全文获取类型
收费全文 | 16746篇 |
免费 | 2671篇 |
国内免费 | 2618篇 |
专业分类
化学 | 13136篇 |
晶体学 | 226篇 |
力学 | 914篇 |
综合类 | 215篇 |
数学 | 2130篇 |
物理学 | 5414篇 |
出版年
2024年 | 24篇 |
2023年 | 207篇 |
2022年 | 377篇 |
2021年 | 418篇 |
2020年 | 538篇 |
2019年 | 578篇 |
2018年 | 487篇 |
2017年 | 424篇 |
2016年 | 811篇 |
2015年 | 758篇 |
2014年 | 991篇 |
2013年 | 1248篇 |
2012年 | 1373篇 |
2011年 | 1425篇 |
2010年 | 1143篇 |
2009年 | 1097篇 |
2008年 | 1272篇 |
2007年 | 1092篇 |
2006年 | 1027篇 |
2005年 | 838篇 |
2004年 | 771篇 |
2003年 | 658篇 |
2002年 | 900篇 |
2001年 | 747篇 |
2000年 | 552篇 |
1999年 | 385篇 |
1998年 | 260篇 |
1997年 | 197篇 |
1996年 | 187篇 |
1995年 | 166篇 |
1994年 | 158篇 |
1993年 | 133篇 |
1992年 | 110篇 |
1991年 | 107篇 |
1990年 | 82篇 |
1989年 | 62篇 |
1988年 | 53篇 |
1987年 | 50篇 |
1986年 | 43篇 |
1985年 | 52篇 |
1984年 | 40篇 |
1983年 | 19篇 |
1982年 | 21篇 |
1981年 | 25篇 |
1980年 | 16篇 |
1979年 | 29篇 |
1978年 | 18篇 |
1977年 | 12篇 |
1974年 | 15篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
41.
A new chemiluminescence method for the determination of carbamazepine (CBZ) has been developed. The method is based on the chemiluminescence produced in the reaction of tris(2,2'-bipyridine)ruthenium(III) and CBZ in an acidic medium. The chemiluminescence intensity was enhanced by organic solvents in the reaction system. Under the optimum experimental conditions, the calibration curve was linear over the range 4.0 x 10(-3)-8.6 x 10(-7) mol/L for CBZ. The detection limit (S/N = 3) was 2.5 x 10(-7) mol/L and the relative standard deviation of six replicate measurements was 2.6% for 4.0 x 10(-4) mol/L of CBZ. The possible reaction mechanism were also discussed. The chemiluminescence method was successfully applied to assay the CBZ contents in pharmaceutical tablets. 相似文献
42.
43.
A facile, rapid and regioselective method for the 1-O-deacylation of peracylated glycopyranoses is described which occurs under mild conditions by absorption onto alumina using microwave irradiation. 相似文献
44.
Discrete global descent method for discrete global optimization and nonlinear integer programming 总被引:2,自引:0,他引:2
A novel method, entitled the discrete global descent method, is developed in this paper to solve discrete global optimization
problems and nonlinear integer programming problems. This method moves from one discrete minimizer of the objective function
f to another better one at each iteration with the help of an auxiliary function, entitled the discrete global descent function.
The discrete global descent function guarantees that its discrete minimizers coincide with the better discrete minimizers
of f under some standard assumptions. This property also ensures that a better discrete minimizer of f can be found by some classical local search methods. Numerical experiments on several test problems with up to 100 integer
variables and up to 1.38 × 10104 feasible points have demonstrated the applicability and efficiency of the proposed method. 相似文献
45.
本文得到Ω满足Dini型条件时,Marcinkiewicz积分交换子μΩ,b(f)的端点估计:|{x∈R~n:μΩ,b(f)(x)>λ}|≤c‖b‖BMO∫_(R~n)(|f(x)|)/λ(1+log+(|f(x)|)/λ)dx. 相似文献
46.
This paper discusses a class of second-order derivative nonlinear Schrödinger equations which are used to describe the upper-hybrid oscillation propagation. By establishing a variational problem, applying the potential well argument and the concavity method, we prove that there exists a sharp condition for global existence and blow-up of the solutions to the nonlinear Schrödinger equation. In addition, we also answer the question: how small are the initial data, the global solutions exist? 相似文献
47.
48.
生物小分子与铜锌超氧化物歧化酶相互作用的波谱学研究及其应用 总被引:1,自引:0,他引:1
本工作以ESR和NMR为主要手段,并结合其它生化方法,考察了氨基酸、核酸碱基、糖等生命基本物质,和抗坏血酸等生命必需物质与钢锌超氧化物歧化酶的相互作用,实验观测到氨基酸、核酸碱基和抗坏血酸在水溶液中可以与酶中的Cu2+作用而使其脱离活性部位,以小分子络合物形式游离在溶液中,同时使酶失活,脱离活性部位的Cu2+的比例和酶的失活程度取决于小分子配体的加入量及其与Cu2+的络合能力。此外,首次尝试使用ESR方法,并借助氨基酸与酶的作用,考察了铜锌超氧化物歧化酶在盐酸胍变性和热变性过程中的构象变化行为,结果表明这一方法是直观而有效的。 相似文献
49.
本文通过对有效需求一物价指数统计模型的研究 ,估计出了有效需求方程 ,并且通过对模型的估计结果分析得出如下结论 :物价指数对有效需求的影响是显著的 :通货紧缩、物价指数持续走低是有效需求不足的主要原因 ,治理通货紧缩应该是解决我国有效需求不足的主要任务。 相似文献
50.
The purpose of the present study was to describe the effects ofacute laryngitis on some aerodynamic, acoustic, and perceptual measures. Eleven subjects with diagnosed acute laryngitis due to upper respiratory infection were recorded during a laryngitic episode and 1 week to 10 days after amelioration of the laryngitic condition. Fundamental frequency values, collapsed across the five vowels, were significantly reduced in the laryngitic compared with the normal speaking condition. The decrease in fundamental frequency associated with acute laryngitis suggests an increase in the mass of the vocal folds. In addition, aerodynamic values differed significantly for the laryngitic condition compared with the normal speaking condition, suggesting the presence of laryngeal hypofunction. Perceptual data indicated that speakers in the laryngitic condition were judged to have a hoarse voice when compared with the normal speaking condition. 相似文献