全文获取类型
收费全文 | 64609篇 |
免费 | 1189篇 |
国内免费 | 364篇 |
专业分类
化学 | 37154篇 |
晶体学 | 807篇 |
力学 | 2258篇 |
综合类 | 3篇 |
数学 | 8941篇 |
物理学 | 16999篇 |
出版年
2022年 | 472篇 |
2021年 | 612篇 |
2020年 | 653篇 |
2019年 | 623篇 |
2018年 | 787篇 |
2017年 | 735篇 |
2016年 | 1296篇 |
2015年 | 1018篇 |
2014年 | 1359篇 |
2013年 | 2972篇 |
2012年 | 2881篇 |
2011年 | 3530篇 |
2010年 | 2277篇 |
2009年 | 2143篇 |
2008年 | 2978篇 |
2007年 | 2960篇 |
2006年 | 2930篇 |
2005年 | 2585篇 |
2004年 | 2449篇 |
2003年 | 2080篇 |
2002年 | 1975篇 |
2001年 | 1799篇 |
2000年 | 1370篇 |
1999年 | 1195篇 |
1998年 | 992篇 |
1997年 | 1012篇 |
1996年 | 904篇 |
1995年 | 829篇 |
1994年 | 832篇 |
1993年 | 731篇 |
1992年 | 783篇 |
1991年 | 782篇 |
1990年 | 736篇 |
1989年 | 698篇 |
1988年 | 698篇 |
1987年 | 646篇 |
1986年 | 619篇 |
1985年 | 800篇 |
1984年 | 839篇 |
1983年 | 655篇 |
1982年 | 732篇 |
1981年 | 691篇 |
1980年 | 653篇 |
1979年 | 670篇 |
1978年 | 678篇 |
1977年 | 673篇 |
1976年 | 614篇 |
1975年 | 532篇 |
1974年 | 517篇 |
1973年 | 504篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
J. Xu J. Mei X.H. Huang X. Li Z. Li W. Li K. Chen 《Applied Physics A: Materials Science & Processing》2005,80(1):123-126
The effect of nitrogen surface doping on the electron field emission characteristics of hydrogenated amorphous carbon films was studied. It was found that the emission threshold electric field decreased after nitrogen surface doping which indicated the reduction of the emission barrier at the film surface. It was demonstrated that this improvement arose from the decrease of the effective work function due to the formation of a dipole layer induced by chemical termination and chemical structural change on the film surface. PACS 52.75.Xx; 73.30 +y; 73.61.Jc 相似文献
152.
153.
Q.-Y. Shao A.-D. Li J.-B. Cheng H.-Q. Ling D. Wu Z.-G. Liu N.-B. Ming C. Wang H.-W. Zhou B.-Y. Nguyen 《Applied Physics A: Materials Science & Processing》2005,81(6):1181-1185
LaAlO3 (LAO) gate dielectric films were deposited on Si substrates by low-pressure metalorganic chemical vapor deposition. The interfacial structure and composition distribution were investigated by high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), secondary-ion mass spectroscopy (SIMS), and Auger-electron spectroscopy (AES). HRTEM confirms that there exists an interfacial layer between LAO and Si in most samples. AES, SIMS, and XPS analyses indicate that the interfacial layer is compositionally graded La–Al silicate and the Al element is severely deficient close to the Si surface. Electrical properties of LAO films were evaluated. No evident difference in electrical properties between samples with and without native SiO2 layers was observed. The electrical properties are discussed in terms of LAO growth mechanisms, in relation to the interfacial structure. PACS 73.40.Qv; 81.15.Gh; 77.55.+f; 68.35.-p 相似文献
154.
We compare the efficiency of two Faddeev-type approaches for the nuclear three-body Coulomb problem. The first one is a modification
of Noble’s approach, the second one is due to Sasakawa and Sawada. In an integral-equation formulation both of these methods
rely on the same Green’s operators and driving terms. The differences lie in the treatment of the long-range Coulomb potentials.
Numerical examples show that the modified Faddeev-Noble approach provides for faster convergence. 相似文献
155.
J. MALINEN O. NEVANLINNA V. TURUNEN Z. YUAN 《数学学报(英文版)》2007,23(4):745-748
Let T be a bounded linear operator in a Banach space, with σ(T)={1}. In 1983, Esterle-Berkani' s conjecture was proposed for the decay of differences (I - T) T^n as follows: Eitheror lim inf (n→∞(n+1)||(I-T)T^n||≥1/e or T = I. We prove this claim and discuss some of its consequences. 相似文献
156.
Differentiation of functions w.r.t. finite atomless measures with compact support on the real line is introduced. The related harmonic calculus is similar to that of the classical Lebesgue case. As an application we obtain the Weyl exponent for the spectral asymptotics of the Laplacians w.r.t. linear Cantor-type measures with arbitrary weights. 相似文献
157.
Ohne ZusammenfassungDiese Arbeit wurde während eines Aufenthaltes von Schmidt in der Bundesrepublik Deutschland als Preisträger der Alexander von Humboldt-Stiftung geschrieben. 相似文献
158.
Dr. Z. Livne 《International Journal of Game Theory》1987,16(3):223-242
The Bargaining Problem paradigm is extended to time-consuming conflict situations. Such a situation can be represented by a chain of bargaining domains, each representing the conflict at a different point in time. The solution function selects a point in the union of all these domains. We characterize a solution function which satisfies several requirements and explore its properties. One of the results is that an extension of the Adding requirement (Thomson-Myerson 1980) is enough, under some conditions, to yield a solution point, so there is no need to extend the stronger requirements of Independence of Irrelevant Alternatives (Nash 1950) or Monotonicity (Kalai-Smorodinsky 1975). 相似文献
159.
Butyltins were analyzed in waters from California river and lake marinas and were detected at the part per trillion (ppt) level in most locations. The tributyltin:dibutyltin (TBT/DBT) ratios in the fresh waters were similar to those in their saline counterparts indicating like rates of degradation in the two salinity regimes. 相似文献
160.
We give a new and comparably short proof of Gittins’ index theorem for dynamic allocation problems of the multi-armed bandit type in continuous time under minimal assumptions. This proof gives a complete characterization of optimal allocation strategies as those policies which follow the current leader among the Gittins indices while ensuring that a Gittins index is at an all-time low whenever the associated project is not worked on exclusively. The main tool is a representation property of Gittins index processes which allows us to show that these processes can be chosen to be pathwise lower semi-continuous from the right and quasi-lower semi-continuous from the left. Both regularity properties turn out to be crucial for our characterization and the construction of optimal allocation policies. 相似文献