全文获取类型
收费全文 | 107024篇 |
免费 | 5215篇 |
国内免费 | 3495篇 |
专业分类
化学 | 45909篇 |
晶体学 | 1128篇 |
力学 | 8216篇 |
综合类 | 157篇 |
数学 | 34834篇 |
物理学 | 25490篇 |
出版年
2024年 | 101篇 |
2023年 | 594篇 |
2022年 | 1085篇 |
2021年 | 1134篇 |
2020年 | 1316篇 |
2019年 | 1215篇 |
2018年 | 11281篇 |
2017年 | 10952篇 |
2016年 | 7397篇 |
2015年 | 2273篇 |
2014年 | 1928篇 |
2013年 | 2643篇 |
2012年 | 6379篇 |
2011年 | 12984篇 |
2010年 | 7317篇 |
2009年 | 7721篇 |
2008年 | 8497篇 |
2007年 | 10443篇 |
2006年 | 1836篇 |
2005年 | 2769篇 |
2004年 | 2637篇 |
2003年 | 2920篇 |
2002年 | 1966篇 |
2001年 | 964篇 |
2000年 | 856篇 |
1999年 | 740篇 |
1998年 | 625篇 |
1997年 | 525篇 |
1996年 | 588篇 |
1995年 | 441篇 |
1994年 | 353篇 |
1993年 | 322篇 |
1992年 | 261篇 |
1991年 | 252篇 |
1990年 | 208篇 |
1989年 | 185篇 |
1988年 | 163篇 |
1987年 | 139篇 |
1986年 | 135篇 |
1985年 | 123篇 |
1984年 | 101篇 |
1983年 | 71篇 |
1982年 | 72篇 |
1981年 | 73篇 |
1980年 | 66篇 |
1979年 | 55篇 |
1914年 | 45篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
991.
Junfeng Zhou Xiaochen Dong Tao Chen Qiang Yang Qiaohua Tan Jianjun Wang 《European Polymer Journal》2007,43(5):2088-2095
A series of well-defined two-armed polymers containing a crown ether core, poly(stearyl methacrylate)-crown ether-poly(stearyl methacrylate) (PSMA-crown-PSMA), with different molecular weight were synthesized via atom transfer radical polymerization (ATRP). The resultant polymers were characterized by 1H NMR and GPC. The self-assembly behaviors of this kind of polymer in selective solvents were studied by TEM, and it was found that polymers with different molecular weight can directly self-assemble into hollow spheres, solid spheres and a monolayer film with regular pores by varying molecular weight and water content. The possible molecular packing motels for their self-assembly behaviors were proposed. 相似文献
992.
Takayuki Abe Shingo Higashide Mitsuhiro Inoue Satoshi Akamaru 《Plasma Chemistry and Plasma Processing》2007,27(6):799-811
Fine particles were modified with a thin film of SnO2 by using a barrel sputtering system that is a dry process. The conditions for the preparation of SnO2 were studied by reactive sputtering onto a glass plate substrate. The optimal conditions for the preparation of tetragonal
SnO2 were identified as 60% partial oxygen pressure and 1.0 Pa total gas pressure with the substrate at room temperature. Under
the optimized conditions, the surfaces of Al flake particles were modified with a thin film of SnO2. XRD and SEM/EDS analysis of the prepared samples showed that the Al particle surfaces were uniformly modified by a thin
film of SnO2 in all cases. The film thicknesses were 80, 130, and 180 nm at RF outputs of 195, 350, and 490 W. These measured thicknesses
coincided with the values estimated from the interference colors of the samples. 相似文献
993.
Separation of salidroside from Rhodiola crenulata by high-speed counter-current chromatography 总被引:3,自引:0,他引:3
High-speed counter-current chromatography (HSCCC) was used to purify salidroside from an extract of Rhodiola crenulata with two steps using a two-phase solvent system composed of ethyl acetate-n-butanol-water (1:4:5, v/v) in the first run and chloroform-methanol-isopropanol-water (5:6:1:4) in the second run. The method yielded 21.9 mg of salidroside from 1.216 g of the crude sample at 98% purity determined by HPLC analyses. Identification was performed by 1H NMR, 13C NMR, and MS. 相似文献
994.
995.
三(2-苯并咪唑亚甲基)胺硝酸镍(Ⅱ)配合物的合成及结构 总被引:5,自引:0,他引:5
三(2-苯并咪唑亚甲基)胺简称NTB与Ni(Ⅱ)的硝酸盐形成配合物C28H35N9O9S2Ni。本文报道其合成,红外光谱及晶体结构。该化合物为三斜晶系,空间P1↑-,a=9.650(3),b=12.716(2),c=14.436A,α=11.46(2),β=91.66(3),γ=97.55(2)°,V=1718(2)A^3,Z=2,F(000)=793,Dc=1.48g/cm^3,Mr=764.1 相似文献
996.
Jin Yan Dong Ye Gao Chen Hong Chuan Song Yan Ping He Lei Li Yong Ping Zhong Yan Hui Zhu Jie Cao Luo Wang Ke Qin Zhang Laboratory for Conservation Utilization of Bioresources Yunnan University Kunming China Department of Chemistry Yunnan Normal University Kunming China Provincial Key Lab of Rural Energy Engineering Yunnan Normal University Kunming China 《中国化学快报》2007,18(2):165-167
Microbial transformation of nigranoic acid by Caryospora carllicarpa YMF1.01026 afforded the new derivative 6β-hydro-xynigranoic acid. Its structure was elucidated by spectroscopic methods. 相似文献
997.
A simple and novel method was developed to successfully synthesize N-succinyl-O-carboxymethylchitosan (NSOCMCS) using N-acylation of chitosan with succinic anhydride. The NSOCMCS structure was characterized by Fourier transform infrared and
1H nuclear magnetic resonance. The aggregation behaviors of NSOCMCS were studied using fluorescence spectroscopy, dynamic light
scattering, and atomic force microscopy techniques. The critical aggregation concentration of NSOCMCS in water was determined
to be 0.2–0.3 mg/ml. The apparent hydrodynamic radium of an NSOCMCS aggregate was dependent on the concentration. The aggregates
demonstrated a much swollen association conformation in aqueous solution. The possible aggregation mechanisms for the NSOCMCS
in water are discussed. Moreover, a driving force to form an open aggregation morphology was revealed in this study. Aggregation
behaviors are important physicochemical properties of NSOCMCS, which impact the potential application in the biomedical field. 相似文献
998.
I. K. Battisha A. El Beyally S. Abd El Mongy A. M. Nahrawi 《Journal of Sol-Gel Science and Technology》2007,41(2):129-137
Structural characteristics of pure silica gel (silica-xerogel, SiO2) and silica gel doped with some rare earth elements (REEs) such as, praseodymium Pr3+, and Europium Eu3+, Erbium Er3+ and Holmium Ho3+ ions, with different concentrations ranging from 1 up to 6%, in the form of monolith materials were prepared by sol-gel technique,
Using tetra-ethoxysilane as precursor materials, which are of particular interest for sol-gel integrated optics applications.
Some structural features of sol-gel derived monolith are analyzed, namely the structure of nano-particle momolith samples,
based on X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR). We show that the XRD spectra of α-crystobalite are
obtained for the pure samples at 1100°C and even by doping with the four REEs ions. 相似文献
1000.
There have been remarkable progresses in manipulating heterogeneous catalysts' nanostructures in the past decade. The concept of single atom alloy (SAA) was firstly proposed in 2012 when researchers successfully stabilized single Pd atoms on the Cu(111) surface. However, earlier work in 2009, which focused on replacing one Au atom with a Pd atom in thiolate protected Au25 nanoclusters, could also be considered as the pioneer work of single atom alloy. Both kinds of single atom alloys exhibited the potential of maximum utilization of scarce elements and attractive catalytic performances. The well‐defined structures of SAA catalysts make accurate modeling possible, which further realizes the rational design of single atom alloy catalysts. In this review, we summarize the research trajectory of single atom alloys as well as recent achievements in this field. We also introduce several commonly adopted characterization methods for SAA catalysts such as scanning tunneling microscopy (STM), temperature programmed reaction (TPR), extended X‐ray absorption fine structure (EXAFS) spectra, matrix assisted laser desorption/ionization mass spectrum (MALDI‐MS) and differential pulse voltammetry (DPV). Through discussing recent progresses in SAA catalysts, we propose that future researches in this filed should be focused on exploring new kinds of metal nanocrystals and controlling the nanostructure of SAA even more precisely. 相似文献