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   245010篇
  免费   2788篇
  国内免费   874篇
化学   132113篇
晶体学   3696篇
力学   9933篇
综合类   3篇
数学   27498篇
物理学   75429篇
  2020年   1775篇
  2019年   2046篇
  2018年   2479篇
  2017年   2414篇
  2016年   3843篇
  2015年   2617篇
  2014年   3922篇
  2013年   11238篇
  2012年   8135篇
  2011年   10052篇
  2010年   6608篇
  2009年   6503篇
  2008年   9040篇
  2007年   9209篇
  2006年   8432篇
  2005年   7886篇
  2004年   7030篇
  2003年   6254篇
  2002年   6174篇
  2001年   7222篇
  2000年   5379篇
  1999年   4238篇
  1998年   3570篇
  1997年   3609篇
  1996年   3317篇
  1995年   3161篇
  1994年   2991篇
  1993年   3028篇
  1992年   3318篇
  1991年   3359篇
  1990年   3172篇
  1989年   3138篇
  1988年   3190篇
  1987年   3067篇
  1986年   2956篇
  1985年   4032篇
  1984年   4202篇
  1983年   3430篇
  1982年   3799篇
  1981年   3695篇
  1980年   3557篇
  1979年   3587篇
  1978年   3839篇
  1977年   3664篇
  1976年   3859篇
  1975年   3423篇
  1974年   3550篇
  1973年   3865篇
  1972年   2358篇
  1971年   1832篇
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
991.
We construct division algebras with involution containing a Baer ordering with noninvariant order ring. This gives a negative answer to a question of Holland, whether the order ring is always invariant under inner automorphisms. Furthermore, we give examples of any index. Previously, the only known examples of division algebras containing Baer orderings were of index 2 n or of indexp forp a prime of the form 4m + 3. Supported in part by the National Science Foundation.  相似文献   
992.
Summary We report on neutron emission in palladium and titanium electrolitically charged with deuterium. The detection of neutrons is observed after thermal treatment of the electrode. In the hypothesis that neutrons came from cold fusion processes, we estimate a fusion rate as high as 1.3·10−21 fusions/deuteron pair/second.  相似文献   
993.
We consider equations of motion for some massiveN=1 supermultiplets of fields, using superfields and their superderivatives. The formalism is based on the superprojectors.  相似文献   
994.
A comparison of results of indirect and direct electrochemical fluorosulfation of nonsaturated fluorocarbons shows that the main or the only product in potentiostatic conditions is vicinal fluorosulfates. Owing to a high rate of the electrochemical step, which exceeds the rate of desorption of intermediate radicals from the electrode surface into solution, it is possible to improve the process selectivity by increasing the contribution of the ionic reaction route.  相似文献   
995.
The interaction of Ag and In with a thin film of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) was studied by near-edge X-ray absorption fine structure (NEXAFS). Upon Ag deposition on a PTCDA film of 20 nm thickness the relative intensities and lineshapes, as well as the angular dependence of the spectra remains unchanged, illustrating the formation of a chemically unreactive Ag/PTCDA interface. On the other hand, the adsorption of 0.3 nm In strongly decreases the intensity of the π* resonances in C and O K-edge NEXAFS spectra. This is attributed to a strong charge transfer between In and PTCDA, leading to a redistribution of the charge in the molecule. However, the absence of a strong shift or new features and negligible dependence of peak intensities corresponding to π* resonances on the In thickness indicate that the interaction between In and PTCDA is not accompanied by a covalent bond formation.  相似文献   
996.
997.
4(3H)-Quinazolinones have been synthesized in high to excellent yields through the one-pot condensation of anthranilic acid, trimethyl orthoformate and primary amines in the presence of 5 mol % of Bi(TFA)3 immobilized on [nbp]FeCl4 as a room temperature ionic liquid.  相似文献   
998.
To examine the association between frequency resolution and speech recognition, auditory filter parameters and stop-consonant recognition were determined for 9 normal-hearing and 24 hearing-impaired subjects. In an earlier investigation, the relationship between stop-consonant recognition and the articulation index (AI) had been established on normal-hearing listeners. Based on AI predictions, speech-presentation levels for each subject in this experiment were selected to obtain a wide range of recognition scores. This strategy provides a method of interpreting speech-recognition performance among listeners who vary in magnitude and configuration of hearing loss by assuming that conditions which yield equal audible spectra will result in equivalent performance. It was reasoned that an association between frequency resolution and consonant recognition may be more appropriately estimated if hearing-impaired listeners' performance was measured under conditions that assured equivalent audibility of the speech stimuli. Derived auditory filter parameters indicated that filter widths and dynamic ranges were strongly associated with threshold. Stop-consonant recognition scores for most hearing-impaired listeners were not significantly poorer than predicted by the AI model. Furthermore, differences between observed recognition scores and those predicted by the AI were not associated with auditory filter characteristics, suggesting that frequency resolution and speech recognition may appear to be associated primarily because both are degraded by threshold elevation.  相似文献   
999.
This paper proposes an extension of the expansions of analytic functions in the An polynomials defined by Adomian [1] to consider piecewise-differentiable functions.  相似文献   
1000.
A novel method to eliminate T3 from gross sera/plasma based on prior treatment with 8-anilino-1-naphthalene sulphonic acid has been standardized. This method is rapid with a minimum loss of protein and uses only small quantities of charcoal. The treated sera have been tested for acceptance in the RIA system for routine assays.  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