全文获取类型
收费全文 | 12887篇 |
免费 | 2039篇 |
国内免费 | 1775篇 |
专业分类
化学 | 9344篇 |
晶体学 | 165篇 |
力学 | 769篇 |
综合类 | 129篇 |
数学 | 1622篇 |
物理学 | 4672篇 |
出版年
2024年 | 47篇 |
2023年 | 187篇 |
2022年 | 396篇 |
2021年 | 452篇 |
2020年 | 448篇 |
2019年 | 452篇 |
2018年 | 411篇 |
2017年 | 396篇 |
2016年 | 565篇 |
2015年 | 588篇 |
2014年 | 747篇 |
2013年 | 931篇 |
2012年 | 1092篇 |
2011年 | 1223篇 |
2010年 | 881篇 |
2009年 | 893篇 |
2008年 | 1013篇 |
2007年 | 870篇 |
2006年 | 799篇 |
2005年 | 608篇 |
2004年 | 457篇 |
2003年 | 371篇 |
2002年 | 418篇 |
2001年 | 349篇 |
2000年 | 320篇 |
1999年 | 269篇 |
1998年 | 201篇 |
1997年 | 177篇 |
1996年 | 205篇 |
1995年 | 174篇 |
1994年 | 107篇 |
1993年 | 106篇 |
1992年 | 87篇 |
1991年 | 85篇 |
1990年 | 67篇 |
1989年 | 66篇 |
1988年 | 40篇 |
1987年 | 40篇 |
1986年 | 36篇 |
1985年 | 25篇 |
1984年 | 19篇 |
1983年 | 22篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1974年 | 4篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
Yan Sun Laixin Luo Fang Wang Jianqiang Li Yongsong Cao 《Analytical and bioanalytical chemistry》2009,395(2):465-471
A novel method based on solid-phase extraction was studied for the extraction of amitrole (3-amino-1,2,4-triazole), and its
residue determination in apples has been developed. The samples were derivatized with 4-chloro-3,5-dinitrobenzotrifluoride
(CNBF). The derivatization conditions and the influence of elution composition on the separation were investigated. In pH
9.5 H3BO3–Na2B4O7 media, the reaction of amitrole with CNBF was complete at 60°C after 30 min. The separation of derivatized amitrole was achieved
at room temperature within 13 min by gradient elution mode with cetyltrimethylammonium bromide in mobile phase as ion-pair
reagent. The method correlation coefficient was 0.9996, in concentrations ranging from 1.66 to 415 mg L−1. The calculated recoveries of the proposed method were from 94.17% to 105.67%, and relative standard deviations were 1.57%
to 6.44% in the application to the quantitative determination of amitrole in apples. The detection limit of amitrole was 0.10 mg L−1 with a signal-to-noise ratio of 3.
Figure Residue determination of amitrole in apple by ion-pairing high-performance liquid chromatography 相似文献
912.
报道了3',4'-二(对苯甲酰基苯甲氧)基-4-硝基二苯乙烯(C1)的合成与表征. 研究了在不同溶剂中分子的吸收与荧光发射. 分子在可见光区的吸收可以归于生色团对硝基二苯乙烯部分的贡献, 而其在短波长区的吸收主要由二苯甲酮部分提供. 分子在中等极性溶剂中表现出较强的荧光发射. 系统研究了3',4'-二(对苯甲酰基苯甲氧)基-4-硝基二苯乙烯与2',4'-二(对苯甲酰基苯甲氧)基-4-硝基二苯乙烯(C2)两种A-B2型分子的双光子性质与电化学行为. 结果表明, 在800 nm波长的飞秒激光激发下, 两个分子皆表现出明显的上转换荧光发射, 其双光子吸收横截面的大小与二苯甲酮取代位置表现出一定的相关性. 分子结构优化与电化学的研究表明, 两个分子的电子密度分布与前线轨道能量亦与二苯甲酮取代位置表现出一定的相关性. 相似文献
913.
Pengzuo Chen Kun Xu Zhiwei Fang Yun Tong Junchi Wu Xiuli Lu Xu Peng Hui Ding Changzheng Wu Yi Xie 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(49):14923-14927
Designing highly efficient electrocatalysts for oxygen evolution reaction (OER) plays a key role in the development of various renewable energy storage and conversion devices. In this work, we developed metallic Co4N porous nanowire arrays directly grown on flexible substrates as highly active OER electrocatalysts for the first time. Benefiting from the collaborative advantages of metallic character, 1D porous nanowire arrays, and unique 3D electrode configuration, surface oxidation activated Co4N porous nanowire arrays/carbon cloth achieved an extremely small overpotential of 257 mV at a current density of 10 mA cm−2, and a low Tafel slope of 44 mV dec−1 in an alkaline medium, which is the best OER performance among reported Co‐based electrocatalysts to date. Moreover, in‐depth mechanistic investigations demonstrate the active phases are the metallic Co4N core inside with a thin cobalt oxides/hydroxides shell during the OER process. Our finding introduces a new concept to explore the design of high‐efficiency OER electrocatalysts. 相似文献
914.
Poly(styrene-co-glycidyl methacrylate) latex microspheres with uniform size and high-density epoxy groups on the surface were prepared by soap-free emulsion polymerization with batch wise operation mode in the presence of 2.2′- azobis(2-methylpropionamidine) dihydrochloride as an initiator.The kinetics of soap-free emulsion polymerization and the effects of polymerization factors were examined.In addition,the optimum polymerization conditions of poly(styrene-co- glycidyl methacrylate) latex microspheres ... 相似文献
915.
A series of poly(dimethylsiloxane)(PDMS)-4,4′-diphenylmethanediisocyanate(MDI)-poly(ethylene glycol)(PEG) multiblock copolymers were synthesized by employing two-step growth polymerization and investigated by AFM,XPS. contact angle system,protein adsorption and platelets adhesion measurements,respectively.It was found that as the molecular weight of PDMS increased,the surface of copolymers had increasing phase separation,while the increase in the molecular weight of PEG decreased the phase separation ext... 相似文献
916.
茶叶中有机氯和拟除虫菊酯多种农药残留同时分析的样品前处理研究 总被引:1,自引:0,他引:1
建立了茶叶中同时分析12种有机氯和拟除虫菊酯类农药残留的样品提取和固相萃取(SPE)前处理方法.试样在超声条件下用正己烷提取后用自制弗罗里圭(florisil)/石墨化碳复合固相萃取小柱净化,然后采用气相色谱-电子捕获检测器(GC-ECD)测定.研究结果表明,当茶叶中农药加标在4.93~201.00 ng/g范围内时,添加回收率为68.9%~112.2%,相对标准偏差为2.43%~15.8%,方法的检出限范围在2.52~10.59 ng/g. 相似文献
917.
918.
Song-hua Ye Sheng Chen Fan Zhang Wei Wang Qin Tian Jin-zhi Liu Fang Chen Jin-ku Bao 《Applied biochemistry and biotechnology》2009,158(3):615-630
Plant lectins have been reported as transgenic resistance factors against a variety of insect pests. Herein, homologous analysis
demonstrated that Zephyranthes grandiflora agglutinin (ZGA) exhibited high similarity with other monocot mannose-binding lectins (MBLs). Phylogenetic analysis revealed
that it had taxonomical relationships with insecticidal MBLs. Subsequently, a plasmid expression vector pBI121 containing
zga gene (pBIZGA) was constructed using the zga sequence, under the control of CaMV35S promoter and nos terminator. pBIZGA was then integrated into the genome of Nicotiana tabacum L. Polymerase chain reaction and Southern blot analysis demonstrated that this zga gene was integrated into the plant genome. Western blotting and agglutinating activity analysis also showed that transgenic
tobacco plants expressed different levels of ZGA. Carbohydrate inhibition analysis indicated that recombinant ZGA and the
native shared the same carbohydrate-binding specificity. Moreover, genetic analysis confirmed Mendelian segregation (3:1)
of the transgenic in T1 progenies. In planta bioassays on T0 plants and their progenies indicated that expressed ZGA had an
effect on reducing the survivability and fecundity of tobacco aphids (Myzus nicotianae). These findings demonstrate that the novel zga gene of ZGA can be expressed in crop plants susceptible to various sap-sucking insects. 相似文献
919.
Fang Zhu 《Analytica chimica acta》2009,650(2):202-196
A method based on solid-phase microextraction (SPME) and gas chromatography with mass spectrometry (GC/MS) for the determination of 18 organophosphorus pesticides (OPPs) in textiles is described. Commercially available SPME fibers, 100 μm PDMS and 85 μm PA, were compared and 85 μm PA exhibited better performance to the OPPs. Various parameters affecting SPME, including extraction and desorption time, extraction temperature, salinity and pH, were studied. The optimized conditions were: 35 min extraction at 25 °C, 5% NaSO4 content, pH 7.0, and 3.5 min desorption in GC injector port at 250 °C. The linear ranges of the SPME-GC/MS method were 0.1-500 μg L−1 for most of the OPPs. The limits of detection (LODs) ranged from 0.01 μg L−1 (for bromophos-ethyl) to 55 μg L−1 (for azinphos-methyl) and the RSDs were between 0.66% and 9.22%. The optimized method was then used to analyze 18 OPPs in textile sample, and the determined recoveries were ranged from 76.7% to 126.8%. Moreover, the distribution coefficients of the OPPs between 85 μm PA fiber and simulative sweat solution (Kpa/s) were determined. The determined Kpa/s of the OPPs correlated well with their octanol-water partition coefficients (r = 0.764 and 0.678) and water solubility (r = −0.892 and −0.863). 相似文献
920.
A novel strategy to fabricate hydrogen peroxide (H2O2) sensor was developed based on multi-wall carbon nanotube/silver nanoparticle nanohybrids (MWCNT/Ag nanohybrids) modified gold electrode. The process to synthesize MWCNT/Ag nanohybrids was facile and efficient. In the presence of carboxyl groups functionalized multi-wall carbon nanotubes (MWCNTs), silver nanoparticles (Ag NPs) were in situ generated from AgNO3 aqueous solution and readily attached to the MWCNTs convex surfaces at room temperature, without any additional reducing reagent or irradiation treatment. The formation of MWCNT/Ag nanohybrids product was observed by transmission electron microscope (TEM), and the electrochemical properties of MWCNT/Ag nanohybrids modified gold electrode were characterized by electrochemical measurements. The results showed that this sensor had a favorable catalytic ability for the reduction of H2O2. The resulted sensor could detect H2O2 in a linear range of 0.05-17 mM with a detection limit of 5 × 10−7 M at a signal-to-noise ratio of 3. The sensitivity was calculated as 1.42 μA/mM at a potential of −0.2 V. Additionally, it exhibited good reproducibility, long-term stability and negligible interference of ascorbic acid (AA), uric acid (UA), and acetaminophen (AP). 相似文献