全文获取类型
收费全文 | 494篇 |
免费 | 4篇 |
国内免费 | 1篇 |
专业分类
化学 | 342篇 |
晶体学 | 4篇 |
力学 | 13篇 |
数学 | 100篇 |
物理学 | 40篇 |
出版年
2023年 | 6篇 |
2022年 | 16篇 |
2021年 | 12篇 |
2020年 | 13篇 |
2019年 | 7篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 8篇 |
2015年 | 3篇 |
2014年 | 16篇 |
2013年 | 25篇 |
2012年 | 30篇 |
2011年 | 34篇 |
2010年 | 24篇 |
2009年 | 13篇 |
2008年 | 35篇 |
2007年 | 26篇 |
2006年 | 26篇 |
2005年 | 23篇 |
2004年 | 15篇 |
2003年 | 25篇 |
2002年 | 19篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 12篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 2篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1989年 | 2篇 |
1984年 | 4篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1968年 | 3篇 |
1915年 | 1篇 |
1912年 | 2篇 |
1905年 | 1篇 |
1903年 | 1篇 |
1899年 | 1篇 |
1897年 | 2篇 |
1894年 | 1篇 |
1892年 | 1篇 |
1889年 | 2篇 |
1888年 | 1篇 |
1882年 | 1篇 |
排序方式: 共有499条查询结果,搜索用时 15 毫秒
451.
Gallo V Mastrorilli P Nobile CF Braunstein P Englert U 《Dalton transactions (Cambridge, England : 2003)》2006,(19):2342-2349
N-substituted dppa ligands Ph2P-NR-PPh2 [R = -CH2CH2SCH2C6H5 (1), -CH2CH2S(CH2)5CH3 (2), -(CH2)9CH3 (3), -C6H5 (4)] were used for the synthesis of cis-[PtCl2{Ph2PN(R)PPh2}] complexes [R = -CH2CH2SCH2C6H5 (5), -CH2CH2S(CH2)5CH3 (6), -(CH2)9CH3 (7), -C6H5 (8)] and heterotrinuclear clusters of formula [PtCo2(CO)7{Ph2PN(R)PPh2}] [R = -CH2CH2SCH2C6H5 (9), -CH2CH2S(CH2)5CH3 (10), -(CH2)9CH3 (11), -C6H5 (12)]. The presence of relatively bulky substituents on N resulted in a higher chelating power of the ligands. The thermodynamic study of the equilibrium between the chelate and the bridged forms of clusters 9-11 showed that the bridged form is favoured by enthalpic factors whereas entropic factors favour chelation. The structures of 5 and 9 were determined by single crystal X-ray diffraction. 相似文献
452.
Khan AS Mujer CV Alefantis TG Connolly JP Mayr UB Walcher P Lubitz W Delvecchio VG 《Journal of chemical information and modeling》2006,46(1):111-115
The potential devastation resulting from an intentional outbreak caused by biological warfare agents such as Brucella abortus and Bacillus anthracis underscores the need for next generation vaccines. Proteomics, genomics, and systems biology approaches coupled with the bacterial ghost (BG) vaccine delivery strategy offer an ideal approach for developing safer, cost-effective, and efficacious vaccines for human use in a relatively rapid time frame. Critical to any subunit vaccine development strategy is the identification of a pathogen's proteins with the greatest potential of eliciting a protective immune response. These proteins are collectively referred to as the pathogen's immunome. Proteomics provides high-resolution identification of these immunogenic proteins using standard proteomic technologies, Western blots probed with antisera from infected patients, and the pathogen's sequenced and annotated genome. Selected immunoreactive proteins can be then cloned and expressed in nonpathogenic Gram-negative bacteria. Subsequently, a temperature shift or chemical induction process is initiated to induce expression of the PhiX174 E-lysis gene, whose protein product forms an E tunnel between the inner and outer membrane of the bacteria, expelling all intracellular contents. The BG vaccine system is a proven strategy developed for many different pathogens and tested in a complete array of animal models. The BG vaccine system also has great potential for producing multiagent vaccines for protection to multiple species in a single formulation. 相似文献
453.
Banci L Bertini I Calderone V Cefaro C Ciofi-Baffoni S Gallo A Tokatlidis K 《Journal of the American Chemical Society》2012,134(3):1442-1445
The oxidative folding mechanism in the intermembrane space of human mitochondria underpins a disulfide relay system consisting of the import receptor Mia40 and the homodimeric FAD-dependent thiol oxidase ALR. The flavoprotein ALR receives two electrons per subunit from Mia40, which are then donated through one-electron reactions to two cytochrome c molecules, thus mediating a switch from two-electron to one-electron transfer. We dissect here the mechanism of the electron flux within ALR, characterizing at the atomic level the ALR intermediates that allow electrons to rapidly flow to cytochrome c. The intermediate critical for the electron-transfer process implies the formation of a specific inter-subunit disulfide which exclusively allows electron flow from Mia40 to FAD. This finding allows us to present a complete model for the electron-transfer pathway in ALR. 相似文献
454.
Vito Vitrih 《Journal of Computational and Applied Mathematics》2010,235(1):154-164
In this paper, (d+1)-pencil lattices on simplicial partitions in Rd, which are not simply connected, are studied. It is shown, how the fact that a partition is not simply connected can be used to increase the flexibility of a lattice. A local modification algorithm is developed also to deal with slight partition topology changes that may appear afterwards a lattice has already been constructed. 相似文献
455.
We present effective upper and lower bounds for the distance from \(\displaystyle \left( 1 + \frac{a}{n}\right) ^n \) to \(\displaystyle e^a \) for an element a of a complex unital Banach algebra and positive integer n. Specifically where \(\sigma (a)\) is the spectrum of a. The symbol \(\lesssim _{(p)}\) means “less than or equal to, up to a term of order \(n^{-p}\)”as discussed below. Following some technical preliminaries (Sect. 1) we treat the real case (Sect. 2), extend to the complex case (Sect. 3), and then generalise to the case of a norm-unital Banach algebra (Sect. 4).
相似文献
$$\begin{aligned} \frac{1}{2n} \sup \left\{ \left| \mathfrak {R}(z^2) \right| e^{\mathfrak {R}(z)} : z \in \sigma (a) \right\} \lesssim _{(2)} \left\| e^a - \left( 1 + \frac{a}{n}\right) ^n \right\| \le \frac{ \left\| a \right\| ^2}{2n} \ e^{ \left\| a \right\| }, \end{aligned}$$
456.
The regularization parameter choice is a fundamental problem in Learning Theory since the performance of most supervised algorithms
crucially depends on the choice of one or more of such parameters. In particular a main theoretical issue regards the amount
of prior knowledge needed to choose the regularization parameter in order to obtain good learning rates. In this paper we
present a parameter choice strategy, called the balancing principle, to choose the regularization parameter without knowledge
of the regularity of the target function. Such a choice adaptively achieves the best error rate. Our main result applies to
regularization algorithms in reproducing kernel Hilbert space with the square loss, though we also study how a similar principle
can be used in other situations. As a straightforward corollary we can immediately derive adaptive parameter choices for various
kernel methods recently studied. Numerical experiments with the proposed parameter choice rules are also presented. 相似文献
457.
Uncovering Intramolecular π‐Type Hydrogen Bonds in Solution by NMR Spectroscopy and DFT Calculations
Prof. Dr. Piero Mastrorilli Prof. Vito Gallo Dr. Stefano Todisco Prof. Mario Latronico Dr. Giacomo Saielli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(23):7964-7969
Reaction between the phosphinito bridged diplatinum species [(PHCy2)Pt(μ‐PCy2){κ2P,O‐μ‐P(O)Cy2}Pt(PHCy2)](Pt–Pt) ( 1 ), and (trimethylsilyl)acetylene at 273 K affords the σ‐acetylide complex [(PHCy2)(η1‐Me3SiC≡C)Pt(μ‐PCy2)Pt(PHCy2){κP‐P(OH)Cy2}](Pt–Pt) ( 2 ) featuring an intramolecular π‐type hydrogen bond. Scalar and dipolar couplings involving the POH proton were detected by 2D NMR experiments. Relativistic DFT calculations of the geometry, relative energy, and NMR properties of model systems of 2 confirmed the structural assignment and allowed the energy of the π‐type hydrogen bond to be estimated (ca. 22 kJ mol?1). 相似文献
458.
Francesco Epifano Serena Fiorito Marcello Locatelli Vito Alessandro Taddeo Salvatore Genovese 《Natural product research》2015,29(2):180-184
As a continuation of our ongoing studies aimed to reveal the presence of oxyprenylated anthraquinones in plants claimed to have a laxative effect, in this article, we describe the extraction and HPLC separation of madagascin (3-isopentenyloxyemodin) and 3-geranyloxyemodine from dried leaves and fruits of Senna alexandrina Mill. (Leguminosae) and leaves and gel of Aloe vera (L.) Burm. F. (Xanthorrhoeaceae). Both compounds are described herein for the first time as components of extracts of the title plants. 相似文献
459.
Dr. Giuseppe Dilauro Dr. Luciana Cicco Prof. Paola Vitale Prof. Filippo Maria Perna Prof. Vito Capriati 《European journal of organic chemistry》2023,26(3):e202200814
A Deep Eutectic Solvent, choline chloride/glycerol (1 : 2 mol mol−1), proved to be an effective and sustainable reaction medium to promote telescoped, one-pot Mizoroki-Heck cross-coupling/reduction processes between 2,3-dihydrofuran or 3,4-dihydro-2H-pyran and several (hetero)aryl halides to easily access valuable 2-(hetero)aryl tetrahydrofuran (THF) or tetrahydropyran derivatives in up to 95 % yield. Notably, the whole transformation takes place under aerobic conditions, in the absence of additional ligands, and with a good substrate scope. The practicability of the method is also exemplified by the sustainable synthesis of two key THF derivatives, which are side chains of pharmacologically relevant inhibitors of Kv1.2 channel. 相似文献
460.
Dr. Michael Gock Dr. Michael Lutter Dr. Anna Pintus Dr. Dieter Schollmeier Prof. Dr. Massimiliano Arca Prof. Dr. Vito Lippolis Prof. Dr. Klaus Jurkschat 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(58):e202201447
The sequence of reactions of the phosphorus-containing aryllithium compound 5-t-Bu-1,3-[(P(O)(O-i-Pr)2]2C6H2Li (ArLi) with Ph2PCl, KMnO4, elemental sulfur and elemental selenium, respectively, gave the aryldiphenylphosphane chalcogenides 5-t-Bu-1,3-[(P(O)(O-i-Pr)2]2C6H2P(E)Ph2 ( 1 , E=O; 2 , E=S; 3 , E=Se). Compound 1 partially hydrolysed giving [5-t-Bu-1-{(P(O)(O-i-Pr)2}-3-{(P(O)(OH)2}C6H2]P(O)Ph2 ( 4 ). The reaction of ArLi with PhPCl2 provided the benzoxaphosphaphosphole [1(P), 3(P)-P(O)(O-i-Pr)OPPh-6-t-Bu-4-P(O)(O-i-Pr)2]C6H2P ( 5i ) as a mixture of the two diastereomers. The oxidation of 5i with elemental sulfur gave the benzoxaphosphaphosphole sulfide [1(P), 3(P)-P(O)(O-i-Pr)OP(S)Ph-6-t-Bu-4-P(O)(O-i-Pr)2]C6H2 ( 5 ) as pair of enantiomers P1(R), P3(S)/P1(S), P3(R) of the diastereomer (RS/SR)- 5 ( 5b ). The aryldiphenylphosphane 5-t-Bu-1,3-[(P(O)(O-i-Pr)2]2C6H2PPh2 ( 6 ) was obtained from the reaction of the corresponding aryldiphenylphosphane sulfide 2 with either sodium hydride, NaH, or disodium iron tetracarbonyl, Na2Fe(CO)4. The oxidation of the aryldiphenylphosphane 6 with elemental iodine and subsequent hydrolysis yielded the aryldiphenyldioxaphosphorane 9-t-Bu-2,6-(OH)-4,4-Ph2-3,5-O2-2,6-P2-4λ5-P-[5.3.1.0]-undeca-1(10),7(11),8-triene ( 7 ). Both of its diastereomers, (RR/SS)- 7 ( 7a ) and (RS/SR)- 7 ( 7b ), were separated as their chloroform and i-propanol solvates, 7a ⋅2CHCl3 and 7b ⋅i-PrOH, respectively. DFT calculations accompanied the experimental work. 相似文献