全文获取类型
收费全文 | 9434篇 |
免费 | 813篇 |
国内免费 | 517篇 |
专业分类
化学 | 2913篇 |
晶体学 | 55篇 |
力学 | 1047篇 |
综合类 | 111篇 |
数学 | 2728篇 |
物理学 | 1673篇 |
无线电 | 2237篇 |
出版年
2024年 | 7篇 |
2023年 | 117篇 |
2022年 | 227篇 |
2021年 | 229篇 |
2020年 | 289篇 |
2019年 | 253篇 |
2018年 | 191篇 |
2017年 | 277篇 |
2016年 | 348篇 |
2015年 | 352篇 |
2014年 | 520篇 |
2013年 | 674篇 |
2012年 | 504篇 |
2011年 | 589篇 |
2010年 | 503篇 |
2009年 | 632篇 |
2008年 | 587篇 |
2007年 | 696篇 |
2006年 | 510篇 |
2005年 | 473篇 |
2004年 | 420篇 |
2003年 | 382篇 |
2002年 | 344篇 |
2001年 | 257篇 |
2000年 | 248篇 |
1999年 | 211篇 |
1998年 | 182篇 |
1997年 | 143篇 |
1996年 | 110篇 |
1995年 | 81篇 |
1994年 | 87篇 |
1993年 | 53篇 |
1992年 | 59篇 |
1991年 | 35篇 |
1990年 | 36篇 |
1989年 | 16篇 |
1988年 | 22篇 |
1987年 | 15篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 15篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Yawei CHU 《Frontiers of Mathematics in China》2012,7(1):19-27
Let (M
n
, g) be an n-dimensional complete noncompact Riemannian manifold with harmonic curvature and positive Sobolev constant. In this paper,
by employing an elliptic estimation method, we show that (M
n
, g) is a space form if it has sufficiently small L
n/2-norms of trace-free curvature tensor and nonnegative scalar curvature. Moreover, we get a gap theorem for (M
n
, g) with positive scalar curvature. 相似文献
92.
We propose subject matter expert refined topic (SMERT) allocation, a generative probabilistic model applicable to clustering freestyle text. SMERT models are three‐level hierarchical Bayesian models in which each item is modeled as a finite mixture over a set of topics. In addition to discrete data inputs, we introduce binomial inputs. These ‘high‐level’ data inputs permit the ‘boosting’ or affirming of terms in the topic definitions and the ‘zapping’ of other terms. We also present a collapsed Gibbs sampler for efficient estimation. The methods are illustrated using real world data from a call center. Also, we compare SMERT with three alternative approaches and two criteria. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
93.
Anandamayee Majumdar Debashis Paul 《Journal of computational and graphical statistics》2016,25(3):727-747
We introduce new classes of stationary spatial processes with asymmetric, sub-Gaussian marginal distributions using the idea of expectiles. We derive theoretical properties of the proposed processes. Moreover, we use the proposed spatial processes to formulate a spatial regression model for point-referenced data where the spatially correlated errors have skewed marginal distribution. We introduce a Bayesian computational procedure for model fitting and inference for this class of spatial regression models. We compare the performance of the proposed method with the traditional Gaussian process-based spatial regression through simulation studies and by applying it to a dataset on air pollution in California. 相似文献
94.
95.
通过若干实例,运用高等数学中的微分方程方法建立数学模型,提高学生学习高等数学的兴趣并逐步了解数学建模的方法和思想;提高课堂讲课效果、实践素质教育改革. 相似文献
96.
Recent experiments by Ross and co-workers proved the possibility of a mononuclear regime with heterogeneous nucleation as well as jerky growth in the vapor–liquid–solid (VLS) process for silicon nanowires. In this work, a theoretical model is presented which incorporates the effects of (i) a mononuclear regime with layer by layer growth, (i) heterogeneous nucleation of each new layer at the edge of a Au–Si droplet, (iii) drop of supersaturation after each successful nucleation and respective fast layer growth, (iv) time-dependent nucleation barrier during each new waiting period and (v) correlation between subsequent waiting periods (non-Markovian sequence of waiting periods). 相似文献
97.
98.
A. Herbon E. Khmelnitsky F. Blanchini 《Journal of Optimization Theory and Applications》2003,116(2):283-310
The impact of uncertain future events on decision making in a stochastic environment is modeled in this paper. Such modeling is presented for both feedback and optimal control problems. This research overcomes the difficulties of forecasting that arise when considering future information. In this paper, we seek to find the minimum amount of information (effective information) necessary to evaluating system performance offline or to optimally control a system. The existence of effective information is proved and a methodology for determining it is developed. It is also shown that ignoring information beyond the planning horizon leads to significant performance loss and may even lead to violating the constraints of a control problem. 相似文献
99.
Andriy Fedorov Jacob Fluckiger Gregory D. Ayers Xia Li Sandeep N. Gupta Clare Tempany Robert Mulkern Thomas E. Yankeelov Fiona M. Fennessy 《Magnetic resonance imaging》2014
Multi-parametric Magnetic Resonance Imaging, and specifically Dynamic Contrast Enhanced (DCE) MRI, play increasingly important roles in detection and staging of prostate cancer (PCa). One of the actively investigated approaches to DCE MRI analysis involves pharmacokinetic (PK) modeling to extract quantitative parameters that may be related to microvascular properties of the tissue. It is well-known that the prescribed arterial blood plasma concentration (or Arterial Input Function, AIF) input can have significant effects on the parameters estimated by PK modeling. The purpose of our study was to investigate such effects in DCE MRI data acquired in a typical clinical PCa setting. First, we investigated how the choice of a semi-automated or fully automated image-based individualized AIF (iAIF) estimation method affects the PK parameter values; and second, we examined the use of method-specific averaged AIF (cohort-based, or cAIF) as a means to attenuate the differences between the two AIF estimation methods. 相似文献
100.
本文对 Jordan标准形定理给出了一种使用初等变换的证明 ,直观意义明显、易于理解 ,可用于线性代数教学 . 相似文献