全文获取类型
收费全文 | 19530篇 |
免费 | 1715篇 |
国内免费 | 2309篇 |
专业分类
23554篇 |
出版年
2024年 | 57篇 |
2023年 | 290篇 |
2022年 | 625篇 |
2021年 | 993篇 |
2020年 | 738篇 |
2019年 | 866篇 |
2018年 | 878篇 |
2017年 | 648篇 |
2016年 | 858篇 |
2015年 | 1220篇 |
2014年 | 1495篇 |
2013年 | 1536篇 |
2012年 | 1872篇 |
2011年 | 1644篇 |
2010年 | 1020篇 |
2009年 | 960篇 |
2008年 | 1092篇 |
2007年 | 961篇 |
2006年 | 920篇 |
2005年 | 696篇 |
2004年 | 602篇 |
2003年 | 513篇 |
2002年 | 413篇 |
2001年 | 261篇 |
2000年 | 237篇 |
1999年 | 224篇 |
1998年 | 180篇 |
1997年 | 157篇 |
1996年 | 144篇 |
1995年 | 129篇 |
1994年 | 139篇 |
1993年 | 99篇 |
1992年 | 134篇 |
1991年 | 114篇 |
1990年 | 114篇 |
1989年 | 77篇 |
1988年 | 70篇 |
1987年 | 54篇 |
1986年 | 47篇 |
1985年 | 56篇 |
1984年 | 55篇 |
1983年 | 41篇 |
1982年 | 35篇 |
1981年 | 43篇 |
1980年 | 26篇 |
1979年 | 24篇 |
1978年 | 21篇 |
1977年 | 23篇 |
1975年 | 23篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Desert algae are important components of the desert soil crust and play an essential role in desert soil ecosystem development. Owing to their special habitat, desert algae are often exposed to harsh environments, among which drought represents the most common stress. Green algae are considered to have drought tolerance potential; however, only a few studies have investigated this. In this study, we selected the green alga Chlorella sp., which was isolated from desert soil, and studied its physiological response to polyethylene glycol (PEG) 6000-induced drought stress. The results showed that drought stress can affect the photosynthetic efficiency of Chlorella sp., reduce its water retention ability, and destroy its ultrastructure. However, Chlorella sp. can cope with drought stress through a series of physiological regulatory strategies. Protective strategies include quick recovery of photosynthetic efficiency and increased chlorophyll content. In addition, induced synthesis of soluble proteins, lipids, and extracellular polysaccharide (EPS), and accumulation of osmotic regulatory substances, such as sucrose and trehalose, also contribute to improving drought tolerance in Chlorella sp. This study provides insights into the physiological responses of Chlorella sp. to drought stress, which may be valuable for understanding the underlying drought adaptation mechanisms of desert green algae. 相似文献
63.
汉族ABO血型的皮纹特征分析 总被引:2,自引:1,他引:1
作者对芜湖地区382例(男220人;女162人)汉族ABO血型的皮纹特征进行了分析,其中O型130人,A型113人,B型101人,AB型38人。分析比较了指纹类型、指纹组合格局、指嵴纹计数、掌嵴纹计数、atd角,掌部真实花纹,掌褶纹和拇趾球纹等项参数,结果表明,ABO各血型的皮纹参数间有若干统计学差异。 相似文献
64.
<正>中国是全球生物多样性大国,也是世界上植物种类最多的国家之一。据《中国生物物种名录》(2022版)(http://www.sp2000.org.cn/Co LChina)记载,中国产高等植物物种总计483科4,275属38,287种及7,506个种下类群,其中维管植物占绝对优势,共有323科3,643属35,179种及7,258个种下类群,且仍以平均每年220个新分类群及32个国家级分布新记录的速度持续增长(Du et al,2020)。 相似文献
65.
Nurfida Ablajan Wen-Juan Xue Jiang-Yu Zhao Abdubakiev Sardorbek Nurmirza Boymirzayevich Begmatov Shamansur Sagdullaev Bo Zhao Haji Akber Aisa 《化学与生物多样性》2023,20(3):e202200936
Shawurenine C ( 1a ) and D ( 1b ), a new pair of regioisomeric C19-diterpenoid alkaloids, and five known C19-diterpenoid alkaloids ( 2 – 6 ) were isolated from the aerial part of Delphinium shawurense W. T. Wang. The chemical structures of new compounds were established based on spectroscopic analyses: HR-ESI-MS, and 1D, 2D NMR spectroscopic data. The anti-inflammatory and cytotoxic activities of these diterpenoid alkaloids were also evaluated. 相似文献
66.
Mengyi Ba Ruonan Chen Qiuchen Huang Yanli Song Wen Li Yuanyuan Zhang Haixin Liu Xiang Xu Weidong Zhang Zhiqiang Cai Tao Sun 《化学与生物多样性》2023,20(8):e202300350
This work firstly reported a new polycaprolactone based material functionalized with guanidinium ionic liquid (PCL-GIL) as the stationary phase with high resolution performance for capillary gas chromatography (GC). It is composed of polycaprolactone (PCL) and guanidinium ionic liquid (GIL) with amphiphilic conformation. The PCL-GIL capillary column coated by static method exhibited high column efficiency of 3942 plates/m and moderate polarity. As a result, the PCL-GIL column exhibited high-resolution capability. For a mixture of 27 analytes with a wide ranging polarity and outperformed the PCL-2OH and HP-35 columns, showing its advantageous separation capability for analytes of diverse types. Moreover, the PCL-GIL column showed high resolving capability for various positional isomers and cis-/trans-isomers, including alkylbenzenes, chlorobenzenes, naphthalenes, bromonitrobenzenes, chloronitrobenzenes, benzaldehydes, phenols, alcohols, respectively. In a word, PCL derivatized by GIL units as a new type of stationary phase has a promising future in GC separations. 相似文献
67.
68.
Summary A thymus cyst was discovered in connection with autoradiographical studies on sulphur metabolism of the rat. The coincidence must be considered unique and has motivated amplifying histochemical investigations.The cyst-content showed a strong positive PAS-reaction and after toluidine blue -metachromasia, which along with the incorporation of S35 makes the presence of acid mucopolysaccharides likely. A strong blackening was noticed on the autoradiogram over the greater part of the cyst. This infers that the content has been metabolized here, in contradistinction to the centre with inactive colloid. 相似文献
69.
70.