全文获取类型
收费全文 | 349篇 |
免费 | 47篇 |
国内免费 | 64篇 |
出版年
2024年 | 4篇 |
2023年 | 11篇 |
2022年 | 20篇 |
2021年 | 19篇 |
2020年 | 17篇 |
2019年 | 14篇 |
2018年 | 20篇 |
2017年 | 22篇 |
2016年 | 26篇 |
2015年 | 26篇 |
2014年 | 45篇 |
2013年 | 25篇 |
2012年 | 23篇 |
2011年 | 27篇 |
2010年 | 14篇 |
2009年 | 11篇 |
2008年 | 15篇 |
2007年 | 9篇 |
2006年 | 21篇 |
2005年 | 18篇 |
2004年 | 13篇 |
2003年 | 9篇 |
2002年 | 13篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 7篇 |
1996年 | 7篇 |
1992年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有460条查询结果,搜索用时 46 毫秒
91.
近年来,随着城市交通拥堵和环境污染等问题的日益凸显,自行车作为通勤出行方式的地位逐渐上升,通勤者对建立不受机动车干扰的、连续的、具备通勤功能的城市绿色道路的需求也在不断增加。绿色道路的线路建设不仅要保障空间可实施性和交通环境质量,还要与居民的通勤出行需求紧密结合,实现绿道使用的综合效益最大化。基于此,研究以北京市回龙观地区为对象,采用与居民出行行为有关的数据,识别郊区居民中短程通勤特征,划定主要通勤范围,探究基于居民真实出行的多源大数据的选线方法,通过基于通勤出行需求强度与吸引强度的绿道节点甄选与路段适宜性的评价分析。最后,通过GIS网络分析功能进行最优线路选择,并结合城市公园、绿地、河流等资源的分布情况进行修正,形成一条满足居民通勤需求的、完整互联的、安全的且具备较强实施性的绿色通道。最终达到降低居民通勤时耗、提升区域可达性、完善城市慢行系统网络的目的。 相似文献
92.
Enantioselective resolution of Rac‐terbutaline and evaluation of optically pure R‐terbutaline hydrochloride as an efficient anti‐asthmatic drug 下载免费PDF全文
Terbutaline is a β2‐adrenoceptor agonist for the treatment of asthma and chronic obstructive pulmonary disease (COPD). Among the two isomers of terbutaline (TBT 2), R‐isomer was found to be the potent enantiomer in generating therapeutic effect, while S‐isomer has been reported to show side effects. In this study, R‐terbutaline hydrochloride (R‐TBH 6) was synthesized through chiral resolution from the racemic terbutaline sulfate (rac‐TBS 1) with 99.9% enantiomeric excess (ee) in good overall yield (53.6%). Further, R‐TBH 6 nebulized solution was prepared in half dosage of Bricanyl®, which is a marketed product of racemic terbutaline and evaluated in vitro aerosol performance and in vivo anti‐asthmatic effect on guinea pigs via. pulmonary delivery. From the investigation, it is evident that R‐TBH 6 nebulized solution of half dosage performed similar fine aerosol characteristics and anti‐asthmatic effect with Bricanyl®. 相似文献
93.
The C2H2 zinc‐finger protein SlZF3 regulates AsA synthesis and salt tolerance by interacting with CSN5B 下载免费PDF全文
Ying Li Zhuannan Chu Jinying Luo Yuhong Zhou Yujing Cai Yongen Lu Junhui Xia Hanhui Kuang Zhibiao Ye Bo Ouyang 《Plant biotechnology journal》2018,16(6):1201-1213
Abiotic stresses are a major cause of crop loss. Ascorbic acid (AsA) promotes stress tolerance by scavenging reactive oxygen species (ROS), which accumulate when plants experience abiotic stress. Although the biosynthesis and metabolism of AsA are well established, the genes that regulate these pathways remain largely unexplored. Here, we report on a novel regulatory gene from tomato (Solanum lycopersicum) named SlZF3 that encodes a Cys2/His2‐type zinc‐finger protein with an EAR repression domain. The expression of SlZF3 was rapidly induced by NaCl treatments. The overexpression of SlZF3 significantly increased the levels of AsA in tomato and Arabidopsis. Consequently, the AsA‐mediated ROS‐scavenging capacity of the SlZF3‐overexpressing plants was increased, which enhanced the salt tolerance of these plants. Protein–protein interaction assays demonstrated that SlZF3 directly binds CSN5B, a key component of the COP9 signalosome. This interaction inhibited the binding of CSN5B to VTC1, a GDP‐mannose pyrophosphorylase that contributes to AsA biosynthesis. We found that the EAR domain promoted the stability of SlZF3 but was not required for the interaction between SlZF3 and CSN5B. Our findings indicate that SlZF3 simultaneously promotes the accumulation of AsA and enhances plant salt‐stress tolerance. 相似文献
94.
95.
96.
97.
Xikun Song Cinzia Gravili Jianjun Wang Yacheng Deng Yongqiang Wang Lu Fang Heshan Lin Shaoqing Wang Yiting Zheng Junhui Lin 《Polar Biology》2016,39(3):461-471
The marine benthic fauna in Arctic shallow-water is reported to be a relatively young assemblage by species of either Pacific or Atlantic affinity. Whether current deep-sea Pacific species are included in the affinity or not is unknown. Combining morphological comparisons and genetic analyses, a new deep-sea hydroid to science, Sertularia xuelongi sp. nov. (Cnidaria: Hydrozoa: Sertulariidae), is described from the northern margin of the Bering Sea Basin at depths of 800–1570 m collected in 2010. It is characterized by slender and zigzag-shaped hydrocauli, alternately arranged hydrothecae and the absence of distal-lateral horns in fully matured female gonothecae. Its distribution, currently known only from Bering Sea Basin, suggests that it could not be an Arctic species with Pacific affinity. However, phylogenetic analyses based on the mitochondrial 16S rRNA gene show that it is clustered into a distinctive clade with four closely related species recorded from shallow-water of Northwest France, Iceland, Chukchi Sea and/or Bering Sea. In addition, its sequence similarity is highly relevant to these four species: Sertularia argentea (98.6 %), S. cupressina (98.8 %), S. plumosa (98.8 %) and S. robusta (99.4 %). All these provide a new insight into the relevance of North Pacific deep-sea species to the benthic fauna in Arctic and adjacent shallow-water. The taxonomic restriction of the genus Sertularia and the re-validation of the genus Polyserias are discussed. Future researches on more deep-sea species from Pacific and/or Atlantic are required to understand the evolution and speciation pattern involved in polar relevance. 相似文献
98.
99.
100.