全文获取类型
收费全文 | 6644篇 |
免费 | 211篇 |
国内免费 | 33篇 |
专业分类
化学 | 5140篇 |
晶体学 | 61篇 |
力学 | 90篇 |
数学 | 410篇 |
物理学 | 1187篇 |
出版年
2023年 | 24篇 |
2022年 | 39篇 |
2021年 | 60篇 |
2020年 | 72篇 |
2019年 | 101篇 |
2018年 | 57篇 |
2017年 | 57篇 |
2016年 | 126篇 |
2015年 | 115篇 |
2014年 | 156篇 |
2013年 | 329篇 |
2012年 | 350篇 |
2011年 | 421篇 |
2010年 | 229篇 |
2009年 | 277篇 |
2008年 | 437篇 |
2007年 | 444篇 |
2006年 | 470篇 |
2005年 | 420篇 |
2004年 | 386篇 |
2003年 | 319篇 |
2002年 | 304篇 |
2001年 | 122篇 |
2000年 | 100篇 |
1999年 | 80篇 |
1998年 | 79篇 |
1997年 | 85篇 |
1996年 | 78篇 |
1995年 | 69篇 |
1994年 | 56篇 |
1993年 | 54篇 |
1992年 | 48篇 |
1991年 | 57篇 |
1990年 | 37篇 |
1989年 | 29篇 |
1988年 | 45篇 |
1987年 | 48篇 |
1986年 | 59篇 |
1985年 | 85篇 |
1984年 | 72篇 |
1983年 | 34篇 |
1982年 | 70篇 |
1981年 | 64篇 |
1980年 | 55篇 |
1979年 | 54篇 |
1978年 | 43篇 |
1977年 | 43篇 |
1976年 | 31篇 |
1975年 | 25篇 |
1973年 | 19篇 |
排序方式: 共有6888条查询结果,搜索用时 265 毫秒
21.
Spacetime correlation functions of the time-varying speckle intensity have been evaluated for the case where speckle patterns are produced in the Fresnel diffraction region by light propagating through a series of moving random-phase screens. The correlation functions are given by a set of recursion formulae which are useful for numerical computations. Three statistical quantities relating to the motion of speckle patterns are derived to examine the relationship between the velocity distribution of the phase screens and the temporal behaviour of resultant speckle patterns. It is found that the velocity differences between the phase screens have a strong effect on both the decorrelation of speckle patterns and the fluctuating speed of the speckle intensity. 相似文献
22.
This article concerns several geometric properties of metricmeasure spaces satisfying the measure contraction property (MCP),which can be considered as a generalized notion of lower Riccicurvature bounds. We prove that the MCP of spaces descends totheir products and Euclidean cones. We also show that a positivelycurved space in terms of the MCP with a maximal diameter canbe represented as the spherical suspension of some topologicalmeasure space. 相似文献
23.
Takashi Nakamura 《Journal of Number Theory》2007,123(1):1-9
In this paper, we define λ-joint, a′-joint, (λ,λ)-joint, (λ,a′)-joint and (a′,a′)-joint t-universality of Lerch zeta functions and consider the relations among those. Next we show the existence of (λ,λ)-joint t-universality. Finally, we also show the existence of λ-joint, a′-joint, (λ,a′)-joint and (a′,a′)-joint t-universality by using inversion formulas. 相似文献
24.
In this article a stability result for the Falk model system is proven. The Falk model system describes the martensitic phase transitions in shape memory alloys. In our setting, the steady state is a nonlocal elliptic problem. We show the dynamical stability for the linearized stable critical point of the corresponding functional. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
25.
26.
A convergent synthesis of the key synthetic intermediate of hemibrevetoxin B was achieved via the intramolecular allylation of an α-chloroacetoxy ether and subsequent ring-closing metathesis. 相似文献
27.
A new 20-membered macrolide designated exiguolide has been isolated from the marine sponge Geodia exigua, and its structure determined by interpretation of spectroscopic data. Exiguolide specifically inhibited fertilization of sea urchin (Hemicentrotus pulcherrimus) gametes but not embryogenesis of the fertilized egg. 相似文献
28.
Takashi Seo 《Journal of multivariate analysis》2006,97(9):1976-1983
In this paper, we consider simultaneous confidence intervals for all contrasts in the means when the observations are missing at random in the intraclass correlation model. An exact test statistic for the equality of the means and Scheffé, Bonferroni and Tukey types of simultaneous confidence intervals are given by an extension of Bhargava and Srivastava [On Tukey's confidence intervals for the contrasts in the means of the intraclass correlation model, J. Royal Statist. Soc. B35 (1973) 147-152] when the missing observations are of the monotone type. Finally, numerical results of simultaneous confidence intervals are presented. 相似文献
29.
Hoon Kim Toshihiko Koseki Tomohiro Ohta Hiroshi Sato Yukihiro Shimogaki 《Applied Surface Science》2006,252(11):3938-3942
The adhesion of Cu on Ru substrates with different crystal orientations was evaluated. The crystal orientation of sputter deposited Ru could be changed from (1 0 0) to (0 0 1) by annealing at 650 °C for 20 min. The adhesion of Cu was evaluated by the degree of Cu agglomeration on Ru. Cu films on annealed Ru films with the (0 0 1) crystal orientation showed 28% lower RMS values and 50% lower Ru surface coverage than Cu as-deposited on Ru having the (1 0 0) crystal orientation after annealing at 550 °C for 30 min, which suggest that Cu wettability on the Ru(0 0 1) was better than that on the Ru(1 0 0) plane. The low lattice misfit of 4% between Cu(1 1 1) and Ru(0 0 1) may be the reason for this good adhesion property. 相似文献
30.
Analysis of Spectral Reflectance Using Normalization Method from Endoscopic Spectroscopy System 总被引:2,自引:0,他引:2
Masao Sambongi Makoto Igarashi Takashi Obi Masahiro Yamaguchi Nagaaki Ohyama Masahiko Kobayashi Yasushi Sano Shigeaki Yoshida Kazuhiro Gono 《Optical Review》2002,9(6):238-243
Objective assessment of gastrointestinal mucosal color is extremely important in the endoscopic diagnosis of digestive tract disease. In this paper, we propose a method to clarify the spectral characteristics of gastric and colon cancer. A large number of spectral reflectance data of mucous membrane are measured by the endoscopic spectroscopy system (ESS) in the National Cancer Center Hospital East, Kashiwa, Japan and the Department of Internal Medicine, Self-Defense Force Center Hospital, Tokyo, Japan. We assume that early cancer appears primarily in the spectral data of short wavelength, because it is usually present in a superficial cell where short wavelength light is scattered more strongly than long wavelength light. To identify the features in the short wavelength components, the spectral reflectance was divided by the reflectance of a long wavelength. We investigated the possibility of distinguishing early cancer from normal spectral data through statistical analysis, employing the projection axis as the mean difference between them. Early cancer and normal spectral data were projected on the projection axis, and the Student’s T-test was applied to evaluate the mean of the distribution between these data. 相似文献