全文获取类型
收费全文 | 7515篇 |
免费 | 755篇 |
国内免费 | 411篇 |
专业分类
化学 | 5607篇 |
晶体学 | 77篇 |
力学 | 251篇 |
综合类 | 45篇 |
数学 | 822篇 |
物理学 | 1879篇 |
出版年
2024年 | 10篇 |
2023年 | 91篇 |
2022年 | 148篇 |
2021年 | 200篇 |
2020年 | 209篇 |
2019年 | 238篇 |
2018年 | 198篇 |
2017年 | 180篇 |
2016年 | 337篇 |
2015年 | 296篇 |
2014年 | 397篇 |
2013年 | 547篇 |
2012年 | 606篇 |
2011年 | 638篇 |
2010年 | 440篇 |
2009年 | 382篇 |
2008年 | 512篇 |
2007年 | 422篇 |
2006年 | 424篇 |
2005年 | 355篇 |
2004年 | 314篇 |
2003年 | 274篇 |
2002年 | 274篇 |
2001年 | 191篇 |
2000年 | 131篇 |
1999年 | 103篇 |
1998年 | 74篇 |
1997年 | 63篇 |
1996年 | 75篇 |
1995年 | 59篇 |
1994年 | 61篇 |
1993年 | 52篇 |
1992年 | 51篇 |
1991年 | 52篇 |
1990年 | 43篇 |
1989年 | 25篇 |
1988年 | 19篇 |
1987年 | 20篇 |
1986年 | 15篇 |
1985年 | 25篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1973年 | 5篇 |
1971年 | 6篇 |
排序方式: 共有8681条查询结果,搜索用时 31 毫秒
41.
Biological transformation of volatile organic compounds is one of the key factors that influence contaminant-plume evolution
and thus natural attenuation. In this study we investigate the effect of biological transformation on the transport of contaminants
in the aqueous and gaseous phases. The analysis includes the study of the effect of density-driven advection of contaminants
in the gaseous phase on multiphase and multispecies flow, fate and transport modeling in the subsurface. Trichloroethylene
(TCE) and its two byproducts, dichloroethylene and vinyl chloride, are analyzed as the target contaminants. Our results indicate
that density-driven advection of the gaseous phase, which is initiated by evaporation of TCE as a nonaqueous phase liquid,
increases the downward and also the lateral migration of TCE within the unsaturated zone. This process also influences the
location of high-concentration zones of the byproducts of TCE in the unsaturated and the saturated zones. Biotransformation
of TCE contributes to the reduction of dissolved TCE plume development as expected. The daughter byproducts, which are introduced
into the subsurface system, show distinct transport patterns as they are affected by their independent degradation kinetics
and density-driven advection. These observations, which are based on our simulation results for biotransformation and transport
of TCE and its byproducts, are useful in evaluating the natural attenuation processes, its potential health hazards and also
the evaluation of potential plume development at contaminated sites. 相似文献
42.
Do Young Kim Ji Sim Jung Young Rae Jang Kun Ho Yoo Jin Jang 《Physica E: Low-dimensional Systems and Nanostructures》2003,16(3-4):400
We studied the growth of nanocrystalline silicon (nc-Si) thin film exhibiting a strong room temperature photoluminescence (PL) at 1.81–2.003 eV. The amorphous silicon was crystallized by Ni silicide mediated crystallization (Ni SMC) and then Secco-etched to exhibit the PL. The PL peak energy and intensity increase with increasing the metal density on the a-Si because of the reduction in the grain size down to 2 nm. The photoluminescence energy and peak intensity depend strongly on the Secco etch time because the grain size is reduced by etching the grain boundaries. 相似文献
43.
Ha Yong Lee Se Hun Jung Soo Yong Lee Young Ho You Kyung Hyun Ko 《Applied Surface Science》2005,252(5):1891-1898
Al-Al2O3 composite coatings with different Al2O3 particle shapes were prepared on Si and Al substrate by cold spray. The powder compositions of metal (Al) and ceramic (Al2O3) having different sizes and agglomerations were varied into ratios of 10:1 wt% and 1:1 wt%. Al2O3 particles were successfully incorporated into the soft metal matrix of Al. It was found that crater formation between the coatings and substrate, which is typical characteristic signature of cold spray could be affected by initial starting Al2O3 particles. In addition, when the large hard particles of fused Al2O3 were employed, the deep and big craters were generated at the interface between coatings and hard substrates. In the case of pure soft metal coating such as Al on hard substrate, it is very hard to get proper adhesion due to lack of crater formation. Therefore, the composite coating would have certain advantages. 相似文献
44.
45.
μ子动量谱的精确测量是L3C宇宙线实验最重要的目标之一.事例重建的好坏是该测量的关键,而能量确定的衰变为双μ子的事例是检验重建程序的最好手段.该数据分析利用在2000年中获取的数据作为样本,筛选出了LEP在2000年4月、5月、8月和9月等Z0能量运行期间L3C宇宙线实验数据中记录的Z0→μ+μ-事例数据,得到通过重建程序后动量为45GeV的μ子动量分辨率为(5.4?7±0.25)%. 相似文献
46.
47.
48.
Finite element analysis of fluid flow with moving free surface has been performed in 2‐D and 3‐D. The new VOF‐based numerical algorithm that has been proposed by the present authors (Int. J. Numer. Meth. Fluids, submitted) was applied to several 2‐D and 3‐D free surface flow problems. The proposed free surface tracking scheme is based on two numerical tools; the orientation vector to represent the free surface orientation in each cell and the baby‐cell to determine the fluid volume flux at each cell boundary. The proposed numerical algorithm has been applied to 2‐D and 3‐D cavity filling and sloshing problems in order to demonstrate the versatility and effectiveness of the scheme. The proposed numerical algorithm resolved successfully the free surfaces interacting with each other. The simulated results demonstrated applicability of the proposed numerical algorithm to the practical problems of large free surface motion. It has been also demonstrated that the proposed free surface tracking scheme can be easily implemented in any irregular non‐uniform grid systems and can be extended to 3‐D free surface flow problems without additional efforts. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
49.
50.
第Ⅰ种强度不对称三态叠加多模叠加态光场N次方Y压缩—第一正交相位分量的压缩情况 总被引:2,自引:0,他引:2
根据量子力学中的线性叠加原理,构造了由三个强度不等的多模相干态光场|{Zj(A)}>q、|{Zj(B)}>q和|{Zj(C)}>q的线性叠加所组成的第Ⅰ种强度不对称三态叠加多模叠加态光场|ψl(ABC)>q.利用多模压缩态理论,研究了态|ψl(ABC)>q的第一正交方分量(即磁场分量)的广义非线性等幂次N次方Y压缩特性.结果发现:①在上述各多模相干态光场中各模的强度和各模的初始相位各不相等的情况下,态|ψl(ABC)>q的第一正交分量-磁场分量在一定的条件下,总可呈现出周期性变化的、任意等幂次的N次方Y压缩效应;②当上述各多模相干态光场的强度和各模的初始相位相等时,态|ψl(ABC)>q的磁场分量的N次方Y压缩现象消失,态|ψl(ABC)>q可恒处于等幂次N-Y最小测不准态. 相似文献