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   29439篇
  免费   3661篇
  国内免费   3212篇
化学   21264篇
晶体学   364篇
力学   1451篇
综合类   235篇
数学   3569篇
物理学   9429篇
  2024年   79篇
  2023年   456篇
  2022年   802篇
  2021年   889篇
  2020年   937篇
  2019年   950篇
  2018年   813篇
  2017年   784篇
  2016年   1170篇
  2015年   1188篇
  2014年   1411篇
  2013年   1970篇
  2012年   2326篇
  2011年   2533篇
  2010年   1777篇
  2009年   1751篇
  2008年   1950篇
  2007年   1782篇
  2006年   1596篇
  2005年   1404篇
  2004年   1118篇
  2003年   905篇
  2002年   890篇
  2001年   740篇
  2000年   625篇
  1999年   588篇
  1998年   512篇
  1997年   447篇
  1996年   476篇
  1995年   386篇
  1994年   370篇
  1993年   344篇
  1992年   326篇
  1991年   277篇
  1990年   233篇
  1989年   191篇
  1988年   167篇
  1987年   129篇
  1986年   144篇
  1985年   155篇
  1984年   101篇
  1983年   64篇
  1982年   71篇
  1981年   53篇
  1980年   52篇
  1979年   58篇
  1978年   40篇
  1976年   37篇
  1974年   40篇
  1973年   45篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
94.
95.
This paper is a continuation of the research carried out in [1]–[2], where the robustness analysis for stochastic approximation algorithms is given for two cases: 1. The regression function and the Liapunov function are not zero at the sought-forx 0; 2. lim sup n a131n i=1 n i+1 is not zero, where { i } are the measurement errors and {a n} are the weighting coefficients in the algorithm. Allowing these deviations from zero to occur simultaneously but to remain small, this paper shows that the estimation error is still small even for a class of measurement errors more general than that considered in [2].This project is supported by the National Natural Science Foundation of China.  相似文献   
96.
97.
The electrical behavior of the cationic, polyacetylene-based, conjugated ionomer, poly[(2-cyclooctatetraenylethyl)trimethylammonium trifluoromethanesulfonate], sandwiched between gold electrodes is reported. The steady-state current of this mixed ionically/electronically conducting system is assigned to be unipolar diffusive hole transport for voltages below approximately 1.4 V, giving way to bipolar migratory transport above approximately 1.4 V. In the low-voltage regime, a non-Faradaically controlled doping model is proposed where p-doping at the anode is balanced by the charging of an ionic double layer at the cathode. In the high-voltage regime, n- and p-type regions extend from the electrodes as the voltage becomes sufficient to drive disproportionation and the electric field required by the redistribution of ions begins to substantially influence carrier transport. The assignment of a transport mechanism is primarily based on analyzing the decay of the steady-state system under short-circuit and open-circuit conditions. First, it is shown that the power describing the power-law decay of the short-circuit current is characteristic of the steady-state carrier profile. Second, it is argued that a component of the time-dependent, open-circuit voltage decaying more rapidly than the time scale for ion motion is indicative of a substantial migratory component to steady-state transport, as observed in the high-voltage regime. The hole and electron mobilities are estimated to be on the order of 10(-7)-10(-6) cm(2) V(-1) s(-1).  相似文献   
98.
Papers on braid theory and some of its generalization and applications, reviewed in Referativnyi Zhurnal Matematika during 1953–1977, as well as individual papers on an earlier period, are surveyed.Translated from Itogi Nauki i Tekhniki, Algebra, Topologiya, Geometriya, Vol. 17, pp. 159–227, 1979.  相似文献   
99.
C, N, O, F, Cl, and Br red and infrared laser emission was investigated using hollow cathode discharges in gas mixtures of helium and molecules containing the corresponding atoms. A total of 33 laser lines with wavelengths from 0.7 to 2.0m was observed. Three laser lines of atomic C, five laser lines of atomic N, two laser lines of atomic Cl and five laser lines of atomic Br were observed for the first time. Dissociation charge transfer and dissociative excitation transfer are suggested as being responsible for populating the upper laser levels.  相似文献   
100.
A new method for the simultaneous determination of anions (sulfate, nitrate, and chloride) and cations (sodium, ammonium, potassium, magnesium, and calcium) in acid rain waters was investigated using high-performance ion-exclusion/cation-exchange chromatography with conductimetric detection on a separation column packed with a polymethacrylate-based weakly acidic cation-exchange resin in the hydrogen-form and an eluent comprising 1.5 mM sulfosalicylic acid–6 mM 18-crown-6 at pH 2.6, operated at 1.5 ml/min. Effective separation and highly sensitive conductimetric detection for the anions and the cations was achieved in about 14 min. Since the ionic balance (equivalents of anions/equivalents of cations) of acid rain waters of different pH (4.40–4.67) ranged from 0.97 to 0.94, evaluation of the water quality of acid rain was possible. This method was successfully applied to the simultaneous determination of the anions and the cations in acid rain transported from mainland China and North Korea to central Japan monitored by a meteorological satellite data analyzer.  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