全文获取类型
收费全文 | 5822篇 |
免费 | 890篇 |
国内免费 | 1314篇 |
专业分类
化学 | 5003篇 |
晶体学 | 98篇 |
力学 | 333篇 |
综合类 | 131篇 |
数学 | 692篇 |
物理学 | 1769篇 |
出版年
2024年 | 21篇 |
2023年 | 137篇 |
2022年 | 204篇 |
2021年 | 226篇 |
2020年 | 284篇 |
2019年 | 284篇 |
2018年 | 209篇 |
2017年 | 257篇 |
2016年 | 323篇 |
2015年 | 319篇 |
2014年 | 376篇 |
2013年 | 474篇 |
2012年 | 521篇 |
2011年 | 560篇 |
2010年 | 360篇 |
2009年 | 397篇 |
2008年 | 403篇 |
2007年 | 327篇 |
2006年 | 311篇 |
2005年 | 294篇 |
2004年 | 219篇 |
2003年 | 238篇 |
2002年 | 275篇 |
2001年 | 230篇 |
2000年 | 158篇 |
1999年 | 136篇 |
1998年 | 65篇 |
1997年 | 40篇 |
1996年 | 54篇 |
1995年 | 57篇 |
1994年 | 56篇 |
1993年 | 44篇 |
1992年 | 24篇 |
1991年 | 18篇 |
1990年 | 26篇 |
1989年 | 15篇 |
1988年 | 9篇 |
1987年 | 16篇 |
1986年 | 19篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1959年 | 4篇 |
1957年 | 5篇 |
1936年 | 2篇 |
排序方式: 共有8026条查询结果,搜索用时 15 毫秒
961.
Low-bandgap donor-acceptor conjugated polymer sensitizers for dye-sensitized solar cells 总被引:1,自引:0,他引:1
A set of two donor-acceptor type conjugated polymers with carboxylic acid side groups have been synthesized and utilized as active materials for dye-sensitized solar cells (DSSCs). The polymers feature a π-conjugated backbone consisting of an electron-poor 2,1,3-benzothiadiazole (BTD, acceptor) unit, alternating with either a thiophene-fluorene-thiophene triad (2a) or a terthiophene (3a) segment as the donor. The donor-acceptor polymers absorb broadly throughout the visible region, with terthiophene-BTD polymer 3a exhibiting an absorption onset at approximately 625 nm corresponding to a ~1.9 eV bandgap. The polymers adsorb onto the surface of nanostructured TiO(2) due to interaction of the polar carboxylic acid units with the metal oxide surface. The resulting films absorb visible light strongly, and their spectra approximately mirror the polymers' solution absorption. Interestingly, a series of samples of 3a with different molecular weight (M(n)) adsorb to TiO(2) to an extent that varies inversely with M(n). DSSCs that utilize the donor-acceptor polymers as sensitizers were tested using an I(-)/I(3)(-) electrolyte. Importantly, for the set of polymer sensitizers 3a with varying M(n), the DSSC efficiency varies inversely with M(n), a result that reflects the difference in adsorption efficiency observed in the film absorption experiments. The best DSSC cell tested is based on a sample of 3a with M(n) ~ 4000, and it exhibits a ~65% peak IPCE with J(sc) ~12.6 mA cm(-2) under AM1.5 illumination and an overall power conversion efficiency of ~3%. 相似文献
962.
Shi H Fang L Tan C Shi L Zhang W Li CC Luo T Yang Z 《Journal of the American Chemical Society》2011,133(38):14944-14947
Development of a gold-catalyzed tandem reaction of 1,7-diynes with both internal and external nucleophiles was realized, which constructed five chemical bonds, two rings, and two stereogenic centers in a single step. Based on the novel cascade transformation, we achieved a unified strategy toward the stereoselective total syntheses of C-15 oxygenated drimane-type sesquiterpenoids and their analogues, which provided the natural products kuehneromycin A, antrocin, anhydromarasmone, and marasmene as a proof-of-concept study. 相似文献
963.
用等体积浸渍法制备了SBA-15担载的钒基氧化物催化剂,使用X射线衍射(XRD)分析、氮气吸附、紫外激光拉曼、傅里叶变换红外(FTIR)光谱和紫外-可见漫反射(UV-Vis DRS)光谱对催化剂的结构进行了表征,并评价了催化剂对丙烷选择氧化的活性与选择性.实验结果表明SBA-15载体对丙烷选择氧化的活性优于常规的SiO2载体.SBA-15担载的低载量催化剂是高分散的催化剂体系,在低钒载量(n(V)/n(Si)<2.5%)时,催化剂具有规则的六方介孔结构.低钒载量(n(V)/n(Si)<0.1%)时,隔离四配位的钒氧化物是丙烷选择氧化生成醛类化合物的活性物种;高钒载量(n(V)/n(Si)>2.5%)时,聚合六配位的钒氧化物和微晶钒氧化物是丙烷脱氢或深度氧化的活性物种. 相似文献
964.
Yun Chuan Xiao Jing Xie Min Yu Miao Liu Jian Ran Zhen Xi Wei Li Jing Huang 《中国化学快报》2011,22(12):1457-1460
A new skeleton bisabolane-type sesquiterpene curcuminoid,bisabocurcumin(1),along with 5 known compounds,curcumin(2), demethoxycurcumin(3),bidemethoxycurcumin(4),(1E,4E)-1,5-bis(4-hydroxy-3-methoxyphenyl)-penta-1,4-dien-3-one(5),and (1E,4E)-1-(4-hydroxy-3-methoxyphenyl)-5-(4-hydroxy phenyl-)-penta-1,4-dien-3-one(6)were isolated from the rhizomes of Curcuma longa L.Their structures were determined on the basis of spectroscopic analysis.Bisabocurcumin(1) is firstly obtained from nature with a new skeleton combined by a bisabolane-type sesquiterpene and a 1,7-diphenylheptanoid through a C-C bond. 相似文献
965.
Zhi Guo Qiao Tian Hua Shen Zhen Fang Fu Jun Qi Li Hong Wang Qing Bao Song 《中国化学快报》2011,22(11):1265-1268
A series of C2-symmetric and asymmetric chiral thiourea derivatives were synthesized from commercial L-phenylalanine.All of the new compounds have been fully characterized by IR,1H NMR,13C NMR,MS spectra and elemental analyses.The chiral thioureas were used as chiral ligands in the catalytic enantioselective ethylation of aldehydes with diethylzinc,the corresponding sec-alcohols were gained with excellent enantioselectivities(up to 87.1%ee) and high yields(up to 76.7%) after the conditions were optimized. 相似文献
966.
967.
The waterborne polyurethane (WPU) was synthesized from the polycondensation between isophorone diisocyanate (IPDI) and polyoxypropylene glycol (N‐210) and then dispersed into water. Subsequently, the WPU emulsion was modified with antimony doped tin oxide (ATO) nanoparticle by ultrasonic dispersion. The ATO/WPU emulsion was cast onto Teflon molds. After being dried, ATO/WPU films were prepared. TEM indicated that the ATO nanoparticles were homogeneously dispersed in the polymer matrix at the nanometer scale. DSC showed that the ATO/WPU nanocomposites displayed increased glass transition temperatures compared to the control WPU. The mechanical properties of the films were characterized by dynamic‐mechanical analysis (DMA). The higher glass transition temperature and storage modulus indicates the superior mechanical properties of WPU modified by ATO nanoparticles over the conventional unmodified WPU. The thermal behaviors of the films were evaluated by thermogravimetric analysis (TGA). It could be found that the incorporation of ATO into WPU can improve the thermal stability dramatically. The results from UV–visible–near infrared spectra indicated that the ATO/WPU films could decrease the infrared transmission effectively. The heat‐insulation measurements showed that glass coated with ATO/WPU films possessed better heat‐insulating effect than empty glass. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
968.
Jiamei Liu Fang Wang Zhen Li Jianwei Zhou Jing Chen Chungu Xia 《Structural chemistry》2011,22(5):1119-1130
A new zwitterion containing 1,1,3,3-tetramethylguanidine was synthesized using a simple method, and the physicochemical properties
as well as the crystal structure of the compound were also studied. Two new acidic ionic liquids (ILs) were synthesized using
the zwitterion as the precursor and the physicochemical properties including density, viscosity, thermal property, and acidic
scale of the ILs were investigated. A density functional theory investigation of the geometrical structures and electronic
properties of the guanidinium triflate ionic liquid was also presented for better understanding the new ILs. 相似文献
969.
Hollow micron-sized poly(styrene-co-divinylbenzene) particles were produced in seeded emulsions in the presence of swelling solvents. The size and morphology
of the resulting polymer particles can be altered by varying swelling solvent in seeded polymerization at elevated temperature.
The effects of swelling agents, including hydrophobic solvents, hydrophilic solvents and solvent mixtures, on the microstructure
of particles were investigated. The formation of hollow poly(styrene-co-divinylbenzene) particles depended significantly on a fast and effective phase separation between the cross-linked shell
and the swollen core, that occurred only in the presence of an appropriate swelling solvent. 相似文献
970.
Pyrene derivative 1 containing four trimethylsilylethynyl substituents was synthesized and investigated as a chromogenic and fluorescent chemodosimeter sensor for fluoride ions. 1 showed a high sensitivity and specific selectivity over a rapid response time toward fluoride anions compared to other anions, such as Cl(-), Br(-), ClO(4)(-), H(2)PO(4)(-) and HPO(4)(2-). TD-DFT calculations showed that the delocalization of the σ-electrons of the silicon destabilized the HOMO energy level of 1, thus red shifting both its absorption and emission spectrum. The addition of F(-) removed the trimethylsilyl substituents and resulted in a blue shift of both the absorption and fluorescent spectra of 1, which could be monitored by the color change with the naked-eye. Moreover, an easy to prepare test paper, which was obtained by immersing a filter paper into a THF solution of 1, could be utilized to detect and estimate the concentration of fluoride anions in water. 相似文献