全文获取类型
收费全文 | 286038篇 |
免费 | 5474篇 |
国内免费 | 2634篇 |
专业分类
化学 | 134747篇 |
晶体学 | 4325篇 |
力学 | 10278篇 |
综合类 | 101篇 |
数学 | 24161篇 |
物理学 | 78630篇 |
无线电 | 41904篇 |
出版年
2021年 | 2617篇 |
2020年 | 2883篇 |
2019年 | 2946篇 |
2018年 | 3487篇 |
2017年 | 3440篇 |
2016年 | 5166篇 |
2015年 | 3456篇 |
2014年 | 5440篇 |
2013年 | 12451篇 |
2012年 | 9528篇 |
2011年 | 11378篇 |
2010年 | 8480篇 |
2009年 | 8774篇 |
2008年 | 10672篇 |
2007年 | 10975篇 |
2006年 | 10394篇 |
2005年 | 9357篇 |
2004年 | 8508篇 |
2003年 | 7846篇 |
2002年 | 7485篇 |
2001年 | 9047篇 |
2000年 | 7129篇 |
1999年 | 5862篇 |
1998年 | 4837篇 |
1997年 | 4738篇 |
1996年 | 4537篇 |
1995年 | 4237篇 |
1994年 | 4072篇 |
1993年 | 3854篇 |
1992年 | 4530篇 |
1991年 | 4442篇 |
1990年 | 4267篇 |
1989年 | 4035篇 |
1988年 | 3963篇 |
1987年 | 3607篇 |
1986年 | 3373篇 |
1985年 | 4141篇 |
1984年 | 4169篇 |
1983年 | 3280篇 |
1982年 | 3378篇 |
1981年 | 3379篇 |
1980年 | 3125篇 |
1979年 | 3447篇 |
1978年 | 3412篇 |
1977年 | 3497篇 |
1976年 | 3343篇 |
1975年 | 2997篇 |
1974年 | 2927篇 |
1973年 | 2876篇 |
1972年 | 2060篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
We study the full counting statistics of transport electrons through a semiconductor two-level quantum dot with Rashba spin–orbit (SO) coupling, which acts as a nonabelian gauge field and thus induces the electron transition between two levels along with the spin flip. By means of the quantum master equation approach, shot noise and skewness are obtained at finite temperature with two-body Coulomb interaction. We particularly demonstrate the crucial effect of SO coupling on the super-Poissonian fluctuation of transport electrons, in terms of which the SO coupling can be probed by the zero-frequency cumulants. While the charge currents are not sensitive to the SO coupling. 相似文献
2.
Synthesis of Highly Substituted γ‐Butyrolactones by a Gold‐Catalyzed Cascade Reaction of Benzyl Esters 下载免费PDF全文
Maria Camila Blanco Jaimes Alexander Ahrens Daniel Pflästerer Dr. Matthias Rudolph Prof. Dr. A. Stephen K. Hashmi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):427-433
Easily accessible benzylic esters of 3‐butynoic acids in a gold‐catalyzed cyclization/rearrangement cascade reaction provided 3‐propargyl γ‐butyrolactones with the alkene and the carbonyl group not being conjugated. Crossover experiments showed that the formation of the new C?C bond is an intermolecular process. Initially propargylic–benzylic esters were used, but alkyl‐substituted benzylic esters worked equally well. In the case of the propargylic–benzylic products, a simple treatment of the products with aluminum oxide initiated a twofold tautomerization to the allenyl‐substituted γ‐butyrolactones with conjugation of the carbonyl group, the olefin, and the allene. The synthetic sequence can be conducted stepwise or as a one‐pot cascade reaction with similar yields. Even in the presence of the gold catalyst the new allene remains intact. 相似文献
3.
4.
5.
6.
K.V. Stepurska О.О. Soldatkin I.S. Kucherenko V.M. Arkhypova S.V. Dzyadevych A.P. Soldatkin 《Analytica chimica acta》2015
This study was aimed at the development of a conductometric biosensor based on acetylcholinesterase considering the feasibility of its application for the inhibitory analysis of various toxicants. In this paper, the optimum conditions for enzyme immobilization on the transducer surface are selected as well as the optimum concentration of substrate for inhibitory analysis. Sensitivity of the developed biosensor to different classes of toxic compounds (organophosphorus pesticides, heavy metal ions, surfactants, aflatoxin, glycoalkaloids) was tested. It is shown that the developed biosensor can be successfully used for the analysis of pesticides and mycotoxins, as well as for determination of total toxicity of the samples. A new method of biosensor analysis of toxic substances of different classes in complex multicomponent aqueous samples is proposed. 相似文献
7.
Mass concentration and isotopic values δ13C and 14C are presented for the water-insoluble refractory carbon(WIRC) component of total suspended particulates(TSP),collected weekly during 2003,as well as from October 2005 to May 2006 at the WMO-GAW Mt.Waliguan(WLG) site.The overall average WIRC mass concentration was(1183±120)ng/m3(n = 79),while seasonal averages were 2081 ±1707(spring),454±205(summer),650±411(autumn),and 1019±703(winter) ng/m3.Seasonal variations in WIRC mass concentrations were consistent with black carbon measurements from an aethalometer,although WIRC concentrations were typically higher,especially in winter and spring.The δ13C PDB value(-25.3 ± 0.8)%.determined for WIRC suggests that its sources are C3 biomass or fossil fuel combustion.No seasonal change in δ13C PDB was evident.The average percent Modern Carbon(pMC) for 14C in WIRC for winter and spring was(67.2 ± 7.7)%(n = 29).Lower pMC values were associated with air masses transported from the area east of WLG,while higher pMC values were associated with air masses from the Tibetan Plateau,southwest of WLG.Elevated pMC values with abnormally high mass concentrations of TSP and WIRC were measured during a dust storm event. 相似文献
8.
9.
10.