全文获取类型
收费全文 | 2329篇 |
免费 | 70篇 |
国内免费 | 3篇 |
专业分类
化学 | 1463篇 |
晶体学 | 15篇 |
力学 | 42篇 |
数学 | 306篇 |
物理学 | 576篇 |
出版年
2021年 | 20篇 |
2020年 | 41篇 |
2019年 | 27篇 |
2018年 | 23篇 |
2016年 | 51篇 |
2015年 | 42篇 |
2014年 | 51篇 |
2013年 | 91篇 |
2012年 | 90篇 |
2011年 | 119篇 |
2010年 | 69篇 |
2009年 | 56篇 |
2008年 | 102篇 |
2007年 | 93篇 |
2006年 | 97篇 |
2005年 | 91篇 |
2004年 | 75篇 |
2003年 | 48篇 |
2002年 | 46篇 |
2001年 | 31篇 |
2000年 | 35篇 |
1999年 | 32篇 |
1998年 | 28篇 |
1997年 | 25篇 |
1996年 | 26篇 |
1995年 | 30篇 |
1994年 | 47篇 |
1993年 | 24篇 |
1992年 | 21篇 |
1991年 | 20篇 |
1990年 | 19篇 |
1988年 | 17篇 |
1987年 | 19篇 |
1986年 | 19篇 |
1985年 | 29篇 |
1984年 | 26篇 |
1983年 | 27篇 |
1982年 | 18篇 |
1981年 | 21篇 |
1980年 | 27篇 |
1979年 | 21篇 |
1978年 | 29篇 |
1977年 | 21篇 |
1976年 | 22篇 |
1975年 | 17篇 |
1974年 | 16篇 |
1972年 | 18篇 |
1968年 | 41篇 |
1967年 | 21篇 |
1901年 | 16篇 |
排序方式: 共有2402条查询结果,搜索用时 343 毫秒
111.
Felix Krupp Wolfgang Frey Clemens Richert 《Angewandte Chemie (International ed. in English)》2020,59(37):15875-15879
The most reliable method to determine the absolute configuration of chiral molecules is X‐ray crystallography, but small molecules can be difficult to crystallize. We report rapid co‐crystallization of tetraaryladamantanes with small molecules as different as n‐decane to nicotine to produce crystals for X‐ray analysis and the assignment of absolute configuration when the molecules are chiral. A screen of 52 diverse compounds gave inclusion in co‐crystals for 88 % of all cases and a high‐resolution structure in 77 % of cases. Furthermore, starting from three milligrams of analyte, a combination of NMR spectroscopy and X‐ray crystallography produced a full structure in less than three days using an adamantane crystallization chaperone that encapsulates the analyte at room temperature. 相似文献
112.
Hg1−xCdxTe layers on CdTe substrates were grown from Te-rich melt solutions by a vertical dipping technique using a special quasi-closed system with ground-glass sealing. Results are good reproducibilities of the electrical properties after annealing in Hg-rich atmosphere (p77 ≈ 2 · 1016 cm−3 μ77 ≈ 500 cm2 V−1 s−1) and of the x-value, respectively. A horizontal position of the substrate downwards to the melt solution yields, in difference to a vertical one, to homogeneous layer thicknesses. Short meltback steps before growth leads to sharper profiles of composition. 相似文献
113.
Cokes rich in sulphur usually show throughout the high temperature treatment between 1500 and 1800 °C an irreversible dilatation which can be suppressed by additives of inorganic oxides or salts. In brown coal pitch cokes with high content of sulphur and mineral impurities (ash), however, this suphur puffing cannot be observed. Basic ash components (e. g. CaO, Fe2O3, MgO) are responsible for the puffing inhibition. The inhibition is already sufficient if the concerntration of basic ash components equals the suphur conentration. 相似文献
114.
Walther C Rothe J Fuss M Büchner S Koltsov S Bergmann T 《Analytical and bioanalytical chemistry》2007,388(2):409-431
Polynuclear species of zirconium in acidic aqueous solution are investigated by combining X-ray absorption spectroscopy (XAFS)
and nanoelectrospray mass spectrometry (ESI-MS). Species distributions are measured between pHC 0 and pHC 3 for [Zr] = 1.5–10 mM. While the monomer remains a minor species, with increasing pH the degree of polymerization increases
and the formation of tetramers, pentamers, octamers, and larger polymers is observed. The high resolution of the mass spectrometer
permits the unambiguous determination of polynuclear zirconium hydroxide complexes by means of their isotopic patterns. The
relative abundances of mononuclear and polynuclear species present simultaneously in solution are measured, even if one of
the species contributes only 0.1% of the Zr concentration. For the first time it has been directly observed that the hydrolysis
of polynuclear Zr species is a continuous process which leads to charge compensation through the sequential substitution of
water molecules by hydroxide ligands until doubly charged polymers dominate at conditions (H+ and Zr concentrations) close to the solubility of Zr(OH)4(am). The invasiveness of the electrospray process was minimized by using very mild declustering conditions, leaving the polynuclear
species within a solvent shell of approximately 20 water molecules.
Figure Schematic Diagram of Multiplexed Measurement of 9 Anti-Nuclear Antibodies Using the AtheNa Multilyte Assay 相似文献
115.
DNA‐Hybrid‐Gated Multifunctional Mesoporous Silica Nanocarriers for Dual‐Targeted and MicroRNA‐Responsive Controlled Drug Delivery 下载免费PDF全文
Penghui Zhang Fangfang Cheng Ri Zhou Dr. Juntao Cao Dr. Jingjing Li Prof. Dr. Clemens Burda Dr. Qianhao Min Prof. Dr. Jun‐Jie Zhu 《Angewandte Chemie (International ed. in English)》2014,53(9):2371-2375
The design of an ideal drug delivery system with targeted recognition and zero premature release, especially controlled and specific release that is triggered by an exclusive endogenous stimulus, is a great challenge. A traceable and aptamer‐targeted drug nanocarrier has now been developed; the nanocarrier was obtained by capping mesoporous silica‐coated quantum dots with a programmable DNA hybrid, and the drug release was controlled by microRNA. Once the nanocarriers had been delivered into HeLa cells by aptamer‐mediated recognition and endocytosis, the overexpressed endogenous miR‐21 served as an exclusive key to unlock the nanocarriers by competitive hybridization with the DNA hybrid, which led to a sustained lethality of the HeLa cells. If microRNA that is exclusively expressed in specific pathological cell was screened, a combination of chemotherapy and gene therapy should pave the way for a targeted and personalized treatment of human diseases. 相似文献
116.
Dongyi Liu Ahmed M. El‐Zohry Maria Taddei Clemens Matt Laura Bussotti Zhijia Wang Jianzhang Zhao Omar F. Mohammed Mariangela Di Donato Stefan Weber 《Angewandte Chemie (International ed. in English)》2020,59(28):11591-11599
We prepared conceptually novel, fully rigid, spiro compact electron donor (Rhodamine B, lactam form, RB)/acceptor (naphthalimide; NI) orthogonal dyad to attain the long‐lived triplet charge‐transfer (3CT) state, based on the electron spin control using spin‐orbit charge transfer intersystem crossing (SOCT‐ISC). Transient absorption (TA) spectra indicate the first charge separation (CS) takes place within 2.5 ps, subsequent SOCT‐ISC takes 8 ns to produce the 3NI* state. Then the slow secondary CS (125 ns) gives the long‐lived 3CT state (0.94 μs in deaerated n‐hexane) with high energy level (ca. 2.12 eV). The cascade photophysical processes of the dyad upon photoexcitation are summarized as 1NI*→1CT→3NI*→3CT. With time‐resolved electron paramagnetic resonance (TREPR) spectra, an EEEAAA electron‐spin polarization pattern was observed for the naphthalimide‐localized triplet state. Our spiro compact dyad structure and the electron spin‐control approach is different to previous methods for which invoking transition‐metal coordination or chromophores with intrinsic ISC ability is mandatory. 相似文献
117.
Röntgenographically identified single-phase ZnSiP2 of stoichiometric composition which has been grown in gas phase has a specific resistance of > 103 Ωcm and locally limited luminescence spectra. The presence of foreign phases and inhomogeneities as well as stoichiometric deviations in the ZnSiP2 are possible causes of these physical properties. An attempt was made to grow, in the gas phase, ZnSiP2 containing foreign phases. For this purpose, synthesis and crystallization of ZnSiP2 were carried out using non-stoichiometric proportions of silicon. The phase composition of the crystals was investigated by means of light microscopy and electron-beam microanalysis. In the case of hypostoichiometric silicon amounts (–50 mole% Si) the ZnSiP2 matrix contains the binary phases ZnP2 and Zn3P2. Under hyperstoichiometric conditions (> 100 mole% Si) ZnS13P2 layers are deposited on the ZnSiP2. Distinct differences between the physical properties of stoichiometric single-phase ZnSiP2 and ZnSiP2 containing foreign phases could not be detected. 相似文献
118.
119.
Synthesis and characterisation of the SrxBa1−xFeO3−y-system and the fluorinated phases SrxBa1−xFeO2F
Oliver Clemens Robert Haberkorn Peter R. Slater Horst Philipp Beck 《Solid State Sciences》2010,12(8):1455-1463
Compounds in the system SrxBa1?xFeO3?y have been prepared under different partial pressures of oxygen. In this system, different perovskite-type structures are found depending highly on the values of x and y. Fluorination using polyvinylidenedifluoride (PVDF) gives oxyfluoride materials of composition SrxBa1?xFeO2F, which normally crystallize in the cubic perovskite structure. Rietveld refinement results provide information about the packing density for oxide and oxyfluoride samples and allow a general comparison between these two different types of materials. Furthermore, the determination of the average iron oxidation state also showed that the oxygen deficiency, y, depends significantly on the value of x and the structure determined by the Sr/Ba ratio. 相似文献
120.
Gary E. Martin R. Thomas Williamson Kirill A. Blinov Clemens G. Anklin Wolfgang Bermel 《Magnetic resonance in chemistry : MRC》2012,50(10):691-695
1,1‐ADEQUATE and the related long‐range 1,n‐ and n,1‐ADEQUATE variants were developed to provide an unequivocal means of establishing 2JCH and the equivalent of nJCH correlations where n = 3,4. Whereas the 1,1‐ and 1,n‐ADEQUATE experiments have two simultaneous evolution periods that refocus the chemical shift and afford net single quantum evolution for the carbon spins, the n,1‐variant has a single evolution period that leaves the carbon spin to be observed at the double quantum frequency. The n,1‐ADEQUATE experiment begins with an HMBC‐type nJCH magnetization transfer, which leads to inherently lower sensitivity than the 1,1‐ and 1,n‐ADEQUATE experiments that begin with a 1JCH transfer. These attributes, in tandem, serve to render the n,1‐ADEQUATE experiment less generally applicable and more difficult to interpret than the 1,n‐ADEQUATE experiment, which can in principle afford the same structural information. Unsymmetrical and generalized indirect covariance processing methods can complement and enhance the structural information encoded in combinations of experiments e.g. HSQC‐1,1‐ or ?1,n‐ADEQUATE. Another benefit is that covariance processing methods offer the possibility of mathematically combining a higher sensitivity 2D NMR spectrum with for example 1,1‐ or 1,n‐ADEQUATE to improve access to the information content of lower sensitivity congeners. The covariance spectrum also provides a significant enhancement in the F1 digital resolution. The combination of HMBC and 1,1‐ADEQUATE spectra is shown here using strychnine as a model compound to derive structural information inherent to an n,1‐ADEQUATE spectrum with higher sensitivity and in a more convenient to interpret single quantum presentation. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献