全文获取类型
收费全文 | 9181篇 |
免费 | 1727篇 |
国内免费 | 1477篇 |
专业分类
化学 | 7235篇 |
晶体学 | 134篇 |
力学 | 505篇 |
综合类 | 112篇 |
数学 | 1034篇 |
物理学 | 3365篇 |
出版年
2024年 | 19篇 |
2023年 | 191篇 |
2022年 | 377篇 |
2021年 | 380篇 |
2020年 | 469篇 |
2019年 | 492篇 |
2018年 | 397篇 |
2017年 | 369篇 |
2016年 | 516篇 |
2015年 | 529篇 |
2014年 | 594篇 |
2013年 | 738篇 |
2012年 | 883篇 |
2011年 | 833篇 |
2010年 | 559篇 |
2009年 | 539篇 |
2008年 | 600篇 |
2007年 | 508篇 |
2006年 | 448篇 |
2005年 | 389篇 |
2004年 | 323篇 |
2003年 | 280篇 |
2002年 | 372篇 |
2001年 | 310篇 |
2000年 | 209篇 |
1999年 | 183篇 |
1998年 | 149篇 |
1997年 | 82篇 |
1996年 | 91篇 |
1995年 | 67篇 |
1994年 | 69篇 |
1993年 | 59篇 |
1992年 | 87篇 |
1991年 | 54篇 |
1990年 | 55篇 |
1989年 | 34篇 |
1988年 | 26篇 |
1987年 | 25篇 |
1986年 | 25篇 |
1985年 | 15篇 |
1984年 | 9篇 |
1983年 | 13篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1971年 | 1篇 |
1959年 | 2篇 |
1957年 | 2篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 28 毫秒
991.
Two isomorphic organically templated zinc/cobalt oxalates, (dmdabco)[Zn2(C2O4)3]·4H2O (1), and (dmdabco)[Co2(C2O4)3]·4H2O (2) (C2O42? = oxalate; dmdabco = N,N′-dimethyl-1,4-diazabicyclo[2,2,2]octane), have been prepared under solvothermal conditions and characterized by X-ray structural analyses. The dmdabco2+ templating agent was derived from simple in situ N-alkylation between methanol and 1,4-diazabicyclo[2,2,2]octane (dabco). Distinct from conventional Eschweiler-Clarke methylation containing excess formic acid and formaldehyde, such one-step methylation from methanol molecules is convenient. Both 1 and 2 exhibit a uninodal 3-connected 3-D interrupted open-framework, in which oxalate ligands have in-plane and out-of-plane connection modes. 相似文献
992.
Zhou Cai-bin Li Jing Yi Zhe Ai Hong-jun 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2017,91(10):2044-2051
Russian Journal of Physical Chemistry A - Imidazolium ionic liquids with alanine anion, [C n mim][Ala] (n = 2, 3, 4, 5, 6), were prepared and characterized. The standard addition method was used to... 相似文献
993.
Wang Jia Liu Yuan Deng Xiling Zhao Na Ying Xue Ye Bang-Ce Li Yingchun 《Mikrochimica acta》2017,184(10):3893-3900
Microchimica Acta - The authors describe an electrochemical sensor for ultrasensitive voltammetric of histamine (HA) by using a gold electrode that was modified with a film consisting of... 相似文献
994.
Xuan Ma Xu-Hua Nong Zhe Ren Jie Wang Xiao Liang Lu Wang Shu-Hua Qi 《Tetrahedron letters》2017,58(12):1151-1155
A new cyclic pentapeptide and three new linear peptides, namely, aspergillipeptides D–G (1–4), were isolated from a culture broth of marine gorgonian-derived fungus Aspergillus sp. SCSIO 41501. Their structures were elucidated by spectroscopic analysis, and their absolute configurations were confirmed by Marfey’s method. Compounds 1 and 2 showed evident antiviral activity against herpes simplex virus type 1 (HSV-1) with IC50 values of 9.5 and 19.8 µM under their non-cytotoxic concentrations against a Vero cell line, respectively, and 1 also had antiviral activity against acyclovir-resistant clinical isolates of HSV-1. 相似文献
995.
A pyrene-based dual chemosensor for colorimetric detection of Cu2+ and fluorescent detection of Fe3+
Yuxin Guo Lei Wang Jiezhen Zhuo Bo Xu Xue Li Jianyu Zhang Zhiqiang Zhang Haijun Chi Yan Dong Gonghao Lu 《Tetrahedron letters》2017,58(42):3951-3956
A pyrene based chemosensor was designed and synthesized. The pyrene fluorophore was connected with a pyridine unit through a Schiff base structure to give the sensor (L). L was tested with a variety of metal ions and exhibited high colorimetric selectivities for Cu2+ and Fe3+ over other ions. Upon binding with Cu2+ or Fe3+, L showed an obvious optical color change from colorless to pink for Cu2+ or orange for Fe3+ over a wide pH range from 3 to 12. Moreover, the fluorescence of L at 370 nm decreased sharply after bonding with Fe3+, while other metal ions including Cu2+ had no apparent interference. Thus, using such single chemosensor, Cu2+ and Fe3+ can be detected independently with high selectivity and sensitivity. The limits of detection toward Cu2+ and Fe3+ were 8.5 and 2.0 μM, respectively. DFT calculation results also proved the formation of stable coordination complexes and the phenomenon of fluorescence quenching by Fe3+. Furthermore, L was also successfully used as a bioimaging reagent for detection of Fe3+ in living cells. 相似文献
996.
Zhe Han Jing Yan Hou Quan Tang Yuan He Ying Zhu Yan Qing Ge 《Tetrahedron letters》2017,58(13):1254-1257
A novel pyrazoline with benzimidazole substituent was conveniently synthesized, starting from a chalcone and 2-hydrazinylpyridine. The addition of Ni2+ to ethanol solution of the synthesized pyrazoline resulted in a rapid color change from blue to green which allows the selective detection of Ni2+ ion over a great number of other metal ions. The association constant for the 1:1 complex was determined to be 2.72 × 107 M?1. 相似文献
997.
Immobilization of silver nanoparticles into POEGMA polymer brushes as SERS‐active substrates 下载免费PDF全文
Qian Zhang Jun‐Jiao Yin Feng Liu Xue‐Na Zou Li‐Qiang Chu 《Surface and interface analysis : SIA》2017,49(4):316-322
Surface‐enhanced Raman scattering (SERS) has attracted a great deal of interest during the past four decades and emerged as an ultrasensitive optical technique for chemical and biomedical analysis. It is widely accepted that the facile fabrication of SERS substrates with high activity and good reproducibility is of crucial importance for their applications. Herein, we report on a fast and robust method for the synthesis and immobilization of silver nanoparticles (AgNPs) into poly(oligo(ethylene glycol) methacrylate) (POEGMA) brushes under mild conditions without using any reducing agents. POEGMA brushes of different chain lengths were synthesized directly on silicon wafers by surface‐initiated atom transfer radical polymerization with various reaction time. X‐ray photoelectron spectroscopy and field emission scanning electron microscope measurements indicated that the AgNPs were firmly and homogeneously embedded into POEGMA brushes. The resulting POEGMA–AgNP hybrid films were employed as SERS substrates for the detection of 4‐aminothiophenol, giving rise to an enhancement factor of up to 1.9 × 106. The influence of the POEGMA's chain length on SERS performance was also investigated. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
998.
Danlu Xue Chunyi Liu Xiaomin Li Jie Tang Lihua Cao Yi Liu Zhengping Chen 《Journal of Radioanalytical and Nuclear Chemistry》2017,313(2):419-428
We studied on the structural requirement of C11b chirality of tetrabenazine (TBZ) analogs as vesicular monoamine transporter 2 (VMAT2) ligands. TBZ analogs (2, 6a, 6b) and 18F-radiolabeled [18F]6a and [18F]6b with eliminated C11b chirality were synthesized and characterized. Competition studies demonstrated that 2, 6a and 6b displayed much lower in vivo VMAT2 bindings than TBZ. MicroPET imaging studies of [18F]6a and [18F]6b showed negligible accumulation in VMAT2-enriched regions as compared with the known VMAT2 ligand 18F-FP-(+)-DTBZ. These results suggest that C11b chirality of TBZ analogs is essential for in vivo VMAT2 binding bioactivity. 相似文献
999.
建立快速高分离度液相色谱-四极杆飞行时间质谱联用方法(RRLC-Q-TOF-MS),分析人参皂苷Rb2在大鼠体内的药代动力学行为,并探索人参皂苷Rb2在大鼠体内的代谢过程.采用Agilent SB-C18色谱柱,流动相A为0.1%甲酸溶液,B为乙腈,流速为0.2 mL/min,进样量为5μL,二元线性梯度洗脱分离,采用电喷雾负离子模式进行质谱检测.方法的检出限(S/N=3)和定量限(S/N=10)分别为0.08 μg/mL和0.1 μg/mL,线性范围为0.10~ 1.26 μg/mL.结果表明,人参皂苷Rb2静脉注射后的体内代谢过程符合二室模型特征,血药浓度半衰期的α相(t1/2α)和β相(t1/2β)分别为(23.58±1.10)和(1306.55±147.23) min.通过对静脉注射人参皂苷Rb2的大鼠尿液和口服后的粪便样本进行分析,发现Rb2的代谢产物为M6,M2(C-Y),F2,C-K. 相似文献
1000.
Molecular bulks are favorable for the thermal and morphological stability in organic wide-bandgap semiconducting polymers with potential applications in both information and energy electronics. In this review, we present our progress in the design of fluorene-based bulky semiconductors with a fractal four-element pattern. Firstly, we established one-pot methods to spirofluorenes, especially spiro[fluorene-9,9′-xanthene](SFX) serving as the next-generation spiro-based semiconductors. Secondly, we observed the supramolecular forces at the bulky groups and discovered the supramolecular steric hindrance(SSH) effect on polymorphisms, nanocrystals as well as device performance. Thus, a synergistically molecular attractor-repulsor theory(SMART) was proposed for the control of nanocrystal morphology, thin film phase and morphology. Thirdly, the third possible type of defects has been identified to generate green band(g-band) emission in widebandgap semiconductors by the introduction of molecular strain design of cyclofluorene. Finally, the first bulky polydiarylfluorene with highly crystalline and β conformation was achieved by an attractor-repulsor design of tadpole-shape monomer, which offered an effective platform to fabricate stable wide-bandgap semiconducting devices. All the discoveries offer the solid basis to break through bottlenecks of organic/polymer wide-bandgap semiconductors by the improvements of overall performances. 相似文献