全文获取类型
收费全文 | 8649篇 |
免费 | 708篇 |
国内免费 | 148篇 |
专业分类
系统科学 | 1166篇 |
丛书文集 | 62篇 |
教育与普及 | 68篇 |
理论与方法论 | 285篇 |
现状及发展 | 913篇 |
研究方法 | 27篇 |
综合类 | 6984篇 |
出版年
2024年 | 6篇 |
2023年 | 24篇 |
2022年 | 38篇 |
2021年 | 46篇 |
2020年 | 29篇 |
2019年 | 7篇 |
2018年 | 740篇 |
2017年 | 750篇 |
2016年 | 455篇 |
2015年 | 77篇 |
2014年 | 75篇 |
2013年 | 79篇 |
2012年 | 342篇 |
2011年 | 1050篇 |
2010年 | 894篇 |
2009年 | 559篇 |
2008年 | 624篇 |
2007年 | 887篇 |
2006年 | 105篇 |
2005年 | 153篇 |
2004年 | 227篇 |
2003年 | 218篇 |
2002年 | 144篇 |
2001年 | 98篇 |
2000年 | 114篇 |
1999年 | 197篇 |
1998年 | 175篇 |
1997年 | 182篇 |
1996年 | 173篇 |
1995年 | 169篇 |
1994年 | 158篇 |
1993年 | 132篇 |
1992年 | 114篇 |
1991年 | 100篇 |
1990年 | 79篇 |
1989年 | 92篇 |
1988年 | 67篇 |
1987年 | 54篇 |
1986年 | 30篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1970年 | 3篇 |
1969年 | 2篇 |
1968年 | 3篇 |
1967年 | 3篇 |
排序方式: 共有9505条查询结果,搜索用时 15 毫秒
951.
952.
导出了漂浮载体弹性机械臂系统约束方程和动力学方程,利用逐次近似法讨论了机械臂结构弹性和负载位姿的影响,提出消除弹性影响的控制方法,并通过算例加以说明。 相似文献
953.
溜井放矿在矿山生产中占有重要地位。溜井中滞流区矿石的频繁堵塞是影响正常生产的关键因素。本文从理论的角度阐述了矿石在溜井中的成拱原因及振动出矿的破拱机理,剖析了我国在大运量溜井中成功使用振动出矿机的最新经验;同时指出了以振动出矿为主要内容的溜井强化出矿新工艺对促进出矿自动化和连续化具有重大的意义。 相似文献
954.
The composite membranes with cellulose acetate (CA) as the separating layer material and polyacrylonitrile (PAN) as the supporting
layer material were prepared for separating caprolactam (CPL) from CPL/water mixtures by pervaporation technique. The swelling
experiments were carried out to investigate the effects of swelling time and CPL concentration on the degree of swelling.
The results showed that the CA membrane reached swelling equilibrium within 24 h, and the degree of swelling first slightly
decreased then increased with the increase of CPL concentration in the feed under the experimental conditions. Respectively
comparing flux with permeance, and separation factor with selectivity, we found out that the separation performance of the
CA/PAN composite membrane is more strongly dependent on its hydrophilic/hydrophobic nature as well as on the effects of operating
parameters, such as feed composition concentration and feed temperature. 相似文献
955.
<正> This paper considers the problem of actuator failure compensation for a class of nonlinearsystems in the form of output-feedback.MT-filters are exploited to estimate the unmeasured states.The backsteppping technique is used to construct the controller recursively.The proposed compensationscheme can grantee the boundedness of all the closed-loop signals and asymptotic output tracking.Thetheoretical results are illustrated by a simulation example. 相似文献
956.
957.
LI Li LU XiaoYu CAO ChongDe & DAI FuPing Department of Applied Physics Northwestern Polytechnical University Xi’an China 《科学通报(英文版)》2010,55(16):1674-1678
Solidification of Fe-7.5%Mo-16.5%Si ternary quasiperitectic alloy is investigated by using differential scanning calorimetry (DSC) and drop tube containerless processing techniques.The primary phase is identified as R (Fe5Mo3Si2) and the quasiperitectic phases are τ1 (Fe5MoSi4) and Fe3Si.With the decrease of droplet diameter, the cooling rate and undercooling of the droplets in-crease rapidly.The experiment result indicates that the solidification microstructure is composed of remnant primary phase, qua-sip... 相似文献
958.
<正> This paper discusses the null boundary controllability of two PDE's,modeling a compositesolid with different physical properties in each layer.Interface conditions are imposed. 相似文献
959.
Compared with traditional structure-based approaches for the identification of species-specific ligands, the ab initio approach, based on large-scale protein sequences from different species, has been used to locate specific sites that may be important to the molecular selectivity of species. Statistically significant differences in the distribution of residues in different species and differences in the physicochemical properties of residue-specific sites may largely account for species selectivity. The nicotinic acetylcholine receptor (nAChR), an important neuro-receptor with significantly different ligand selectivity in different species, was used to test our method. Because of the lack of nAChR structural information, the mechanism of ligand discrimination is unclear which hinders attempts at novel molecular design. In this study, the specific site residues 186 and 189 in the principal subunits and residues 34, 55, 56, 57, 106 and 112 in complementary subunits of nAChR were identified by applying our method with stringent statistical cutoffs. These sites were predicted to contribute to ligand selectivity and this result coincides well with the known experimental data. 相似文献
960.
分析了自整角机的工作原理及作为位置检测传感器的优缺点,指出了它在活动桥控制系统中作为检测元件所产生的问题,介绍了一种新型的高精度数字传感器—旋转编码器,并叙述了由旋转编码器构成的全数字化活动桥控制系统 相似文献