全文获取类型
收费全文 | 12874篇 |
免费 | 2121篇 |
国内免费 | 1822篇 |
专业分类
化学 | 9496篇 |
晶体学 | 159篇 |
力学 | 764篇 |
综合类 | 135篇 |
数学 | 1649篇 |
物理学 | 4614篇 |
出版年
2024年 | 13篇 |
2023年 | 187篇 |
2022年 | 276篇 |
2021年 | 371篇 |
2020年 | 453篇 |
2019年 | 459篇 |
2018年 | 403篇 |
2017年 | 401篇 |
2016年 | 566篇 |
2015年 | 598篇 |
2014年 | 742篇 |
2013年 | 937篇 |
2012年 | 1137篇 |
2011年 | 1277篇 |
2010年 | 911篇 |
2009年 | 914篇 |
2008年 | 1036篇 |
2007年 | 890篇 |
2006年 | 830篇 |
2005年 | 628篇 |
2004年 | 480篇 |
2003年 | 395篇 |
2002年 | 420篇 |
2001年 | 346篇 |
2000年 | 309篇 |
1999年 | 267篇 |
1998年 | 212篇 |
1997年 | 186篇 |
1996年 | 210篇 |
1995年 | 176篇 |
1994年 | 120篇 |
1993年 | 114篇 |
1992年 | 89篇 |
1991年 | 89篇 |
1990年 | 67篇 |
1989年 | 66篇 |
1988年 | 39篇 |
1987年 | 38篇 |
1986年 | 39篇 |
1985年 | 25篇 |
1984年 | 19篇 |
1983年 | 21篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1974年 | 4篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Wenhe Yu Prof. Xiaowen Wu Bohao Cheng Dr. Tianyi Tao Dr. Xin Min Dr. Ruiyu Mi Prof. Zhaohui Huang Prof. Minghao Fang Prof. Yangai Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(11):e202102787
Silicoaluminophosphate zeolite (SAPO-34) has been attracting increasing attention due to its excellent form selection and controllability in the chemical industry, as well as being one of the best industrial catalysts for methanol-to-olefin (MTO) reaction conversion. However, as a microporous molecular sieve, SAPO-34 easily generates carbon deposition and rapidly becomes inactivated. Therefore, it is necessary to reduce the crystal size of the zeolite or to introduce secondary macropores into the zeolite crystal to form a hierarchical structure in order to improve the catalytic effect. In this review, the synthesis methods of conventional SAPO-34 molecular sieves, hierarchical SAPO-34 molecular sieves and nanosized SAPO-34 molecular sieves are introduced, and the properties of the synthesized SAPO-34 molecular sieves are described, including the phase, morphology, pore structure, acid source, and catalytic performance, in particular with respect to the synthesis of hierarchical SAPO-34 molecular sieves. We hope that the review can provide guidance to the preparation of the SAPO-34 catalysts, and stimulate the future development of high-performance hierarchical SAPO-34 catalysts to meet the growing demands of the material and chemical industries. 相似文献
72.
Cheng Sheng Dr. Zheng Ling Dr. Tanveer Ahmad Prof. Dr. Fang Xie Prof. Dr. Wanbin Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(23):e202200128
Regioselective [3+3] annulation of alkynyl ketimines with α-cyano ketones for the synthesis of polysubstituted 4H-pyran derivatives with a quaternary CF3-containing center has been realized by using Cu(OAc)2 as the catalyst. The novel strategy tolerates a wide range of α-CF3 alkynyl ketimines and α-cyano ketones with both aryl and alkyl substitutents. A preliminary asymmetric synthesis of chiral product 3 has been attempted by using copper and chiral thiourea as the cocatalyst with excellent yields (86-99 %) and good enantioselectivities (71–78 % ee). Furthermore, product 3 aa could be obtained on a gram-scale reaction with 75 % yield and 99 % ee after recrystallization. Several products were also transformed readily. Control experiments indicate that the reaction involves a process with a base-catalyzed or chiral thiourea-catalyzed Mannich-type reaction followed by a highly regioselective copper-catalyzed ring-closing reaction on the alkynyl moiety in a 6-endo-dig fashion. 相似文献
73.
Zhao Tianqi Luo Tianzi Fang Bo Shi Lijiang Jin Yongxing Zhou Pengwei Yao Dong Li Chenxia Jing Xufeng Hong Zhi 《Journal of Russian Laser Research》2021,42(5):586-597
Journal of Russian Laser Research - The zero-refractive-index metamaterials have excellent electromagnetic properties, which provide new ideas and methods to realize the control of electromagnetic... 相似文献
74.
Yang Shaoming Deng Kaiqiang Shao Shan Zhang Jian Peng Jiaxi Fang Zhili Xu Wenyuan 《Journal of Solid State Electrochemistry》2022,26(3):821-830
Journal of Solid State Electrochemistry - A molecularly imprinted photoelectrochemical (PEC) cathodic sensor was developed for the detection of bovine serum albumin (BSA). The PEC sensor was... 相似文献
75.
Journal of Visualization - In the in situ visualization of large-scale simulation, if using the traditional sort-last parallel rendering method, the performance cannot be fully improved due to the... 相似文献
76.
Fang Su Yunlin Yang Yiyi Ou Dr. Weijie Zhou Dr. Fengkai Ma Dr. Jianhui Zhang Prof. Mikhail G. Brik Prof. Hongbin Liang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(30):e202200381
Eu2+-, Mn2+- and Eu2+−Mn2+-doped CaMgSi2O6 phosphors have been prepared by a high-temperature solid-state reaction. Systematic investigation of the concentration- and temperature-dependent luminescence of Mn2+ showed that Mn2+ ions occupy two distinct sites in CaMgSi2O6. Electron–vibration interaction (EVI) analyses of Mn2+ ions revealed Huang–Rhys factors of 4.73 and 2.82 as well as effective phonon energies of 313 and 383 cm−1 for the two sites. Eu2+−Mn2+ energy transfer is also discussed, and its efficiency is estimated by lifetime and luminescence spectra. The different thermal quenching behaviours of Eu2+ and Mn2+, the distinct emission colours of Eu2+ (blue, band peak at ∼451 nm) and Mn2+ (yellow–red range, band peaks at ∼583 and 693 nm) endow the co-doped samples with potential applications in luminescence thermometry and temperature-/excitation wavelength-responsive dual anti-counterfeiting. 相似文献
77.
This review examines the most recent electrochemical developments for nitrate, nitrite and ammonium detection for on-site water monitoring. There remains a high demand for effective field-based detection of the dissolved inorganic nitrogen (DIN) analytes to aid in mitigating nitrogen loading. Electrochemical approaches show increasing potential to fill this role as advancements in nanotechnology continually improve analytical performance and on-site applicability. However, translating these improvements into the field still faces the resonating challenges of reaching analytical proficiency (selectivity, sensitivity, robustness, stability), practical end-user functionality, minimal matrix interferences and cost effectiveness. Herein, we elaborate on these challenges via a critical evaluation of current studies and examine how realistic the prospects of on-site nitrate, nitrite and ammonium are. We also present recommendations in addressing these gaps to conclude the review. 相似文献
78.
Two new eupodienone lignans from Gymnotheca chinensis 总被引:1,自引:0,他引:1
Two new eupodienone lignans, named gymnothelignan T(1) and gymnothelignan U(2) were isolated from the whole plants of endemicmedicinal plant of Gymnotheca chinensis(Saururaceae). The structures of the new compounds were elucidated by means of HRMS, 1D and 2D NMR. Compound 1 was tested for cytotoxic activity in HCT15, HCT116, A549, MCF-7 and HepG2 cells and exhibited no appreciable activity against these tested cell lines with IC50 values above 50 mmol/L. 相似文献
79.
Yinlong Du Shuling Zhang Xu Jiang Kai Zhu Zhi Geng Yu Fang Pengfei Huo Chuan Liu Yinglin Song Guibin Wang 《Journal of polymer science. Part A, Polymer chemistry》2014,52(9):1282-1290
A series of novel soluble poly(aryl ether ketone)s (PAEKs) based on 5,10‐bis(4‐hydroxyphenyl)?15,20‐diphenylporphyrin (cis‐DHTPP), 4,4′‐(hexafluoroisopropylidene) diphenol (6FBPA) and 4,4′‐difluorobenzophenone (DFB) were synthesized and characterized by FT‐IR, 1H‐NMR, UV–vis and fluorescence spectroscopies. The intrinsic photophysical properties of porphyrins were preserved because of the absence of photoinduced electron transfer in the polymer chains. Investigation of the copolymers thermal properties indicated that these polymers had high glass transition temperatures and excellent thermal stabilities. The results of Z‐scan and optical limiting measurements manifested that incorporation of the porphyrin chromophore into the main chain engendered the novel PAEKs with superior nonlinear optical properties and optical limiting function, which could be effectively tuned by varying the molar ratio of porphyrin monomers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1282–1290 相似文献
80.
Huanian Zhang Xiaohan Chen Qingpu Wang Xingyu Zhang Jun Chang Liang Gao Hongbin Shen Zhenhua Cong Zhaojun Liu Huaijin Zhang Jing Li Ping Li 《Applied physics. B, Lasers and optics》2014,114(3):313-317
With graphene as saturable absorber, an Nd:KLu(WO4)2 eye-safe laser operating at 1,425 nm is demonstrated. To the best of our knowledge, this is the first demonstration that an Nd:KLu(WO4)2 laser operates at the eye-safe 1.4-μm region. A maximum total average output power of 170 mW is obtained under the pump power of 9.6 W, corresponding to an optical–optical efficiency of 1.77 %. The minimum pulse width and the highest pulse repetition rate are 153 ns and 97 kHz, respectively. Also the characteristics of the graphene used as saturable absorber for a 1.4-μm laser were studied for the first time. 相似文献