全文获取类型
收费全文 | 1949篇 |
免费 | 136篇 |
专业分类
林业 | 100篇 |
农学 | 97篇 |
基础科学 | 21篇 |
384篇 | |
综合类 | 64篇 |
农作物 | 208篇 |
水产渔业 | 221篇 |
畜牧兽医 | 686篇 |
园艺 | 62篇 |
植物保护 | 242篇 |
出版年
2023年 | 17篇 |
2022年 | 54篇 |
2021年 | 73篇 |
2020年 | 77篇 |
2019年 | 120篇 |
2018年 | 85篇 |
2017年 | 121篇 |
2016年 | 100篇 |
2015年 | 69篇 |
2014年 | 83篇 |
2013年 | 145篇 |
2012年 | 120篇 |
2011年 | 132篇 |
2010年 | 81篇 |
2009年 | 61篇 |
2008年 | 75篇 |
2007年 | 61篇 |
2006年 | 65篇 |
2005年 | 70篇 |
2004年 | 44篇 |
2003年 | 43篇 |
2002年 | 47篇 |
2001年 | 27篇 |
2000年 | 19篇 |
1999年 | 25篇 |
1998年 | 14篇 |
1997年 | 14篇 |
1996年 | 11篇 |
1995年 | 11篇 |
1994年 | 11篇 |
1993年 | 19篇 |
1992年 | 11篇 |
1991年 | 14篇 |
1990年 | 14篇 |
1989年 | 8篇 |
1988年 | 12篇 |
1987年 | 11篇 |
1985年 | 8篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1979年 | 13篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1971年 | 6篇 |
1969年 | 4篇 |
1967年 | 7篇 |
1966年 | 4篇 |
排序方式: 共有2085条查询结果,搜索用时 15 毫秒
61.
Peixin YANG Mohamed S. MEDAN Koji Y. ARAI Wanzhu JIN Gen WATANABE Kazuyoshi TAYA 《Animal Science Journal》2005,76(5):427-434
The ontogeny of testicular inhibin/activin in ducks was investigated. Testicular localization of three inhibin/activin subunits (α, βA and βB) was determined in embryonic and newly hatched ducks from 12 days of incubation to 1 day of age, in immature ducks and in adult ducks. In the duck embryonic testis, positive α‐subunit immunostaining was first detected in the Leydig cells and Sertoli cells on day 15 of incubation, whereas βA‐subunit and βB‐subunit immunostaining were found in Sertoli cells and primary germ cells on day 18 of incubation. In 1 month old ducks, intense staining of α‐subunit was present in the seminiferous epithelium consistent with localization in Sertoli cells and primary germ cells, and the immunostaining of the βA‐ and βB‐subunit was also present in Sertoli cells and primary germ cells. Specific immunostaining with inhibin/activin α‐, βA‐ and βB‐subunits antisera occurred in Sertoli cells in the adult duck testes. In conclusion, it was shown that, in the duck testis, the majority of α‐, βA‐ and βB‐subunits are colocalized in Sertoli cells with a certain degree of staining in germ cells and the α‐subunit is present in Leydig cells of embryonic testes before day 18 of incubation. These results indicate that Sertoli cells and possibly germ cells in the embryonic testes of late stage of incubation and newly hatched ducks, immature ducks and mature ducks may produce bioactive inhibin dimers, inhibin A and inhibin B, as a possible regulator of follicle‐stimulating hormone secretion. Free inhibin/activin subunits and their dimers may also play an autocrine/paracrine role in the development of the testis and spermatogenesis. Furthermore, early onset of the α‐subunit in duck testes indicates that it may have an autocrine/paracrine effect on steroid hormones, which is important for sex differentiation. 相似文献
62.
El Mahi E. Gubran Robert Delorme Dnielle Aug Jean P. Moreau 《Pest management science》1992,35(2):101-107
The resistance to insecticides of three Sudanese strains of A. gossypii (Glov.) collected from cotton fields in the Sudan Gezira Scheme over three seasons (1988, 1989, 1990) and that of two French strains was studied in the laboratory. When compared with a known susceptible strain, the aphids were found to be resistant-to the eight insecticides tested. Evolution of resistance in Sudanese strains during the three crop seasons was observed. Assay of aphid homogcnate for carboxytesterase activity towards the substrates α-naphthyl acetate and β-naphthyl acetate showed that there was no enhancement of this class of enzyme and thus it was not a cause of resistance in this species. A study of interaction between the acetylcholinesterase (AchE) and pirimicarb established the kinetics of the inhibition process. I50 values were found to be much higher for the Sudanese strains than for the susceptible strain. First-order inhibition kinetics revealed that resistance towards pirimicarb in Sudanese-strains was caused by a modified AchE which had a reduced affinity (higher Ka value) and poor carbamylation ability (lower K2 value) for pirimicarb. The resistance mechanisms for the other insecticides remain to be studied. 相似文献
63.
C. El Modafar A. Clérivet A. Vigouroux J. J. Macheix 《European journal of plant pathology / European Foundation for Plant Pathology》1995,101(5):503-509
Inoculation of leaves of resistantPlatanus occidentalis and susceptiblePlatanus acerifolia leaves withCeratocystis fimbriata f. sp.platani, the canker stain disease agent, induced foliar necrosis and biosynthesis of two phytoalexins, scopoletin and umbelliferone. Foliar symptoms keep localized and accumulation of coumarin phytoalexins was rapid for incompatible interactions. Necrosis spread widely and accumulation of these phenolic compounds was much later and lower for compatible interactions. The differential response could be used in a genetic improvement program for resistance against canker stain. 相似文献
64.
Haematological estimations and serum biochemical analyses were made on 100 samples collected from clinically healthy Hijin racing camels (Camelus dromedarius) in Kuwait. The red blood cell counts, packed cell volume, haemoglobin concentration, mean corpuscular volume, mean corpuscular haemoglobin, mean corpuscular haemoglobin concentration and total white blood cell counts were estimated. In the serum biochemical analyses, sodium, potassium, iron, calcium, phosphorus, magnesium, total bilirubin, blood urea nitrogen, creatinine, glucose, total protein and cholesterol concentrations were measured, as were the alanine aminotransferase, aspartate aminotransferase, -glutamyltransferase, creatine kinase and alkaline phosphatase activities. The results are discussed in relation to other findings reported in camels. 相似文献
65.
A. F. Ibrahim A. N. Sharaan A. W. El Wakil 《Journal of Agronomy and Crop Science》1991,167(3):170-175
Two promising selected land races of safflower ( Carthamns tinctorious L.) designated as line 11 and line 13, together with the local variety Giza 1 , were examined under three levels of moisture depletions, i.e. 40, 60 and 80 % ASMD at Fayoum, Middle Egypt during 1986/87 and 1987/88 seasons. In both growing seasons, the second irrigation treatment i.e. 60 % ASMD gave the highest means for growth characters as well as seed yield and most of its components. Seed oil content per cent exhibited an increased as soil moisture depletion increased with no significant difference between entries. Safflower entries showed clear differences in some yield components which compensate each other and resulted in no significant difference in seed yield per hectar.
Consumptive use of water by safflower plants increased as the available soil moisture around the root zone increased. No significant differences were found in water consumed by safflower entries used in all experiments.
In the two experimental seasons, the best water use efficiency (WUE) for seed production was obtained also from the second treatment (60 % ASMD). The line 11 gave the best WUE. 相似文献
Consumptive use of water by safflower plants increased as the available soil moisture around the root zone increased. No significant differences were found in water consumed by safflower entries used in all experiments.
In the two experimental seasons, the best water use efficiency (WUE) for seed production was obtained also from the second treatment (60 % ASMD). The line 11 gave the best WUE. 相似文献
66.
67.
Mohamed T Oikawa S Nakada K Kurosawa T Sawamukai Y Sato H 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2003,65(7):821-824
A new method for catheterization of the portal and hepatic veins in cattle by means of the over-the-wire system was investigated to maintain more reliable long-term patency of catheters. Four cattle were used to evaluate the success rate, patency and safety of the procedure. The catheters, coated by urokinase were patent as long as they were in situ. In addition, the introducer was useful to prevent the catheter from being broken. No complications developed during the10 days after the procedure. Two cows were then euthanized. Post mortem findings were minimal. The results of the study reported here are promising, the benefits are significant and there is no apparent disadvantage to its use. 相似文献
68.
ABSTRACT The PaEXG2 gene, encoding an exo-beta-1,3-glucanase, was isolated from the biocontrol agent Pichia anomala strain K. PaEXG2 has the capacity for coding an acidic protein of 427 amino acids with a predicted molecular weight of 45.7 kDa, a calculated pI of 4.7, and one potential N-glycosylation site. PaEXG2 was disrupted by the insertion of the URA3 marker gene, encoding orotidine monophosphate decarboxylase in strain KU1, a uracil auxotroph derived from strain K. Strain KU1 showed inferior biocontrol activity and colonization of wounds on apples, compared to the prototrophic strain. Antagonism and colonization were recovered after the restoration of prototrophy by transformation with the URA3 gene. Integrative transformation was shown to be mostly ectopic in strain K descendants (only 4% of integration by homologous recombination). PaEXG2 disruption abolished all detectable extracellular exo-beta-1,3-glucanase activity in vitro and in situ but did not affect biocontrol of Botrytis cinerea on wounded apples. 相似文献
69.
70.
Growth and Apparent Absorption of Minerals in Broiler Chicks Fed Diets with Low or High Tannin Contents 总被引:5,自引:1,他引:4
Sorghum grains with low (0.28 per cent catechin equivalent (%CE) or high (1.36 %CE)) tannin contents were used to study the effect of tannin on growth and on the apparent absorption of Ca, P, Mg, Na, K, Fe and Co by chickens. High-tannin sorghum caused a highly significant (p0.01) reduction in the weight gain and feed intake of broiler chicks compared to low-tannin sorghum and increased the feed conversion ratio (p0.01). The amount of tannin did not affect mortality. The apparent absorption of Ca, P, Mg, Na, K, Fe and Co was reduced (p0.01) by feeding sorghum grains with a high tannin content. 相似文献