anderer einjähriger Wildarten. Es wurde beobachtet, daß die intraspezifische Enzym-Variation vonSecale größer war als die interspezifische. Die esterase-elektrophoretischen Formen erwiesen sich als sehr empfindliche Indikatoren für die Variation der Roggenarten.

Secale L.
Secale L. . 11 ; :S. kuprijanovii Grossh.,S. chaldicum Fed.,S. montanum Guss.,S. anatolicum Boiss.; : S. silvestreHost,S. vavilovii Grossh.,S. ancestrale Zhuk.,S. dighoricum Vav.,S. afghanicum Vav.,S. segetale Roshev. S. cereale L., . , , ( — ). : (. . 3. 1. 1.) (. . 1. 11. 1. 7.). , ë . S. silvestre . ,S. vavilovii, ,S. segetale S. dighoricum. , , , . Secale , . .


Presented as poster  相似文献   
53.
In a pot trial in which soybean [Glycine max (L.) Merr.] plants were overfertilized by boron (B) at rates of 5, 10, and 15 mg per pot in 6 kg of soil, a reduction of shoot weight and seed yield was obtained. Boron limited protein synthesis and inhibited dipeptidase activity. Under the effect of B overfertilization, the rates of absorption and accumulation of major macronutrients was remarkably decreased. Foliar treatment with gibberellin (A3) in the early phases of plant development partly compensated for the negative effect of B overdosing.  相似文献   
54.
Summary

Four narcissus cultivars were forced under artificial light using fluorescent lamps which emitted white (307 – 770 nm), blue (393 – 580 nm), red (540 – 760 nm), yellow (450 – 750 nm), or green (387 – 680 nm) light. The photosynthetic photon flux density was 12.5 μmol m–2 s–1, with a 6 h photoperiod. Light colour (wavelength) had no significant effect on flowering date, or on the number of flowers collected (P < 0.05). Narcissus bulbs exposed to blue light (393 – 580 nm) formed shorter, more rigid shoots of lower weight with 13 – 40% shorter leaves.  相似文献   
55.

Purpose

The study aimed to characterise a fossil permafrost-affected (Stagnic Fluvisol Relictiturbic) soil, occurring in a cliff in the central part of the Polish Baltic coastal zone near Orzechowo (54° 35.664′ N, 16° 54.123′ E).

Materials and methods

The soil was sampled at 22 points and analysed using standard procedures in soil science. After standard preparation, disturbed and undisturbed soil samples were made subject to laboratory analyses concerning their physical and chemical properties. Radiocarbon dates and pollen analysis results were also obtained for the selected soil samples.

Results and discussion

The permafrost-affected soil lies beneath a fossil Dystric Histic Stagnosol, which is covered by about 8 m of aeolian deposits. The radiocarbon age of the Dystric Histic Stagnosol was 3061 ± 60 cal. years BP, and that of the Stagnic Fluvisol Relictiturbic 10,161 ± 110 cal. years BP. However, the results of pollen analysis suggest rejuvenation of the obtained dates. The Stagnic Fluvisol Relictiturbic developed in the marginal part of a body of water, from fluvioglacial and aeolian sands deposited on grey glacial till. The mineral substrates of the soil are moderately and poorly sorted sands and silt loam in the bottom part of the profile. This fine-textured material has been moved to the upper parts of the profile due to the impact of the water freezing and thawing cycles in the permafrost active layer. The observed microstructures on quartz grain (0.5–1.0 mm) surfaces, including conchoidal fractures, breakage blocks and v-shaped pits, are typical for periglacial soils. The fossil Stagnic Fluvisol Relictiturbic is poor in total iron. The observed vertical distribution of free iron oxides suggests their displacement in the permafrost active layer. Soil organic matter was found to be moderately or strongly humified, which is not typical for permafrost-affected soils and can suggest its allochthonous, probably alluvial, character.

Conclusions

The studied Stagnic Fluvisol Relictiturbic developed at the close of the Pleistocene in the marginal part of a body of water. It constitutes a sequence of horizons of varied thickness and abundance in organic matter. The influence of a periglacial environment is reflected in morphology of the soil (cryoturbations) and some chemical properties and partially in microstructures observed on quartz grain surfaces.
  相似文献   
56.

Purpose

The impacts of fly ash on the chemistry of forest floors were previously described in literature, while impacts on soil properties were less recognised. Soil investigations were focussed mainly on increases of pH and base saturations in surface horizons. The purpose of this study was to describe the influence of alkaline fly ash blown out from the dumping site of a lignite-fired power plant on pH changes of ectohumus horizons of Podzols and the morphology of deeper horizons.

Materials and methods

We investigated the soil profiles of Podzols derived from loose quartz sand and developed under pine forest surrounding the dumping site of the power plant Be?chatów, central Poland. In the vicinity of the fly ash dumping site, five Podzol profiles located at a distance of 50 m from the dumping site were investigated, as well as soil profiles located along the transect set at distances of 50, 300, 800 and 2000 m from the dumping site. Control profiles were located at a distance of 7.3 km from the dumping site. Soil morphology was described in the field and the following properties were determined: soil texture, hydrolytic acidity, exchangeable cations, total organic carbon and total nitrogen content.

Results and discussion

The pH values of Podzol ectohumus horizons located close to the dumping site ranged from 6.01 to 7.34 compared to a range of 3.08–3.72 in the control. Ectohumus horizon located 300 m from the dumping site showed a pH range of 4.13–4.26, while at a distance of 800 m, the pH values did not differ from those of the control site. The upper part of the eluvial soil horizons located close to the dumping site had been transformed into transitional AE horizons in which humic substances translocated from ectohumus horizons were accumulated. Moreover, the organic carbon content of this horizon increased compared to the carbon content of the illuvial Bs horizon located below it. Under the influence of alkalisation of upper horizons, the illuvial Bhs horizons vanished and were transformed into Bs horizons.

Conclusions

Changes in soils affected by fly ashes are connected with alkalinisation of ectohumus horizons. Podzolisation processes can be reduced or even completely stopped regarding the distance from the dumping site. Eluvial Podzol horizons located close to the dumping site may be transformed into AE horizons in which humic substances translocated from ectohumus horizons are accumulated. Due to transformation and translocation of organic components, Bhs horizons can be transformed into Bs horizons.
  相似文献   
57.
The promyelocytic leukemia (PML) tumor suppressor is a pleiotropic modulator of apoptosis. However, the molecular basis for such a diverse proapoptotic role is currently unknown. We show that extranuclear Pml was specifically enriched at the endoplasmic reticulum (ER) and at the mitochondria-associated membranes, signaling domains involved in ER-to-mitochondria calcium ion (Ca(2+)) transport and in induction of apoptosis. We found Pml in complexes of large molecular size with the inositol 1,4,5-trisphosphate receptor (IP(3)R), protein kinase Akt, and protein phosphatase 2a (PP2a). Pml was essential for Akt- and PP2a-dependent modulation of IP(3)R phosphorylation and in turn for IP(3)R-mediated Ca(2+) release from ER. Our findings provide a mechanistic explanation for the pleiotropic role of Pml in apoptosis and identify a pharmacological target for the modulation of Ca(2+) signals.  相似文献   
58.
Polish garlic and white and red onions were subjected to blanching, boiling, frying, and microwaving for different periods of time, and then their bioactive compounds (polyphenols, flavonoids, flavanols, anthocyanins, tannins, and ascorbic acid) and antioxidant activities were determined. It was found that blanching and frying and then microwaving of garlic and onions did not decrease significantly the amounts of their bioactive compounds and the level of antioxidant activities ( P > 0.05). The HPLC profiles of free and soluble ester- and glycoside-bound phenolic acids showed that trans-hydroxycinnamic acids (caffeic, p-coumaric, ferulic, and sinapic) were as much as twice higher in garlic than in onions. Quercetin quantity was the highest in red onion among the studied vegetables. The electrophoretic separation of nonreduced garlic and onion proteins after boiling demonstrated their degradation in the range from 50 to 112 kDa.  相似文献   
59.
The effect of coniferyl alcohol on removal of chlorinated phenols from a water environment byRhizoctonia praticola andCerrena unicolor laccases was studied. At optimal conditions in which 7 mM coniferyl alcohol and laccase were added to chlorinated phenols over 20h, about 34% of the radioactivity of 4-chlorophenol, 57% of 2,4-dichlorophenol, 66% of 2,4,5-trichlorophenol, and 85% of pentachlorophenol were removed from the supernatants, compared to the level without laccase activity. After 12-h incubation periods at the optimal concentrations of coniferyl alcohol and laccase (added simultaneously), the fast first phase of chlorophenol removal was complete in 1 h, and eventually coniferyl alcohol enhanced the removal of 4-chlorophenol by 40%, 2,4-dichlorophenol by 54%, 2,4,5-trichlorophenol by 60%, and pentachlorophenol by 76%.  相似文献   
60.

Background

The development of cell pattern in the surface cell layer of the shoot apex can be investigated in vivo by use of a time-lapse confocal images, showing naked meristem in 3D in successive times. However, how this layer is originated from apical initials and develops as a result of growth and divisions of their descendants, remains unknown. This is an open area for computer modelling. A method to generate the surface cell layer is presented on the example of the 3D paraboloidal shoot apical dome. In the used model the layer originates from three apical initials that meet at the dome summit and develops through growth and cell divisions under the isotropic surface growth, defined by the growth tensor. The cells, which are described by polyhedrons, divide anticlinally with the smallest division plane that passes depending on the used mode through the cell center, or the point found randomly near this center. The formation of the surface cell pattern is described with the attention being paid to activity of the apical initials and fates of their descendants.

Results

The computer generated surface layer that included about 350 cells required about 1200 divisions of the apical initials and their derivatives. The derivatives were arranged into three more or less equal clonal sectors composed of cellular clones at different age. Each apical initial renewed itself 7–8 times to produce the sector. In the shape and location and the cellular clones the following divisions of the initial were manifested. The application of the random factor resulted in more realistic cell pattern in comparison to the pure mode. The cell divisions were analyzed statistically on the top view. When all of the division walls were considered, their angular distribution was uniform, whereas in the distribution that was limited to apical initials only, some preferences related to their arrangement at the dome summit were observed.

Conclusions

The realistic surface cell pattern was obtained. The present method is a useful tool to generate surface cell layer, study activity of initial cells and their derivatives, and how cell expansion and division are coordinated during growth. We expect its further application to clarify the question of a number and permanence or impermanence of initial cells, and possible relationship between their shape and oriented divisions, both on the ground of the growth tensor approach.
  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号