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   211720篇
  免费   2308篇
  国内免费   737篇
化学   119084篇
晶体学   3428篇
力学   8365篇
综合类   4篇
数学   20986篇
物理学   62898篇
  2016年   2581篇
  2015年   1958篇
  2014年   2706篇
  2013年   8619篇
  2012年   5999篇
  2011年   7640篇
  2010年   4882篇
  2009年   4810篇
  2008年   6821篇
  2007年   7032篇
  2006年   6815篇
  2005年   6240篇
  2004年   5730篇
  2003年   5160篇
  2002年   4990篇
  2001年   6043篇
  2000年   4624篇
  1999年   3692篇
  1998年   2936篇
  1997年   2990篇
  1996年   2964篇
  1995年   2730篇
  1994年   2590篇
  1993年   2453篇
  1992年   2949篇
  1991年   2840篇
  1990年   2767篇
  1989年   2763篇
  1988年   2739篇
  1987年   2730篇
  1986年   2516篇
  1985年   3486篇
  1984年   3527篇
  1983年   2891篇
  1982年   3152篇
  1981年   3066篇
  1980年   2985篇
  1979年   3106篇
  1978年   3348篇
  1977年   3157篇
  1976年   3078篇
  1975年   2917篇
  1974年   2858篇
  1973年   2896篇
  1972年   1843篇
  1971年   1543篇
  1968年   1973篇
  1967年   2182篇
  1966年   1950篇
  1965年   1513篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
Dielectric relaxation measurements of 5 mole % 4-n-hexyloxycyanobenzene (I) dissolved in 4-n-pentyloxyphenyl-trans-4-n-octylcyclohexylcarboxylate (II) were carried out from 1 kHz to 10 MHz in the nematic, smectic A and smectic B phases. The relaxation frequency of I parallel to the director is about 05 MHz in the SBphase and increases rapidly at the transition from SB to SA.  相似文献   
94.
Let M be a symplectic manifold with a Hamiltonian circle action with isolated fixed points. We prove that σ (M) = b0(M) − b2(M) + b4(M) − b6(M) + … where σ (M) is the signature of M and bi(M) is the ith Betti number of M.  相似文献   
95.
In this article we survey the Trefftz method (TM), the collocation method (CM), and the collocation Trefftz method (CTM). We also review the coupling techniques for the interzonal conditions, which include the indirect Trefftz method, the original Trefftz method, the penalty plus hybrid Trefftz method, and the direct Trefftz method. Other boundary methods are also briefly described. Key issues in these algorithms, including the error analysis, are addressed. New numerical results are reported. Comparisons among TMs and other numerical methods are made. It is concluded that the CTM is the simplest algorithm and provides the most accurate solution with the best numerical stability. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007  相似文献   
96.
Summary The influence of different preparation conditions and substrate surface orientations on the superconducting properties of thin YBa2Cu3O7–x (YBCO) films on silicon was studied. Comparative electrical and surface spectroscopic measurements were performed. SAM and SIMS depth profile analysis show an enrichment of barium at the interface between the superconductor and silicon for samples with Tc<76 K. Comparison with XPS data obtained for thin silicon films on YBCO indicates the formation of barium and yttrium silicates at the interface under these conditions.  相似文献   
97.
The soft physics, pT<2 GeV/c, observables at both RHIC and the SPS have now been mapped out in quite specific detail. From these results there is mounting evidence that this regime is primarily driven by the multiplicity per unit rapidity, dNch/dη. This suggests that the entropy of the system alone is the underlying driving force for many of the global observables measured in heavy-ion collisions. That this is the case and there is an apparent independence on collision energy is surprising. I present the evidence for this multiplicity scaling and use it to make some extremely naive predictions for the soft sector results at the LHC.  相似文献   
98.
This paper records two results about graded Hopf algebras that do not appear to be stated explicitly in the literature. Let B be a graded set, graded by the positive integers. Let V be the graded vector space with basis B over a field K of characteristic zero and V'=KV, where K is in grading zero. Let L ne the free graded Lie algebra on B over K and let T be the free graded tensor algebra on B. The first result is the "graded Witt formula" giving the dimension of the subspace of L in each grading. The second result is the observation that any graded coassociative, co-commutative comultiplication Δ:V'V'V', with co-unit the projection V1K. extends to a graded Hopf algebra structure on T that is in fact isomorphic to the natural graded Hopf algebra structure on T. In the ungraded case the statement analogous to the second result is false.  相似文献   
99.
100.
Mechanical, thermal, and electrical properties of graphite/PMMA composites have been evaluated as functions of particle size and dispersion of the graphitic nanofiller components via the use of three different graphitic nanofillers: “as received graphite” (ARG), “expanded graphite,” (EG) and “graphite nanoplatelets” (GNPs) EG, a graphitic materials with much lower density than ARG, was prepared from ARG flakes via an acid intercalation and thermal expansion. Subsequent sonication of EG in a liquid yielded GNPs as thin stacks of graphitic platelets with thicknesses of ~10 nm. Solution‐based processing was used to prepare PMMA composites with these three fillers. Dynamic mechanical analysis, thermal analysis, and electrical impedance measurements were carried out on the resulting composites, demonstrating that reduced particle size, high surface area, and increased surface roughness can significantly alter the graphite/polymer interface and enhance the mechanical, thermal, and electrical properties of the polymer matrix. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2097–2112, 2007  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