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   2752篇
  免费   185篇
  国内免费   4篇
林业   166篇
农学   88篇
基础科学   13篇
  462篇
综合类   350篇
农作物   102篇
水产渔业   243篇
畜牧兽医   1207篇
园艺   44篇
植物保护   266篇
  2023年   21篇
  2022年   36篇
  2021年   70篇
  2020年   94篇
  2019年   122篇
  2018年   73篇
  2017年   61篇
  2016年   89篇
  2015年   78篇
  2014年   88篇
  2013年   134篇
  2012年   168篇
  2011年   206篇
  2010年   115篇
  2009年   90篇
  2008年   152篇
  2007年   176篇
  2006年   149篇
  2005年   138篇
  2004年   128篇
  2003年   121篇
  2002年   105篇
  2001年   23篇
  2000年   17篇
  1999年   22篇
  1998年   26篇
  1997年   23篇
  1996年   36篇
  1995年   21篇
  1994年   21篇
  1993年   29篇
  1992年   17篇
  1991年   15篇
  1990年   12篇
  1989年   19篇
  1988年   12篇
  1987年   17篇
  1986年   9篇
  1985年   13篇
  1984年   7篇
  1983年   11篇
  1982年   8篇
  1981年   19篇
  1980年   13篇
  1979年   9篇
  1978年   10篇
  1977年   6篇
  1976年   7篇
  1958年   6篇
  1945年   5篇
排序方式: 共有2941条查询结果,搜索用时 31 毫秒
71.
The relationship between some skin characteristics and hemoglobin values during the growth period were statistically examined in standard male minks. Significant correlations) (P < 0.05–0.001) were found between the hemoglobin concentrations determined at 3 points during the growth period (in July, August and November) and the density and colour of underfur, and skin length, respectively. According to the study even the early hemoglobin values in July and August have a significant influence on the size and quality of the pelt. Mink kits with low hemoglobin values are liable to develop a winter fur coat with defective pigmentation and hair structure of the underfur. Anemic minks develop the most extreme stage of the pigmentation defect and these so-called cotton fur skins have little value in the fur garment industry. When these abnormal hemoglobin values are recognized at an early stage, cotton fur skins may be avoided, and larger skins of better quality may be produced.  相似文献   
72.
73.
Postrace urine samples from thoroughbred horses were examined to compare osmolality and specific gravity between horses treated with furosemide and those not treated. Samples were assigned to groups in relation to reported medication (furosemide) status, race finish position, and distance of race. Urine osmolality was significantly (P <.05) lower in samples from horses treated with furosemide when compared with untreated horses. Specific gravity determinations are less precise at measuring urine osmolality at lower levels (1.01 g/ml or less). The measurement of osmolality is a superior method for determining the urine solute concentration and facilitating the regulation of furosemide.  相似文献   
74.
ABSTRACT Diverse isolates of the soilborne wilt fungi Verticillium dahliae and V. albo-atrum were studied to understand the nature and origins of those infecting cruciferous hosts. All isolates from cruciferous crops produced microsclerotia, and the majority produced long conidia with a high nuclear DNA content; these isolates were divided into two groups by amplified fragment length polymorphism (AFLP) analysis. One group could be subdivided by other criteria such as rRNA sequences and mitochondrial DNA restriction fragment length polymorphism (RFLP) analysis. Two crucifer isolates were short spored and had a low nuclear DNA content. The results are consistent with the crucifer isolates being interspecific hybrids. The long-spored isolates are best regarded as amphihaploids (or allodiploids) with the AFLP groups probably each representing separate interspecific hybridization events. The short-spored crucifer isolates appear to be derived from interspecific hybrids and are here called 'secondary haploids'. Molecular evidence suggests that one parent in the crosses was similar to V. dahliae. The other parent of the amphihaploids seems to have been more similar to V. albo-atrum than to V. dahliae, but was distinct from all isolates of either species so far studied. The implications for the taxonomy of crucifer isolates are discussed and the use of the name V. longisporum, proposed elsewhere for just some of these isolates, is discouraged.  相似文献   
75.
Effect of rice growth stages and silicon on sheath blight development   总被引:1,自引:0,他引:1  
ABSTRACT The objective of this study was to determine the effect of silicon (Si) and rice growth stages on tissue susceptibility to sheath blight (Rhizoctonia solani Kühn) under controlled conditions. Rice plants (cv. Rio Formoso) were grown in pots containing low-Si soil amended with Si at 0, 0.48, 0.96, 1.44, and 1.92 g pot(-1) and inoculated with R. solani at the following days after emergence: 45 (four-leaf stage), 65 (eight-leaf stage), 85 (tillering), 117 (booting), and 130 (panicle exsertion). For plants inoculated with R. solani at all growth stages, Si concentration in straw increased as rate of Si increased from 0 to 1.92 g pot(-1). Concentration of calcium in the straw did not differ among plant growth stages. Although incubation period was not affected by the amount of Si added to the soil, this variable was shorter at booting and panicle exsertion stages. As the rates of Si increased in the soil, the total number of sheath blight lesions on sheaths and total area under the relative lesion extension curve decreased at all plant growth stages. The severity of sheath blight was lower at booting and panicle exsertion stages as the rates of Si increased in the soil. In general, plants grown in Si-nonamended pots and inoculated with R. solani were more vulnerable to infection at all growth stages, but especially at 45 days after emergence. Plant dry weights for inoculated plants increased as the Si rates increased from 0 to 1.92 g pot(-1). The greatest dry weight increases occurred for plants inoculated at booting and panicle exsertion stages. Si fertilization is a promising method for controlling sheath blight in areas where soil is Si deficient and when cultivars that exhibit an acceptable level of resistance to sheath blight are not available for commercial use.  相似文献   
76.
77.
Specific antibodies were produced ex vivo from intestinal culture of Eimeria tenella infected chickens. The specificity of these intestinal antibodies was tested against different parasite stages. These antibodies were used to immunoscreen first generation schizont and sporozoite cDNA libraries permitting the identification of new E. tenella antigens. We obtained a total of 119 cDNA clones which were subjected to sequence analysis. The sequences coding for the proteins inducing local immune responses were compared with nucleotide or protein databases and with expressed sequence tags (ESTs) databases. We identified new Eimeria genes coding for heat shock proteins, a ribosomal protein, a pyruvate kinase and a pyridoxine kinase. Specific features of other sequences are discussed.  相似文献   
78.
The prophylactic efficacy of microdoses of injectable and pour-on ivermectin formulations against larval stages of Przhevalskiana silenus was assessed in naturally infected goats in the region of Calabria (southern Italy).Sixty-eight goats from two goat farms were divided into five groups: one group remained untreated, while the other four groups were treated with microdoses of ivermectin (5 and 10 microg/kg injectable formulation and 10 and 20 microg/kg pour-on formulation).The microdoses of ivermectin were fully effective in the treatment of goat warble fly infestation (GWFI) as no larvae emerged from the warbles in the treated groups, while all the larvae emerged in the control groups. Irrespective of the type of formulation used, the difference between the treated groups and the control group was statistically significant (P< 0.001). By contrast, no statistical differences were found between the goats treated with the injectable formulation and those receiving the pour-on applications, and between the two doses of the injectable and pour-on formulations used. Given the plasma concentrations it attains at its lowest dose (0.052 - 0.042 ng/ml for the injectable formulation and 0.030 ng/ml for the pour-on) the injectable formulation seems to offer the most reliable route for the administration of ivermectin microdoses and it is acceptable for milk consumption. The introduction of ivermectin in the early eighties and the use of microdoses in some cases have made it possible to control cattle hypodermosis in large areas of Europe. As with cattle hypodermosis, the administration of ivermectin microdoses in goats is particularly interesting because of the low costs involved and the low levels of residues found in goat milk; it may thus constitute the basis for GWFI control campaigns in areas where the disease is prevalent.  相似文献   
79.
Transvenous retrograde portography for identification and characterization of portosystemic shunts in dogs A method for transvenous retrograde portography (TRP) in dogs suspected to have a portosystemic shunt (PSS) and results in 20 dogs are described. For TRP, dogs were anesthetized and positioned in left lateral recumbency A dual-lumen balloon-tipped catheter was inserted into the right jugular vein and advanced into the azygos vein. The balloon was inflated to occlude the azygos vein, and contrast material was injected during fluoroscopic evaluation. The catheter was then positioned in the caudal vena cava just cranial to the diaphragm. The balloon was again inflated to occlude the vena cava, and contrast material was again injected. Once a shunt was identified, selective catheterization was attempted with a guide wire and angled catheter. A PSS was identified in 18 of the 20 dogs. In 10 of the 18, the shunt vessel could be selectively catheterized, allowing measurement of portal pressures while the shunt was occluded with the balloon. In 1 dog, results of TRP were normal, but subsequent exploratory celiotomy revealed a single extrahepatic PSS, which was surgically attenuated. The other dog in which results of TRP were normal did not have a macroscopic PSS. In dogs suspected to have a PSS, TRP may be a useful adjunctive diagnostic test that is less invasive than operative mesenteric vein portography and allows measurement of portal pressures before and after temporary shunt occlusion.  相似文献   
80.
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