全文获取类型
收费全文 | 304341篇 |
免费 | 8976篇 |
国内免费 | 4935篇 |
专业分类
化学 | 167600篇 |
晶体学 | 4630篇 |
力学 | 14361篇 |
综合类 | 294篇 |
数学 | 33881篇 |
物理学 | 97486篇 |
出版年
2021年 | 2997篇 |
2020年 | 3531篇 |
2019年 | 3692篇 |
2018年 | 4356篇 |
2017年 | 4271篇 |
2016年 | 6239篇 |
2015年 | 4399篇 |
2014年 | 6405篇 |
2013年 | 13326篇 |
2012年 | 11258篇 |
2011年 | 13204篇 |
2010年 | 9344篇 |
2009年 | 9117篇 |
2008年 | 11705篇 |
2007年 | 11675篇 |
2006年 | 10949篇 |
2005年 | 9676篇 |
2004年 | 8697篇 |
2003年 | 7819篇 |
2002年 | 7653篇 |
2001年 | 8091篇 |
2000年 | 6476篇 |
1999年 | 5150篇 |
1998年 | 4563篇 |
1997年 | 4500篇 |
1996年 | 4260篇 |
1995年 | 3942篇 |
1994年 | 4024篇 |
1993年 | 3613篇 |
1992年 | 4072篇 |
1991年 | 3988篇 |
1990年 | 3896篇 |
1989年 | 3689篇 |
1988年 | 3771篇 |
1987年 | 3632篇 |
1986年 | 3436篇 |
1985年 | 4509篇 |
1984年 | 4734篇 |
1983年 | 3943篇 |
1982年 | 4064篇 |
1981年 | 3967篇 |
1980年 | 3924篇 |
1979年 | 3886篇 |
1978年 | 4190篇 |
1977年 | 4109篇 |
1976年 | 4173篇 |
1975年 | 3849篇 |
1974年 | 3893篇 |
1973年 | 4050篇 |
1972年 | 2851篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The satisfiability (SAT) problem is a core problem in computer science. Existing studies have shown that most industrial SAT instances can be effectively solved by modern SAT solvers while random SAT instances cannot. It is believed that the structural characteristics of different SAT formula classes are the reasons behind this difference. In this paper, we study the structural properties of propositional formulas in conjunctive normal form (CNF) by the principle of structural entropy of formulas. First, we used structural entropy to measure the complex structure of a formula and found that the difficulty solving the formula is related to the structural entropy of the formula. The smaller the compressing information of a formula, the more difficult it is to solve the formula. Secondly, we proposed a -approximation strategy to approximate the structural entropy of large formulas. The experimental results showed that the proposed strategy can effectively approximate the structural entropy of the original formula and that the approximation ratio is more than 92%. Finally, we analyzed the structural properties of a formula in the solution process and found that a local search solver tends to select variables in different communities to perform the next round of searches during a search and that the structural entropy of a variable affects the probability of the variable being flipped. By using these conclusions, we also proposed an initial candidate solution generation strategy for a local search for SAT, and the experimental results showed that this strategy effectively improves the performance of the solvers CCAsat and Sparrow2011 when incorporated into these two solvers. 相似文献
82.
Santosh S. Bhujbal Chawale Bhushankumar G. Kale Mayuri A. 《Journal of Analytical Chemistry》2022,77(4):473-483
Journal of Analytical Chemistry - HPTLC is a widely used tool in standardization of herbs because of its ability to estimate the presence of active components in samples. HPTLC-bioautography is a... 相似文献
83.
Ding Q. Yao M. Wu Sh. Zeng M. Xue N. Wu D. Xu J. 《Journal of Applied Spectroscopy》2022,89(4):712-718
Journal of Applied Spectroscopy - Based on partial least squares (PLS) analysis, the effects of different smoothing points and different preprocessing methods on the accuracy and precision of the... 相似文献
84.
Transport in Porous Media - The theme of coupling problems for adsorption, absorption and thermochemical transport in porous media is very important for engineering applications. Based on the... 相似文献
85.
Differential Equations - We study a mixed problem for systems of one-dimensional semilinear hyperbolic equations with variable nonlinearity growth rate and nonlinear boundary conditions. Theorems... 相似文献
86.
Manjumol K. A. Jayasankar M. Vidya K. Mohamed A. Peer Nair Balagopal N. Warrier K. G. K. 《Journal of Sol-Gel Science and Technology》2015,74(1):161-167
Journal of Sol-Gel Science and Technology - High temperature stable brookite rich titanium dioxide of average crystallite size 20&;nbsp;nm has been prepared by a novel aqueous sol–gel... 相似文献
87.
Saleh Z. M. Nasser H. Özkol E. Günöven M. Abak K. Canli S. Bek A. Turan R. 《Journal of nanoparticle research》2015,17(10):1-12
Journal of Nanoparticle Research - Plasmonic interfaces consisting of silver nanoparticles of different sizes (50–100&;nbsp;nm) have been processed by the self-assembled dewetting... 相似文献
88.
E. V. Shadrina O. N. Malinkina T. G. Khonina A. B. Shipovskaya V. I. Fomina E. Yu. Larchenko N. A. Popova I. G. Zyryanova L. P. Larionov 《Russian Chemical Bulletin》2015,64(7):1633-1639
The biomimetic sol—gel synthesis of silicon—chitosan-containing glycerohydrogels was carried out using silicon tetraglycerolate as a precursor. It was found that chitosan accelerates gel formation in weakly acidic media. In more acidic media, the kinetics of the process changes according to the curve with a maximum, which can be attributed to different mechanisms of silanol condensation before and after the isoelectric point. The investigated silicon—chitosan-containing glycerohydrogels exhibit antibacterial, anti-inflammatory, and wound healing activity. The synthesized hybrid glycerohydrogels are promising materials for biomedical applications. 相似文献
89.
90.