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   265623篇
  免费   3172篇
  国内免费   1009篇
化学   146505篇
晶体学   3877篇
力学   10313篇
综合类   2篇
数学   30143篇
物理学   78964篇
  2021年   1880篇
  2020年   2195篇
  2019年   2451篇
  2018年   2756篇
  2017年   2647篇
  2016年   4472篇
  2015年   3155篇
  2014年   4571篇
  2013年   12256篇
  2012年   9494篇
  2011年   11555篇
  2010年   7494篇
  2009年   7245篇
  2008年   10261篇
  2007年   10335篇
  2006年   9569篇
  2005年   8945篇
  2004年   7975篇
  2003年   6950篇
  2002年   6917篇
  2001年   7579篇
  2000年   5692篇
  1999年   4538篇
  1998年   3868篇
  1997年   3879篇
  1996年   3609篇
  1995年   3385篇
  1994年   3244篇
  1993年   3280篇
  1992年   3531篇
  1991年   3504篇
  1990年   3347篇
  1989年   3275篇
  1988年   3340篇
  1987年   3180篇
  1986年   3072篇
  1985年   4229篇
  1984年   4371篇
  1983年   3565篇
  1982年   3917篇
  1981年   3802篇
  1980年   3678篇
  1979年   3689篇
  1978年   3939篇
  1977年   3762篇
  1976年   3928篇
  1975年   3503篇
  1974年   3654篇
  1973年   3921篇
  1972年   2401篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
111.
112.
A combined-modality treatment program consisting of botulinum toxin injection (Botox) and voice therapy was used to treat 17 subjects diagnosed with adductor spasmodic dysphonia (ADD SD). Ten subjects with ADD SD served as the control and were given Botox only. Voice therapy after Botox injection was directed toward reducing the hyperfunctional vocal behaviors, primarily glottal overpressure at voice onset and anterior-posterior squeezing. The results indicated that subjects who underwent combined-modality treatment maintained significantly higher mean airflow rates for significantly longer periods. Moreover, there was a carryover effect in these patients when they received Botox only. Adductor spasmodic dysphonia is treated most effectively when intrinsic laryngeal muscle spasms are reduced or eliminated by Botox injection and extrinsic hyperfunctional vocal behaviors are treated with voice therapy  相似文献   
113.
114.
Interpolation formulas for higher-order derivatives which guarantee the invariance of the results under changes of coordinates are obtained for functions of a vector argument.Translated from Matematicheskie Metody i Fiziko-Mekhanicheskie Polya, No. 25, pp. 22–25, 1987.  相似文献   
115.
Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 313–314, March–April, 1995. Original article submitted November 7, 1994.  相似文献   
116.
A novel method for measuring AMP-deaminase activity in human erythrocytes is presented, based on the determination of the reaction product, IMP, using high performance liquid chromatography. IMP formation was found to be proportional both to the incubation time and the amount of haemolysate over a wide range. The minimal detectable AMP-deaminase activity was more than 1000 times lower than the mean activity found in healthy controls (1083 nmol/h/mg Hb). No marked difference of activity was found in the patients with the following inherited purine disorders: familial juvenile gouty nephropathy and deficiencies of adenosine deaminase, hypoxanthine-guanine phosphoribosyltransferase or adenine phosphoribosyltransferase. The activity in the erythrocytes of patients with chronic renal failure was also similar to controls. The existence of subjects with low erythrocyte AMP-deaminase activity in the population has been confirmed.  相似文献   
117.
Prism-coupling work in polymer aligned liquid crystal layers is presented with special emphasis being placed on the ferroelectric chiral smectic C phase, of interest to electro-optic device fabrication. Experimental results as a function of temperature, wavelength and DC applied voltage are presented, together with a study of sp mixing which may have potential device applications as well as being an elegant technique with which to establish the optical dielectric tensor configuration in thin, aligned liquid crystal layers.  相似文献   
118.
The hydrocarbon discovery prediction problem is important to firms having to make decisions about the deployment of scarce exploration resources. Traditional methods for estimating the discovery rate rely on the completion of time consuming simulation experiments. A rapid approximation that does not require the completion of simulation exists and has been shown to have some promise as a prediction tool. This paper investigates the accuracy of the approximation method under a wide variety of distributional and drilling efficiency assumptions. The results indicate that the approximation produces predictions close to those of simulation under most of the tested conditions. This suggests that resource exploration firms could conveniently use the method for a wide variety of planning purposes without incurring the same costs in time and personnel required for simulation.  相似文献   
119.
To correlate the appearance of poststenotic jets on gradient echo images with features of localized Doppler spectra of the jets, we studied an in vitro model of steady flow-through stenoses of 86, 96, and 99% area reduction. As fluids, water and a 40% glycerol solution in water were used. MRI was performed with a 1.5 T whole body imager and gradient echo images were obtained in planes parallel to the direction of flow. Doppler spectra were acquired separately from the MR measurements at 1 cm intervals for a distance of 10 cm downstream from the stenosis. Poststenotic signal void was observed for water and for the 40% glycerol solution only if the mean velocity within the stenosis exceeded a limit of 50–60 cm/sec. On the MR images, the jets could be divided into two segments: A proximal jet segment of uniform width equal to the diameter of the stenosis, followed by a distal jet segment which was characterized by broadening and then dissipating signal void. Except for the 99% stenosis, a high signal intensity core was present within the proximal jet segment. In the proximal jet segment, the Doppler measurements showed a low temporal fluctuation of the maximal flow velocity and only little flow opposite to the main flow direction. In the distal jet segment, the velocity fluctuation and the intensity of reverse flow increased sharply. The high signal intensity core of the jet was associated with a poststenotic zone of constant maximal flow velocity. The results demonstrate a close relationship between characteristic features of poststenotic jets in MRI and pulsed Doppler sonography.  相似文献   
120.
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