全文获取类型
收费全文 | 1803篇 |
免费 | 248篇 |
国内免费 | 242篇 |
专业分类
林业 | 4篇 |
农学 | 37篇 |
基础科学 | 4篇 |
34篇 | |
综合类 | 716篇 |
农作物 | 5篇 |
水产渔业 | 1301篇 |
畜牧兽医 | 184篇 |
植物保护 | 8篇 |
出版年
2024年 | 7篇 |
2023年 | 24篇 |
2022年 | 37篇 |
2021年 | 41篇 |
2020年 | 75篇 |
2019年 | 72篇 |
2018年 | 59篇 |
2017年 | 113篇 |
2016年 | 85篇 |
2015年 | 62篇 |
2014年 | 64篇 |
2013年 | 124篇 |
2012年 | 152篇 |
2011年 | 166篇 |
2010年 | 125篇 |
2009年 | 105篇 |
2008年 | 87篇 |
2007年 | 89篇 |
2006年 | 115篇 |
2005年 | 71篇 |
2004年 | 52篇 |
2003年 | 62篇 |
2002年 | 51篇 |
2001年 | 58篇 |
2000年 | 51篇 |
1999年 | 33篇 |
1998年 | 36篇 |
1997年 | 34篇 |
1996年 | 37篇 |
1995年 | 39篇 |
1994年 | 35篇 |
1993年 | 42篇 |
1992年 | 28篇 |
1991年 | 16篇 |
1990年 | 14篇 |
1989年 | 11篇 |
1988年 | 6篇 |
1987年 | 11篇 |
1986年 | 4篇 |
排序方式: 共有2293条查询结果,搜索用时 46 毫秒
81.
82.
Nitric oxide synthase (NOS) is an enzyme that catalyzes the formation of nitric oxide (NO), an important biological messenger from L-arginine. There are considerable evidence showing the expression of NOS in mammalian tissues. Information on distribution of NOS activities in various organs and tissues of fish is rare. Non-functional NOS activities were documented in fish semi-quantitatively either by an indirect nicotine-adenine-dinucleotide-phosphate diaphorase (NADPH-d) activity histochemical staining method or by an immunohistochemical method using a cross-reacting antibody to brain NOS. Report on the functional levels of NOS activities in fish is lacking. This report represent the first attempt to document the functional NOS levels in various fish organs and tissues. Constitutive NOS (cNOS) activities in various organs of big-head carp (Aristichthys nobilis) was measured by a chemiluminescence method with a detection limit as low as 10 mol of NO produced. It was found that constitutive NOS activity was highest in the brain, followed by the intestine, stomach, retina, olfactory lobe, swim bladder, skeletal muscle, heart, kidney, ovary and liver. NOS activity could not be detected in the gill filaments. Omission of NADPH in the reaction mixture caused a 57–100% decrease in cNOS activities. However, omission of arginine in the mixture only caused a 56–87% drop in cNOS activities. When compared with cNOS activities documented from other species, a similar pattern of cNOS activities in the various organs and tissues of big-head carp could be seen. 相似文献
83.
Characterization of acetylcholinesterase and its molecular forms in organs of five freshwater teleosts 总被引:1,自引:0,他引:1
J. Ferenczy T. Szegletes T. Bálint M. Ábrahám J. Nemcsók 《Fish physiology and biochemistry》1997,16(6):515-529
The activity and molecular forms of acetylcholinesterase (AChE, EC 3.1.1.7) were characterized in the brain, heart, white skeletal muscle and liver of the Siberian sturgeon (Acipenser baeri), European eel (Anguilla anguilla), wels (Silurus glanis), common carp (Cyprinus carpio) and silver carp (Hypophthalmichthys molitrix), belonging in four families. The brain had the highest (between 183.2±10.6 and 1361.2±189.7 mU mg-1 protein and between 4.7±0.4 and 23.5±2.7 U g-1 wet tissue) and the liver the lowest (between 25.3±1.9 and 126.5±22.7 mU mg-1 protein and between 1.0±0.1 and 4.5±0.5 U g-1 wet tissue) activity in all these fish, with the exception of the wels, where the heart contained the smallest amount of AChE (26.2±7.5 mU mg-1 protein and 1.2±0.3 U g-1 wet tissue). The highest tissue AChE activity was found in the carp and lowest in the sturgeon. The solubility properties and molecular forms of AChE in the four tissues were studied by extraction in high-salt medium (1.0 M NaCl) with and without the detergent Triton X-100 (0.5%, v/v). The proportions of detergent-soluble (DS) and salt-soluble (SS) forms of AChE varied considerably from one species to another, but a general tendency could be observed: the proportion of DS AChE was generally higher in the brain (between 70.4±4.1 and 82.5±1.2%) and lower in the heart (between 12.0±2.0 and 51.3±2.3%) and skeletal muscle (between 16.0±2.0 and 64.4±0.7%). Velocity sedimentation centrifugation revealed that most tissues contained the G4 or A4 form. Three tissues (brain, heart, and liver) of the Siberian sturgeon contained a relatively high proportion of the G1 form (between 24.3±2.4 and 28.6±4.9%), while the skeletal muscle of the wels contained only the most complex type of AChE, i.e., A12. Amongst the tissues studied, the brain and liver mostly contained amphiphilic globular forms of the G4 type, while the heart and skeletal muscle were rich in asymmetric forms (A4 and A12). It was concluded that the differences revealed in the activities of AChE and in the distribution of its molecular forms may be connected with the variation in behavioral habits (feeding and swimming patterns), and the developmental stage of the nervous system. 相似文献
84.
采用耳石日轮鉴定了19988年采自长江九江江段和1999年分别采自长江石码头和纱帽江段的草鱼仔鱼的日龄,并依据日龄推算了仔鱼的孵化期和估计了日生长率.采自九江、石码头和纱帽江段的仔鱼的平均日龄分别为10.7d,8.8~16.0d和7.0d.石码头江段仔鱼中,5月16日样本的日龄稍高(16.0d),其余样本的日龄比较接近(8.8~9.5d).采自石码头江段的所有仔鱼的体长平均生长率为0.11mm·d-1,特定生长率为 1.32%.各批次仔鱼的体长与其日龄的相关性通常很差,这表明长江中游仔鱼的生长不整齐,部分个体可能遭受了营养缺乏的影响. 相似文献
85.
86.
The effects of fingerlings immersion in low‐dose benzocaine (15 and 30 mg L−1, silver carp and rohu) and quinaldine (100 μL L−1 silver crap and 250 μL L−1 rohu) for 1, 3 and 6 h on stress responses and survival of rohu, Labeo rohita and silver carp, Hypophthalmichthys molitrix fingerlings were evaluated in a transport simulation experiment. Both quinaldine and benzocaine showed low mortalities (0–2%). The total mortality in control (with no anaesthesia) was 30% for rohu and 14% for silver carp. Quinaldine and benzocaine‐treated fingerlings had significantly higher plasma chloride levels than the control in both species. Benzocaine, quinaldine, as well as the control, had an initial elevation of plasma cortisol levels. Benzocaine lost its effectiveness after 3 h exposure while quinaldine persisted throughout the 6 h experimental period. Both sedatives reduced bacterial build‐up compared with the control. No post‐exposure mortality was observed for any of the transport methods assessed 48 h after the treatment. This study suggests that the use of low‐dose benzocaine or quinaldine during transport has positive effect on the survival and health of rohu and silver carp fingerlings. 相似文献
87.
在32℃下对嗜水气单胸菌H20株作振荡培养,1%福尔马林、60℃灭活1hr.,制备白鲢暴发病菌苗。用该菌苗免疫白鲢,18-20℃水温下饲养10天后,白鲢血清中凝集抗体效价达1:1128左右,未免疫对照组凝集抗体效价约为1:8。免疫鱼的抗感染保护力达80%。 相似文献
88.
David E. Kime Mohammad A. S. Abdullah Miroslawa Sokolowska-Mikolajczyk Piotr Epler 《Fish physiology and biochemistry》1994,13(4):317-324
Carp ovarian tissue was incubated with 3H-17-hydroxyprogesterone in the presence of 0, 0.1, 1, 10, and 100 μg ml−1 unlabeled 17-hydroxyprogesterone. The pattern of metabolites formed showed a marked variation with substrate concentration.
Formation of glucuronide and sulphate conjugates was important only at low substrate concentration. At high substrate concentration
(10 and 100 μg ml−1) 17,20α-dihydroxy-4-pregnen-3-one was the major metabolite, but at intermediate concentrations polar 7α-hydroxypregnanetetrols
predominated. The results support the hypothesis that at low substrate concentrations conjugating, 5α-reducing and 7α-hydroxylating
enzymes, of high activity but low capacity, act as scavengers to deactivate any steroids formed during the relatively low
pituitary gonadotrophin secretions which are necessary for oocyte development, but that during the prespawning gonadotrophin
surge when high levels of substrate are present these enzymes are saturated and 17,20α-dihydroxy-4-pregnen-3-one (17,20αP)
becomes the major ovarian steroid. The possible role of 17,20αP during oocyte final maturation requires further examination. 相似文献
89.
90.