全文获取类型
收费全文 | 107936篇 |
免费 | 6041篇 |
国内免费 | 2808篇 |
专业分类
林业 | 5905篇 |
农学 | 6061篇 |
基础科学 | 2620篇 |
13432篇 | |
综合类 | 22130篇 |
农作物 | 4539篇 |
水产渔业 | 4949篇 |
畜牧兽医 | 48713篇 |
园艺 | 1775篇 |
植物保护 | 6661篇 |
出版年
2021年 | 1416篇 |
2020年 | 1386篇 |
2019年 | 1442篇 |
2018年 | 1624篇 |
2017年 | 2081篇 |
2016年 | 1879篇 |
2015年 | 1988篇 |
2014年 | 2271篇 |
2013年 | 4416篇 |
2012年 | 3693篇 |
2011年 | 4359篇 |
2010年 | 3335篇 |
2009年 | 3253篇 |
2008年 | 3983篇 |
2007年 | 3731篇 |
2006年 | 3787篇 |
2005年 | 3346篇 |
2004年 | 2660篇 |
2003年 | 2580篇 |
2002年 | 2430篇 |
2001年 | 3141篇 |
2000年 | 3328篇 |
1999年 | 2764篇 |
1998年 | 1422篇 |
1997年 | 1323篇 |
1996年 | 1236篇 |
1995年 | 1438篇 |
1994年 | 1304篇 |
1993年 | 1220篇 |
1992年 | 2234篇 |
1991年 | 2341篇 |
1990年 | 2144篇 |
1989年 | 2118篇 |
1988年 | 1976篇 |
1987年 | 2025篇 |
1986年 | 2032篇 |
1985年 | 1894篇 |
1984年 | 1499篇 |
1983年 | 1326篇 |
1979年 | 1370篇 |
1978年 | 1122篇 |
1977年 | 973篇 |
1976年 | 937篇 |
1975年 | 983篇 |
1974年 | 1272篇 |
1973年 | 1298篇 |
1972年 | 1234篇 |
1971年 | 1147篇 |
1970年 | 1087篇 |
1969年 | 964篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
45.
基于‘罗氏沼虾’养殖尾水灌溉条件下稻田养分利用效能提升技术研究 总被引:1,自引:0,他引:1
为了实现稻田消纳罗氏沼虾养殖尾水过程中水稻稳产及养分利用效率最大化,设置CK(空白对照)、BC(添加生物炭)、TG(添加土壤改良液)、BT(生物炭及土壤改良液分别减半)4个处理,依据养分运移状况及水稻生长指标的比较,筛选适宜材料类型。结果表明,BC、TG及BT的添加对表层土壤(0~10cm)TN累积、土壤(0~25cm)TP累积及养分损失,BC、TG对土壤(0~25cm)TN累积及养分损失均存在正面效应;TG显著促进表层土壤(0~10 cm)NO3 -累积(P<0.05);除BC外,其他材料的养分表聚作用均促使TN、TP向根部运移(P<0.05);BT处理中灌浆期叶绿素含量显著高于TG和CK(P<0.05),材料处理组在第一节间长度均显著低于CK(P<0.05),其余处理间的差异性均未达到显著水平(P>0.05)。各处理的理论和实际产量间的差异性均未达到显著水平(P>0.05)。综上所述,相较于其他材料,有效截留NO3 -为主氮素养分,提高养殖尾水养分利用率,降低淋洗污染风险;显著控制水稻底部节间生长,降低倒伏风险;且其对水稻生长及产量性状并无显著抑制作用,因而将其作为水稻消纳罗氏沼虾养殖尾水中养分利用效率提升材料具有一定应用潜力。 相似文献
46.
47.
Epidermal growth factor (EGF)-like activity was measured in mares' colostrum and milk by radioreceptor assay. Milk samples were collected from 22 mares 1 or more times during early lactation. Samples of colostrum were taken after parturition and before the foal first suckled (presuckle), within 6 hours after the foal first suckled (postsuckle), and on days 1, 2, 4, and 8 of lactation. In the 5 mares from which milk samples were obtained at each sampling time, presuckle colostral mean EGF-like activity (17.8 ng/ml) was greatest (P less than 0.05). The mean values for EGF-like activity at all other sampling times were not significantly different from each other (postsuckle colostrum, 9.7 ng/ml; day 1, 9.6 ng/ml; day 2, 8.5 ng/ml; day 4, 8.0 ng/ml; day 8, 7.8 ng/ml). 相似文献
48.
K A Hahn D W Knapp R C Richardson C L Matlock 《Journal of the American Veterinary Medical Association》1992,200(3):355-357
In 11 dogs with nasal adenocarcinoma, IV treatment with 2 to 8 cycles of cisplatin at a dosage of 60 mg/m2 of body surface, given at 3-week intervals, resulted in a survival time of 8 to 128 weeks (mean, 32.7 weeks; median, 20 weeks). Radiography revealed complete remission in 2 dogs and partial remission in 1 dog, for an overall response rate of 27%. Clinical problems such as nasal discharge (n = 11), sneezing (n = 6), and epistaxis (n = 4) resolved in 1 to 2 weeks in all dogs after beginning chemotherapy. 相似文献
49.
Historical and physical signs associated with prostatic disease diagnosed in dogs over a 5.5-year period were defined. One hundred seventy-seven male dogs were determined to have prostatic abnormality. Of the 177 dogs, 87 were determined to have specific prostatic disease. The most common prostatic disease identified in this study was bacterial prostatitis, followed by prostatic cyst, prostatic adenocarcinoma, and benign hyperplasia. The most common prostatic disease identified in neutered dogs was prostatic adenocarcinoma. Mean age at onset of prostatic disease was 8.9 years; statistically significant difference was not observed between age at onset of the various types of prostatic disease identified. Doberman Pinscher was the most common breed with prostate disease. Twenty-nine percent of dogs with a specifically identifiable prostatic disease had signs of systemic illness, 41% had signs of lower urinary tract disease, 28% had signs of gastrointestinal tract abnormalities, and 13% had signs of locomotor difficulty. 相似文献
50.
The influence of extruded oilseeds on total tract digestibility and ruminal digestion in dairy cows was studied in three cows fed a hay-concentrate (60.5/39.5; 3.7% fatty acids in diet on DM basis) control diet (C) or the same diet supplemented with raw (R) or extruded (ER) rapeseeds (8.0% fatty acids in diet DM). The experimental design was a 3 x 3 Latin square design. Compared with diet C, diets containing rapeseed decreased ruminal OM digestibility (9.5%, P less than .10) and increased (P less than .05) the proportion of propionate in ruminal fluid VFA. Extrusion had no effect on DM and OM total tract digestibilities and increased (P less than .10) N digestion. Microbial N flow at the duodenum was calculated taking into account solid-adherent bacteria (SAB) and liquid-associated bacteria (LAB). Duodenal flows of total, SAB, and LAB of OM and N did not change with diet. Extrusion of the rapeseeds did not modify (P less than .10) the proportion of bacterial N at the duodenum and had no effect on crude fiber digestibility. This trial demonstrates that rapeseeds in hay-based diets can be fed at levels of up to 14% of the diet without adversely affecting crude fiber digestibility. 相似文献