全文获取类型
收费全文 | 715篇 |
免费 | 48篇 |
国内免费 | 78篇 |
专业分类
化学 | 278篇 |
晶体学 | 11篇 |
力学 | 15篇 |
综合类 | 9篇 |
数学 | 101篇 |
物理学 | 122篇 |
综合类 | 305篇 |
出版年
2024年 | 8篇 |
2023年 | 20篇 |
2022年 | 46篇 |
2021年 | 30篇 |
2020年 | 41篇 |
2019年 | 31篇 |
2018年 | 21篇 |
2017年 | 30篇 |
2016年 | 26篇 |
2015年 | 37篇 |
2014年 | 57篇 |
2013年 | 41篇 |
2012年 | 52篇 |
2011年 | 55篇 |
2010年 | 35篇 |
2009年 | 37篇 |
2008年 | 30篇 |
2007年 | 38篇 |
2006年 | 31篇 |
2005年 | 23篇 |
2004年 | 8篇 |
2003年 | 10篇 |
2002年 | 5篇 |
2001年 | 9篇 |
2000年 | 11篇 |
1999年 | 14篇 |
1998年 | 15篇 |
1997年 | 23篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有841条查询结果,搜索用时 0 毫秒
11.
沥青混合料低温性能J-积分的研究 总被引:5,自引:0,他引:5
应用弹塑性断裂力学的J-积分评价沥青混合料的低温断裂性能,并将计算而青材料的J-积分的表达式分为弹性和塑性两个部分,推导出J-积分的更为明确的计算式,它清楚地表明了沥青混合料在低温状态下由塑性体向弹性体转化的过程,并把定义沥青混合科的脆化点的方法量化.采用了两种沥青混合料对上述推论进行了试验验证.证明不同性能的沥青混合科其J-积分值有明显差别. 相似文献
12.
Fangjun Liu Dun Wang Jiaqi Wang Liwei Ma Cuiyun Yu Hua Wei 《Molecules (Basel, Switzerland)》2022,27(9)
Bottlebrush copolymers with different chemical structures and compositions as well as diverse architectures represent an important kind of material for various applications, such as biomedical devices. To our knowledge, zwitterionic conjugated bottlebrush copolymers integrating fluorescence imaging and tumor microenvironment-specific responsiveness for efficient intracellular drug release have been rarely reported, likely because of the lack of an efficient synthetic approach. For this purpose, in this study, we reported the successful preparation of well-defined theranostic zwitterionic bottlebrush copolymers with unique brush-on-brush architecture. Specifically, the bottlebrush copolymers were composed of a fluorescent backbone of polyfluorene derivate (PFONPN) possessing the fluorescence resonance energy transfer with doxorubicin (DOX), primary brushes of poly(2-hydroxyethyl methacrylate) (PHEMA), and secondary graft brushes of an enzyme-degradable polytyrosine (PTyr) block as well as a zwitterionic poly(oligo (ethylene glycol) monomethyl ether methacrylate-co-sulfobetaine methacrylate) (P(OEGMA-co-SBMA)) chain with super hydrophilicity and highly antifouling ability via elegant integration of Suzuki coupling, NCA ROP and ATRP techniques. Notably, the resulting bottlebrush copolymer, PFONPN9-g-(PHEMA15-g-(PTyr16-b-P(OEGMA6-co-SBMA6)2)) (P2) with a lower MW ratio of the hydrophobic side chains of PTyr and hydrophilic side chains of P(OEGMA-co-SBMA) could self-assemble into stabilized unimolecular micelles in an aqueous phase. The resulting unimolecular micelles showed a fluorescence quantum yield of 3.9% that is mainly affected by the pendant phenol groups of PTyr side chains and a drug-loading content (DLC) of approximately 15.4% and entrapment efficiency (EE) of 90.6% for DOX, higher than the other micelle analogs, because of the efficient supramolecular interactions of π–π stacking between the PTyr blocks and drug molecules, as well as the moderate hydrophilic chain length. The fluorescence of the PFONPN backbone enables fluorescence resonance energy transfer (FRET) with DOX and visualization of intracellular trafficking of the theranostic micelles. Most importantly, the drug-loaded micelles showed accelerated drug release in the presence of proteinase K because of the enzyme-triggered degradation of PTyr blocks and subsequent deshielding of P(OEGMA-co-SBMA) corona for micelle destruction. Taken together, we developed an efficient approach for the synthesis of enzyme-responsive theranostic zwitterionic conjugated bottlebrush copolymers with a brush-on-brush architecture, and the resulting theranostic micelles with high DLC and tumor microenvironment-specific responsiveness represent a novel nanoplatform for simultaneous cell image and drug delivery. 相似文献
13.
Liwei Zhang Guiqiang Du Yewen Zhang 《Applied Physics A: Materials Science & Processing》2012,109(4):851-856
We present a theoretical investigation into the energy transport and transient wave propagation in metamaterial tunneling structures consisting of ??-negative (ENG) and ??-negative (MNG) materials. It is proved that a conjugated matched ENG/MNG bilayer and a (zero-index-material doped) photonic crystal heterostructure can work as a sub-wavelength resonator at tunneling frequency. The tunneling modes need a certain time to achieve the steady state and the charge up characteristic time increases (nearly) exponentially with the thickness of the structures. Under the steady state, the wave in the single-negative-material structures is not evanescent, but a hybrid of a traveling wave and a reactive standing wave. The phase difference between the electric field and the magnetic field varies with the position and time. The investigation of transient wave propagation in the metamaterial tunneling structures will help us to understand the interaction process between wave and metamaterial and to design special functional apparatus. 相似文献
14.
15.
Effect of Polymerizable Photoinitiators on the UV‐polymerization behaviors of photosensitive polysiloxane 下载免费PDF全文
Bo Jiang Tong Zhang Liwei Zhao Zhiming Xu Yudong Huang 《Journal of polymer science. Part A, Polymer chemistry》2017,55(10):1696-1705
In this contribution, three polymerizable benzophenone photoinitiators containing maleimide group including 4‐maleimidebenzophenone (MBP), 4‐chlorine‐4′‐maleimide benzophenone (CMBP), and 4‐maleimide‐4′‐[(4‐maleimide)thiophenyl]benzophenone (MMTBP) were designed and synthesized to enhance the polymerization degree of photosensitive polysiloxane containing methacryloxy active groups (MAPSO). The polymerization behaviors of the MAPSO cured by different photoinitiators were investigated using Fourier transform infrared (FTIR). It was noted that the MAPSO initiated by MMTBP showed a high carbon–carbon double bond conversion above 80% because of the existence of thiophenyl group which could generate more radicals from the photolysis reaction at the C? S bond. In addition, the thermal stability of the UV‐cured MAPSO were studied by thermogravimetric analysis (TGA), the result showed that the initial 5% mass loss (T 5%) and residual weight percent at 800 °C in nitrogen of the UV‐cured MAPSO initiated by MMTBP systems was 200 °C and 33.8%. Thus, this work provides a new perspective and efficient strategy to improve the polymerization degree of UV‐curable polysiloxanes with carbon–carbon double bonds. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1696–1705 相似文献
16.
茚三酮衍生高效毛细管电泳法测定纯奶中的甘氨酸含量 总被引:1,自引:0,他引:1
建立了茚三酮衍生高效毛细管电泳法测定纯奶中甘氨酸含量的方法,该法可选择性测定甘氨酸含量。使用氯化镁为蛋白沉淀剂,沉淀效果较好,研究了甘氨酸–茚三酮聚合物衍生条件,确定最佳实验条件为:未涂层弹性石英毛细管柱(60 cm×75μm,有效长度49 cm),分离缓冲溶液为3.5 mmol磷酸二氢钾–8.2 mmol磷酸氢二钠(pH 6.8),检测波长为570 nm,电泳电压为25 kV,进样压力为25 kPa,进样时间为3 s,电泳温度为室温。甘氨酸的线性范围为2.00~200.00μg/mL,检出限为0.14μg/mL,线性相关系数不小于0.999。甘氨酸的加标回收率为88.7%~107.2%,测定结果的相对标准偏差为2.9%~4.2%(n=6)。该法简便、快速、准确,可用于测定纯奶中甘氨酸含量。 相似文献
17.
Qiaoxia Guo Wennian Wang Weiling Teng Liwei Chen Yanqing Wang Baojian Shen 《合成通讯》2013,43(17):2574-2584
A convenient one-pot method for the synthesis of substituted quinolines via the reaction of aniline and aldehyde in the presence of a Lewis acid (AlCl3) and an oxidant (H2O2) has been developed. Hydrogen peroxide was found to promote the reaction by its function as a hydrogen hunter, hindering the formation of by-product N-alkylaniline. The effect of the oxidant on the yield and selectivity was studied. When the molar ratio of aniline, n-butyraldehyde, and H2O2 was 1:3:0.5 at 25 °C, the yield of 3-ethyl-2-propylquinoline was improved from 64% (reaction without H2O2) to 84% (with H2O2), and the quinoline selectivity was improved to almost 100%. Moreover, the reaction time was obviously reduced. The substituent effect was also investigated in this work. 相似文献
18.
In this paper, we consider the optimal problem of channels sharing with heterogeneous traffic(real-time service and non-real-time service) to reduce the data conflict probability of users. Moreover, a multi-dimensional Markov chain model is developed to analyze the performance of the proposed scheme. Meanwhile, performance metrics are derived. Numerical results show that the proposed scheme can effectively reduce the forced termination probability, blocking probability and spectrum utilization. 相似文献
19.
噻虫胺分子印迹电化学传感器的制备与应用EI北大核心CSCD 总被引:1,自引:0,他引:1
以噻虫胺为模板分子,通过恒电位沉积壳聚糖,在还原氧化石墨烯(RGO)修饰的玻碳电极表面制备了可特异性识别噻虫胺的分子印迹传感器。采用交流阻抗法(EIS)、差分脉冲伏安法(DPV)和循环伏安法(CV)对传感器的电化学性能进行表征,优化了电沉积时间、洗脱圈数、孵化时间及溶液pH等实验条件。在优化条件下,以K_(3)[Fe(CN)_(6)]作为电活性探针,DPV峰电流强度与噻虫胺浓度在1.0~1000 nmol/L范围内呈良好的线性关系,检出限0.46 nmol/L。将本方法应用于实际样品中噻虫胺的含量测定,加标回收率为97.6%~103.2%。 相似文献
20.