全文获取类型
收费全文 | 4075篇 |
免费 | 620篇 |
国内免费 | 557篇 |
专业分类
化学 | 3074篇 |
晶体学 | 41篇 |
力学 | 198篇 |
综合类 | 55篇 |
数学 | 469篇 |
物理学 | 1415篇 |
出版年
2024年 | 10篇 |
2023年 | 68篇 |
2022年 | 95篇 |
2021年 | 115篇 |
2020年 | 161篇 |
2019年 | 160篇 |
2018年 | 151篇 |
2017年 | 122篇 |
2016年 | 166篇 |
2015年 | 185篇 |
2014年 | 194篇 |
2013年 | 265篇 |
2012年 | 313篇 |
2011年 | 356篇 |
2010年 | 239篇 |
2009年 | 215篇 |
2008年 | 289篇 |
2007年 | 199篇 |
2006年 | 208篇 |
2005年 | 202篇 |
2004年 | 165篇 |
2003年 | 179篇 |
2002年 | 211篇 |
2001年 | 178篇 |
2000年 | 119篇 |
1999年 | 107篇 |
1998年 | 89篇 |
1997年 | 50篇 |
1996年 | 98篇 |
1995年 | 71篇 |
1994年 | 50篇 |
1993年 | 30篇 |
1992年 | 32篇 |
1991年 | 29篇 |
1990年 | 30篇 |
1989年 | 18篇 |
1988年 | 16篇 |
1987年 | 15篇 |
1986年 | 9篇 |
1985年 | 15篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1974年 | 1篇 |
1959年 | 1篇 |
1957年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有5252条查询结果,搜索用时 15 毫秒
81.
Magnetic NiFe particles were synthesized through hydrothermal method using hydrazine as reductant. Composite particles with core-shell structure were further achieved by depositing silicon dioxide generated via carbonation decomposition of sodium silicate solution on the surface of magnetic cores. Characterized by XRD, the Ni9Fe particles are of fcc-type structure, and the structure of magnetic cores in composite particles was maintained despite being covered by SiO2 shell. The existence of SiO2 shells in the composite particles were demonstrated by SEM, EDS and IR. The results from TG and VSM indicated that the shell structure affected the physiochemical properties. The composite particles exhibited remarkable resistance to oxidation in comparison with Ni9Fe particles due to being protected by SiO2 shell. Meanwhile, both of them are soft magnetic materials, but Ms, Mr and Hc in Ni9[email protected]2 particle decreased compared with magnetic NiFe particles. The formation mechanisms of Ni9Fe micro-particles and composite Ni9Fe particles were discussed. 相似文献
82.
Bao Shan Huang Mary Jane Lauzon James C. Parham 《Journal of heterocyclic chemistry》1979,16(4):811-813
Alkylation of 4(5)-nitroimidazole-5(4)-sulfonamide with benzyl bromide occurred on both ring nitrogens. The structures of the products could be assigned by comparison of the chemical shifts of the sulfonamide hydrogens in the nmr spectra with those of the isomeric methyl derivatives, which were prepared by differing routes. Uv and nmr spectral data are reported for a number of bromo-, nitro-, mercapto-, sulfamyl- and amino- substituted imidazoles as well as for both of the isomeric methylated derivatives of the series. 相似文献
83.
84.
环己烷中苯甲酰苯胺的双重荧光--分子内电荷转移的直接光谱证据 总被引:2,自引:0,他引:2
自从O Connell等[1]报道苯甲酰苯胺(BA)在EPA玻璃体中异常的长波长荧光发射特性以来, 已有众多学者尝试解释该"异常"荧光的发射态性质[2~12]. Kasha等[2~7]认为长波长荧光是质子转移(PT)和电荷转移(CT)两种激发态发射的叠加, 而Azumaya等[8]则认为发射态只包含分子内扭转电荷转移(TICT)态. 应该指出的是, 在上述研究中, 电荷转移态的指认并无有力的实验事实, 而主要是依据与具有CT双重荧光的对二甲氨基苯甲氰[13,14]的类比. 显然, 有关苯甲酰苯胺的长波长荧光发射态的准确性质仍待实验阐明 相似文献
85.
Wen-Jia Zhou Shu-Juan Bao Yan-Yu Liang Ben-Lin He Hu-Lin Li 《Journal of Solid State Electrochemistry》2006,10(5):277-282
Pure-phase and well-crystallized spinel LiMn2O4 powders were successfully synthesized by a simple rheological phase method. The thermal behavior and structure properties
of the powders prepared by the rheological phase method compared with the solid-state reaction were investigated by thermogravimetry,
powder X-ray diffraction , scanning electron microscopy and transmission electron microscopy. According to the results of
the electrochemical tests, it is obvious that the sample resulting from the rheological phase method shows higher discharge
capacity and better cycling stability than one formed in the solid-state reaction. The cyclic voltammogram and columbic efficiency
curves also confirm that the product by the rheological phase method has a good cycling performance due to its fine cubic
spinel structure and morphology. 相似文献
86.
建立了超高效液相色谱-三重四极杆质谱联用技术测定血浆和尿液中马桑中毒标志物马桑亭和马桑宁的方法。血浆和尿液样品经固相支持液液萃取法提取净化后,溶于15%(v/v)甲醇水溶液中,以Cortecs C18色谱柱(100 mm×2.1 mm,1.6 μm)作为分析柱进行分离,电喷雾负离子多反应监测(MRM)模式下检测,以氟苯尼考作为内标物,基质工作曲线内标法定量。血浆和尿液中马桑亭和马桑宁的平均加标回收率为86.2%~110%,相对标准偏差为5.1%~14.6%(n=6),血浆中马桑亭和马桑宁的检出限(S/N=3)分别为0.01 μg/L和0.1 μg/L,尿液中马桑亭和马桑宁的检出限分别为0.03 μg/L和0.3 μg/L。本法简单、灵敏、准确,可用于血浆和尿液中马桑亭和马桑宁的中毒检测。 相似文献
87.
A bio-mimic bulk acoustic wave (BAW) sensor was fabricated by coating the caffeine (CAF) template molecular imprinting polymer (MIP). This sensor exhibited high selectivity and a sensitive mass response to CAF. The response range of the sensor was between 5.0 x 10(-9) and 1.0 x 10(-4) M with a detection limit of 5.0 x 10(-9) M at pH 8.0. Recoveries were 96.1-105.6%. Influencing factors were investigated in detail and optimized. When employed to detect real samples, the proposed method proved to be a convenient method with the advantages of high sensitivity, good selectivity and ease of handling. 相似文献
88.
A microchip CE-amperometric detection (AD) system has been fabricated by integrating a two-dimensionally adjustable CE microchip and an AD cell containing a one-dimensionally adjustable disk detection electrode in a Plexiglas holder. It facilitates the precise 3-D alignment between the channel outlet and the detection electrode without a complicated 3-D manipulator. The performance of this unique system was demonstrated by separating five aromatic amines (1,4-phenyldiamine, aniline, 2-methylaniline, 4-chloroaniline, and 1-naphthylamine) of environmental concern. Factors influencing their separation and detection processes were examined and optimized. The five analytes have been well separated within 140 s in a 74 cm long separation channel at a separation voltage of +2500 V using a 10 mM phosphate buffer (pH 3.5). Highly linear response is obtained for the five analytes over the range 20-200 microM with the detection limits ranging from 0.46 to 1.44 microM, respectively. The present system demonstrated long-term stability and reproducibility with RSDs of less than 5% for the peak current (n = 9). The new approach for the microchannel-electrode alignment should find a wide range of applications in CE, flowing injection analysis, and other microfluidic analysis systems. 相似文献
89.
Bao J Baker RK Doss GA Kayser F Kotliar A Miao S Parsons WH Rupprecht KM 《Organic letters》2002,4(11):1871-1873
[reaction: see text] Pentacyclic triterpenoid natural product correolide (1) was converted to ketone 2 via ozonolysis. An unusual fragmentation reaction of ketone 2 with LiCl was discovered. This reaction is general among several similar substrates examined and appears to be specific for the correolide-type E-ring structure (ketone). A mechanism involving a retroaldol reaction, a nucleophilic opening of the epoxide, and a subsequent acetoxy elimination reaction was proposed. 相似文献
90.
Wei Lun-Cún Bao Shanglian Yang Qixiang Yang Xihong 《Journal of Radioanalytical and Nuclear Chemistry》1991,151(1):75-81
Combining the Charged Particle Activation Analysis (CPAA) and the Channeling Technique, the partial concentrations of the impurity carbon atoms in different crystal lattice locations of GaAs were claculated. The calculated results show that at lower total concentrations (0.3 ppm), carbon atoms occupy principally the octahedral and displaced octahedral interstitial positions, but at higher total concentrations (2 ppm), the substitutional carbon plays a principal role. 相似文献