全文获取类型
收费全文 | 18302篇 |
免费 | 2465篇 |
国内免费 | 2874篇 |
专业分类
化学 | 14413篇 |
晶体学 | 284篇 |
力学 | 784篇 |
综合类 | 264篇 |
数学 | 1987篇 |
物理学 | 5909篇 |
出版年
2024年 | 33篇 |
2023年 | 170篇 |
2022年 | 418篇 |
2021年 | 452篇 |
2020年 | 485篇 |
2019年 | 544篇 |
2018年 | 455篇 |
2017年 | 421篇 |
2016年 | 713篇 |
2015年 | 783篇 |
2014年 | 933篇 |
2013年 | 1322篇 |
2012年 | 1486篇 |
2011年 | 1526篇 |
2010年 | 1170篇 |
2009年 | 1139篇 |
2008年 | 1401篇 |
2007年 | 1286篇 |
2006年 | 1181篇 |
2005年 | 990篇 |
2004年 | 937篇 |
2003年 | 851篇 |
2002年 | 936篇 |
2001年 | 754篇 |
2000年 | 577篇 |
1999年 | 444篇 |
1998年 | 282篇 |
1997年 | 287篇 |
1996年 | 240篇 |
1995年 | 214篇 |
1994年 | 190篇 |
1993年 | 182篇 |
1992年 | 161篇 |
1991年 | 117篇 |
1990年 | 106篇 |
1989年 | 91篇 |
1988年 | 57篇 |
1987年 | 52篇 |
1986年 | 44篇 |
1985年 | 38篇 |
1984年 | 31篇 |
1983年 | 20篇 |
1982年 | 14篇 |
1981年 | 15篇 |
1980年 | 13篇 |
1979年 | 9篇 |
1978年 | 13篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Thanh Duc Mai Benjamin Bomastyk Hong Anh Duong Hung Viet Pham Peter C. Hauser 《Analytica chimica acta》2012
An extension of a capillary electrophoresis instrument coupled to a sequential injection analysis manifold was developed for automated measurements with on-line solid-phase extraction preconcentration. An in-house built capacitively coupled contactless conductivity detector was employed for sensitive detection with narrow capillaries of 25 μm internal diameter. The system was assembled into standardized 19 in. frames and racks for easy transport and mobile deployment. The system can be left running unattendedly without manual intervention with good operation stability. To demonstrate the application of the system, a method for the determination of four drugs, namely ibuprofen, diclofenac, naproxen and bezafibrate, was developed with enrichment factors of up to several hundreds. Detection of the drug residues down to the nM-scale was found possible and the method was found suitable for the detection of ibuprofen in the waste water of a hospital in Hanoi. 相似文献
992.
Thermal stability of ester linkage in the presence of 1,2,3‐Triazole moiety generated by click reaction
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Kyu Seong Lee So Yeong Park Hong Chul Moon Jin Kon Kim 《Journal of polymer science. Part A, Polymer chemistry》2017,55(3):427-436
The copper(I)‐catalyzed alkyne‐azide cycloaddition (CuAAC), so‐called “click” reaction, is one of most useful synthetic strategies to connect two polymer chains. 1,2,3‐Triazole ring (TA) produced by the click reaction has good thermal and chemical stability. However, we observed that block copolymers synthesized by the click reaction showed thermal degradation to give homopolymers when they are thermally annealed at high temperature, which is required for obtaining equilibrium microdomain structure. To investigate the origin of thermal instability of block copolymers, we synthesized model polystyrenes (PSs) using systematically designed bi‐functional atom transfer radical polymerization (ATRP) initiators containing TA. PS including both ester and TA groups showed thermal decomposition at relatively low temperature (e.g., 140 °C). MALDI‐TOF analysis clearly demonstrated that the cleavage site is the ester group adjacent to TA. We also found that the bromine group located at the polymer chain end plays an important role in pyrolysis of ester groups at low temperature. The pyrolysis occurs by syn‐elimination of the ester group. This result implies that the phase behavior of block copolymer synthesized by click reaction should be carefully investigated when high temperature thermal annealing is required. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 427–436 相似文献
993.
As stimulated Brillouin scattering (SBS) materials, solids have many advantages such as compactness, innoxiousness, and ease of handling. The SBS threshold and reflectivity of K8 glass, a solid material, are investigated. A SBS phase control experiment using K8 glass to achieve coherent beam combination is performed with a self-phase-control technique below the optical damage threshold. The experimental results show that the short-term phase has been stabilized well with λ/33.8 fluctuation during 256 shots (25.6 s), and that the long-term phase change with non-convective K8 glass is much slower than that with convective HT-70 liquid. 相似文献
994.
995.
正Optical lens is of fundamental importance in both scientific researches and industrial communities,especially for the aspects of optical focusing and imaging.In traditional optics,the light modulation property is limited by the Rayleigh Criterion(0.61λ/NA),and therefore the development of an ideal lens that produces sub-diffraction limit focusing and imaging has been a dream of lens makers all the time.Intensive effort 相似文献
996.
An autonomous stochastic predator–prey model with time delays is investigated. Almost sufficient and necessary conditions for stability in the mean and extinction of each population are established. Numerical simulations are introduced to support the results. 相似文献
997.
998.
999.
1000.
Dinuclear Cu(II) complexes based on p‐xylylene‐bridged bis(1,4,7‐triazacyclononane) ligands: Synthesis,characterization, DNA cleavage abilities and evaluation of superoxide dismutase‐ and catalase‐like activities
下载免费PDF全文
![点击此处可从《应用有机金属化学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Three new dinuclear Cu(II) complexes with the formulas [Cu2(pxdmbtacn)Cl4] ( 1 ), [Cu2(pxdmbtacn)Cl0.7(NO3)1.3(OH)2(H2O)1.3]?6H2O ( 2 ) and [Cu2(pxdiprbtacn)Cl4] ( 3 ) together with one previously reported complex, [Cu2(pxbtacn)Cl4] ( 4 ), were obtained from Cu(II) salts with three p‐xylylene‐bridged bis‐tacn ligands bearing pendant alkyl substituents or without pendant group. Complex 2 was structurally characterized as a centrosymmetric dinuclear molecule with each metal center being coordinated to some labile ligands in addition to one tacn ring. Based on the results of mass spectrometry and UV–visible spectroscopy, complexes 1 and 3 are capable of existing in aqueous solution as dinuclear species but 4 can partially form a dimer of the original dinuclear motif. Complexes 1 , 3 and 4 can all effectively cleave supercoiled DNA oxidatively in the presence of hydrogen peroxide. The superoxide dismutase (SOD) activities of 1 and 3 measured under physiological conditions are comparable to that of the native CuZnSOD enzyme but the enzymatic activity of 4 is about three‐ to fourfold lower. Furthermore, complexes 1 , 3 and 4 demonstrate moderate scavenging effect on hydrogen peroxide and their catalase activities are in the decreasing order of 3 > 1 > 4 . 相似文献