全文获取类型
收费全文 | 60841篇 |
免费 | 12092篇 |
国内免费 | 19765篇 |
专业分类
化学 | 43735篇 |
晶体学 | 2454篇 |
力学 | 4716篇 |
综合类 | 2215篇 |
数学 | 9718篇 |
物理学 | 29860篇 |
出版年
2024年 | 159篇 |
2023年 | 655篇 |
2022年 | 2152篇 |
2021年 | 2136篇 |
2020年 | 2087篇 |
2019年 | 2097篇 |
2018年 | 1935篇 |
2017年 | 2800篇 |
2016年 | 2237篇 |
2015年 | 3146篇 |
2014年 | 3852篇 |
2013年 | 5037篇 |
2012年 | 4966篇 |
2011年 | 5306篇 |
2010年 | 5225篇 |
2009年 | 5395篇 |
2008年 | 6075篇 |
2007年 | 5344篇 |
2006年 | 5235篇 |
2005年 | 4606篇 |
2004年 | 3533篇 |
2003年 | 2606篇 |
2002年 | 2669篇 |
2001年 | 2542篇 |
2000年 | 2562篇 |
1999年 | 1506篇 |
1998年 | 837篇 |
1997年 | 667篇 |
1996年 | 608篇 |
1995年 | 520篇 |
1994年 | 584篇 |
1993年 | 536篇 |
1992年 | 460篇 |
1991年 | 328篇 |
1990年 | 320篇 |
1989年 | 358篇 |
1988年 | 292篇 |
1987年 | 226篇 |
1986年 | 173篇 |
1985年 | 141篇 |
1984年 | 127篇 |
1983年 | 141篇 |
1982年 | 117篇 |
1981年 | 99篇 |
1980年 | 78篇 |
1979年 | 68篇 |
1978年 | 38篇 |
1977年 | 19篇 |
1976年 | 19篇 |
1959年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
1.
Yuanbo Gao Tingting Yang Xueli Wang Jizong Chen Yong He 《Journal of polymer science. Part A, Polymer chemistry》2022,60(10):1610-1623
Two series of novel alternating copolyoxamides (PAnT-alt-n2 and PAn2-alt-62) are synthesized via solution/solid-state polycondensation (SSP). The alternating structures are analyzed carefully with 1H NMR and 13C NMR spectra. The melting behaviors, thermal stabilities, crystal structures and crystallinities are systematically evaluated by DSC, TGA and WAXD. The results reveal that these alternating copolyoxamides possess almost perfect alternating chain structures and have high melting temperature (Tm > 270 °C), high crystallinity (Xc > 32%) and high decomposition temperature (T5 > 405 °C) as well as low saturated water absorption (<3.5 wt%), which suggests that they have high potential as engineering plastic of high heat resistant. 相似文献
2.
Qianqian Fan Zirui Liu Feng Qiu Prof. Yong Mao Prof. Qingju Liu Prof. Longzhou Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(63):e202202700
The artificially accurate design of nonmetal electrocatalysts’ active site has been a huge challenge because no pure active species with the specific structure could be strictly controlled by traditional synthetic methods. Species with a multiconfiguration in the catalyst hinder identification of the active site and the subsequent comprehension of the reaction mechanism. We have developed a novel electro-assisted molecular assembly strategy to obtain a pure pentagon ring on perfect graphene avoiding other reconstructed structures. More importantly, the active atom was confirmed by the subtle passivation process as the topmost carbon atom. Recognition of the carbon-defect electrocatalysis reaction mechanism was first downsized to the single-atom scale from the experimental perspective. It is expected that this innovative electro-assisted molecular assembly strategy could be extensively applied in the active structure-controlled synthesis of nonmetal electrocatalysts and verification of the exact active atom. 相似文献
5.
以羧甲基纤维素(CMC)、明胶和MOF(Cu)@biochar为原料,采用简单有效的冷冻干燥方法制备了(CMC/Gelatin/MOF(Cu)@biochar)杂化气凝胶,并用傅里叶变换红外光谱(FT-IR)、热重分析(TG)、X射线粉末衍射(XRD)、扫描电镜(SEM)和X射线光电子能谱(XPS)技术对其进行了表征;研究了MOF(Cu)@biochar含量、pH和不同的盐水溶液对杂化气凝胶溶胀行为的影响;以该气凝胶负载氯化铵,制备了一种新型缓释肥料(SRF),并研究了含2%(wt)SRF的沙性土壤的保水能力;SRF在土壤中第30天的累积释放率为79.4%;肥料在土壤中释放符合非Fickian扩散和阳离子交换的协同作用机理。 相似文献
6.
A numerical model was developed and validated to investigate the fluid–structure interactions between fully developed pipe flow and core–shell-structured microcapsule in a microchannel. Different flow rates and microcapsule shell thicknesses were considered. A sixth-order rotational symmetric distribution of von Mises stress over the microcapsule shell can be observed on the microcapsule with a thinner shell configuration, especially at higher flow rate conditions. It is also observed that when being carried along in a fully developed pipe flow, the microcapsule with a thinner shell tends to accumulate stress at a higher rate compared to that with a thicker shell. In general, for the same microcapsule configuration, higher flow velocity would induce a higher stress level over the microcapsule shell. The deformation gradient was used to capture the microcapsule's deformation in the present study. The effect of Young's modulus on the microcapsule shell on the microcapsule deformation was investigated as well. Our findings will shed light on the understanding of the stability of core–shell-structured microcapsule when subjected to flow-induced shear stress in a microfluidic system, enabling a more exquisite control over the breakup dynamics of drug-loaded microcapsule for biomedical applications. 相似文献
7.
8.
UJ24型电位差计使用时出现的故障,可以利用数字万用表排查故障,提出排查方案,进行维修与调节,使它尽快恢复到最佳工作状态,这样既节省厂家的维修时间又节省学校的维修费用。 相似文献
9.
10.
Yi Han Zibo Xue Dr. Guangwu Li Dr. Yanwei Gu Dr. Yong Ni Dr. Shaoqiang Dong Prof. Chunyan Chi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(23):9111-9116
Incorporation of a non-hexagonal ring into a nanographene framework can lead to new electronic properties. During the attempted synthesis of naphthalene-bridged double [6]helicene and heptagon-containing nanographene by the Scholl reaction, an unexpected azulene-embedded nanographene and its triflyloxylated product were obtained, as confirmed by X-ray crystallographic analysis and 2D NMR spectroscopy. A 5/7/7/5 ring-fused substructure containing two formal azulene units is formed, but only one of them shows an azulene-like electronic structure. The formation of this unique structure is explained by arenium ion mediated 1,2-phenyl migration and a naphthalene to azulene rearrangement reaction according to an in-silico study. This report represents the first experimental example of the thermodynamically unfavorable naphthalene to azulene rearrangement and may lead to new azulene-based molecular materials. 相似文献