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   84834篇
  免费   594篇
  国内免费   377篇
化学   28281篇
晶体学   950篇
力学   6862篇
数学   33223篇
物理学   16489篇
  2022年   47篇
  2021年   81篇
  2020年   129篇
  2019年   176篇
  2018年   10556篇
  2017年   10410篇
  2016年   6420篇
  2015年   1124篇
  2014年   662篇
  2013年   1010篇
  2012年   4130篇
  2011年   10823篇
  2010年   5872篇
  2009年   6274篇
  2008年   6990篇
  2007年   9079篇
  2006年   557篇
  2005年   1548篇
  2004年   1741篇
  2003年   2121篇
  2002年   1143篇
  2001年   350篇
  2000年   392篇
  1999年   214篇
  1998年   264篇
  1997年   190篇
  1996年   256篇
  1995年   170篇
  1994年   115篇
  1993年   123篇
  1992年   92篇
  1991年   123篇
  1990年   94篇
  1989年   114篇
  1988年   113篇
  1987年   107篇
  1986年   106篇
  1985年   149篇
  1984年   144篇
  1983年   102篇
  1982年   102篇
  1981年   106篇
  1980年   108篇
  1979年   97篇
  1978年   72篇
  1977年   51篇
  1976年   60篇
  1975年   54篇
  1973年   54篇
  1914年   45篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
81.
For ϕ a δ-subharmonic function, sharp results are obtained that connectA(r, ϕ), B(r, ϕ) andT(r, ϕ), whereA(r, ϕ)=inf|z|=r ϕ(z),B(r, ϕ)=sup|z|=r ϕ(z), andT(r, ϕ) is the Nevanlinna characteristics.  相似文献   
82.
The purpose of this paper is to investigate the asymptotic properties of the least squares estimates (L 2-estimates) and the least absolute deviation estimates (L 1-estimates) of the parameters of a nonlinear regression model subject to a set of equality and inequality restrictions, which has a long-range dependent stationary process as its stochastic errors. Then we will compare the asymptotic relative efficiencies of the above estimators.  相似文献   
83.
84.
85.
86.
The vibrational dynamics of protein folding is analyzed in the framework of Tsallis statistics. We employ exact expressions for classical harmonic oscillators by considering the unnormalized constraints. As q→1, we show that these approximations agree with the result of Gaussian network model.  相似文献   
87.
The fusion evaporation reaction 122Sn(14N, 4n)132La was used to populate the high-spin states of 132La at the beam energy of 60 MeV. A new band consisting of mostly E2 transitions has been discovered. This band has the interesting links to the ground state 2- and the isomeric state 6-. A new transition of energy 351 keV connecting the low-spin states of the positive-parity band based on the πh 11/2 ⊗ νh 11/2 particle configuration, has been found. This has played a very important role in resolving the existing ambiguities and inconsistencies in the spin assignment of the band head. Received: 12 August 2002 / Accepted: 18 March 2003 / Published online: 7 May 2003  相似文献   
88.
The results of a numerical study are described in which the interactions of a primary shock wave with a secondary diaphragm in expansion tubes are taken into account. The developing wave pattern in the interacting process of the shock with a secondary diaphragm are visualized by many kinds of figures (e.g., the time-distance diagrams of the wave phenomena on the axis, the acoustic impedance contours, and the time histories of the pitot pressure on the axis), and the influences of the shape and rupture process of the diaphragm on the quality of the test gas are explored.  相似文献   
89.
The annual turnover of online auctions is already in tens of billions of dollars and this amount is predicted to grow substantially over the next few years. Hence, it is important to know how buyers and sellers can influence their chances of success. Therefore, data were collected from eBay auctions for three different categories of collectible items, namely those with a published guide price, those with a rough guide price and those having no easily obtainable guide price. The options available to buyers and sellers of items were then analysed. It was found that it was hard for the seller to influence an item's achieved price significantly, apart from items with no guide price where the starting price could have an effect. Most bidders bid close to the current value and so there were insufficient data to determine the consequences of timing on the placing of high bids. For low bids, delaying a bid was found to improve significantly the chances of winning for one of the data sets.  相似文献   
90.
This paper proposes kernel estimation of the occurrence rate function for recurrent event data with informative censoring. An informative censoring model is considered with assumptions made on the joint distribution of the recurrent event process and the censoring time without modeling the censoring distribution. Under the validity of the informative censoring model, we also show that an estimator based on the assumption of independent censoring becomes inappropriate and is generally asymptotically biased. To investigate the asymptotic properties of the proposed estimator, the explicit form of its asymptotic mean squared risk and the asymptotic normality are derived. Meanwhile, the empirical consistent smoothing estimator for the variance function of the estimator is suggested. The performance of the estimators are also studied through Monte Carlo simulations. An epidemiological example of intravenous drug user data is used to show the influence of informative censoring in the estimation of the occurrence rate functions for inpatient cares over time.  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