全文获取类型
收费全文 | 6984篇 |
免费 | 1175篇 |
国内免费 | 746篇 |
专业分类
化学 | 4677篇 |
晶体学 | 71篇 |
力学 | 420篇 |
综合类 | 44篇 |
数学 | 684篇 |
物理学 | 3009篇 |
出版年
2023年 | 148篇 |
2022年 | 118篇 |
2021年 | 159篇 |
2020年 | 272篇 |
2019年 | 235篇 |
2018年 | 215篇 |
2017年 | 191篇 |
2016年 | 296篇 |
2015年 | 300篇 |
2014年 | 369篇 |
2013年 | 508篇 |
2012年 | 561篇 |
2011年 | 606篇 |
2010年 | 404篇 |
2009年 | 410篇 |
2008年 | 442篇 |
2007年 | 375篇 |
2006年 | 364篇 |
2005年 | 341篇 |
2004年 | 289篇 |
2003年 | 203篇 |
2002年 | 220篇 |
2001年 | 170篇 |
2000年 | 173篇 |
1999年 | 183篇 |
1998年 | 128篇 |
1997年 | 132篇 |
1996年 | 161篇 |
1995年 | 108篇 |
1994年 | 118篇 |
1993年 | 108篇 |
1992年 | 99篇 |
1991年 | 82篇 |
1990年 | 62篇 |
1989年 | 75篇 |
1988年 | 52篇 |
1987年 | 46篇 |
1986年 | 38篇 |
1985年 | 34篇 |
1984年 | 19篇 |
1983年 | 18篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1970年 | 3篇 |
1957年 | 3篇 |
排序方式: 共有8905条查询结果,搜索用时 46 毫秒
51.
Guilong Peng Qiang He Daniel Mmereki Guangming Zhou Weiliang Pan Li Gu Leilei Fan Xiaohui Tang Junhua Chen Yufeng Mao 《Journal of separation science》2015,38(20):3487-3493
Vortex‐assisted liquid–liquid microextraction followed by high‐performance liquid chromatography with UV detection was applied to determine Isocarbophos, Parathion‐methyl, Triazophos, Phoxim and Chlorpyrifos‐methyl in water samples. 1‐Bromobutane was used as the extraction solvent, which has a higher density than water and low toxicity. Centrifugation and disperser solvent were not required in this microextraction procedure. The optimum extraction conditions for 15 mL water sample were: pH of the sample solution, 5; volume of the extraction solvent, 80 μL; vortex time, 2 min; salt addition, 0.5 g. Under the optimum conditions, enrichment factors ranging from 196 to 237 and limits of detection below 0.38 μg/L were obtained for the determination of target pesticides in water. Good linearities (r > 0.9992) were obtained within the range of 1–500 μg/L for all the compounds. The relative standard deviations were in the range of 1.62–2.86% and the recoveries of spiked samples ranged from 89.80 to 104.20%. The whole proposed methodology is simple, rapid, sensitive and environmentally friendly for determining traces of organophosphorus pesticides in the water samples. 相似文献
52.
We successfully synthesized the first hemin-montmorillonite bio-conjugate with an amino acid residue to mimic natural peroxidase enzyme. Histamine was intercalated in montmorillonite by cation exchange, then a hemin molecule was loaded onto the histamine-montmorillonite with an adsorption capacity of 7.0 mg g-1. The hemin-histamine-montmorillonite conjugate shows high peroxidase activity as indicated by the oxidation of guaiacol, which is attributed to the activation of hemin by Fe–N complex formation between the imidazole group in histamine and the iron ion in the hemin molecule. Temperature- dependent peroxidase activity for this synthesized biomimetic material indicates that raising the reaction temperature could significantly enhance the activity of the conjugate. The biomimetic catalyst has good reusability; nearly 100% activity can be retained after three cycles. Because montmorillonite clay is widely distributed in the environment, this material offers great potential for in situ and ex situ remediation of many organic contaminants in surface/subsurface soils. 相似文献
53.
Hyun‐Chul Kim Ja‐Min Gu Seong Huh Chul‐Hyun Yo Youngmee Kim 《Acta Crystallographica. Section C, Structural Chemistry》2015,71(10):929-935
Two new one‐dimensional CuII coordination polymers (CPs) containing the C2h‐symmetric terphenyl‐based dicarboxylate linker 1,1′:4′,1′′‐terphenyl‐3,3′‐dicarboxylate (3,3′‐TPDC), namely catena‐poly[[bis(dimethylamine‐κN)copper(II)]‐μ‐1,1′:4′,1′′‐terphenyl‐3,3′‐dicarboxylato‐κ4O,O′:O′′:O′′′] monohydrate], {[Cu(C20H12O4)(C2H7N)2]·H2O}n, (I), and catena‐poly[[aquabis(dimethylamine‐κN)copper(II)]‐μ‐1,1′:4′,1′′‐terphenyl‐3,3′‐dicarboxylato‐κ2O3:O3′] monohydrate], {[Cu(C20H12O4)(C2H7N)2(H2O)]·H2O}n, (II), were both obtained from two different methods of preparation: one reaction was performed in the presence of 1,4‐diazabicyclo[2.2.2]octane (DABCO) as a potential pillar ligand and the other was carried out in the absence of the DABCO pillar. Both reactions afforded crystals of different colours, i.e. violet plates for (I) and blue needles for (II), both of which were analysed by X‐ray crystallography. The 3,3′‐TPDC bridging ligands coordinate the CuII ions in asymmetric chelating modes in (I) and in monodenate binding modes in (II), forming one‐dimensional chains in each case. Both coordination polymers contain two coordinated dimethylamine ligands in mutually trans positions, and there is an additional aqua ligand in (II). The solvent water molecules are involved in hydrogen bonds between the one‐dimensional coordination polymer chains, forming a two‐dimensional network in (I) and a three‐dimensional network in (II). 相似文献
54.
Porous organic polymers (POPs) have recently emerged as promising candidates for catalyzing oxygen reduction reaction (ORR). Compared to conventional Pt-based ORR catalysts, these newly developed porous materials, including both non-precious metal based catalysts and metal-free catalysts, are more sustainable and cost-effective. Their porous structures and large surface areas facilitate mass and electron transport and boost the ORR kinetics. This mini-review will give a brief summary of recent development of POPs as electrocatalysts for the ORR. Some design principles, different POP structures, key factors for their ORR catalytic performance, and outlook of POP materials will be discussed. 相似文献
55.
Construction of Renewable Superhydrophobic Surfaces via Thermally Induced Phase Separation and Mechanical Peeling 下载免费PDF全文
We report a simple preparation method of a renewable superhydrophobic surface by ther-mally induced phase separation (TIPS) and mechanical peeling. Porous polyvinylidene fluo-ride (PVDF) membranes with hierarchical structures were prepared by a TIPS process under different cooling conditions, which were confirmed by scanning electron microscopy and mer-cury intrusion porosimetry. After peeling off the top layer, rough structures with hundreds of nanometers to several microns were obtained. A digital microscopy determines that the surface roughness of peeled PVDF membranes is much higher than that of the original PVDF membrane, which is important to obtain the superhydrophobicity. Water contact angle and sliding angle measurements demonstrate that the peeled membrane surfaces display super-hydrophobicity with a high contact angle (152°) and a low sliding angle (7.2°). Moreover, the superhydrophobicity can be easily recovered for many times by a simple mechanical peel-ing, identical to the original superhydrophobicity. This simple preparation method is low cost, and suitable for large-scale industrialization, which may offer more opportunities for practical applications. 相似文献
56.
本文考察了一类弱奇性积分微分方程的级数展开数值解法,并给出了相应的收敛性分析.理论分析结果表明,若用已知函数的谱配置多项式逼近已知函数,那么方程的数值解以谱精度逼近方程的真解.数值实验数据也验证了这一理论分析结果. 相似文献
57.
Alberto Lumbreras Julien Velcin Marie Guégan Bertrand Jouve 《Computational Statistics》2017,32(1):145-177
We present a dual-view mixture model to cluster users based on their features and latent behavioral functions. Every component of the mixture model represents a probability density over a feature view for observed user attributes and a behavior view for latent behavioral functions that are indirectly observed through user actions or behaviors. Our task is to infer the groups of users as well as their latent behavioral functions. We also propose a non-parametric version based on a Dirichlet Process to automatically infer the number of clusters. We test the properties and performance of the model on a synthetic dataset that represents the participation of users in the threads of an online forum. Experiments show that dual-view models outperform single-view ones when one of the views lacks information. 相似文献
58.
Shuangxi Jing Ren Sheng Dr. Xinxin Liang Prof. Dong Gu Dr. Yuhao Peng Prof. Juanxiu Xiao Prof. Yijun Shen Prof. Di Hu Prof. Wei Xiao 《Angewandte Chemie (International ed. in English)》2023,62(6):e202216315
An overall carbon-neutral CO2 electroreduction requires enhanced conversion efficiency and intensified functionality of CO2-derived products to balance the carbon footprint from CO2 electroreduction against fixed CO2. A liquid Sn cathode is herein introduced into electrochemical reduction of CO2 in molten salts to fabricate core–shell Sn−C spheres (Sn@C). An in situ generated Li2SnO3/C directs a self-template formation of Sn@C. Benefitting from the accelerated reaction kinetics from the liquid Sn cathode and the core–shell structure of Sn@C, a CO2-fixation current efficiency higher than 84 % and a high reversible lithium-storage capacity of Sn@C are achieved. The versatility of this strategy is demonstrated by other low melting point metals, such as Zn and Bi. This process integrates energy-efficient CO2 conversion and template-free fabrication of value-added metal-carbon, achieving an overall carbon-neutral electrochemical reduction of CO2. 相似文献
59.
Di Liu Jiyan Pei Prof. Xu Zhang Xiao-Wen Gu Prof. Hui-Min Wen Prof. Banglin Chen Prof. Guodong Qian Prof. Bin Li 《Angewandte Chemie (International ed. in English)》2023,62(12):e202218590
Developing porous materials for C3H6/C3H8 separation faces the challenge of merging excellent separation performance with high stability and easy scalability of synthesis. Herein, we report a robust Hofmann clathrate material (ZJU-75a), featuring high-density strong binding sites to achieve all the above requirements. ZJU-75a adsorbs large amount of C3H6 with a record high storage density of 0.818 g mL−1, and concurrently shows high C3H6/C3H8 selectivity (54.2) at 296 K and 1 bar. Single-crystal structure analysis unveil that the high-density binding sites in ZJU-75a not only provide much stronger interactions with C3H6 but also enable the dense packing of C3H6. Breakthrough experiments on gas mixtures afford both high separation factor of 14.7 and large C3H6 uptake (2.79 mmol g−1). This material is highly stable and can be easily produced at kilogram-scale using a green synthesis method, making it as a benchmark material to address major challenges for industrial C3H6/C3H8 separation. 相似文献
60.
Mingxia Guo Long Fang Linlin Zhang Mingzhu Li Meiyu Cong Xiping Guan Chuanwei Shi ChunLei Gu Xia Liu Yong Wang Xin Ding 《Angewandte Chemie (International ed. in English)》2023,62(13):e202217635
Atomically dispersed Fe was designed on TiO2 and explored as a Janus electrocatalyst for both nitrogen oxidation reaction (NOR) and nitrogen reduction reaction (NRR) in a two-electrode system. Pulsed electrochemical catalysis (PE) was firstly involved to inhibit the competitive hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Excitingly, an unanticipated yield of 7055.81 μmol h−1 g−1cat. and 12 868.33 μmol h−1 g−1cat. were obtained for NOR and NRR at 3.5 V, respectively, 44.94 times and 7.8 times increase in FE than the conventional constant voltage electrocatalytic method. Experiments and density functional theory (DFT) calculations revealed that the single-atom Fe could stabilize the oxygen vacancy, lower the energy barrier for the vital rupture of N≡N, and result in enhanced N2 fixation performance. More importantly, PE could effectively enhance the N2 supply by reducing competitive O2 and H2 agglomeration, inhibit the electrocatalytic by-product formation for longstanding *OOH and *H intermediates, and promote the non-electrocatalytic process of N2 activation. 相似文献