全文获取类型
收费全文 | 30091篇 |
免费 | 1606篇 |
国内免费 | 654篇 |
专业分类
化学 | 20140篇 |
晶体学 | 320篇 |
力学 | 1102篇 |
综合类 | 46篇 |
数学 | 2862篇 |
物理学 | 7881篇 |
出版年
2023年 | 261篇 |
2022年 | 609篇 |
2021年 | 808篇 |
2020年 | 654篇 |
2019年 | 662篇 |
2018年 | 578篇 |
2017年 | 552篇 |
2016年 | 945篇 |
2015年 | 826篇 |
2014年 | 1112篇 |
2013年 | 1869篇 |
2012年 | 2282篇 |
2011年 | 2477篇 |
2010年 | 1617篇 |
2009年 | 1425篇 |
2008年 | 2048篇 |
2007年 | 1766篇 |
2006年 | 1779篇 |
2005年 | 1529篇 |
2004年 | 1320篇 |
2003年 | 1101篇 |
2002年 | 1061篇 |
2001年 | 668篇 |
2000年 | 580篇 |
1999年 | 436篇 |
1998年 | 306篇 |
1997年 | 285篇 |
1996年 | 346篇 |
1995年 | 248篇 |
1994年 | 245篇 |
1993年 | 252篇 |
1992年 | 197篇 |
1991年 | 174篇 |
1990年 | 154篇 |
1989年 | 120篇 |
1988年 | 91篇 |
1987年 | 93篇 |
1986年 | 67篇 |
1985年 | 92篇 |
1984年 | 62篇 |
1983年 | 53篇 |
1982年 | 75篇 |
1981年 | 68篇 |
1979年 | 49篇 |
1978年 | 47篇 |
1977年 | 37篇 |
1976年 | 42篇 |
1975年 | 40篇 |
1974年 | 37篇 |
1973年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 41 毫秒
21.
Laser welding is one of the most precise welding processes in joining sheet metals. In laser welding, performing real time evaluation of the welding quality is very important to enhance the efficiency of the welding process. In this study, the plasma and spatter, which are generated during laser welding, are measured using UV and IR photodiodes. The factors that influence weld quality are classified into five categories; optimal heat input, slightly low heat input, low heat input, partial joining due to gap mismatch, and nozzle deviation. The data number deviated from reference signals and their standard deviations were also considered to evaluate the qualities. A system was also formulated to perform real time evaluations of the weld quality using a fuzzy multi-feature pattern recognition with the measured signals. 相似文献
22.
23.
24.
Jong Uhn Kim 《Transactions of the American Mathematical Society》2002,354(3):1117-1135
In this paper we discuss an initial-boundary value problem for a stochastic nonlinear equation arising in one-dimensional viscoelasticity. We propose to use a new direct method to obtain a solution. This method is expected to be applicable to a broad class of nonlinear stochastic partial differential equations.
25.
Gauss periods give an exponentiation algorithm that is fast for many finite fields but slow for many other fields. The current paper presents a different method for construction of elements that yield a fast exponentiation algorithm for finite fields where the Gauss period method is slow or does not work. The basic idea is to use elements of low multiplicative order and search for primitive elements that are binomial or trinomial of these elements. Computational experiments indicate that such primitive elements exist, and it is shown that they can be exponentiated fast. 相似文献
26.
Neodymium-substituted Bi4Ti3O12 (BNdT) thin films were prepared by a chemical solution deposition technique on platinum- coated silicon substrates. All of
the samples were annealed at the relatively low temperature of 600 °C by a rapid thermal annealing process in different atmospheres,
such as O2, air, and nitrogen, and vacuum. Irrespective of different annealing atmospheres, all of the BNdT thin films exhibit good
ferroelectric properties, such as a saturated hysteresis loop, good fatigue endurance, and low leakage current density. A
large remanent polarization (Pr) of ∼48 μC/cm2 with an electric field of 240 kV/cm was observed from the BNdT thin film annealed in O2 atmosphere. The BNdT thin films annealed in nitrogen and vacuum, at reduced oxygen partial pressures, exhibit smaller Pr than that annealed in oxygen. The difference of Pr of the BNdT thin films annealed in different atmospheres may originate from differences in the grain sizes and the number
of oxygen vacancies.
PACS 77.55.+f; 77.80.-e; 77.80.Fm; 81.15.-z 相似文献
27.
28.
Let G=(V(G),E(G)) be a graph. A (n,G, λ)‐GD is a partition of the edges of λKn into subgraphs (G‐blocks), each of which is isomorphic to G. The (n,G,λ)‐GD is named as graph design for G or G‐decomposition. The large set of (n,G,λ)‐GD is denoted by (n,G,λ)‐LGD. In this work, we obtain the existence spectrum of (n,P3,λ)‐LGD. © 2002 Wiley Periodicals, Inc. J Combin Designs 10: 151–159, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jcd.10008 相似文献
29.
Taekyun Kim 《Journal of Mathematical Analysis and Applications》2002,273(1):236-242
The purpose of this paper is to give a proof of Kummer type congruence for the q-Bernoulli numbers of higher order, which is an answer to a part of the problem in a previous publication (see Indian J. Pure Appl. Math. 32 (2001) 1565-1570). 相似文献
30.
非傍轴平顶高斯光束M2因子两种定义的比较研究 总被引:3,自引:2,他引:1
基于功率密度的二阶矩方法,推导出了非傍轴平顶高斯(FG)光束束宽和远场发散角的解析表达式·研究表明,当w0/λ→0时,远场发散角趋于渐近值θmax=63.435°,与阶数无关·使用非傍轴高斯光束代替傍轴高斯光束作为理想光束,研究了非傍轴FG光束的M2因子,并与传统定义的M2因子作了比较·在非傍轴范畴,非傍轴FG光束的M2因子不仅与阶数N有关,而且与w0/λ有关·按照定义,当w0/λ→0时,非傍轴FG光束的M2因子不等于0,对阶数N=1,2,3时,M2因子分别趋于0.913,0.882和0.886·当N→∞时,M2因子取最小值M2min=0.816· 相似文献