全文获取类型
收费全文 | 31675篇 |
免费 | 5332篇 |
国内免费 | 3799篇 |
专业分类
化学 | 22353篇 |
晶体学 | 298篇 |
力学 | 2251篇 |
综合类 | 302篇 |
数学 | 3662篇 |
物理学 | 11940篇 |
出版年
2024年 | 76篇 |
2023年 | 652篇 |
2022年 | 756篇 |
2021年 | 1094篇 |
2020年 | 1329篇 |
2019年 | 1222篇 |
2018年 | 1037篇 |
2017年 | 879篇 |
2016年 | 1460篇 |
2015年 | 1427篇 |
2014年 | 1717篇 |
2013年 | 2297篇 |
2012年 | 2780篇 |
2011年 | 3000篇 |
2010年 | 1950篇 |
2009年 | 1871篇 |
2008年 | 1990篇 |
2007年 | 1806篇 |
2006年 | 1732篇 |
2005年 | 1457篇 |
2004年 | 1218篇 |
2003年 | 986篇 |
2002年 | 881篇 |
2001年 | 761篇 |
2000年 | 694篇 |
1999年 | 704篇 |
1998年 | 631篇 |
1997年 | 537篇 |
1996年 | 577篇 |
1995年 | 524篇 |
1994年 | 467篇 |
1993年 | 371篇 |
1992年 | 368篇 |
1991年 | 291篇 |
1990年 | 283篇 |
1989年 | 216篇 |
1988年 | 146篇 |
1987年 | 137篇 |
1986年 | 110篇 |
1985年 | 104篇 |
1984年 | 57篇 |
1983年 | 54篇 |
1982年 | 49篇 |
1981年 | 30篇 |
1980年 | 19篇 |
1979年 | 10篇 |
1977年 | 5篇 |
1975年 | 6篇 |
1969年 | 4篇 |
1957年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
991.
The geometric and electronic structures of FeS(2) (100) surface have been studied by a quantum-mechanical calculation using a total-energy pseudopotential code, CASTEP. The (100) surface is very stable and does not give any significant geometric relaxation. The electronic structure of FeS(2) (100) surface is characterized by the appearance of new native surface states in the bulk band gap, which correspond to antibonding mixed Fea-Ssp(3) states. These surface states play an important role as mediators of electron transfer on both anodic and cathodic sites in the incipient oxidation of pyrite. Moreover, the (100) surface has small band gaps and shows some metallic character. It is predicted that the rate of cathodic reductive reaction of O(2) in the incipient oxidation of pyrite is much faster than previously considered. The transport of electrons from the anodic sites to the cathodic sites on the (100) surface is faster and hole injection of anodic sites is not the rate-determining step. So we can deduce that the rate-determining step of incipient oxidation for pyrite consists of both electron transfer of pyrite/aqueous O(2) interface and the splitting of H(2)O. 相似文献
992.
993.
994.
The surfactant-encapsulated cluster (SEC) composed of a hydrophobic dimethyl dioctadecyl ammonium (DODA) shell and an encapsulated hydrophilic polyoxoanion core can form casting films. The structure of the casting film is influenced by evaporation rates of organic solvent. When the casting films are prepared by slow evaporation of chloroform, the alkyl chains are considered to possess a partial interdigitation, and the interdigitated length is 1.6 nm. The casting film structure is characterized by scanning force microscopy (SFM), Fourier transformation infrared (FT-IR), wide-angle X-ray diffraction, and differential scanning calorimetry (DSC). 相似文献
995.
Ti基IrO2+Ta2O5阳极在H2SO4溶液中的电解时效行为 总被引:5,自引:0,他引:5
研究了450 ℃制备所得Ti/70%IrO2 30%Ta2O5(摩尔分数)高寿命阳极在H2SO4溶液电解过程中电极的物理、化学及电化学性能的时效行为.结果发现,整个电解过程可分为“活化”、“稳定”及“失效”三个阶段.在“活化”及“稳定”区内主要发生电极表面活性氧化物的溶解,涂层中IrO2金红石相的(110)、(101)晶面择优取向随电解时间延长而减弱,而(002)晶面择优增强.但是在“失效区”内,各晶面的择优程度却不随电解时间的变化而变化,这表明在“失效区”内氧化物的损失机制发生了变化.电化学阻抗谱测试表明,电极的析氧电化学反应电阻随电解时间的延长发生缓慢而连续的上升,而整个电极的物理阻抗在“失效区”内却发生突升现象.X射线衍射分析(XRD)表明,随电解时间的延长TiO2金红石相的衍射强度增大,达“失效区”时衍射强度发生突升.根据实验现象特别是“失效区”内阳极的时效行为提出高寿命Ti基氧化物涂层阳极的失效机制. 相似文献
996.
A flow injection method combined with Resonance light scattering detection was developed for the determination of protein
concentration in human serum samples. This method is based on the enhanced RLS signals of protein binding with the dye acid
chrome blue K. The enhanced RLS intensities at 264 nm, in an acidic aqueous solution, were proportional to the protein concentration
over the range of 2.0–40.0 μg·mL−1 for human serum albumin (HSA) and the limit of detection (3σ) is 85 ng·mL−1. This method was successfully applied to the quantification of total proteins in human serum samples. The maximum relative
standard deviation is less than 2% and the recovery is between 97 and 103% for the standard addition method. The sample throughput
was 60 h−1. 相似文献
997.
混合三烃基锡衍生物的研究:X.甲基二环己基锡二硫代磷酸酯的合成及生… 总被引:4,自引:2,他引:4
合成了10种甲基二环己基锡-O,O-二烃基二硫代磷酸酯,利用IR,NMR,MS及元素分析确证了化合物的结构,生物活性测试结果表明,这类化合物具有较高的杀螨和除草活性。 相似文献
998.
从自模式曲线分辨到渐进类因子分析法 总被引:1,自引:1,他引:1
本文对自模式曲线分辨法的发展作了简要回顾,其中特别对近来来迅速发展的一类用于色谱波谱联用仪产生的二维分析数据的渐进类分析法作了详尽的讨论。这些新化学计量学方法的涌现,对复杂的未知分析体系的定性定量分析,将带来深刻的变化。 相似文献
999.
A new separation matrix, consisting of polymer poly(N-isopropylacrylamide) (PNIPAM) and small molecule additive mannitol, was used for double-stranded (ds) DNA and plasmid DNA separation by capillary electrophoresis. The matrix had a low viscosity, which made it very easy to handle. The additive mannitol dramatically enhanced the sieving performance of PNIPAM in TBE buffer. The optimal mannitol concentration 6% in polymer solution, was determined with the consideration of both speed and resolution. A resolution of 0.95 was achieved on the separation of 271/281 bp in the phiX174/HaeIII digest by using 1.5% PNIPAM + 6% mannitol, while the supercoiled, linear and nicked conformers of lambda plasmid were separated in 1% PNIPAM + 6% mannitol, demonstrating the potential use of this new matrix for effective DNA separations. The dramatic impact of mannitol on sieving performance of PNIPAM solution was investigated. pH dependent self-coating ability of PNIPAM was revealed. The presence of mannitol in TBE buffer decreased the pH of the buffer, which led to more efficient self-coating ability of PNIPAM probable due to the formation of hydrogen bonds between PNIPAM molecules and silanol groups at the silica wall. 相似文献
1000.
Qing Yan Li Hong Liang Hu Biao Chen Bin Wang Yu Ying Zhao 《中国化学快报》2007,18(7):843-845
One new cucurbitane-type triterpenoid saponin, 5b,19-epoxycucurbita-6,23-diene-3b,19,25-triol-3-O-b-D-allopyranoside (1), named momordicoside P was isolated from the fresh fruits of Momordica charantia. The structure of the saponin was elucidated byspectral methods, including 2D-NMR spectra. 相似文献