全文获取类型
收费全文 | 698篇 |
免费 | 38篇 |
国内免费 | 24篇 |
专业分类
林业 | 102篇 |
农学 | 80篇 |
基础科学 | 21篇 |
135篇 | |
综合类 | 181篇 |
农作物 | 58篇 |
水产渔业 | 21篇 |
畜牧兽医 | 144篇 |
园艺 | 12篇 |
植物保护 | 6篇 |
出版年
2024年 | 6篇 |
2023年 | 16篇 |
2022年 | 21篇 |
2021年 | 40篇 |
2020年 | 18篇 |
2019年 | 15篇 |
2018年 | 17篇 |
2017年 | 20篇 |
2016年 | 23篇 |
2015年 | 25篇 |
2014年 | 21篇 |
2013年 | 38篇 |
2012年 | 45篇 |
2011年 | 36篇 |
2010年 | 23篇 |
2009年 | 35篇 |
2008年 | 33篇 |
2007年 | 36篇 |
2006年 | 45篇 |
2005年 | 24篇 |
2004年 | 24篇 |
2003年 | 18篇 |
2002年 | 12篇 |
2001年 | 13篇 |
2000年 | 18篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 12篇 |
1996年 | 17篇 |
1995年 | 11篇 |
1994年 | 8篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 9篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有760条查询结果,搜索用时 15 毫秒
1.
2.
Zong-Qing Huo Feng Zhu Xing-Wang Zhang Xiao Zhang Hong-Bao Liang Jing-Chun Yao Zhong Liu Gui-Min Zhang Qing-Qiang Yao Guo-Fei Qin 《Marine drugs》2022,20(5)
Flexible marine natural products (MNPs), such as eribulin and bryostatin, play an important role in the development of modern marine drugs. However, due to the multiple chiral centers and geometrical uncertainty of flexible systems, configuration determinations of flexible MNPs face great challenges, which, in turn, have led to obstacles in druggability research. To resolve this issue, the comprehensive use of multiple methods is necessary. Additionally, configuration assignment methods, such as X-ray single-crystal diffraction (crystalline derivatives, crystallization chaperones, and crystalline sponges), NMR-based methods (JBCA and Mosher’s method), circular dichroism-based methods (ECCD and ICD), quantum computational chemistry-based methods (NMR calculations, ECD calculations, and VCD calculations), and chemical transformation-based methods should be summarized. This paper reviews the basic principles, characteristics, and applicability of the methods mentioned above as well as application examples to broaden the research and applications of these methods and to provide a reference for the configuration determinations of flexible MNPs. 相似文献
3.
为了探究长江十年禁渔后安庆江段刀鲚的生境履历,利用X射线电子探针微区分析技术研究安庆江段不同类型长颌刀鲚(Coilia nasus)和短颌刀鲚的耳石Sr和Ca微化学特征。结果显示,根据耳石Sr/Ca值的变化值将安庆江段的短颌刀鲚分为2类,一类是其比值为一直小于3.0的低值,表明其纯淡水的生境履历;另一类是其比值不仅有小于3.0的低值区,还有大于3.0的高值区(小于7.0),表明其不仅有淡水的生境履历,还有高盐度的河口半咸水生境履历。长颌刀鲚的耳石Sr/Ca值均具有小于3.0的低值区和大于3.0 (甚至大于7.0)高值区的显著波动,表现为典型的淡水、河口半咸水及海水的溯河洄游型生境履历,Sr含量面分析图谱也可印证上述结果。本研究表明,长江安庆江段刀鲚群体组成较为复杂,同时存在溯河洄游型、淡水定居型短颌刀鲚和溯河洄游型长颌刀鲚3种生态表型个体。 相似文献
4.
5.
目的探讨螺旋CT在胃肠道穿孔定位诊断中的价值。方法对32例手术证实成人胃肠道穿孔病人进行回顾性分析。结果32例患者中,胃、十二指肠球部穿孔20例,十二指肠腹膜后段穿孔1例,空回肠穿孔6例,阑尾穿孔3例,结肠穿孔2例。提示穿孔部位CT征象有:气腹、腹膜腔及腹膜后间隙积液、穿孔部位局限性肠壁增厚和周围脂肪间隙模糊。结论螺旋CT不仅能确定有无胃肠道穿孔,而且能初步判断其穿孔部位。其中局限性肠壁增厚及周围脂肪间隙密度增高、邻近腹腔、腹膜后间隙积液为诊断穿孔部位较为特异性征象。 相似文献
6.
随着宠物诊疗技术和设备的逐渐完善,一些宠物体内外的肿瘤可以通过X光和B超得以发现,并通过病理切片判定肿瘤的性质和可能的生发细胞,为宠物肿瘤病的研究提供临床资料。本文就是对临床检查怀疑患腹腔恶性肿瘤的金毛,采取腹部X光摄影结合B超诊断为肝癌病例的报告,为以后相关病例的诊断和对肿瘤的发生率的统计提供参考。 相似文献
7.
Pierre-Olivier Godart Yannick Ruel Mileva Bertal Shanti Esmieu Vassiliki Gouni Albert Agoulon Hugues Gaillot 《Veterinary radiology & ultrasound》2023,64(2):173-182
Thoracic radiography is commonly used to assess the size of the heart and diagnose cardiac disease in ferrets. Several standardized radiographic heart size indicators have been introduced in this species and values in healthy ferrets have been reported. To date, none of these indicators has been tested in ferrets with cardiac disease. The aim of this prospective and retrospective, analytical observational design study was to assess the accuracy of the modified vertebral heart score (mVHS) and the cardio-vertebral ratio (CVR) in the radiographic detection of cardiomegaly in ferrets. Thoracic radiographs of 24 ferrets with confirmed heart diseases, 22 ferrets with non-cardiac diseases and normal-sized hearts on echocardiogram, and 24 healthy ferrets were mixed and examined by three independent and blinded radiologists who measured mVHS and CVR in right lateral (RL) and ventrodorsal (VD) radiographs. For all readers, ferrets with cardiac disease had significantly higher mVHS and CVR than ferrets without cardiac disease on echocardiography. Optimal cut-points for predicting cardiac enlargement were 6.25 vertebrae and 7.25 vertebrae for RL-mVHS and VD-mVHS, and 1.58 and 1.80 for RL-CVR and VD-CVR, respectively. Using these cut-points, the accuracy was good for indicators measured in RL radiographs (92.9% for RL-mVHS; 91.4% for RL-CVR) and moderate for indicators measured in VD radiographs (88.6% for VD-mVHS; 85.7% for VD-CVR). Findings supported the use of mVHS and CVR for evaluating the size of the heart in diseased ferrets, with caution in values interpretation when pericardial fat prevents precise delineation of the cardiac silhouette contour especially on VD radiographs. 相似文献
8.
A method of measuring eyeglass lens power is proposed. A position detector and 3 beams of ray are used to measure the prismatic, spherical and astigmatic powers. Based on the method, an automatic focimeter with simple structure can be developed. The measure errors of prismatic and spherical powers are analyzed, from which it is concluded that the precision of the position detector is the key to the method. 相似文献
9.
Chen Jingqiu 《保鲜与加工》1992,(2):26-31
By the use of a numerical scheme of chisnell-Chester-Whitham Method (CCW), some numerical solutions to the problems of shock wave focusing are completed successfully and simply. 相似文献
10.
液滴法[1]是制作薄膜样品的最简单方法,本文介绍了使用该方法制作薄膜样品的具体步骤.由于样品在自然蒸发过程中具有结晶效应,使得最终形成的样品极不均匀.如果使用这种样品刻度系统的灵敏度曲线,样品的不均匀性会引起严重的实验误差.利用使用X光会聚透镜的XRF系统[2]形成的小束斑,可对样品的均匀度进行分析.另外文中给出了在使用此种样品刻度系统灵敏度曲线时,消除样品不均匀性引起误差的方法. 相似文献