全文获取类型
收费全文 | 6202篇 |
免费 | 2205篇 |
国内免费 | 1293篇 |
专业分类
化学 | 1704篇 |
晶体学 | 262篇 |
力学 | 1236篇 |
综合类 | 194篇 |
数学 | 270篇 |
物理学 | 6034篇 |
出版年
2024年 | 58篇 |
2023年 | 194篇 |
2022年 | 263篇 |
2021年 | 218篇 |
2020年 | 182篇 |
2019年 | 212篇 |
2018年 | 128篇 |
2017年 | 228篇 |
2016年 | 238篇 |
2015年 | 270篇 |
2014年 | 675篇 |
2013年 | 429篇 |
2012年 | 397篇 |
2011年 | 473篇 |
2010年 | 425篇 |
2009年 | 515篇 |
2008年 | 583篇 |
2007年 | 400篇 |
2006年 | 393篇 |
2005年 | 363篇 |
2004年 | 333篇 |
2003年 | 427篇 |
2002年 | 395篇 |
2001年 | 318篇 |
2000年 | 260篇 |
1999年 | 200篇 |
1998年 | 153篇 |
1997年 | 128篇 |
1996年 | 131篇 |
1995年 | 168篇 |
1994年 | 109篇 |
1993年 | 71篇 |
1992年 | 81篇 |
1991年 | 75篇 |
1990年 | 66篇 |
1989年 | 69篇 |
1988年 | 27篇 |
1987年 | 18篇 |
1986年 | 8篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1979年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有9700条查询结果,搜索用时 15 毫秒
51.
series of chitosan samlpes with 91% deacetylation but different molecular weight were obtained by varying the time of chitosan solution in acetic acid aqueous solution at 70℃.The viscosities and flow behavior of the concentrated solutions of chitosan were investigated in 10% (vol%) formic acid aqueous solution after the solutions were prepared for two days by using RPX-705 Rheopexy Analyzer.For each chitosan sample,at the concentration of 3.5 g/100ml,the log (ηr/η0)versus lgγη0,M curves superimpose each other within the same rheogramme. Then the relationship between log nr and lgM was studied under different shear rates.For the highest M sample, the experimental data deviate from the straight lines greatly. This was because the chitosan chain degradated in acid solution during dissolving. The molecular weights were measured in acid solution after two days of dissolving, they were right on their own straight lines. However,no obvious degradation was observed after two days in the same solution for the other lower M chitosan sam-ples. In addition, the plot of nr against M was not a straight line,probaly due to particular interaction of chitosan. 相似文献
52.
Ga^3+的新萃取体系的界面特性和胶团化作用研究 总被引:1,自引:0,他引:1
研究了Ga~(3+)协萃体系(Ga~(3+)-D_2EHPA-H_2MPA-正十二烷-H_2SO_4)的界面吸附和胶团形成热力学,发现该萃取体系中[H_2MPA]影响D_2EHPA和H_2MPA的界面吸附性质。在中、高[H_2MPA]范围内D_2EHPA与H_2MPA的界面吸附行为相反,D_2EHPA的存在也影响H_2MPA的界面吸附行为。研究了界面张力与各因素关系的数学模型,并获得某些胶团形成和界面吸附特性的物化参数。 相似文献
53.
ZHU Zhi-cheng SUN Mei ZHANG Xing-yi LIU Ke-xiang SHI Dong-lei LI Jin-dong SU Ji-quan XU Yue-chi FU Xue-qi 《高等学校化学研究》2007,23(3):289-296
This study objective was to express and characterize the catalytic domain of the human T cell protein tyrosine phosphatase(△TC-PTP) and to study immunohistochemically the expression of △TC-PTP in human non-small cell lung cancers. △TC-PTP gene was PCR amplified with the cDNA of human TC-PTP as template, and cloned into the pT7 expression vector. The recombinant pT7-△TC-PTP was expressed in E. coli Rosetta ( DE3 ) host cells and puri- fied. The enzymatic characteristics of △TC-PTP including enzyme activity and kinetics assay were measured. The antiserum was prepared by immunizing rabbit with the purified recombinant △TC-PTP. Rabbit polyclonal antibody against △TC-PTP was purified by PVDF immobilized antigen affinity chromatography. Immunohistochemical staining of lung cancer tissues was performed with antibody against △TC-PTP protein. △TC-PTP gene was correctly cloned, expressed, and purified. The recombinant △TC-PTP had a highly catalytic activity of PTPase. Squamous cell lung carcinoma showed a significantly higher expression rate of △TC-PTP (76. 92%, 10/13 ) than adenocarcinoma (57.14%, 4/7) and normal lung tissue(20%, 1/5 ). This study represents the first demonstration that △TC-PTP is highly expressed in human squamous cell lung carcinomas. In addition, this study provides an important basis for further studying the biological function of TC-PTP and its relationship with lung carcinomas and other diseases. 相似文献
54.
粘度国家基准装置测量结果的不确定度 总被引:1,自引:1,他引:1
分析粘度国家基准装置测量结果不确定度的来源并进行评定。影响粘度国家基准装置测量不确定度的主要因素有温度、时间、表面张力、空气浮力以及动能修正等。根据2002年粘度国家基准量值复测的结果,以及改造后新基准装置和辅助设备的状态,计算得粘度国家基准装测量结果的扩展不确定度为0.038%-0.4%。 相似文献
55.
56.
57.
用柠檬酸盐法合成出La_(1-_x)Sr_xFeO_3(x=0.1,0.2,0.3,0.4)原粉,再经固相反应得到纳米晶粉末,用TG、DTA、XRD、IR进行了表征,确证复合氧化物La_(1-_x)Sr_xFeO_3为钙钛矿型结构,粒径在10~25nm之间。实验结果表明,随着固相反应条件不同,产物粒径呈规律性变化.气敏特性研究表明,该纳米晶材料对乙醇有较高的选择性和灵敏度,其选择性顺序为La_(0.9)Sr_(0.1)FeO_3>LaFeO_3>LaFeO_3(大晶粒)。 相似文献
58.
本文提出了从未知样品的特性粘数和GPC图谱计算重均分子量的新方法,该方法可用于计算窄分布和宽分布的未知Mark-Houwink 常数的样品的重均分子量。用七个不同分子量和不同分布的实例验证了所提出的方法。结果与已知Mark-Houwink常数用普适校准法得到的结果一致。 相似文献
59.
Organic photovoltaic (OPV) cells were fabricated via vacuum vapor deposition with {4-[2-(3-di-cyanomethylidene-5,5-dimethylcyclohexenyl)vinyl]phenyl}di(1-naphthyl)amine (DNP-2CN) as the electron donor, and fullerene (C60) as the electron acceptor. A thin film (10 nm) of tris(8-quinolinolato)aluminum (Alq3) was adopted as the buffer layer. A device based on this DNP-2CN exhibited an open circuit voltage (Voc) of 370 mV, a short-circuit current density (Jsc) of 0.61 mAocm 2, and a white-light power conversion efficiency ( η) of 0.09% (AM1.5, 75 mW.cm^- 2). 相似文献
60.
磁化作用对汽油动态挥发性影响的研究 总被引:1,自引:0,他引:1
用热重(TG)分析和自行设计的原位动态挥发实验,研究了在不同条件下汽油的挥发性,结果表明,磁化空气或磁化汽油都可提高汽油的挥发性,而汽油和空气共同磁化,可更大幅度地提高汽油的挥发性。 相似文献