全文获取类型
收费全文 | 879篇 |
免费 | 20篇 |
国内免费 | 46篇 |
专业分类
化学 | 255篇 |
晶体学 | 2篇 |
力学 | 60篇 |
综合类 | 2篇 |
数学 | 220篇 |
物理学 | 406篇 |
出版年
2024年 | 1篇 |
2023年 | 11篇 |
2022年 | 16篇 |
2021年 | 11篇 |
2020年 | 20篇 |
2019年 | 11篇 |
2018年 | 11篇 |
2017年 | 15篇 |
2016年 | 20篇 |
2015年 | 11篇 |
2014年 | 50篇 |
2013年 | 57篇 |
2012年 | 36篇 |
2011年 | 56篇 |
2010年 | 60篇 |
2009年 | 75篇 |
2008年 | 53篇 |
2007年 | 79篇 |
2006年 | 51篇 |
2005年 | 51篇 |
2004年 | 34篇 |
2003年 | 32篇 |
2002年 | 26篇 |
2001年 | 11篇 |
2000年 | 21篇 |
1999年 | 11篇 |
1998年 | 22篇 |
1997年 | 7篇 |
1996年 | 14篇 |
1995年 | 10篇 |
1994年 | 6篇 |
1993年 | 11篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有945条查询结果,搜索用时 171 毫秒
11.
H. Wätzig 《Chromatographia》1992,33(5-6):218-224
Summary It is still difficult to determine peaks and peak boundaries properly, though peak recognition is very important for the precision of quantitative data. A new computer program overcomes these problems using a method which is adapted from human judgements. The algorithm was developed for HPLC but can also be used in other fields of analytical chemistry. 相似文献
12.
13.
Multivariate classification methods were used to evaluate data on the concentrations of eight metals in human senile lenses measured by atomic absorption spectrometry. Principal components analysis and hierarchical clustering separated senile cataract lenses, nuclei from cataract lenses, and normal lenses into three classes on the basis of the eight elements. Stepwise discriminant analysis was applied to give discriminant functions with five selected variables. Results provided by the linear learning machine method were also satisfactory; the k-nearest neighbour method was less useful. 相似文献
14.
Direct CI mass spectrometry profiling of fatty acid methyl esters (FAMEs) from in situ thermal hydrolysis/methylation (THM) of whole bacterial cells with tetramethylammonium hydroxide (TMAH) has been demonstrated as a potential method for real time and fieldable detection/identification of microorganisms. Bacillus anthracis (Ames), Yersinia pestis (Nair. Kenya), Vibrio cholerae (E1 Tor), Brucella melitensis (Abortus wild) and Francisella tularensis (LVS vaccine) were profiled by this method during a 10-month period. Repeatability of the in situ FAME data was calculated using one-way analysis of variance (ANOVA) and a t-test. Artificial neural network (ANN) and multivariate statistics of the FAME profiles were also compared for bacterial identification/classification. Equivalent results were obtained with a multivariate rule building expert system (MuRES) and the ANN. However, the ANN analysis required much less computer time and was deemed the best choice for this application. In situ THM FAME profiles of the bacterial samples provided comparable results with those obtained from the Microbial Identification System (MIDI) (Newark, DE) wet chemistry-gas chromatographic based system. 相似文献
15.
16.
模式识别—人工神经网络在化学中的若干新应用 总被引:2,自引:0,他引:2
本文通过我们应用模式识别-人工神经网络方法预报新化合物、熔盐相图以及复杂化学反应体系的研究,展示应用模式识别-人工神经网络方法与物理化学理论相结合,研究化学现象的可能性和应用价值。 相似文献
17.
Tsuneo Okubo 《Colloid and polymer science》2006,284(12):1395-1401
Sedimentation and drying dissipative structural patterns formed in the course of drying colloidal silica spheres (1.2 μm in diameter) in aqueous suspension have been studied in a glass dish and a polystyrene dish. The broad ring patterns are formed within a short time in suspension state by the convection flow of water and colloidal spheres. The broad ring patterns are not formed when a dish is covered with a cap, which demonstrates the important role of the convectional flow of silica spheres and water accompanied with the evaporation of water on the air-suspension interface. The sedimentary spheres always move by the convectional flow of water, and the broad ring patterns became sharp with time. Broad ring and microscopic fine structures are formed in the solidification processes on the bases of the convectional and sedimentation patterns. Drying patterns of the colloidal suspensions containing sodium chloride are star-like ones, which strongly supports the synchronous cooperative interactions between the salt and colloidal spheres. 相似文献
18.
We study a nonlinear fourth order evolution equation arising in the context of sand ripple dynamics. We analyse the set of stationary solutions and travelling waves in order to recover the observed phenomenology such as different wavelengths ripples, travelling waves, coarsening and time scales. Moreover, we construct an approximate solution which describes the early stages of the dynamics and which suggests the existence of coarsening and of time scales with different dynamical behaviour. 相似文献
19.
Tamás F. Móri 《Journal of Theoretical Probability》1995,8(1):139-164
Considering an infinite string of i.i.d. random letters drawn from a finite alphabet we define the cover timeW
n
as the number of random letters needed until each pattern of lenghtn appears at least once as a substring. Sharp weak and a.s. limit results onW
n
are known in the symmetric case, i.e., when the random letters are uniformly distributed over the alphabet. In this paper we determine the limit distribution ofW
n
in the nonsymmetric case asn. Generalizations in terms of point processes are also proved.Dedicated to Endre Csáki on his 60th birthday. 相似文献
20.
Kehayias JJ 《Analytical and bioanalytical chemistry》2004,379(2):188-191
Body composition has become the main outcome of many nutritional intervention studies including osteoporosis, malnutrition, obesity, AIDS, and aging. Traditional indirect body composition methods developed with healthy young adults do not apply to the elderly or diseased. Fast neutron activation (for N and P) and neutron inelastic scattering (for C and O) are used to assess in vivo elements characteristic of specific body compartments. Non-bone phosphorus for muscle is measured by the 31P(n,)28Al reaction, and nitrogen for protein via the 14N(n,2n)13N fast neutron reaction. Inelastic neutron scattering is used to measure total body carbon and oxygen. Body fat is derived from carbon after correcting for contributions from protein, bone, and glycogen. Carbon-to-oxygen ratio (C/O) is used to measure the distribution of fat and lean tissue in the body and to monitor small changes of lean mass. A sealed, D–T neutron generator is used for the production of fast neutrons. Carbon and oxygen mass and their ratio are measured in vivo at a radiation exposure of less than 0.06 mSv. Gamma-ray spectra are collected using large BGO detectors and analyzed for the 4.43 MeV state of carbon and 6.13 MeV state of oxygen, simultaneously with the irradiation. P and N analysis by delayed fast neutron activation is performed by transferring the patient to a shielded room equipped with an array of NaI(Tl) detectors. A combination of measurements makes possible the assessment of the quality of fat-free mass. The neutron generator system is used to evaluate the efficacy of new treatments, to study mechanisms of lean tissue depletion with aging, and to investigate methods for preserving function and quality of life in the elderly. It is also used as a reference method for the validation of portable instruments of nutritional assessment. 相似文献