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991.
992.
An experiment was conducted to test the hypothesis that for cows with high levels of milk yield, rotational grazing produces higher milk yields than continuous grazing. The comparison of grazing systems was made at two levels of milk yield (initially 20·3 and 32·5 kg d?1), and interactions with sward height and concentrate level were also examined. The study used 48 multiparous Holstein Friesian cows over a period of 62 d. Mean milk yield, its persistency and composition, live weight, body condition score and liveweight gain were not significantly affected by grazing system at either level of milk yield. There were no significant interactions between grazing system and sward height or concentrate level for any milk production measurement. Mean estimated herbage and total dry matter (DM) intake (P < 0·01), grazing time (P < 0·05) and ruminating time (P < 0·01) were significantly greater on the continuous grazing system. The cows in the higher milk yield group and those grazed at the higher sward height had a significantly (P < 0·05) higher estimated daily herbage DM intake and rate of herbage intake on the continuous grazing system than those on the rotational grazing system. There was no evidence to support the hypothesis that rotational grazing systems support higher levels of milk production than continuous grazing for cows of high milk yield. The shorter grazing time on the rotational grazing system indicated that cows may anticipate the timing of the daily movement of the electric fence, and this reduces their time spent grazing residual herbage. 相似文献
993.
994.
不同种源杉木幼苗早期造林生长状况比较分析 总被引:1,自引:0,他引:1
该文以1.5代种子实生苗、2代种子实生苗、3代种子实生苗、延平种子苗、顺昌无性系5种不同类型的杉木优良材料为研究对象,在南平延平区林地泛自然条件下进行了早期造林生长比较试验。调查分析结果表明,2代、3代种子苗的树高、地径生长在前2a略占优势;2a后,1.5代种子苗逐渐表现出优势,而顺昌无性系不论是树高、地(胸)径,还是单株材积,在参试的5种杉木材料中表现都不及其他。据此推断,延平种子苗可能更适宜南平延平区生长,其次是1.5代种子苗,但仍需继续跟踪调查。 相似文献
995.
Summary This second paper of the review describes the development of the potato tuber and whole plant based on research data and literature.
The development and growth, daily changes of fresh and dry matter, and of the contents of organic and inorganic components
(dry matter, starch, sugars, organic acids, ascorbic acid, nitrogenous compounds, nitrate, crude lipid, glycoalkaloids, P,
K, Ca, Mg, Mn, Na), discolouration indices, and physiological parameters (rate of assimilation and respiration, activity of
enzymes) are reviewed. 相似文献
996.
997.
Two factorial design experiments were carried out in the spring of 1994 and 1995, each of 6 weeks, to quantify the effects of sward height (SH), concentrate level (CL) and initial milk yield (IMY) on milk production and grazing behaviour of continuously stocked dairy cows. In Experiment 1, forty‐five Holstein Friesian cows were in five groups with initial milk yields of 16·9, 21·1, 28·0, 31·5 and 35·5 kg d–1, grazed sward heights were 3–5, 5–7 and 7–9 cm (LSH, MSH and HSH respectively), and concentrates were fed at rates of 0, 3 and 6 kg d–1. In Experiment 2, 48 cows were in two groups with IMY of 21·3 and 35·5 kg d–1, grazed sward heights were 3–5 and 7–9 cm (LSH and HSH), and concentrates were fed at 0 and 6 kg d–1 and ad libitum. Multiple regression models were used to quantify the effects of the three variables on milk yield persistency (MYP), estimated herbage dry‐matter (DM) intake (HDMI), grazing time (GT) and rate of DM intake (RI). The partial regression coefficients showed that increased SH led to increased MYP (Experiment 1 P < 0·001, Experiment 2 P < 0·05), increased HDMI (P < 0·01, P < 0·01), increased GT (P < 0·001, P < 0·05) and increased RI (P < 0·001, P < 0·05). Increasing CL led to increased MYP (NS, P < 0·001), decreased HDMI (P < 0·001, P < 0·001), decreased GT (NS, P < 0·001) and decreased RI (P < 0·001, P < 0·001). Higher IMY level of cows decreased MYP (P < 0·001, P < 0·001), increased HDMI (P < 0·001, P < 0·001), increased GT (P < 0·001, P < 0·05) and increased RI (P < 0·05, P < 0·01). The models were highly significant (P < 0·001), and accounted for 0·48–0·87 of the total variance. The partial regression coefficients quantified the extent to which GT and RI by cows respond positively to higher IMY, and negatively to increased CL, but respond differently (GT declines in response to a higher RI) with increasing SH. 相似文献
998.
利用三年分期播种试验资料,通过统计分析,说明株高可以作蓖麻营养生长(生长量)的生态指标,以此建立了蓖麻株高增长过程的标准模式.着重分析了气温、日照、降水等气象因子对株高增长的影响,确定了与株高增长有关的气象指标. 相似文献
999.
间伐是最有效、最常用的森林调控措施,研究间伐对直径生长的影响及直径分布动态,可为科学制定经营措施及森林精准经营提供技术依据。本研究以塞罕坝华北落叶松人工纯林(幼龄林、中龄林、近熟林)为研究对象,每种龄组设置间伐和对照样地各3块,共18块,基于2014-2018年直径数据,采用单因素方差分析和三参数Weibull分布,探究间伐后不同龄组林分直径生长规律。结果表明:(1)间伐促进了不同龄组华北落叶松的直径生长,间伐样地后2年直径生长量明显大于前2年(P<0.05),对照样地则差异不显著(P>0.05);间伐对林分直径生长量的促进作用表现为:中龄林>幼龄林>近熟林。(2)不同龄组间伐和对照样地的直径分布均符合三参数Weibull分布,且中龄林的拟合效果最好;2014-2018年,间伐样地的拟合参数c趋近于3.6,直径分布趋于对称分布,对照样地则变化不大。(3)间伐样地后2年林分直径分布曲线较前2年向右移动距离大,幼龄林的直径分布由右偏趋于对称,中龄林、近熟林则由左偏趋于对称。总之,间伐可有效促进华北落叶松幼龄林、中龄林、近熟林的直径生长,对中龄林的生长促进作用最强。 相似文献
1000.