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   410篇
  免费   7篇
  国内免费   3篇
林业   40篇
农学   16篇
基础科学   1篇
  119篇
综合类   50篇
农作物   28篇
水产渔业   10篇
畜牧兽医   112篇
园艺   3篇
植物保护   41篇
  2022年   8篇
  2021年   7篇
  2020年   9篇
  2019年   7篇
  2018年   10篇
  2017年   9篇
  2016年   5篇
  2015年   3篇
  2014年   10篇
  2013年   30篇
  2012年   18篇
  2011年   20篇
  2010年   10篇
  2009年   12篇
  2008年   18篇
  2007年   18篇
  2006年   17篇
  2005年   14篇
  2004年   14篇
  2003年   12篇
  2002年   13篇
  2001年   8篇
  2000年   4篇
  1999年   5篇
  1998年   4篇
  1997年   5篇
  1996年   7篇
  1995年   5篇
  1994年   4篇
  1991年   3篇
  1988年   6篇
  1987年   4篇
  1986年   3篇
  1985年   8篇
  1984年   4篇
  1983年   3篇
  1980年   4篇
  1977年   4篇
  1976年   3篇
  1974年   4篇
  1973年   4篇
  1970年   6篇
  1969年   5篇
  1967年   4篇
  1966年   4篇
  1960年   2篇
  1951年   3篇
  1948年   2篇
  1940年   2篇
  1924年   3篇
排序方式: 共有420条查询结果,搜索用时 31 毫秒
31.
32.
Zusammenfassung Es wird über ein Vorkommen der bisher nur aus China bekannten Süßwasser-RotalgeBatrachospermum intortum Jao 1941 an mehreren Standorten im gebirgigen Osten (Provinz Oriente) der Insel Kuba berichtet. Es dürfte sich um den ersten Nachweis der Gattung für diese Antilleninsel handeln.
ABatrachospermum, Sect. Contorta Skuja from Cuba
Summary Batrachospermum intortum hitherto known only from China, was found on several localities in the mountainous eastern part of Cuba (Prov. Oriente). This may be the first report of the genus for this island.

Batrachospermum Contorta Skuja
Batrachospermum intortum Jao 1941, , . ( ). .


Ergebnisse der 1. Kubanisch-deutschen Alexander von Humboldt-Expedition 1967/68, Nr. 33.  相似文献   
33.
34.
A study was conducted to determine the extent of genetic diversity among African cassava (Manihot esculenta Crantz) accessions resistant to the cassava mosaic virus disease (CMD), using simple sequence repeat (SSR) markers. The accessions included a breeding stock (clone 58308), five improved lines, 62 CMD resistant and 10 CMD susceptible landraces. Genetic diversity was assessed among accessions in five cluster groups derived from UPGMA analysis on data from 18 SSR primer pairs. Average gene diversity, He, was high in all cluster groups, with an average heterozygosity of 0.591 ± 0.061. The estimator of inbreeding Fis revealed a low level of inbreeding within groups and averaged −0.262 ± 0.142. Gene diversity among all accessions was 51.4% and gene diversity within cluster groups was 46.6%, while 4.8% was due to diversity between the different cluster groups. The amount of genetic differentiation measured by Gst and Fst were 9.6% and 12.1% respectively, indicating a weak genetic structure.  相似文献   
35.
Zusammenfassung In Algenaufsammlungen aus dem Harzgebiet wurden achtSpirogyra-Arten gefunden, an Freiland- sowie Kulturmaterial untersucht und dabei die Variationsbreite einiger Merkmale durch umfangreiche Messungen geprüft.
On someSpirogyra species of the Harz mountains
Summary Eight species ofSpirogyra found in collections of algae from the Harz mountains were studied on living material from the natural site and on cultures derived from it. Based on numerous measurements, the variability of some characteristics is investigated.

8 Spirogyra. ; .
  相似文献   
36.
Hordeum chilense Roem. et Schult. is a diploid wild South American barley that contains genes of interest for cereal breeding, many of them located on chromosome 1Hch. In the current study, two H. chilense-wheat addition lines with deletions in the 1Hch chromosome were used for sub-arm localization of five prolamin (glutenin and gliadin) loci and 33 EST-SSR marker loci on chromosome 1Hch. The two sets of markers were distributed across five sub-arm chromosome regions. Three glutenin loci (Glu-H ch 2, Glu-H ch 3, Glu-H ch 4) together with the gliadin locus Gli-H ch 1 were located on the distal 20% of the 1HchS arm, whereas the glutenin locus Glu-H ch 1 was on the proximal 88% region of 1HchL. Among 33 EST-SSR marker loci, 7 (21.2%) were on the 1HchS arm and, of them, 3 (9.1%) were on the distal 20% end and 4 (12.1%) on the proximal 80% region. The 26 loci (78.8%) on 1HchL were distributed across three different regions: 18 (78.8%) in the proximal 88%, 3 (9.1%) in the distal 12% and 5 (15.2%) in a region less than 12% from the distal end. The deletions in the 1Hch chromosome added to the common wheat background were thus shown to be useful for determining the sub-arm location of EST-SSR and prolamin loci. This could facilitate the identification of molecular markers linked to genes of agronomic interest and the isolation of such genes for use in common wheat improvement.  相似文献   
37.
Undoped, high-quality diamond is, under almost all circumstances, one of the best insulators known. However, diamond covered with chemically bound hydrogen shows a pronounced conductivity when exposed to air. This conductivity arises from positive-charge carriers (holes) and is confined to a narrow near-surface region. Although several explanations have been proposed, none has received wide acceptance, and the mechanism remains controversial. Here, we report the interactions of hydrogen-terminated, macroscopic diamonds and diamond powders with aqueous solutions of controlled pH and oxygen concentration. We show that electrons transfer between the diamond and an electrochemical reduction/oxidation couple involving oxygen. This charge transfer is responsible for the surface conductivity and also influences contact angles and zeta potentials. The effect is not confined to diamond and may play a previously unrecognized role in other disparate systems.  相似文献   
38.
Aho AV 《Science (New York, N.Y.)》2004,303(5662):1331-1333
Although software is the key enabler of the global information infrastructure, the amount and extent of software in use in the world today are not widely understood, nor are the programming languages and paradigms that have been used to create the software. The vast size of the embedded base of existing software and the increasing costs of software maintenance, poor security, and limited functionality are posing significant challenges for the software R&D community.  相似文献   
39.
Polypeptide with broad biological activity: isolation from small intestine   总被引:50,自引:0,他引:50  
S I Said  V Mutt 《Science (New York, N.Y.)》1970,169(951):1217-1218
A polypeptide, which has potent and diverse biological action-including systemic vasodilation, hypotension, increased cardiac output, respiratory stimulation, and hyperglycemia-was isolated from the small intestine of the hog. The peptide has 28 amino acid residues and is chemically distinct from the kinins, "substance P," glucagon, and secretin.  相似文献   
40.
Hypoxic ventilation of isolated perfused cat lungs caused the frequent appearance in pulmonary perfusates of biologically active substances, which included prostaglandins or prostaglandin-like compounds. In anesthetized cats, inhibition of prostaglandin biosynthesis with infusions of aspirin (more than 50 milligrams per kilogram) reduced the pulmonary vasoconstrictor and bronchoconstrictor responses to hypoxic breathing.  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