全文获取类型
收费全文 | 2913篇 |
免费 | 70篇 |
国内免费 | 222篇 |
专业分类
林业 | 613篇 |
农学 | 658篇 |
基础科学 | 383篇 |
202篇 | |
综合类 | 1020篇 |
农作物 | 69篇 |
水产渔业 | 28篇 |
畜牧兽医 | 130篇 |
园艺 | 72篇 |
植物保护 | 30篇 |
出版年
2024年 | 3篇 |
2023年 | 25篇 |
2022年 | 36篇 |
2021年 | 53篇 |
2020年 | 48篇 |
2019年 | 64篇 |
2018年 | 49篇 |
2017年 | 90篇 |
2016年 | 98篇 |
2015年 | 85篇 |
2014年 | 110篇 |
2013年 | 149篇 |
2012年 | 210篇 |
2011年 | 178篇 |
2010年 | 149篇 |
2009年 | 155篇 |
2008年 | 153篇 |
2007年 | 185篇 |
2006年 | 184篇 |
2005年 | 173篇 |
2004年 | 157篇 |
2003年 | 149篇 |
2002年 | 128篇 |
2001年 | 84篇 |
2000年 | 73篇 |
1999年 | 65篇 |
1998年 | 46篇 |
1997年 | 31篇 |
1996年 | 41篇 |
1995年 | 37篇 |
1994年 | 41篇 |
1993年 | 28篇 |
1992年 | 23篇 |
1991年 | 23篇 |
1990年 | 21篇 |
1989年 | 22篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1976年 | 2篇 |
1956年 | 1篇 |
排序方式: 共有3205条查询结果,搜索用时 15 毫秒
1.
蒸压加气混凝土是一种新型的节能、环保墙体材料 ,它在基本建设中运用具有良好的综合经济效益和社会效益。这里以加气混凝土在建筑中的应用实例 ,从材料、施工、抹灰及存在的问题等方面论述了它的运用情况 ,可供有关设计和施工人员参考。 相似文献
2.
3.
本文论述了在工程建设中钢筋混凝土质量优劣的重要性,并结合当前施工中存在的一些问题,探讨了该采取的方法,以达到控制工程质量的目的。 相似文献
4.
5.
6.
7.
Capnographic documentation of nasoesophageal and nasogastric feeding tube placement in dogs 总被引:1,自引:0,他引:1
Paula A. Johnson DVM F. A. Mann DVM MS DACVS DACVECC John Dodam DVM MS PhD DACVA Keith Branson DVM MS DACVA Colette Wagner-Mann DVM PhD Mark A. Brady DVM Elizabeth Dunphy DVM 《Journal of Veterinary Emergency and Critical Care》2002,12(4):227-233
Objective: To evaluate the ability of capnography to document proper placement of nasoesophageal (NE) and nasogastric (NG) feeding tubes. This study was conducted in 3 phases. Phase I of this study was designed in order to test the efficacy of capnography to distinguish placement of a feeding tube in the alimentary tract versus the respiratory tract. Phase II was designed in order to document that carbon dioxide (CO2) could be measured through a polyvinyl chloride (PVC) feeding tube. Phase III was performed in order to evaluate the technique of continuous monitoring during insertion of the feeding tube into the esophagus and stomach as would be performed during a clinical‐tube placement. Design: Prospective study. Setting: Research laboratory. Animals: 24 adult dogs. Interventions: In Phase I, sedated dogs were instrumented with an intratracheal catheter and an 8 French feeding tube placed nasally into the distal esophagus and later advanced into the stomach. In Phase II, dogs were anesthetized and an 8 French feeding tube was placed down the endotracheal tube, then into the esophagus and later advanced into the stomach. In Phase III, sedated dogs were instrumented with an 8 French feeding tube inserted intranasally and then advanced to the level of the nasopharynx, distal esophagus and, lastly, the stomach. Fluoroscopy was used in order to determine location of the feeding tube. Measurements and main results: Phase I measurements included respiratory rate and CO2 from the trachea, esophagus, and stomach and pH of gastric fluid sample. Phase II measurements included respiratory rate and CO2 from the endotracheal tube, feeding tube in the endotracheal tube, feeding tube in the distal esophagus, and feeding tube in the stomach. Phase III data collection included respiratory rate and CO2 as the tube was passed through the nasal cavity, nasopharynx, esophagus and stomach. Phase I fluid samples were collected from 5 of the 9 dogs and had pH values from 1.68 to 4.20. In both phases, values for the respiratory rate and CO2 from the esophagus and stomach were 0 ± 0, significantly lower (P < 0.001) than the values from the trachea. In Phase II, there was no significant difference between the respiratory rates (P = 0.886) and CO2 (P = 0.705) readings obtained from the endotracheal tube compared to readings from the feeding tube in the endotracheal tube. In Phase III, there was a significant difference (P < 0.001) between the respiratory rates and CO2 readings obtained from the nasal cavity and the nasopharynx when compared to those readings obtained from the esophagus and stomach. Measurement of CO2 and respiratory rate resulted in a reading of 0 every time the feeding tube was in the esophagus or stomach. Conclusions: Capnography may be used in order to detect airway placement of NE and NG tubes. 相似文献
8.
9.
A semi-energy method to analyse the buckling behaviour of edge-stiffened plates under combined compression and bending is presented in this paper, One unloaded edge of the plate is restrained elastically against rotation and the other is stiffened by a st 相似文献
10.
本文在文献[1]基础上,运用金相,电化学方法研究了50Mn18Cr4电机护环钢依照QHJ-79试验标准在硝酸盐介质中应力腐蚀开裂(即SCC)的性质,结果指出,此体系中SCC的控制过程为阳极溶解。 相似文献