全文获取类型
收费全文 | 430篇 |
免费 | 17篇 |
专业分类
林业 | 75篇 |
农学 | 12篇 |
基础科学 | 1篇 |
161篇 | |
综合类 | 43篇 |
农作物 | 14篇 |
水产渔业 | 5篇 |
畜牧兽医 | 95篇 |
园艺 | 3篇 |
植物保护 | 38篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 5篇 |
2017年 | 8篇 |
2016年 | 9篇 |
2015年 | 5篇 |
2014年 | 15篇 |
2013年 | 36篇 |
2012年 | 18篇 |
2011年 | 30篇 |
2010年 | 15篇 |
2009年 | 16篇 |
2008年 | 33篇 |
2007年 | 22篇 |
2006年 | 24篇 |
2005年 | 23篇 |
2004年 | 15篇 |
2003年 | 20篇 |
2002年 | 14篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 9篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1993年 | 8篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1984年 | 2篇 |
1980年 | 2篇 |
1976年 | 5篇 |
1973年 | 2篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1966年 | 4篇 |
1965年 | 4篇 |
1953年 | 2篇 |
1933年 | 1篇 |
1932年 | 5篇 |
1930年 | 1篇 |
1928年 | 2篇 |
1926年 | 1篇 |
排序方式: 共有447条查询结果,搜索用时 203 毫秒
151.
152.
Shiva Shankar Pandey Tek Narayan Maraseni Geoff Cockfield Karin Gerhard 《Journal of Sustainable Forestry》2013,32(8):796-813
Community forestry is expanding in developing countries but there is limited knowledge of, and contradictory findings about, its contribution to biodiversity conservation. This study aims at increasing the understanding of tree species diversity in community forests compared to National Parks. A forest inventory was carried out in four community forests and one National Park in the mid-hills of central Nepal. The study found that community forestry has contributed to high tree species diversity where forest management communities have interests in multiple species, but most community forests are moving toward promoting limited timber yielding species that have high economic value. Linking community forestry with economic incentives for conserving multiple tree species could therefore be a strategy to conserve biodiversity outside of protected areas. 相似文献
153.
Anna Carbone Barbara Parrino Paola Barraja Virginia Spanò Girolamo Cirrincione Patrizia Diana Armin Maier Gerhard Kelter Heinz-Herbert Fiebig 《Marine drugs》2013,11(3):643-654
2,5-bis(3′-Indolyl)pyrroles, analogues of the marine alkaloid nortopsentin, were conveniently prepared through a three step procedure in good overall yields. Derivatives 1a and 1b exhibited concentration-dependent antitumor activity towards a panel of 42 human tumor cell lines with mean IC50 values of 1.54 μM and 0.67 μM, respectively. Investigating human tumor xenografts in an ex-vivo clonogenic assay revealed selective antitumor activity, whereas sensitive tumor models were scattered among various tumor histotypes. 相似文献
154.
155.
Schröder B Breves G 《Animal health research reviews / Conference of Research Workers in Animal Diseases》2006,7(1-2):31-41
Adequate blood calcium (Ca) concentrations are a prerequisite to maintain several physiological functions of mammals such as pig and ruminants. Thus, blood Ca levels have to be regulated within very close limits. This is basically ensured through the coordinated effects of the calcitropic hormones parathyroid hormone (PTH) and calcitriol (1,25-dihydroxyvitamin D3). If plasma Ca decreases, one main effect of subsequently secreted PTH is the stimulation of renal reabsorption of Ca from the glomerular filtrate to reduce urinary Ca loss. Another important action of PTH is the induction of the renal enzyme 1 alpha-hydroxylase, which is responsible for the production of calcitriol. In most monogastric species, so far investigated, one of the most important effects of calcitriol is to stimulate active absorption of Ca from the gastrointestinal tract, particularly the upper small intestines, via a vitamin D-receptor-mediated genomic action. Whether this concept can be transferred without any constrictions to ruminants is still under discussion. Marked interspecies differences have to be recognized with respect to ruminant or non-ruminant animals, particularly with respect to individual segments along the gastrointestinal axis and with respect to vitamin D sensitivity of Ca transport mechanisms. This review will elucidate some of the current concepts related to the mechanisms and sites of Ca absorption in pigs and ruminants with special emphasis on dairy cows where Ca homeostasis is occasionally compromised at the time of parturition. 相似文献
156.
Investigations on the water intake of growing bulls 总被引:1,自引:1,他引:0
The voluntary water intake was evaluated in 62 growing Holstein bulls (mean body weight range = 193 to 550 kg) during a whole fattening period. The diet was composed of corn silage and concentrates. Water was offered for ad libitum consumption. A total of 17,772 measurements of water intake were recorded over 282 days. The average daily water consumption was 18 kg/animal (S.D. = 6.7 kg). Applying a multiple regression analysis to the data set yielded the following equation: voluntary water intake (kg/day) = − 3.85 + 0.507 average ambient temperature (°C) + 1.494 dry matter intake (kg/day) − 0.141 roughage part of the diet (%) + 0.248 dry matter content of roughage (%) + 0.014 body weight (kg). The incorporation of the variables body weight gain, relative humidity, maximum ambient temperature, Na intake, and K intake into the equation did not increase the accuracy of the prediction. 相似文献
157.
Guillaume Besnard Virginie Acheré Sylvain Jeandroz Øystein Johnsen Patricia Faivre Rampant Rüdiger Baumann Gerhard Müller-Starck Torre Skrøppa Jean-Michel Favre 《Annals of Forest Science》2008,65(1):109-109
In forest trees, environmental conditions during reproduction can greatly influence progeny performance. This phenomenon probably results from adaptive phenotypic plasticity but also may be associated with genotypic selection. In order to determine whether selective effects during the reproduction are environment specific, single pair-crosses of Norway spruce were studied in two contrasted maternal environments (warm and cold conditions). One family expressed large and the other small phenotypic differences between these crossing environments. The inheritance of genetic polymorphism was analysed at the seed stage. Four parental genetic maps covering 66 to 78% of the genome were constructed using 190 to 200 loci. After correcting for multiple testing, there is no evidence of locus under strong and repeatable selection. The maternal environment could thus only induce limited genotypic-selection effects during reproductive steps, and performance of progenies may be mainly affected by a long-lasting epigenetic memory regulated by temperature and photoperiod prevailing during seed production. 相似文献
158.
Daniel Goitom Asfaha Christophe R. Quétel Freddy Thomas Micha Horacek Bernhard Wimmer Gerhard Heiss Christian Dekant Peter Deters-Itzelsberger Stefan Hoelzl Susanne Rummel Christophe Brach-Papa Marleen Van Bocxstaele Eric Jamin Malcolm Baxter Katharina Heinrich Simon Kelly Daniela Bertoldi Luana Bontempo Federica Camin Roberto Larcher Matteo Perini Andreas Rossmann Antje Schellenberg Claus Schlicht Heinz Froeschl Jurian Hoogewerff Henriette Ueckermann 《Journal of Cereal Science》2011
The aim of this work (from the FP6 project TRACE) was to develop methods based on the use of geochemical markers for the authentication of the geographical origin of cereal samples in Europe (cf. EC regulations 2081/92 and 1898/06). For the first time, the potential usefulness of combining n(87Sr)/n(86Sr) and δ13C, δ15N, δ18O and δ34S isotopic signatures, alone or with key element concentrations ([Na], [K], [Ca], [Cu] and [Rb], progressively identified out of 31 sets of results), was investigated through multiple step multivariate statistics for more than 500 cereal samples collected over 2 years from 17 sampling sites across Europe representing an extensive range of geographical and environmental characteristics. 相似文献
159.
Lompe T Ottenstein TB Serwane F Wenz AN Zürn G Jochim S 《Science (New York, N.Y.)》2010,330(6006):940-944
The quantum mechanical three-body problem is one of the fundamental challenges of few-body physics. When the two-body interactions become resonant, an infinite series of universal three-body bound states is predicted to occur, whose properties are determined by the strength of the two-body interactions. We used radio-frequency fields to associate Efimov trimers consisting of three distinguishable fermions. The measurements of their binding energy are consistent with theoretical predictions that include nonuniversal corrections. 相似文献
160.
Before 2006, agents of class II pyrethroids were used to control rape pests including the rape pollen beetle mainly. Thus, the selection of pyrethroids-resistant pollen beetle populations was encouraged. The aim of our study was to identify ways to combat these populations. Therefore, data of 465 real on-farm insecticide applications from nine years since 2006 were analyzed with regard to their effects on the pollen beetle and own experiments were carried out to test the efficacy of approved insecticides and control strategies. The analysis showed that the highest efficiencies were obtained with agents of the group of organophosphates and with the active substances indoxacarb and pymetrozine. Beyond that, the data examined revealed that the efficiency of thiacloprid (an insecticide of the class of neonicotinoids) has remained relatively constant throughout the observation period. In contrast, the increase in pyrethroid-resistant pollen beetle populations reflects the further decrease in efficacy of class II pyrethroids in the period 2011–2014.In summary, it should be noted that currently available insecticides achieve a maximal abatement level of 80–85?%. Therefore, an economic damage cannot be prevented on rapeseed locations with a very strong pollen beetle infestation even if multiple use of insecticides happens.To prevent further escalation of the resistance problem, another aspect should be given greater attention in the future. 55?% of the insecticide applications in the practice dataset where carried out before the control threshold (BRW) for weakly developed oilseed rape crops was achieved; often in the stage of micro-bud (BBCH 51). In compliance with the currently suggested higher control threshold, only 15?% of the insecticide applications would have been necessary. Thus, a reduction of the number of insecticide applications could be achieved by considering the higher thresholds. This would significantly reduce the selection pressure. Therefore, plant protection advice should mediate between exploiting the control thresholds and using the most appropriate insecticide. 相似文献