全文获取类型
收费全文 | 2406篇 |
免费 | 79篇 |
国内免费 | 106篇 |
专业分类
系统科学 | 90篇 |
丛书文集 | 81篇 |
教育与普及 | 42篇 |
理论与方法论 | 4篇 |
现状及发展 | 14篇 |
研究方法 | 9篇 |
综合类 | 2350篇 |
自然研究 | 1篇 |
出版年
2024年 | 18篇 |
2023年 | 23篇 |
2022年 | 35篇 |
2021年 | 52篇 |
2020年 | 33篇 |
2019年 | 19篇 |
2018年 | 25篇 |
2017年 | 37篇 |
2016年 | 38篇 |
2015年 | 48篇 |
2014年 | 81篇 |
2013年 | 86篇 |
2012年 | 93篇 |
2011年 | 111篇 |
2010年 | 93篇 |
2009年 | 143篇 |
2008年 | 131篇 |
2007年 | 149篇 |
2006年 | 116篇 |
2005年 | 117篇 |
2004年 | 111篇 |
2003年 | 81篇 |
2002年 | 88篇 |
2001年 | 76篇 |
2000年 | 72篇 |
1999年 | 91篇 |
1998年 | 92篇 |
1997年 | 81篇 |
1996年 | 78篇 |
1995年 | 66篇 |
1994年 | 49篇 |
1993年 | 42篇 |
1992年 | 46篇 |
1991年 | 45篇 |
1990年 | 39篇 |
1989年 | 23篇 |
1988年 | 21篇 |
1987年 | 13篇 |
1986年 | 23篇 |
1985年 | 3篇 |
1982年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有2591条查询结果,搜索用时 500 毫秒
231.
Duan Jinqing Zhang Xinian Liu Hongbin Liu Zheng Liu Guozhen Lu Hongrnin Liu Junxin Ge Rili 《中国工程科学》2006,4(2):187-191
Study Objective : To evaluate the treatment effect of HAPE with HBO in situ at an extreme altitude of 4636 m. To investigate the relationship between pulmonary hypertension (PH) and HAPE. To emphasize the importance of the treatment in situ. Methods: The 32 patients from the plateau of 4636 - 5130 m (the barometric pressure: 57.41 - 53.28 kPa/431.6 - 400.6 mmHg(1 mmHg = 133.3224 Pa), the partial pressure of oxygen: 12.0 - 11.6 kPa/90.0 - 87.0 mmHg) were treated in situ of 4636 m altitude with HBO. Before and after the treatment, the clinical symptoms / signs, radiographic evidence, SaO2, and MPAP were compared. Results: The clinical symptoms/signs, and all the targets of the patients were improved dramatically (p 〈 0.001). Conclusions: Treating HAPE with HBO is the most effective method among various therapies in situ at an extreme altitude. The pulmonary -artery pressure was significantly decreased. All eases showed improved immediately. Among the subjects, 11 eases (34.3 %) were cured at once. The therapy made it possible for patients to get further treatment at a lower altitude area with prospective good results. We suggested that treating HAPE with HBO should be the first choice in situ. There must be PH in the patients of HAPE, but the reverse is not the true. The PH is a mechanism of normal compensation of the body exposing in the hypoxie environment. It is very necessary for us to explore the threshold of PH when a HAPE happens. 相似文献
232.
综合多种健美操教学方法,分析其优劣,提出在健美操教学中应当根据教学目的、内容与教学对象,适时调整教学方法,以发挥每种教学方法的优势,提高教学效果. 相似文献
233.
Jing Li XiaoMan Liu YueTong Ji ZhenHui Qi Yan Ge JiaYun Xu JunQiu Liu GuiMin Luo JiaCong Shen 《科学通报(英文版)》2008,53(16):2454-2461
Glutathione peroxidase (GPx, EC1.11.1.9), an important anti-oxidative selenoenzyme, can catalyze the reduction of harmful hydroperoxides with concomitant glutathione, thereby protecting cells and other biological issues against oxidative damage. It captures considerable interest in redesign of its function for either the mechanism study or the pharmacological development as an antioxidant. In order to develop a general strategy for specifically targeting and operating selenium in active sites of enzymes, the catalytically essential residue selenocysteine (Sec) was first successfully bioincorporated into the catalytic center of subtilisin by using an auxotrophic expression system. The studies of the catalytic activity and the steady-state kinetics demonstrated that selenosubtilisin is an excellent GPx-like biocatalyst. In comparison with the chemically modified method, biosynthesis exhibits obvious advantages: Sec could be site-directly incorporated into active sites of enzymes to overcome the non-specificity generated by chemical modification. This study provides an important strategy for specifically targeting and operating selenium in the active site of an enzyme. 相似文献
234.
Ge Changchun Xia Yttanluo Chen Limin Laboratory of Special Ceramics Powder Metallurgy 《北京科技大学学报》1991,(Z2)
Si3N4 ceramics with AZ-type non-toxic, non-oxide additives canbe highly densified. In this work densification behavior and mechanism ofSi3N4 with AZ-type additives were investigated. 相似文献
235.
本研究对英国沙能山羊的杂种,进行了长达十数年的系列研究,不仅测定了一、二、三代杂种羊从初生到成年8个主要阶段的生长发育特点,而且将处于同等饲养条件下的父、母系品种作为对照,进行了同样测定,从而揭示了各代杂种羊的生长发育规律和体重体尺等性状的遗传特点。 相似文献
236.
大学新生心理健康状况的调查分析 总被引:6,自引:0,他引:6
使用SCL-90评定长沙大学2001级新生的心理健康状况。结果显示,有10.9%的新生存着各种明显的心理健康问题。男女学生、本专科学生之间心理健康水平存在显著差异。 相似文献
237.
238.
YU Ge ZHENG Yiqun & KE Xiankun . Nanjing Institute of Geography Limnology Chinese Academy of Sciences Nanjing China . Institute of Meteorology the Chinese People’s Liberation Army Uni- versity of Sciences Technology Nanjing China . Department of Geography University of Regina SK SSA Canada 《科学通报(英文版)》2005,50(1):58-67
Interglacial or postglacial climates are all of charac-teristic of warmer conditions. However, if condition asso-ciated with the warm feature is wetter or drier than today,it would produce different impacts on natural environ-ments and human society. Quaternary studies found thatclimate with warm-dry or warm-wet conditions had oc-curred in China during the last 40—30 ka BP[1]. For ex-ample, it was warmer than the present during themid-Holocene (3—8 ka BP) and the late phases of MarineIsot… 相似文献
239.
对移栽至南京林业大学南大山苗圃的湿地松组培再生植株进行了苗高、地径、干形的比较。结果表明,各家系及无性系的生长状态存在差异。组培苗与实生苗间苗高差异较大,组培苗在早期生长速度不及实生苗,且抗病的家系不及普通的家系,抗病的8#和32#家系苗高差异不显著;实生苗、组培苗斜生现象严重;继代次数对组培苗的苗高、地径生长影响不大;组培苗年龄越大,苗高生长势越好,地径差异小;8#家系组培苗各无性系间苗高差异显著,地径差异不显著。 相似文献
240.
计算有效弹性厚度和不同尺度的拉张因子,并结合裂后的沉积记录可以反映一个伸展性盆地的形成演化特征.运用基于弹性梁模型和挠曲均衡原理的二维构造模拟软件重点对横穿台西南盆地的一条地震地质剖面进行模拟.分析结果表明:1.5km为台西南盆地最合适的有效弹性厚度;岩石圈尺度的拉张因子在1.2~4.8之间,上地壳尺度的拉张因子在1.0~1.2之间,全地壳尺度的拉张因子在1.1~3.0之间,岩石圈伸展具有横向的非均质性和深度的依赖性;台西南盆地裂后阶段受陆架坡折形成、东沙运动两期构造运动影响较大,不同于典型伸展性盆地裂后沉降模式,沉降特征无明显规律性. 相似文献