全文获取类型
收费全文 | 53974篇 |
免费 | 9823篇 |
国内免费 | 7835篇 |
专业分类
化学 | 39834篇 |
晶体学 | 811篇 |
力学 | 3413篇 |
综合类 | 573篇 |
数学 | 5961篇 |
物理学 | 21040篇 |
出版年
2024年 | 115篇 |
2023年 | 1010篇 |
2022年 | 1859篇 |
2021年 | 1909篇 |
2020年 | 2130篇 |
2019年 | 2170篇 |
2018年 | 1825篇 |
2017年 | 1842篇 |
2016年 | 2537篇 |
2015年 | 2702篇 |
2014年 | 3244篇 |
2013年 | 4126篇 |
2012年 | 5015篇 |
2011年 | 5229篇 |
2010年 | 3743篇 |
2009年 | 3696篇 |
2008年 | 4062篇 |
2007年 | 3578篇 |
2006年 | 3280篇 |
2005年 | 2745篇 |
2004年 | 2023篇 |
2003年 | 1706篇 |
2002年 | 1673篇 |
2001年 | 1333篇 |
2000年 | 1123篇 |
1999年 | 1062篇 |
1998年 | 768篇 |
1997年 | 745篇 |
1996年 | 646篇 |
1995年 | 573篇 |
1994年 | 584篇 |
1993年 | 464篇 |
1992年 | 365篇 |
1991年 | 337篇 |
1990年 | 313篇 |
1989年 | 199篇 |
1988年 | 165篇 |
1987年 | 150篇 |
1986年 | 129篇 |
1985年 | 88篇 |
1984年 | 67篇 |
1983年 | 51篇 |
1982年 | 36篇 |
1981年 | 32篇 |
1980年 | 21篇 |
1979年 | 19篇 |
1977年 | 11篇 |
1975年 | 8篇 |
1957年 | 12篇 |
1925年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
采用甚高频等离子体增强化学气相沉积技术制备了系列微晶硅薄膜太阳电池,指出了气体总流量和背反射电极的类型对电池性能参数的影响.电池的I-V测试结果表明:随反应气体总流量的增加,对应电池的短路电流密度、开路电压和填充因子都有很大程度的提高,结果使得电池的光电转换效率得以提高.另外,ZnO/Ag/Al背反射电极能明显提高电池的短路电流密度,进而也提高了电池的光电转换效率.对气体总流量和背反射电极类型影响电池效率的原因进行了分析.
关键词:
微晶硅薄膜太阳电池
气体流量
ZnO/Ag/Al背反射电极 相似文献
83.
The drawbacks of our earlier report of preparing fuel cell catalyst arrays by borohydride reduction of inkjet prepared arrays of metal salts are discussed along with the need for inclusion of state-of-the-art metrics in all array screening. An alternative method for screening of hydrogen/air cathode catalysts, direct methanol fuel cell (DMFC) anode catalysts, and catalyst loading studies is provided. State-of-the-art Johnson Matthey catalysts were used in control experiments to demonstrate the utility of the array fuel cell for high throughput screening of fuel cell catalysts in the 3-4 mg/cm2 range. This report lays out hard learned rules for high throughput screening and demonstrates that the array fuel cell can be used for very precise screening of libraries of membrane electrode assembly (MEA) components without the pitfalls discussed in the introduction. 相似文献
84.
T-型树谱唯一性的一个简单刻画 总被引:1,自引:0,他引:1
图G称为谱唯一的,如果任何与G谱相同的图一定与G同构.一棵树称为T-型树如果其仅有一个最大度为3的顶点.本文给出了T-型树谱唯一性的一个简单刻画,从而完全解决了T-型树的谱唯一性问题. 相似文献
85.
86.
87.
Let T be a bounded linear operator on Hilbert space H, M an invariant subspace of T. If there exists another invariant subspace N of T such that H = M + N and M ∩ N = 0, then M is said to be a completely reduced subspace of T. If T has a nontrivial completely reduced subspace, then T is said to be completely reducible; otherwise T is said to be completely irreducible. In the present paper we briefly sum up works on completely irreducible operators that
have been done by the Functional Analysis Seminar of Jilin University in the past ten years and more.
The paper contains four sections. In section 1 the background of completely irreducible operators is given in detail. Section
2 shows which operator in some well-known classes of operators, for example, weighted shifts, Toeplitz operators, etc., is
completely irreducible. In section 3 it is proved that every bounded linear operator on the Hilbert space can be approximated
by the finite direct sum of completely irreducible operators. It is clear that a completely irreducible operator is a rather
suitable analogue of Jordan blocks in L(H), the set of all bounded linear operators on Hilbert space H. In section 4 several questions concerning completely irreducible operators are discussed and it is shown that some properties
of completely irreducible operators are different from properties of unicellular operators.
__________
Translated from Acta Sci. Nat. Univ. Jilin, 1992, (4): 20–29 相似文献
88.
Propagation of the Hermite–Gaussian beams through misaligned optical system with a circular aperture
By means of expanding a hard-edged aperture into a finite sum of complex Gaussian functions, the approximate analytical formula of one kind of higher-order Gaussian beams called the Hermite–Gaussian beams (HGBs) passing through circular apertured and misaligned optical system is obtained in this paper. The result provides more convenience for studying its propagation than the usual way by using diffraction integral directly. Some numerical simulations are also given for illustrating the propagation properties of the HGBs through the circular apertured optical systems. 相似文献
89.
基于同步辐射加速器的康普顿背散射γ射线源(Ⅰ)产生MeV量级γ光子的数值计算 总被引:1,自引:0,他引:1
提出在筹建的上海同步辐射装置上建造一条MeV量级γ射线束及应用站,采用μm波长的红外(或远红外)激光与储存环中3.5GeV电子束进行康普顿背散射,从而获得能区为1—25MeV的康普顿背散射γ光子束,该光子束具有高强度、高极化度(线和圆极化)、准单色、方向性好的优点,可以广泛地应用于核物理和核天体物理基础研究及相关的应用研究领域.介绍了康普顿背散射的基本原理,并结合储存环参数给出了光子束性能的数值计算结果. 相似文献
90.
Wei Shi Yujie J. Ding Changshui Fang Qiwei Pan Qingtian Gu 《Optics and Lasers in Engineering》2002,38(6):361-371
Mode-matching and effective index methods are used to analyze single-mode operation of optical rib polymer waveguides. Their single-mode waveguiding conditions are determined. Single-mode rib waveguides fabricated from guest–host polyetherketone are presented. The estimated propagation loss of straight rib-waveguides is 0.7 dB/cm at 1.55 μm. Furthermore, by using the mode field-transfer matrix method, 2×2 and 4×4 polymer Mach–Zehnder interference switch operating at 1.55 μm wavelength has been designed based on optical multi-mode interference. 相似文献