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   1998篇
  免费   53篇
  国内免费   8篇
化学   1606篇
晶体学   11篇
力学   18篇
数学   89篇
物理学   335篇
  2023年   17篇
  2022年   24篇
  2021年   28篇
  2020年   25篇
  2019年   29篇
  2018年   30篇
  2017年   16篇
  2016年   44篇
  2015年   37篇
  2014年   53篇
  2013年   107篇
  2012年   161篇
  2011年   129篇
  2010年   74篇
  2009年   87篇
  2008年   133篇
  2007年   147篇
  2006年   144篇
  2005年   109篇
  2004年   94篇
  2003年   72篇
  2002年   56篇
  2001年   37篇
  2000年   34篇
  1999年   14篇
  1998年   16篇
  1997年   11篇
  1996年   16篇
  1995年   16篇
  1994年   11篇
  1993年   16篇
  1992年   14篇
  1991年   14篇
  1990年   15篇
  1989年   13篇
  1988年   16篇
  1987年   8篇
  1986年   11篇
  1985年   21篇
  1984年   18篇
  1983年   13篇
  1982年   12篇
  1981年   12篇
  1980年   8篇
  1979年   15篇
  1978年   12篇
  1977年   10篇
  1976年   10篇
  1975年   7篇
  1974年   10篇
排序方式: 共有2059条查询结果,搜索用时 15 毫秒
961.
Phenomenology of neutralino dark matter in the minimal supersymmetric model is discussed for a scenario where the lightest Higgs boson mass is lighter than 114.4 GeV114.4 GeV. We show that the scenario is consistent not only with many collider experiments but also with the observed relic abundance of dark matter. The allowed region may be probed by experiments of Bs→μ+μBsμ+μ in near future. The scenario predicts a large scattering cross section between the dark matter and ordinary matter and thus it may be tested in present direct detection experiments of dark matter.  相似文献   
962.
We investigated the magnetic structure of an orthorhombic YMnO(3) thin film by resonant soft x-ray and hard x-ray diffraction. We observed a temperature-dependent incommensurate magnetic reflection below 45 K and a commensurate lattice-distortion reflection below 35 K. These results demonstrate that the ground state is composed of coexisting E-type and cycloidal states. Their different ordering temperatures clarify the origin of the large polarization to be caused by the E-type antiferromagnetic states in the orthorhombic YMnO(3) thin film.  相似文献   
963.
Let \(U'_q(\mathfrak {g})\) be a twisted affine quantum group of type \(A_{N}^{(2)}\) or \(D_{N}^{(2)}\) and let \(\mathfrak {g}_{0}\) be the finite-dimensional simple Lie algebra of type \(A_{N}\) or \(D_{N}\). For a Dynkin quiver of type \(\mathfrak {g}_{0}\), we define a full subcategory \({\mathcal C}_{Q}^{(2)}\) of the category of finite-dimensional integrable \(U'_q(\mathfrak {g})\)-modules, a twisted version of the category \({\mathcal C}^{(1)}_{Q}\) introduced by Hernandez and Leclerc. Applying the general scheme of affine Schur–Weyl duality, we construct an exact faithful KLR-type duality functor \({\mathcal F}_{Q}^{(2)}:\mathrm{Rep}(R) \rightarrow {\mathcal C}_{Q}^{(2)}\), where \(\mathrm{Rep}(R)\) is the category of finite-dimensional modules over the quiver Hecke algebra R of type \(\mathfrak {g}_{0}\) with nilpotent actions of the generators \(x_k\). We show that \({\mathcal F}_{Q}^{(2)}\) sends any simple object to a simple object and induces a ring isomorphism Open image in new window .  相似文献   
964.
Elemental distribution of calcium, phosphorus, oxygen, and carbon in a single collagen fibril obtained from tilapia fish scales was identified with an electron energy-loss spectroscopy and an energy-filtered transmission electron microscopy, for the first time. The carbon intensity profile of the single collagen fibril showed the specific D-periodic pattern at 67 nm of type I collagen fibrils. The calcium L2,3-edge and oxygen K-edge peak positions were detected at 347/350 eV and 137 eV, respectively, and these positions were identical to those of hydroxyapatite. Calcium, phosphorus, and oxygen were present in the hole zones as the amorphous phase, while carbon was present in the overlap zone. Our results indicated that the hole zones preferentially attract calcium and phosphate ions and thus serve as possible nucleation sites for mineralization.  相似文献   
965.
We have studied environment-resistive coatings (ERC) for the thin-film-based superconducting fault-current limiter (SFCL) Ag/Au–Ag/YBa2Cu3O7/CeO2/Al2O3. We evaluated nine candidate ERC materials by two accelerating-environment tests, and revealed that the shellac- and the fluorine-resin have a high environmental resistance. Especially, the shellac resin almost completely protected Jc of an element exposed to 60 °C saturated water vapor for 2 h (3.4–>3.2 MA/cm2). We also performed a practical operation test of SFCL using an element half covered by shellac, and found that the ERC does not diminish the current limiting properties similarly to the previous results of the Teflon-coated SFCL [1].  相似文献   
966.
Transparent and flexible carbon doped ZnO (C:ZnO) field emission device was successfully fabricated on an arylite substrate. Excellent adhesion of deposited C:ZnO on the flexible substrate was achieved with low sputtering power and Ar flow rate. In the fabricated device, nanostructured C:ZnO and as‐deposited thin films were used as field emitter and phosphor screen, respectively. The C:ZnO thin film showed a transparency of about 80% at 550 nm wavelength and average sheet resistance of 1.96 kΩ/□. The C:ZnO phosphor screen emitted red light during the field emission measurement, correlating the dominant cathodoluminescence peak at 646 nm. Thus, a promising transparent and flexible field emission display can be realized with C:ZnO based material.

Transparent and flexible C:ZnO film phosphor screen (anode) and nanocone emitters (cathode) for field emission device.  相似文献   

967.
We investigated the application of a high-resolution Orbitrap mass spectrometer equipped with an electrospray ionization (ESI) source and a matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) mass spectrometer to the metabolite profiling of a model small interfering RNA (siRNA) duplex TSR#34 and compared their functions and capabilities. TSR#34 duplex was incubated in human serum in vitro, and the duplex and its metabolites were then purified by ion exchange chromatography in order to remove the biological matrices. The fraction containing the siRNA duplex and its metabolites was collected and desalted and then subjected to high-performance liquid chromatography (HPLC) equipped with a reversed phase column. The siRNA and its metabolites were separated into single strands by elevated chromatographic temperature and analyzed using the ESI-Orbitrap or the MALDI-TOF mass spectrometer. Using this method, the 5' and/or 3' truncated metabolites of each strand were detected in the human serum samples. The ESI-Orbitrap mass spectrometer enabled differentiation between two possible RNA-based sequences, a monoisotopic molecular mass difference which was less than 2 Da, with an intrinsic mass resolving power. In-source decay (ISD) analysis using a MALDI-TOF mass spectrometer allowed the sequencing of the RNA metabolite with characteristic fragment ions, using 2,4-dihydroxyacetophenone (2,4-DHAP) as a matrix. The ESI-Orbitrap mass spectrometer provided the highest mass accuracy and the benefit of on-line coupling with HPLC for metabolite profiling. Meanwhile, the MALDI-TOF mass spectrometer, in combination with 2,4-DHAP, has the potential for the sequencing of RNA by ISD analysis. The combined use of these methods will be beneficial to characterize the metabolites of therapeutic siRNA compounds. Copyright ? 2012 John Wiley & Sons, Ltd.  相似文献   
968.
We consider a system associated to Klein–Gordon equations with homogeneous time-dependent electric fields. The upper and lower boundaries of a time-evolution propagator for this system were proven by Veseli? (J Oper Theory 25:319–330, 1991) for electric fields that are independent of time. We extend this result to time-dependent electric fields.  相似文献   
969.
We present the geometrical minimum units of fracture patterns in two-dimensional space. For this analysis, a new method is developed from the algebraic approach: the concept of lattice (a type of partially ordered set) is applied to the discrete Walsh functions that have been used to measure symmetropy (an object related to symmetry and entropy) of fracture patterns. We concluded that the minimum units of fracture patterns can be expressed as three kinds of lattice. Our model is applied to the temporal change of the spatial pattern of acoustic-emission events in a rock-fracture experiment. As a result, the symmetropy of lattice decreases with the evolution of fracture process. We find that the pre-nucleation process of fracture corresponds to the subcritical states, and the propagation process to the critical states. Moreover, using a particular mathematical structure called sheaf on a lattice, we suggest the algebraic interpretation of fracture process, and provide justification to regard fracturing as an irreversible process.  相似文献   
970.
Selective and quantitative cyclotrimerization of p‐tolylisocyanate proceeded by using sodium p‐toluenesulfinate as a catalyst and 1,3‐dimethylimidazolidinone as a solvent. Exploitation of this system to the cyclotrimerization of methylene diphenyl 4,4′‐diisocyanate (MDI) permitted formation of the corresponding networked polymer, which was selectively consisted of isocyanurate moiety and thus exhibited excellent thermal stability. Utilization of phenyl isocyanate (PhNCO) as a comonomer with varying feed ratio [MDI]0/[PhNCO]0 allowed successful control of flexibility of the networked polymers, while retaining its high thermal stability. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011  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