全文获取类型
收费全文 | 8286篇 |
免费 | 1300篇 |
国内免费 | 734篇 |
专业分类
化学 | 2265篇 |
晶体学 | 114篇 |
力学 | 950篇 |
综合类 | 217篇 |
数学 | 2507篇 |
物理学 | 4267篇 |
出版年
2024年 | 15篇 |
2023年 | 91篇 |
2022年 | 218篇 |
2021年 | 233篇 |
2020年 | 223篇 |
2019年 | 186篇 |
2018年 | 199篇 |
2017年 | 327篇 |
2016年 | 357篇 |
2015年 | 300篇 |
2014年 | 508篇 |
2013年 | 661篇 |
2012年 | 443篇 |
2011年 | 520篇 |
2010年 | 450篇 |
2009年 | 560篇 |
2008年 | 597篇 |
2007年 | 554篇 |
2006年 | 527篇 |
2005年 | 456篇 |
2004年 | 357篇 |
2003年 | 356篇 |
2002年 | 272篇 |
2001年 | 265篇 |
2000年 | 237篇 |
1999年 | 206篇 |
1998年 | 185篇 |
1997年 | 164篇 |
1996年 | 137篇 |
1995年 | 147篇 |
1994年 | 81篇 |
1993年 | 75篇 |
1992年 | 61篇 |
1991年 | 44篇 |
1990年 | 49篇 |
1989年 | 42篇 |
1988年 | 36篇 |
1987年 | 21篇 |
1986年 | 19篇 |
1985年 | 31篇 |
1984年 | 29篇 |
1983年 | 8篇 |
1982年 | 22篇 |
1981年 | 13篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1977年 | 5篇 |
1974年 | 2篇 |
1973年 | 6篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
151.
Schock (Ref. 1) considered a general a posteriori parameter choice strategy for the Tikhonov regularization of the ill-posed operator equationTx=y which provides nearly the optimal rate of convergence if the minimal-norm least-squares solution
belongs to the range of the operator (T
*
T)
v
, o<v1. Recently, Nair (Ref. 2) improved the result of Schock and also provided the optimal rate ifv=1. In this note, we further improve the result and show in particular that the optimal rate can be achieved for 1/2v1.The final version of this work was written while M. T. Nair was a Visiting Fellow at the Centre for Mathematics and Its Applications, Australian National University, Canberra, Australia. The work of S. George was supported by a Senior Research Fellowship from CSIR, India. 相似文献
152.
Kyle Siegrist 《Journal of Theoretical Probability》1994,7(4):725-737
Three fundamental characterizations of the standard exponential distribution on [0, ) are the remaining life, memoryless and constant failure properties. Analogs of these properties are studied for distributions on a class of semigroups in which the semigroup operation replaces addition, a compatible partial order replaces the ordinary order, and a left-invariant measure replaces Lebesgue measure. Partial characterizations of exponential distributions on such semigroups are obtained and the semigroup formulation provides new characterizations of certain aging properties studied in reliability-increasing failure rate, new better than used, and increasing failure rate average. 相似文献
153.
Masakiyo Miyazawa 《Queueing Systems》1994,15(1-4):1-58
We survey the rate conservation law, RCL for short, arising in queues and related stochastic models. RCL was recognized as one of the fundamental principles to get relationships between time and embedded averages such as the extended Little's formulaH=G, but we show that it has other applications. For example, RCL is one of the important techniques for deriving equilibrium equations for stochastic processes. It is shown that the various techniques, including Mecke's formula for a stationary random measure, can be formulated as RCL. For this purpose, we start with a new definition of the rate with respect to a random measure, and generalize RCL by using it. We further introduce the notion of quasi-expectation, which is a certain extension of the ordinary expectation, and derive RCL applicable to the sample average results. It means that the sample average formulas such asH=G can be obtained as the stationary RCL in the quasi-expectation framework. We also survey several extensions of RCL and discuss examples. Throughout the paper, we would like to emphasize how results can be easily obtained by using a simple principle, RCL. 相似文献
154.
Muhammad El-Taha 《Queueing Systems》1996,22(1-2):47-63
An input-output processZ = {Z(t), t 0} is said to be-rate stable ifZ(t) = o((t)) for some non-negative function(t). We prove that the processZ is -rate stable under weak conditions that include the assumption that input satisfies a linear burstiness condition and Z is asymptotically average stable. In many cases of interest, the conditions for-rate-stability can be verified from input data. For example, using input information, we establish-rate stability of the workload for multiserver queues, an ATM multiplexer, and-rate stability of queue-length processes for infinite server queues. 相似文献
155.
《Electroanalysis》2003,15(13):1109-1114
The electrochemical characterization of a hydrogen peroxide sensor based on a ferrocene‐containing polymer electrochemically deposited onto a platinum electrode is described. The redox polymer consists of a siloxane‐based homopolymer, with pendant electronically communicated ferrocenyl moieties. The electrodes were used as the transducer for glucose and lactate‐sensing enzyme sensors. Amperometric biosensors were prepared by immobilization of glucose oxidase (Gox) or lactate oxidase (Lox) onto these modified electrodes. The steady‐state amperometric response of the sensors is investigated as a function of the applied potential and substrate concentration. Interferences, sensitivity and stability of the sensors were also studied. 相似文献
156.
We investigate a piecewise linear (area-preserving) mapT describing two coupled baker transformations on two squares, with coupling parameter 0c1. The resulting dynamical system is Kolmogorov for anyc0. For rational values ofc, we construct a generating partition on whichT induces a Markov chain. This Markov structure is used to discuss the decay of correlation functions: exponential decay is found for a class of functions related to the partition. Explicit results are given forc=2–n. The macroscopic analog of our model is a leaking process between two (badly) stirred containers: according to the Markov analysis, the corresponding progress variable decays exponentially, but the rate coefficients characterizing this decay are not those determined from the one-way flux across the cell boundary. The validity of the macroscopic rate law is discussed. 相似文献
157.
本文运用PM3算法计算得到氯酚(CPs)的分子结构参数,并结合光解速率进行PLS分析,建立了速率与量子化参数之间的关系模型,模型的Q2cum分别为0.8776和0.9545(>0.5),具有良好的预测能力。研究结果表明,参数Ehomo、Elumo Ehomo、Elumo、N、Mw、Elumo-Ehomo、(Elumo-Ehomo)2是决定CPs光解速率的主要因素;CPs的光解速率随Ehomo、Elumo Ehomo、Elumo、Elumo-Ehomo、(Elumo-Ehomo)2的增大而增大,随N、Mw的增大而减小。 相似文献
158.
S. Padmaja V. Ramakrishnan J. Rajaram J. C. Kuriacose 《Journal of Chemical Sciences》1988,100(4):297-303
The borate radical is produced by the flash photolysis of an aqueous alkaline solution of NaBO2 and K2S2O8. The absorption spectrum of the transient borate radical shows two maxima. The self decay of this radical is second order.
Rate constants for the reactions of this radical with some organic substrates have been determined. 相似文献
159.
根据Fe(Ⅲ)、Mo(Ⅵ)对H2O2氧化邻氨基酚的催化反应速率不同,结合流动注射停留技术,建立了同时测定Fe(Ⅲ)、Mo(Ⅵ)的速差动力学分光光度法.测定铁和钼的线性范围分别为0.1~2.5μg/mL和0.5~15μg/mL.除W(Ⅵ)的允许量较小外,其它离子不干扰测定.用本法测定了合成样液中铁和钼含量,结果满意. 相似文献
160.
WANG Qin-Sun ZHU Chang-Shou YAN Bing-WenNational Laboratory of Elemento-Organic Chemistry Nankai University Tianjin China 《中国化学》1995,(2)
A computer-assisted advanced simplex method is presented for the simultaneous optimization of multifactor ( stationary phase loading, carrier gas flow rate and column temperature ) for separation of ten compounds in gas chromatography. A three factors factorial design was used. The method was based on a special polynomial established from fifteen preliminary runs, using resolution as the selection criterion, with connection to a general simplex method. Excellent agreement is found between the predicted data and the experimental results, and most of experiments required in the general simplex method can be omitted. 相似文献