全文获取类型
收费全文 | 233770篇 |
免费 | 45164篇 |
国内免费 | 35643篇 |
专业分类
化学 | 108021篇 |
晶体学 | 1950篇 |
力学 | 10600篇 |
综合类 | 699篇 |
数学 | 19969篇 |
物理学 | 81115篇 |
综合类 | 92223篇 |
出版年
2024年 | 1069篇 |
2023年 | 3127篇 |
2022年 | 4889篇 |
2021年 | 5210篇 |
2020年 | 5946篇 |
2019年 | 8407篇 |
2018年 | 8074篇 |
2017年 | 8746篇 |
2016年 | 10499篇 |
2015年 | 10990篇 |
2014年 | 12214篇 |
2013年 | 14822篇 |
2012年 | 15961篇 |
2011年 | 17255篇 |
2010年 | 18120篇 |
2009年 | 17817篇 |
2008年 | 11794篇 |
2007年 | 10929篇 |
2006年 | 9272篇 |
2005年 | 8995篇 |
2004年 | 9068篇 |
2003年 | 7262篇 |
2002年 | 6682篇 |
2001年 | 6370篇 |
2000年 | 5239篇 |
1999年 | 6704篇 |
1998年 | 5809篇 |
1997年 | 5586篇 |
1996年 | 5684篇 |
1995年 | 5613篇 |
1994年 | 5364篇 |
1993年 | 5231篇 |
1992年 | 4498篇 |
1991年 | 4135篇 |
1990年 | 3381篇 |
1989年 | 3266篇 |
1988年 | 3104篇 |
1987年 | 2031篇 |
1986年 | 1842篇 |
1985年 | 1297篇 |
1984年 | 1201篇 |
1983年 | 555篇 |
1982年 | 1014篇 |
1981年 | 828篇 |
1980年 | 831篇 |
1979年 | 575篇 |
1978年 | 565篇 |
1977年 | 688篇 |
1976年 | 1089篇 |
1972年 | 566篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
Hong-Xing Zheng Dao-Yin Yu 《International Journal of Infrared and Millimeter Waves》2005,26(9):1343-1353
In this paper, a very useful numerical technique has been developed for analyzing the transient characteristics of a planar-spiral inductor on-chip. A locally conformal technique and an alternating-direction implicit scheme are applied to the finite-difference time-domain method. A formulation for solving three dimensional Maxwell’s equations is proposed. Using the proposed method, various parameters of the planar-spiral inductors have been analyzed and an equivalent circuit, which includes frequency-independent circuit elements, has been introduced. Highly computational efficiency is implemented. Numerical results show excellent agreement with the measured data over a wide frequency range. 相似文献
152.
T Utsunomiya M. Sekine 《International Journal of Infrared and Millimeter Waves》2005,26(11):1651-1660
We have conducted a millimeter wave propagation experiment at 103 GHz (2.9 mm) on a propagation path of 390 m. The results
were compared with the rain attenuation calculations from the Marshall-Palmer, Best, Joss-Thomas-Waldvogel and Weibull distributions
for raindrop-size. It has been shown that the Weibull distribution has a good agreement with the experiments. 相似文献
153.
Yan WANG Rong Quan FENG 《数学学报(英文版)》2005,21(4):773-778
A Cayley map is a Cayley graph embedded in an orientable surface such that. the local rotations at every vertex are identical. In this paper, balanced regular Cayley maps for cyclic groups, dihedral groups, and generalized quaternion groups are classified. 相似文献
154.
155.
勿庸置疑,课堂只是学生腾飞的基地,社会才是学生飞翔的天空.如何架设课堂与社会之间的桥梁,使学生从理论走向实践,从空想走向实际,是每位教师必须思考的问题.就物理教学而言,实验是架设课堂和社会的桥梁之一.那就是通过物理实验来实现. 相似文献
156.
We present all-atom molecular dynamics simulations ofn-hexane on the basal plane of graphite at monolayer and multilayer coverages. In keeping with experimental data, we find the
presence of ordered adsorbed layers both at single monolayer coverage and when the adsorbed layer coexists with excess liquid
adsorbate. Using a simulation method that does not impose any particular periodicity on the adsorbed layer, we quantitatively
compare our results to the results of neutron diffraction experiments and find a structural transition from a uniaxially incommensurate
lattice to a fully commensurate structure on increasing the coverage from a monolayer to a multilayer. The zig-zag backbone
planes of all the alkane molecules lie parallel to the graphite surface at the multilayer coverage, while a few molecules
are observed to attain the perpendicular orientation at monolayer coverage.
Dedicated to Professor C N R Rao on his 70th birthday 相似文献
157.
证明了当超越亚纯函数的级小于1时,其Norel例外值最多只有一个.由于存在任何级的整函数,因此一个例外值总可达到,故所得结果不能再改进。 相似文献
158.
灾害的破坏程度不仅取决于地震能量(受控于现代构造应力场的特征),同时也受岩溶塌陷,采空区塌陷等其他灾害的影响,故采用人工神经网络模型评价灾害危险性。借助地理信息系统软件,计算了唐山市各居住小区的建筑密度和建筑容积率,结合灾害危险性评价结果。确定了从防灾角度考虑的土地开发强度评价指标。应用Maplnfo自带二次开发语言MapBasic及Visual Basic进行二次开发,炳述了二次开发的步骤和过程。依据系统评价结果,对唐山市的城市规划布局和土地利用方向提出了几点建议。 相似文献
159.
A fluorous osmium catalyst was firstly developed. It had been effectively used as recoverable and reusable catalyst in the dihydroxylation of olefins. 相似文献
160.
Fei Chang Dongheng Zhang Haijian Yang Haibin Song 《Journal of organometallic chemistry》2004,689(5):936-946
The synthesized 1-aryliminomethylenylnaphthalen-2-ol derivatives reacted with nickel chloride to form bis(1-aryliminomethylenylnaphthalen-2-oxy)nickel complexes. All resultant compounds were structurally characterized by elemental analyses, IR and H NMR, and the structures of the formed complexes were elucidated by X-ray crystal structure analysis. The complexes show high catalytic activities for the vinyl polymerization of norbornene in the presence of methylaluminoxane. The catalytic activity variations have been followed by gas chromatography through monitoring the conversion of norbornene. 相似文献