全文获取类型
收费全文 | 5507篇 |
免费 | 291篇 |
国内免费 | 554篇 |
专业分类
林业 | 557篇 |
农学 | 469篇 |
基础科学 | 369篇 |
1200篇 | |
综合类 | 2000篇 |
农作物 | 292篇 |
水产渔业 | 438篇 |
畜牧兽医 | 682篇 |
园艺 | 137篇 |
植物保护 | 208篇 |
出版年
2024年 | 34篇 |
2023年 | 100篇 |
2022年 | 133篇 |
2021年 | 149篇 |
2020年 | 193篇 |
2019年 | 201篇 |
2018年 | 144篇 |
2017年 | 271篇 |
2016年 | 292篇 |
2015年 | 258篇 |
2014年 | 275篇 |
2013年 | 390篇 |
2012年 | 446篇 |
2011年 | 407篇 |
2010年 | 328篇 |
2009年 | 312篇 |
2008年 | 279篇 |
2007年 | 328篇 |
2006年 | 296篇 |
2005年 | 206篇 |
2004年 | 182篇 |
2003年 | 135篇 |
2002年 | 124篇 |
2001年 | 112篇 |
2000年 | 99篇 |
1999年 | 81篇 |
1998年 | 73篇 |
1997年 | 52篇 |
1996年 | 65篇 |
1995年 | 74篇 |
1994年 | 45篇 |
1993年 | 54篇 |
1992年 | 49篇 |
1991年 | 39篇 |
1990年 | 43篇 |
1989年 | 39篇 |
1988年 | 17篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1962年 | 1篇 |
排序方式: 共有6352条查询结果,搜索用时 0 毫秒
921.
922.
花生AhFAD2-1由位于不同基因组上的两个非等位基因AhFAD2-1A和AhFAD2-1B共同编码,这两个基因的突变引起酶结构、酶活性或表达调控的变化,共同导致高油酸性状的产生。本研究通过对13个不同花生品种(系)的AhFAD2-1基因进行测序和比对分析,查找点突变或插入位点,寻找与高油酸性状关联的基因位点。结果表明:E11、花育30、鲁花12、豫花15、河北高油的基因型是OL_1OL_1OL_2OL_2,其相应的O/L值为1.01~1.40;鲁花14、花育17、花育19、花育23、E12S的基因型是ol_1ol_1OL_2OL_2,其中E12S较特殊O/L值为9.05,其他品种O/L值为1.54~1.97;E16、E18和花育32号的基因型是ol_1ol_1ol_2ol_2,其相应O/L值为12.3~41.85。本研究结果对于高油酸性状的分子鉴定以及高油酸花生新品种的培育具有一定的参考价值。 相似文献
923.
外源甘氨酸态氮、硝态氮和铵态氮的浓度配比对小白菜生长和品质的影响 总被引:2,自引:0,他引:2
为优化不同形态氮浓度配比,提高设施栽培蔬菜营养品质,在局部无菌水培条件下,研究了不同外源甘氨酸态氮、硝态氮和铵态氮的浓度配比对小白菜生物量、根系形态及营养品质的影响.结果表明,小白菜生物量及其营养品质受外源氮浓度组成影响差异显著(P <0.05).在高甘氨酸态氮(2500 μmol·L-1)和铵态氮(2500 μmol·L-1)、低硝态氮(250 μmol·L-1)浓度处理中,小白菜生物量最高,达94.5 mg·株-1,且小白菜总根长、根表面积、根体积、根系活力等指标的变化趋势与生物量一致;在高甘氨酸态氮、低无机氮浓度处理中,小白菜可溶性蛋白、游离氨基酸和可溶性糖含量最高,分别为26.2、126、24.0 mg·kg-1,且硝酸盐含量较高无机氮处理显著降低(P <0.05).适当提高甘氨酸态氮浓度、降低无机氮(尤其是硝态氮)浓度能够一定程度改善其营养品质. 相似文献
924.
混纺比对麻涤纱线性能的影响 总被引:2,自引:0,他引:2
本文通过对不同混纺比下的麻涤混纺纱的性能测试分析得出:涤纶比例必须达到一定量(40%)后,混纺纱的断裂伸长率才能随着涤纶比列的提高而逐渐改善;随着混纺比的改变,在涤纶含量为50%左右,混纺纱的断裂强力将出现一个低谷;随着涤纶含量的增加,毛羽和条干指标得以改善。 相似文献
925.
V. Agarwal B. M. Chauhan 《Plant foods for human nutrition (Dordrecht, Netherlands)》1989,39(2):161-167
Isoproteinous diets containing 1% cholesterol and 10% fibre derived from plant foods namely,peepalbanti (Ficus religiosa),barbanti (Ficus bengalensis),gullar (Ficus glomerata),teent (Capparis decidua) andkhejri beans (Prsopsis cineria) or pure cellulose, were fed to rats for 40 days. Effect of incorporation of these whole plant parts on feed intake, weight gain, feed efficiency ratio (FER), dry matter digestibility (DMD) and true protein digestibility (TPD) in weanling rats was studied. Their inclusion did not affect the weight gain significantly whereas all other parameters were influenced to a varying extent. Foods rich in lignin had relatively lower FER, DMD and TPD whereas cellulose and pectin rich foods had higher DMD and TPD. 相似文献
926.
The present paper reports the detailed study on the splicing behavior of viscose staple fiber yarns made from ring, rotor,
friction and air-jet spinning technologies. The linear density of all the yearns was kept constant at 29.5 tex. The splicing
parameters like splicing pressure and duration of the splicing were taken as variables. Three levels of splicing pressure
at constant splicing duration and three levels of splicing durations at constant splicing pressure were considered. Splices
were introduced at all these levels for the four different technologies. These splices were tested for their tensile properties
and the properties of splices were evaluated in terms of retained splice strength (RSS) and splice break ratio (SBR). The
splice photographs were taken and splices were analyzed for their structure and for diameter profile along the length of the
splice. 相似文献
927.
2014年8月3日16时30分,云南省鲁甸县发生6.5级地震,地震造成两岸山体塌方形成堰塞湖.在堰塞体右岸边坡有大量岩体崩塌,坡度为70°~90°,部分地方有倒悬体,常规手段难以布设仪器监测.故采用先进的GB-SAR系统IBIS-L对右岸裸露新岩体进行变形监测,通过此方式获取的GB-SAR影像质量直接关系到干涉图的生成、相位滤波和相位解缠.该研究根据IBIS-L采集的云南鲁甸红石岩堰塞湖边坡监测数据,通过Kaiser-Bessel窗进行加窗处理后,选用估计热信噪比(TSNR)、时间和空间相关系数、相位稳定性等能够直接表征观测相位的稳定程度特征量,间接分析了GB-SAR影像采集的质量好坏,为进行连续高质量的影像选择提供依据. 相似文献
928.
中国新疆绿洲地区多时空尺度上土壤盐分变化特征及其相关驱动因素研究 总被引:1,自引:0,他引:1
Located in the inland arid area of central Asia, salt-affected farmlands take up one third of the total irrigated land area in Xinjiang of Northwest China. Spatio-temporal variability of soil salinity and the underlying mechanism are fundamental problems challenging the sustainability of oasis agriculture in China. In this study, the data of total dissolved solids(TDS) measured for soil samples collected from 27 representative study areas in the oasis areas of Xinjiang were analyzed and the coefficient of variation(CV) and stratification ratio(SR) of TDS were used to describe the lateral and vertical soil salinity variations, respectively. Weekly, monthly,and annual changes in soil salinity were also summarized. Results showed that the top(0–20 cm) soil salinity was highly variable(CV 75%) for most studied areas. Lateral variation of soil salinity was significantly correlated with the sampling interval; as a result, a maximum sampling interval of 0.9 m was found for reducing evaluation uncertainty. The top 0–20 cm soil salt accounted for about25.2% of the total salt in the 0–100 cm soil profile. The stratification ratio values(the ratio of TDS at the 20–40 cm depth to that at the 0–20 cm depth) were mostly smaller than 1 and on average 0.92, illustrating that the top 0–20 cm soil contained slightly more salt and a considerable amount of salt still existed in subsurface and deep horizons. Irrigation reduced top soil salinity by 0.52 g kg-1, or14.6%, within the first week. On average, the relative range of soil salinity, calculated to indicate monthly changes in soil salinity, was58.2% from May to September. A 27-year experiment indicated that cultivation increased soil salinity by 44.4% at a rate of 0.14 g kg-1year-1. At small spatio-temporal scales, soil salinity variation was mainly affected by anthropogenic factors, such as irrigation and land use. However, natural factors, including groundwater, topography, and climate conditions, mainly influenced soil salinity variation at large spatio-temporal scales. This study displayed the highly variable nature of soil salinity in space and time. Those driving factors identified in this study could provide guidelines for developing sustainable agriculture in the oasis areas and combating salinization in arid regions of China. 相似文献
929.
硝/铵营养对香蕉枯萎病尖孢镰刀菌生长的影响 总被引:2,自引:2,他引:0
通过室内平板培养,研究了不同硝/铵配比的氮源,以及不同的pH对香蕉枯萎病尖孢镰刀菌生长的影响。结果表明: 1)在所有不同硝/铵配比处理中,低pH(pH=4)均抑制尖孢镰刀菌的生长。在相同pH值条件下,100%铵态氮处理中尖孢镰刀菌的生长受到明显抑制,其菌落直径均小于4 cm; 2)在不同浓度铵处理后,尖孢镰刀菌的生长在铵态氮大于5 mmol/L时受到强烈的抑制; 3)通过模拟植物细胞壁被尖孢镰刀菌侵染并穿透的过程中发现,尖孢镰刀菌在100%铵态氮处理下不能穿透赛璐膜。本研究结果说明,铵态氮能够控制香蕉尖孢镰刀菌的生长,并抑制其侵染穿透寄主细胞壁。 相似文献
930.
子代测定是林木抗病育种的一个必要环节,亲本的抗病性以及生长性状在子代会发生变异。本项研究对福建省湿地松抗褐斑病种子园8年生的6个单系和6年生的5个单系子代抗病性和生长进行了测定。结果表明,针叶感病率性状在各家系间呈极显著差异,抗病选育具有良好的效果。本试验选出的抗病性表现强(针叶感病率低于15%)且稳定的家系有32、8和10号,值得推广。 相似文献