全文获取类型
收费全文 | 8024篇 |
免费 | 1269篇 |
国内免费 | 1021篇 |
专业分类
化学 | 4275篇 |
晶体学 | 42篇 |
力学 | 462篇 |
综合类 | 36篇 |
数学 | 794篇 |
物理学 | 2583篇 |
无线电 | 2122篇 |
出版年
2024年 | 23篇 |
2023年 | 207篇 |
2022年 | 241篇 |
2021年 | 264篇 |
2020年 | 263篇 |
2019年 | 294篇 |
2018年 | 228篇 |
2017年 | 238篇 |
2016年 | 353篇 |
2015年 | 385篇 |
2014年 | 392篇 |
2013年 | 478篇 |
2012年 | 676篇 |
2011年 | 685篇 |
2010年 | 503篇 |
2009年 | 437篇 |
2008年 | 539篇 |
2007年 | 476篇 |
2006年 | 454篇 |
2005年 | 420篇 |
2004年 | 331篇 |
2003年 | 241篇 |
2002年 | 234篇 |
2001年 | 197篇 |
2000年 | 168篇 |
1999年 | 196篇 |
1998年 | 175篇 |
1997年 | 168篇 |
1996年 | 176篇 |
1995年 | 164篇 |
1994年 | 108篇 |
1993年 | 97篇 |
1992年 | 87篇 |
1991年 | 76篇 |
1990年 | 80篇 |
1989年 | 61篇 |
1988年 | 45篇 |
1987年 | 28篇 |
1986年 | 36篇 |
1985年 | 31篇 |
1984年 | 14篇 |
1983年 | 10篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
181.
182.
Wenjie Jin Sungbo Cho Namujila Laxi Terigele Bao Lili Dai Hongzhen Yu Rigeer Qi Junqing Zhang Genna Ba Minghai Fu 《Molecules (Basel, Switzerland)》2022,27(10)
Ixeris chinensis (Thunb.) Nakai (IC) is a folk medicinal herb used in Mongolian medical clinics for the treatment of hepatitis and fatty liver diseases even though its pharmacological mechanism has not been well characterized. This study investigated the hepatoprotective mechanism of IC on mice with nonalcoholic fatty liver disease (NAFLD) by integrating gut microbiota and metabolomic analysis. A high-fat diet (HFD) was used to develop nonalcoholic fatty liver disease, after which the mice were treated with oral IC (0.5, 1.5 and 3.0 g/kg) for 10 weeks. HFD induced NAFLD and the therapeutic effects were characterized by pathological and histological evaluations, and the serum indicators were analyzed by ELISA. The gut microbial and metabolite profiles were studied by 16S rRNA sequencing and untargeted metabolomic analysis, respectively. The results showed that the administration of IC resulted in significant decreases in body weight; liver index; serum biomarkers such as ALT, TG, and LDL-C; and the liver inflammatory factors IL-1β, IL-6, and TNF-α. The 16S rRNA sequencing results showed that administration of IC extract altered both the composition and abundance of the gut microbiota. Untargeted metabolomic analysis of liver samples detected a total of 212 metabolites, of which 128 were differentially expressed between the HFD and IC group. IC was found to significantly alter the levels of metabolites such as L-glutamic acid, pyridoxal, ornithine, L-aspartic acid, D-proline, and N4-acetylaminobutanal, which are involved in the regulation of glutamine and glutamate, Vitamin B6 metabolism, and arginine and proline metabolic pathways. Correlation analysis indicated that the effects of the IC extract on metabolites were associated with alterations in the abundance of Akkermansiaceae, Lachnospiraceae, and Muribaculaceae. Our study revealed that IC has a potential hepatoprotective effect in NAFLD and that its function might be linked to improvements in the composition of gut microbiota and their metabolites. 相似文献
183.
Jie Wang Yuntian Xing Yang Dai Yingnan Li Wenyan Xiang Jianrong Dai Fei Xu 《Molecules (Basel, Switzerland)》2022,27(13)
Pomacea canaliculata, one of the 100 most destructive invasive species in the world, and it is an important intermediate host of Angiostrongylus cantonensis. The molluscicides in current use are an effective method for controlling snails. However, most molluscicides have no slow-release effect and are toxic to nontarget organisms. Thus, these molluscicides cannot be used on a large scale to effectively act on snails. In this study, gelatin, a safe and nontoxic substance, was combined with sustained-release molluscicide and was found to reduce the toxicity of niclosamide to nontarget organisms. We assessed the effects of gelatin and molluscicide in controlling P. canaliculata snails and eggs. The results demonstrated that the niclosamide retention time with 1.0% and 1.5% gelatin sustained-release agents reached 20 days. Additionally, the mortality rate of P. canaliculata and their eggs increased as the concentration of the niclosamide sustained-release agents increased. The adult mortality rate of P. canaliculata reached 50% after the snails were exposed to gelatin with 0.1 mg/L niclosamide for 48 h. The hatching rate of P. canaliculata was only 28.5% of the normal group after the treatment was applied. The sustained-release molluscicide at this concentration was less toxic to zebrafish, which means that this molluscicide can increase the safety of niclosamide to control P. canaliculata in aquatic environments. In this study, we explored the safety of using niclosamide sustained-release agents with gelatin against P. canaliculata. The results suggest that gelatin is an ideal sustained-release agent that can provide a foundation for subsequent improvements in control of P. canaliculata. 相似文献
185.
186.
187.
TD-SCDMA和WCDMA系统基站的共容分析 总被引:3,自引:0,他引:3
戴玉强 《电信工程技术与标准化》2008,21(11):40-43
主要探讨了WCDMA系统与TD-SCDMA系统基站间的共存问题,并从邻频干扰的角度进行了深入的分析,采用确定性计算方法和静态仿真方法研究TD—SCDMA基站对WCDMA基站产生的邻频干扰,并提出相应的解决方法。 相似文献
188.
Yuanjie Li Jincheng Dai Zhongwei Si Kai Niu Chao Dong Jiaru Lin Sen Wang Yifei Yuan 《中国通信》2022,(3):70-87
Unsourced multiple access(UMA) is a multi-access technology for massive, low-power, uncoordinated, and unsourced Machine Type Communication(MTC) networks. It ensures transmission reliability under the premise of high energy efficiency.Based on the analysis of the 6G MTC key performance indicators(KPIs) and scenario characteristics,this paper summarizes its requirements for radio access networks. Following this, the existing multiple access models are analyzed under these standards to determine U... 相似文献
189.
工程应用中,平面微弹簧存在弹性系数的非线性现象且难以被忽略,弹簧结构的几何非线性是引起这种现象的主要原因。针对特定形状的弹簧运用Ansys软件进行了非线性有限元静力学仿真,计算出弹簧弹性力F与弹性形变x之间的对应关系,并与采用MEMS微细加工技术制得弹簧样品实测实验结果比较,相对误差低于3.2%,验证了分析模型的可靠性。而后设计了5种不同平面形状的微弹簧,仿真计算它们的力学性能曲线,以及改变弹簧臂宽度厚度后的力学性能曲线,分别进行比较以讨论影响非线性的主要因素,为弹簧的设计工作提供参考依据。 相似文献
190.
戴国胜 《电子科学学刊(英文版)》1989,6(1):34-41
New concepts of reducible independent cutset and reducible independent loop are developedthrough an analysis of the ladder network.A new analytic method,named structural analysis method,is pres-entod.It evaluates the controllability and observability of a network based on its structure rather than onits state equation.Some problems in the conventional network analysis can be solved using this method.Re-sults obtained by this method are in good agreement with those obtained by that of state space analysis,butthis method is much simpler in use.A practical example is given. 相似文献