全文获取类型
收费全文 | 36940篇 |
免费 | 6171篇 |
国内免费 | 4127篇 |
专业分类
化学 | 26458篇 |
晶体学 | 427篇 |
力学 | 2406篇 |
综合类 | 317篇 |
数学 | 4036篇 |
物理学 | 13594篇 |
出版年
2024年 | 123篇 |
2023年 | 765篇 |
2022年 | 1168篇 |
2021年 | 1270篇 |
2020年 | 1410篇 |
2019年 | 1399篇 |
2018年 | 1168篇 |
2017年 | 1134篇 |
2016年 | 1676篇 |
2015年 | 1698篇 |
2014年 | 2009篇 |
2013年 | 2553篇 |
2012年 | 3294篇 |
2011年 | 3374篇 |
2010年 | 2250篇 |
2009年 | 2010篇 |
2008年 | 2332篇 |
2007年 | 2207篇 |
2006年 | 2061篇 |
2005年 | 1763篇 |
2004年 | 1288篇 |
2003年 | 1131篇 |
2002年 | 1088篇 |
2001年 | 868篇 |
2000年 | 741篇 |
1999年 | 817篇 |
1998年 | 633篇 |
1997年 | 618篇 |
1996年 | 584篇 |
1995年 | 523篇 |
1994年 | 497篇 |
1993年 | 404篇 |
1992年 | 361篇 |
1991年 | 365篇 |
1990年 | 302篇 |
1989年 | 234篇 |
1988年 | 167篇 |
1987年 | 156篇 |
1986年 | 137篇 |
1985年 | 103篇 |
1984年 | 95篇 |
1983年 | 67篇 |
1982年 | 57篇 |
1981年 | 49篇 |
1980年 | 43篇 |
1978年 | 24篇 |
1977年 | 25篇 |
1976年 | 23篇 |
1974年 | 20篇 |
1973年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
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
54.
以CF4和C6H6的混合气体作为气源,在微波电子回旋共振化学气相沉积(ECRCVD)装置中制备了氟化非晶碳薄膜(aC:F),并在N2气氛中作了退火处理以考察其热稳定性.通过傅里叶变换红外吸收谱和紫外可见光谱获得了薄膜中CC双键的相对含量和光学带隙,发现膜中CC键含量与光学带隙之间存在着密切的关联,在高微波功率下沉积的氟化非晶碳膜具有低的光学带隙和较好的热稳定性.
关键词:
氟化非晶碳膜
光学带隙
退火温度
热稳定性 相似文献
55.
56.
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
57.
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
58.
59.
S. J. Cheng W. Sheng P. Hawrylak S. Raymond S. Studenikin A. Sachrajda Z. Wasilewski A. Babinski M. Potemski G. Ortner M. Bayer 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):211
We present results of calculations and experiments on electron–hole complexes in InGaAs/GaAs self-assembled quantum dots in high magnetic field (B). Due to hidden symmetries, the chemical potential of an N-exciton system at special B fields becomes insensitive to the exciton number as well as the magnetic field. This results in plateau regions of high intensity in measured magneto-PL spectrum. Theoretical calculations using exact diagonalization techniques successfully explain the measured magneto-photoluminescence spectrum with B fields up to 28 T. 相似文献
60.