全文获取类型
收费全文 | 2304篇 |
免费 | 144篇 |
国内免费 | 215篇 |
专业分类
化学 | 1339篇 |
晶体学 | 91篇 |
力学 | 556篇 |
综合类 | 23篇 |
数学 | 100篇 |
物理学 | 554篇 |
出版年
2024年 | 7篇 |
2023年 | 64篇 |
2022年 | 57篇 |
2021年 | 52篇 |
2020年 | 63篇 |
2019年 | 45篇 |
2018年 | 35篇 |
2017年 | 62篇 |
2016年 | 84篇 |
2015年 | 71篇 |
2014年 | 102篇 |
2013年 | 136篇 |
2012年 | 92篇 |
2011年 | 124篇 |
2010年 | 100篇 |
2009年 | 141篇 |
2008年 | 152篇 |
2007年 | 143篇 |
2006年 | 127篇 |
2005年 | 127篇 |
2004年 | 111篇 |
2003年 | 99篇 |
2002年 | 89篇 |
2001年 | 82篇 |
2000年 | 68篇 |
1999年 | 65篇 |
1998年 | 65篇 |
1997年 | 50篇 |
1996年 | 41篇 |
1995年 | 44篇 |
1994年 | 36篇 |
1993年 | 22篇 |
1992年 | 18篇 |
1991年 | 20篇 |
1990年 | 14篇 |
1989年 | 8篇 |
1988年 | 18篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1979年 | 3篇 |
1957年 | 2篇 |
排序方式: 共有2663条查询结果,搜索用时 281 毫秒
991.
毛细管电泳紫外吸收法分离检测海洋生物样品中不同形态的砷化合物 总被引:3,自引:1,他引:2
本研究建立了对亚砷酸盐As(Ⅲ)、二甲基砷(DMA)、对甲基苯砷酸(p-As)、一甲基砷(MMA)、砷酸盐(As(Ⅴ)) 5种不同形态的砷化合物的毛细管区带电泳(CZE)分离紫外检测方法,研究了检测波长、缓冲体系种类、pH值及其浓度、分离电压、温度、进样时间等因素对5种形态砷化合物的分离度、灵敏度、重现性等的影响.结果表明,在25 ℃、195 nm、20 mmol/L NaH2PO4-5 mmol/L Na2B4O7(pH=6.25)缓冲溶液、20 kV运行电压、3.0 kPa压力进样10 s条件下,5种不同形态砷化合物在11 min内取得完全分离,5种不同形态砷化合物的迁移时间和峰面积的RSD为0.50%~1.51%和1.65%~3.36%,检出限(3S/N)为0.004~0.30 mg/L.本法成功地应用于虾米中不同砷形态含量的测定,其回收率在93%~106%之间. 相似文献
992.
993.
采用差热-热重(TG-DTA)、恒电流充放电和交流阻抗(EIS)分析了二氟草酸硼酸锂(LiODFB)的热稳定性,研究了LiODFB/碳酸乙烯酯(EC)+碳酸二甲酯(DMC)电解液的电化学性能及界而特征.实验结果表明,LiODFB不仅具有更高的热稳定性,而且在EC+DMC溶剂中具有较好的电化学性能.与使用LiPF6/EC+DMC的电解液相比,锂离子电池应用LiODFB基电解液在55℃的高温具有更好的容量保持能力;以0.5C、1C(1C=250 mA·g-1)倍率循环放电,两种电池间的倍率性能差别较小;LiODFB能够在1.5 V(vs Li/Li+)左右在石墨电极表面还原形成一个优异稳定的保护性固体电解质相界面膜(SEI膜);交流阻抗表明,使用LiODFB基电解液的锂离子电池仅具有稍微增加的界面阻抗.因此LiODFB是一种非常有希望替代LiPF6用作锂离子电池的新盐. 相似文献
994.
995.
In the paper, a new kind of vitamin B12 (acquo-cobalamine) chemically modified electrode was fabricated and applied in capillary zone electrophoresis coupled with amperometric detection (CZE-AD) for simultaneous determination of six antioxidants in fruits and vegetables. The catalytic electrochemical properties of the chemically modified electrode could obviously enhance oxidation peak heights responses by about five times to glutathione, ascorbic acid, vanillic acid, chlorogenic acid, salicylic acid, and caffeic acid compared with common carbon disk electrode. Furthermore, the effects of working electrode potential, pH and concentration of running buffer, separation voltage and injection time on CZE-AD were investigated. Under the optimum conditions, the six analytes could be completely separated and detected in a borate-phosphate buffer (pH 8.4) within 15 min. Their linear ranges were from 2.5 × 10−7 to 1.0 × 10−4 mol L−1 and the detection limits were as low as 10−8 mol L−1 magnitude (S/N = 3). The proposed method has been successfully employed to monitor the six analytes in practical samples with recoveries in the range 96.0-106.0% and RSDs less than 5.0%. Above results demonstrate that capillary zone electrophoresis coupled with electrochemical detection using vitamin B12 modified electrode as detector is of convenient preparation, high sensitivity, good repeatability, and could be used in the rapid determination of practical samples. 相似文献
996.
Xueping Ge Mozhen Wang Xiang Ji Xuewu Ge Huarong Liu 《Colloid and polymer science》2009,287(7):819-827
The effects of the concentration of polyoxyethylene octylphenyl ether (OP-10) as a nonionic surfactant and the molecular weight
of polymers (polystyrene (PS) and poly(methyl methacrylate) (PMMA)) on the morphology of anisotropic PS/PMMA composite particles
were investigated. In the case of polymers with lower molecular weight (M
w ≈ 6.0 × 104 g/mol), the PS/PMMA composite particles have dimple, via acorn, to hemispherical shapes along with the increase of the OP-10
concentration. On the other hand, when the polymers have higher molecular weight (M
w ≈ 3.3 × 105 g/mol), the morphology of PS/PMMA composite particles changed from dimple, via hemispherical, to snowman-like structure while
the concentration of OP-10 was increased. Furthermore, thermodynamic analysis was first simply made by spreading coefficients,
and the results indicated that both the concentration of OP-10 aqueous solution and the molecular weight of polymers were
very important to the final morphology of anisotropic composite particles. 相似文献
997.
Surface hydrophilization for polypropylene microporous membranes: A facile interfacial crosslinking approach 总被引:2,自引:0,他引:2
A hydrophilic surface is very important for hydrophobic separation membranes such as polypropylene microporous membranes (PPMMs). In this work a facile and effective method, interfacial crosslinking combined with pretreatment by dielectric barrier discharge plasma at atmospheric pressure, was developed for endowing PPMMs with a hydrophilic and charged surface. Poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) and p-xylylene dichloride were selected for quaternization crosslinking to form a positively charged coating layer, which was characterized with FT-IR/ATR, XPS, and FESEM. Water contact angle and pure water flux measurements were conducted to evaluate the surface hydrophilicity. The influence of surface charges on protein filtration was also investigated. It is found that the mass gain of interfacial crosslinking increases almost linearly with increasing the PDMAEMA concentration from 0.5 to 10 g/L. The crosslinking degree is larger than 80% according to the XPS results, ensuring the stability of the crosslinking layer. The surface hydrophilicity is demonstrated by the sharp decrease of water contact angle from 145° to 20°. The pure water flux also increases 3 times under the optimized conditions. Furthermore, the results of protein filtration suggest that these highly hydrophilic and charged surfaces can effectively resist the fouling of proteins. 相似文献
998.
Electrospun polyacrylonitrile (PAN) nanofibrous scaffold was used as a mid-layer support in a new kind of high flux thin film nanofibrous composite (TFNC) membranes for nanofiltration (NF) applications. The top barrier layer was produced by interfacial polymerization of polyamides containing different ratios of piperazine and bipiperidine. The filtration performance (i.e., permeate flux and rejection) of TFNC membranes based on electrospun PAN nanofibrous scaffold was compared with those of conventional thin film composite (TFC) membranes consisting of (1) a commercial PAN ultrafiltration (UF) support with the same barrier layer coating and (2) two kinds of commercial NF membranes (i.e., NF90 and NF270 from Dow Filmtec). The nanofiltration test was carried out by using a divalent salt solution (MgSO4, 2000 ppm) and a cross-flow filtration cell. The results indicated that TFNC membranes exhibited over 2.4 times more permeate flux than TFC membranes with the same chemical compositions, while maintaining the same rejection rate (ca. 98%). In addition, the permeate flux of hand-cast TFNC membranes was about 38% higher than commercial NF270 membrane with the similar rejection rate. 相似文献
999.
1000.
Existing cohesive zone models assume that actual fracture zone of non-zero mass can be modeled by a line segment (cohesive zone) with no mass and inertia. In the present work, a simplified mass-spring model is presented to study inertia effect of cohesive zone on a mode-I steady-state moving crack. It is showed that fracture energy predicted by the present model increases dramatically when a finite limiting crack speed is approached. Reasonable agreement with known experiments indicates that the present model has the potential to catch the inertia effect of cohesive zone which has been ignored in existing cohesive zone models and better simulate dynamic fracture at high crack speed. 相似文献