全文获取类型
收费全文 | 57012篇 |
免费 | 13220篇 |
国内免费 | 5626篇 |
专业分类
化学 | 57891篇 |
晶体学 | 697篇 |
力学 | 1533篇 |
综合类 | 314篇 |
数学 | 4292篇 |
物理学 | 11131篇 |
出版年
2024年 | 75篇 |
2023年 | 446篇 |
2022年 | 910篇 |
2021年 | 1042篇 |
2020年 | 2146篇 |
2019年 | 3418篇 |
2018年 | 1833篇 |
2017年 | 1575篇 |
2016年 | 4448篇 |
2015年 | 4654篇 |
2014年 | 4863篇 |
2013年 | 5805篇 |
2012年 | 5119篇 |
2011年 | 4456篇 |
2010年 | 4520篇 |
2009年 | 4340篇 |
2008年 | 4044篇 |
2007年 | 3230篇 |
2006年 | 2834篇 |
2005年 | 2688篇 |
2004年 | 2235篇 |
2003年 | 1957篇 |
2002年 | 2735篇 |
2001年 | 1997篇 |
2000年 | 1737篇 |
1999年 | 826篇 |
1998年 | 341篇 |
1997年 | 273篇 |
1996年 | 191篇 |
1995年 | 190篇 |
1994年 | 144篇 |
1993年 | 148篇 |
1992年 | 116篇 |
1991年 | 103篇 |
1990年 | 71篇 |
1989年 | 66篇 |
1988年 | 51篇 |
1987年 | 54篇 |
1986年 | 51篇 |
1985年 | 34篇 |
1984年 | 18篇 |
1983年 | 14篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1975年 | 4篇 |
1957年 | 5篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
A numerical model was developed and validated to investigate the fluid–structure interactions between fully developed pipe flow and core–shell-structured microcapsule in a microchannel. Different flow rates and microcapsule shell thicknesses were considered. A sixth-order rotational symmetric distribution of von Mises stress over the microcapsule shell can be observed on the microcapsule with a thinner shell configuration, especially at higher flow rate conditions. It is also observed that when being carried along in a fully developed pipe flow, the microcapsule with a thinner shell tends to accumulate stress at a higher rate compared to that with a thicker shell. In general, for the same microcapsule configuration, higher flow velocity would induce a higher stress level over the microcapsule shell. The deformation gradient was used to capture the microcapsule's deformation in the present study. The effect of Young's modulus on the microcapsule shell on the microcapsule deformation was investigated as well. Our findings will shed light on the understanding of the stability of core–shell-structured microcapsule when subjected to flow-induced shear stress in a microfluidic system, enabling a more exquisite control over the breakup dynamics of drug-loaded microcapsule for biomedical applications. 相似文献
2.
Mathematical Programming - We seek tight bounds on the viable parallelism in asynchronous implementations of coordinate descent that achieves linear speedup. We focus on asynchronous coordinate... 相似文献
3.
Mathematical Programming - In the general equilibrium with incomplete asset markets (GEI) model, the excess demand functions are typically not continuous at the prices for which the assets have... 相似文献
4.
For an integer , a graph is -hamiltonian if for any vertex subset with , is hamiltonian, and is -hamiltonian connected if for any vertex subset with , is hamiltonian connected. Thomassen in 1984 conjectured that every 4-connected line graph is hamiltonian (see Thomassen, 1986), and Ku?zel and Xiong in 2004 conjectured that every 4-connected line graph is hamiltonian connected (see Ryjá?ek and Vrána, 2011). In Broersma and Veldman (1987), Broersma and Veldman raised the characterization problem of -hamiltonian line graphs. In Lai and Shao (2013), it is conjectured that for , a line graph is -hamiltonian if and only if is -connected. In this paper we prove the following.(i) For an integer , the line graph of a claw-free graph is -hamiltonian if and only if is -connected.(ii) The line graph of a claw-free graph is 1-hamiltonian connected if and only if is 4-connected. 相似文献
5.
6.
Chemical versus Electrochemical Synthesis of Carbon Nano‐onion/Polypyrrole Composites for Supercapacitor Electrodes 下载免费PDF全文
Olena Mykhailiv Monika Imierska Martyna Petelczyc Prof. Dr. Luis Echegoyen Dr. Marta E. Plonska‐Brzezinska 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(15):5783-5793
The development of high‐surface‐area carbon electrodes with a defined pore size distribution and the incorporation of pseudo‐active materials to optimize the overall capacitance and conductivity without destroying the stability are at present important research areas. Composite electrodes of carbon nano‐onions (CNOs) and polypyrrole (Ppy) were fabricated to improve the specific capacitance of a supercapacitor. The carbon nanostructures were uniformly coated with Ppy by chemical polymerization or by electrochemical potentiostatic deposition to form homogenous composites or bilayers. The materials were characterized by transmission‐ and scanning electron microscopy, differential thermogravimetric analyses, FTIR spectroscopy, piezoelectric microgravimetry, and cyclic voltammetry. The composites show higher mechanical and electrochemical stabilities, with high specific capacitances of up to about 800 F g?1 for the CNOs/SDS/Ppy composites (chemical synthesis) and about 1300 F g?1 for the CNOs/Ppy bilayer (electrochemical deposition). 相似文献
7.
Dr. Sabin Llona‐Minguez Dr. Matthieu Desroses Artin Ghassemian Dr. Sylvain A. Jacques Dr. Lars Eriksson Rebecka Isacksson Tobias Koolmeister Dr. Pål Stenmark Dr. Martin Scobie Prof. Thomas Helleday 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(20):7394-7398
A two‐step synthesis of structurally diverse pyrrole‐containing bicyclic systems is reported. ortho‐Nitro‐haloarenes coupled with vinylic N‐methyliminodiacetic acid (MIDA) boronates generate ortho‐vinyl‐nitroarenes, which undergo a “metal‐free” nitrene insertion, resulting in a new pyrrole ring. This novel synthetic approach has a wide substrate tolerance and it is applicable in the preparation of more complex “drug‐like” molecules. Interestingly, an ortho‐nitro‐allylarene derivative furnished a cyclic β‐aminophosphonate motif. 相似文献
8.
Interactions of Pt‐ttpy with G‐Quadruplexes Originating from Promoter Region of the c‐myc Gene Deciphered by NMR and Gel Electrophoresis Analysis 下载免费PDF全文
9.
Analysis and pharmacokinetic study of polyphyllin H in beagle dog plasma after oral administration of Rhizoma Paridis Extracts by LC‐MS/MS 下载免费PDF全文
10.
Jing Zhihong Ling Baoping Yu Yang Qi Wei Zhang Shufang 《Journal of Sol-Gel Science and Technology》2015,73(1):112-117
Journal of Sol-Gel Science and Technology - A novel gas sensing material, La–Y co-doped TiO2 nanoparticles, was synthesized by sol–gel method and applied to detect organic pollutants... 相似文献