全文获取类型
收费全文 | 9526篇 |
免费 | 1802篇 |
国内免费 | 638篇 |
专业分类
化学 | 523篇 |
晶体学 | 10篇 |
力学 | 84篇 |
综合类 | 119篇 |
数学 | 156篇 |
物理学 | 2515篇 |
无线电 | 8559篇 |
出版年
2024年 | 45篇 |
2023年 | 99篇 |
2022年 | 164篇 |
2021年 | 197篇 |
2020年 | 248篇 |
2019年 | 165篇 |
2018年 | 175篇 |
2017年 | 270篇 |
2016年 | 381篇 |
2015年 | 368篇 |
2014年 | 699篇 |
2013年 | 625篇 |
2012年 | 771篇 |
2011年 | 784篇 |
2010年 | 652篇 |
2009年 | 562篇 |
2008年 | 687篇 |
2007年 | 694篇 |
2006年 | 688篇 |
2005年 | 589篇 |
2004年 | 538篇 |
2003年 | 510篇 |
2002年 | 384篇 |
2001年 | 343篇 |
2000年 | 239篇 |
1999年 | 189篇 |
1998年 | 154篇 |
1997年 | 114篇 |
1996年 | 132篇 |
1995年 | 102篇 |
1994年 | 98篇 |
1993年 | 66篇 |
1992年 | 64篇 |
1991年 | 53篇 |
1990年 | 37篇 |
1989年 | 27篇 |
1988年 | 24篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 1篇 |
1976年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
本文首先对国内半导体分立器件和半导体集成电路的质量水平做了估价,接着进行了国内半导体器件市场分析,讨论了器件销售所面临的困难和造成困难的原因,探讨了器件生产厂家的出路和发展方向,并对国产器件所存在的问题做了评述。文中还对半导体器件引进生产线情况做了介绍。本文在概述了分立器件的发展方向之后,重点阐述国内半导体集成电路的发展动态(我国IC工业发展现状、国内生产IC的主要品种、“七五”期间IC工业的发展及ASIC),并对国外IC发展动态做了扼要说明。 相似文献
52.
53.
54.
为了解海生物对钢板管椿腐蚀之影响 ,将SS4 1金属试片浸渍于高雄港 #1 4码头水深 3m处及实验室人造海水中 .试验期间 ,以DC直流动电位极化曲线扫描与AC交流电阻抗分析现场量测各试片的瞬间腐蚀速率 .结果发现 :宏观地看 ,海生物在金属 (或锈层 )表面的附著可以减缓金属腐蚀 ,但从微观 (micro)的观点推论 ,海生物在金属表面的附著亦可以造成氧差或浓度差异电池 ,促成局部腐蚀 .此外 ,等效电路的模拟 ,有助于了解海生物附著对金属腐蚀的影响 ,即随浸渍时间的延长 ,金属表面因锈层增厚且趋于致密 ,以致锈层电阻增加 ;又因海生物种类不同 ,含水量不同 ,海生物电阻可能会有极大的差异 相似文献
55.
The MReaDy program was designed for studying Multiprocess Reactive Dynamic systems, that is, complex chemical systems involving different and concurrent reactions. It builds a global potential energy surface integrating a variety of potential energy surfaces, each one of them representing an elementary reaction expected to play a role in the chemical process. For each elementary reaction, energy continuity problems may happen in the transition between potential energy surfaces due to differences in the functional form for each of the fragments, especially if built by different authors. A N‐dimensional switch function is introduced in MReaDy in order to overcome such a problem. As an example, results of a collision trajectory calculation for H2 + OH → H3O are presented, showing smooth transition in the potential energy, leading to conservation in the total energy. Calculations for a hydrogen combustion system from 1000 K up to 4000 K shows a variation of 0.012% when compared to the total energy of the system. © 2016 Wiley Periodicals, Inc. 相似文献
56.
A method for the rapid trace analysis of 24 residual pesticides in apple juice by multidimensional gas chromatography–mass spectrometry (MD-GC/MS) using dispersive liquid–liquid microextraction (DLLME) was developed and optimized. Several parameters of the extraction procedure such as type and volume of extraction solvent, type and volume of dispersive solvent and salt addition were evaluated to achieve the highest yield and to attain the lowest detection limits. The DLLME procedure optimized consists in the formation of a cloudy solution promoted by the fast addition to the sample (5 ml) of a mixture of carbon tetrachloride (extraction solvent, 100 μl) and acetone (dispersive solvent, 400 μl). The tiny droplets formed and dispersed among the aqueous sample solution are further joined and sedimented (85 μl) in the bottom of the conical test tube by centrifugation. Once extracted, all the 24 pesticides were directly injected and separated by a dual GC column system, comprising a short wide-bore DB-5 capillary column with low film thickness connected by a Deans switch system to a second chromatographic narrower column, with identical stationary phase. The instrumental setting used, in combination with carefully optimized operational fast GC and MS parameters, markedly decreased the retention times of the targeted analytes. The total chromatographic run was 8 min. Mean recoveries for apple juice spiked at three concentrations ranged from 60% to 105% and the intra-repeatability ranged from 1% to 21%. The limits of detection of the 24 pesticides ranged from 0.06 to 2.20 μg/L. In 2 of a total of 28 analysed samples were found residues of captan, although at levels below the maximum limit legal established. 相似文献
57.
Multiplexed solid-contact ion-selective electrodes (SCISEs) are fabricated using printed circuit board (PCB) and mesoporous carbon black (MCB) as ion-to-electron transducer (solid contact). Four sensor configurations were examined and showed that in addition to MCB, the sensor configuration plays crucial role in the stability of the potential response. The enhanced sensor stability was also linked with suppression of transmembrane flux of water. The sensors exhibited near-Nernstian sensitivity (58.1 mV/dec for K+ ISEs and −55.1 mV/dec for NO3- ISEs), low detection limits (1.5–2.2 μM), and good short-term stability (∼0.1 mV/min). Sensors can be stored dry and used without preconditioning. This work demonstrates a promising approach to combining PCB technology and carbon black for large-scale production of low cost ISEs for point-of-care testing, wearables, or in situ field measurements. 相似文献
58.
A novel photochromic Schiff base derivative, 5,17-N,N′-(5,5′-di-methoxyl-benzlaldehyde)diimine-25,27-dipropoxy-calix[4]arene has been synthesized through incorporation of two imine groups into the upper rims of calix[4]arene. The experiments showed that the addition of Dy3+ or Er3+ ions to compound 4 results in the solution color change, but other metal ions caused less change. It indicated that the synthetic receptor can selectively recognize Dy3+ and Er3+ ion by naked eye over other lanthanide cations. Thus, these systems can be applied as chemosensor for Dy3+ and Er3+ ion in analytical chemistry. 相似文献
59.
S-nitrosylated proteins are biomarkers of oxidative damage in aging and Alzheimer's disease (AD). Here, we report a new method for detecting and quantifying nitrosylated proteins by capillary gel electrophoresis with laser induced fluorescence detection (CGE-LIF). Dylight 488 maleimide was used to specifically label thiol group (SH) after switching the S-nitrosothiol (S-NO) to SH in cysteine using the "fluorescence switch" assay. In vitro nitrosylation model-BSA subjected to S-nitrosoglutathione (GSNO) optimized the labeling reactions and characterized the response of the LIF detector. The method proves to be highly sensitive, detecting 1.3 picomolar (pM) concentration of nitrosothiols in nanograms of proteins, which is the lowest limit of detection of nitrosothiols reported to date. We further demonstrated the direct application of this method in monitoring protein nitrosylation damage in MQ mediated human colon adenocarcinoma cells. The nitrosothiol amounts in MQ treated and untreated cells are 14.8±0.2 and 10.4±0.5 pmol/mg of proteins, respectively. We also depicted nitrosylated protein electrophoretic profiles of brain cerebrum of 5-month-old AD transgenic (Tg) mice model. In Tg mice brain, 15.5±0.4 pmol of nitrosothiols/mg of proteins was quantified while wild type contained 11.7±0.3 pmol/mg proteins. The methodology is validated to quantify low levels of S-nitrosylated protein in complex protein mixtures from both physiological and pathological conditions. 相似文献
60.
Xiaobo ZhouYunguo Lu Jian-Fa ZhuWing-Hong Chan Albert W.M. LeePui-Shan Chan Ricky N.S. WongN.K. Mak 《Tetrahedron》2011,67(19):3412-3419
By appending a pair of carboxamidoquinoline pendants onto 1,2-diaminocyclohexane scaffold via N-alkylation, multifunctionalized ACAQ was designed and synthesized as a water soluble fluorescent ratiometric chemosensor for Zn2+. In 50% aqueous methanol buffer pH 7.4 solution, upon excitation at 316 nm, ACAQ (5 μM) displayed a selective ratiometric fluorescence changes with a shift from 410 to 490 nm in response to the interaction with Zn2+. After binding with 1 equiv of Zn2+, ACAQ exhibited a 12-fold enhancement in I490/I410 characterized by a clear isoemissive point at 440 nm. The metal sensor binding mode was established by Job’s plot and the combined fluorescence and 1H NMR spectroscopic method. The selectivity of the probe toward biological relevant cations and transition metal ions was proven to be good. In addition, the interference caused by Cu2+ and Cd2+ in the quantitation of Zn2+ can be completely eliminated by the use of diethyldithiocarbamate as the screening agent. Exploitation of ACAQ as the sensing probe, ratiometric determination of Zn2+ with the limit of detection (LOD) at 28.3 nm can be realized. In addition, the unique responsive properties of the probe toward Fe3+ and Zn2+ were used to construct a fluorescent switch. The membrane permeability of ACAQ to living cells and bio-imaging of Zn2+ were demonstrated. 相似文献