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   858篇
  免费   26篇
  国内免费   50篇
林业   41篇
农学   21篇
基础科学   16篇
  71篇
综合类   284篇
农作物   45篇
水产渔业   78篇
畜牧兽医   250篇
园艺   6篇
植物保护   122篇
  2023年   8篇
  2022年   22篇
  2021年   29篇
  2020年   16篇
  2019年   14篇
  2018年   7篇
  2017年   13篇
  2016年   8篇
  2015年   12篇
  2014年   18篇
  2013年   35篇
  2012年   54篇
  2011年   49篇
  2010年   52篇
  2009年   53篇
  2008年   47篇
  2007年   51篇
  2006年   35篇
  2005年   27篇
  2004年   27篇
  2003年   14篇
  2002年   17篇
  2001年   10篇
  2000年   7篇
  1999年   10篇
  1998年   13篇
  1997年   13篇
  1996年   20篇
  1995年   12篇
  1994年   11篇
  1993年   20篇
  1992年   11篇
  1991年   10篇
  1990年   11篇
  1989年   14篇
  1988年   7篇
  1987年   13篇
  1986年   7篇
  1985年   9篇
  1983年   5篇
  1982年   5篇
  1981年   11篇
  1980年   9篇
  1979年   8篇
  1978年   5篇
  1976年   6篇
  1958年   6篇
  1954年   4篇
  1947年   4篇
  1945年   5篇
排序方式: 共有934条查询结果,搜索用时 15 毫秒
91.
92.
93.
The level of the plasma prothrombin in the circulating blood is decreased during its passage through the pulmonary capillaries. In 85 per cent. of samples, plasma prothrombin has been found to be less in the blood of the left ventricle than in that from the right ventricle. This difference averaged 10.6 per cent. and ranged from 4 to 19 per cent. In no instance was the level in the right ventricle lower than that in the left. In samples of blood taken from the arterial and venous supply of the head, liver, spleen, intestine, kidney and hind limbs, no significant difference in plasma prothrombin levels was found. A possible explanation of this role of the lung in the loss of plasma prothrombin is thought to be the production of blood platelets in this organ, as demonstrated by Howell and Donahue. Platelets, as they undergo disintegration, initiate the first stage of the clotting process by releasing thromboplastin, which, in the presence of calcium, changes prothrombin to thrombin.  相似文献   
94.
95.
E8启动子是番茄果实成熟乙烯响应性基因E8的启动子区。这个区域中存在着一些响应乙烯以及在果实发育和成熟过程中起调节作用的顺式作用元件,调节E8基因在果实成熟过程中表达(Deikmaa et al.,1998)。本研究根据GenBank中E8基因的启动子区序列设计引物,从番茄基因组中克隆了该启动子,构建了番茄果实特异表达载体,并通过RT-PCR和gus基因检测了该表达载体的果实特异表达活性。  相似文献   
96.
Résumé— Cet article décrit un cas de nevus épidermique linéaire unilatéral chez un veau de six mois. Histologiquement, les lésions consistaient en une alternance de zones d'hiper et de parakératose avec une inflammation dermique distincte. Le diagnostic de nevus linéaire inflammatoire a été posé sur la base des lésions macro et microscopiques. [Deprez, P., De Coole, H., Sustronk, B., Muille, E., Ducatelle, R. A case of bovine linear keratosis (A propos d'un cas de kératose linéaire chez un bovin).
Resumen— En este artículo se describe un caso de nevos epidérmicos lineares unilaterales en un bo vino de seis meses de edad. Las lesiones histológicas consistian zonas donde se alternaba hiper i paraqueratosis, mientras que la dermis presentaba una marcada inflamación. Se diagnosticó un nevo epidérmico verrucoso linear e inflamatorio a partir de las lesiones clinicas e histopatológicas [A case of bovine linear keratosis (Un caso de queratosis linear bovina).
Abstract— This report describes a case of unilateral linear epidermal nevi in a 6-month-old bovine. Histologicalli, the lesions consisted of alternating areas of hiper- and parakeratosis with a distinct dermal inflammation. A diagnosis of inflammatori linear verrucous epidermal nevus was made based on the clinical and histopathological lesions.  相似文献   
97.
Two strains of rabbits (strains 1077 and 2066) have been selected since 1974 for increased litter size. Each strain is split into a fixed number of reproduction groups. The mating scheme is similar to random non-sib herd mating. The number of animals per generation is higher in strain 1077 (28 mated bucks and 104 mated does) than in strain 2066 (17 and 59, respectively). The increase of the inbreeding coefficient is higher in strain 2066 than in strain 1077 (27 and 21%, respectively, at generation 20). The mean standard deviation of the individual inbreeding coefficients per generation is low (less than 4%) in both strains. Short-term inbreeding is stable over generations. The observed inbreeding effective size Ne f and the observed familial structure effective size Ne h converge to the same value. The number of founder genomes still present in the genetic pool of the generation decreases regularly: from 5.6 to 2.4 between G6 and G20 for strain 1077. It is a bit lower over time for strain 2066 (from 5.7 to 1.9 between G6 and G20). The effective number of founders is nearly twice as small as the total number: 30 for strain 1077 and 15 for strain 2066. The effective number of major ancestors decreases slightly in strain 1077 (13.6 in G6 and 12.9 in G20) and regularly in strain 2066 (13.8 in G6 and 9.4 in G20).  相似文献   
98.
99.
Fiber types distribution in the diagastric muscle of tufted capuchin monkey was studied by means of NADH-TR, myosin-ATPase, after alkaline and acid preincubations and SDH histochemical reactions. Three different types of fibers were found presenting an equal distribution. The percentage and types of fibers were as follow: 18.2 % SO (Slow Oxydative), 38.4 % FOG (Fast Oxydative Glycolytic) and 43.4 % FG (Fast Glycolytic). FG fibers revealed the largest area. The relatively high concentration of fast twitch (81.2 %) seems to indicate this muscle is involved with the acceleration and fast speed of jaw movements. Aerobic metabolism represented by SO + FOG fibers (56.6 %) suggestes that this muscle possesses an additional role than that related to the lowering of the jaw.  相似文献   
100.
Peru is one of the 20 botanically extremely diverse countries in the world, with >17 000 flowering plants, of which 30% are endemic. So far, no systematic research has been conducted on the screening of the allelopathic plants. In this study, the allelopathic activity of 170 species from 61 families of Peruvian plants that were collected from the three main regions of Peru – the Costa (Pacific coastline), the Sierra (Andean mountains), and the Selva (Amazonian rainforest) – was evaluated. The allelopathic activity was determined by the Sandwich Method, which can evaluate the activity of leaf leachates. The species that were found to be highly inhibitory in this screening, under the criterion of >90% inhibition of the radicle of lettuce (Lactuca sativa) seedlings, were Aristeguietia ballii and Diplostephium foliosissimum (Asteraceae) and Spondias mombin (Anacardiaceae). All of these species are native plants from Peru. This study gives a strong clue regarding the potential of isolating potent allelochemicals from these plants in the future.  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