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   122213篇
  免费   7810篇
  国内免费   8149篇
化学   58737篇
晶体学   1452篇
力学   9036篇
综合类   592篇
数学   36873篇
物理学   31482篇
  2024年   138篇
  2023年   829篇
  2022年   1562篇
  2021年   1699篇
  2020年   1848篇
  2019年   1912篇
  2018年   11720篇
  2017年   11619篇
  2016年   8156篇
  2015年   3177篇
  2014年   3131篇
  2013年   3890篇
  2012年   7687篇
  2011年   14443篇
  2010年   8726篇
  2009年   8984篇
  2008年   9880篇
  2007年   11634篇
  2006年   3036篇
  2005年   3619篇
  2004年   3358篇
  2003年   3427篇
  2002年   2618篇
  2001年   1592篇
  2000年   1467篇
  1999年   1070篇
  1998年   860篇
  1997年   684篇
  1996年   719篇
  1995年   560篇
  1994年   510篇
  1993年   440篇
  1992年   313篇
  1991年   327篇
  1990年   285篇
  1989年   204篇
  1988年   194篇
  1987年   158篇
  1986年   165篇
  1985年   147篇
  1984年   85篇
  1983年   82篇
  1982年   71篇
  1981年   59篇
  1980年   60篇
  1979年   64篇
  1978年   43篇
  1914年   45篇
  1909年   41篇
  1908年   40篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
Vasily L. Morgunov 《Pramana》2007,69(6):1097-1100
A new calorimeter energy calibration method was developed for the proposed ILC detectors. The method uses the center-of-mass energy of the accelerator as the reference. It has been shown that using the energy conservation law it is possible to make ECAL and HCAL cross calibration to reach a good energy resolution for the simple calorimeter energy sum.   相似文献   
104.
105.
In a conventional diffractometer having single monochromator, only one position, parallel position, is used for the diffraction experiment (i.e. detection) because the resolution property of the other one, anti-parallel position, is very poor. However, a bent perfect crystal (BPC) monochromator at monochromatic focusing condition can provide a quite flat and equal resolution property at both parallel and anti-parallel positions and thus one can have a chance to use both sides for the diffraction experiment. From the data of the FWHM and the Δd/d measured on three diffraction geometries (symmetric, asymmetric compression and asymmetric expansion), we can conclude that the simultaneous diffraction measurement in both parallel and anti-parallel positions can be achieved.  相似文献   
106.
Forecasting electricity prices in presentday competitive electricity markets is a must for both producers and consumers because both need price estimates to develop their respective market bidding strategies. This paper proposes a transfer function model to predict electricity prices based on both past electricity prices and demands, and discuss the rationale to build it. The importance of electricity demand information is assessed. Appropriate metrics to appraise prediction quality are identified and used. Realistic and extensive simulations based on data from the PJM Interconnection for year 2003 are conducted. The proposed model is compared with naïve and other techniques.  相似文献   
107.
Imaging mass spectrometry requires the acquisition and interpretation of hundreds to thousands of individual spectra in order to map the mineral phases within heterogeneous geomatrices. A fuzzy logic inference engine (FLIE) was developed to automate data interpretation. To evaluate the strengths and limitations of FLIE, the chemical images obtained using FLIE were compared with those developed using two chemometric methods: principle component analysis (PCA) and cluster analysis (K-Means). Two heterogeneous geomatrices, a low-grade chalcopyrite ore and basalt, were imaged using a laser-desorption Fourier transform mass spectrometer. Similar mineral distribution patterns in the chalcopyrite ore sample were obtained by the three data analysis methods with most of the differences occurring at the interfaces between mineral phases. PCA missed one minor mineral phase in the chalcopyrite ore sample and did not clearly differentiate among the mineral classes of the basalt. K-Means cluster analysis differentiated among the various mineral phases in both samples, but improperly grouped some spectra in the chalcopyrite sample that only contained unanticipated high mass peaks. Unlike the chemometric methods, FLIE was able to classify spectra as unknowns for those spectra that fell below the confidence level threshold. A nearest neighbor approach, included in FLIE, was used to classify the unknowns to form a visually complete image; however, the unknowns identified by FLIE can be informative because they highlight potential problems or overlooked results. In conclusion, this study validated the fuzzy logic-based approach used in our laboratory and reveald some limitations in the three techniques that were evaluated.  相似文献   
108.
In this paper we generalize to coisotropic actions of compact Lie groups a theorem of Guillemin on deformations of Hamiltonian structures on compact symplectic manifolds. We show how one can reconstruct from the moment polytope the symplectic form on the manifold. Received: 21 March 2006  相似文献   
109.
We investigate the variety of residuated lattices with a commutative and idempotent monoid reduct.  相似文献   
110.
For given a graph H, a graphic sequence π = (d 1, d 2,..., d n) is said to be potentially H-graphic if there is a realization of π containing H as a subgraph. In this paper, we characterize the potentially (K 5e)-positive graphic sequences and give two simple necessary and sufficient conditions for a positive graphic sequence π to be potentially K 5-graphic, where K r is a complete graph on r vertices and K r-e is a graph obtained from K r by deleting one edge. Moreover, we also give a simple necessary and sufficient condition for a positive graphic sequence π to be potentially K 6-graphic. Project supported by National Natural Science Foundation of China (No. 10401010).  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