全文获取类型
收费全文 | 5904篇 |
免费 | 920篇 |
国内免费 | 738篇 |
专业分类
林业 | 24篇 |
农学 | 110篇 |
基础科学 | 56篇 |
189篇 | |
综合类 | 1310篇 |
农作物 | 88篇 |
水产渔业 | 4423篇 |
畜牧兽医 | 1206篇 |
园艺 | 130篇 |
植物保护 | 26篇 |
出版年
2024年 | 47篇 |
2023年 | 104篇 |
2022年 | 154篇 |
2021年 | 298篇 |
2020年 | 336篇 |
2019年 | 444篇 |
2018年 | 295篇 |
2017年 | 438篇 |
2016年 | 361篇 |
2015年 | 274篇 |
2014年 | 332篇 |
2013年 | 497篇 |
2012年 | 386篇 |
2011年 | 398篇 |
2010年 | 314篇 |
2009年 | 275篇 |
2008年 | 274篇 |
2007年 | 305篇 |
2006年 | 233篇 |
2005年 | 215篇 |
2004年 | 195篇 |
2003年 | 173篇 |
2002年 | 127篇 |
2001年 | 163篇 |
2000年 | 138篇 |
1999年 | 114篇 |
1998年 | 73篇 |
1997年 | 84篇 |
1996年 | 92篇 |
1995年 | 84篇 |
1994年 | 71篇 |
1993年 | 63篇 |
1992年 | 51篇 |
1991年 | 33篇 |
1990年 | 25篇 |
1989年 | 43篇 |
1988年 | 16篇 |
1987年 | 15篇 |
1986年 | 14篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1956年 | 2篇 |
排序方式: 共有7562条查询结果,搜索用时 470 毫秒
51.
To study the expression pattern of THBS3 gene in different tissues and during skeletal muscle development, the THBS3 gene expression in different tissues and skeletal muscles during prenatal periods (33, 45, 65, 70 and 90 d) and postnatal periods (0, 9, 30, 60, 120 and 160 d) from Landrace and Tongcheng pigs were detected by Real-time quantification PCR.The results showed that THBS3 gene widely expressed in all tissues examined, exhibiting similar spatial expression patterns with expression peaks in lung in both pig breeds except in stomach and intestine.Moreover, although THBS3 gene showed a significant higher expression level in gestation than after birth in Landrace and Tongcheng pigs (P<0.05), it exhibited different expression patterns between Landrace and Tongcheng pigs, the expression peak was detected at gestation day 45 in Landrace pig, while was detected at gestation day 65 in Tongcheng pig.The results suggested that THBS3 gene involved in skeletal muscle growth and development in pigs, as well as the regulation of asynchronization of skeletal muscle development in different pig breeds. 相似文献
52.
Apparent ileal digestibility of nutrients and amino acids in soybean meal,fish meal,spray‐dried plasma protein and fermented soybean meal to weaned pigs 下载免费PDF全文
This study sought to determine whether fermentation could increase apparent ileal digestibility (AID) of dry matter (DM), nitrogen (N), energy (E) and amino acids (AA) in fermented soybean meal (FSBM) greater than that of soybean meal (SBM) in weaned pigs. Four weaned pigs (10.00 ± 0.30 kg) were surgically equipped with T‐cannulas and randomly followed a 4 × 4 Latin square design of treatments (SBM, FSBM, fish meal and spray‐dried plasma protein). Overall, the fermentation process was able to reduce the amount of anti‐nutritional factors (ANF), including trypsin inhibitors, raffinose and stachyose, in the FSBM diet, which were significantly reduced by 39.4, 92.2, and 92.9%, respectively, as compared to the SBM diet. As a consequence of ANF reduction in FSBM, the AID of DM, N and E as well as AA was significantly greater with FSBM than SBM. Taken all together, the fermentation process improved the nutritional quality of SBM, due to ANF reduction, leading to improvement of digestibility of AA. As such, FSBM can be potentially used as a specialized feed ingredient, especially for young animal diets in an attempt to reduce diet costs. 相似文献
53.
A 14‐year‐old neutered male Dachshund presented for the evaluation of oculus dexter (OD) third eyelid elevation ongoing for approximately 2 months. Complete ophthalmic examination revealed a large, nonpainful, well‐demarcated, soft mass at the base of the right third eyelid causing elevation and mild hyperemia. The mass was freely moveable with the third eyelid, and no right globe deviation was noted. No other abnormalities were noted on physical examination, routine blood chemistry, complete blood count, serum T4, urinalysis, or urine cortisol/creatinine ratio. Ocular B‐mode ultrasonography showed an anechoic, well‐demarcated, homogenous, soft tissue mass at the base of the third eyelid with no orbital extension. A leiomyoma was diagnosed after multiple punch biopsies were obtained from the palpebral surface of the mass. The right third eyelid was excised surgically. Histopathology confirmed a completely excised, nodular, unencapsulated, expansile mass within the third eyelid. Positive smooth muscle actin and negative S‐100 immunohistochemistry confirmed a leiomyoma. Bundles of normal smooth muscle were also present adjacent to the mass. The mass was compressing the adjacent lacrimal gland and associated with moderate dacryoadenitis. Twelve months postoperatively, the right globe position and motility remain normal with no evidence of mass regrowth. To the author's knowledge, this is the first reported case of a leiomyoma of the third eyelid in any species. In this case, the mass was completely excised and no regrowth has occurred twelve months after surgery. This case along with independently reviewed canine third eyelids clearly demonstrates the presence of smooth muscle within the canine third eyelid. 相似文献
54.
Physiological and biochemical changes of females of Piracanjuba,subjected to induced reproduction 下载免费PDF全文
M. A. Zanoni F. G. Costa S. de Carvalho F. R. F. Seiva 《Journal of animal physiology and animal nutrition》2016,100(4):673-679
The aim of this experiment was to compare the level of fish female stress during induced reproduction with pituitary extract by two different methods, natural and semiextruded. The reproductive efficiency was 62.5% in the seminatural treatment and 100% in the extruded. Obtained egg volume was 5200 ml and 4000 ml, for seminatural and extruded treatments respectively. The mean number of eggs was 46.7 for the seminatural and 52.0 and for the extruded treatment. The percentage of viable eggs was, respectively, 87.2% and 8.17% for the natural treatment and extruded semimethods. Blood samples were collected to quantify cortisol and glucose levels, as well as red cell series and lymphocyte count. Fishes submitted to induction procedures showed elevated cortisol and glucose levels, compared to the control animals. The results for haematocrit, haemoglobin concentration and red blood cell count showed no significant differences among groups. Significant differences found in the number of lymphocytes and monocytes suggest the general adaptation syndrome. Our results suggest the reproductive induction process with extrusion of gametes as a more stressful method than seminatural reproduction process. 相似文献
55.
Two single nucleotide polymorphisms in the promoter of the ovine myostatin gene (MSTN) and their effect on growth and carcass muscle traits in New Zealand Romney sheep 下载免费PDF全文
J. Wang H. Zhou J. Hu S. Li Y. Luo J.G.H. Hickford 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2016,133(3):219-226
Myostatin is a negative regulator of muscle growth and development in mammals, and variation in ovine myostatin gene (MSTN) has been demonstrated to be associated with variation in the muscularity of sheep. Polymerase chain reaction–single‐stranded conformational polymorphism (PCR–SSCP) was used to look for single nucleotide polymorphisms (SNPs) in a 304‐bp amplicon from the promoter region of ovine MSTN. Sequence analyses revealed two previously identified SNPs (c.?2449G/C and c. ?2379T/C) that resulted in three haplotypes (H1 (c.[?2449G; ?2379C]), H2 (c.[?2449C; ?2379C]) and H3 (c.[?2449G; ?2379T]). The effect of these SNPs on growth and carcass traits was investigated in 357 NZ Romney lambs. General linear mixed‐effect models revealed that sheep with the genotype c.?2449GC had a higher loin meat yield (p = 0.032) and proportion loin yield (p = 0.028), than those with the genotype c.?2449GG. The genotype c.?2379CC was associated with an increase in three weight traits: birthweight (p = 0.003), tailing weight (p = 0.009) and weaning weight (p = 0.028), when compared with the genotype c.?2379TC, but it was not found to have an association with growth rate. This suggests that c.?2379T/C has an effect that originates at, or before birth. Haplotype H3 was associated with a decrease in birthweight (p = 0.002), tailing weight (p = 0.003) and weaning weight (p = 0.011). Haplotype H2 was associated with increased loin yield (p = 0.012) and proportion loin yield (p = 0.002). The SNPs may have value as genetic markers for improved Romney breeding. 相似文献
56.
本研究旨在比较不同生长阶段隔日限饲(早期限饲:1~14日龄限饲,后期限饲:50~63日龄限饲)对肉鸡肌肉生长及相关激素水平的影响,并探讨早期限饲对肉鸡肌肉生长的程序化作用。试验结果:1)早期限饲组整个试验阶段体重均极显著低于对照组,后期限饲组限饲一周后体重显著低于对照组并于63日龄实现完全补偿生长;2)早期限饲组14日龄和63日龄胸肌、腓肠肌重均显著低于对照组;后期限饲组63日龄胸肌、腓肠肌重均显著低于对照组,且二者与早期限饲组均差异不显著;3)早期限饲显著降低了14日龄肉鸡肌肉中DNA、RNA和蛋白含量,63日龄恢复至正常水平,且核酸、蛋白水平在胸肌和腓肠肌内的趋势表现不一致;4)早期限饲组14日龄血清中T3、T4水平均显著低于对照组,63日龄血清T3水平仍显著低于对照组;后期限饲组63日龄血清T3水平显著低于对照组,T4水平与对照组差异不显著。结果表明:1)限饲可显著阻碍肉鸡肌肉的生长;2)不同部位的肌肉对限饲的敏感度不同;3)早期营养因子对肉鸡肌肉的生长具有"程序化"作用,甲状腺激素可能参与这些过程的调节。 相似文献
57.
58.
59.
AIM To investigate the effects of 17β-estradiol (E2) treatment on the mesenteric lymphatic microcirculation and isolated lymphatic contractility in rats after hemorrhagic shock, and to explore the relationship between contractility and the difference between intra- and extracellular calcium ion concentrations ([Ca2+]) of lymphatic smooth muscle cells (LSMCs). METHODS Male Wistar rats were divided into sham group, shock group and shock+E2 group. The rats were subjected to hemorrhage [(40±2) mmHg for 90 min] and resuscitation with or without subcutaneous injection of E2 (2 mg/kg). After resuscitation for 3 h, the mesenteric lymphatic microcirculation in vivo was observed. Moreover, the isolated mesenteric microlymphatic rings were prepared for the observations of lymphatic contractility evaluated by the indexes including end-systolic diameter, end-diastolic diameter, contraction frequency (CF) and passive diameter. Meanwhile, the difference between intra- and extracellular [Ca2+] of LSMCs was recorded during lymphatic contraction. RESULTS Treatment with E2 significantly enhanced the CF, total contractile fraction and lymphatic dynamics index in vivo in the rats after hemorrhagic shock, and increased the CF, the fractional pump flow and the difference between intra- and extracellular [Ca2+] of LSMCs in isolated lymphatics from the shocked rats (P <0.05). CONCLUSION Estrogen treatment enhances lymphatic contractility in rats after hemorrhagic shock, which is related to enhancement of difference between intra- and extracellular [Ca2+] of LSMCs. 相似文献
60.