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   13848篇
  免费   814篇
  国内免费   1382篇
林业   1190篇
农学   1496篇
基础科学   963篇
  1802篇
综合类   5551篇
农作物   907篇
水产渔业   657篇
畜牧兽医   1926篇
园艺   819篇
植物保护   733篇
  2024年   76篇
  2023年   239篇
  2022年   568篇
  2021年   635篇
  2020年   617篇
  2019年   589篇
  2018年   395篇
  2017年   651篇
  2016年   455篇
  2015年   754篇
  2014年   727篇
  2013年   814篇
  2012年   1029篇
  2011年   1080篇
  2010年   959篇
  2009年   863篇
  2008年   834篇
  2007年   733篇
  2006年   743篇
  2005年   582篇
  2004年   367篇
  2003年   317篇
  2002年   419篇
  2001年   316篇
  2000年   279篇
  1999年   173篇
  1998年   109篇
  1997年   94篇
  1996年   86篇
  1995年   88篇
  1994年   79篇
  1993年   56篇
  1992年   69篇
  1991年   70篇
  1990年   33篇
  1989年   43篇
  1988年   33篇
  1987年   26篇
  1986年   9篇
  1985年   11篇
  1984年   2篇
  1983年   4篇
  1982年   6篇
  1981年   3篇
  1979年   2篇
  1978年   1篇
  1964年   2篇
  1962年   1篇
  1956年   3篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
诸暨市经济林白蚁为害现状及其防治对策   总被引:2,自引:0,他引:2  
调查表明,诸暨市经济林受2科8属12种白蚁的为害,其中黑翅土白蚁和黄翅大白蚁是优势种.经济林受白蚁为害的程度与经济林种类及林内植被覆盖度有关.白蚁防治措施包括物理措施和化学措施,其中诱杀法不仅简便易行,而且成本低、效果好.  相似文献   
992.
Nitrification is the biological conversion of organic or inorganic nitrogen compounds from a reduced to a more oxidized state. Denitrification is generally referred to as the microbial reduction of nitrate to nitrite and further gaseous forms of nitric oxide, nitrous oxide and molecular nitrogen. They are functionally interconnected processes in the soil nitrogen cycle that are involved in the control of long-term nitrogen losses in ecosystems through nitrate leaching and gaseous N losses. In order to better understand how nitrification and denitrification change during the process of ecosystem restoration and how they are affected by various controlling factors, gross nitrification rates and denitrification rates were determined using the barometric process separation (BaPS) technique in subalpine coniferous forests of different restoration stages. The results showed that forest restoration stage had no significant effects on gross nitrification rates or denitrification rates (One-way ANOVA (analysis of variance), p < 0.05). There was no significant difference in the temperature coefficient (Q 10) for gross nitrification rate among all the forest sites (One-way ANOVA, p < 0.05). Gross nitrification rates were positively correlated with water content (p < 0.05), but not with soil pH, organic matter, total nitrogen, or C/N ratios. Denitrification rates in all the forest soils were low and not closely correlated with water content, soil pH, organic matter, or total nitrogen. Nevertheless, we found that C/N ratios obviously affected denitrification rates (p < 0.05). Results from this research suggest that gross nitrification is more responsible for the nitrogen loss from soils compared with denitrification. Translated from Journal of Plant Ecology, 2006, 30(1): 90–96 [译自: 植物生态学报]  相似文献   
993.
杨梅苗圃地接技术试验   总被引:1,自引:0,他引:1  
杨梅产区传统采用嫁接法繁殖,杨梅嫁接按是否移动砧木的位置被分为掘接和地接。利用1年生实生苗砧木的几乎都采用掘接,而采用地接的一般成活率仅在10%-20%。通过苗圃地接技术试验,使杨梅苗圃地接成活率稳定在90%以上,且生长快。  相似文献   
994.
银杏愈伤组织超低温保存的研究   总被引:13,自引:0,他引:13  
本文对银杏子叶愈伤组织进行了超低温保存研究。结果表明 ,冰冻保护剂、冷冻速度对解冻后材料相对存活率影响较大 ,冻前预培养和预冻至某一温度停留一段时间也较为重要。在含高浓度山梨醇或甘露醇的培养基上预培养 2d的愈伤组织 ,用 10 %二甲基亚砜 +0 .5mol·L- 1 山梨醇作为冰冻保护剂 ,以 1℃·min- 1 速度降温 ,在 - 15℃、- 35℃分别停留 10min和 30min后 ,投入液氮中保存 1d ,细胞相对存活率可达 6 0 %以上。再培养时 ,细胞能恢复生长。  相似文献   
995.
作者根据多年的实践经验,总结了香椿的栽培技术,包括采种、播种、育苗、种植、管理、病虫害防治及菜用林培育等技术。  相似文献   
996.
WZF—88型微机呼吸测定仪,是由吸收系统、二氧化碳气敏传感器和测试系统三部分组成的一种新型呼吸测定仪器,使用这种仪器时,被测定生物活体在呼吸过程中释放的CO_2,经过NaOH液吸收装置,成为碳酸化合物,随后用HCl酸化,使其再转化为CO_2。通过与测试系统相匹配的二氧化碳气敏传感器,测定溶液中CO_2的分压(或浓度),即可求得其呼吸强度。实验表明,这种仪器的性能稳定,操作简便、快速,测试精度高、适用范围广,生产成本也比较低廉,是很有竞争能力的一种高精度呼吸强度测定仪器。通过技术鉴定,现已在江苏电分析仪器厂投入小批量生产。  相似文献   
997.
Fe and Zn deficiencies are global nutritional problems. N supply could increase Fe and Zn concentrations in wheat grain. This study was conducted to determine the impacts of different N rates (0, 122, 174, and 300 kg/ha) on the distribution and speciation of Fe and Zn in wheat grain milling fractions under field conditions. Zn and protein concentrations were increased, whereas Fe was less affected in the flour fractions with increasing N rates. Further analysis with size‐exclusion chromatography coupled with inductively coupled plasma mass spectrometry revealed that Fe and Zn bound to low‐molecular‐weight (LMW) compounds in the flour fractions (probably Fe‐nicotianamine [NA], Fe‐deoxymugineic acid, or Zn‐NA) were less affected by increasing N supply, representing 3.5–10.9% of total Fe and 2.5–56.6% of total Zn. In the shorts fraction, LMW‐Fe was absent, and LMW‐Zn with higher N supply was over twice as high as that in control and 3–27 times as high as that in the other milling fractions. In the flour fractions, the molar ratios of phytic acid (PA)/Fe and PA/Zn (both less than 30.5) decreased, whereas soluble LMW‐Fe/Zn was not affected with increasing N rates.  相似文献   
998.
几种造纸用丛生竹秆节育苗试验   总被引:1,自引:0,他引:1       下载免费PDF全文
在福建省邵武市对椽竹、孝顺竹、坭竹等几种造纸用丛生竹进行秆节育苗试验表明,用平埋方法育苗显著优于斜埋和直插,竹蔸平埋效果更佳;不同竹种秆节育苗成活率存在明显差异;不同年龄的秆节育苗成活率在不同竹种间表现不同;不同育苗时间(3月或5月)的成活率差异不显著。竹秆不同粗细、不同部位、单节段或双节段育苗对比试验,结果以细秆(胸径2.5cm)、上部节段、双节段育苗成活率较粗秆(胸径4.6cm)、下部节段、单节段的为高。椽竹秆节径用不同激素处理后,处理间成苗率差异显著,以2,4-D20mg/kg处理5h和硼酸20mg/kg处理24h的效果最佳。几种造纸用丛生竹秆节育苗试验*张文燕周道三马乃训叶长青曹德友张华明  相似文献   
999.
There is a growing desire to improve the properties and use of nonwood plant materials as supplements to wood materials for wood cement-bonded boards (WCBs). This study was conducted to determine the comparative properties of WCBs containing various amounts of discontinuous inorganic fiber materials, such as alkali-resistant glass fiber, normal glass fiber, mineral wool, and nonwood plant materials such as retted flax straw and wheat straw particles. Tested cement-bonded boards were made at wood/additive compositions of 100/0, 90/10, 80/20, 70/30, 60/40, and 50/50 (weight percentages). Seventy-eight laboratory-scale WCBs were produced. Various board properties, such as the modulus of rupture (MOR), internal bonding strength (IB), water absorption (WA), thickness swelling (TS), and linear expansion (LE), were studied. The test results showed that three types of discontinuous inorganic fiber used as reinforcing materials in composites significantly enhanced and modified the performance of WCBs. The mechanical properties and dimensional stability of cement-bonded board were significantly improved with increasing amounts of the additives. MOR and IB were increased; and WA, TS, and LE of boards were reduced by combination with the inorganic fiber materials. The results also indicated that combination with retted flax straw particles only slightly increased the MOR of boards, and wheat straw particles led to marked decreases in all the mechanical properties and the dimensional stability of WCBs.Part of this report was presented at the 50th Annual Meeting of the Japan Wood Research Society, Kyoto, April 2000  相似文献   
1000.
昆明市云南松梢木蠹象危害情况调查   总被引:3,自引:0,他引:3  
云南松梢木蠹象(Pissodes sp.)主要危害云南松(Pinus yunnanensis)幼树,目前仅在昆明市嵩明县大哨乡海拔2 200~2 600m范围内的云南松纯林以及混交林幼林中发生.通过3年的调查,基本掌握了该虫的危害程度及危害特点.调查结果表明大哨乡云南松梢木蠹象危害严重时期松林受害面积达351hm2,其补充营养株率、枝干受害株率、危害指数分别为90.5%、37.1%、42.1%;枝干受害株率和危害指数与该虫补充营养株率之间存在明显相关性.  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