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   470286篇
  免费   4736篇
  国内免费   1477篇
化学   222448篇
晶体学   6385篇
力学   24384篇
综合类   7篇
数学   85000篇
物理学   138275篇
  2020年   2030篇
  2019年   2014篇
  2018年   18876篇
  2017年   19472篇
  2016年   12546篇
  2015年   4896篇
  2014年   4900篇
  2013年   14524篇
  2012年   17796篇
  2011年   33086篇
  2010年   19616篇
  2009年   19893篇
  2008年   27449篇
  2007年   32468篇
  2006年   12732篇
  2005年   19285篇
  2004年   14810篇
  2003年   13771篇
  2002年   10913篇
  2001年   10475篇
  2000年   8222篇
  1999年   6302篇
  1998年   5098篇
  1997年   4883篇
  1996年   5071篇
  1995年   4569篇
  1994年   4272篇
  1993年   4096篇
  1992年   4553篇
  1991年   4421篇
  1990年   4122篇
  1989年   3954篇
  1988年   4255篇
  1987年   3916篇
  1986年   3799篇
  1985年   5446篇
  1984年   5524篇
  1983年   4498篇
  1982年   4870篇
  1981年   4900篇
  1980年   4670篇
  1979年   4790篇
  1978年   4800篇
  1977年   4696篇
  1976年   4668篇
  1975年   4570篇
  1974年   4412篇
  1973年   4620篇
  1972年   2612篇
  1971年   1904篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
In this paper a new definition of a lattice valued intuitionistic fuzzy set (LIFS) is introduced, in an attempt to overcome the disadvantages of earlier definitions. Some properties of this kind of fuzzy sets and their basic operations are given. The theorem of synthesis is proved: For every two families of subsets of a set satisfying certain conditions, there is an lattice valued intuitionistic fuzzy set for which these are families of level sets. The research supported by Serbian Ministry of Science and Technology, Grant No. 1227.  相似文献   
992.
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   
993.
In the present paper, Daubechies' wavelets and the computation of their scaling coefficients are briefly reviewed. Then a new method of computation is proposed. This method is based on the work [7] concerning a new orthonormality condition and relations among scaling moments, respectively. For filter lengths up to 16, the arising system can be explicitly solved with algebraic methods like Gröbner bases. Its simple structure allows one to find quickly all possible solutions.  相似文献   
994.
Auslander’s representation dimension measures how far a finite dimensional algebra is away from being of finite representation type. In [1], M. Auslander proved that a finite dimensional algebra A is of finite representation type if and only if the representation dimension of A is at most 2. Recently, R. Rouquier proved that there are finite dimensional algebras of an arbitrarily large finite representation dimension. One of the exciting open problems is to show that all finite dimensional algebras of tame representation type have representation dimension at most 3. We prove that this is true for all domestic weakly symmetric algebras over algebraically closed fields having simply connected Galois coverings.  相似文献   
995.
996.
997.
Let ε be the collection of those rings S such that, for every S-module V and every homogeneous function ?. V → V, ?(sv) = s?(v), s ∈ S, v ∈ V, ? is linear on V. In this paper we characterize those Stanley-Reisner rings, R, such that D(R) is in ε.  相似文献   
998.
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   
999.
R.J Hand 《Journal of Non》2003,315(3):276-287
Glass may be strengthened by epoxy coatings although the strengthening mechanisms remain unclear. Possible strengthening mechanisms are reviewed and are used to analyse strength data for both a solvent based and a water based coating system. The coatings either fill (solvent based coatings), or partially fill (water based coatings) surface cracks and it is shown that closure stresses arising from the thermal expansion mismatch of the coating within these cracks can account for the observed degrees of strengthening. It is also demonstrated that other suggested mechanisms such as flaw healing cannot fully account for the observed degree of strengthening.  相似文献   
1000.
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   
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