全文获取类型
收费全文 | 3411篇 |
免费 | 413篇 |
国内免费 | 435篇 |
专业分类
化学 | 1936篇 |
晶体学 | 95篇 |
力学 | 428篇 |
综合类 | 38篇 |
数学 | 393篇 |
物理学 | 1369篇 |
出版年
2024年 | 3篇 |
2023年 | 25篇 |
2022年 | 78篇 |
2021年 | 107篇 |
2020年 | 94篇 |
2019年 | 85篇 |
2018年 | 89篇 |
2017年 | 147篇 |
2016年 | 173篇 |
2015年 | 117篇 |
2014年 | 132篇 |
2013年 | 340篇 |
2012年 | 196篇 |
2011年 | 205篇 |
2010年 | 172篇 |
2009年 | 226篇 |
2008年 | 232篇 |
2007年 | 221篇 |
2006年 | 206篇 |
2005年 | 183篇 |
2004年 | 153篇 |
2003年 | 141篇 |
2002年 | 128篇 |
2001年 | 94篇 |
2000年 | 111篇 |
1999年 | 78篇 |
1998年 | 85篇 |
1997年 | 70篇 |
1996年 | 59篇 |
1995年 | 63篇 |
1994年 | 50篇 |
1993年 | 33篇 |
1992年 | 19篇 |
1991年 | 19篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 8篇 |
1986年 | 12篇 |
1985年 | 13篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1976年 | 2篇 |
1973年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有4259条查询结果,搜索用时 31 毫秒
991.
Suction Induced Effects on the Fabric of a Structured Soil 总被引:3,自引:0,他引:3
Azad Koliji Lyesse Laloui Olivier Cusinier Laurent Vulliet 《Transport in Porous Media》2006,64(2):261-278
This paper presents the mathematical modelling of the modification of the pore space geometry of a structured soil subjected
to suction increase. Structured soil concepts are first introduced considering different fabric units, such as aggregates
and fissures. The numerical modelling of the structural evolution is based on experimental test results in which the evolution
of the structure of the samples subjected to different suctions is determined using the mercury intrusion porosimetry technique.
From this information, the macro and micropore volume evolutions are determined. The results show that drying produces a reduction
in the soil total porosity which mainly corresponds to a reduction of the macropore volume. Associated with this phenomenon,
an increase in micropore volume is also observed. The proposed model divides pore size distribution into three pore classes
(micropores, macropores and non-affected areas). Using the concept of a suction-influenced domain, the proposed model is able
to reproduce the main observed fabric evolution between the saturated and dry states. 相似文献
992.
Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies. 相似文献
993.
Au nanoparticlesAuNPswere synthesized by chemical reduction methodand its surface was chiral modified with serine to prepare Ser-AuNPs. The synthesis effect and particle size distribution of AuNPs and Ser-AuNPs were characterized by UV-Vis spectrophotometry and laser particle size analyzer. The Ser-AuNPs was used as a chiral selector for the enantiomeric separation of three adrenaline drugs by capillary zone electrophoresis. The influences of the binding concentration of serinebuffer pHseparation voltage and capillary temperature on the enantioseparation were investigated. The results showed that the enantiomeric separation of isoprenaline adrenaline and noradrenaline could achieve baseline separation at the optimal separation conditions. The corresponding resolutions were 3.192.85 and 3.77 for isoprenalineadrenaline and noradrenalinerespectively. And this method possessed good reproducibility and precision. © 2022, Youke Publishing Co.,Ltd. All rights reserved. 相似文献
994.
Dr. Jingchun Guo Dr. Shilong Jiao Xiuying Ya Dr. Huiling Zheng Dr. Ran Wang Dr. Jiao Yu Dr. Huanyu Wang Dr. Zhilin Zhang Dr. Wei Liu Dr. Congxiao He Prof. Xucheng Fu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(69):e202202221
In recent years, intermetallic nanocrystals (IMNCs) have attracted extensive attention in the field of electrocatalysis. However, precise control over the size, shape, composition, structure, and exposed crystal facet of IMNCs seems to be a challenge to the traditional method of high-temperature annealing although these parameters have a significant effect on the electrocatalytic performance. Controllable synthesis of IMNCs by the wet chemistry method in the liquid phase shows great potential compared with the traditional high-temperature annealing method. In this Review, we attempt to summarize the preparation of IMNCs by the seed-mediated synthesis in the liquid phase, as well as their applications in electrocatalytic reduction reactions. Several representative examples are purposely selected for highlighting the huge potential of the seed-mediated synthesis approach in chemical synthesis. Specifically, we personally perceive the seed-mediated synthesis approach as a promising tool in the future for precise control over the size, shape, composition, structure, and exposed crystal facet of IMNCs. 相似文献
995.
996.
997.
Effect of hypercrosslinking conditions on pore size distribution and efficiency of monolithic stationary phases 下载免费PDF全文
Three dihalogenic solvents differing in the length of alkyl chain (1,2‐dichloroethane, 1,4‐dichlorobutane, and 1,6‐dichlorohexane) with three Friedel–Crafts alkylation catalysts varying in reactivity (AlCl3, FeCl3, and SnCl4) have been used to prepare hypercrosslinked poly(styrene‐co‐vinylbenzyl chloride‐co‐divinylbenzene) columns. Hydrodynamic characteristics as well as column efficiency and mass transfer resistance were tuned by the combination of swelling solvent and alkylation reaction catalyst in the modification mixture. The column swelled in 1,6‐dichlorohexane and hypercrosslinked in the presence of AlCl3 provided the highest column efficiency and enabled fast isocratic separations of small molecules in a RP mode. To uncover factors controlling the efficiency of hypercrosslinked monolithic columns, we have studied pore volume distribution of prepared columns. We found that column efficiency increases with the higher pore volume of pores smaller than 2 nm. 相似文献
998.
999.
Hien Phan Robert I. Minut Phoebe McCrorie Catherine Vasey Ryan R. Larder Eduards Krumins Maria Marlow Ruman Rahman Cameron Alexander Vincenzo Taresco Amanda K. Pearce 《Journal of polymer science. Part A, Polymer chemistry》2019,57(17):1801-1810
The production of well‐defined and reproducible polymeric nanoparticles (NPs), in terms of size and stability in biological environments, is undoubtedly a fundamental challenge in the formulation of novel and more effective nanomedicines. The adoption of PEGylated lactide (LA) block copolymers as biodegradable and biocompatible nanocarriers at different clinical stages has rendered these materials an attractive polymeric platform to be exploited and their formulation is further understood. In the present work, we synthesized a library of linear polyethylene glycol‐poly(D,L‐lactide) block copolymers with different lengths of LA (15, 25, 50, and 100 LA units) via simple and metal‐free ring‐opening polymerization, in order to alter the amphiphilic balance of the different macromolecules. The produced polymers were formulated into NPs while varying a series of key parameters in the solvent displacement process, including solvent:nonsolvent ratios and the nature of the two media, and the effect on size and stability was assessed. In addition, stability to protein–NPs interaction and aggregation was studied, highlighting the different NP final properties according to the nature of the amphiphilic balance and nanoformulation conditions. Therefore, we have illustrated a systematic and methodological process to optimize a series of NPs parameters balancing particle size, size distribution, surface charge, and stability to guide future works in the nanoformulation field. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1801–1810 相似文献
1000.
We study the iron atomic aggregates deposited on silicone oil surfaces by using atomic force microscopy.The aggregates are composed of disk-shaped nanoparticles with the mean diameterΦc≈31.7 nm and height Hc≈4.5 nm,which are nearly independent of the nominal film thickness.The experiment shows that a material condensation process must occur in the nanoparticles during the growth period.The anomalous phenomenon is explained. 相似文献