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   12176篇
  免费   1433篇
  国内免费   834篇
化学   2408篇
晶体学   59篇
力学   1359篇
综合类   181篇
数学   6842篇
物理学   3594篇
  2024年   24篇
  2023年   121篇
  2022年   211篇
  2021年   231篇
  2020年   339篇
  2019年   330篇
  2018年   332篇
  2017年   368篇
  2016年   426篇
  2015年   310篇
  2014年   478篇
  2013年   1076篇
  2012年   539篇
  2011年   657篇
  2010年   553篇
  2009年   665篇
  2008年   742篇
  2007年   758篇
  2006年   699篇
  2005年   637篇
  2004年   616篇
  2003年   523篇
  2002年   471篇
  2001年   412篇
  2000年   424篇
  1999年   351篇
  1998年   286篇
  1997年   300篇
  1996年   201篇
  1995年   214篇
  1994年   162篇
  1993年   142篇
  1992年   123篇
  1991年   107篇
  1990年   80篇
  1989年   49篇
  1988年   49篇
  1987年   50篇
  1986年   49篇
  1985年   54篇
  1984年   45篇
  1983年   27篇
  1982年   41篇
  1981年   23篇
  1980年   25篇
  1979年   22篇
  1978年   20篇
  1977年   23篇
  1974年   10篇
  1973年   17篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
含余割核奇异积分修改的反演问题   总被引:1,自引:0,他引:1  
针对含余害核奇异积分反演问题在指κ<0时一般无解的情况,本文提出并求解两种修改的反演问题,而后一种修改反演问题的提法与此前类似问题颇不相同,由于运用了推广的留数定理和Bertrand型换序公式使本问题及类似问题解法得以简化。  相似文献   
122.
Management of moisture penetration and hydrolytic degradation of polylactide (PLA) is extremely important during the manufacturing, shipping, storage, and end-use of PLA products. Moisture transport, crystallization, and degradation, in PLA have been measured through a variety of experimental techniques including size-exclusion chromatography, differential scanning calorimetry, and X-ray diffraction. Quartz crystal microbalance and dynamic vapor sorption experiments have also been used to measure moisture sorption isotherms in PLA films with varying crystallinity. A surprising result is that, within the accuracy of the experiments, crystalline and amorphous PLA films exhibit identical sorption isotherms.  相似文献   
123.
On the numerical solution of a class of Stackelberg problems   总被引:1,自引:0,他引:1  
This study tries to develop two new approaches to the numerical solution of Stackelberg problems. In both of them the tools of nonsmooth analysis are extensively exploited; in particular we utilize some results concerning the differentiability of marginal functions and some stability results concerning the solutions of convex programs. The approaches are illustrated by simple examples and an optimum design problem with an elliptic variational inequality.Prepared while the author was visiting the Department of Mathematics, University of Bayreuth as a guest of the FSP Anwendungsbezogene Optimierung und Steuerung.  相似文献   
124.
We present some asymptotic results for the family of pausing time densities having the asymptotic (t) property(t) [t ln1+(t/T)]–1. In particular, we show that for this class of pausing time densities the mean-squared displacement r 2(t) is asymptotically proportional to ln(t/T), and the asymptotic distribution of the displacement has a negative exponential form.  相似文献   
125.
LetX,X 1,X 2,... be i.i.d. random vectors in d. The limit laws that can arise by suitable affine normalizations of the partial sums,S n=X 1+...+X n, are calledoperator-stable laws. These laws are a natural extension to d of the stable laws on. Thegeneralized domain of attraction of [GDOA()] is comprised of all random vectorsX whose partial sums can be affinely normalized to converge to . If the linear part of the affine transformation is restricted to take the formn –B for some exponent operatorB naturally associated to thenX is in thegeneralized domain of normal attraction of [GDONA()]. This paper extends the theory of operator-stable laws and their domains of attraction and normal attraction.  相似文献   
126.
We study a one-dimensional model for fracture, identifying fractured areas with intervals on which a stress field exceeds a threshold value. When is a diffusion process, the cumulative numberN(l) of fractured areas whose length is greater thanl obeys a power lawCl p asl0 with probability one. The exponentp and the constantC are determined. The exponentp agrees with the Hausdorff dimension of the end points of fractured areas, i.e., –1(). Even if is self-similar with parameterH>0, i.e.,(cx)– is equivalent toc H {(x)–} for anyc>0, the exponentp does not depend solely onH;p=H, where(0, 1/H) is another parameter characterizing. Non-diffusion processes are given whereN(l) does not follow a power law.  相似文献   
127.
The solid diffusion coefficient of lithium-ion in LiCoO2 cathode material has been investigated by the capacity intermittent titration technique (CITT) at different voltages and at different charge/discharge cycles. By SEM, XRD and FTIR techniques, the structure of LiCoO2 was studied before and after charge-discharge cycles, and the relationship between solid diffusion coefficient and crystal structure was further discussed. CITT results show that the value of Li+ solid diffusion coefficient of LiCoO2 is about 10-12 cm2·s-1. During the whole charge-discharge cycles, the Li+ solid diffusion coefficient decreased within the voltage of 4.0~4.3 V, which is attributed to the change of the structure of LiCoO2.  相似文献   
128.
129.
The inhibitory effect of a series of neutral lipophilic solutes (methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-amylalcohol, n-hexanol, diethylether, nitrobenzene, and pyridine) on the diffusional water permeability (Pd, tot) of bovine erythrocyte membrane at 25 degrees C was studied in comparison to that of p-chloromercuri benzoate (pCMB). Permeability data were obtained by measuring the transmembrane diffusional water exchange time tau(exch) using an 1H-T2 NMR technique. Maximal inhibition by approximately 50% of Pd, tot was produced by 2 mM pCMB which completely blocked the membrane water channels in 20 min, hence suggesting the channel-to-lipid diffusional water permeability ratio of about 1:1. Furthermore, the maximal inhibitory effect of pCMB in combination with the lipophilic solutes was lower than that of pCMB alone. As pCMB does not interfere with the lipid bilayer, and provided that it blocks the water channels in solute presence as well, this confirms that the solutes induce an increase in the lipid-mediated background water permeability contribution (Pd, lipid) by the formation of aqueous leaks in the membrane hydrophobic barrier. However, faster but less efficient in permeability inhibition than pCMB (either alone or combined with solutes) were the lipophilic solutes alone. Taken together, the results indicate that the lipophilic solutes suppress the membrane total permeability Pd, tot by two opposing effects: a reduction of its channel-mediated part (Pd, channel) to the extent exceeding that of a simultaneous Pd, lipid increase. The inhibitory potency of the solutes tested appears to be correlated with their solubility in the membrane medium.  相似文献   
130.
季斌  邰子厚   《无机化学学报》1996,12(3):260-266
本文合成并研究了1-酰基二茂铁在CH2Cl2中的伏安行为,测定了它们在CH2Cl2中不同支持电解质浓度时的扩散系数,并分明用Z.Galus和K.Aoki方法计算了两种状态下的电子迁移速率常数。讨论了取代基的诱导效应和共轭效应及其链长对1-酰基二茂铁的动力学性质的影响以及支持电解质及其浓度等因素对伏安曲线的影响。  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