全文获取类型
收费全文 | 8970篇 |
免费 | 765篇 |
国内免费 | 222篇 |
专业分类
系统科学 | 1228篇 |
丛书文集 | 95篇 |
教育与普及 | 84篇 |
理论与方法论 | 306篇 |
现状及发展 | 892篇 |
研究方法 | 14篇 |
综合类 | 7338篇 |
出版年
2024年 | 19篇 |
2023年 | 46篇 |
2022年 | 79篇 |
2021年 | 114篇 |
2020年 | 63篇 |
2019年 | 27篇 |
2018年 | 764篇 |
2017年 | 793篇 |
2016年 | 488篇 |
2015年 | 131篇 |
2014年 | 161篇 |
2013年 | 135篇 |
2012年 | 406篇 |
2011年 | 1086篇 |
2010年 | 929篇 |
2009年 | 591篇 |
2008年 | 686篇 |
2007年 | 898篇 |
2006年 | 152篇 |
2005年 | 166篇 |
2004年 | 210篇 |
2003年 | 235篇 |
2002年 | 129篇 |
2001年 | 85篇 |
2000年 | 104篇 |
1999年 | 176篇 |
1998年 | 159篇 |
1997年 | 153篇 |
1996年 | 149篇 |
1995年 | 140篇 |
1994年 | 107篇 |
1993年 | 86篇 |
1992年 | 94篇 |
1991年 | 94篇 |
1990年 | 73篇 |
1989年 | 79篇 |
1988年 | 60篇 |
1987年 | 42篇 |
1986年 | 24篇 |
1985年 | 15篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1967年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有9957条查询结果,搜索用时 15 毫秒
981.
LIANG Yan ZUO JianRu YANG WeiCai 《科学通报(英文版)》2007,52(13):1729-1733
Arabidopsis thaliana, a model plant species, has a number of advantages over other plant species as an experimental organism due to many of its genetic and genomic features. The Chinese Arabidopsis community has made significant contributions to plant biology research in recent years[1,2]. In 2006, studies of plant biology in China received more attention than ever before, especially those pertaining to Arabidopsis research. Here we briefly summarize recent advances in Arabidopsis re-search in China. 相似文献
982.
LU Zhengding WEN Zhumu TANG Zhuo LI Ruixuan 《武汉大学学报:自然科学英文版》2007,12(5):955-960
This paper proposes a method to formalize the interoperation in multi-domain environment. Through employing the algebra method, we conclude four types of the conflicts for the interoperation, and analyzes the cause of the policy conflicts. For each type of conflicts, we formalize it and proposes the method of detection and resolution. Finally, the method is illuminated be effective through comparing our work with others. 相似文献
983.
己被国内地质学界广为重视的黔西南地区微粒侵染型金矿,矿床的分布和富集严格受低角度断层控制。笔者从地壳内多层滑脱的观点出发,结合研究区的典型矿床实例,将该区域内不同矿区,不同控矿特征的金矿床,纳入地壳浅部多层滑脱构连的统一模式中进行讨论,并据此对深部原生矿产富集的有利部位进行了预测分析。本文的目的在于,通过黔西南地区地壳浅层构造的理论分析,为该区的金矿普查与勘探提供一条新的思路。 相似文献
984.
本工作利用灌流技术观察了3种脑-肠肽(P物质,CCK及NT)对新鲜人工流产的绒毛hCG分泌的影响。结果表明,P物质,CCK及NT均明显刺激绒毛释放hCG,并发现CCK作用大于P物质及NT。提示,hCG的分泌可能受这3种脑-肠肽的调节。 相似文献
985.
研究被孢霉生产γ-亚麻酸的方法,并通过诱变获得了GLA大幅度提高的高产菌株。 相似文献
986.
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
987.
<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
988.
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
989.
<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
990.
Ni-and Cu-free Zr-Al-Co-Nb glassy alloys with different Nb and Co contents were synthesized by melt spinning and copper mold casting.The effects of Nb addition to partially replace Co in the Zr55Al20Co25 glassy alloy on the glass-forming ability,thermal properties,in-vitro biocorrosion behavior and surface wettability of the metallic glasses were investigated.Although addition of Nb up to 5 at.% slightly decreased the supercooled liquid region and the glass-forming ability(GFA),the alloys could be casted in a bulk glassy rod form with diameters up to 3mm.The Zr-Al-Co-Nb glassy alloys were spontaneously passivated with low passive current densities in phosphate buffered saline and Hanks’ solution.Substitution of "toxic" Co by Nb is effective in improved the corrosion resistance of the Zr-Al-Co glassy alloy.Water contact angle measurements showed that Nb addition increased the hydrophilicity of the glassy alloys,which may enhance cell adhesion of the alloys in biomedical applications. 相似文献