全文获取类型
收费全文 | 97306篇 |
免费 | 3580篇 |
国内免费 | 3054篇 |
专业分类
化学 | 38816篇 |
晶体学 | 1048篇 |
力学 | 7752篇 |
综合类 | 172篇 |
数学 | 34231篇 |
物理学 | 21921篇 |
出版年
2024年 | 75篇 |
2023年 | 422篇 |
2022年 | 723篇 |
2021年 | 747篇 |
2020年 | 863篇 |
2019年 | 864篇 |
2018年 | 10949篇 |
2017年 | 10709篇 |
2016年 | 6972篇 |
2015年 | 1821篇 |
2014年 | 1493篇 |
2013年 | 1853篇 |
2012年 | 5498篇 |
2011年 | 12157篇 |
2010年 | 6858篇 |
2009年 | 7076篇 |
2008年 | 7770篇 |
2007年 | 9815篇 |
2006年 | 1290篇 |
2005年 | 2224篇 |
2004年 | 2251篇 |
2003年 | 2583篇 |
2002年 | 1713篇 |
2001年 | 838篇 |
2000年 | 699篇 |
1999年 | 550篇 |
1998年 | 524篇 |
1997年 | 444篇 |
1996年 | 494篇 |
1995年 | 360篇 |
1994年 | 320篇 |
1993年 | 290篇 |
1992年 | 215篇 |
1991年 | 224篇 |
1990年 | 169篇 |
1989年 | 178篇 |
1988年 | 154篇 |
1987年 | 113篇 |
1986年 | 105篇 |
1985年 | 109篇 |
1984年 | 96篇 |
1983年 | 70篇 |
1982年 | 71篇 |
1981年 | 57篇 |
1980年 | 64篇 |
1979年 | 52篇 |
1978年 | 45篇 |
1914年 | 46篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
941.
An improved synthesis of pennogenin, a bioactive component of Chinese herb “Chonglou” (Paris), is described. A ring-switching process opened the ring E of diosgenin and allowed the use of a hydroxyl-directed diboration/oxidation to introduce C17α-OH, hence eliminating the use of OsO4. This strategy might be rendered to synthesize similar steroids with C17α-OH. 相似文献
942.
Yong Zhang Yonghai Liu Shuai Zhang Lei Shi Wei Wang Hao Li 《Tetrahedron letters》2019,60(22):1463-1466
An acid-promoted 2-component Mannich annulation reaction of readily available acetylbenzaldehydes and secondary amines has been reported. The approach provides a simple and efficient method under mild conditions to synthesize 3-aminoindan-1-one derivatives in moderate to good yields. 相似文献
943.
944.
Hang Xu Chun‐Shuai Cao Han‐Shi Hu Shi‐Bin Wang Jin‐Cheng Liu Peng Cheng Nikolas Kaltsoyannis Jun Li Bin Zhao 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(18):6083-6088
Assembled from [Th48Ni6] nanocages, the first transition‐metal (TM)‐thorium metal–organic framework (MOF, 1 ) has been synthesized and structurally characterized. 1 exhibits high solvent and acid/base stability, and resistance to 400 kGy β irradiation. Notably, 1 captures ReO4? (an analogue of radioactive 99TcO4?, a key species in nuclear wastes) with a maximum capacity of 807 mg g?1, falling among the largest values known to date. Furthermore, 1 can enrich methylene blue (MB) and can also serve as an effective and recyclable catalyst for CO2 fixation with epoxides; there is no significant loss of catalytic activity after 10 cycles. Theoretical studies with nucleus‐independent chemical shifts and natural bond orbital analysis reveal that the [Th6O8] clusters in 1 have a unique stable electronic structure with (d–p)π aromaticity, partially rationalising 1 ′s stability. 相似文献
945.
946.
以碱提取、酸沉淀和silicagel、Al2O3及sephadexG-25柱层析分离纯化等步骤,从悬铃木落叶中制备得到一种暗棕色化合物,经PAGE、PLC及TLC检测均为单一谱带或单一斑点;该有色化合物熔点282.59~283.29℃,λKOHmax:215nm,E1%1cm:348.7,肩峰:256nm,pI:3.5,对大肠杆菌、金黄葡萄球菌、巨大芽孢杆菌及枯草杆菌有较强的抑菌活性 相似文献
947.
The extraordinarily rapid growth of malignant tumors depends heavily on the glucose metabolism by the pathways of glycolysis and mitochondrial oxidative phosphorylation to generate adenosine 5′-triphosphate (ATP) for maintaining cell proliferation and tumor growth. This study reports a tumor chemical suffocation therapeutic strategy by concurrently suppressing both glycolysis and mitochondrial oxidative phosphorylation (OXPHOS) via the co-deliveries of EDTA and rotenone into a glutathione (GSH)-overexpressed tumor microenvironment. EDTA is to block the glycolytic pathway through inhibiting the activity of glycolytic enzymes via the chelation of magnesium ion, a co-worker of glycolytic enzymes, despite the presence of Ca2+. Meanwhile rotenone is to inhibit the mitochondrial OXPHOS. This work provides a novel tumor suffocation strategy by the co-deliveries of glucose metabolism inhibitors, especially by de-functioning glycolytic enzymes via eliminating their co-worker magnesium.The EDTA- and Rotenone-loaded MPER nanoparticles have been synthesized to suffocate tumor cells to death through inhibiting glycolytic process and mitochondrial oxidative phosphorylation simultaneously in vitro and in vivo. 相似文献
948.
949.
Zhang Yingying Bi Haijie Wu Bingwei Yuan Da Shi Yan Feng Xiandong 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(9):3723-3733
The NaI(Tl) detector has been an important research topic and application in the field of in situ marine radioactive automatic monitoring because of its advantages of low power consumption, low cost, and good efficiency. However, its energy resolution is not high enough. This paper investigated an analytical method: spectrum de-noising, background correction based on the SNIP operator, peak search based on the top-hat transform and peak fitting using Gaussian distribution. Simulation and gamma spectra measured from seawater showed that the established energy spectrum analysis method presents satisfactory automatic analytical ability for identification and quantitatively analysis.
相似文献950.
Ajay M. Sorty Kamlesh K. Meena Khushboo Choudhary Utkarsh M. Bitla P. S. Minhas K. K. Krishnani 《Applied biochemistry and biotechnology》2016,180(5):872-882
Halotolerant bacteria associated with Psoralea corylifolia L., a luxuriantly growing annual weed in salinity-affected semi-arid regions of western Maharashtra, India were evaluated for their plant growth-promoting activity in wheat. A total of 79 bacteria associated with different parts viz., root, shoot and nodule endophytes, rhizosphere, rhizoplane, and leaf epiphytes, were isolated and grouped based on their habitat. Twelve bacteria isolated for their potential in plant growth promotion were further selected for in vitro studies. Molecular identification showed the presence of the genera Bacillus, Pantoea, Marinobacterium, Acinetobacter, Enterobacter, Pseudomonas, Rhizobium, and Sinorhizobium (LC027447-53; LC027455; LC027457, LC027459, and LC128410). The phylogenetic studies along with carbon source utilization profiles using the Biolog® indicated the presence of novel species and the in planta studies revealed promising results under salinity stress. Whereas the nodule endophytes had minute plant growth-promoting (PGP) activity, the cell free culture filtrates of these strains enhanced seed germination of wheat (Triticum aestivum L). The maximum vigor index was monitored in isolate Y7 (Enterobacter sp strain NIASMVII). Indole acetic acid (IAA) production by the isolates ranged between 0.22 and 25.58 μg mL?1. This signifies the need of exploration of their individual metabolites for developing next-generation bio-inoculants through co-inoculation with other compatible microbes. This study has potential in utilization of the weed-associated microbiome in terms of alleviation of salinity stress in crop plants. 相似文献