全文获取类型
收费全文 | 49630篇 |
免费 | 2789篇 |
国内免费 | 33篇 |
专业分类
林业 | 1756篇 |
农学 | 1680篇 |
基础科学 | 253篇 |
5950篇 | |
综合类 | 8301篇 |
农作物 | 1568篇 |
水产渔业 | 2763篇 |
畜牧兽医 | 26681篇 |
园艺 | 594篇 |
植物保护 | 2906篇 |
出版年
2019年 | 441篇 |
2018年 | 799篇 |
2017年 | 847篇 |
2016年 | 763篇 |
2015年 | 634篇 |
2014年 | 770篇 |
2013年 | 1773篇 |
2012年 | 1409篇 |
2011年 | 1761篇 |
2010年 | 1187篇 |
2009年 | 1124篇 |
2008年 | 1721篇 |
2007年 | 1637篇 |
2006年 | 1528篇 |
2005年 | 1408篇 |
2004年 | 1411篇 |
2003年 | 1396篇 |
2002年 | 1204篇 |
2001年 | 1918篇 |
2000年 | 1998篇 |
1999年 | 1505篇 |
1998年 | 572篇 |
1997年 | 500篇 |
1996年 | 453篇 |
1995年 | 616篇 |
1994年 | 526篇 |
1993年 | 461篇 |
1992年 | 1165篇 |
1991年 | 1214篇 |
1990年 | 1180篇 |
1989年 | 1101篇 |
1988年 | 1062篇 |
1987年 | 1085篇 |
1986年 | 1036篇 |
1985年 | 970篇 |
1984年 | 806篇 |
1983年 | 689篇 |
1982年 | 422篇 |
1981年 | 384篇 |
1979年 | 636篇 |
1978年 | 508篇 |
1977年 | 442篇 |
1976年 | 411篇 |
1975年 | 453篇 |
1974年 | 526篇 |
1973年 | 510篇 |
1972年 | 532篇 |
1971年 | 454篇 |
1970年 | 427篇 |
1969年 | 467篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
In this paper, a case of otitis media with effusion (‘glue ear’) is described in a Cavalier King Charles spaniel. Its presentation, diagnosis and surgical management by the insertion of a trans-tympanic ventilation tube (grommet) is discussed. 相似文献
162.
163.
164.
Distribution of Cytochrome P450-side Chain Cleavage in the Theca Interna Layers of Bovine Small Antral and Cystic Follicles 总被引:1,自引:0,他引:1
Cystic follicle is anovulatory follicular structure that is caused by an endocrine imbalance. The activity of cytochrome P450‐side chain cleavage (P450scc) is essential for the initiation of steroidogenesis in the follicle. The present study was designed to compare the frequency of cells containing P450scc between healthy and atretic small antral follicles, and among several types (I, II and III, classified based on the presence of granulosa layer) of cystic follicles. Paraffin sections of healthy (2–5 mm in diameter), atretic (2–5 mm) and cystic follicles (>25 mm) were immunohistochemically stained with rabbit polyclonal antibody to bovine P450scc. The P450scc‐positive cells were counted in four different regions of the follicles from the apical to the basal side. In small antral follicles and cystic follicles, P450scc‐positive cells were localized in the theca interna layers but not granulosa layers. The P450scc‐positive cell populations decreased in the late atretic follicles compared with the early and advanced atretic follicles at all the regions of follicle. Type III cystic follicles showed significantly lower frequencies of P450scc‐positive cells than those in the types I and II cystic follicles. These results suggest that in both small and cystic follicles in cows, total loss of granulosa cells may be associated with the reduction of frequency of P450scc‐positive cells in theca interna layer. 相似文献
165.
166.
167.
Sugarcane yields have been severely reduced by white leaf and grassy shoot phytoplasma diseases in many parts of Asia. Australian sugarcane crops are not known to be affected by these diseases, but plant pathogenic phytoplasmas found in other introduced and native grasses in northern Australia could pose a serious threat to the Australian sugarcane industry. To further evaluate this threat, leaves from plants of 20 grass species, with and without symptoms, were collected during field surveys in northern Australia and tested to determine whether phytoplasmas were present and whether symptoms were reliable indicators of phytoplasma presence. Molecular tools were used to detect and characterize phytoplasmas. Four different phytoplasmas were found in seven grass species known to grow near healthy sugarcane crops. All the phytoplasmas were closely related to sugarcane white leaf phytoplasma (SCWL), one of the phytoplasmas that causes disease in sugarcane in Asia. Four of the host plant species and two of the phytoplasmas were new records. The relationship between symptoms and phytoplasma presence was poor. Because some plants with symptoms tested negative for phytoplasmas, a series of surveys was carried out in which flowers, leaves, roots and stems of two known host plant species, Whiteochloa cymbiformis and Sorghum stipoideum, were tested separately on nine occasions during two wet seasons. This was done to investigate the distribution of phytoplasmas within plants over time. Results showed that spatial and temporal variation of phytoplasmas occurred in these two host plant species. Hence, evaluation of disease distribution within a region requires repeated testing of all plant parts from plants without symptoms, as well as those with symptoms. To date, there is no report of a vector capable of transmitting to Australian sugarcane the phytoplasmas found in grasses in this study. If one is present, or occurs in the future, then native and introduced grasses could constitute a large reservoir of phytoplasma for vectors to draw on. This work provides an early warning for the sugarcane industry that the potential for infection exists. 相似文献
168.
Chaiyan Kasorndorkbua Brad J. Thacker Patrick G. Halbur Denis K. Guenette Ryan M. Buitenwerf Ryan L. Royer Xiang-Jin Meng 《Canadian journal of veterinary research》2003,67(4):303-306
To determine the effect of swine hepatitis E virus (HEV) infection on pregnant gilts, their fetuses, and offspring, 12 gilts were intravenously inoculated with swine HEV. Six gilts, who were not inoculated, served as controls. All inoculated gilts became actively infected and shed HEV in feces, but vertical transmission was not detected in the fetuses. There was no evidence of clinical disease in the gilts or their offspring. Mild multifocal lymphohistiocytic hepatitis was observed in 4 of 12 inoculated gilts. There was no significant effect of swine HEV on fetal size, fetal viability, or offspring birth weight or weight gain. The offspring acquired anti-HEV colostral antibodies but remained seronegative after the antibodies waned by 71 days of age. Swine HEV infection induced subclinical hepatitis in pregnant gilts, but had no effect on the gilts' reproductive performance, or the fetuses or offspring. Fulminant hepatitis associated with HEV infection was not reproduced in gilts. 相似文献
169.
170.
G H Wentink S van Dijk S A Goedegebuure J Vos T Wensing 《The Veterinary quarterly》1992,14(4):159-160
A syndrome very similar to hepatic lipidosis is described in dairy cows during the dry period. After being sent to pasture the animals did not eat well for undetermined reasons. The disease phenomena were mainly observed in animals carrying twins. At post mortem examination severe falty infiltration was found in the 3 animals made available for post mortem examination. Increase of the energy supply to the dry cows by addition of maize silage to the ration prevented new cases. 相似文献