全文获取类型
收费全文 | 4412篇 |
免费 | 254篇 |
国内免费 | 786篇 |
专业分类
林业 | 428篇 |
农学 | 628篇 |
基础科学 | 356篇 |
969篇 | |
综合类 | 1658篇 |
农作物 | 152篇 |
水产渔业 | 151篇 |
畜牧兽医 | 757篇 |
园艺 | 151篇 |
植物保护 | 202篇 |
出版年
2024年 | 43篇 |
2023年 | 93篇 |
2022年 | 152篇 |
2021年 | 182篇 |
2020年 | 194篇 |
2019年 | 232篇 |
2018年 | 156篇 |
2017年 | 241篇 |
2016年 | 302篇 |
2015年 | 199篇 |
2014年 | 264篇 |
2013年 | 285篇 |
2012年 | 335篇 |
2011年 | 365篇 |
2010年 | 233篇 |
2009年 | 243篇 |
2008年 | 189篇 |
2007年 | 220篇 |
2006年 | 229篇 |
2005年 | 166篇 |
2004年 | 134篇 |
2003年 | 124篇 |
2002年 | 102篇 |
2001年 | 109篇 |
2000年 | 97篇 |
1999年 | 95篇 |
1998年 | 70篇 |
1997年 | 60篇 |
1996年 | 48篇 |
1995年 | 34篇 |
1994年 | 44篇 |
1993年 | 41篇 |
1992年 | 37篇 |
1991年 | 38篇 |
1990年 | 23篇 |
1989年 | 27篇 |
1988年 | 19篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有5452条查询结果,搜索用时 15 毫秒
81.
Performance analysis of transcritical organic rankine cycle 总被引:1,自引:0,他引:1
The performance analysis of a transcritical organic Rankine cycle system driven by exhaust heat is presented by using 24 organic working fluids. Four parameters, such as the net power output, thermal efficiency, exergy efficiency, and mass flow rate of working fluid, are used to evaluate the performance of this recovery cycle. The results reveal that the maximum net power can be obtained for the saturated ORC, when T1/TC is about 0.98~0.99,and the working fluid with higher critical temperature has more net power output. For the supercritical ORC, the higher expander inlet temperature will benefit the net power output, thermal efficiency, and exergy efficiency, as long as the expander inlet pressure isnnot too low. However, the influences of expander inlet pressure on these performance parameters are linked with the expander inlet temperature and working fluids. The capability of doing power output of supercritical ORC is not always better than that of subcritical ORC. Parameters, such as net power, thermal efficiency, and exergy efficiency, and mass flow rate are discontinuous in the process from subcritical conditions to supercritical conditions. 相似文献
82.
83.
Yukinobu Nakamura Koshiro Migita Akihiro Okitani Masanori Matsuishi 《Animal Science Journal》2014,85(5):595-601
Water‐holding capacity (WHC) of heat‐induced pork gels was examined. The heat‐induced gels were obtained from meat homogenates prepared by adding nine volumes of 0.3–0.5 mol/L NaCl solutions containing 9–36 mmol/L disodium inosine‐5′‐monophosphate (IMP) or 9 mmol/L tetrapotassium pyrophosphate (KPP) to minced pork. IMP at 36 mmol/L enhanced the WHC to the same level as attained by KPP. Physical and sensory properties of heat‐induced gels were also examined. The heat‐induced gels were prepared from porcine meat homogenates containing 0.3 mol/L NaCl and 9–36 mmol/L IMP or 9 mmol/L KPP. IMP at 36 mmol/L enhanced the values of hardness, cohesiveness, gumminess and springiness, measured with a Tensipresser, and several organoleptic scores to the same level as the score attained by KPP. Thus, it is concluded that IMP is expected to be a practical substitute for pyrophosphates to improve the quality of sausages. 相似文献
84.
Seiju Ishikawa 《Journal of General Plant Pathology》2004,70(5):249-255
Simple diagnosis by ethanol immersion (SDEI) to detect Glomerella cingulata was used to detect three other fungi that also cause latent infection of strawberry plants. Signs on strawberry leaves with asymptomatic latent infection by Colletotrichum acutatum became visible using SDEI. Salmon-pink conidial masses were produced in the acervuli on the treated leaves 5 days after incubation at 28°C. In the case of Dendrophoma obscurans, pycnidia with amber conidial masses formed 5 days after incubation at 28°C. The pycnidia were observed mainly on the ribs, and conidial masses exuded from the ostiole. These macroscopic conidial masses were similar to those of G. cingulata and C. acutatum. When water was dripped onto a lesion caused by D. obscurans, the pycnidia exuded white filamentous conidial masses, making the distinction of D. obscurans from G. cingulata or C. acutatum. On petioles with latent infection by Fusarium oxysporum f. sp. fragariae, white aerial hyphae grew out from the vascular tissues on the cut surface 3 days after incubation at 28°C and were easily observed by eye or with a loupe. Thus, SDEI was also useful for diagnosing latent infection of strawberry plants by C. acutatum, D. obscurans, and F. oxysporum f. sp. fragariae. 相似文献
85.
Qingru Zhang Yaodi Ni Hongbin Guo Chunguang Wang 《Frontiers of Agriculture in China》2007,1(4):478-480
In order to investigate the effects of a Chinese herbal formula Heat-stress-releasing on the antioxidant function in dairy
cows, ten dairy cows were randomly divided into the control group and the experimental group, with five cows in each group.
All the cows were fed with a basal diet. The animals in the experimental group were given with 220 g of herbs per day in addition
to the basal diet. The trial was conducted for 14 days. Blood samples were taken from the vena cava at day 0, day 7, and day
15, respectively. The antioxidant statuses were examined. The results are as follows. (1) Heat-Stress-releasing formula can
significantly increase the milk yield of dairy cows under heat stress. Compared with the control group, the milk yield of
the herb-treated group increased by 14.01% (P<0.05), 14.32% (P<0.05) and 15.01% (P<0.05) in prophase, metaphase and anaphase of the test, respectively. (2) Heat-Stress-releasing formula can increase significantly
the antioxidant status of the heat stressed dairy cows. Compared with the control group, the superoxide dismutase (SOD) activity
increased by 45.93% (P<0.01) at day 7 and by 54.40% (P<0.01) at day 15. The Glutathioneperoxidase (GSH-PX) activity of the test group increased by 17.99% (P<0.05) at day 7 and 25.98% (P<0.01) at day 15. The total antioxidant capacity (T-AOC) of the test group increased by 43.64% (P<0.01) at day 7 and 46.35% (P<0.01) at day 15. The malondaldehyd (MDA) content of test group declined by 23.88% (P<0.01) at day 7 and 25.32% (P<0.01) at day 15. 相似文献
86.
Shuming Zou Sifa Li Wanqi Cai Huaiyu Yang & Xiayun Jiang 《Aquaculture Research》2008,39(12):1322-1327
Interspecific allo-tetraploidy was induced by a combination of hybridization of Megalobrama amblycephala ♀× Megalobrama terminalis ♂ and thermal shock. A thermal shock at 40 °C for 2 min applied to eggs 33 or 26 min (τ0 : 1.40) after fertilization resulted in a significantly ( P <0.01) higher yield of allo-tetraploids than hybrid crosses without heat shock. The yield of allo-tetraploids in embryos from mid-gastrula to hatching stages was 15.7–24.4% in different thermal shock treatment groups. The allo-tetraploidy rate in 330-day-old juveniles was 9.3% and 6.7% in different year treatment groups. After 2 years of rearing, allo-tetraploidy males attained sexual maturity with milk-like milt at the age of 2+, while allo-tetraploidy females at the age of 2+, and even at 3+, did not show any signs of sexual maturation exhibiting obviously delayed maturity. Only a few allo-tetraploidy females (three individuals) showed maturation characters at the age of 4+ and these females were induced to spawn. 相似文献
87.
回热型热泵木材干燥机的分析和研究 总被引:2,自引:0,他引:2
介绍了空气回热和热泵系统回热两种不同的回热型热泵木村干燥机及其优缺点,阐述了采用空气回热的热泵木材干燥机的优越性,并对其运行特性进行了分析和探讨。通过分析和试验结果表明,采用空气回热的热泵木材干燥机较不采用空气回热的热泵木村干燥机的除湿量大大提高。 相似文献
88.
为探究高温胁迫对禾谷镰孢生长和致病力的影响, 本研究测定了禾谷镰孢5株耐高温菌株和4株温度敏感型菌株在25℃和30℃下的菌丝生长速率、产孢量、孢子萌发率以及不同胁迫压力下的生长速率、致病力和DON毒素含量等。结果表明, 不论耐高温菌株还是温度敏感型菌株, 30℃高温对其菌丝生长均有抑制作用, 但对产孢量和孢子萌发有促进作用;30℃高温能减轻NaCl和CaCl2胁迫对禾谷镰孢生长的抑制, 但是不影响KCl、刚果红, SDS和H2O2对病原菌的抑制作用;在30℃下, 大部分耐高温菌株的致病力不变或降低, 而大部分温度敏感型菌株的致病力反而增加, 30℃对大部分菌株的DON毒素产量有一定促进作用。研究结果可为研究气候变化下小麦赤霉病的流行和预测提供理论基础。 相似文献
89.
持续日变高温对肉鸡矿物质代谢的影响 总被引:2,自引:1,他引:1
为研究持续日变高温环境对肉仔鸡矿物质代谢的影响,选用体重接近的20只肉仔鸡,随机分为两组,另选体重接近的4只肉仔鸡,施人工肛门手术。试验组持续日变高温环境设为25~35℃,其中每日35℃持续3h。对照组为20℃恒温。在人工气候舱内适应8d后,每只鸡收集3d尿和总排泄物,并对其中矿物质排出量进行测量,分别对试验前及试验结束时血液中矿物质浓度进行测量。结果表明:持续日变高温使肉仔鸡血清中K浓度显著下降,Zn浓度上升,其它矿物质元素浓度无显著变化,在限饲相同进食量情况下,热应激使K、P、Mg、Na和Co的排出量明显低于对照组,而其它矿物元素排出量与对照组无显著差异,尿中矿物质浓度无显著变化。 相似文献
90.
ABSTRACT: The depletion of ascorbic acid derivatives in fish feed during the feed processing (extrusion cooking and drying) was studied at five extrusion cooking temperatures and at 85°C for 2 h dryer processing temperature. Three ascorbic acid derivatives were used: L-ascorbyl-2-mono-phosphate Mg (APM), L-ascorbic acid sodium (AAS) and L-ascorbic acid palmitic acid ester (AAP). Samples were collected after drying and ascorbic acid derivatives losses evaluated. APM was found to be quiet stable with an average retention of 88%, but AAS and AAP were unstable and the depletion was very high. 相似文献