全文获取类型
收费全文 | 33216篇 |
免费 | 3518篇 |
国内免费 | 6069篇 |
专业分类
化学 | 29193篇 |
晶体学 | 1314篇 |
力学 | 791篇 |
综合类 | 232篇 |
数学 | 2080篇 |
物理学 | 9193篇 |
出版年
2024年 | 71篇 |
2023年 | 379篇 |
2022年 | 949篇 |
2021年 | 888篇 |
2020年 | 1121篇 |
2019年 | 1103篇 |
2018年 | 913篇 |
2017年 | 1258篇 |
2016年 | 1287篇 |
2015年 | 1167篇 |
2014年 | 1559篇 |
2013年 | 2821篇 |
2012年 | 1925篇 |
2011年 | 2372篇 |
2010年 | 1990篇 |
2009年 | 2263篇 |
2008年 | 2308篇 |
2007年 | 2285篇 |
2006年 | 2136篇 |
2005年 | 1993篇 |
2004年 | 1771篇 |
2003年 | 1452篇 |
2002年 | 1242篇 |
2001年 | 1051篇 |
2000年 | 999篇 |
1999年 | 805篇 |
1998年 | 682篇 |
1997年 | 602篇 |
1996年 | 516篇 |
1995年 | 526篇 |
1994年 | 466篇 |
1993年 | 396篇 |
1992年 | 306篇 |
1991年 | 218篇 |
1990年 | 138篇 |
1989年 | 135篇 |
1988年 | 118篇 |
1987年 | 72篇 |
1986年 | 75篇 |
1985年 | 67篇 |
1984年 | 52篇 |
1983年 | 33篇 |
1982年 | 43篇 |
1981年 | 46篇 |
1980年 | 49篇 |
1979年 | 43篇 |
1978年 | 32篇 |
1977年 | 27篇 |
1976年 | 14篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
Ioan Tomescu 《Journal of Graph Theory》2003,43(3):210-222
In the set of graphs of order n and chromatic number k the following partial order relation is defined. One says that a graph G is less than a graph H if ci(G) ≤ ci(H) holds for every i, k ≤ i ≤ n and at least one inequality is strict, where ci(G) denotes the number of i‐color partitions of G. In this paper the first ? n/2 ? levels of the diagram of the partially ordered set of connected 3‐chromatic graphs of order n are described. © 2003 Wiley Periodicals, Inc. J Graph Theory 43: 210–222, 2003 相似文献
103.
Kai Kamada Shintaro Udo Shuichi Yamashita Yuko Tsutsumi Yasumichi Matsumoto 《Solid State Ionics》2003,160(3-4):389-394
Quantitative analysis of metal cation doping by solid oxide electrochemical doping (SOED) has been performed under galvanostatic doping conditions. A M–β″-Al2O3 (M=Ag, Na) microelectrode (contact radius: about 10 μm) was used as cation source to attain a homogeneous solid–solid contact between the β″-Al2O3 and doping target. In Ag doping into alkali borate glass, the measured dopant amount closely matched the theoretical value. High Faraday efficiencies of above 90% were obtained. This suggests that the dopant amount can be precisely controlled on a micromole scale by the electric charge during electrolysis. On the other hand, current efficiencies of Na doping into Bi2Sr2CaCu2Oy (BSCCO) ceramics depended on the applied constant current. Efficiencies of above 80% were achieved at a constant current of 10 μA (1.6 A cm−2). The relatively low efficiencies were explained by the saturation of BSCCO grain boundaries with Na. By contrast, excess Na was detected on the anodic surface of ceramics at a constant current of 100 μA (16 A cm−2). In the present study, we demonstrate that SOED enables micromole-scale control over dopant amount. 相似文献
104.
105.
Glucose, maltose, sucrose, lactose, ethanol and urea concentrations were monitored simultaneously during the cultivation of Escherichia coli and Saccharomyces cerevisiae by means of enzyme field effect transistors (EnFETs) applying glucose dehydrogenase (GDH), maltase (MAL)/GDH, invertase (INV)/GDH, β-galactosidase (β-GAL)/galactosedehydrogenase (GALDH), alcoholdehydrogenase (ADH)/aldehydedehydrogenase (ALDH), and urease. These enzymes were (co)immobilized on the pH sensitive gates of an eight-FET array. The FET array was integrated in a commercial FIA system. 相似文献
106.
D—^3He聚变动力可行性研究 总被引:9,自引:3,他引:6
本文首先简要地讨论D-3He聚变的物理要求并与D-T聚变作相应的比较,然后运用目前的约束定律和第一稳定区β极限,对计划的近期ETR规模装置(如CIT,TIBER,FER,NET)进行D-3He得失相当和点火实验的可行性研究,并对高径比第二稳定区D-3He托卡马克堆进行参数学研究,最后指出潜在的缩短商用化进程可能性。 相似文献
107.
In this paper, numerical simulation of three-dimensional supersonic flow in a duct is presented. The flow field in the duct is complex and can find its applications in the inlet of air-breathing engines. A unique streamwise marching Lagrangian method is employed for solving the steady Euler equations. The method was first initiated by Loh and Hui (1990) for 2-D steady supersonic flow computations and then extended to 3-D computation by the present authors Loh and Liou (1992). The new scheme is shown to be capable of accurately resolving complicated shock or contact discontinuities and their interactions. In all the computations, a free stream of Mach numberM=4 is considered.This article was processed using Springer-Verlag TEX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society. 相似文献
108.
A molecular dynamics method has been used to simulate the argon ion-assisted deposition of Cu/Co/Cu multilayers and to explore ion beam assistance strategies that can be used during or after the growth of each layer to control interfacial structures. A low-argon ion energy of 5–10 eV was found to minimize a combination of interfacial roughness and interlayer mixing (alloying) during the ion-assisted deposition of multilayers. However, complete flattening with simultaneous ion assistance could not be achieved without some mixing between the layers when a constant ion energy approach was used. It was found that multilayers with lower interfacial roughness and intermixing could be grown either by modulating the ion energy during the growth of each metal layer or by utilizing ion assistance only after the completion of each layers deposition. In these latter approaches, relatively high-energy ions could be used since the interface is buried and less susceptible to intermixing. The interlayer mixing dependence upon the thickness of the over layer has been determined as a function of ion energy. 相似文献
109.
本文描述了利用KTP晶体和腔的基波输出镜构成非线性镜实现1.08μmNd:YAP激光器的被动锁模。实验表明,这种新的锁模技术比用染料作可饱和吸收体的被动锁模技术有很多突出的优点,具有很大的发展潜力。实验测得锁模时基波1.08μm输出2.4mJ,二次谐波0.54μm输出0.5mJ(同样条件下的静态输出为2.5mJ),基波脉冲的平均脉宽为40ps。 相似文献
110.
Ummadisetty Subramanyam Swaminathan Sivaram 《Journal of polymer science. Part A, Polymer chemistry》2007,45(2):191-210
Homopolymerization of octadecene‐1 at different reaction conditions has been studied. Significant chain running can be seen at higher polymerization temperatures. Interestingly, insertion of octadecene‐1 into a sterically hindered nickel‐cation/carbon (secondary) bond is observed. The microstructure of the polymer was established using NMR spectroscopy. The effects of chain running on polymer melting, crystallization behavior, and dynamic mechanical thermal properties were studied using DSC and DMTA. The extent of chain running (i.e., 2,ω‐, 1,ω‐enchainments) decreases with an increase in the carbon number of α‐olefins. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 191–210, 2007 相似文献