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   1826篇
  免费   74篇
  国内免费   5篇
化学   1346篇
晶体学   2篇
力学   10篇
数学   265篇
物理学   282篇
  2023年   10篇
  2022年   25篇
  2021年   23篇
  2020年   32篇
  2019年   37篇
  2018年   15篇
  2017年   20篇
  2016年   42篇
  2015年   64篇
  2014年   57篇
  2013年   79篇
  2012年   105篇
  2011年   110篇
  2010年   78篇
  2009年   65篇
  2008年   93篇
  2007年   112篇
  2006年   89篇
  2005年   107篇
  2004年   65篇
  2003年   65篇
  2002年   72篇
  2001年   47篇
  2000年   32篇
  1999年   26篇
  1998年   32篇
  1997年   25篇
  1996年   28篇
  1995年   18篇
  1994年   31篇
  1993年   14篇
  1992年   17篇
  1991年   18篇
  1990年   16篇
  1989年   13篇
  1988年   5篇
  1987年   21篇
  1986年   11篇
  1985年   13篇
  1984年   13篇
  1983年   8篇
  1982年   21篇
  1981年   16篇
  1980年   13篇
  1979年   11篇
  1977年   6篇
  1973年   6篇
  1970年   6篇
  1927年   4篇
  1926年   4篇
排序方式: 共有1905条查询结果,搜索用时 15 毫秒
31.
32.
33.
A single-mode fiber laser based on an intracavity core-cladding mode conversion is demonstrated. The fiber laser consists of an Er-doped active fiber and two fiber Bragg gratings. One Bragg grating is a core-cladding mode converter, and the other Bragg grating is a narrowband high reflector that selects the lasing wavelength. Coupling a single core mode and a single cladding mode by the grating mode converter, the laser operates as a hybrid single-mode laser. This approach for designing a laser cavity provides a much larger mode area than conventional large-mode-area step-index fibers.  相似文献   
34.
Optical Review - Terahertz (THz) spectra from the pure forms [i.e. the active pharmaceutical ingredients (APIs)] of four commonly used antimalarial drugs are reported. The well-defined spectral...  相似文献   
35.
36.
A water-soluble fluorescent probe, rhodamine B hydrazide (RBH), was prepared and its properties for recognition of diacetyl were studied. The method employs the reaction of diacetyl with RBH, a colorless and non-fluorescent rhodamine B spiro form derivative to give a pink-colored fluorescent substance. In weakly acidic media, RBH reacts more selectively with diacetyl than with other carbonyls, causing a large increase in fluorescence intensity and thereby providing an easy assay for the determination of diacetyl.  相似文献   
37.
Three cis-dioxovanadium(V) complexes with similar N-salicylidenehydrazide ligands modeling hydrogen bonding interactions of vanadate relevant for vanadium haloperoxidases are studied by (51)V solid-state NMR spectroscopy. Their parameters describing the quadrupolar and chemical shift anisotropy interactions (quadrupolar coupling constant C(Q), asymmetry of the quadrupolar tensor eta(Q), isotropic chemical shift delta(iso), chemical shift anisotropy delta(sigma), asymmetry of the chemical shift tensor eta(sigma) and the Euler angles alpha, beta and gamma) are determined both experimentally and theoretically using DFT methods. A comparative study of different methods to determine the NMR parameters by numerical simulation of the spectra is presented. Detailed theoretical investigations on the DFT level using various basis sets and structural models show that by useful choice of the methodology, the calculated parameters agree to the experimental ones in a very good manner.  相似文献   
38.
Kramer A  Müller P  Lott U  Kuster N  Bomholt F 《Optics letters》2006,31(16):2402-2404
We present a miniature fiber-optic electromagnetic field (EMF) sensor that is capable of simultaneously detecting the amplitude and phase of an EMF in the range of 0.1-6 GHz. We focus on magnetic field measurements, since the H-field is more significant in our target applications due its direct relation to the current. The sensor is based on an open optical platform to which various antennas can be attached and contains a radio-frequency amplifier for signal conditioning and a vertical-cavity surface-emitting laser as an electro-optic converter. The millimeter size and the full electrical isolation of the sensor allow EMF detection with minimal disturbance. We have characterized the sensor in the near field of a lambda/2 dipole, a rectangular waveguide, and a microstrip line, and we explain the experimental results with a simple theoretical model confirming the mapped near-field distribution of the investigated field source.  相似文献   
39.
The photophysical properties of a series of structurally related 4-aminophthalimides and the corresponding 5-aminophthalic hydrazides (luminols) are reported. Absorption, steady-state, and time-resolved fluorescence spectra of luminols exhibited substitution, solvent, and pH dependence. Singlet lifetimes have been determined by time-resolved laser flash spectroscopy. UV spectra in gas phase and DMSO solution were calculated by TD-DFT which revealed the existence of two low-energy excited singlet states with strong pH-sensitivity.  相似文献   
40.
A method is presented to solve two-phase problems involving soluble surfactants. The incompressible Navier-Stokes equations are solved along with equations for the bulk and interfacial surfactant concentrations. A non-linear equation of state is used to relate the surface tension to the interfacial surfactant concentration. The method is based on the use of a diffuse interface, which allows a simple implementation using standard finite difference or finite element techniques. Here, finite difference methods on a block-structured adaptive grid are used, and the resulting equations are solved using a non-linear multigrid method. Results are presented for a drop in shear flow in both 2D and 3D, and the effect of solubility is discussed.  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