全文获取类型
收费全文 | 53108篇 |
免费 | 6585篇 |
国内免费 | 5225篇 |
专业分类
化学 | 12551篇 |
晶体学 | 985篇 |
力学 | 10423篇 |
综合类 | 808篇 |
数学 | 24077篇 |
物理学 | 16074篇 |
出版年
2024年 | 85篇 |
2023年 | 511篇 |
2022年 | 791篇 |
2021年 | 1106篇 |
2020年 | 1387篇 |
2019年 | 1277篇 |
2018年 | 1274篇 |
2017年 | 1752篇 |
2016年 | 2029篇 |
2015年 | 1553篇 |
2014年 | 2598篇 |
2013年 | 3904篇 |
2012年 | 3124篇 |
2011年 | 3514篇 |
2010年 | 3009篇 |
2009年 | 3436篇 |
2008年 | 3424篇 |
2007年 | 3440篇 |
2006年 | 3176篇 |
2005年 | 2887篇 |
2004年 | 2453篇 |
2003年 | 2245篇 |
2002年 | 2078篇 |
2001年 | 1788篇 |
2000年 | 1642篇 |
1999年 | 1519篇 |
1998年 | 1373篇 |
1997年 | 1145篇 |
1996年 | 973篇 |
1995年 | 794篇 |
1994年 | 720篇 |
1993年 | 582篇 |
1992年 | 584篇 |
1991年 | 460篇 |
1990年 | 372篇 |
1989年 | 276篇 |
1988年 | 250篇 |
1987年 | 192篇 |
1986年 | 143篇 |
1985年 | 192篇 |
1984年 | 184篇 |
1983年 | 86篇 |
1982年 | 126篇 |
1981年 | 83篇 |
1980年 | 60篇 |
1979年 | 84篇 |
1978年 | 52篇 |
1977年 | 64篇 |
1976年 | 31篇 |
1974年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 43 毫秒
991.
牛血清白蛋白与Indo-1相互作用的荧光光谱法研究 总被引:12,自引:4,他引:12
以牛血清白蛋白(Bovine serum albumin, BSA)与荧光探针Indo-1为蛋白质和配体模型, 基于Indo-1的荧光强度与BSA的分析浓度间的关系, 建立了计算二者相互作用位点数的方法, 并利用荧光共振能量转移及各种荧光技术对Indo-1和BSA的相互作用进行了研究. 结果表明, Indo-1在BSA中有3个作用位点, 这3个作用位点与BSA中的212位色氨酸(Trp 212)间的距离分别为2.93, 2.57和2.40 nm; Indo-1通过疏水性作用进入到BSA的3个疏水性空腔. 在荧光猝灭实验中, 通过Microlab 500 系列进样器和PTI荧光仪的联用实现了荧光强度的自动和实时记录. 相似文献
992.
993.
Koichiro Fukuda Miyuki Hisamura Nobuyuki Tera 《Journal of solid state chemistry》2007,180(6):1809-1815
A new quaternary layered carbide, Zr2[Al3.56Si0.44]C5, has been synthesized and characterized by X-ray powder diffraction, transmission electron microscopy and thermopower and electrical conductivity measurements. The crystal structure was successfully determined using direct methods, and further refined by the Rietveld method. The crystal is trigonal (space group R3m, Z=3) with lattice dimensions of a=0.331059(5), c=4.09450(5) nm and V=0.38864(1) nm3. The final reliability indices calculated from the Rietveld refinement were Rwp=6.24%, Rp=4.21% and RB=0.82%. The crystal structure is composed of electroconductive NaCl-type ZrC slabs separated by Al4C3-type [Al3.56Si0.44]C3 layers. This material had thermoelectric properties superior to those of the ternary layered carbides Zr2Al3C4 and Zr3Al3C5, with the power factor reaching 7.6×10−5W m−1 K−2. 相似文献
994.
Thermodynamic studies were performed on 12 pairs of N-trifluoroacetyl-O-alkyl nipecotic acid ester enantiomers on diluted permethylated beta-cyclodextrin stationary phase (CP Chirasil-Dex CB). The influence of ester alkyl group structure on interaction with permethylated beta-cyclodextrin (Me-CD) and enantioselectivity was studied. The types of alkyl groups studied included n-alkyl (C1-C5) and groups containing branching at differing locations relative to the chiral center of the molecule. The results show that for a given molecular weight, the n-alkyl esters have stronger interactions with Me-CD than esters containing branched alkyl groups. However, although having weaker interactions with Me-CD, esters containing alpha-branched alkyl groups exhibit higher enantioselectivity than the corresponding n-alkyl or beta-branched isobutyl esters. From the retention data, thermodynamic parameters were estimated using the retention increment method and enthalpy-entropy compensation plots (ln R' versus deltaH) were constructed. The results suggest that ester enantiomers with branching at the alpha-carbon of the ester alkyl group have additional and/or different types of enantioselective interactions with Me-CD than the C1-C5 n-alkyl esters or beta-branched isobutyl ester. In order to obtain a qualitative sense of the interaction with Me-CD, structures of the diastereomeric complexes formed between Me-CD and some of the ester enantiomers were modeled using simulated annealing molecular dynamics. 相似文献
995.
996.
997.
本文发现6~40号元素对能量为20keV的X_射线的质量吸收系数和质量相干散射系数之间呈二次幂函数关系,并据此提出了X_射线荧光定量分析校正基体效应的新方法——RhKa相干散射平方法.用国家标准物质GBW对该原理进行了验证.本法用于硅酸盐地质样品中微量元素的测定取得令人满意的结果. 相似文献
998.
The nano-ZnFe2O4/TiO2 films possess the functions of desulfurization and degradation for organic pollutants. The sols of ZnFe2O4/TiO2 were prepared by sol-gel method and coated on glass and porous ceramic by vertical coating and dipping-lift processes, respectively, and the samples were obtained after drying and sintering. The composition, appearance, absorption spectrum of the films, and the influence of the film on porous ceramic performances were analyzed using SEM, AFM, UV-Vis spectrometer, and mercury porosimeter, respectively, to determine the operation parameters of the multifunction porous ceramic elements for gas-purification. 相似文献
999.
A new compound of 4,4'-diamino-N,N'-diethyl bisbenzenesulfamide (C18H26N4O4S2,Fw = 426.55) has been synthesized and its structure was determined by X-ray crystallography method. The crystal belongs to the monoclinic system, space group P21/c with a = 10.0623(9), b =13.6759(13), c =15.5309(14) (A),β = 100.482(2)°, V= 2101.6(3)(A)3, Dc = 1.348 g/cm3, F(000) = 904,μ = 0.285 mm-1, Z = 4, the final R = 0.0512 and wR = 0.1363 for 3485 observed reflections with I >2σ(Ⅰ). The structure of the title compound is pseudo secondary axisymmetric, and the two sulfamide-groups show distorted tetrahedral configurations. 相似文献
1000.