全文获取类型
收费全文 | 92512篇 |
免费 | 5878篇 |
国内免费 | 100篇 |
专业分类
林业 | 3936篇 |
农学 | 3724篇 |
基础科学 | 669篇 |
11784篇 | |
综合类 | 13948篇 |
农作物 | 3470篇 |
水产渔业 | 5155篇 |
畜牧兽医 | 48649篇 |
园艺 | 1220篇 |
植物保护 | 5935篇 |
出版年
2020年 | 765篇 |
2019年 | 1030篇 |
2018年 | 1711篇 |
2017年 | 1969篇 |
2016年 | 1767篇 |
2015年 | 1520篇 |
2014年 | 1832篇 |
2013年 | 3860篇 |
2012年 | 3096篇 |
2011年 | 3762篇 |
2010年 | 2513篇 |
2009年 | 2462篇 |
2008年 | 3619篇 |
2007年 | 3362篇 |
2006年 | 3272篇 |
2005年 | 2805篇 |
2004年 | 2660篇 |
2003年 | 2677篇 |
2002年 | 2418篇 |
2001年 | 3469篇 |
2000年 | 3410篇 |
1999年 | 2636篇 |
1998年 | 1029篇 |
1997年 | 1097篇 |
1996年 | 928篇 |
1995年 | 1060篇 |
1994年 | 914篇 |
1993年 | 916篇 |
1992年 | 1881篇 |
1991年 | 1959篇 |
1990年 | 1892篇 |
1989年 | 1877篇 |
1988年 | 1631篇 |
1987年 | 1610篇 |
1986年 | 1641篇 |
1985年 | 1540篇 |
1984年 | 1233篇 |
1983年 | 1041篇 |
1982年 | 718篇 |
1979年 | 1064篇 |
1978年 | 820篇 |
1975年 | 815篇 |
1974年 | 898篇 |
1973年 | 866篇 |
1972年 | 806篇 |
1971年 | 799篇 |
1970年 | 802篇 |
1969年 | 782篇 |
1968年 | 708篇 |
1967年 | 738篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
The biology of latent infection by bovine herpesvirus 2 (BoHV-2), the agent of mammillitis in cows, remains largely unknown. We herein report attempts to reactivate the latent infection and investigated the sites of BoHV-2 latency in experimentally infected sheep. Ewes inoculated with BoHV-2 in the udder’s skin shed virus for up to five days, developed mammillitis and seroconverted. However, attempts to reactivate latent infection by dexamethasone administration at day 40 pi failed. Nevertheless, viral DNA - and not infectious virus - was detected by PCR in several nerve ganglia and/or regional lymph nodes (LNs) of all animals at day 40 post-reactivation. Likewise, lambs previously inoculated with BoHV-2 in the nose harbored latent viral DNA in trigeminal ganglia, tonsils and regional LNs. These results demonstrate that BoHV-2 establishes latent infection in nerve ganglia and in regional lymphoid tissues, yet virus reactivation is not easily achieved by standard protocols used. 相似文献
212.
A batch-wise small-scale wet-processing laboratory for whole wheat kernel has been designed and constructed to produce wheat starch and gluten from wheat grains. Hard red winter wheat kernels were steeped in three steeping media: SO2 solution, lactic acid, and hydrochloric acid. Acid concentrations of 0.1, 0.3, and 0.5%, were used for SO2 solutions and hydrochloric acid, and 0.1, 0.6, and 3.0% for lactic acid. After 16, 20, and 24 hr of steeping, the wheat was wet-milled. Yields and protein contents of wet-milling fractions were compared. Both high concentration of steeping media and long steeping time increased the starch yield and decreased the protein contents of the starch. However, the steeping time and acid concentration could be reduced from 24 to 20 hr and from 0.5 to 0.3%, respectively, without any statistically significant difference in starch yields or protein contents of the starch. Consistency and color of the starch were affected by both steeping time and acid concentrations of steeping media. 相似文献
213.
214.
J. Jiang L. Feng Y. Liu W.‐D. Jiang K. Hu S.‐H. Li X.‐Q. Zhou 《Aquaculture Nutrition》2014,20(6):731-740
Glutaminase (GLS) is the key enzyme of glutamine (Gln) metabolism and utilization. In this study, a cDNA encoding GLS protein was identified from common carp Cyprinus carpio intestine. The open reading frame of GLS cDNA encodes a polypeptide of 595 amino acids, which shows a high similarity with its zebrafish Danio rerio counterpart. Bioinformatic analysis showed the protein belongs to kidney‐type GLS. The putative protein has glutaminase domain and ankyrin repeats domain, which are highly conserved among vertebrate orthologues. Real‐time quantitative PCR analysis revealed that the abundance of GLS mRNA was the highest in the white muscle, followed by the brain, eyeball and pituitary. Glutaminase was ubiquitously expressed in all intestinal segments of common carp. The activity of GLS did not distribute uniformly along the entire length of the intestine. In primary culture enterocyte, and the expression of GLS mRNA is up‐regulated quickly and effectively by Gln. 相似文献
215.
Summary Nucleus substitution of Brassica japonica (2n=20) with Raphanus sativus (2n=18) was carried out by means of repeated backcrossing of Brassicoraphavus (2n=37) to R. sativus as a pollen donor. In the course of nucleus substitution, chlorophyll deficiency appeared. Plants with more than 28 chromosomes, like their parents, had green leaves and those with 24 to 26 chromosomes had yellowish green ones. Almost all plants with 18 to 23 chromosomes showed yellow or whitish yellow. The R. sativus with B. japonica cytoplasm (2n=18) was obtained after four successive backerosses. The completely substituted R. sativus showed the same fertility as the true R. sativus used as a recurrent parent. It is assumed that the chlorophyll deficiency is caused by disharmony between the B. japonica cytoplasm and the R. sativus nucleus. The chlorophyll deficiency is discussed in comparison with male sterility or other characters which sometimes occur in alloplasmic Raphanus and Brassica species. 相似文献
216.
217.
218.
S. Skov Hansen C. Mattei H. Treffenberg Pettersson M. Grabski 《Equine Veterinary Education》2021,33(11):e433-e437
This report describes successful surgical correction and long-term survival of a case of large colon atresia in a 24-h-old Warmblood colt, referred with signs of unrelenting abdominal pain and a suspicion of meconium impaction. Radiographic and ultrasonographic examination was indicative of large colon meconium impaction with secondary ileus. Due to deterioration of the foal, surgery was recommended. An atretic segment was found between the left ventral and dorsal large (ascending) colon. A band of fibrous tissue with no identifiable lumen connected the segments. Surgical correction was done by performing a stapled side-to-side anastomosis. Twelve days after surgery, the foal was discharged. Twenty-two months after discharge, the owner reported the foal developing as expected compared with its peers, but had a mild, self-limiting episode of colic at 20 months of age. 相似文献
219.
220.
The quantity of water available for irrigation is getting scarce in many countries and it assumes great importance for assured crop production, especially in view of the erratic behavior of the monsoon. Thus, there is a pressing need to improve the water efficiency of irrigation systems. One-way of improving the efficiency of the irrigation system is reusing the return flow from the irrigation system. This task requires quantification of return flow, which still remains as a grey area in irrigation water management. The estimation of return flow from the irrigation system is usually obtained using thumb rules depending upon the site-specific conditions like command area conditions and soil properties. In this paper, a hierarchical modeling technique, namely, regression tree is developed for return flow estimation. Regression tree is built through binary recursive partitioning. The effective rainfall, inflow, consumptive water demand, and percolation loss are taken as predictor variables and return flow is treated as the target variable. The applicability of the hierarchical model is demonstrated through a case study of Periyar-Vaigai Irrigation System in Tamil Nadu, India. The model performance shows a good match between the simulated and the field measured return flow values. Results of statistical analysis indicated that the correlation coefficients are high for both single as well as double crop seasons. 相似文献