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   168366篇
  免费   2613篇
  国内免费   626篇
化学   93030篇
晶体学   2219篇
力学   6061篇
综合类   11篇
数学   20196篇
物理学   50088篇
  2020年   1163篇
  2018年   1170篇
  2016年   2412篇
  2015年   1858篇
  2014年   2368篇
  2013年   6858篇
  2012年   5216篇
  2011年   6317篇
  2010年   4072篇
  2009年   3661篇
  2008年   5772篇
  2007年   5736篇
  2006年   5691篇
  2005年   5476篇
  2004年   4783篇
  2003年   4277篇
  2002年   4086篇
  2001年   4424篇
  2000年   3432篇
  1999年   2701篇
  1998年   2334篇
  1997年   2339篇
  1996年   2359篇
  1995年   2269篇
  1994年   2083篇
  1993年   2093篇
  1992年   2372篇
  1991年   2172篇
  1990年   2110篇
  1989年   2114篇
  1988年   2080篇
  1987年   2086篇
  1986年   1974篇
  1985年   2746篇
  1984年   2834篇
  1983年   2318篇
  1982年   2693篇
  1981年   2478篇
  1980年   2582篇
  1979年   2564篇
  1978年   2675篇
  1977年   2621篇
  1976年   2568篇
  1975年   2482篇
  1974年   2299篇
  1973年   2501篇
  1972年   1504篇
  1971年   1202篇
  1968年   1261篇
  1967年   1337篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
This note discusses the need to use various data-compaction schemes in the implementation of sophisticated large-scale linear programming codes on modest personal computers. It demonstrates a method whereby the overhead of using these schemes is significantly reduced on Intel 80 x 86 processors.  相似文献   
113.
Measurements from depolarized lidars provide a promising method to retrieve both cloud and aerosol properties and a versatile complement to passive satellite-based sensors. For lidar observations of clouds and aerosols, multiple scattering plays an important role in the scattering process. Monte Carlo simulations are carried out to investigate the sensitivity of lidar backscattering depolarization to cloud and aerosol properties. Lidar parameters are chosen to be similar to those of the upcoming space-based CALIPSO lidar. Cases are considered that consist of a single cloud or aerosol layer, as well as a case in which cirrus clouds overlay different types of aerosols. It is demonstrated that besides thermodynamic cloud phase, the depolarized lidar signal may provide additional information on ice or aerosol particle shapes. However, our results show little sensitivity to ice or aerosol particle sizes. Additionally, for the case of multiple but overlapping layers involving both clouds and aerosols, the depolarized lidar contains information that can help identify the particle properties of each layer.  相似文献   
114.
The basic damage and failure models of multiaxially reinforced composites with a thermoplastic matrix are presented and verified. Within the framework of continuum damage mechanics, a phenomenological model is introduced, where the damage is defined as a change in the elasticity tensor. For damage identification, a specific ultrasonic device was developed. A combination of an immersion set-up and a contact coupling device formed a system for an efficient determination of stiffness-tensor components from convenient sets of velocity measurements. Linked to a tensile machine, it allowed us to measure the anisotropic damage of the new materials group caused by tensile loading. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 2, pp. 221–234, March–April, 2006.  相似文献   
115.
Hyperfine Interactions - Rotational J=1→J=0 transitions in muonic molecule, (3Heμd) J ++, in [(3Heμd)++,2e]–D and [(3Heμd)++,e]+–D collisions are considered. The...  相似文献   
116.
This report focuses on a theoretical study of the cobalt-cabon bond activation mechanism in Vitamin B12, its co enzyme complexes, and model compounds such as cobalamins (Cbl), cobaloximes and cobalt porphyrins. In particular, emphasis is placed on the nucleotide loop and its role in the base on and base off mechanism.  相似文献   
117.
Manning's method of calculating the ratio of mobility and diffusion coefficient in ionic conductors, sensitive to the type of particle jumps, is analytic. This paper presents a computer orientated treatment in terms of an averaging procedure recently proposed.  相似文献   
118.
We discuss some variant superfield representations which can arise by the replacement of some of the usual fields in a multiplet with p-form gauge fields.  相似文献   
119.
In this study a novel technique for 2D spray temperature measurement is presented. For this purpose the thermographic phosphor (TP) Mg4GeO5.5F:Mn was dispersed in n-dodecane and atomised using a conventional semi solid-cone nozzle. The thermographic phosphor was excited electronically by a frequency tripled Nd:YAG laser (355 nm). An ICCD-camera in combination with an image doubler detected the subsequently emitted phosphorescence at both peak emission wavelengths located at 633 nm and 659 nm, respectively. Utilising suitable calibration measurements, the local spray temperature was determined by evaluating the intensity ratio of both emission wavelengths. To the knowledge of the authors this is the first approach of spray temperature measurement exploiting the temperature dependent intensity ratio of thermographic phosphors. PACS 07.20.Dt; 32.50.+d  相似文献   
120.
We examine the optical near-field interaction between different types of scanning tips and single oriented fluorescent molecules. We demonstrate the influence of a tip on the excitation intensity as well as on the integrated fluorescence signal, the excited state lifetime, and the angular emission of single molecules. By using a standard model describing the radiation of an oscillating dipole close to a nanosphere or a flat interface, we interpret our observations and describe some central criteria for obtaining fluorescence enhancement or quenching. PACS 33.80.-b; 07.79.Fc; 78.90.+t  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