全文获取类型
收费全文 | 46215篇 |
免费 | 8236篇 |
国内免费 | 8316篇 |
专业分类
化学 | 20263篇 |
晶体学 | 865篇 |
力学 | 2157篇 |
综合类 | 964篇 |
数学 | 3884篇 |
物理学 | 13598篇 |
无线电 | 21036篇 |
出版年
2024年 | 233篇 |
2023年 | 901篇 |
2022年 | 1650篇 |
2021年 | 1809篇 |
2020年 | 1652篇 |
2019年 | 1475篇 |
2018年 | 1411篇 |
2017年 | 1879篇 |
2016年 | 1733篇 |
2015年 | 2141篇 |
2014年 | 2586篇 |
2013年 | 3288篇 |
2012年 | 3619篇 |
2011年 | 3740篇 |
2010年 | 3529篇 |
2009年 | 3519篇 |
2008年 | 3750篇 |
2007年 | 3551篇 |
2006年 | 3320篇 |
2005年 | 2964篇 |
2004年 | 2162篇 |
2003年 | 1627篇 |
2002年 | 1540篇 |
2001年 | 1539篇 |
2000年 | 1425篇 |
1999年 | 926篇 |
1998年 | 575篇 |
1997年 | 489篇 |
1996年 | 530篇 |
1995年 | 410篇 |
1994年 | 386篇 |
1993年 | 317篇 |
1992年 | 316篇 |
1991年 | 235篇 |
1990年 | 235篇 |
1989年 | 194篇 |
1988年 | 176篇 |
1987年 | 161篇 |
1986年 | 131篇 |
1985年 | 97篇 |
1984年 | 100篇 |
1983年 | 88篇 |
1982年 | 70篇 |
1981年 | 55篇 |
1980年 | 43篇 |
1979年 | 38篇 |
1978年 | 20篇 |
1977年 | 12篇 |
1965年 | 19篇 |
1964年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
331.
Developing low-cost and high-activity transition metal oxide electrocatalysts for an efficient oxygen evolution reaction (OER) at a large current density is highly demanded for industrial application and remains a big challenge. Herein, we report vertically aligned cobalt doped Ni–Fe based oxide (Co–NiO/Fe2O3) arrays as a robust OER electrocatalyst via a simple method combining hydrothermal reaction with heat treatment. Density functional theory calculation and XRD Rietveld refinement reveal that Co preferentially occupies the Ni sites compared to Fe in the Ni–Fe based oxides. The electronic structures of the Co–NiO/Fe2O3 could be further optimized, leading to the improvement of the intrinsic electronic conductivity and d-band center energy level and the decrease in the reaction energy barrier of the rate-determining step for the OER, thus accelerating its OER electrocatalytic activity. The Co–NiO/Fe2O3 nanosheet arrays display state-of-the-art OER activities at a large current density for industrial demands among Fe–Co–Ni based oxide electrocatalysts, which only require an ultra-low overpotential of 230 mV at a high current density of 500 mA cm−2, and exhibit superb durability at 500 mA cm−2 for at least 300 h without obvious degradation. The Co–NiO/Fe2O3 nanosheet arrays also have a small Tafel slope of 33.9 mV dec−1, demonstrating fast reaction kinetics. This work affords a simple and effective method to design and construct transition metal oxide based electrocatalysts for efficient water oxidation.Co–NiO/Fe2O3 nanosheets featuring Co substitution on Ni sites can effectively regulate electronic structures and exhibit high OER activities with low overpotential (η500 = 230 mV), small Tafel slope (33.9 mV dec−1) and superb durability for 300 h. 相似文献
332.
Xinhua Zhou Xu Chen Liping Fan Huirong Dong Yan Ren Xiangming Chen 《Molecules (Basel, Switzerland)》2022,27(23)
Diterpenoids are considered the major bioactive components in Scutellaria barbata to treat cancer and inflammation, but few comprehensive profiling studies of diterpenoids have been reported. Herein, a stepwise diagnostic product ions (DPIs) filtering strategy for efficient and targeted profiling of diterpenoids in Scutellaria barbata was developed using UHPLC-Q-Exactive-Orbitrap-MS. After UHPLC-HRMS/MS analysis of six diterpenoid reference standards, fragmentation behaviors of these references were studied to provide DPIs. Then, stepwise DPIs filtering aimed to reduce the potential interferences of matrix ions and achieve more chromatographic peaks was conducted to rapidly screen the diterpenoids. The results demonstrated that stepwise DPIs were capable of simplifying the workload in data post-processing and the effective acquisition of low abundance compounds. Subsequently, DPIs and MS/MS fragment patterns were adopted to identify the targeted diterpenoids. As a result, 381 diterpenoids were unambiguously or tentatively identified, while 141 of them with completely new molecular weights were potential new diterpenoids for Scutellaria barbata. These results demonstrate that the developed stepwise DPIs filtering method could be employed as an efficient, reliable, and valuable strategy to screen and identify the diterpenoid profile in Scutellaria barbata. This might accelerate and simplify target constituent profiling from traditional Chinese medicine (TCM) extracts. 相似文献
333.
334.
集成毛细管电泳芯片及其制作技术的进展 总被引:7,自引:0,他引:7
集成毛细管电泳芯片是一个新兴的微量分析装置,它具有高效、快速、度样用量少、节约药品等优点。文章回顾了集成毛细管电泳芯片的历史,介绍了毛细管电泳芯片在原材料、制作方法、表征、进样、分离、检测等方面的进展,并展望了毛细管电泳芯片的前景。 相似文献
335.
336.
采用近红外光谱技术和二维相关分析法研究尼龙1010膜在升温过程中的结构变化. 为了排除非晶区域酰胺基团的影响, 事先对尼龙1010的样品膜进行了氘代, 并测量了其最终氘代率. 结果证明, 尼龙1010的结晶区域在升温过程中被逐渐破坏, 首先是其主链碳氢结构发生调整, 进一步影响到结合酰胺, 导致氢键作用减弱并最后生成自由胺基. 相似文献
337.
NOVEL pH-SENSITIVE DRUG DELIVERY SYSTEM BASED ON NATURAL POLYSACCHARIDE FOR DOXORUBICIN RELEASE 总被引:2,自引:0,他引:2
A novel pH-sensitive nanoparticle drug delivery system (DDS) derived fl'om natural polysaccharide pullulan for doxorubicin (DOX) release was prepared.Pullulan was functionalized by successive carboxymethylization and amidation to introduce hydrazide groups.DOX was then grafted onto pullulan backbone through the pH-sensitive hydrazone bond to form a pullulan/DOX conjugate.This conjugate self-assembled to form nano-sized particles in aqueous solution as a result of the hydrophobic interaction of the DOX.Tr... 相似文献
338.
Pei L Bao Y Wang H Yang F Xu B Wang S Yang X Du G 《Biomedical chromatography : BMC》2008,22(7):786-794
Salvianolic acid A (SAA), a major effective constituent of Salvia miltiorrhizas, is widely used in traditional Chinese medicine. A sensitive rapid analytical method was established and validated for SAA in rat plasma, which was further applied to assess the pharmacokinetics of SAA in rats receiving a single oral dose of SAA. The method used liquid chromatography tandem mass spectrometry in multiple reaction monitoring mode with chloramphenicol as the internal standard. A simple liquid-liquid extraction based on ethyl acetate was employed. The combination of a simple sample cleanup and short chromatographic run time (3 min) increased the throughput of the method substantially. The method was validated over the range 1.4-1000 ng/mL with a correlation coefficient >0.99. The lower limit of quantification was 1.4 ng/mL for SAA in plasma. Intra- and inter-day accuracies for SAA were 95-113 and 98-107%, and the inter-day precision was less than 12%. This method is more sensitive and faster than previous methods. After a single oral dose of 100 mg/kg of SAA, the mean peak plasma concentration (Cmax) of SAA was 318 ng/mL at 0.5 h, the area under the plasma concentration-time curve (AUC0-12 h) was 698 +/- 129 ng.h/mL, and the elimination half-life (T1/2) was 3.29 h. 相似文献
339.
Microwave-assisted growth and characterization of water-dispersed CdTe/CdS core-shell nanocrystals with high photoluminescence 总被引:5,自引:0,他引:5
He Y Lu HT Sai LM Lai WY Fan QL Wang LH Huang W 《The journal of physical chemistry. B》2006,110(27):13370-13374
A novel microwave-assisted method of growth of high-quality CdTe/CdS core-shell nanocrystals in the aqueous phase is presented in this paper. The photoluminescence quantum yield (PLQY) is greatly enhanced by epitaxial growth of the CdS shell. Under optimum conditions, the PLQY of as-prepared nanocrystals reaches as high as 75% without any post-treatment. Furthermore, these investigations demonstrate that microwave irradiation is tremendously useful for fast epitaxial growth of nanocrystals due to its special characteristics. As a result, the microwave synthesis is sufficiently time-economizing (only five minutes are required) to obtain optimum amounts of CdTe/CdS core-shell nanocrystals in comparison to the conventional illumination method (several days are required). Therefore, this current research not only provides a rapid microwave synthesis for producing highly fluorescent CdTe/CdS core-shell nanocrystals, but also it presents some advantages of the microwave synthesis in comparison to the illumination method. 相似文献
340.
[reaction: see text] The preparation of cyclopropene alpha-amino acids via the enantioselective desymmetrization of cyclopropene bis-carboxylic acid derivatives is described. The amino acids are stable to harsh reaction conditions, and a derivative has been incorporated into a tripeptide using conventional methods for peptide synthesis. 相似文献