全文获取类型
收费全文 | 845篇 |
免费 | 61篇 |
国内免费 | 132篇 |
专业分类
林业 | 110篇 |
农学 | 115篇 |
基础科学 | 27篇 |
160篇 | |
综合类 | 303篇 |
农作物 | 24篇 |
水产渔业 | 96篇 |
畜牧兽医 | 139篇 |
园艺 | 23篇 |
植物保护 | 41篇 |
出版年
2024年 | 2篇 |
2023年 | 11篇 |
2022年 | 32篇 |
2021年 | 33篇 |
2020年 | 39篇 |
2019年 | 31篇 |
2018年 | 26篇 |
2017年 | 52篇 |
2016年 | 46篇 |
2015年 | 39篇 |
2014年 | 58篇 |
2013年 | 54篇 |
2012年 | 61篇 |
2011年 | 55篇 |
2010年 | 40篇 |
2009年 | 56篇 |
2008年 | 57篇 |
2007年 | 40篇 |
2006年 | 33篇 |
2005年 | 33篇 |
2004年 | 23篇 |
2003年 | 25篇 |
2002年 | 24篇 |
2001年 | 23篇 |
2000年 | 18篇 |
1999年 | 14篇 |
1998年 | 15篇 |
1997年 | 12篇 |
1996年 | 13篇 |
1995年 | 7篇 |
1994年 | 16篇 |
1993年 | 13篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1980年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有1038条查询结果,搜索用时 15 毫秒
101.
102.
103.
黔南州近年年初常出现低温冻害天气,冻害发生时气温在0℃以下,造成全州油菜、小麦、蔬菜和果树等农作物生产受到严重影响.据黔南州农业部门统计,2011-2013年平均每年农作物受灾面积为26700hm2,成灾面积4860hrn2,绝收面积660hm2,因灾造成直接经济损失5636.18万元.严重影响了农业增效,农民增收.针对黔南州农作物受低温冻害影响情况进行了调查,经详细分析提出低温冻害前农作物生产防冻措施,以减轻灾害给农业带来的损失. 相似文献
104.
《Journal of Crop Improvement》2013,27(1-2):37-52
Summary Studies of herbaceous plants suggest that cold hardiness is a complex, quantitatively inherited trait. Although development of cold hardiness is an integral part of the life cycle of woody perennial plants, studies on the genetic control of cold hardiness in woody perennials are scarce. A better understanding of the genetic control of cold hardiness would be valuable for developing more effective strategies to increase cold hardiness and, hence, climatic adaptation of woody perennial crops. In blueberry, three major dehydrins of 65, 60, and 14 kDa have been found to increase with cold acclimation and decrease with deac-climation. A comparison of these dehydrin levels among various blueberry cultivars and selections has revealed their level of accumulation to be closely associated with cold hardiness level. Efforts are underway to isolate and map the dehydrin genes of blueberry utilizing blueberry populations that segregate for cold hardiness in order to determine if the dehydrin genes map to or co-segregate with QTLs controlling cold hardiness. Progress has been made toward this goal. Cold hardiness levels were determined for a portion of the blueberry mapping populations (derived from testcrosses of Vaccinium darrowi Camp X V. caesariense Mackenz. F1s to another V. darrowi and another V. caesariense) using a laboratory controlled freeze-thaw regime, followed by visual assessment of injury to floral buds. As expected, the V. darrowi and V. caesariense parents were found to differ significantly in terms of cold hardiness levels (LT50s of -13°C and -20°C, respectively). Mean cold hardiness level of F1s (LT50 of -14.7°C) was skewed toward the V. darrowi parents suggesting that cold hardiness is a partially recessive trait. The sequence of a 2.0 kb cDNA clone, which encodes the 60 kDa blueberry dehydrin, was used to map a dehydrin-related gene to current linkage group 12 of the V. caesariense testcross population. A preliminary comparison of the segregation pattern of the dehydrin-related gene to that of the cold hardiness trait suggests that the marker does not segregate with cold hardiness. 相似文献
105.
以东北地区棕壤为研究对象,通过人工控温和土柱淋洗试验,研究了不同冻融处理下铅污染土柱中土壤胶体和胶体结合态铅的迁移特征。结果表明:土壤高含水量(田间持水量100%)条件下冻融作用促进土壤胶体的迁移;土壤低含水量(田间持水量10%)条件下冻融作用对土壤胶体的影响减弱。淋洗试验中,土壤胶体在前20 min内大量淋失出土体,随后淋失量急剧减少;且前20 min内的土壤胶体淋失量随着冻融次数的增加先增加后减少。污染土柱中铅主要以胶体结合态的形式迁移,其迁移特征和受冻融作用影响的趋势与土壤胶体类似。冻融处理后滞留在土柱深层的铅含量较高,表明冻融作用能够促进铅向深层土壤迁移。 相似文献
106.
Experimental snowpack reduction alters organic matter and net N mineralization potential of soil macroaggregates in a northern hardwood forest 总被引:1,自引:0,他引:1
J. Megan Steinweg Melany C. Fisk Benjamin McAlexander Peter M. Groffman Janet P. Hardy 《Biology and Fertility of Soils》2008,45(1):1-10
Climate change is predicted to reduce or delay annual wintertime snow pack formation in the forests of the northeastern US.
Any delay in snowpack formation could increase soil freezing in winter and, thereby, alter soil characteristics and processes.
We examined the hypothesis that delayed snowpack would disrupt soil structure and change organic matter bioavailability in
an experimental snow removal study at the Hubbard Brook Experimental Forest (HBEF), NH, USA. Pairs of reference and snow removal
treatment plots were studied in four different sites at HBEF. Snow was removed from November–January of two winters, inducing
soil freezing throughout both winters. Size class distribution and organic matter concentration and content of aggregates,
and carbon and nitrogen mineralization potential of size fractions were quantified for surface mineral soils in the spring
of both years immediately after snowmelt. In the first year of sampling, the only significant effect of snow removal was an
increase in the smallest (<53 μm) size fraction of mineral soil. In the second year, snow removal increased organic matter
concentrations of macroaggregate (250–2,000 μm) and microaggregate (53–250 μm) size fractions. This change corresponded to
an increase in net N mineralization potential and the ratio of N to C mineralized in the macroaggregate fraction, but there
were no effects of snow removal on C mineralization. We propose that soil freezing increases the movement of organic matter
from organic to mineral soil horizons and increases the N content of mineralizable substrates in mineral soil following years
with delayed snowpack formation. 相似文献
107.
108.
Temperature Before Cold Acclimation Affects Cold Tolerance and Photoacclimation in Timothy (Phleum pratense L.), Perennial Ryegrass (Lolium perenne L.) and Red Clover (Trifolium pratense L.)
下载免费PDF全文
![点击此处可从《Journal of Agronomy and Crop Science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
S. Dalmannsdottir M. Rapacz M. Jørgensen L. Østrem A. Larsen R. Rødven O. A. Rognli 《Journal of Agronomy and Crop Science》2016,202(4):320-330
The expected temperature rise in late summer/early autumn can change the conditions for acclimation and affect the winter survival of perennial crops. This study examined the effect of the temperature just before the onset of cold acclimation (pre‐acclimation) on freezing tolerance of timothy (Phleum pratense L.), perennial ryegrass (Lolium perenne L.) and red clover (Trifolium pratense L.) populations (both cultivars and breeding populations) adapted to either northern or southern parts of Norway. Using phytotron experiments, we studied whether increasing pre‐acclimation temperature delays growth cessation, affects photoacclimation and reduces freezing tolerance. Furthermore, we assessed whether these effects were related to the latitudinal adaptation of the plant material. The results showed that a rise in pre‐acclimation temperature decreased both cold acclimation capacity and photoacclimation in these species. This affected the freezing tolerance, which was reduced significantly more in northern‐adapted population of timothy and perennial ryegrass compared with southern‐adapted populations. Red clover was less affected by temperature changes than the grasses. 相似文献
109.
根据霜冻和无霜期对农作物生长的影响及农业气候区划的指导意义,比较无霜期与严格意义上的“无冻期”的关系和区别,分析霜冻出现的初、终日与霜、结冰现象及气温、地面温度、草面温度≤0℃出现的初日、终日之间的关系,探讨“无霜冻期”的合理统计方法,并通过对鄂东地区的麻城、浠水、黄石三地的无霜期和“无冻期”的统计,总结两者的差异和特征,从而为正确理解和统计无霜冻期,提出一套新的观点和方法,为指导农业生产和农业气候区划提供依据。 相似文献
110.
国内犬精液冷冻保存技术起步较晚,尚处在研究探索阶段,犬精液冷冻保存技术还不成熟,冷冻精液受胎率、窝产仔数与自然交配相比还有一定的差距,而且品种、地域、采精时间的不同,精液冷冻效果也不一致。从犬精液的冷冻保存方法、冷冻保护剂、解冻方法三个方面,综述了近年来国内外的犬精液冷冻研究成果,为探索更加有效的犬精液冷冻技术,提高犬精液冷冻效果提供参考。 相似文献