全文获取类型
收费全文 | 4505篇 |
免费 | 275篇 |
国内免费 | 584篇 |
专业分类
林业 | 628篇 |
农学 | 382篇 |
基础科学 | 577篇 |
595篇 | |
综合类 | 1690篇 |
农作物 | 230篇 |
水产渔业 | 261篇 |
畜牧兽医 | 650篇 |
园艺 | 52篇 |
植物保护 | 299篇 |
出版年
2024年 | 47篇 |
2023年 | 129篇 |
2022年 | 178篇 |
2021年 | 237篇 |
2020年 | 230篇 |
2019年 | 250篇 |
2018年 | 133篇 |
2017年 | 251篇 |
2016年 | 294篇 |
2015年 | 238篇 |
2014年 | 332篇 |
2013年 | 292篇 |
2012年 | 332篇 |
2011年 | 326篇 |
2010年 | 228篇 |
2009年 | 230篇 |
2008年 | 214篇 |
2007年 | 230篇 |
2006年 | 206篇 |
2005年 | 160篇 |
2004年 | 135篇 |
2003年 | 138篇 |
2002年 | 102篇 |
2001年 | 58篇 |
2000年 | 59篇 |
1999年 | 63篇 |
1998年 | 43篇 |
1997年 | 29篇 |
1996年 | 31篇 |
1995年 | 31篇 |
1994年 | 26篇 |
1993年 | 22篇 |
1992年 | 15篇 |
1991年 | 13篇 |
1990年 | 19篇 |
1989年 | 12篇 |
1988年 | 17篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1981年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有5364条查询结果,搜索用时 15 毫秒
41.
The objective of this study was to evaluate the response of healthy housebound domestic cats to the simultaneous provision of 2 litterboxes of differing sizes by recording the average daily frequency of urination and defecation in each box. Forty-three households with 74 privately owned cats were each provided with 2 different-sized plastic containers, with the larger box being 86 cm in length, exceeding the size of commercially available litterboxes. Owners were also provided with an unlimited supply of clumping cat litter and a logbook to record daily urine and fecal deposits in the boxes as they were scooped over a 4-week period. The 2 litterboxes were initially placed at opposite sides of the same room in the owner's home. After 2 weeks, the boxes were emptied completely, refilled with clean clumping litter, and replaced in the opposite location. Results were recorded as simple counts of urine and fecal deposits for each day and each household. Over the 28-day period, there were a total of 5031 urine and fecal deposits in the larger boxes and 3239 urine and fecal deposits in the regular boxes. The effects of phase (days 1-14 vs. 15-28) and box size (regular vs. large) on the number of deposits per cat were evaluated using a linear mixed model. In addition to evaluating phase and box size, the effects of number of cats in the house, their average age, and gender were also evaluated. Urine deposits were significantly more frequent than fecal deposits. Large boxes were preferentially selected over regular boxes in both phases, but this difference was greater in phase 1 than phase 2. Further analysis indicated that there was a location preference during the first 2 days in phase 2, and this effect decreased as the study progressed. Results indicate that most cats show a definite preference for a larger litterbox than is typically available to them in homes and that other factors such as box cleanliness and location may have a compounding influence on this choice. 相似文献
42.
利用博弈论的方法对国防工业发展中已进入国防工业的企业群、待进入国防工业的企业群和政府的对策进行分析,并得出结论:政府首先要指导已进入国防工业的企业群合理定位;其次要考虑制定多大程度的保护政策来保护已进入国防工业企业的发展和利益;最后政府需要对军工企业的诉讼制定合理的支持标准,使已进入国防工业企业始终处于竞争环境良性发展.当然政府作出以上决策的主要依据是在保证本国安全的前提下使国防工业企业的利润实现最大化. 相似文献
43.
Pharmacokinetics of xylazine after 2-, 4-, and 6-hr durations of continuous rate infusions in horses
Klaus Hopster Lawrence R. Soma Xiaoqing Li Charlotte Hopster-Iversen Raymond C. Boston Bernd Driessen 《Journal of veterinary pharmacology and therapeutics》2020,43(6):557-564
Intravenous (i.v.) bolus administration of xylazine (XYL) (0.5 mg/kg) immediately followed by a continuous rate infusion (CRI) of 1 mg kg−1 hr−1 for 2, 4, and 6 hr produced immediate sedation, which lasted throughout the duration of the CRI. Heart rate decreased and blood pressure increased significantly (p > .05) in all horses during the first 15 min of infusion, both returned to and then remained at baseline during the duration of the infusion. Compartmental models were used to investigate the pharmacokinetics of XYL administration. Plasma concentration–time curves following bolus and CRI were best described by a one-compartment model. No differences were found between pharmacokinetic estimates of the CRIs for the fractional elimination rate constant (Ke), half-life (t1/2e), volume of distribution (Vd), and clearance (Cl). Median and range were 0.42 (0.15–0.97)/hr, 1.68 (0.87–4.52) hr, 5.85 (2.10–19.34) L/kg, and 28.7 (19.6–39.5) ml min−1 kg−1, respectively. Significant differences were seen for area under the curve ( ) (p < .0002) and maximum concentration (Cmax) (p < .04). This indicates that with increasing duration of infusion, XYL may not accumulate in a clinically relevant way and hence no adjustments are required in a longer XYL CRI to maintain a constant level of sedation and a rapid recovery. 相似文献
44.
为了降低机插稻育秧、运秧劳动强度,在云南籼稻地区探索籼稻小苗机插技术。以吉优716为材料,设置160 g/盘(T1 )和180 g/盘(T2)2个播种量处理,秧龄9 d,每667 m2大田用秧6盘。以常规播种量70 g/盘,15 d秧龄,每667 m2用秧15盘为对照,比较分析了不同处理间秧苗素质、栽插质量、茎蘖动态和产量的差异。结果表明,虽然密播小苗处理秧苗素质不如对照,并且缺丛率较高,但每丛基本苗数、各时期的茎蘖数和有效穗数均显著高于对照,最终产量均高于对照。较高的有效穗数是机插密播小苗技术增产的主要原因。其中,T1处理用种量比对照减少了8.57%,秧盘数比对照减少60%,但产量比对照增加了9.0%,节本增效的效果明显,具有较大的推广潜力。 相似文献
45.
46.
对农村初中留守儿童问题行为的状况进行调查和分析,并提出相应的建议或干预措施。 相似文献
47.
在问卷调查的基础上,对合福高铁旅客的出游目的、旅游目的地偏好、旅游线路等旅游消费行为特征进行分析,结果表明:预订率最高的3趟班次依次为G28(09:52~13:31)、G322(09:12~13:36)、G1612(16:50~21:22);旅客出行目的以商旅为主;旅游目的地偏好依次为黄山、婺源、武夷山、三清山;旅客普遍使用旅游相关的APP。合福高铁沿线应从微旅游市场开发、移动智能营销平台建设、高铁配套设施、区域旅游合作等方面加强旅游联合营销。 相似文献
48.
采用正交试验对ZL101合金进行了成分优化设计,并分析了合金元素对铝硅合金力学性能的影响.对改良后的合金进行了热处理工艺研究,其最佳热处理工艺条件为:500 ℃×5.5 h+180 ℃×5 h.研究结果表明,改良合金在铸态下的力学性能为:抗拉强度为244.57 MPa,伸长率为5.95%,硬度为75.1 HB;在T6态下的力学性能为:抗拉强度为397.92 MPa,伸长率为4.68%,硬度为141.2 HB. 相似文献
49.
50.
Mayara Aline Baller Peterson Dante Gavasso Pacheco Amanda Vitta-Takahashi Thaila Cristina Putarov Ricardo Souza Vasconcellos Aulus Cavalieri Carciofi 《Journal of animal physiology and animal nutrition》2021,105(Z1):76-90
The influence of specific thermal energy (STE) applications on extruder preconditioner was evaluated in a dry food for cats. In the first study, six STE applications were tested with mass temperatures of 45°C, 55°C, 65°C, 75°C, 85°C and 95°C. The extrusion parameters, starch gelatinization and kibble formation were evaluated. Diets were given to cats to evaluate digestibility, faecal characteristics and palatability. In the second experiment, three treatments were compared: low STE—a preconditioner temperature of 45°C (LSTE); high STE—a preconditioner temperature of 95°C (HSTE); high STE (preconditioner temperature of 95°C) combined with an increase in the mass flow rate to obtain a motor amperage similar to that of the LSTE (HSTEflow). Data were analysed by polynomial contrasts (Experiment 1) or Tukey's test (Experiment 2; p < 0.05). An increase in STE reduced motor amperage, mass pressure and specific mechanical energy (SME) implementation (p < 0.001) and increased total specific energy (TSE) and mass temperature (p < 0.01). The increase in STE induced greater kibble expansion and starch gelatinization (p < 0.001). No changes in apparent nutrient digestibility or faeces characteristics were observed (p > 0.05). Lower STE and starch gelatinization induced higher butyrate and total volatile fatty acid (VFA) contents in faeces (p < 0.01). Cats showed greatest preference for the formulation with the highest STE (p < 0.01). In the second experiment, when the motor amperage was increased in the HSTEflow treatment to a value similar to that of the LSTE, the mass flow rate increased 40%, and the electric energy consumption remained unchanged (p < 0.001), with gains observed for efficiency and cost. In conclusion, STE application is important for sufficient TSE implementation, enhancing kibble expansion, starch gelatinization, cat preferences for food, extruder productivity and reducing SME application. Foods with lower starch gelatinization lead to increased VFA in faeces, with possible implications for gut health. 相似文献