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   11187篇
  免费   1792篇
  国内免费   745篇
化学   6624篇
晶体学   57篇
力学   409篇
综合类   71篇
数学   1575篇
物理学   4988篇
  2024年   100篇
  2023年   252篇
  2022年   294篇
  2021年   336篇
  2020年   326篇
  2019年   322篇
  2018年   293篇
  2017年   393篇
  2016年   357篇
  2015年   380篇
  2014年   472篇
  2013年   807篇
  2012年   895篇
  2011年   739篇
  2010年   570篇
  2009年   649篇
  2008年   549篇
  2007年   740篇
  2006年   629篇
  2005年   533篇
  2004年   474篇
  2003年   474篇
  2002年   349篇
  2001年   322篇
  2000年   303篇
  1999年   220篇
  1998年   237篇
  1997年   195篇
  1996年   211篇
  1995年   151篇
  1994年   155篇
  1993年   109篇
  1992年   150篇
  1991年   85篇
  1990年   84篇
  1989年   84篇
  1988年   73篇
  1987年   62篇
  1986年   52篇
  1985年   55篇
  1984年   59篇
  1983年   32篇
  1982年   37篇
  1981年   30篇
  1980年   23篇
  1979年   28篇
  1978年   15篇
  1977年   4篇
  1976年   4篇
  1974年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The perturbation of the generator of a Borel right process by a signed measure is investigated, using probabilistic and analytic potential theoretical methods. We establish a Feynman-Kac formula associated with measures charging no polar set and belonging to an extended Kato class. A main tool of this approach is the validity of a Khas’minskii Lemma for Stieltjes exponentials of positive left continuous additive functionals.   相似文献   
82.
83.
Clear signs of excess dileptons above the known sources have been found at the SPS for a long time. However, a real clarification of these observations was only recently achieved by NA60, measuring dimuons with unprecedented precision in 158A GeV In-In collisions. The excess mass spectrum in the region is consistent with a dominant contribution from π+πρμ+μ annihilation. The associated ρ spectral function shows a strong broadening, but essentially no shift in mass. In the region , the excess is found to be prompt, not due to enhanced charm production. The inverse slope parameter associated with the transverse momentum spectra rises with mass up to the ρ, followed by a sudden decline above. While the initial rise, coupled to a hierarchy in hadron freeze-out, points to radial flow of a hadronic decay source, the decline above signals a transition to a low-flow source, presumably of partonic origin. The mass spectra show a steep rise towards low masses characteristic of Planck-like radiation. The polarization of the excess referred to the Collins Soper frame is found to be isotropic. All observations are consistent with a global interpretation of the excess as thermal radiation. We conclude with a short discussion of a possible link to direct photons.  相似文献   
84.
Herein the fundamentally new unit for production of silicate refractory melts with the use of high-concentrated heat fluxes is considered. Mathematical model describing temperature fields in skull layer in the process of the plasma flow interaction with the particles of refractory silicate material has been developed. Typical numerical results of temperature distribution in various sections of the skull layer are presented. Numerical and experimental data have been compared, and their fair agreement is obtained. The work was financially supported by RF President (Grant No. MK 1110.2008.8).  相似文献   
85.
Langmuir双探针诊断Ne辉光放电管电子密度   总被引:2,自引:0,他引:2  
应用Langmuir双探针诊断理论,对充有氖气的石英放电管中的辉光放电等离子体进行了诊断,通过实验测得伏安特性曲线,计算得出电子温度和电子密度,讨论了等离子体的宏观参量与电子温度和电子密度的关系.采用直径为0.1 mm的探针对等离子体进行诊断,不仅减小了对所测等离子体区域的扰动,而且减小了读取伏安特性曲线所带来的误差.  相似文献   
86.
本文提出了一种全新的基于整体柱材料的SERS检测方法。通过将探针分子和银溶胶混合后滴加在整体柱上, 我们可以得到浓度低至10-18 mol/L的罗丹明6G(R6G)及10-16 mol/L的对巯基苯胺(PATP)的SERS信号。利用原子力显微镜(AFM)和扫描电镜(SEM)对银溶胶及整体柱材料进行了表征。通过实验结果可以初步推测, 整体柱材料的表面形态和孔结构可以促进银溶胶产生“热点”。  相似文献   
87.
冯光辉  郝东山 《光学技术》2012,38(4):482-487
应用多光子非线性Compton散射模型和有限时域差分法,对Compton散射对磁化等离子体光子晶体缺陷模密温特性的影响进行了理论分析和数值模拟。结果表明,与Compton散射前的情况相比,Compton散射使低温低频处光子禁带中存在缺陷模的明显度降低,缺陷模频率增大,缺陷模和透射率峰值减小;使高温高频处缺陷模和透射率峰值、缺陷模频率显著增大,禁带宽减小,缺陷模位置向高频方向移动。随着电子密度的增大,散射减小了禁带增大效应和缺陷模减小效应,增强了缺陷模频率增大效应;随着电子密度的降低,散射增强了禁带变窄效应、缺陷模峰值增大效应和缺陷模频率减小效应。利用Compton散射,可实现对缺陷模密温特性的有效控制。  相似文献   
88.
The results of spectroscopic investigation of plane plasma discharge and sputtering processes in the triode system are presented. The forced electric discharge with currents of 1–4 A at an argon pressure of 1 mTorr was studied using the emission spectroscopy method. The spectra of plasma discharge were observed in the 200–1100 nm wavelength range. Two metal targets, gold and silver, were used for sputtering. It was found that a part of sputtered particles is ionized in plasma. The emission spectra of the ionized gold and silver species were observed as a function of target voltage while sputtering. It was shown that the number of ionized metal species depends on the energy of argon ions.  相似文献   
89.
给出了寂静放电产生的非平衡态氧等离子体特性的实验研究结果,并对空气中及氧气中合成臭氧的特性进行了研究,得到了在纯氧放电时臭氧质量浓度C= 18.9m g ·L- 1、臭氧产率Q=1800m g ·h- 1、臭氧单能产率η= 70g ·(kW ·h)- 1 的实验结果,同时对影响C、Q的因素也进行了研究。最后,就臭氧对造纸黑液的脱色、降粘及脱木素的作用进行了实验探讨  相似文献   
90.
A new method of online concentration capillary electrochromatography using a lauryl methacrylate-based monolithic column was developed for determination of three β(2)-agonists including salbutamol, procaterol, and formoterol. The separation parameters including acetonitrile concentration, running buffer pH, and concentration were evaluated. To improve the sensitivity, an online concentration method with combination of the chromatographic zone-sharpening effect and field-enhanced sample-stacking effect has been developed in which the concentration parameters including injection voltage, injection time, as well as sample matrix were systematically studied. Under the optimized conditions, baseline separation of three β(2)-agonists was achieved within 4 min. When compared to the conventional sample injection, this online concentration technique increased their corresponding sensitivities up to 45-, 36-, and 320-fold, respectively. Furthermore, good repeatability was obtained with relative standard deviations (RSDs) for migration times within 0.84% and those for peak areas less than 6.35% (n = 5) in the experiment. The proposed method was successfully applied to the determination of above-mentioned β(2)-agonists in urine sample. The recoveries of spiked urine samples were between 82.4% and 109.1% with RSDs less than 9.97%.  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