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   281652篇
  免费   2400篇
  国内免费   961篇
化学   127196篇
晶体学   4091篇
力学   15908篇
综合类   5篇
数学   53706篇
物理学   84107篇
  2021年   1704篇
  2020年   1882篇
  2019年   2097篇
  2018年   12898篇
  2017年   12598篇
  2016年   9776篇
  2015年   3186篇
  2014年   3994篇
  2013年   9559篇
  2012年   11044篇
  2011年   19046篇
  2010年   11600篇
  2009年   11852篇
  2008年   14421篇
  2007年   16599篇
  2006年   8043篇
  2005年   8220篇
  2004年   7976篇
  2003年   7588篇
  2002年   6510篇
  2001年   6691篇
  2000年   5239篇
  1999年   3952篇
  1998年   3230篇
  1997年   3189篇
  1996年   3014篇
  1995年   2753篇
  1994年   2570篇
  1993年   2462篇
  1992年   2767篇
  1991年   2751篇
  1990年   2658篇
  1989年   2467篇
  1988年   2521篇
  1987年   2529篇
  1986年   2354篇
  1985年   3021篇
  1984年   3282篇
  1983年   2681篇
  1982年   2860篇
  1981年   2834篇
  1980年   2699篇
  1979年   2791篇
  1978年   2863篇
  1977年   2853篇
  1976年   2914篇
  1975年   2700篇
  1974年   2659篇
  1973年   2812篇
  1972年   1785篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
831.
In this paper we obtain some metrics results about large partial quotients in the continued fraction expansion.  相似文献   
832.
The paper describes a methodology that has been implemented in a major British airline to find the optimal price to charge for airline tickets under one-way pricing. An analytical model has been developed to describe the buying behaviour of customers for flights over the selling period. Using this model and a standard analytical method for constrained optimization, we can find an expression for the optimal price structure for a flight. The expected number of bookings made on each day of the selling period and in each fare class given these prices can then be easily calculated. A simulation model is used to find the confidence ranges on the numbers of bookings and these ranges can be used to regulate the sale of tickets. A procedure to update the price structure based on the remaining capacity has also been developed.  相似文献   
833.
We have fabricated a field effect transistor (FET) based on an organic ferroelectric insulator and molecular conductor, and investigated the electrical properties and memory effects on the PEN-FET. We have observed a drastic change in the drain current at around the coercive electric fieldE c of the organic ferroelectric insulator in not only a FET (PEN-FET) based on a pentacene (PEN) film but also a FET (IPEN-FET) based on an iodine doped PEN film. The magnitude of the change of the drain current for the IPEN-FET is 200 times larger than that for the PEN-FET. It is expected from these results that the PEN-FET (especially the IPEN-FET) is an improvement in such devices, since it operates at a low gate electric field accompanied by the appearance of the spontaneous polarization in the organic ferroelectric insulator. In addition, we have found that the drain current for the PEN-FET does not return to the initial drain current ofE G =0 V/cm for more than one week, even if the gate electric field is changed to 0 V/cm from 500 V/cm(>E c ). From these results, it is suggested that the PEN-FET becomes a memory device.  相似文献   
834.
The time delay experiment proposed by I.I. Shapiro in 1964 and conducted in the seventies was the most precise experiment of general relativity until that time. Further experimentation has improved the accuracy level of both the time delay and the light deflection experiments. A simulation model is proposed that involves only a simple mass and time transformation factor involving velocity of light. The light deflection and the time delay experiments are numerically simulated using this model that does not use the general relativistic equations. The computed values presented in this paper compare well with recent levels of accuracy of their respective experimental results.  相似文献   
835.
The European Physical Journal C - We discuss possible searches for the new particles predicted by Little Higgs Models at the LHC. By using a simulation of the ATLAS detector, we demonstrate how the...  相似文献   
836.
The behavior of dimethylamino-substituted 7H-benzo[de]pyrazolo[5,1-a]isoquinoline-7-ones, synthesized for the first time, under conditions of the Vilsmeier-Haack reaction. It has been shown that, on heating with POCl3 and DMF, they are converted by electrophilic substitution at the position ortho to the dimethylamino group, followed by cyclization of the iminium adduct to a quinazolinium salt. When an acetyl group is present, the Arnold reaction, leading to the formation of a chloroaryl, accompanies the heterocyclization. The rates and proportion of the reaction products depend on the position of the dimethyl groups relative to the pyrazole ring.  相似文献   
837.
In this paper, we construct some continuous but non-differentiable functions defined by quinary decimal, that are Kiesswetter-like functions. We discuss their properties, then investigate the Hausdorff dimensions of graphs of these functions and give a detailed proof.  相似文献   
838.
A band-dominant function on the Euclidean sphere embedded in R q+1 is the restriction to this sphere of an entire function of q+1 complex variables having a finite exponential type in each of its variables. We develop a method to represent such a function using finitely many bits, using the values of the function at scattered sites on the sphere. The number of bits required in our representation is asymptotically the same as the metric entropy of the class of such functions with respect to any of the L p norms on the sphere.  相似文献   
839.
840.
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