全文获取类型
收费全文 | 5911篇 |
免费 | 630篇 |
国内免费 | 32篇 |
专业分类
系统科学 | 1095篇 |
丛书文集 | 9篇 |
教育与普及 | 37篇 |
理论与方法论 | 275篇 |
现状及发展 | 868篇 |
研究方法 | 2篇 |
综合类 | 4287篇 |
出版年
2024年 | 6篇 |
2023年 | 4篇 |
2022年 | 17篇 |
2021年 | 11篇 |
2020年 | 10篇 |
2019年 | 4篇 |
2018年 | 730篇 |
2017年 | 734篇 |
2016年 | 433篇 |
2015年 | 41篇 |
2014年 | 9篇 |
2013年 | 9篇 |
2012年 | 276篇 |
2011年 | 959篇 |
2010年 | 831篇 |
2009年 | 468篇 |
2008年 | 531篇 |
2007年 | 784篇 |
2006年 | 16篇 |
2005年 | 49篇 |
2004年 | 134篇 |
2003年 | 159篇 |
2002年 | 65篇 |
2001年 | 14篇 |
2000年 | 17篇 |
1999年 | 31篇 |
1998年 | 39篇 |
1997年 | 37篇 |
1996年 | 18篇 |
1995年 | 27篇 |
1994年 | 26篇 |
1993年 | 13篇 |
1992年 | 15篇 |
1991年 | 18篇 |
1990年 | 12篇 |
1989年 | 5篇 |
1988年 | 14篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有6573条查询结果,搜索用时 15 毫秒
51.
WANG Yi CHU Wuyang SU Yanjing GAO Kewei & QIAO Lijie Department of Materials Physics University of Science & Technology Beijing Beijing China 《科学通报(英文版)》2003,48(12):1203-1206
It is known that some types of ceramics, like Al2O3 and ZrO2, undergo stress corrosion cracking (SCC) or static fatigue fracture under static loading, ever in a rela-tively mild environment, such as moist atmosphere or water at room temperature, which leads to a time-dependent fracture[1—4]. For a transmission electron microscopy specimen of YBa2Cu3O7-x ceramics superconductor, SCC induced by residual stress can occur in an atmosphere with low moisture content[5]. For a lead zirconate ti… 相似文献
52.
Do multiple cycles of aeolian deposit-pedogenesis exist in the reticulate red clay sections in southern China? 总被引:4,自引:0,他引:4
HU Xuefeng CHENG Tianfan & WU Hexin Department of Environmental Science Engineering Shanghai Uni-versity Shanghai China Correspondence should be addressed to Hu Xuefeng 《科学通报(英文版)》2003,48(12):1251-1258
Since the Quaternary scientists successfully dis-closed the paleoclimatic significance of the loess-paleo- sol sequence in the Loess Plateau, Northwest China, the loess-paleosol sequence has become well-known terres-trial materials revealing the multiple cyclic changes of Quaternary climates. As a carrier of paleoenvironmental information, it could compare beauty with the deep ocean deposit[8]. In recent years, however, the researchers began to put their sights to southern China. They try t… 相似文献
53.
The age of formation of the mirabilite and sand wedges in the Hexi Corridor and their paleoclimatic interpretation 总被引:7,自引:0,他引:7
WANG Nai''''ang ZHANG Jianming CHENG Hongyi GUO Jianying & ZHAO Qiang . College of Earth Environment Sciences Lanzhou University Lanzhou China . Cold Arid Regions Environmental Engineering Research Institute Chinese Academy of Sciences Lanzhou China 《科学通报(英文版)》2003,48(14):1439-1445
The Hexi Corridor is located at the transition zone of the Asian summer monsoon and westerly airflow, and lies in an important position in terms of its ecological fragility and climatic sensitivity. During a recent field expedition to this region, we found a sedimentary mirabilite layer in a number of localities including Suwushan, Yanchi, Baitujing, Yanchi Gaotai, Huahai, Yumen, Halanuo扙r, and Dunhuang (Fig. 1), which have the potential to provide important information about environmenta… 相似文献
54.
YANGBao A.Braeuning SHIYafeng ZHANGJiawu 《科学通报(英文版)》2003,48(14):1446-1450
The paleoclimate data recovered from ice cores,tree rings and lake sediments indicate regional features of cfimatic change on the Tibeta n Plateau (TP) during the last 2000 years. The composite temperature reconstructions in-dicate that several main climatic episodes, such as the “LittleIce Age“ between 1400 and 1900, the “Medieval Warm Pe-riod“ in 1150-1400, a less warm period in 800-1100, and an earlier cold period between the 3rd and 5th centuries,occurred in the TP. In addition, temperature varied from region to region. The period from AD 800 to 1100, which waswarm in northeastern TP, was contemporaneous with cool-ing in the western and southern TP. The southern TP ex-perienced warming between 1150 and 1400. For western TP,the δ^18O records of the Guliya ice core indicate that the pe-Hod 1250-1500 witnessed a clear warming. Large-scaletrends in the temperature history from northeastern TP aremore similar to those in eastern China than are the trendsfrom the Guliya ice cap far to the west and southern TP. The most prominent similarities between the temperature varia-tions of the TP and eastern China are such cold phases as 1100-1150, 1500-1550, 1650-1700 and 1800-1850, andthe latter three cold events match with three widespreadg lacial advances which occurred on the TP during the Little Ice A2e. 相似文献
55.
WUGuang ZHOUChunyuan ZENGHeping 《科学通报(英文版)》2003,48(16):1704-1708
We introduce a stable, long-distance singlephoton Sagnac interferometer, which has a balanced configuration to efficiently compensate phase drift caused by change of the fiber-optic path. By using time-division phase modulation, single-photon interference was realized at 1550nm in a 5-km-long as well as 27-km-long Sagnac fiber loops,with a fringe visibility higher than 90% and long-term stability. The stable performance of the single-photon interference indicated that the time-division phase-modulated Sagnac interferometer might readily lead to practical applications in single-photon routing and quantum cryptography. 相似文献
56.
57.
ZHUHuanzhang CHENXiaoguang LIFeng GONGJuli XUEJinglun 《科学通报(英文版)》2003,48(20):2196-2200
To explore the expression of human clotting factor Ⅸ (hFⅨ) cDNA in vitro and the feasibility of gene therapy for hemophilia B mice mediated by recombinant lentiviral vector, a recombinant hFⅨ lentiviral vector driven by ubiquitin-C promoter, FUXW, and by ABP liver specific promoter, FAXW, was constructed respectively. Recombinant lentivirus was harvested from 293T cells by calcium phosphate-mediated transient cotransfection of three plasmids (transgene vector, CMV腞8.2, VSV-G). hFⅨ expression was detected in supernatant of 293T, BHK and L-02 cells infected with FUXW virus, whereas higher expression of hFⅨ levels (630 ng/106 cells/48 h) was detected only in L-02 cells infected with FAXW virus. Serum hFⅨ antigen was detected in all hemophilia B mice treated with FAXW virus by tail vein injection, an efficiency level of hFⅨ was observed (45 ng/mL, approximately 1% of normal human levels), the expression lasted for more than 60 d. The results indicated that HIV-based lentiviral vectors offer a promising approach to the gene therapy of hemophilia B. 相似文献
58.
低饱和场巨磁电阻金属多层膜Ni80Fe20/Cu的结构与磁电阻 总被引:1,自引:0,他引:1
采用磁控溅射方法,获得了具有低饱和场巨磁电阻的Ni80Fe20/Cu金属多层膜,在室温下,其磁电阻和层间耦合状态随Cu层厚度的增加呈振荡变化,在Cu层厚度tCu=1.0nm,2.2nm时磁电阻出现2个峰值分别为19.4%和11.7%,饱和场约为6.4×10^4A/m和8×10^3A/m低温下(77K)磁电阻为33.2%和27.6%,系统地研究了NiFe层厚度和周期数对多层膜磁电阻的影响,用真空退火 相似文献
59.
考察了HDEHP在不同稀释剂中对Zn(Ⅱ)的萃取平衡,探讨了萃取平衡常数与稀释剂性质间的关系,建立了平衡常数与稀释剂极性参数(DP和S)间的经验方程.求得萃合物ZnA2·2HA的溶解度参数为16.5J1/2.cm-3/2. 相似文献
60.
提出了一种新型的开环自适应解耦控制器。该控制算法将简化解耦原理应用于自适应系统,可实现静态解耦和动态近似解耦,给出了当系统存在有界扰动、未建模动态和解耦残差时的鲁棒性分析。利用动态补偿和按区域极点配置两种方法,得到了可以提高鲁棒解耦算法暂态性的一些初步结果。 相似文献