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   59511篇
  免费   790篇
  国内免费   308篇
化学   27742篇
晶体学   1044篇
力学   3208篇
综合类   8篇
数学   4683篇
物理学   23924篇
  2022年   563篇
  2021年   504篇
  2020年   468篇
  2019年   449篇
  2018年   598篇
  2017年   514篇
  2016年   911篇
  2015年   650篇
  2014年   1018篇
  2013年   2548篇
  2012年   2376篇
  2011年   3064篇
  2010年   2160篇
  2009年   2190篇
  2008年   2765篇
  2007年   2616篇
  2006年   2479篇
  2005年   2189篇
  2004年   1996篇
  2003年   1755篇
  2002年   1656篇
  2001年   3007篇
  2000年   2153篇
  1999年   1555篇
  1998年   1083篇
  1997年   1059篇
  1996年   890篇
  1995年   784篇
  1994年   711篇
  1993年   625篇
  1992年   953篇
  1991年   949篇
  1990年   851篇
  1989年   750篇
  1988年   734篇
  1987年   797篇
  1986年   659篇
  1985年   885篇
  1984年   835篇
  1983年   571篇
  1982年   566篇
  1981年   540篇
  1980年   501篇
  1979年   625篇
  1978年   656篇
  1977年   666篇
  1976年   578篇
  1975年   484篇
  1974年   521篇
  1973年   454篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Y. Pugai 《JETP Letters》2004,79(10):457-463
The algebra of fused vertex operators for the ABF model is defined and studied in the free fields approach. Vacuum expectation values of local operators in the scaling theory are reproduced from the matrix elements of the fused vertex operators.  相似文献   
52.
The frequency or dispersion relation for the least‐squares mixed formulation of the shallow‐water equations is analysed. We consider the use of different approximation spaces corresponding to co‐located and staggered meshes, respectively. The study includes the effect of Coriolis, and the dispersion properties are compared analytically and graphically with those of the mixed Galerkin formulation. Numerical solutions of a test problem to simulate slow Rossby modes illustrate the theoretical results. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
53.
54.
The NOAA National Status and Trends (NS&T) Program determines the current status of, and changes over time in the environmental health of U.S estuarine and coastal waters. Concentrations of organic and inorganic contaminants are determined in bivalves, bottom-dwelling fish and sediments. The quality of the analytical data generated by the NS&T Program is over-seen by the performance-based Quality Assurance Project, which is designed to document sampling protocols, analytical procedures, and laboratory performance, and to reduce intralaboratory and interlaboratory variation. All NS&T cooperating laboratories are required to participate in yearly intercomparison exercises. The analysis of reference materials, such as the National Research Council of Canada's Certified Reference Materials (CRMs) and National Institute of Standards and Technology's (NIST) Standard Reference Materials (SRMs), and of control materials, is required. Because of the need for marine matrix reference materials and standards, NOAA contributed to the production of eight NIST SRMs and seven internal standard solutions. Analytical data from all control materials and all matrix reference materials are reported to the Program office.  相似文献   
55.
Decomposition methods: A new proof of convergence   总被引:6,自引:0,他引:6  
We propose a new convergence proof of Adomian's technique based on properties of convergent series. Then we deduce some results about the speed of convergence of this method allowing us to solve nonlinear functional equations.  相似文献   
56.
Blends of the natural polymer cellulose with a synthetic polymer, polyamide 66, are studied in order to determine if the expected strong interaction between them, due to hydrogen bonds, could improve their mechanical properties such as strength and elongation at break. In a previous work {Part I, J. Polym. Sci. Polym. Phys., 32 , 1437 (1994)}, the preparation technique and the characterization of cellulose-polyamide 66 (PA66) blends were described in detail. Several samples in the composition range between 0 to 70 wt % of PA66 were carefully dried and examined using dynamic mechanical and tensile tests. Based on previous work a new percolation model has been developed. It takes both linear and nonlinear mechanical behaviors into account and allows for the effect of adhesion between material domains. From comparison between experimental and predicted data, it is concluded that a partial miscibility between the amorphous phases of cellulose and PA66 exists and is responsible for a strong adhesion at their interface. Solid-state 13C nuclear magnetic resonance has also been used to study these samples and supports the existence of strong interactions between both homopolymers. © 1995 John Wiley & Sons, Inc.  相似文献   
57.
Results from a systematic experiment on isolated perfused rat heart and isolated myocytes of adult rat showed that the mechanism of calcium influx during myocardial ischemia-reperfusion is due to the development of intracellular sodium overload during ischemic period; on reperfusion, the high intracellular Na+ content activated the reverse direction of Na(+)-Ca2+ exchange over myocardial sarcolemma (SL), thus a large quantity of extracellular Ca2+ fluxed over the SL to the intracellular space, forming a condition of intracellular Ca2+ overload, which leads to irreversible damage of the myocardium.  相似文献   
58.
A high performance liquid chromatographic (HPLC) system is described for determination of the unsaturated disaccharide (delta Di-HA) derived from hyaluronic acid (HA) in human urine by digestion with hyaluronidase SD. The effects of eluents on the separation of delta Di-HA and delta Di-0S, which is derived from the reaction of chondroitin with the enzyme, have been studied. The established chromatographic conditions were as follows--column: a stainless steel tube (4 mm i.d. x 250 mm) packed with TSKgel NH2-60; eluent: a mixture of acetonitrile and 0.1 M Tris-HCl buffer containing 0.1 M boric acid and 10 mM sodium sulphate, pH 7.0 (64:36, v/v). The strong fluorescence of unsaturated disaccharide after the reaction with 2-cyanoacetamide in alkaline medium was used for post-column detection. The calibration curve for delta Di-HA was linear in the range 5 pmol-5nmol with a practical detection limit of 2 pmol. The assay coefficients of variation (n = 5) at 200 pmol for delta Di-HA and delta Di-0S were 1.7 and 1.5%, respectively. This HPLC system has been applied to the determination of HA in human urine.  相似文献   
59.
I. Last  Y. Shima 《Chemical physics》1986,110(2-3):287-293
The quasiclassical trajectory calculation of the I + HI collision is performed in order to study the exchange and endothermic reaction channels. The rate constant of the exchange reaction I′ + HI → HI′ + I is found to be equal to 7.7 × 1011 cm3/mol s at room temperature of 300 K. The study of the endothermic reaction I + HI → H + I2 shows that it takes place only in configurations with large bend angles. Due to the non-collinear character of this reaction its threshold (2 eV) exceeds significantly the threshold of the minimal energy (collinear) reaction path (1.55 eV).  相似文献   
60.
Cold-drawn Nylon-11 films, which were prepared by stretching the melt-quenched films to a draw ratio of 2.8: 1 at room temperature, were found to exhibit an electric displacement versus electric field hysteresis loop. The results confirmed that the Nylon-11 film exhibited ferroelectric behavior at or below room temperature. The coercive fields were 65, 98, 125, 160, and 215 MV/m at 20, 0, ?20, ?40, and ?60°C and the remanent polarization at ?20°C (where there was considerably less dc conduction) was 56 mC/m2. Switching of the polarization was almost completed within 20 ms.  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