全文获取类型
收费全文 | 9629篇 |
免费 | 1320篇 |
国内免费 | 1159篇 |
专业分类
化学 | 7069篇 |
晶体学 | 121篇 |
力学 | 449篇 |
综合类 | 145篇 |
数学 | 1205篇 |
物理学 | 3119篇 |
出版年
2024年 | 32篇 |
2023年 | 174篇 |
2022年 | 338篇 |
2021年 | 349篇 |
2020年 | 366篇 |
2019年 | 417篇 |
2018年 | 348篇 |
2017年 | 331篇 |
2016年 | 481篇 |
2015年 | 450篇 |
2014年 | 594篇 |
2013年 | 676篇 |
2012年 | 794篇 |
2011年 | 805篇 |
2010年 | 578篇 |
2009年 | 542篇 |
2008年 | 648篇 |
2007年 | 533篇 |
2006年 | 498篇 |
2005年 | 417篇 |
2004年 | 371篇 |
2003年 | 299篇 |
2002年 | 360篇 |
2001年 | 293篇 |
2000年 | 206篇 |
1999年 | 161篇 |
1998年 | 117篇 |
1997年 | 88篇 |
1996年 | 100篇 |
1995年 | 100篇 |
1994年 | 90篇 |
1993年 | 59篇 |
1992年 | 52篇 |
1991年 | 72篇 |
1990年 | 45篇 |
1989年 | 34篇 |
1988年 | 23篇 |
1987年 | 32篇 |
1986年 | 23篇 |
1985年 | 29篇 |
1984年 | 14篇 |
1983年 | 22篇 |
1982年 | 16篇 |
1981年 | 14篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 13篇 |
1977年 | 9篇 |
1975年 | 10篇 |
1968年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Shan Li Zhi Qin Zhenghu Shen Xiaorong Tan Ping Shi Yafu Wang Ruolan Dai 《Journal of Radioanalytical and Nuclear Chemistry》2001,247(3):545-548
A convenient procedure for preparing a multitracer solution from irradiated silver foils by 80 MeV/nucleon 20Ne ions was developed. The carrier-free and salt-free solution containing 19 essential elements or trace elements for plant growth were prepared, and had been applied to study the regulation effect of metal ions on somatic embryogenesis of Lycium barbarum L. 相似文献
992.
Yan‐Long Qian Xin‐Rong Qin Ji‐Ling Huang Albert Sun‐Chi Chan Shou‐Shan Chen Hong‐Gen Wang 《中国化学》2001,19(1):97-101
The syntheses of a series of l‐methyl‐3‐aryl‐substituted titanocene and zirconocene dichlorides are reported. These complexes are synthesized by the reaction of 2‐ and 3‐methyl‐6, 6‐dimethylfulvenes (1:4) with aryllithium, followed by the reaction with TiCl4·2THF, ZrCl4 and (CpTiCl2)2O respectively, to give complexes 1–5. The complex [η5‐1‐methyl‐3‐(α, α‐dimethylbenzyl) cyclopentadienyl] titanium dichloride has been studied by X‐ray diffraction. The red crystal of this complex is monoclinic, space group P2t/C with unit cell parameters: a =6.973(6) × 10?1 nm, b =36.91(2) × 10?1 nm, c = 10.063(4) × 10?1 nm, α=β= γ = 93.35(5)°, V = 2584(5) × 10?3 nm3 and Z = 4. Refinement for 1004 observed reflections gives the final R of 0.088. There are four independent molecules per unit cell. 相似文献
993.
AbstractNew insights for the effects of organic solvent polarities and solvent-monomer interactions on the radical copolymerization for an important copolymer, poly(acrylonitrile-co-methyl acrylate) (PAN-co-MA), were provided in this research. Solvents, dimethylformamide (DMF), dimethylacetamide (DMAc) and dimethyl sulfoxide (DMSO), were used as reaction media. The polarity of these solvents was in the sequence of DMAc?<?DMF?<?DMSO. By studying the reactivity ratios of AN and MA, the triad fractions of the resultant copolymers, the interactions between monomers and solvents, and the compositions of copolymers at various conversions, we concluded that the solvent polarity had minimal influence on the copolymerization of AN and MA, while the solvent-monomer interactions played important roles. The interactions between monomer-monomer, monomer-solvent, and solvent-solvent, were calculated based on quantum chemistry methods. Both theoretical calculations and experimental results suggested that AN and MA in DMSO tended to aggregate locally, while they could be homogeneously dissolved in DMAc and DMF. The interactions between solvent and monomers could cause local monomer concentration variations, or ‘bootstrap’ effect, which is one of the critical factors affecting the copolymerization process of AN and MA and the chemical structures of the resultant polymers. 相似文献
994.
以4-(1H-1,2,4-三氮唑)苯甲酸为配体,采用水热法合成了2种稀土配位聚合物[Tb(tbc3)(H2O)3]n(1)和{[Nd(tbc3)(H2O)3]·H2O}n(2)(Htbc=4-(1H-1,2,4-三氮唑)苯甲酸)。运用X-射线单晶衍射法对该配位聚合物进行了结构测定,并对其进行了元素分析、红外光谱、TG及荧光光谱表征。单晶结构表明,配位聚合物1为三斜晶系,空间群P1,配位聚合物2属于单斜晶系,空间群为P21/c。配位聚合物1和2均为一维链结构,均通过非共价键作用形成三维超分子构造。 相似文献
995.
Sun L Tao D Han B Ma J Zhu G Liang Z Shan Y Zhang L Zhang Y 《Analytical and bioanalytical chemistry》2011,399(10):3387-3397
The solubility and digestion efficiency are two crucial factors that might affect the identification of integral membrane
proteins (IMPs). In this work, 1% (v/v) ionic liquid (IL), 1-butyl-3-methyl imidazolium tetrafluoroborate (BMIM BF4), added in NH4HCO3 buffer (pH 8.3), was applied as a sample preparation buffer for IMPs analysis. Compared to the commonly used sodium dodecyl
sulfate and methanol methods, the number of identified IMPs from rat brain by microcolumn reversed phase liquid chromatography
(μRPLC)-electrospray ionization tandem mass spectrometry (ESI-MS/MS) was improved by over three times, which might be due
to the fact that BMIM BF4 offered high solubilizing ability for IMPs and good compatibility for tryptic digestion. Furthermore, compared to Rapigest
and urea methods, with BMIM BF4 method, the number of identified IMPs from rat brain could be improved 25% and 80%, respectively, which might be contributed
to the good solubilizing ability and high thermal stability of such IL. With the sample treated by BMIM BF4 method, by 2D-nanoSCX-RPLC-ESI-MS/MS, 1,450 non-redundant proteins and 7,978 unique peptides were identified from rat brain,
and 418 proteins contained at least one predicted transmembrane domain, with false discovery rates of less than 1% for peptide
identification, and at least two identified unique peptides per protein. All these results demonstrate that the BMIM BF4 method is of high potential for the large-scale identification of IMPs. 相似文献
996.
J.-M. Liu N. Chong H.L.W. Chan K.H. Wong C.L. Choy 《Applied Physics A: Materials Science & Processing》2003,76(1):93-96
Epitaxial (001) aluminum nitride (AlN) thin films on (111) Si substrates are prepared using pulsed-laser deposition. The epitaxial
structure of the as-prepared thin films is characterized by checking the X-ray-diffraction θ-2 θ scan and pole-figure, using
scanning electron microscopy, infrared radiation (IR) spectroscopy and Raman spectroscopy. The surface acoustic-wave resonance
at 345 MHz for a 1.5 μm thick AlN film on a (111) Si substrate is observed using an inter-digital electrode.
Received: 18 September 2001 / Accepted: 29 January 2002 / Published online: 3 June 2002
RID="*"
ID="*"Corresponding author. Fax: +86-25/359-5535, E-mail: liujm@nju.edu.cn 相似文献
997.
Bao Shan Huang Mary Jane Lauzon James C. Parham 《Journal of heterocyclic chemistry》1979,16(4):811-813
Alkylation of 4(5)-nitroimidazole-5(4)-sulfonamide with benzyl bromide occurred on both ring nitrogens. The structures of the products could be assigned by comparison of the chemical shifts of the sulfonamide hydrogens in the nmr spectra with those of the isomeric methyl derivatives, which were prepared by differing routes. Uv and nmr spectral data are reported for a number of bromo-, nitro-, mercapto-, sulfamyl- and amino- substituted imidazoles as well as for both of the isomeric methylated derivatives of the series. 相似文献
998.
Light‐Induced Reversible Reconfiguration of DNA‐Based Constitutional Dynamic Networks: Application to Switchable Catalysis 下载免费PDF全文
Dr. Shan Wang Dr. Liang Yue Zi‐Yuan Li Dr. Junji Zhang Prof. He Tian Prof. Itamar Willner 《Angewandte Chemie (International ed. in English)》2018,57(27):8105-8109
The light‐induced reversible and cyclic reconfiguration of constitutional dynamic networks, consisting of supramolecular nucleic acid structures as constituents and a photoisomerizable trans/cis‐azobenzene‐functionalized nucleic acid as the trigger is demonstrated. In addition, the cyclic photochemical reconfiguration of the constitutional dynamic networks guides the switchable on/off operation of an emerging hemin/G‐quadruplex DNAzyme. 相似文献
999.
The slippage effect of the polymer chains is investigated in the dewetting process of the polymer solution film. The solvent-induced dewetting is used in our experiments to study the dynamics of hole growth in the dewetting process of the polymer solution film. Our results show that in the case of the low molecular weight polystyrene (PS) film, the slippage effect of the polymer chains is not displayed and the radius of the holes is R approximately exp(t/tau); in the case of the higher molecular weight PS film, the slippage effect of the polymer chain is not valid in the case of the thin film and that is valid in the case of the thick film, and the dynamic process of hole growth divides into three stages (R approximately t, and then R approximately t(x) (23相似文献
1000.
A palladium-catalyzed ortho-selective C–H bond chlorination reaction for the preparation of 2-chloro aromatic ketones was described. Both electron-withdrawing and electron-donating groups on the aromatic rings are well tolerated under the optimized conditions. The 2-chloro aromatic ketones obtained by our method could be applied to synthesize the derivatives of 1H-indazole or benzo[d]isoxazole. 相似文献