全文获取类型
收费全文 | 135857篇 |
免费 | 7400篇 |
国内免费 | 84篇 |
专业分类
林业 | 5181篇 |
农学 | 4034篇 |
基础科学 | 847篇 |
14769篇 | |
综合类 | 28206篇 |
农作物 | 5447篇 |
水产渔业 | 6154篇 |
畜牧兽医 | 68725篇 |
园艺 | 1620篇 |
植物保护 | 8358篇 |
出版年
2018年 | 1569篇 |
2017年 | 1778篇 |
2016年 | 1688篇 |
2015年 | 1465篇 |
2014年 | 1755篇 |
2013年 | 4841篇 |
2012年 | 3425篇 |
2011年 | 4070篇 |
2010年 | 2656篇 |
2009年 | 2599篇 |
2008年 | 3957篇 |
2007年 | 3838篇 |
2006年 | 3709篇 |
2005年 | 3565篇 |
2004年 | 3325篇 |
2003年 | 3476篇 |
2002年 | 3295篇 |
2001年 | 3914篇 |
2000年 | 3820篇 |
1999年 | 3118篇 |
1998年 | 1377篇 |
1997年 | 1302篇 |
1995年 | 1411篇 |
1994年 | 1325篇 |
1993年 | 1271篇 |
1992年 | 2756篇 |
1991年 | 2845篇 |
1990年 | 2841篇 |
1989年 | 2969篇 |
1988年 | 2667篇 |
1987年 | 2725篇 |
1986年 | 2811篇 |
1985年 | 2715篇 |
1984年 | 2225篇 |
1983年 | 1959篇 |
1982年 | 1435篇 |
1981年 | 1294篇 |
1979年 | 1998篇 |
1978年 | 1643篇 |
1977年 | 1454篇 |
1976年 | 1337篇 |
1975年 | 1515篇 |
1974年 | 1919篇 |
1973年 | 1901篇 |
1972年 | 1918篇 |
1971年 | 1836篇 |
1970年 | 1722篇 |
1969年 | 1542篇 |
1968年 | 1219篇 |
1967年 | 1382篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The design, construction and use of a device to detect changes in deer pedicle volume are described. The device is highly sensitive for detecting the initiation of pedicle growth. Between-sample differences of 170 mm3 in the pedicle volume of live deer were detected (triplicate measurements) using the detector; these correspond to a change in height of the pedicle of at most 0.67 mm. The within sample coefficient of variation was 1.4%. The pedicle growth detector enables more precise measurements to be obtained for identifying the onset of pedicle development to the nearest week than is currently possible with palpation. 相似文献
992.
993.
Populations of intracellular symbiotes declined significantly in brachypterous females of the brown planthopper,Nilaparvata lugens (Stål), which were stressed during nymphal development by caging them on IR20 rice plants treated with 3% neem oil, 5% neem seed kernel aqueous extract, or 10% neem cake aqueous extract. In addition, nymphs grew poorly and symbiote populations in prospective females declined, when reared on rice plants grown in soil treated with neem cake; this indicates systemic action of bioac-tive neem constituents. Addition of custard-apple oil to neem oil did not enhance the inhibitory effects. The effects of neem derivatives on the symbiotes may be either host-mediated — possibly through disturbed neuroendocrine homeostasis, or direct — leading to perturbations of host-symbiote equilibrium. 相似文献
994.
1. Brown egg laying pullets were transferred from an 8‐h photoperiod to an 8‐, 10‐, 13‐ or 16‐h photoperiod at 6, 9, 12, 15, 18 or 20–3 weeks of age. Plasma luteinising hormone (LH) concentrations were measured at transfer and 7 and 14 d afterwards.
2. Significant increases in plasma LH occurred following light stimulations at 6, 9 and 12 weeks of age.
3. Changes in LH concentration 7 d after a light increase from 8 h to 8, 10, 13, 16 h were highly correlated with photoperiod length at 9 and 12 weeks of age.
4. Changes in LH were generally poorly correlated with age at sexual maturity, although the reduced influence on age at first egg of a light increase given close to sexual maturity was reflected in minimal LH responses at 18 and 20.3 weeks. 相似文献
995.
Chicken anaemia virus was isolated for the first time in New Zealand from the New Zealand domestic chicken population. The virus was recovered from diseased birds in five separate flocks of broiler chickens aged between 14 and 33 days of age. Six isolates were obtained from bone marrow and lymphoid tissues using the MDCC-MSB1 cell line derived from Marek's disease lymphoma. All isolates were resistant to chloroform and survived exposure to 70 degrees C for 5 minutes. The main clinical features consistently associated with the disease outbreaks were increased mortality, yolk sac infections, sub-cutaneous haemorrhages and atrophy of the thymus. Fungal pneumonia occurred in two flocks, and gangrenous dermatitis as a result of bacterial infection in another flock. Microscopic examination showed atrophy of the thymus, reduced medullary haematopoiesis and inflammation resulting from secondary infections. 相似文献
996.
997.
Seedlings of three families of jack pine (Pinus banksiana Lamb.) were subjected to 16 combinations of photoperiod, growth environment (outdoors, greenhouse and biotron) and gibberellin (GA(4/7)) treatment. After 14 months, which included two dormancy induction periods, ovulate flowering was observed. There was a strong positive correlation between flowering and seedling height; female flower production was stimulated by both a declining photoperiod during bud development and GA(4/7) treatment; and there was an interaction between GA(4/7) treatment and family, such that the difference in flowering intensity between a late-flowering and an early-flowering family was eliminated by GA(4/7) treatment. The results suggest that the genetic control over the time of onset of flowering, and GA(4/7)-induction of flowering depend on a common mechanism. 相似文献
998.
999.
1000.