全文获取类型
收费全文 | 1440篇 |
免费 | 96篇 |
专业分类
林业 | 31篇 |
农学 | 17篇 |
基础科学 | 7篇 |
143篇 | |
综合类 | 388篇 |
农作物 | 67篇 |
水产渔业 | 44篇 |
畜牧兽医 | 732篇 |
园艺 | 11篇 |
植物保护 | 96篇 |
出版年
2020年 | 20篇 |
2019年 | 15篇 |
2018年 | 14篇 |
2017年 | 16篇 |
2016年 | 17篇 |
2014年 | 21篇 |
2013年 | 91篇 |
2012年 | 56篇 |
2011年 | 59篇 |
2010年 | 23篇 |
2009年 | 16篇 |
2008年 | 45篇 |
2007年 | 42篇 |
2006年 | 46篇 |
2005年 | 50篇 |
2004年 | 49篇 |
2003年 | 41篇 |
2002年 | 39篇 |
2001年 | 23篇 |
2000年 | 31篇 |
1999年 | 38篇 |
1998年 | 20篇 |
1997年 | 12篇 |
1995年 | 20篇 |
1993年 | 13篇 |
1992年 | 25篇 |
1991年 | 33篇 |
1990年 | 28篇 |
1989年 | 27篇 |
1988年 | 29篇 |
1987年 | 24篇 |
1986年 | 18篇 |
1985年 | 29篇 |
1984年 | 30篇 |
1982年 | 16篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 14篇 |
1978年 | 22篇 |
1977年 | 17篇 |
1975年 | 19篇 |
1974年 | 19篇 |
1973年 | 12篇 |
1972年 | 13篇 |
1971年 | 15篇 |
1970年 | 14篇 |
1969年 | 11篇 |
1968年 | 15篇 |
1966年 | 11篇 |
1937年 | 11篇 |
排序方式: 共有1536条查询结果,搜索用时 15 毫秒
61.
Methyl anthranilate (MA), a food grade flavor and fragrance additive, has been reported to be an effective non-lethal bird repellent in a variety of situations. Despite the experimental success of MA, field studies have yielded widely differing levels of efficacy. Diminished efficacy in some field trials probably results from the failure of specific formulations to retain or protect the active ingredient under natural conditions. Therefore, a clearer understanding of the physical and chemical factors affecting the stability of MA is needed. We undertook a series of laboratory studies on hydrolysis, photolysis and microbial degradation of MA, the results of which could be useful in the development of appropriate formulation strategies and residue analyses. We found the n-octanol:water partition coefficient, (P) to be 84. MA is not subject to hydrolysis at 25°C in phosphate buffer media at pH 5·0, 7·0 and 9·0. MA slowly photodegrades under simulated UV ‘sunlight’. Forty-four percent of MA is lost after 432 h illuminance at 1·25 mW cm−2, which is equivalent to approximately 1200 h natural sunlight (40°N, noontime, June). Kinetic data indicate that the initial step of photolysis, subsequent to excitation, is a second-order reaction with respect to MA. A major photodegradation product appeared in an amount of about 10% of the mass balance and was determined to be an oxidized trimer of MA. MA is primarily affected by aerobic microbial degradation. For a 12:12 h light:dark, under laboratory illumination, 12% of water-solubilized material can be lost in the first seven days. Losses were 30% and 42% at 16 and 27 days, respectively. Under conditions of optimal bacterial growth (warmth and darkness) loss of MA was 22% at nine days and 100% by 20 days. The susceptibility of MA to microbial degradation is promising for the prospects of developing formulated, environmentally safe, bird repellents. 相似文献
62.
C E Greene A K Prestwood J D Clark D D Adams 《American journal of veterinary research》1985,46(12):2648-2653
A technique for rapidly separating platelets from small quantities of whole blood is described. The isolation method allowed for counting and sizing platelets by electronic means, and counts with this new method were closely correlated with those obtained by phase microscopy. Platelet sizing was possible because of the inert and isotonic nature of the density-gradient medium used in the procedure. The technique was applicable to samples of blood from persons, horses, cattle, sheep, goats, pigs, dogs, mice, rats, guinea pigs, and rabbits. The isolation of platelets from whole blood of various species of animals was necessary for electronic counting because of the great variation in sizes of platelets and erythrocytes and the variable sedimentation properties of animal blood. 相似文献
63.
Influence of type of enclosure on exercise fitness of dogs 总被引:1,自引:0,他引:1
The effect of various confinement conditions on physical fitness in dogs was evaluated. Eighteen 9.5- to 10-month-old female purpose-bred Beagles were maintained individually for 3 months at a time in 1 of 6 confinement conditions: Condition A--an outdoor housing area with a conventional dog house and free access to a 6.1 x 9.1-m pen; condition B--outdoor kennel with a conventional dog house and free access to a 1.8 x 6.1-m run; condition C--indoor environmentally controlled 1.2 x 3.66-m run; condition D-0.9 x 1.2 x 0.84-m conventional laboratory cage in an indoor environmentally controlled room; condition E--0.9 x 1.2 x 0.84-m conventional laboratory cage in an indoor environmentally controlled room with treadmill exercise (7 km/h at a 10% grade) for 30 min/d, 5 d/wk; condition F--0.71 x 0.86 x 0.69-m conventional laboratory cage in an indoor environmentally controlled room. During the final week of each 3-month interval, muscle succinate dehydrogenase enzyme activities and submaximal exercise heart rates (during treadmill exercise) were determined to estimate physical fitness. Also, 5 days after being moved into a different housing condition, blood samples were collected for plasma cortisol determination. The type of confinement condition for dogs had little effect on muscle succinate dehydrogenase activity, but had a modest effect on submaximal exercise heart rates of dogs.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
64.
Tom turkey carcasses with partial green discolored livers (n = 191) or normal livers (n = 198) were examined for osteomyelitis and/or associated soft-tissue lesions. Seventy-nine turkeys with green discolored livers had osteomyelitis and/or associated soft-tissue lesions (41.4%), including 53 with just osteomyelitis (27.7%), while 112 (59.6%) had no osteomyelitis and/or soft-tissue lesions. Only five turkeys (2.5%) with normal livers had osteomyelitis. Discolored livers were significantly heavier, but carcasses with discolored livers weighed significantly less than carcasses with normal livers. Bacteria were isolated from 54 of 61 osteomyelitis lesions (88.5%); most frequently staphylococci (50.8%) followed by Escherichia coli (14.8%), Streptococcus sp. (13.1%), and occasional other organisms. Most associated soft-tissue lesions and livers were sterile (74.7%). These finding indicate that although turkey carcasses with green discolored livers are more likely to have osteomyelitis and/or associated soft-tissue lesions than turkey carcasses with normal livers, there is also an approximately equal chance they will not have these lesions. 相似文献
65.
D M Haines J C Kendall B W Remenda M M Breker-Klassen E G Clark 《Journal of veterinary diagnostic investigation》1992,4(4):393-399
Accurate identification of bovine parainfluenza type 3 virus in bovine respiratory disease requires dependable, sensitive, and specific techniques for detection in affected animals. Immunohistochemical testing can be a rapid and reliable means of demonstration of virus in tissues from suspect cases; however, this procedure is dependent upon the quality of the antisera directed against the viral antigens. The production of rabbit polyclonal and murine monoclonal antibodies directed against bovine parainfluenza type 3 virus and techniques for their use in fresh-frozen and formalin-fixed paraffin-embedded tissues in immunofluorescence and immunoperoxidase-based immunohistochemical tests are described. 相似文献
66.
67.
Stressors such as transportation, weaning and co-mingling increase susceptibility to bacterial pneumonia in cattle and are associated with elevated levels of endogenous glucocorticoids. To determine the effect of glucocorticoids on the proteins expressed in the fluid lining the respiratory tract, bronchoalveolar lavage (BAL) was performed on cattle treated with dexamethasone or saline and proteins were resolved by two-dimensional electrophoresis (2-DE). Significant changes in expression were observed for 9 of the 363 detected spots, and the identities of these proteins were determined by mass spectrometry. Consistent with the initiation of an acute phase response, the expression of alpha-1-acid glycoprotein (orosomucoid) and alpha-1-antitrypsin was increased and alpha-2-HS-glycoprotein (fetuin) was decreased in the BAL fluid of dexamethasone-treated cattle. In addition, dexamethasone induced the expression of two hydrophobic ligand-binding proteins, adipocyte-fatty acid binding protein and odorant binding protein (OBP), as well as the proteins alpha-enolase, cofilin-1 and immunoglobulin J chain. OBP mRNA expression in bronchial biopsies was quantified by real-time RT-PCR and the 6-fold higher levels of expression observed in dexamethasone- versus saline-treated animals correlated with the changes observed in OBP protein level. These findings demonstrate glucocorticoid-dependent changes in the protein composition of the epithelial lining fluid of the respiratory tract, identifying proteins potentially integral to respiratory disease susceptibility. 相似文献
68.
69.
70.