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   200317篇
  免费   13270篇
  国内免费   637篇
林业   22579篇
农学   13767篇
基础科学   2919篇
  39334篇
综合类   9500篇
农作物   16844篇
水产渔业   15331篇
畜牧兽医   65696篇
园艺   6124篇
植物保护   22130篇
  2021年   2370篇
  2020年   2773篇
  2019年   3569篇
  2018年   3557篇
  2017年   3908篇
  2016年   4495篇
  2015年   4117篇
  2014年   5471篇
  2013年   15993篇
  2012年   4637篇
  2011年   6132篇
  2010年   6626篇
  2009年   7348篇
  2008年   5645篇
  2007年   4575篇
  2006年   5492篇
  2005年   4717篇
  2004年   4626篇
  2003年   4415篇
  2002年   3791篇
  2001年   3857篇
  2000年   3530篇
  1999年   3775篇
  1998年   3914篇
  1997年   3982篇
  1996年   3729篇
  1995年   4250篇
  1994年   3630篇
  1993年   3329篇
  1992年   3040篇
  1991年   3169篇
  1990年   2858篇
  1989年   2823篇
  1988年   2445篇
  1987年   2501篇
  1986年   2372篇
  1985年   2809篇
  1984年   2817篇
  1983年   2747篇
  1982年   2476篇
  1981年   2444篇
  1980年   2446篇
  1979年   2347篇
  1978年   2255篇
  1977年   2174篇
  1976年   2015篇
  1975年   1758篇
  1974年   1758篇
  1973年   1696篇
  1971年   1437篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
141.
142.
Lactate Kinetics in veterinary Critical Care: A Review   总被引:3,自引:0,他引:3  
Elevation in blood lactate concentration, with or without accompanying metabolic acidosis, is a hallmark finding in patients with circulatory compromise, and is also consistently noted in other conditions affecting critically ill or injured individuals. Little is reported in a veterinary literature regarding lactate measurement in the emergency and critical care setting, despite impressive reports of the clinical usefulness of lactate measurement in people. The purpose of this article is to review lactate kinetics and the clinical utility of lactate measurement. Limitations to lactate evaluation will also be discussed.  相似文献   
143.
Results are given of a survey on the occurrence of pathotypes (races) of Synchytrium endobioticum (potato wart) in both parts of re-unified Germany. An assortment of six differential cultivars appears to be sufficient to distinguish between the seven presently important German wart pathotypes. A total of ten pathotypes was recorded. Two West and two East German pathotypes seem to be identical, based on the results obtained with presently available cultivars. In contrast to pathotype 1 (common race) which prior to 1945 was distributed over the whole German territory, the 'new' pathotypes seem to prefer the central and south German mountain areas.  相似文献   
144.
合成了14个含有 N-莰-2-基的磷酰胺和硫代磷酰胺类化合物,用红外、核磁及元素分析确定其结构,并探讨了~(31)Pδ值的规律性变化。初步生物试验表明,磷酰胺类化合物对水稻发芽具有明显的抑制作用,其中化合物Ⅱ1的活性大于对照药剂抗倒胺但低于多效唑。  相似文献   
145.
146.
147.
Abstract. In field and laboratory experiments the conditioner‘Agri-SC’has shown improvements in the structure of loamy sand soils in east Shropshire, UK. It resulted in statistically significant decreases in soil bulk density values and increases in soil porosity and aggregate stability. Further experiments are in progress on both loamy sand and silt loam soils.  相似文献   
148.
Ovarian follicular dynamics and embryo yield were studied during 2 different FSH regimens for superovulation of cattle. Twenty heifers were given intramuscular injections of FSH (total of 35 mg NIH) either once daily for 3 days (Group 3×1) or twice daily for 4 days (Group 4×2). At 72 h after the first FSH injection, each animal was injected with 0.75 mg cloprostenol. Inseminations were performed at 12 h and 24 h after the onset of heat. Transrectal ultrasonography was performed on the day of the first FSH injection, the day of cloprostenol injection, the day of insemination and finally on the day of embryo recovery (day 6 or 7 after heat). The numbers of small (2–4 mm), medium (5–9 mm) and large (>10 mm) size follicles were recorded. The total number of corpora lutea, eggs and transferable embryos were recorded on the day of embryo recovery. No differences were found between the 2 groups in either of the parameters studied (p>0.05). It can be concluded that treatment with this FSH preparation once daily for 3 days gives a folliculogenic and superovulatory response similar to a treatment regimen where it is given twice daily for 4 days.  相似文献   
149.
Summary. A weed management strategy for the control of Rottboellia cochinchinensis (Lour.) W.D. Clayton in maize, based on reducing the level of spikelet germination from the seedbank and reducing the intensity of weed-crop interference, was conducted over two seasons. The management practices evaluated included chemical control (atrazine, metolachlor, pendimethalin, EPTC), cultural control (straw mulch), mechanical control (inter-row cultivation) and biological control (living mulch). The results indicated that the various management practices had no effect on the growth and development of the crop but significantly affected the weed. The pendimethalin (1°5 kg a.i. ha−1) and inter-row cultivation (14 and 28 days after planting) treatments gave satisfactory control of the weed in the crop over the duration of the critical period of weed competition. All other treatments were ineffective. All management practices made significant contributions to the weed seedbank, thus ensuring the predominance of the weed.  相似文献   
150.
Abstract. Comparisons of crop production on recently reinstated soil in Northumberland have shown that the reduced yield potential of such soil may not be inevitable. Storage of soil in bunds did not greatly reduce subsequent crop yields, but failure to drain the land did. Provided an effective drainage scheme was installed, arable and grass crops could be grown successfully, responding very well to additions of nitrogen fertilizer and other normal good husbandry practices. To date it seems that neither deep cultivation nor the use of grass leys were as effective in the restoration process as had been expected.  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