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   5608篇
  免费   140篇
  国内免费   27篇
化学   4090篇
晶体学   66篇
力学   75篇
数学   240篇
物理学   1304篇
  2023年   23篇
  2021年   47篇
  2020年   66篇
  2019年   79篇
  2018年   54篇
  2017年   25篇
  2016年   84篇
  2015年   96篇
  2014年   101篇
  2013年   271篇
  2012年   255篇
  2011年   317篇
  2010年   176篇
  2009年   202篇
  2008年   314篇
  2007年   294篇
  2006年   320篇
  2005年   269篇
  2004年   246篇
  2003年   235篇
  2002年   274篇
  2001年   160篇
  2000年   127篇
  1999年   100篇
  1998年   67篇
  1997年   76篇
  1996年   64篇
  1995年   55篇
  1994年   66篇
  1993年   75篇
  1992年   86篇
  1991年   70篇
  1990年   57篇
  1989年   64篇
  1988年   48篇
  1987年   64篇
  1986年   57篇
  1985年   86篇
  1984年   72篇
  1983年   52篇
  1982年   50篇
  1981年   59篇
  1980年   53篇
  1979年   69篇
  1978年   55篇
  1977年   41篇
  1976年   47篇
  1975年   39篇
  1974年   34篇
  1973年   33篇
排序方式: 共有5775条查询结果,搜索用时 917 毫秒
11.
利用在束γ谱学实验技术, 通过173Yb(19F,4nγ)反应 布居了188Au的高自旋态, 并对其准粒子带结构进行了研究. 基于实验测量结果, 对原有的双奇核188Au能级纲图做了较大的修改. 通过系统性比较, 对15+以上的能级结构进行了讨论.  相似文献   
12.
This paper presents a method of measuring a light field of a light source with high directional resolution using a mirrored ball and a pinhole camera. The light field describes a spatial and directional distribution of radiances from the light source. The directional distribution is expanded by a reflection on the mirrored ball, and the radiances are measured by a charge-coupled device (CCD) camera with a pinhole lens. The light source is laterally moved by a robot arm to measure the directionally expanded light field, and each pixel on a CCD can obtain the radiances from the light source through the pinhole lens with high directional resolution. The light field is estimated from the pixel value and the position of each pixel using a ray tracing technique. The light field of a krypton lamp was experimentally measured by the proposed method, and the accuracy of the measurement was evaluated against the irradiances measured by a spectro-radiometer at sample points.  相似文献   
13.
A new method for the construction of the AB-ring core of Taxol was developed utilizing a new skeletal transformation protocol as a pivotal step. The acid-catalyzed rearrangement of the cyclopentenone-allene photoadduct gave a bridged seven-membered ketone, which was easily transformed, using the intramolecular Suzuki reaction and the oxidative cleavage of the vicinal diol, to the bicyclic diketone.  相似文献   
14.
In this paper we prove the following kind of unique continuation property. That is, the zero on each geodesic of the solution in a real analytic hypersurface for second order anisotropic hyperbolic systems with real analytic coefficients can be continued along this curve.

  相似文献   

15.
16.
17.
Hydro-membrane gas chromatography (HMGC) is achieved by the annular condensation of water in a capillary column at less than 70 degrees C. The annular membrane of water is formed as a result of the wettability of the stationary phase, which is induced at a water contact angle ranging from 75 degrees to 79 degrees, as derived from a solubility parameter (delta) range of 15.7 +/- 0.3 MPa(1/2) of the coated resin. The range of the liquid to gas volume ratio (beta) required to support the annular membrane should be kept between 0.00005 and 0.0003. In the case of a 0.25-mm i.d. column, the ratio can be set by the combination of a 0.1 to 0.2 microl min(-1) water supply rate and helium gas flow rate. Separation by HMGC develops not only a gas-solid partition but also a focusing effect on the water membrane. One feature of HMGC is that it gives a non-adsorption chromatogram based on the blocking effect of pre-adsorbed water; furthermore, despite the presence of a relatively large quantity of water, the electron impact ionization efficiency is kept the same as in the usual GC/MS condition. The detection limit with the injection of 1 microl of aquatic solution was estimated to be less than 0.1 ppb of low-molecular-weight fatty acids with s/n = 5 on a mass chromatogram at m/z 45. The HMGC/EI-MS system can be applied to the trace analysis of C1 to C3 volatile acids, volatile inorganic acids, and halogenated organic acids in water.  相似文献   
18.
In this paper, we define λ-joint, a-joint, (λ,λ)-joint, (λ,a)-joint and (a,a)-joint t-universality of Lerch zeta functions and consider the relations among those. Next we show the existence of (λ,λ)-joint t-universality. Finally, we also show the existence of λ-joint, a-joint, (λ,a)-joint and (a,a)-joint t-universality by using inversion formulas.  相似文献   
19.
20.
A next-generation slow radioactive nuclear ion beam facility (SLOWRI) which provides slow, high-purity and small emittance ion beams of all elements is being build as one of the principal facilities at the RIKEN RI-beam factory (RIBF). High energy radioactive ion beams from the projectile fragment separator BigRIPS are thermalized in a large gas catcher cell. The thermalized ions in the gas cell are guided and extracted to a vacuum environment by a combination of dc electric fields and inhomogeneous rf fields (rf carpet ion guide). From there the slow ion beam is delivered via a mass separator and a switchyard to various devices: such as an ion trap, a collinear fast beam apparatus, and a multi-reflection time of flight mass spectrometer. In the R&D works at the present RIKEN facility, an overall efficiency of 5% for a 100A MeV 8Li ion beam from the present projectile fragment separator RIPS was achieved and the dependence of the efficiency on the ion beam intensity was investigated. Recently our first spectroscopy experiment at the prototype SLOWI was performed on Be isotopes. Energetic ions of 10Be and 7Be from the RIPS were trapped and laser cooled in a linear rf trap and the specific mass shifts of these isotopes were measured for the first time.  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