首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   295796篇
  免费   2166篇
  国内免费   632篇
化学   142506篇
晶体学   4465篇
力学   14640篇
综合类   4篇
数学   42912篇
物理学   94067篇
  2018年   10455篇
  2017年   11374篇
  2016年   6454篇
  2015年   2598篇
  2014年   2521篇
  2013年   7952篇
  2012年   9653篇
  2011年   19474篇
  2010年   11923篇
  2009年   11927篇
  2008年   16979篇
  2007年   20685篇
  2006年   6105篇
  2005年   12700篇
  2004年   8645篇
  2003年   7915篇
  2002年   5724篇
  2001年   5936篇
  2000年   4693篇
  1999年   3553篇
  1998年   2789篇
  1997年   2796篇
  1996年   2899篇
  1995年   2619篇
  1994年   2478篇
  1993年   2366篇
  1992年   2847篇
  1991年   2737篇
  1990年   2687篇
  1989年   2718篇
  1988年   2669篇
  1987年   2669篇
  1986年   2480篇
  1985年   3352篇
  1984年   3384篇
  1983年   2807篇
  1982年   2998篇
  1981年   2925篇
  1980年   2736篇
  1979年   2928篇
  1978年   3195篇
  1977年   2929篇
  1976年   2909篇
  1975年   2744篇
  1974年   2696篇
  1973年   2753篇
  1972年   1758篇
  1968年   2023篇
  1967年   2164篇
  1966年   1968篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Crystal Structure of the Zinc Amide Zn[N(SiMe3)2]2 X‐ray quality crystals of Zn[N(SiMe3)2]2 (monoclinic, P21/c) are obtained by sublimation of the zinc amide Zn[N(SiMe3)2]2 at —30 °C in vacuo (300 torr). According to the result of the X‐ray structural analysis, Zn[N(SiMe3)2]2 contains an almost linear N‐Zn‐N unit with two short N‐Zn bonds.  相似文献   
952.
The dependence of structural properties and surface morphology of Cu-In alloy layers on the composition and sputtering deposition sequence were investigated by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The properties of the co-sputtered alloy layers changed abruptly around the composition boundary when the Cu/In ratio reached 1/2. This can be explained by the effective heat of formation (EHF) model, which has been used to predict the sequence of phase formation for metal diffusion couples. The use of a co-sputtered alloy layer with a high In concentration was not suitable for fabricating solar cells, because the film had a very rough morphology due to large In islands formed on the CuIn2 phase. However, it was possible to minimize this phase by In sputtering followed by co-sputtering with a Cu/In ratio of 1 (Cu-In/In/Glass). This permitted the fabrication of a homogeneous Cu-In alloy layer, which was not possible through the simple co-sputtering.  相似文献   
953.
For a linear complementarity problem with inconsistent system of constraints a notion of quasi-solution of Tschebyshev type is introduced. It’s shown that this solution can be obtained automatically by Lemke’s method if the constraint matrix of the original problem is copositive plus or belongs to the intersection of matrix classes P 0 and Q 0.  相似文献   
954.
Here we prove a limit theorem in the sense of the weak convergence of probability measures in the space of meromorphic functions for a general Dirichlet series. The explicit form of the limit measure in this theorem is given. Partially supported by Lithuanian Foundation of Studies and Science  相似文献   
955.
In the paper the asymptotics for Dirichlet polynomials associated to certain cusp forms are obtained. Partially supported by Lithuanian Foundation of Studies and Science  相似文献   
956.
957.
The effects of the blend ratio and initiating system on the viscoelastic properties of nanostructured natural rubber/polystyrene‐based interpenetrating polymer networks (IPNs) were investigated in the temperature range of ?80 to 150 °C. The studies were carried out at different frequencies (100, 50, 10, 1, and 0.1 Hz), and their effects on the damping and storage and loss moduli were analyzed. In all cases, tan δ and the storage and loss moduli showed two distinct transitions corresponding to natural rubber and polystyrene phases, which indicated that the system was not miscible on the molecular level. However, a slight inward shift was observed in the IPNs, with respect to the glass‐transition temperatures (Tg's) of the virgin polymers, showing a certain degree of miscibility or intermixing between the two phases. When the frequency increased from 0.1 to 100 Hz, the Tg values showed a positive shift in all cases. In a comparison of the three initiating systems (dicumyl peroxide, benzoyl peroxide, and azobisisobutyronitrile), the dicumyl peroxide system showed the highest modulus. The morphology of the IPNs was analyzed with transmission electron microscopy. The micrographs indicated that the system was nanostructured. An attempt was made to relate the viscoelastic behavior to the morphology of the IPNs. Various models, such as the series, parallel, Halpin–Tsai, Kerner, Coran, Takayanagi, and Davies models, were used to model the viscoelastic data. The area under the linear loss modulus curve was larger than that obtained by group contribution analysis; this showed that the damping was influenced by the phase morphology, dual‐phase continuity, and crosslinking of the phases. Finally, the homogeneity of the system was further evaluated with Cole–Cole analysis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1680–1696, 2003  相似文献   
958.
The thermal expansion coefficients and the thermal conductivity of Bridgman-grown crystals of CuGa1−x InxTe2 solid solutions are investigated. It is found that the thermal expansion coefficient varies with x linearly, while the thermal conductivity is minimal when x=0.5. The Debye temperature and the rms dynamic atomic displacements are calculated from experimental data. It is shown that the Debye temperature decreases and the rms displacements in the crystal lattice sharply increase as the In content in the solid solutions grows.  相似文献   
959.
The environmental cell device discussed in this paper provides a modest low-vacuum scanning electron microscopy (SEM) capability to a standard SEM without requiring additional pumping. This environmental cell confines a volume of low vacuum in contact with the sample surface using a container that has an aperture for admitting the primary electron beam. The aperture is large enough to permit a limited field of view of the sample, and small enough to limit the outflow of gas into the SEM chamber to that which can be accommodated by the standard SEM pumping system. This environmental cell also functions as a gaseous detector device.  相似文献   
960.
The integration procedure based on the generalized Darboux transform is suggested for the Ishimori magnet model. Exact solutions are constructed for the model on the background of spiral structures. The possibility of phase transition in the system is hypothesized.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号