全文获取类型
收费全文 | 139599篇 |
免费 | 27779篇 |
国内免费 | 28530篇 |
专业分类
林业 | 17871篇 |
农学 | 19721篇 |
基础科学 | 14109篇 |
41114篇 | |
综合类 | 52047篇 |
农作物 | 9900篇 |
水产渔业 | 8638篇 |
畜牧兽医 | 17956篇 |
园艺 | 4423篇 |
植物保护 | 10129篇 |
出版年
2024年 | 2235篇 |
2023年 | 2245篇 |
2022年 | 3380篇 |
2021年 | 4194篇 |
2020年 | 5592篇 |
2019年 | 8444篇 |
2018年 | 7512篇 |
2017年 | 8886篇 |
2016年 | 9298篇 |
2015年 | 9959篇 |
2014年 | 9265篇 |
2013年 | 10370篇 |
2012年 | 10805篇 |
2011年 | 10415篇 |
2010年 | 9208篇 |
2009年 | 8524篇 |
2008年 | 7478篇 |
2007年 | 7640篇 |
2006年 | 7145篇 |
2005年 | 6331篇 |
2004年 | 4147篇 |
2003年 | 3710篇 |
2002年 | 3081篇 |
2001年 | 2918篇 |
2000年 | 2998篇 |
1999年 | 3266篇 |
1998年 | 3089篇 |
1997年 | 2801篇 |
1996年 | 2503篇 |
1995年 | 2514篇 |
1994年 | 2324篇 |
1993年 | 2011篇 |
1992年 | 1844篇 |
1991年 | 1537篇 |
1990年 | 1248篇 |
1989年 | 1175篇 |
1988年 | 949篇 |
1987年 | 624篇 |
1986年 | 534篇 |
1985年 | 281篇 |
1984年 | 253篇 |
1983年 | 232篇 |
1982年 | 227篇 |
1981年 | 258篇 |
1980年 | 206篇 |
1979年 | 160篇 |
1978年 | 136篇 |
1975年 | 111篇 |
1965年 | 139篇 |
1964年 | 147篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Xiaolong Wang Kehe Huang Jingbao Gao Xiangzhen Shen Chengyi Lin Gengdi Zhang 《Research in veterinary science》1997,62(3):275
The chemical composition and microstructure of seven uroliths and four urinary sediment samples associated with the feeding of high-level cottonseed meal diet to buffalo calves were examined by chemical qualitative analyses, scanning electron microscopy (
), X-ray diffraction, and X-ray energy dispersive spectrometry (
). Struvite was a major component of kidney stones and of some bladder stones. The kidney stone sample appeared cracked under low power under
, aggregated into tiny balls under high power, and as a bladelike structure under even higher power. The bladder stone samples appeared finely granular or granular with various forms of prismatic crystals. The urinary sediments were prismatic crystals, with granules. The newly found prismatic crystals, which were rich in potassium and similar to struvite in crystal structure, were identified as potassium magnesium phosphate (KMgPO4 · 6H2O) in some bladder stones and urinary sediments. However, crystals which contained Mg and P only, which had been used for struvite identification, were not found by
examination in urinary sediments from fresh urine samples of buffalo calves fed the high-level cottonseed meal diet. 相似文献
82.
M J Lopez M Prichard H Steinberg 《The Canadian veterinary journal. La revue veterinaire canadienne》1997,38(6):377-378
A 2-year-old heifer was presented with masses on her anus that were interfering with cervical manipulation during embryo flushing. The masses had broad stalks attached within the anal sphinchter. Recovery was without incident after surgical resection. No recurrence of the masses had occurred 3 months later. Histologic diagnosis was benign leiomyoma. 相似文献
83.
Wang R Yuan LG He LM Zhu LX Luo XY Zhang CY Yu JJ Fang BH Liu YH 《Journal of veterinary pharmacology and therapeutics》2011,34(3):247-251
Wang, R., Yuan, L.G., He, L.M., Zhu, L.X., Luo, X.Y., Zhang, C.Y., Yu, J.J., Fang, B.H., Liu, Y.H. Pharmacokinetics and bioavailability of valnemulin in broiler chickens. J. vet. Pharmacol. Therap. 34 , 247–251. The objective of this study was to investigate the pharmacokinetics and bioavailability of valnemulin in broiler chickens after intravenous (i.v.), intramuscular (i.m.) and oral administrations of 10 mg/kg body weight (bw). Plasma samples were analyzed by high‐performance liquid chromatography–tandem mass spectrometry (HPLC‐MS/MS). Pharmacokinetic characterization was performed by non‐compartmental analysis using WinNonlin program. After intravenous administration, distribution was wide with the volume of distribution based on terminal phase(Vz) of 4.27 ± 0.99 L /kg. Mean valnemulin t1/2β(h), Clβ(L /h /kg), Vss (L /kg) and AUC(0–∞)(μg·h /mL) values were 2.85, 0.99, 2.72 and 10.34, respectively. After intramuscular administration, valnemulin was rapidly absorbed with a Cmax of 2.2 μg/mL achieved at 0.43 h (tmax), and the absolute bioavailability (F) was 88.81%; and for the oral route the same parameters were 0.66 ± 0.15 μg/mL, 1.54 ± 0.27 h and 74.42%. A multiple‐peak phenomenon was present after oral administration. The plasma profile of valnemulin exhibited a secondary peak during 2–6 h and a tertiary peak at 32 h. The favorable PK behavior, such as the wide distribution, slow elimination and acceptable bioavailability indicated that it is likely to be effective in chickens. 相似文献
84.
85.
Shengjing SONG Aiqing LIN Tinglei JIANG Xin ZHAO Walter METZNER Jiang FENG 《Integrative zoology》2019,14(6):576-588
Many studies based on acute short‐term noise exposure have demonstrated that animals can adjust their vocalizations in response to ambient noise. However, the effects of chronic noise over a relatively long time scale of multiple days remain largely unclear. Bats rely mainly on acoustic signals for perception of environmental and social communication. Nearly all previous studies on noise‐induced vocal adjustments have focused on echolocation pulse sounds. Relatively little is known regarding the effects of noise on social communication calls. Here, we examined the dynamic changes in the temporal parameters of echolocation and communication vocalizations of Vespertilio sinensis when exposed to traffic noise over multiple days. We found that the bats started to modify their echolocation vocalizations on the fourth day of noise exposure, with an increase of 42–91% in the total number of pulse sequences per day. Under noisy conditions, the number of pulses within a pulse sequence decreased by an average of 17.2%, resulting in a significantly slower number of pulses/sequence (P < 0.001). However, there was little change in the duration of a pulse sequence. These parameters were not significantly adjusted in most communication vocalizations under the noise condition (all P > 0.05), except that the duration decreased and the number of syllables/sequences increased in 1 type of communicative vocalization (P < 0.05). This study suggests that bats routinely adjust temporal parameters of echolocation but rarely of communication vocalizations in response to noise condition. 相似文献
86.
87.
88.
89.
90.