全文获取类型
收费全文 | 2751篇 |
免费 | 266篇 |
国内免费 | 88篇 |
专业分类
化学 | 799篇 |
力学 | 172篇 |
综合类 | 100篇 |
数学 | 1194篇 |
物理学 | 840篇 |
出版年
2024年 | 11篇 |
2023年 | 30篇 |
2022年 | 130篇 |
2021年 | 110篇 |
2020年 | 76篇 |
2019年 | 72篇 |
2018年 | 89篇 |
2017年 | 141篇 |
2016年 | 142篇 |
2015年 | 88篇 |
2014年 | 211篇 |
2013年 | 155篇 |
2012年 | 167篇 |
2011年 | 184篇 |
2010年 | 122篇 |
2009年 | 127篇 |
2008年 | 143篇 |
2007年 | 134篇 |
2006年 | 134篇 |
2005年 | 153篇 |
2004年 | 110篇 |
2003年 | 67篇 |
2002年 | 65篇 |
2001年 | 55篇 |
2000年 | 48篇 |
1999年 | 41篇 |
1998年 | 46篇 |
1997年 | 42篇 |
1996年 | 31篇 |
1995年 | 29篇 |
1994年 | 20篇 |
1993年 | 23篇 |
1992年 | 9篇 |
1991年 | 19篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有3105条查询结果,搜索用时 0 毫秒
991.
影响城市地价最优因素组合的选择及权重确定 总被引:3,自引:0,他引:3
笔者在城市土地定级估价综合模型[1] 的基础上 ,应用最优回归自变量集的选择方法[2 ] ,得到了影响城市地价最优因素组合的选择方法及权重的确定方法 ,并将其实际应用于山西省古交市的地产评估 ,结果表明 ,该方法比现行方法节省经费且使评估结果更符合实际。 相似文献
992.
I. David Bough Jr. Reinhardt J. Heuer Robert Thayer Sataloff James R. Hills Jacqueline R. Cater 《Journal of voice》1996,10(2):166-174
Recent advances in the diagnosis and treatment of voice disorders necessitate the need for accurate and reliable objective voice measurements. There are many instruments commonly used to analyze voice data. Many, if not most, of these instruments have not been adequately tested for reliability or consistency. This study evaluates the intrasubject variability of the objective voice measurements from two commonly used voice analysis instruments. The study also presents data correlating subjective mood states, room temperatures, sleep times of the subject, time since last meal, and hydration levels to the various acoustic measures. Several weak but significant correlations were obtained and are discussed. Guidelines for the appropriate use of these instruments are described. 相似文献
993.
Michel Grabisch Jacques Duchêne Frédéric Lino Patrice Perny 《Fuzzy Optimization and Decision Making》2002,1(3):287-312
We study the modelling of the subjective sensation of discomfort for subjects seated during a long time, in terms of local discomforts. The methodology uses fuzzy measures and integrals in a multicriteria decision making process, which enables the modelling of complex interaction between variables. Results of the experiment are detailed, giving models with respect to different kinds of discomfort, and to different macro-zones of the body. 相似文献
994.
Olufemi O. Oguntade 《Fuzzy Sets and Systems》1981,6(2):119-143
A philosophical formalism of a new methodological aspect of humanistic systems design and evaluation is given. A requisite concept of context-dependency is highlighted, and some approaches to fuzzy sets and linguistics subsequently extended. It is consequently shown that a mathematical theory of pragmatic fuzzy subsets is not only conceptually possible but practically implementable in man-machine studies as well. Thus, the important context-dependent implication of the subjective nature of Zadeh's theory of fuzzy sets can be better exploited.As a pragmatic theory, the approach here is a seeming connection between pragmatism and ontology, concepts that are traditionally diametrically opposed to each other. The attitude adopted has been the equation of pragmatism and psychophysical measurements of ontological objects (noumena). Pragmatism is tacitly defined as a form of empiricism whereby linguistic constructs (i.e., linguistic-variable denotions) that represent any aspect(s) of a humanistic system are nothing more than an operational procedure used to achieve psychophysical measurements of the aspect(s). In this fashion, pragmatism would enable the contents of assertions, which are made through declarative propositions, about humanistic systems to be deciphered within relevant contexts. For pragmatism, direct sense experience provides both the meaning and the criterion of reality judgements. The context-dependent nature of the physical reality of ontological entities is, therefore, better understood pragmatically vis-a-vis the appropriate evaluative criteria and interpretative conventions.By emphasizing the distinction between a fuzzy system (naturally fuzzified) and a fuzzified mathematical structure (meta-mathematically fuzzified), the use of the standard fuzzy topologies is justified although it is conceptually possible to develop a yet more general topology or perhaps an alternative one especially in the case of a meta-mathematically fuzzified structure. However, for the express purpose of machine implementation, a naturally fuzzified system, such as a (complex) humanistic system, is more amenable to an initial test of the philosophy of pragmatic fuzzy subsets. Consequently, the fuzzy topology and spaces employed are intended to be devoid of extensive generalities, in this instance. 相似文献
995.
996.
Philippe Nain 《Statistical Inference for Stochastic Processes》2002,5(3):307-320
The impact of bursty traffic on queues is investigated in this paper. We consider a discrete-time single server queue with
an infinite storage room, that releases customers at the constant rate of c customers/slot. The queue is fed by an M/G/∞ process. The M/G/∞ process can be seen as a process resulting from the superposition
of infinitely many ‘sessions’: sessions become active according to a Poisson process; a station stays active for a random
time, with probability distribution G, after which it becomes inactive. The number of customers entering the queue in the time-interval [t, t + 1) is then defined as the number of active sessions at time t (t = 0,1, ...) or, equivalently, as the number of busy servers at time t in an M/G/∞ queue, thereby explaining the terminology. The M/G/∞ process enjoys several attractive features: First, it can
display various forms of dependencies, the extent of which being governed by the service time distribution G. The heavier the tail of G, the more bursty the M/G/∞ process. Second, this process arises naturally in teletraffic as the limiting case for the aggregation
of on/off sources [27]. Third, it has been shown to be a good model for various types of network traffic, including telnet/ftp
connections [37] and variable-bit-rate (VBR) video traffic [24]. Last but not least, it is amenable to queueing analysis due
to its very strong structural properties. In this paper, we compute an asymptotic lower bound for the tail distribution of
the queue length. This bound suggests that the queueing delays will dramatically increase as the burstiness of the M/G/∞ input
process increases. More specifically, if the tail of G is heavy, implying a bursty input process, then the tail of the queue length will also be heavy. This result is in sharp
contrast with the exponential decay rate of the tail distribution of the queue length in presence of ‘non-bursty’ traffic
(e.g. Poisson-like traffic).
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
997.
YunHang Guo XiangJi Chen HongMei Jia Winnie Deuther-Conrad Peter Brust Jörg Steinbach Johnny Vercouillie BoLi Liu 《中国科学B辑(英文版)》2008,51(5):457-463
For the development of new ligands as potential imaging agents for the serotonin transporter (SERT), a series of diphenyl
ether derivatives have been synthesized, characterized, and evaluated for their in vitro binding affinities to the SERT. Among the above compounds, 2-(2-((dimethylamino)methyl)-4-fluorophenoxy)-5-bromobenzenamine
(15) and 2-(2-((dimethylamino)methyl)-4-fluorophenoxy)-5-iodobenzene amine (16) show high binding affinities for the SERT
with K
i values of 0.28 and 0.20 nmol·L−1, respectively. They can be further labeled with carbon-11, fluorine-18, iodine-123 or bromine-76, and evaluated as useful
imaging agents for the SERT. Moreover, the study of the structure-activity relationship (SAR) provides some useful information
for the future design of new ligands.
Supported by the National Natural Science Foundation of China (Grant No. 20471011) 相似文献
998.
Alfredo Deañ o Javier Segura Nico M. Temme. 《Mathematics of Computation》2008,77(264):2277-2293
We identify minimal and dominant solutions of three-term recurrence relations for the confluent hypergeometric functions and , where (not both equal to 0). The results are obtained by applying Perron's theorem, together with uniform asymptotic estimates derived by T. M. Dunster for Whittaker functions with large parameter values. The approximations are valid for complex values of , and , with .
999.
In this study, a hyperspectral imaging system in the spectral region of 400–1000 nm was used for visualization and determination of intramuscular fat concentration in beef samples. Hyperspectral images were acquired for beef samples, and spectral information was then extracted from each single sample from the fat and non-fat regions. The intramuscular fat content was chemically extracted and quantified for the same samples. Chemometrics including analysis of variance (ANOVA) and spectral similarity measures involving spectral angle measure (SAM), and Euclidian distance measure (EDM) were then used to analyze the data. An ANOVA analysis indicates that the two selected spectral variables (e.g., 650.4–736.4 nm) are effective to generate ratio image for visualization of the intramuscular fat distribution in beef. The spectral similarity analysis methods, which is based on the quantifying the spectral similarities by using predetermined endmember spectrum vector, provided comparable results for characterization and detection of intramuscular fat in beef. In term of overall classification accuracy, spectral similarity measure methods outperformed the ratio image of selected bands based on the result of ANOVA analysis. The results demonstrate that proposed technique has a potential for fast and nondestructive determination of intramuscular fat in beef. 相似文献
1000.
采用区间值直觉模糊不确定语言变量建模决策中存在的不确定信息,给出了一个新的不确定环境下的VIKOR方法.首先采用区间直觉模糊不确定语言变量对方案进行评价,然后将VIKOR方法进行推广到新的不确定环境下,给出新的方案排序方法.最后为了说明方法的有效性和合理性,将所给的方法应用于房地产开发方案的风险评价中. 相似文献