全文获取类型
收费全文 | 3143篇 |
免费 | 157篇 |
国内免费 | 2篇 |
专业分类
林业 | 58篇 |
农学 | 112篇 |
基础科学 | 25篇 |
345篇 | |
综合类 | 413篇 |
农作物 | 122篇 |
水产渔业 | 161篇 |
畜牧兽医 | 1780篇 |
园艺 | 58篇 |
植物保护 | 228篇 |
出版年
2021年 | 30篇 |
2020年 | 40篇 |
2019年 | 38篇 |
2018年 | 45篇 |
2017年 | 50篇 |
2016年 | 48篇 |
2015年 | 39篇 |
2014年 | 46篇 |
2013年 | 162篇 |
2012年 | 103篇 |
2011年 | 100篇 |
2010年 | 60篇 |
2009年 | 64篇 |
2008年 | 121篇 |
2007年 | 109篇 |
2006年 | 106篇 |
2005年 | 107篇 |
2004年 | 82篇 |
2003年 | 96篇 |
2002年 | 112篇 |
2001年 | 112篇 |
2000年 | 98篇 |
1999年 | 64篇 |
1998年 | 39篇 |
1997年 | 37篇 |
1996年 | 41篇 |
1995年 | 43篇 |
1994年 | 28篇 |
1992年 | 42篇 |
1991年 | 65篇 |
1990年 | 64篇 |
1989年 | 53篇 |
1988年 | 54篇 |
1987年 | 59篇 |
1986年 | 61篇 |
1985年 | 57篇 |
1984年 | 52篇 |
1983年 | 50篇 |
1982年 | 36篇 |
1981年 | 30篇 |
1979年 | 31篇 |
1978年 | 33篇 |
1977年 | 37篇 |
1976年 | 31篇 |
1975年 | 29篇 |
1974年 | 36篇 |
1973年 | 35篇 |
1972年 | 35篇 |
1971年 | 33篇 |
1970年 | 34篇 |
排序方式: 共有3302条查询结果,搜索用时 437 毫秒
971.
972.
The cat flea, Ctenocephalides felis, is the most important ectoparasite of cats and dogs worldwide as a cause of irritation and health problems. Most products to control these pests in the household environment rely upon a combination of neurotoxic insecticides and insect growth regulators to inhibit development of flea eggs and larvae into adults. However, some of these are affected by problems of insecticide resistance as well as public concerns about their potential for toxicity in domestic use. Heavy synthetic oils, like the siloxane dimeticone, are currently widely used to treat human ectoparasite infestations, acting by a physical mode of action, and have been used in a variety of presentations for killing all life stages of fleas. We have investigated the activity of low concentrations of high molecular weight dimeticone in a volatile silicone base for ability to immobilise flea life stages without asphyxiating them. We found that cat flea adults and larvae were immobilised by a surface film of dimeticone that inhibited movement of cuticular joints, apparently forming an effective sticky trap. When cocoons were treated the fleas continued to develop within the pupae but failed to emerge. An aerosol spray incorporating 0.4% concentration of dimeticone, for use as a residual household treatment, showed no significant difference in knock down capability compared with that of a widely used pyriproxifen/permethrin spray in a repeat challenge test, with effects persisting to inhibit adult flea emergence in the test arena area for more than 3 weeks after application. 相似文献
973.
L-asparaginase-deficient mutants of yeast 总被引:7,自引:0,他引:7
Yeast L-asparaginase is a multimeric enzyme for which only a single structural gene has been found. Fourteen mutants deficient in L-asparaginase have been isolated, and they have been located at one site on the genetic map of Saccharomyces cerevisiae. The L-asparaginase gene (aspl) is located about 18 centimorgans from a gene governing tryptophan synthesis (trp4) on fragment 2 of the map. 相似文献
974.
樟疫霉多聚半乳糖醛酸酶基因9和10的克隆、测序及其遗传转化研究 总被引:3,自引:0,他引:3
研究优化了樟疫霉多聚半乳糖醛酸酶基因9(Pcpg9)和Pcpg10基因克隆的PCR条件,并对其进行了克隆、测序和遗传转化研究。克隆获得了2个基因,其大小前者1059bp,后者1290bp;通过构建表达载体和遗传转化获得了2个基因的转基因菌系;2个基因均能指导合成相应的PG酶蛋白,其中转化Pcpg10基因的酵母菌所分泌的PG酶活性最强,对照Anpg 的PG酶活性次之,Pcpg9的PG酶活性最弱。Westernblotting表明,所克隆的2个基因所指导合成的PG酶蛋白均有不同程度的糖基化。 相似文献
975.
Jones TT 《Science (New York, N.Y.)》2001,292(5526):2431-2432
976.
In nature, infected and uninfected arthropod vectors often feed together on an animal. In mimicking this scenario in the laboratory, uninfected vectors were found to acquire virus while cofeeding on the same host as infected vectors. However, the vertebrate host on which they fed did not develop detectable levels of virus in its blood. These observations were made with Thogoto virus, an influenza-like virus of medical and veterinary significance. Rhipicephalus appendiculatus ticks were used as the vector and guinea pigs as the vertebrate host. The results demonstrate that a vertebrate that is apparently refractory to infection by an arthropod-borne virus can still play an important role in the epidemiology of the virus, and they suggest a novel mode of arthropod-borne virus transmission. 相似文献
977.
The ability of mink, fer rets, skunks, and cats to learn to dis criminate between objects was com pared. Performance of mink and fer rets was similar to that reported for primates. This observation suggests that there is considerable overlap among mammals in ability to form learning sets. 相似文献
978.
The effects of ouabain on potassium accumulation were studied in the dog carotid artery. It was confirmed that vascular smooth muscle lost potassium in the presence of ouabain greater than 10(-9) molar. This effect could be reversed by systematically increasing potassium in the external medium. The action of ouabain on ion accumulation was represented quantitatively with the application of a recent biophysical approach. 相似文献
979.
Kinetics of the reactions of Riftia pachyptila hemoglobin with oxygen were followed spectrophotometrically by stopped-flow and laser flash photolysis techniques. The rate of oxygen dissociation increases eightfold over the range of 5 degrees to 20 degrees C (k = 2.2 sec(-1)at 10 degrees C). Oxygen recombination after flash photolysis was biphasic. The rates of both slow and fast phases of the reaction were independent of temperature from 0 degrees to 20 degrees C(k'fast = 7 x 10(6); k'slow = 1 x 16(6) liter mole (-1) sec(-1)). As the oxygen affinity is relatively temperature independent, analysis in terms of the two-state model of cooperativity requires that the conformational equilibrium constant L decrease by about 50-fold between 3 degrees and 15 degrees C. 相似文献
980.
Rooney HC Van't Klooster JW van der Hoorn RA Joosten MH Jones JD de Wit PJ 《Science (New York, N.Y.)》2005,308(5729):1783-1786
How plants recognize pathogens and activate defense is still mysterious. Direct interaction between pathogen avirulence (Avr) proteins and plant disease resistance proteins is the exception rather than the rule. During infection, Cladosporium fulvum secretes Avr2 protein into the apoplast of tomato leaves and, in the presence of the extracellular leucine-rich repeat receptor-like Cf-2 protein, triggers a hypersensitive response (HR) that also requires the extracellular tomato cysteine protease Rcr3. We show here that Avr2 binds and inhibits Rcr3 and propose that the Rcr3-Avr2 complex enables the Cf-2 protein to activate an HR. 相似文献