全文获取类型
收费全文 | 1371篇 |
免费 | 24篇 |
国内免费 | 16篇 |
专业分类
化学 | 820篇 |
晶体学 | 44篇 |
力学 | 58篇 |
数学 | 128篇 |
物理学 | 361篇 |
出版年
2024年 | 1篇 |
2023年 | 12篇 |
2022年 | 63篇 |
2021年 | 55篇 |
2020年 | 32篇 |
2019年 | 31篇 |
2018年 | 35篇 |
2017年 | 66篇 |
2016年 | 61篇 |
2015年 | 55篇 |
2014年 | 96篇 |
2013年 | 127篇 |
2012年 | 148篇 |
2011年 | 95篇 |
2010年 | 76篇 |
2009年 | 51篇 |
2008年 | 40篇 |
2007年 | 32篇 |
2006年 | 41篇 |
2005年 | 28篇 |
2004年 | 14篇 |
2003年 | 27篇 |
2002年 | 16篇 |
2001年 | 27篇 |
2000年 | 17篇 |
1999年 | 24篇 |
1998年 | 14篇 |
1997年 | 7篇 |
1996年 | 12篇 |
1995年 | 5篇 |
1994年 | 11篇 |
1993年 | 8篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 9篇 |
1987年 | 32篇 |
1986年 | 18篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1976年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有1411条查询结果,搜索用时 31 毫秒
151.
Sriwulan ADJI Rizky ROSJANUARDI 《数学学报(英文版)》2007,23(9):1639-1648
Let г^+ be the positive cone of a totally ordered abelian group г, and σa cocycle in г. We study the twisted crossed products by actions of г+ as endomorphisms of C^*-algebras, and use this to generalize the theorem of Ji. 相似文献
152.
Viscosities of solutions of polystyrene in toluene were measured for concentrations up to 400 kg m?3 at 298 K. Polymers of molecular weights ranging from 8.7 × 103 to 2.4 × 106 were used. It is observed that viscosity of the polymer solution increases with increasing concentration and molecular weight; the rate of increase is greater at higher values of the two parameters. A master curve for the system is constructed by using the experimental data for viscosity, concentration and molecular weight of the polymer. Regions of various polymer interactions in solution are identified. 相似文献
153.
LetLbe a Moufang loop of odd orderpαqα11···qnαnwherepandqiare primes with 3 ≤ p < q1 < ··· < qnand αi ≤ 2. In this paper, we prove thatLis a group ifpandqiare primes with 3 ≤ p < q1 < ··· < qn: (i) α ≤ 3, or (ii) α ≤ 4,p ≥ 5. 相似文献
154.
The apparent molal volume v of sucrose in water has been measured at 25°C in the concentration range 0.04–4.4m from precise density measurements. The same property was also determined for dilute solutions of sucrose in mixed aqueous solvents containing NaCl, KCl, or urea. The limiting values
v
°
and the slopesS
v
*
were obtained in each case, and their significance has been discussed briefly. The mean apparent molal volumes v of the ternary systems were also calculated, and the predictive accuracy of Ward and Millero's modified Young's rule for v was found to be comparable to that for other electrolyte-nonelectrolyte solutions. For the system H2O-sucrose-urea, an additivity rule based simply on total molality predicted v with similar accuracy.Deceased January 15, 1976. 相似文献
155.
A weighing matrix of order n and weight m2 is a square matrix M of order n with entries from {-1,0,+1} such that MMT=m2I where I is the identity matrix of order n. If M is a group matrix constructed using a group of order n, M is called a group weighing matrix. Recently, group weighing matrices were studied intensively, especially when the groups are cyclic and abelian. In this paper, we study the abelian group weighing matrices that are symmetric, i.e.MT=M. Some new examples are found. Also we obtain a few exponent bounds on abelian groups that admit symmetric group weighing matrices. In particular, we prove that there is no symmetric abelian group weighing matrices of order 2pr and weight p2 where p is a prime and p≥ 5.Communicated by: K.T. Arasu 相似文献
156.
Density,viscosity, conductance,and transference number of concentrated aqueous magnesium chloride at 25°C 总被引:1,自引:0,他引:1
The density, viscosity, conductance, and transference number of aqueous magnesium chloride at 298.15°K are reported for the concentration range 0 to 5.7m. The transference numbers were determined using the emf method. It was found that the viscosity, conductance, and transference number of aqueous magnesium chloride are similar to those for aqueous nickel chloride. It was therefore tentatively concluded that incomplete dissociation and complex formation was unlikely to be of importance in nickel chloride solutions. 相似文献
157.
The paper presents the nature of variations of clouds and total ozone over Kolkata (22°34′N, 88°24′E), India. The low-level
cloud over Kolkata has been noticed to occur for many days and nights, particularly in the months from June to September.
The low level cloud occurrences were minimum in winter months. The effect of cloud occurrence on ozone concentration has been
critically analyzed and explained. It has been observed that the concentration of ozone increased with the increase of cloud
occurrence. The related possible chemical explanation for ozone production processes has been offered. 相似文献
158.
X.Z. Wang G.H. Yu C.T. Lin M.X. Cao H. Gong M. Qi A.Z. Li 《Solid State Communications》2010,150(3-4):168-171
A set of GaN films were overgrown by hydride vapor phase epitaxy (HVPE) on nanoporous GaN templates with different pore diameters. These samples have various properties as seen from the measurements of X-ray diffraction (XRD) and photoluminescence (PL). Cross-sectional observations under a scanning electron microscopy (SEM) reveal that the overgrowth mechanism and process are strongly related to the dimension of nanopores, indicating that an optimum diameter exists for the properties of subsequent HVPE–GaN layers. When the diameters of nanopores are less than the optimum value, the pores on top of GaN templates can be left, and the properties of HVPE–GaN films show significant improvement. In contrast, the pores are almost stuffed with HVPE–GaN films, which obviously limit the improvement degree of HVPE–GaN films. 相似文献
159.
In statistical process control (SPC), when dealing with a quality characteristic x that is a variable, it is usually necessary to monitor both the mean value and variability. This article proposes an optimization algorithm (called the holistic algorithm) to design the CUSUM charts for this purpose. It facilitates the determination of the charting parameters of the CUSUM charts and considerably or significantly increases their overall detection effectiveness. A single CUSUM chart (called the ABS CUSUM chart) has been developed by the holistic algorithm and fully investigated. This chart is able to detect two-sided mean shifts and increasing variance shifts by inspecting the absolute value of sample mean shift. The results of performance studies show that the overall performance of the ABS CUSUM chart is nearly as good as an optimal 3-CUSUM scheme (a scheme incorporating three individual CUSUM charts). However, since the ABS CUSUM chart is easier for implementation and design, it may be more suitable for many SPC applications in which both mean and variance of a variable have to be monitored. 相似文献
160.
Michael Boon Chong Khoo Zhang Wu Chung-Ho Chen Kah Wai Yeong 《Computational Statistics》2010,25(2):299-316
Two control charts are usually used to monitor the process mean and variance separately. The mean is monitored using the [`(X)]{\bar{{X}}} chart while the variance using either the standard deviation, S chart, or the range, R chart. Recently, numerous single variable charts are proposed to jointly monitor the mean and variance. Most approaches transform
the sample mean and sample variance into two statistics, each having a standard scale, and either plotting them on the same
chart or combining them into a single statistic to be plotted on a chart. The R chart is more widely used than the S chart but no attempt is made to combine the [`(X)]{\bar{{X}}} and R charts in the construction of a single variable chart and to study its properties and performance. In this paper, we transform
the [`(X)]{\bar{{X}}} and R statistics into two standard normal random variables, used in the computation of two corresponding exponentially weighted
moving average (EWMA) statistics, which are then merged into a single plotting statistic for the proposed chart, called the
EWMA [`(X)]-R{\bar{{X}}-R} chart. 相似文献