全文获取类型
收费全文 | 70547篇 |
免费 | 5484篇 |
国内免费 | 5428篇 |
专业分类
化学 | 47588篇 |
晶体学 | 652篇 |
力学 | 5497篇 |
综合类 | 757篇 |
数学 | 11310篇 |
物理学 | 15655篇 |
出版年
2024年 | 88篇 |
2023年 | 701篇 |
2022年 | 1239篇 |
2021年 | 1944篇 |
2020年 | 2092篇 |
2019年 | 1979篇 |
2018年 | 1751篇 |
2017年 | 2289篇 |
2016年 | 2786篇 |
2015年 | 2297篇 |
2014年 | 3042篇 |
2013年 | 4992篇 |
2012年 | 4010篇 |
2011年 | 4031篇 |
2010年 | 3404篇 |
2009年 | 4289篇 |
2008年 | 4083篇 |
2007年 | 4405篇 |
2006年 | 3803篇 |
2005年 | 3424篇 |
2004年 | 3441篇 |
2003年 | 2731篇 |
2002年 | 2675篇 |
2001年 | 1840篇 |
2000年 | 1656篇 |
1999年 | 1428篇 |
1998年 | 1293篇 |
1997年 | 1171篇 |
1996年 | 1149篇 |
1995年 | 1076篇 |
1994年 | 983篇 |
1993年 | 762篇 |
1992年 | 730篇 |
1991年 | 559篇 |
1990年 | 477篇 |
1989年 | 363篇 |
1988年 | 369篇 |
1987年 | 260篇 |
1986年 | 212篇 |
1985年 | 221篇 |
1984年 | 188篇 |
1983年 | 86篇 |
1982年 | 171篇 |
1981年 | 154篇 |
1980年 | 160篇 |
1979年 | 191篇 |
1978年 | 123篇 |
1977年 | 85篇 |
1976年 | 94篇 |
1973年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
以金属钇和异丙醇为原料,以HgCl2/I2为复合催化剂,通过对金属钇的机械加工以增加其比表面,并将异丙醇脱水使其含水量降低至0.05%,体系在82℃回流5h,经过滤、减压蒸馏,得到了白色海绵状异丙醇钇,其产率高达83%,合成时间比文献报道的缩短了19h,产率提高了8%。文章确定了催化剂的最佳用量为20gY加入60mg HgCl2/I2,研究了合成产率与HgCl2/I2催化剂和HgCl2催化剂的依赖关系及异丙醇中含水量对合成产率的影响,并对HgCl2/I2的催化作用机理进行了初步探讨。 相似文献
82.
A method using third order moments for estimating the regression coefficients as well as the latent state scores of the reduced-rank regression model when the latent variable(s) are non-normally distributed is presented in this paper. It is shown that the factor analysis type indeterminacy of the regression coefficient matrices is eliminated. A real life example of the proposed method is presented. Differences of this solution with the reduced-rank regression eigen solution are discussed. 相似文献
83.
We consider a resource management problem in which the management objective is to minimize fluctuations in resource stocks. Stabilizing management policies constitute the designing of memoryless state feedback control strategies for a discrete time resource model which contains unknown but bounded fluctuations. We also show that the problem of maximizing sustainable yield in an uncertain fishery can be considered as the problem of stabilizing of the stock level.The paper corresponds to an invited talk at the 14th Symposium on Operations Research, Ulm, September 6–8, 1989.The support by Yrjö Jahnsson Foundation is gratefully acknowledged.This work was supported by NSF and AFOSR under grant ECS 8602524. 相似文献
84.
I. L. Davies K. E. Markides M. L. Lee M. W. Raynor K. D. Bartle 《Journal of separation science》1989,12(4):193-207
Although coupled liquid chromatographygas chromatography (LC-GC) was first demonstrated ten years ago, only in the last few years has there been a sudden surge of interest in the technique. Approximately 70% of the total number of LC-GC applications have been published in the last two years (1987–88) alone. This review categorizes LC-GC publications into four main application areas: fossil fuels, foods, environmental samples, biologiical/pharmaceutical samples, and miscellaneous samples. Multidimensional separations carried out using other coupled-column chromatographic techniques (such as supercritical fluid chromatography (SFC) with GC, and on-line trace enrichment-GC) have also been included in this review. 相似文献
85.
Boban Marinković 《Mathematical Methods of Operations Research》2006,63(3):513-524
We present local sensitivity analysis for discrete optimal control problems with varying endpoints in the case when the customary regularity of boundary conditions can be violated. We study the behavior of the optimal solutions subject to parametric perturbations of the problem. 相似文献
86.
We consider the problem of maximizing a linear fractional function on the Pareto efficient frontier of two other linear fractional functions. We present a finite pivoting-type algorithm that solves the maximization problem while computing simultaneously the efficient frontier. Application to multistage efficiency analysis is discussed. An example demonstrating the computational procedure is included. 相似文献
87.
空间遥感相机长条反射镜较圆反射镜的整体刚度相差很大,整个组件在随火箭发射过程中因力学环境引起的自身位置改变导致面形的微小畸变从而对成像质量造成严重影响。因此,反射镜组件的设计就成为整个相机系统研制的重点与难点之一。对其进行科学、严谨的力学环境仿真是设计中的有效辅助手段。对某相机的长条反射镜组件动力学响应进行了较为深入的研究,借助MSC-patran,用有限元法进行了求解。获得了组件的动力学特性。 相似文献
88.
89.
Blaise Faugeras Jé rô me Pousin Franck Fontvieille. 《Mathematics of Computation》2006,75(253):209-222
A numerical scheme based on an operator splitting method and a dense output event location algorithm is proposed to integrate a diffusion-dissolution/precipitation chemical initial-boundary value problem with jumping nonlinearities. The numerical analysis of the scheme is carried out and it is proved to be of order 2 in time. This global order estimate is illustrated numerically on a test case.
90.
A novel technique to overcome the long-term drift and hysteresis of a scanning Fabry–Perot filter was developed and applied to wavelength and power monitoring of DWDM system. By using the comb peaks generated by a temperature-stabilized, near threshold-biased Fabry–Perot diode laser as wavelength reference for the scanning Fabry–Perot filter, wavelength and power measurement accuracy of better than ±10 pm and 0.2 dB, respectively, were achieved. 相似文献