全文获取类型
收费全文 | 14075篇 |
免费 | 1068篇 |
国内免费 | 72篇 |
专业分类
林业 | 626篇 |
农学 | 822篇 |
基础科学 | 125篇 |
2006篇 | |
综合类 | 1665篇 |
农作物 | 497篇 |
水产渔业 | 1047篇 |
畜牧兽医 | 7031篇 |
园艺 | 228篇 |
植物保护 | 1168篇 |
出版年
2023年 | 90篇 |
2021年 | 88篇 |
2020年 | 123篇 |
2019年 | 202篇 |
2018年 | 373篇 |
2017年 | 346篇 |
2016年 | 336篇 |
2015年 | 306篇 |
2014年 | 327篇 |
2013年 | 572篇 |
2012年 | 479篇 |
2011年 | 571篇 |
2010年 | 464篇 |
2009年 | 422篇 |
2008年 | 555篇 |
2007年 | 579篇 |
2006年 | 472篇 |
2005年 | 520篇 |
2004年 | 407篇 |
2003年 | 446篇 |
2002年 | 358篇 |
2001年 | 760篇 |
2000年 | 721篇 |
1999年 | 590篇 |
1998年 | 171篇 |
1997年 | 164篇 |
1996年 | 127篇 |
1995年 | 150篇 |
1994年 | 156篇 |
1993年 | 120篇 |
1992年 | 321篇 |
1991年 | 346篇 |
1990年 | 291篇 |
1989年 | 266篇 |
1988年 | 271篇 |
1987年 | 319篇 |
1986年 | 246篇 |
1985年 | 193篇 |
1984年 | 170篇 |
1983年 | 147篇 |
1982年 | 94篇 |
1981年 | 83篇 |
1980年 | 79篇 |
1979年 | 141篇 |
1978年 | 94篇 |
1977年 | 73篇 |
1975年 | 77篇 |
1974年 | 79篇 |
1971年 | 69篇 |
1969年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Relationship between the serum concentrations of serotonin and lipids and aggression in dogs 总被引:1,自引:0,他引:1
The serum concentrations of serotonin and lipids--triglycerides, total cholesterol, low density lipoprotein, high density lipoprotein and very low density lipoprotein--were determined in 18 normal dogs and 23 dogs diagnosed as aggressive on the basis of interviews with their owners and an assessment of their behaviour with reference to a canine overt aggression chart. The serum serotonin levels in the aggressive dogs were significantly lower than in the normal dogs (P<0.01), but the differences in serum lipids between the two groups were not statistically significant. 相似文献
992.
Kridli RT Momany Shaker M Abdullah AY Muwalla MM 《Tropical animal health and production》2007,39(3):229-235
This study was conducted to evaluate the sexual performance of 10-month-old, ram lambs of different breed groups. Eight ram
lambs each of Awassi (A), F1 Charollais × Awassi (CA) and F1 Romanov × Awassi (RA) breed types were subjected to sexual performance tests by being individually exposed to two oestrous
Awassi ewe lambs for four 20-min periods. Bouts of leg kicking and anogenital sniffing were similar among breed groups. Mounting
frequency was greater (p < 0.05) in RA than in A and CA ram lambs. Tail-raising was greater (p < 0.05) and mating rate tended to be greater (p < 0.10) in A than in RA and CA ram lambs. The number of mounts per tail-raising (efficiency) was influenced by breed group
and test day (p < 0.05). Awassi ram lambs maintained the best efficiency throughout the experiment. Efficiency in RA and CA ram lambs improved
with each test day. Results of the present study indicate that RA ram lambs have greater mounting frequency than A and CA,
while Awassi are more capable of mating with fat-tailed females than the CA and RA ram lambs. 相似文献
993.
994.
995.
Koketsu Y 《Journal of animal science》2007,85(4):1086-1091
Annual performance measurements, age structures of female pig inventories, and by-parity culling rates were abstracted from data files of 110 herds that participated in a data-share program in Japan. Parity at culling was used as a prime measurement of longevity, whereas pigs weaned x mated female(-1) x year(-1) (PWMFY) was a prime measurement of reproductive efficiency. High or low longevity herds were based on the greatest 50% of the herds or the remaining herds ranked by parity at culling, whereas high or low reproductive efficiency herds were grouped according to the greatest 50% of the herds or the remaining herds ranked by PWMFY. Measurements were analyzed as a 2 x 2 factorial arrangement, using the main effects of the 2 herd groups of longevity (high or low) and reproductive efficiency (high or low). Means of parity at culling and PWMFY were 4.6 (SD = 0.82) and 21.2 (SD = 3.02), respectively. The high longevity group had 1.27 greater parities at culling than the low longevity group (P < 0.05), but no differences between the high and low longevity groups were found in PWMFY (P = 0.21). No differences between the high and low efficiency groups were found in parity at culling (P = 0.50). No interactions between the longevity and efficiency groups were found on any longevity or efficiency measurement (P > 0.20). In herd management, the percentage of reserviced females and the percentage of multiple matings were associated with the longevity group and the efficiency group (P < 0.05). The high longevity group had lower culling rates in parity 0 to 6 than the low longevity group (P < 0.05), whereas no differences between the low and high efficiency groups were found in culling rates in parity 0 to 2 (P > 0.20). This study suggests that measures to achieve longevity and high reproductive efficiency in breeding herds do not conflict and that high reproductive efficiency and high longevity can be achieved. 相似文献
996.
997.
Getaneh K. Ayele Azalu A. Gessess Meseret B. Addisie Seifu A. Tilahun Tigist Y. Tebebu Daregot B. Tenessa Eddy J. Langendoen Charles F. Nicholson Tammo S. Steenhuis 《Land Degradation \u0026amp; Development》2016,27(2):270-280
Gully erosion reduces agricultural productivity by destroying valuable land resources, increases sediment concentrations, reduces water quality, and fills up reservoirs. Gully rehabilitation has proven to be challenging especially in the high‐rainfall areas of the Ethiopian Highlands and has therefore had limited success. This paper describes a successful low‐cost gully rehabilitation effort with community participation in the Birr watershed in the Blue Nile basin that begun in early 2013. Initially, farmers were reluctant to participate for religious reasons, but with the aid of local priests and respected elders, community discussions, and a visit to a rehabilitated gully, a consensus was reached to rehabilitate a 0·71‐ha upland gully. The rehabilitation measures consisted of regrading the gully head at a 45° slope, constructing low‐cost check dams from locally available materials, and planting Pennisetum purpureum grass and Sesbania sesban. At the end of the first post‐implementation rainy season, 2,200 tons of soil was conserved by the constructed check dams and newly planted vegetation, compared with soil losses of 680 and 560 tons in two untreated, nearby gullies. In 2014, an additional 3,100 tons of soil was conserved. In 2013, the marginal rate of return (MRR) on the gully rehabilitation investment was 2·6 based on the value of increased forage production alone. When we include trapped soil nutrient values, the rehabilitation MRR was increased to 10. Although these numbers are impressive, the best proof of the success was that farmers on their own initiative rehabilitated an additional five gullies in 2014. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
998.
Cre/loxP定位重组系统在植物雄不育和杂种优势中的利用研究 总被引:4,自引:0,他引:4
Cre—loxP是来源于噬菌体P1的一种位点特异性重组系统。目前,它已广泛应用于基因功能鉴定,动植物及微生物基因组的修饰以及基因的表达和调控。雄性不育系在杂种优势的利用中具有重要意义。本实验是以Cre—loxP系统调控细胞毒素基因barnase在植物雄性器官发育的特异时期在特异组织表达,从而达到控制植物育性的目的。1.在本实验中,通过PCR方法克隆了解淀粉芽孢杆菌Bacillus amyloliquefaciens的barnase基因,及其抑制因子barstar的DNA序列,同时,构建成功双元表达载体及基因枪转化载体,并已获得经分子险测呈阳性的小麦植株。2.osg6B是来源于水稻花药绒毡层的特异性的启动子,它在小孢子发育的四分体时期至单核花粉期在花药绒毡层中特异启动基因的表达,它具有较为严紧的时空特异性。以osg6B为启动子,构建了一组受控于Cre/loxP位点特异性重组系统的适用于基因枪法转化小麦的载体系统。其中,转不育基因(og6B—barnase)小麦植株生长正常,但开花后,花粉量明显减少,自交不能得到正常种子。进行花粉活力检测发现,转基因小麦大部分花粉表现为败育。花粉离体萌发试验表明,转不育基因小麦的花粉离体萌发率极低,几近败育。说明以osg6B驱动barnase在小麦花药中的表达可以导致雄性不育。3.以osg6B为启动子,构建了一组受控于Cre/loxP的用于控制双子叶植物育性的双元表达载体系统。以转cre基因的烟草作为受体,以含阻断序列的质粒农杆菌进行二次转化。二次转化株营养生长正常,但开花期花器官表现异常。具体表现为花瓣异常开裂或不开裂,花丝变短或粘连,花药提早萎蔫或异常开裂。推测这种现象的出现与启动子的组织特异性或barnase的渗露表达有关。4.二次转化株花粉染色因不同株系出现全部败育、部分不育和多数可育的情况。花粉离体萌发实验也得到了相似的结果。这说明通过筛选,利用Cre/loxP得到完全不育的植物株系是完全可行的。5.获得了9个barnase的突变体,初步推测第十四位氨基酸及第八十位氨基酸与核糖核酸酶活性有关。同时,发现barnase的第316位核苷酸序列为易突变位点,自然发生的突变多插入一个C,从而产生终止位点的改变。这或许会为今后barnase的克隆与利用提供一些参考。 相似文献
999.
H.Y. Rey P.A. Sansberro M.M. Collavino J.R. Daviña A.M. Gonzàlez L.A. Mroginski 《Euphytica》2002,123(1):49-56
A protocol for somatic embryogenesis and plant regeneration of Ilexparaguariensis St. Hil. from embryos cultures was developed. Heart stage zygotic embryos were removed from seeds of immature, light green fruit and treated with antimicrotubule agents (0.1; 0.2, and 0.5% colchicine for 24 and 48 h; 1; 10, and 20 M of either trifluralin, - trifluoro- 2,6-dinitro-N,N- dipropyl-p-toluidine, or oryzalin, 3,5-dinitro-N4, N-dipropylsulphate during 48 h). The embryos were cultured aseptically on quarter-strength Murashige and Skoog medium containing 3% sucrose, 0.65% agar (1/4MS), and 0.46 M zeatin. Cultures were incubated in darkness at 27 ± 2 °C. All thetreatments provoked a diminution of the number of germinated embryos and in some of the treated embryos somatic embryogenesis was induced. Somatic embryo maturation and conversion into whole plants could be achieved by culturing the embryos on 1/4MS lacking hormones and incubated at 27 ± 2 °C, 14 h photoperiod (116 mol m-2s-1). Mostof the plants regenerated from somatic embryos appeared morphologically normaland grew under greenhouse conditions. Only 2 plants out of 152 studied contained the tetraploid number of the chromosomes (2n = 4x = 80), meanwhile the rest of the plants had the normal diploid number of chromosomes (2n =2x = 40). Somatic embryos with abnormal morphology were also observed. 相似文献
1000.
Summary Interspecific hybrids have been obtained in an otherwise incompatible cross betweenBrassica juncea × Brassica hirta through the in vitro culture of hybrid ovules and ovaries. The best response was observed from ovules and ovaries cultured 10–15 and 5–7 days after pollination respectively on a basal medium supplemented with indoleacetic acid, kinetin and casein hydrolysate. In some cases the basal cut end of the ovaries proliferated to form callus and shoots. The in vitro-derived hybrid seeds varied in their colour, size and shape, and the F1 plants in the field showed a large diversity in their morphological traits. The hybrids were sterile, and had an intermediate number of chromosomes (2n=30). 相似文献