全文获取类型
收费全文 | 10189篇 |
免费 | 1686篇 |
国内免费 | 2016篇 |
专业分类
化学 | 7880篇 |
晶体学 | 121篇 |
力学 | 611篇 |
综合类 | 149篇 |
数学 | 1328篇 |
物理学 | 3802篇 |
出版年
2024年 | 14篇 |
2023年 | 231篇 |
2022年 | 376篇 |
2021年 | 415篇 |
2020年 | 484篇 |
2019年 | 468篇 |
2018年 | 366篇 |
2017年 | 402篇 |
2016年 | 553篇 |
2015年 | 556篇 |
2014年 | 598篇 |
2013年 | 834篇 |
2012年 | 776篇 |
2011年 | 877篇 |
2010年 | 657篇 |
2009年 | 617篇 |
2008年 | 708篇 |
2007年 | 586篇 |
2006年 | 546篇 |
2005年 | 507篇 |
2004年 | 417篇 |
2003年 | 354篇 |
2002年 | 404篇 |
2001年 | 320篇 |
2000年 | 277篇 |
1999年 | 233篇 |
1998年 | 181篇 |
1997年 | 130篇 |
1996年 | 154篇 |
1995年 | 113篇 |
1994年 | 133篇 |
1993年 | 102篇 |
1992年 | 73篇 |
1991年 | 94篇 |
1990年 | 90篇 |
1989年 | 42篇 |
1988年 | 40篇 |
1987年 | 29篇 |
1986年 | 34篇 |
1985年 | 37篇 |
1984年 | 15篇 |
1983年 | 19篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1971年 | 1篇 |
1957年 | 3篇 |
1936年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 859 毫秒
791.
建立了富硒黑木耳中硒代胱氨酸、硒代半胱氨酸、亚硒酸、硒蛋氨酸、硒酸5种硒形态的液相色谱-原子荧光光谱分析方法。通过链酶蛋白酶E酶解,结合超声提取后,选取Hamilton PRP-X100离子交换色谱柱(250 mm×4.1 mm,10μm),40 mmol/L的磷酸氢二铵为流动相,在16 min内,5种硒形态完全达到基线分离。5种硒形态在线性范围内相关系数R为0.9990~0.9999;加标回收率为76.1%~108%;检出限分别为硒代胱氨酸0.35μg/L、甲基-硒代半胱氨酸0.46μg/L、亚硒酸0.26μg/L、硒代蛋氨酸0.64μg/L、硒酸3.06μg/L;方法应用于富硒黑木耳中硒形态的分析,精密度高、重现性好、方法稳定、准确可靠,是测定富硒黑木耳中硒形态含量的有效方法。 相似文献
792.
超高效液相色谱-四极杆/静电场轨道阱高分辨质谱法非靶向筛查苹果中苯脲类农药 总被引:1,自引:0,他引:1
建立了超高效液相色谱-四极杆/静电场轨道阱高分辨质谱(UPLC-Q/Orbitrap HRMS)非靶向筛查苹果中苯脲类农药的方法。样品采用QuEChERS法提取净化,Acquity BEH C18色谱柱(100 mm × 2.1 mm,1.7 μm)分离,以甲醇和含0.1%甲酸的水溶液为流动相进行梯度洗脱,在电喷雾正离子模式下采用四极杆/静电场轨道阱高分辨质谱进行检测。将13种苯脲类除草剂和9种苯甲酰脲类杀虫剂按化学结构分为4类。首先通过对4类22种典型苯脲类农药标准品的准分子离子和二级质谱碎片进行分析,总结苯脲类农药的质谱裂解规律如下:绿麦隆等9种苯脲类除草剂的主要特征离子碎片为m/z 72.044 59,可通过特征丢失中性分子二甲胺(m/z 45.058 03)产生特征离子碎片;绿谷隆等4种苯脲类除草剂可通过特征丢失中性分子甲醇[CH3OH]或卤化氢[HR1](R=Cl,Br,F)产生离子碎片;除虫脲等7种含氟苯甲酰脲杀虫剂的主要特征离子碎片为 m/z 158.040 47、141.015 00,也可发生特征中性丢失2,6-氟苯甲酰胺结构[C8H3F2O2NH2](m/z 183.013 21);杀铃脲等2种含氯苯甲酰脲类杀虫剂的主要特征离子碎片为m/z 156.020 25、138.993 76、113.015 28。利用该方法对北京12份市售苹果进行非靶向筛查,在1份样品中筛查出绿麦隆。该方法可为快速筛查农产品中相似结构特征的苯脲类化合物提供参考。 相似文献
793.
Nanosized surface-enhanced Raman scattering (SERS) substrates fabricated by the controlled growth of metal nanostructures on water-dispersed two-dimensional nanomaterials can open a new avenue for SERS analysis of liquid samples in biological fields. In this work, regular and uniform Ag nanostructures were grown on the surface of graphene oxide (GO) through a microwave-assisted hydrothermal method. Polyamidoamine (PAMAM) dendrimers were assembled on the surface of GO to form GO/PAMAM templates for growing Ag nanostructures, which are primarily comprised of Ag dimers and trimers. The prepared Ag/GO nanocomposites are highly dispersed and stable in aqueous solution and may be used as substrates for enhanced Raman detection of rhodamine 6?G (R6G) in aqueous solution. This special substrate provides high-performance SERS and suppresses R6G fluorescence in aqueous solution and is promising as a nanosized material for the enhanced Raman detection of liquid samples in biological diagnostics. 相似文献
794.
Chao Tian Yuanli Liang Haixia Lin Jie Song Qi Li Rui Li 《Journal of Dispersion Science and Technology》2019,40(6):892-900
A rosin-based ester tertiary amine salt (RETAS) cationic surfactant was obtained using natural rosin as raw material. GC-MS of RETAS was detailed analyzed. The pH-responsive mechanism of rosin-based ester tertiary amine (RETA) and RETAS was confirmed by applying theoretical calculations about electrostatic potential maps of RETA and RETAS cation using Gaussian software. Mixed system surfactants were obtained by blending RETAS cationic surfactant with sodium dodecyl benzene sulfonate (SDBS) anionic surfactant. The binary mixed surfactant systems of RETAS and SDBS had obvious synergistic effect. The γcmc and CMC were 39.40?mN/m and 0.56?mmol/L at the optimum molar fraction of RETAS (α)?=?0.6, respectively. The stability time of emulsion with the optimum mixed system as emulsifier increased to 309?s at α?=?0.6. The emulsifying capacity of RETAS was much better than that of RETA. RETAS had pH-responsive targeted release and the optimum mixed system showed a relatively sustained drug release by using doxorubicin (DOX) as a model drug. These results indicate that RETAS surfactant and mixed system surfactant are both promising for applications in drug delivery and emulsification. 相似文献
795.
Mo对脱合金制备的Ni-Mo电极骨架结构与析氢性能的影响 总被引:1,自引:0,他引:1
采用快速凝固结合脱合金化方法制备了不同Mo含量的纳米多孔Ni-Mo合金,通过X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和N2吸附-脱附分析等对多孔合金的物相、形貌结构及孔径分布进行了表征,并通过线性扫描伏安、Tafel斜率、交流阻抗和循环伏安等方法测试了多孔合金电极的电催化析氢性能.结果显示,多孔合金电极材料在50 mA/cm2电流密度下析氢过电位随着Mo含量的增加先降低后升高,Ni2.5Mo2.5合金析氢活性最强,过电位为218 mV,析氢过程由Volmer-Heyrovsky步骤控制,交换电流密度为0.29 mA/cm2,经1000周循环后的极化曲线基本保持原状,50 mA/cm2电流密度下过电位增加3.67%,表现出优良的析氢稳定性. 相似文献
796.
797.
Qi Teng Wenxiu Mao Dong Chen Zhen Wang Chen‐Ho Tung Zhenghu Xu 《Angewandte Chemie (International ed. in English)》2020,59(6):2220-2224
A rhodium(I)‐BINAP‐catalyzed highly enantioselective [2+2+2] cycloaddition of enynes with alkynes has been developed. Diverse fused tricyclic hydronaphthofuran scaffolds with three consecutive stereogenic centers were constructed in one step from easily available materials with excellent chemo‐, regio‐, diastereo‐, and enantioselectivity. Notable features of these reactions include 100 % atom economy, very broad scope, and mild reaction conditions. 相似文献
798.
Xue‐Qiang Zhang Tao Li Bo‐Quan Li Rui Zhang Peng Shi Chong Yan Jia‐Qi Huang Qiang Zhang 《Angewandte Chemie (International ed. in English)》2020,59(8):3252-3257
High‐energy‐density Li metal batteries suffer from a short lifespan under practical conditions, such as limited lithium, high loading cathode, and lean electrolytes, owing to the absence of appropriate solid electrolyte interphase (SEI). Herein, a sustainable SEI was designed rationally by combining fluorinated co‐solvents with sustained‐release additives for practical challenges. The intrinsic uniformity of SEI and the constant supplements of building blocks of SEI jointly afford to sustainable SEI. Specific spatial distributions and abundant heterogeneous grain boundaries of LiF, LiNxOy, and Li2O effectively regulate uniformity of Li deposition. In a Li metal battery with an ultrathin Li anode (33 μm), a high‐loading LiNi0.5Co0.2Mn0.3O2 cathode (4.4 mAh cm?2), and lean electrolytes (6.1 g Ah?1), 83 % of initial capacity retains after 150 cycles. A pouch cell (3.5 Ah) demonstrated a specific energy of 340 Wh kg?1 for 60 cycles with lean electrolytes (2.3 g Ah?1). 相似文献
799.
Nan Zhang Leigang Li Juan Wang Zhiwei Hu Qi Shao Xiangheng Xiao Xiaoqing Huang 《Angewandte Chemie (International ed. in English)》2020,59(21):8066-8071
Surface regulation is an effective strategy to improve the performance of catalysts, but it has been rarely demonstrated for nitrogen reduction reaction (NRR) to date. Now, surface‐rough Rh2Sb nanorod (RNR) and surface‐smooth Rh2Sb NR (SNR) were selectively created, and their performance for NRR was investigated. The high‐index‐facet bounded Rh2Sb RNRs/C exhibit a high NH3 yield rate of 228.85±12.96 μg h?1 mg?1Rh at ?0.45 V versus reversible hydrogen electrode (RHE), outperforming the Rh2Sb SNRs/C (63.07±4.45 μg h?1 mg?1Rh) and Rh nanoparticles/C (22.82±1.49 μg h?1 mg?1Rh), owing to the enhanced adsorption and activation of N2 on high‐index facets. Rh2Sb RNRs/C also show durable stability with negligible activity decay after 10 h of successive electrolysis. The present work demonstrates that surface regulation plays an important role in promoting NRR activity and provides a new strategy for creating efficient NRR electrocatalysts. 相似文献
800.
Zifeng Wang Zijie Tang Qi Xue Yan Huang Yang Huang Minshen Zhu Zengxia Pei Hongfei Li Hongbo Jiang Chenxi Fu Chunyi Zhi 《Chemical record (New York, N.Y.)》2016,16(3):1204-1215
Nanomaterials with layered structures, with their intriguing properties, are of great research interest nowadays. As one of the primary two‐dimensional nanomaterials, the hexagonal boron nitride nanosheet (BNNS, also called white graphene), which is an analogue of graphene, possesses various attractive properties, such as high intrinsic thermal conductivity, excellent chemical and thermal stability, and electrical insulation properties. After being discovered, it has been one of the most intensively studied two‐dimensional non‐carbon nanomaterials and has been applied in a wide range of applications. To support the exploration of applications of BNNSs, exfoliation, as one of the most promising approaches to realize large‐scale production of BNNSs, has been intensively investigated. In this review, methods to yield BNNSs by exfoliation will be summarized and compared with other potential fabrication methods of BNNSs. In addition, the future prospects of the exfoliation of h‐BN will also be discussed. 相似文献