全文获取类型
收费全文 | 4209篇 |
免费 | 509篇 |
国内免费 | 312篇 |
专业分类
化学 | 2534篇 |
晶体学 | 55篇 |
力学 | 148篇 |
综合类 | 15篇 |
数学 | 317篇 |
物理学 | 894篇 |
无线电 | 1067篇 |
出版年
2024年 | 7篇 |
2023年 | 59篇 |
2022年 | 64篇 |
2021年 | 136篇 |
2020年 | 128篇 |
2019年 | 148篇 |
2018年 | 114篇 |
2017年 | 103篇 |
2016年 | 179篇 |
2015年 | 216篇 |
2014年 | 249篇 |
2013年 | 315篇 |
2012年 | 353篇 |
2011年 | 326篇 |
2010年 | 240篇 |
2009年 | 259篇 |
2008年 | 286篇 |
2007年 | 238篇 |
2006年 | 204篇 |
2005年 | 208篇 |
2004年 | 141篇 |
2003年 | 150篇 |
2002年 | 140篇 |
2001年 | 94篇 |
2000年 | 66篇 |
1999年 | 69篇 |
1998年 | 54篇 |
1997年 | 39篇 |
1996年 | 30篇 |
1995年 | 37篇 |
1994年 | 33篇 |
1993年 | 20篇 |
1992年 | 21篇 |
1991年 | 21篇 |
1990年 | 17篇 |
1989年 | 13篇 |
1988年 | 6篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 10篇 |
1980年 | 25篇 |
1978年 | 25篇 |
1977年 | 48篇 |
1976年 | 18篇 |
1975年 | 18篇 |
1974年 | 11篇 |
1973年 | 6篇 |
1968年 | 5篇 |
1943年 | 10篇 |
排序方式: 共有5030条查询结果,搜索用时 15 毫秒
991.
992.
Depsides from Prunella vulgaris 总被引:5,自引:0,他引:5
IntroductionPrunella vulgaris L.(Labiatae) is a traditional Chinese drug and has hypotensive, antibacterial, anti-viral, anti-inflammatory, anti-tumor and hypoglycemic activities. Previously, the isolation and structural identification of a new triterpene saponin and five known compounds from the ethanol extracts of P. vulgaris were reported1. In this paper, we describe the isolation of four depsides and two phenylpropanoids from the same source. Their structures were established as butyl ro… 相似文献
993.
994.
Xue Li Jian‐Min Dou Ying Liu Lan‐Ying Zhu Pei‐Ju Zheng 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(10):1185-1187
The novel PtII–dibenzo‐18‐crown‐6 (DB18C6) title complex, μ‐[tetrakis(thiocyanato‐S)platinum(II)]‐N:N′‐bis{[2,5,8,15,18,21‐hexaoxatricyclo[20.4.0.19,14]hexacosa‐1(22),9(14),10,12,23,25‐hexaene‐κ6O]potassium(I)}, [K(C20H24O6)]2[Pt(SCN)4], has been isolated and characterized by X‐ray diffraction analysis. The structure analysis shows that the complex displays a quasi‐one‐dimensional infinite chain of two [K(DB18C6)]+ complex cations and a [Pt(SCN)4]2? anion, bridged by K+?π interactions between adjacent [K(DB18C6)]+ units. 相似文献
995.
带旋转自由度C^0类任意四边形板(壳)单元 总被引:5,自引:0,他引:5
基于Reissner-Mindilin板弯曲理论和Von-Karman大挠度理论,采用单元域内和边界位移插值一致性的概念,将四节点等参弯曲单元与Allman膜变形二次插值模式相结合,对层合板壳的大挠度分析提供了一种实用的带旋转自由度的四节点C^0类板单元。大量算例表明:该单元对板壳结构的线性强度、稳定性和后屈曲分析都表现出良好的收敛性和足够的工程精度。 相似文献
996.
毛细管电动色谱带电环糊精拆分N—FMOC氨基酸对映体 总被引:3,自引:0,他引:3
将负电性磺丁基-β-环糊精手性添加剂应用于毛细管电泳氨基酸对映体的拆分研究中,对8种氨基酸对映体与9-芴甲基氧基甲酰氯(FMOC-Cl)生成的衍生物进行了分离,其中5种得到了基线分离。考察了背景电解质pH值及磺丁基-β-环糊精的浓度对N-FMOC氨基酸对映体拆分的影响。 相似文献
997.
A novel scale of steric substituent constant EsD is defined from the correlation of the logarithms of the internal rotation rate (kr) at 393 K with Hancock (Esc) steric constant by means of dynamic NMR. In the inhibition of Pseudomona species lipase by 2,2′‐bis‐(N‐substituted carbamoylmethyl)biphenyls (1‐8), the logarithms of bimolecular rate constants are multiply correlated with both the Taft substituent constant σ* and EsD. 相似文献
998.
Kyukwan Zong Seung Il Shin Dong Ju Jeon Jung No Lee Eung K. Ryu 《Journal of heterocyclic chemistry》2000,37(1):75-78
3‐Aryl‐4‐methoxycarbonylisoxazoles were prepared from the reaction of a variety of substituted benzonitrile oxides with methyl 3‐(p‐nitrobenzoyloxy)acrylate in moderate to good yields. 相似文献
999.
A new on-chip interconnect crosstalk model and experimentalverification for CMOS VLSI circuit design
Yungseon Eo Eisenstadt W.R. Ju Young Jeong Oh-Kyong Kwon 《Electron Devices, IEEE Transactions on》2000,47(1):129-140
A new, simple closed-form crosstalk model is proposed. The model is based on a lumped configuration but effectively includes the distributed properties of interconnect capacitance and resistance. CMOS device nonlinearity is simply approximated as a linear device. That is, the CMOS gate is modeled as a resistance at the driving port and a capacitance at a driven port. Interconnects are modeled as effective resistances and capacitances to match the distributed transmission behavior. The new model shows excellent agreement with SPICE simulations. Further, while existing models do not support the multiple line crosstalk behaviors, our model can be generalized to multiple lines. That is, unlike previously published work, even if the geometrical structures are not identical, it can accurately predict crosstalk. The model is experimentally verified with 0.35-μm CMOS process-based interconnect test structures. The new model can be readily implemented in CAD analysis tools. This model can be used to predict the signal integrity for high-speed and high-density VLSI circuit design 相似文献
1000.
Kee Soo Nam Ju Wook Lee Sang-Gi Kim Tae Moon Roh Hoon Soo Park Jin Gun Koo Kyung Ik Cho 《Electron Device Letters, IEEE》2000,21(7):365-367
A novel simplified fabrication method of a very high density p-channel trench gate power MOSFET using four mask layers and nitride/TEOS sidewall spacers is realized. The proposed process showed improved on-resistance characteristics of the device with increasing cell density and the cost-effective production capability due to the lesser number of processing steps. By using this process technique, a remarkably increased high density (100 Mcell/inch2) trench gate power MOSFET with a cell pitch of 2.5 μm could be effectively realized. The fabricated device had a low specific on-resistance of 1.1 mΩ-cm2 with a breakdown voltage of -36 V 相似文献