全文获取类型
收费全文 | 92137篇 |
免费 | 5687篇 |
国内免费 | 6653篇 |
专业分类
林业 | 10659篇 |
农学 | 7082篇 |
基础科学 | 5098篇 |
13110篇 | |
综合类 | 45649篇 |
农作物 | 4425篇 |
水产渔业 | 2698篇 |
畜牧兽医 | 8497篇 |
园艺 | 2545篇 |
植物保护 | 4714篇 |
出版年
2024年 | 245篇 |
2023年 | 1391篇 |
2022年 | 2288篇 |
2021年 | 2475篇 |
2020年 | 2449篇 |
2019年 | 2913篇 |
2018年 | 1733篇 |
2017年 | 3099篇 |
2016年 | 3899篇 |
2015年 | 3420篇 |
2014年 | 4686篇 |
2013年 | 4596篇 |
2012年 | 6927篇 |
2011年 | 7163篇 |
2010年 | 5874篇 |
2009年 | 5744篇 |
2008年 | 5234篇 |
2007年 | 6240篇 |
2006年 | 5396篇 |
2005年 | 4491篇 |
2004年 | 3371篇 |
2003年 | 2954篇 |
2002年 | 2235篇 |
2001年 | 2009篇 |
2000年 | 1812篇 |
1999年 | 1438篇 |
1998年 | 1244篇 |
1997年 | 1157篇 |
1996年 | 1121篇 |
1995年 | 1109篇 |
1994年 | 1045篇 |
1993年 | 929篇 |
1992年 | 820篇 |
1991年 | 691篇 |
1990年 | 612篇 |
1989年 | 554篇 |
1988年 | 427篇 |
1987年 | 294篇 |
1986年 | 142篇 |
1985年 | 50篇 |
1984年 | 27篇 |
1983年 | 23篇 |
1982年 | 22篇 |
1981年 | 22篇 |
1980年 | 22篇 |
1979年 | 17篇 |
1978年 | 16篇 |
1976年 | 10篇 |
1962年 | 10篇 |
1955年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Satoshi Saito 《Journal of Forest Research》2002,7(3):137-143
The effects of a typhoon on forest dynamics and the response of major tree species were studied in a warm-temperate evergreen
broad-leaved forest in southwestern Japan. The strongest typhoon on record (T9313) passed through this region in 1993. Return
periods of typhoons over 30 ms−1 in instantaneous wind velocity and T9313 were estimated to be 2.2 and 104.5 years, respectively. Approximately 10% of all
stems suffered some damage from T9313 and annual stem mortality rose from 1.3 to 2.7%. The estimated period that the number
of stems would fall below 10% of the initial was four years shorter with T9313-class typhoons than without them. Thus, the
disturbance by T9313 was not catastrophic at the site although T9313 was an episodic typhoon. The short-term responses of
major tree species to T9313 were classified into four types: 1) blunt-response type with little decrease and recruitment of
stems in the DBH ≥ 5 cm class (Distylium racemosum), 2) retreat type with larger decrease than recruitment (e.g. Quercus acuta), 3) sharp-response type with a large decrease and much recruitment (e.g. Cinnamomum japonicum), and 4) advance type with less decrease than recruitment (Eurya japonica). Among the four regeneration types classified by previous studies (climax, light-demanding, subcanopy, and few-sapling),
the climax and few-sapling types each showed a specific short-term response, the blunt-response and retreat types, respectively,
that explains one aspect of the regeneration strategies of each type. On the other hand, the light-demanding or sub-canopy
type showed multiple short-term responses, indicating that each regeneration type contains species with various regeneration
strategies.
In this paper, I analyzed data from the database that was compiled by the Aya Research Team. 相似文献
992.
第二代杉木林养分动态研究 总被引:3,自引:0,他引:3
根据连续定位观测所取得的数据,对4个小集水区第二代10年生杉木人工林生态系统中的养分循环进行了研究.结果表明.集水区由降水输入的N、P、K、Ca、Mg等营养元素总计为59.285kg/hm2a,径流输出为38.938kg/hm2a,净积累量为20.347kg/hm2a.与该林分7年生时相比,净积累量提高了7.2%,说明集水区第二代杉木林生态恢复处于进展的变化过程. 相似文献
993.
南方红豆杉扦插繁殖技术研究 总被引:6,自引:0,他引:6
2003~2004年应用2年生南方红豆杉幼苗进行扦插试验研究,结果表明:不同时间扦插的插穗生根时间最多相差2个月,2月中旬至3月中旬为最适宜扦插季节,扦插后3~5个月的生根率高于其它月份。用河沙与红泥作基质扦插,在不同季节扦插中以河沙作基质的生根效果比红泥的好。用生根剂处理有利于插穗提早生根及增加生根数量,以冬季及早春应用的效果较为明显,应用生根剂的插穗在扦插3~5个月后的生根率和生根数量与对照比有显著差异。不同类型插穗的扦插生根率在不同月份扦插的结果不同,但其差异不显著。 相似文献
994.
995.
第2代杉木人工林地土壤微生物数量与土壤因子的关系 总被引:14,自引:0,他引:14
根据定位观测数据,对湖南会同第2代杉木人工林地土壤微生物数量与土壤因子的关系进行研究.结果表明:杉木人工林地土壤微生物数量以山洼最多,山坡次之,山脊最少;同一立地类型中,0~20 cm土层中微生物数量最多,20~40 cm次之,40~60 cm最少;在同一立地类型中,微生物总数、细菌的数量秋季最高,冬季最低,而真菌和放线菌的数量夏季最高,秋冬两季最低;同一立地类型的板栗林地土壤微生物总数高于杉木人工林地;微生物总数与土壤含水率呈极显著线性正相关(P<0.01),细菌、放线菌的数量与土壤含水率呈显著线性正相关(P<0.05),真菌的数量与土壤含水率不具有相关性(P>0.05);细菌、真菌、放线菌的数量和微生物总数与10 cm处土壤温度不具有相关性(P>0.05);细菌、真菌的数量和微生物总数与土壤有机碳含量、全氮含量呈极显著线性正相关(P<0.01),放线菌的数量与土壤有机碳含量、全氮含量呈显著线性正相关(P<0.05).土壤温度、土壤含水率、土壤有机碳含量及全氮含量对杉木人工林地土壤微生物数量的贡献率为60%~70%. 相似文献
996.
利用香格里拉市2017年林地变更调查数据,选取斑块数量(PN)、斑块类型面积(CA)、斑块平均大小(MPS)、景观百分比(PLAND)、斑块密度(PD)、分离度(F)、景观多样性指数(SHDI)和香农均匀度指数(SHEI)等8个景观指标,借助Fragstats4.2软件和ArcGIS10软件,从斑块特征、异质性以及多样性3个方面对香格里拉市林地景观格局进行分析。结果表明:香格里拉市林地景观格局类型较为丰富,多样性较高,斑块内部连通性较强;各林地景观类型分布不均,以针叶林景观为主,存在比较明显的异质性;景观类型斑块数量大,非林地景观破碎化严重。提出合理编制林地利用方案、不断提高林地景观格局稳定性,加强资源林政管理、控制林地破碎化程度,加快建设“智慧林业”步伐、高效管理林地资源,抓住林业重点工程建设、全面优化林地景观格局,结合林地适用类别,科学合理规划林地功能等优化策略。 相似文献
997.
《中国林业科技(英文版)》2009,(2)
As an emerging industry,China's wood floor industry dates back to the early 1980s. Despite a late start,it has developed rapidly during the last 20 years.The past decades have witnessed great changes in China's wood floor industry.With high quality,many products"made in China"are available widely abroad nowadays.Current global economic shocks,however,affect China's domestic real estate sector;hence the falling domestic sales of wood floor.The paper aims to identify the current situation of floor industry... 相似文献
998.
999.
Current silvicultural treatments in beech forests are aimed at achieving thick logs without discoloured hardwood. Therefore
intensive thinning is applied already in younger stands with the objective of large-sized trunks at an age of 100 years. However,
this approach bears the risk that dead wood structures and broken trees are completely removed from the forest. The impact
of three different silvicultural management intensity levels on wood-inhabiting fungi over decades was investigated in a large
beech forest (>10,000 ha) in southern Germany in 69 sampling plots: A Intensive Thinning and Logging with high-value trees,
B Conservation-Oriented Logging with integration of special structures such as dead wood and broken trees and C Strict Forest
Reserves with no logging for 30 years. The analysis of community showed marked differences in the fungus species composition
of the three treatments, independent of stand age. The relative frequencies of species between treatments were statistically
different. Indicator species for naturalness were more abundant at sites with low silvicultural management intensity. Fomes fomentarius, the most common fungus in virgin forests and strict forest reserves, is almost missing in forests with high-management intensity.
The species richness seemed to be lower where intensive thinning was applied (P = 0.051). Species characteristic for coarse woody debris were associated to low management intensity, whereas species with
a significant preference for stumps became more frequent with increasing management intensity. A total amount of dead wood
higher than 60 m3/ha was found to enable significantly higher numbers of species indicators of naturalness (P = 0.013). In conclusion, when applying intensive silvicultural treatment, the role of dead wood needs to be actively considered
in order to maintain the natural biocoenosis of beech forests. 相似文献
1000.
采用国家标准森林分析方法进行了沙棘与油松、侧柏人工混交林的水文影响研究,结果表明:混交林内年均降水量较林外减少了20.1%;林内月降水量的季节变化以夏、秋、春、冬依次递减;年均气温比纯林内低0.1℃,相对湿度高4.5%;乔木层年均截留量较纯林提高了56.6%,灌木层提高了395.7%;年均地表径流量105.8 L,径流摸数为10.58 m3·km-2·a-1,纯林分别为1 349.05 L和134.9 m3·km-2·a-1,土壤侵蚀模数为0.65 t·hm-2·a-1,纯林为9.2 t·hm-2·a-1;枯枝落叶层现存量增加了200%;平均容水量为自身质量的3.1倍;土壤密度和土粒密度分别减少了6.3%和17.7%,含水量、孔隙度和通气度分别提高了6.1 %、13.9%、20.3%.不同土层土壤密度和土粒密度由上到下逐渐增大,孔隙度和通气度表层较高,向下逐渐减少;底层、中层和表层土壤非毛管孔隙度分别提高了113.3%、38.6%和32.6%;最大持水量、最小持水量、毛管持水量分别较纯林平均高11.0%、9.8%、10.5%,较荒地高36.0%、16.0%、25.6%;储水量和0~40 cm储水量分别较纯林和荒地提高了12.4%、22.7%,排水能力也较强. 相似文献