全文获取类型
收费全文 | 54748篇 |
免费 | 5661篇 |
国内免费 | 33篇 |
专业分类
林业 | 1822篇 |
农学 | 2057篇 |
基础科学 | 251篇 |
7015篇 | |
综合类 | 8200篇 |
农作物 | 1608篇 |
水产渔业 | 5036篇 |
畜牧兽医 | 29827篇 |
园艺 | 579篇 |
植物保护 | 4047篇 |
出版年
2020年 | 780篇 |
2019年 | 1397篇 |
2018年 | 1550篇 |
2017年 | 1646篇 |
2016年 | 1573篇 |
2015年 | 1335篇 |
2014年 | 1466篇 |
2013年 | 2590篇 |
2012年 | 1752篇 |
2011年 | 2107篇 |
2010年 | 1676篇 |
2009年 | 1321篇 |
2008年 | 1883篇 |
2007年 | 1648篇 |
2006年 | 1581篇 |
2005年 | 1454篇 |
2004年 | 1468篇 |
2003年 | 1448篇 |
2002年 | 1276篇 |
2001年 | 1978篇 |
2000年 | 2076篇 |
1999年 | 1504篇 |
1998年 | 570篇 |
1997年 | 512篇 |
1996年 | 454篇 |
1995年 | 615篇 |
1994年 | 529篇 |
1993年 | 464篇 |
1992年 | 1151篇 |
1991年 | 1212篇 |
1990年 | 1182篇 |
1989年 | 1101篇 |
1988年 | 1057篇 |
1987年 | 1081篇 |
1986年 | 1036篇 |
1985年 | 967篇 |
1984年 | 804篇 |
1983年 | 684篇 |
1982年 | 424篇 |
1979年 | 637篇 |
1978年 | 508篇 |
1977年 | 447篇 |
1976年 | 409篇 |
1975年 | 454篇 |
1974年 | 524篇 |
1973年 | 508篇 |
1972年 | 532篇 |
1971年 | 449篇 |
1970年 | 428篇 |
1969年 | 465篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
83.
84.
T. 《Forstwissenschaftliches Centralblatt》1898,20(2):66-72
Ohne Zusammenfassung 相似文献
85.
86.
J. P. T. Valkonen 《Potato Research》2007,50(3-4):251-254
87.
Metabolic and microbial responses in western crossbred and Meishan growing pigs fed a high-fiber diet 总被引:1,自引:0,他引:1
Four Duroc x White composite crossbred (21.8 +/- 1.0 kg BW) and four 12-wk-old Meishan purebred (20.7 +/- 1.6 kg BW) growing barrows were used to determine the relative breed differences in metabolic and microbial responses to a high-fiber diet. The pigs were trained to consume 700 g of a diet containing 35% (as-fed basis) dehydrated alfalfa meal once daily. The pigs' daily intakes of DM, N, GE, NDF, and ADF were 610 g, 16.6 g, 2.64 Mcal, 150 g, and 88 g, respectively. On d 12 after surgical catheterization of the portal vein, ileal vein, and carotid artery, a 3-d total urine and feces collection was conducted. On d 24 after surgery, each pig was placed in an open-circuit calorimeter, and its catheters were connected to a system for simultaneous measurements of oxygen consumption by portal-drained viscera and by whole body, and the net portal absorption of VFA after a 24-h fasting and during a 5-h postprandial period. The VFA measured included acetic, propionic, isobutyric, butyric, isovaleric, and valeric acids. A second 3-d total urine and feces collection was conducted on d 30 after surgery. There were no differences (P = 0.13) between the first and second collections in apparent total-tract digestibility coefficients for nutrients and N retention of pigs. Compared with Duroc x White composite crossbred pigs, Meishan pigs had lower (P = 0.05) apparent digestibility coefficients for DM, N, NDF, hemicellulose, and N retention, but their portal-drained viscera used a greater (P = 0.05) fraction of whole-body oxygen consumption. No differences (P = 0.12) were found between Duroc x White composite crossbred and Meishan pigs in total viable bacteria and cellulolytic bacteria from fecal samples, in vitro digestibility of alfalfa NDF fractions by fecal inocula, whole-body oxygen consumption, net portal absorption of VFA, total energy of absorbed VFA, and the potential of absorbed VFA for meeting the energy needs for whole-body heat production. These results indicate that, in contrast to previous beliefs, the ability of Meishan growing pigs to utilize a high-fiber diet is not superior to that of Duroc x White composite crossbred growing pigs. 相似文献
88.
Hartnack S Doherr MG Alter T Toutounian-Mashad K Greiner M 《Zoonoses and public health》2009,56(3):117-128
Campylobacter, a major zoonotic pathogen, displays seasonality in poultry and in humans. In order to identify temporal patterns in the prevalence of thermophilic Campylobacter spp. in a voluntary monitoring programme in broiler flocks in Germany and in the reported human incidence, time series methods were used. The data originated between May 2004 and June 2007. By the use of seasonal decomposition, autocorrelation and cross-correlation functions, it could be shown that an annual seasonality is present. However, the peak month differs between sample submission, prevalence in broilers and human incidence. Strikingly, the peak in human campylobacterioses preceded the peak in broiler prevalence in Lower Saxony rather than occurring after it. Significant cross-correlations between monthly temperature and prevalence in broilers as well as between human incidence, monthly temperature, rainfall and wind-force were identified. The results highlight the necessity to quantify the transmission of Campylobacter from broiler to humans and to include climatic factors in order to gain further insight into the epidemiology of this zoonotic disease. 相似文献
89.
Wildtype strains of Fusarium circinatum, the causal agent of pitch canker, were crossed to obtain an F1 generation. Progeny of this cross were tested for virulence by inoculating Pinus radiata seedlings, and were found to induce a wide range of lesion lengths. Two strains from the F1 generation that induced long lesions (= high virulence) were used as parents to produce an F2 generation, followed by a second round of selection for high virulence to obtain an F3 generation. Mean lesion lengths were not significantly different between the three generations (P ≥ 0.196). A parallel set of crosses was performed to select for low virulence by using progeny in the F1 and F2 generations that induced short lesions as parents for F2 and F3 generations, respectively. In this case, both rounds of selection resulted in a significant reduction in mean lesion length, from 33.8 ± 0.8 mm in the F1 generation, to 19.7 ± 0.7 and 12.9 ± 0.7 mm in the F2 and F3 generations, respectively. Thus it is apparent that F. circinatum retains the genetic capacity for avirulence to pines, which could reflect a lack of strong selection for virulence in nature. Progeny of a cross between high and low virulence parents manifested nearly continuous variation in lesion lengths, consistent with virulence being a quantitatively inherited trait. Based on this cross, broad‐sense heritability (H2) was determined to be 0.74, which suggests that virulence is under strong genetic control. 相似文献
90.
The conformation of the urethra, the position of the bladder neck and the distance between the external urethral orifice and the cranial pubic brim were compared in 30 continent and 30 incontinent bitches with incompetence of the urethral sphincter mechanism, using the measurements made from vagino-urethrograms. The bladder neck was significantly (P less than 0.001) further caudal in incontinent dogs than in continent dogs. Its position was not affected by neutering and could not be explained by the degree of urethral curvature. The distance from the external urethral orifice to the cranial pubic brim was correlated (P less than 0.001) with bodyweight but was not significantly different in the continent and incontinent bitches. In neutered animals, the distance between the cranial pubic brim and the external urethral orifice was significantly (P less than 0.05) shorter than in entire animals. 相似文献