全文获取类型
收费全文 | 1907篇 |
免费 | 89篇 |
国内免费 | 26篇 |
专业分类
化学 | 1414篇 |
晶体学 | 25篇 |
力学 | 71篇 |
数学 | 205篇 |
物理学 | 307篇 |
出版年
2024年 | 14篇 |
2023年 | 24篇 |
2022年 | 106篇 |
2021年 | 115篇 |
2020年 | 76篇 |
2019年 | 74篇 |
2018年 | 73篇 |
2017年 | 52篇 |
2016年 | 104篇 |
2015年 | 58篇 |
2014年 | 70篇 |
2013年 | 107篇 |
2012年 | 133篇 |
2011年 | 148篇 |
2010年 | 94篇 |
2009年 | 93篇 |
2008年 | 85篇 |
2007年 | 81篇 |
2006年 | 67篇 |
2005年 | 64篇 |
2004年 | 45篇 |
2003年 | 29篇 |
2002年 | 34篇 |
2001年 | 12篇 |
2000年 | 11篇 |
1999年 | 8篇 |
1998年 | 9篇 |
1997年 | 17篇 |
1996年 | 17篇 |
1995年 | 14篇 |
1994年 | 5篇 |
1993年 | 20篇 |
1992年 | 7篇 |
1991年 | 10篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 17篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1973年 | 7篇 |
1972年 | 6篇 |
1965年 | 4篇 |
排序方式: 共有2022条查询结果,搜索用时 296 毫秒
941.
Wen-Nee Tan Jia-Qin Lim Fatin Afiqah Nik Nur Syazni Nik Mohamed Kamal Fatin Athirah Abdul Aziz Woei-Yenn Tong 《Natural product research》2018,32(7):854-858
Garcinia atroviridis Griff. ex T. Anders. is used as a medication agent in folkloric medicine. The present study was to examine the chemical composition of the stem bark and leaf of G. atroviridis as well as their cytotoxic effects against MCF-7 cells. The constituents obtained by hydrodistillation were identified using GC-MS. The stem bark oil (EO-SB) composed mainly the palmitoleic acid (51.9%) and palmitic acid (21.9%), while the leaf oil (EO-L) was dominated by (E)-β-farnesene (58.5%) and β-caryophyllene (16.9%). Treatment of MCF-7 cells using EO-L (100 μg/mL) caused more than 50% cell death while EO-SB did not induce cytotoxic effect. EO-L has stimulated the growth of BEAS-2B normal cells, but not in MCF-7 cancerous cells. The IC50 of EO-L in MCF-7 and BEAS-2B cells were 71 and 95 μg/mL, respectively. A combination treatment of EO-L and tamoxifen induced more cell death than the treatment with drug alone at lower doses. 相似文献
942.
An Ethylenediamine‐based Switch to Render the Polyzwitterion Cationic at Tumorous pH for Effective Tumor Accumulation of Coated Nanomaterials
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Abdul‐Hackam Ranneh Dr. Hiroyasu Takemoto Shunya Sakuma Dr. Aziz Awaad Dr. Takahiro Nomoto Dr. Yuki Mochida Dr. Makoto Matsui Dr. Keishiro Tomoda Dr. Mitsuru Naito Prof. Dr. Nobuhiro Nishiyama 《Angewandte Chemie (International ed. in English)》2018,57(18):5057-5061
Polyzwitterions are employed as coating polymers for biomaterials to induce an antifouling property on the surface. Fine‐tuning the betaine structure switches the antifouling property to be interactive with anionic tissue constituents in response to a tumorous pH gradient. The ethylenediamine moiety in the carboxybetaine enabled stepwise protonation and initiated the di‐protonation process around tumorous pH (6.5). The net charge of the developed polyzwitterion (PGlu(DET‐Car)) was thus neutral at pH 7.4 for antifouling, but was cationic at pH 6.5 for interaction with anionic constituents. Quantum dots coated with PGlu(DET‐Car) exhibited comparable stealth and enhanced tumor accumulation relative to the PEG system. The present study provides a novel design of smart switchable polyzwitterion based on a precise control of the net charge. 相似文献
943.
Syed M. Qaim Bernhard Scholten Bernd Neumaier 《Journal of Radioanalytical and Nuclear Chemistry》2018,318(3):1493-1509
A brief historical background of the development of the theranostic approach in nuclear medicine is given and seven theranostic pairs of radionuclides, namely 44gSc/47Sc, 64Cu/67Cu, 83Sr/89Sr, 86Y/90Y, 124I/131I, 152Tb/161Tb and 152Tb/149Tb, are considered. The first six pairs consist of a positron and a β?-emitter whereas the seventh pair consists of a positron and an α-particle emitter. The decay properties of all those radionuclides are briefly mentioned and their production methodologies are discussed. The positron emitters 64Cu, 86Y and 124I are commonly produced in sufficient quantities via the (p,n) reaction on the respective highly enriched target isotope. A clinical scale production of the positron emitter 44gSc has been achieved via the generator route as well as via the (p,n) reaction, but further development work is necessary. The positron emitters 83Sr and 152Tb are under development. Among the therapeutic radionuclides, 89Sr, 90Y and 131I are commercially available and 161Tb can also be produced in sufficient quantity at a nuclear reactor. Great efforts are presently underway to produce 47Sc and 67Cu via neutron, photon and charged particle induced reactions. The radionuclide 149Tb is unique because it is an α-particle emitter. The present method of production of 152Tb and 149Tb involves the use of the spallation process in combination with an on-line mass separator. The role of some emerging irradiation facilities in the production of special radionuclides is discussed. 相似文献
944.
Syeda Shahzadi Batool Quratulain Syed Muhammad Salman Haider 《Journal of Coordination Chemistry》2018,71(9):1380-1391
The syntheses, characterization, and crystal structures of the reaction products of Cu2+ with imidazole (Himz) and different aromatic carboxylates, viz.: [Cu(Himz)2(cinn)2(H2O)] (1), [Cu(Himz)2(paba)2] (2) and [Cu(Himz)2(clba)2] (3) (cinn– = C9H7O2–, paba– = C7H6NO2–, clba– = C7H4ClO2–) are described and studied by spectroscopic (UV–visible, FTIR) measurements. Single-crystal X-ray diffraction analyses indicate that each complex is monomeric. The metal ion in 1 adopts square-pyramidal coordination geometry arising from two imidazole nitrogens, two cinnamate oxygens, and an apical aqua. The metal ions of 2 and 3, however, assume a square planar configuration, which is realized by coordination of two nitrogens of two imidazoles and two oxygens; in both complexes, the imidazole moieties are trans to each other. TGA results indicate that upon heating, these complexes lose their carboxylate anions first, followed by removal of the imidazole molecules. 相似文献
945.
Abdoul Aziz Ndiaye Ana Lacoste Alexandre Bès Andrii Zaitsev Fabienne Poncin-Epaillard Dominique Debarnot 《Plasma Chemistry and Plasma Processing》2018,38(4):887-902
In the wavelength range from 200 up to 1000 nm, optical emission from electronically excited fragments (CN, CH, NH, C2, H2, N2, N2+, and H-Balmer) is detected when aniline plasmas are generated in a multi-dipolar microwave reactor. The optical emission spectrum monitored in very low-pressure conditions (~?1 mTorr) shows important characteristics. The Hα, Hβ and CN species are the most radiating systems and according to the NH/N2 intensity ratio, two different operating regimes are observed suggesting a change in the reaction pathways. These two regimes are correlated to changes of the plasma characteristics (electron temperature and density) deduced from Langmuir probe measurements. The plasma thermodynamic state is quantified by implementing numerical simulation codes for synthetic spectra calculations. The rovibrational temperatures (Tr, Tv) are determined for some neutral species (CN, CH). The obtained values of Tr and Tv show the non-local thermodynamic equilibrium of the vibrational and rotational states (Tr?<?Tv). Moreover, the very low pressure aniline-based plasmas deviate substantially from the Boltzmann distribution. Correlation between the optical emission data and the solid phase analysis allows proving that the in situ characterization of the plasma phase is an important predictive tool of physico-chemical properties of the film. From these correlated data, we deduce preponderant chemical reaction pathways which help to better understand the plasma generation. Relative contributions of the dehydrogenation of C–H and N–H groups are established in order to deduce the leading initiation reaction for H-Balmer line formation. 相似文献
946.
947.
Let P(z) be a polynomial of degreen which does not vanish in ¦z¦ <k, wherek > 0. Fork ≤ 1, it is known that, provided ¦P’(z)¦ and ¦Q’(z)¦ become maximum at the same point on ¦z¦ = 1, where\(Q(z) = z^n \overline {P(1/\bar z)} \). In this paper we obtain certain refinements of this result. We also present a refinement of a generalization of the theorem of Tu?an.
相似文献
$$\mathop {\max }\limits_{|z| = 1} |P'(z)| \leqslant \frac{n}{{1 + k^n }}\mathop {\max }\limits_{|z| = 1} |P(z)|$$
948.
Michael B. Hursthouse K. M. Abdul Malik Pradip K. Bakshi A. Afsar Bhuiyan M. Qamrul Ehsan Syed Z. Haider 《Journal of chemical crystallography》1996,26(11):739-745
Thiamine hydrochloride (vitamin B1) reacts with antimony trichloride in methanol to produce a crystalline compound which has been characterized as the salt 2[C12H18N4OS]·[Sb2Cl10] by X-ray crystallography. The compound crystallizes in the triclinic space group
,b=11.029(2),c=12.234(2) Å, =108.75(2), =102.67(2), =103.59(2)°,U=1041.52 Å3,D
c=1.80 g cm–3,Z=1. The crystal structure consists of discrete [C12H18N4OS]2+ cations and chloro bridged [Cl4Sb(-Cl)2SbCl4]4- anions in 2:1 ratio, held together by hydrogen bonds and electrostatic forces. 相似文献
949.
Dennis W. Bennett Tasneem A. Siddiquee Daniel T. Haworth Shariff E. Kabir Md. Iqbal Hyder Syed J. Ahmed 《Journal of chemical crystallography》2004,34(6):361-370
The crystal and molecular structures of Ru3(CO)6{μ 3-OPPh2C2H(C6H4)PPhCH2PPh}-(μ 3-OPPh2)Ph (1) and Ru3(CO)6{μ-OPPh2C2H(C6H4)PPhO}(μ-PPh2)(μ-PPh2O) (2) have been determined by single crystal X-ray diffraction. Both complexes contain oxygen atoms oxidatively inserted into phosphorus–ruthenium bonds, and unique σ/π multidentate ligands formed from C $---{\text{H}}$ H and C $--$ P bond cleavage in bis(diphenylphosphino)acetylene and bis(diphenylphosphino)methane. Complex 1 crystallized in the triclinic space group ${\bar 1}$ , with lattice parameters a = 11.642(4) Å, b = 15.018(5) Å, c =16.587(5) Å, α = 2.48(3)°, β = 76.47(2)°, γ = 70.35(3)°, V = 2651.1(15) Å3, Z = 2. Complex 2 crystallized in the centered monoclinic space group, C2/c, with lattice parameters a = 34.467(4) Å, b = 14.274(2) Å, c = 23.258(3) Å, β = 5.29(1)°, V = 11394(3) Å3, Z = 8. 相似文献
950.
Syed Mohammed Zubair 《Heat and Mass Transfer》1993,28(6):357-364
A closed-form model for the computation of the transient temperature and heat flux distribution in the case of a semi-infinite solid of constant properties is investigated. The temperature and heat flux solutions are presented for time-dependent, surface-heat flux of the forms: (i)
, (ii)
, and (iii)
, where is a real number and is a positive real number. The dimensionless (or reduced) temperature and heat flux solutions are presented in terms of the Whittaker function, the generalized representation of an incomplete Gamma functionI
(b, x) which can also be expressed by the complementary error functions. It is also demonstrated that the present analysis covers some well known (classical) solutions as well as a family of new solutions for the heat transfer through a semi-infinite solid.
Wärmeleitung in einem halbunendlichen Festkörper bei zeitveränderlichem Randwärmefluß: Eine analytische Untersuchung
Zusammenfassung Es wird ein geschlossenes Modell zur Berechnung der nichtstationären Temperatur- and Wärmestromverteilung für einen halbunendlichen Festkörper mit konstanten Stoffwerten untersucht. Die Lösungen für das Temperatur- und Wärmeflußfeld basieren auf folgenden Zeitgesetzen für den Randwärmefluß: (i) , (ii) , und (iii) wobei eine reelle Zahl und eine positive reelle Zahl ist. Die dimensionslosen Lösungen für das Temperatur- und Wärmflußfeld lassen sich in Form der Whittaker- Funktionen, der verallgemeinerten Darstellung einer unvollständigen Gamma-FunktionI (b, x) angeben, welche auch durch das komplementäre Fehlerintegral ausgedrückt werden kann. Es wird ferner gezeigt, daß die hier durchgeführte Untersuchung sowohl einige bekannte (klassische) Lösungen für die Wärmeleitung im halbunendlichen Festkörper liefert, wie auch eine Familie von neuen Lösungen.相似文献