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   13031篇
  免费   3622篇
  国内免费   109篇
林业   847篇
农学   731篇
基础科学   72篇
  3091篇
综合类   393篇
农作物   501篇
水产渔业   3066篇
畜牧兽医   6117篇
园艺   159篇
植物保护   1785篇
  2024年   11篇
  2023年   56篇
  2022年   107篇
  2021年   303篇
  2020年   655篇
  2019年   1191篇
  2018年   1129篇
  2017年   1189篇
  2016年   1164篇
  2015年   987篇
  2014年   1045篇
  2013年   1377篇
  2012年   995篇
  2011年   1030篇
  2010年   953篇
  2009年   559篇
  2008年   627篇
  2007年   448篇
  2006年   416篇
  2005年   406篇
  2004年   367篇
  2003年   351篇
  2002年   318篇
  2001年   224篇
  2000年   238篇
  1999年   105篇
  1998年   46篇
  1997年   57篇
  1996年   29篇
  1995年   40篇
  1994年   31篇
  1993年   27篇
  1992年   22篇
  1991年   19篇
  1990年   23篇
  1989年   30篇
  1988年   15篇
  1987年   9篇
  1986年   12篇
  1985年   13篇
  1984年   14篇
  1983年   9篇
  1982年   9篇
  1978年   10篇
  1977年   11篇
  1976年   5篇
  1975年   5篇
  1971年   5篇
  1970年   5篇
  1918年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
Infection of fruit trees by Pseudomonas syringae is a potentially serious problem that may limit the establishment and sustained productivity of pome and stone fruit orchards in Serbia. To estimate possible diversity of Pseudomonas syringae fruit trees strains, we collected a set of strains in several areas of Serbia. The samples were taken from infected orchards with raspberry, plum, cherry, sour cherry, peach, pear and apple trees. Genetic diversity of P. syringae strains isolated from fruit trees was determined by using SpeI macrorestriction analysis of genomic DNAs by pulsed-field gel electrophoresis (PFGE) and REP-PCR. Molecular analysis showed that most of isolates had unique profiles, with the exception of isolates from plum and cherry that displayed profiles identical to each other and similar to P. syringae pv. morsprunorum. The study presented here clearly demonstrates the discriminative power of molecular techniques in enabling a detailed analysis of the genetic variations between strains of P. syringae from different pome and stone fruit hosts in Serbia.  相似文献   
13.
14.
15.
Larvae of the cereal leaf minerSyringopais temperatella Led. (Lep.: Scythridae) collected from wheat and barley fields in the southeast Anatolian region of Turkey during 2005–2006, and their parasitization rates, were determined in the laboratory,Bracon (Habrobracon) stabilis Wesmael andApanteles sp. (Hymenoptera: Braconidae) were identified as its parasitoids for the first time.  相似文献   
16.
From 1993 to 1997, 327 strains of Haemophilus parasuis were isolated from spanish swine in our Diagnostic Laboratory and 174 strains (53.2%) were serotyped. Four serotypes, sv. 5 (18.4%), sv 4 (16%), sv. 2 (9.2%) and sv. 13 (8%) were the most frequently isolated and 29.3% of the studied strains were classified as non typable. The results obtained indicate that the distribution of the serotypes in Spain is very similar to that found by other researchers in Germany, Australia, Canada and alike to that found in the United States.  相似文献   
17.
Glutaminase (GLS) is the key enzyme of glutamine (Gln) metabolism and utilization. In this study, a cDNA encoding GLS protein was identified from common carp Cyprinus carpio intestine. The open reading frame of GLS cDNA encodes a polypeptide of 595 amino acids, which shows a high similarity with its zebrafish Danio rerio counterpart. Bioinformatic analysis showed the protein belongs to kidney‐type GLS. The putative protein has glutaminase domain and ankyrin repeats domain, which are highly conserved among vertebrate orthologues. Real‐time quantitative PCR analysis revealed that the abundance of GLS mRNA was the highest in the white muscle, followed by the brain, eyeball and pituitary. Glutaminase was ubiquitously expressed in all intestinal segments of common carp. The activity of GLS did not distribute uniformly along the entire length of the intestine. In primary culture enterocyte, and the expression of GLS mRNA is up‐regulated quickly and effectively by Gln.  相似文献   
18.
A new method was developed to simultaneously measure 2 acute-phase proteins (APPs) by time-resolved immunofluorometry. The assay, based on double-label quantification of haptoglobin (Hp) and C-reactive protein (CRP) in meat juice samples from pigs, was constructed by use of a combination of europium and samarium chelate lanthanides as labels. Meat juice samples from 154 pigs were used for analytic and clinical validation of the assay through determination of precision, accuracy, limit of detection, and quantification. The analytic performance of the assay was satisfactory, with good intra-assay and interassay precision and accuracy. The levels of Hp and CRP were increased in the meat juice samples of diseased animals compared with healthy ones. According to the results, higher sensitivity could be achieved if the cut-off values of both proteins were taken into account for clinical relevance rather than used individually. Since the dual assay saved both time and sample, it could be used as a rapid and sensitive screening test in porcine production.  相似文献   
19.
The isolation of (+)-uleine (1) and (+)-demethoxyaspidospermine (2) from the bark of Plumeria lancifolia is reported along with (1)H- and (13)C-NMR data.  相似文献   
20.
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