首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   7430篇
  免费   1181篇
  国内免费   966篇
化学   5404篇
晶体学   54篇
力学   466篇
综合类   76篇
数学   867篇
物理学   2710篇
  2024年   5篇
  2023年   134篇
  2022年   139篇
  2021年   218篇
  2020年   299篇
  2019年   284篇
  2018年   208篇
  2017年   199篇
  2016年   309篇
  2015年   347篇
  2014年   362篇
  2013年   504篇
  2012年   599篇
  2011年   710篇
  2010年   448篇
  2009年   448篇
  2008年   508篇
  2007年   453篇
  2006年   435篇
  2005年   417篇
  2004年   288篇
  2003年   259篇
  2002年   253篇
  2001年   214篇
  2000年   166篇
  1999年   150篇
  1998年   146篇
  1997年   127篇
  1996年   130篇
  1995年   148篇
  1994年   115篇
  1993年   106篇
  1992年   73篇
  1991年   97篇
  1990年   59篇
  1989年   60篇
  1988年   48篇
  1987年   31篇
  1986年   22篇
  1985年   17篇
  1984年   11篇
  1983年   10篇
  1982年   11篇
  1981年   5篇
  1980年   1篇
  1979年   1篇
  1976年   1篇
  1966年   1篇
  1957年   1篇
排序方式: 共有9577条查询结果,搜索用时 31 毫秒
51.
Antimicrobial photodynamic therapy (aPDT) has been recommended for clinical application. Its antibacterial effect on bacteria remained in dentinal tubule was seldom investigated. Here, we evaluated the antibacterial effects of aPDT on Streptococcus mutans (S. mutans) and Lactobacillus acidophilus (L. acidophilus) in planktonic lifestyle, biofilm and carious dentine. Mono-species biofilms or dentinal caries formed on human dentine slices or slabs. Bacterial suspension, biofilms and dentine caries were treated with 0.1 mg mL−1 toluidine Blue O followed by irradiation with a light emission diode (λ − 635 ± 10 nm; 500 mW; 31.5 J cm−2; 60 s) and 0.12% chlorhexidine (CHX), respectively. Residual bacteria were determined by microbial culture analysis and scanning electron microscopy (SEM). One-way analysis of variance (ANOVA) was performed to detect the significance of the variables. Both treatments significantly reduced the number of L. acidophilus in planktonic state, biofilm and carious dentine (< 0.05). For S. mutans, CHX was only bactericidal against suspension (< 0.05), while aPDT was effective on both suspension and biofilm (< 0.05) while not for dentin caries (> 0.05). Under the experimental conditions assessed, aPDT could be an alternative disinfection method for superficial layer of caries cavity. Its disinfection on bacteria in dentinal tubule of deep layer was deficient.  相似文献   
52.
A biochemometrics strategy combining quantitative determination, bioactivity evaluation, and relationship analysis was proposed for identification of analgesic components of herbs. First, a robust liquid chromatography tandem mass spectrometry method was developed for simultaneous determination of nine major alkaloids in crude and vinegar‐processed Corydalis turtschaninovii. Nine alkaloids were separated on a BEH C18 column with a mobile phase consisting of acetonitrile and water spiked with 0.1% formic acid and then detected by multiple reactions monitoring in the positive ion mode. Nitidine chloride was employed as the internal standard. The method displayed good linearity and the precisions of intra‐day and inter‐day were all within 3.0%. The recovery rates of each alkaloid ranged from 97.1 to 102.9%. The method was successfully applied for quantitative analysis of nine alkaloids in ten batches of crude and vinegar‐processed Corydalis turtschaninovii. Second, the analgesic effects of crude and vinegar‐processed Corydalis turtschaninovii were evaluated in mice. Third, principle component analysis, canonical correlation analysis, and partial least squares regression were used to analysis the relationship between the contents of nine major alkaloids and the analgesic effect of different crude and vinegar‐processed samples. Tetrahydropalmatine, coptisine, and dehydrocorydaline have a close positive correlation with the analgesic effect.  相似文献   
53.
Ye  Linglong  Li  Xueshan  Cai  Yunhao  Ryu  Hwa Sook  Lu  Guangkai  Wei  Donghui  Sun  Xiaobo  Woo  Han Young  Tan  Songting  Sun  Yanming 《中国科学:化学(英文版)》2020,63(4):483-489
Benzo[1,2-b:4,5-b′]dithiophene(BDT) has been widely used to construct donor-acceptor(D-A) copolymers in organic solar cells(OSCs). However, benzo[1,2-b:4,5-b′]difuran(BDF), an analogue of BDT, has received less attention than BDT. The photovoltaic performance of BDF copolymers has lagged behind that of BDT copolymers. Here, we designed and synthesized two BDF copolymers, PBF1-C and PBF1-C-2Cl. PBF1-C-2Cl, which is composed of BDF and benzo[1,2-c:4,5-c′]dithiophene-4,8-dione connected by a chlorinated thiophene π-bridge, displays a low-lying highest occupied molecular orbital energy level,which helps in yielding a high open-circuit voltage(V_(oc)) in OSCs. As a result, when blended with Y6, PBF1-C-2Cl-based devices showed a high V_(oc) of 0.83 V and a power conversion efficiency(PCE) of 13.10%. To the best of our knowledge, the PCE of 13.10% is among the highest efficiency values for OSCs based on BDF copolymers.  相似文献   
54.
Red phosphorus is a promising photocatalyst with wide visible-light absorption up to 700 nm, but the fast charge recombination limits its photocatalytic hydrogen evolution reaction (HER) activity. Now, [001]-oriented Hittorf's phosphorus (HP) nanorods were successfully grown on polymeric carbon nitride (PCN) by a chemical vapor deposition strategy. Compared with the bare PCN and HP, the optimized PCN@HP hybrid exhibited a significantly enhanced photocatalytic activity, with HER rates reaching 33.2 and 17.5 μmol h−1 from pure water under simulated solar light and visible light irradiation, respectively. It was theoretically and experimentally indicated that the strong electronic coupling between PCN and [001]-oriented HP nanorods gave rise to the enhanced visible light absorption and the greatly accelerated photoinduced electron–hole separation and transfer, which benefited the photocatalytic HER performance.  相似文献   
55.
The change in phenols, polysaccharides and volatile profiles of noni juice from laboratory- and factory-scale fermentation was analyzed during a 63-day fermentation process. The phenol and polysaccharide contents and aroma characteristics clearly changed according to fermentation scale and time conditions. The flavonoid content in noni juice gradually increased with fermentation. Seventy-three volatile compounds were identified by solid-phase microextraction coupled with gas chromatography–mass spectrometry (SPME-GC-MS). Methyl hexanoate, 3-methyl-3-buten-1-ol, octanoic acid, hexanoic acid and 2-heptanone were found to be the main aroma components of fresh and fermented noni juice. A decrease in octanoic acid and hexanoic acid contents resulted in the less pungent aroma in noni juice from factory-scale fermentation. The results of principal component analysis of the electronic nose suggested that the difference in nitrogen oxide, alkanes, alcohols, and aromatic and sulfur compounds, contributed to the discrimination of noni juice from different fermentation times and scales.  相似文献   
56.
Hu  Qiu-Fen  Zhang  Ling-Fang  Liu  Ming-Xin  Cai  Bing-Biao  Li  Yong  Zhou  Tao  Li  Man-Fei  Wang  Hua-Shun  Xu  Yong  Kong  Wei-Song  Zhou  Min  Yang  Guang-Yu  Jiang  Ju-Xing 《Chemistry of Natural Compounds》2022,58(3):511-515
Chemistry of Natural Compounds - Two new chromeno[3,2-c]pyridin derivatives, 8-acetyl-3-(hydroxymethyl)-7-methoxy-10H-chromeno[3,2-c]pyridin-10-one (1) and...  相似文献   
57.
Journal of Radioanalytical and Nuclear Chemistry - Prostate-specific membrane antigen (PSMA) is a biomarker for prostate cancer, which is commonly used in the development of diagnostic and...  相似文献   
58.
Li  Tengfei  Cai  Guilong  Lin  Yuze  Lu  Xinhui  Zhan  Xiaowei 《高分子科学》2022,40(8):914-920
Chinese Journal of Polymer Science - We synthesize and compare four near-infrared absorbing fused-ring electron acceptors named as nTTIC (n=2, 3, 4, and 5), based on different number of...  相似文献   
59.
Sulfur‐fumigation is known to reduce volatile compounds that are the main active components in herbs used in herbal medicine. We investigated changes in chemical composition between sun‐dried and sulfur‐fumigated Radix Angelicae Dahuricae using a purge and trap technique to capture volatile compounds, and two‐dimensional gas chromatography/time‐of‐flight mass spectrometry for identification. Using sun‐dried Radix Angelicae Dahuricae samples as a reference, the results showed that 73 volatile compounds, including 12 sulfide compounds, were found to be present only in sulfur‐fumigated samples. Furthermore, 32 volatile compounds that were found in sun‐dried Radix Angelicae Dahuricae samples disappeared after sulfur‐fumigation. The proposed method can be applied to accurately discriminate sulfur‐fumigated Radix Angelicae Dahuricae from different commercial sources. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
60.
Autonomous mechanical mass transportation for cargos on the microscale with no need of continuous external powering is of great scientific and technological interest due to their extensive applications. However, it is still challenging to create a self‐driven system applicable to diverse micromaterial transportation demands. In this work, we developed a novel autonomous conveyer gel driven by frontal polymerization (FP). The chemical wave produced in FP was stable, and self‐propagating with a constant velocity, which can be easily monitored by thermal imaging or fluorescence labeling. We investigated the influence of the initiation temperature, swelling ratio of the gel substrate, and the size of the cargos on the motion of driven behavior. Results showed that the driving velocity can be well controlled by altering the initiation temperatures of FP. The swelling ratio and the size of the cargos had a key impact on the feasibility of self‐driven behavior. In addition, powerful driven capability by FP was demonstrated by successfully transporting cargos in series, and further applied for targeted synthesis of CdS nanocrystals. The methodology developed here provides an effective way to convert chemical energy to mechanical work, and may be useful in energy conversion and utilization, mass transportation and other applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1323‐1331  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号