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181.
Beliefs constitute a central part of a person’s professional competencies and are crucial to the perception of situations
as they influence our choice of actions. This paper focuses on epistemological beliefs about the nature of mathematics of
future primary teachers from an international perspective. The data reported are part of a larger sample originating from
the TEDS-M study which compares primary mathematics teacher education in 15 countries. In this paper we examine the pattern
of beliefs of future teachers aiming to teach mathematics at primary level. We explore whether and to what extent beliefs
concerning the nature of mathematics are influenced by cultural factors, in our case the extent to which a country’s culture
can be characterized by an individualistic versus collectivistic orientation according to Hofstede’s terminology. In the first
part of the paper, the literature on epistemological beliefs is reviewed and the role of culture and individualism/collectivism
on the formation of beliefs concerning the nature of mathematics will be discussed. In the empirical part, means and distributions
of belief ratings will be reported. Finally, multilevel analyses explore how much of the variation of belief preferences between
countries can be explained by the individualistic orientation of a country. 相似文献
182.
We investigate force formulae for two rigid magnetic bodies in dependence on their mutual distance. These formulae are derived
as continuum limits of atomistic dipole–dipole interactions. For bodies that are far apart in terms of the typical lattice
spacing we recover a classical formula for magnetic forces. For bodies whose distance is comparable to the atomistic lattice
spacing, however, we discover a new term that explicitly depends on the distance, measured in atomic units, and the underlying
crystal lattice structure. This new term links the classical force formula and a limiting force formula obtained earlier in
the case of two bodies being in contact on the atomistic scale. 相似文献
183.
Kaushik Bhattacharya Anja Schlömerkemper 《Archive for Rational Mechanics and Analysis》2010,196(3):715-751
Shape-memory alloys undergo a solid-to-solid phase transformation involving a change of crystal structure. We examine model
problems in the scalar setting motivated by the situation when this transformation is induced by the application of stress
in a polycrystalline material made of numerous grains of the same crystalline solid with varying orientations. We show that
the onset of transformation in a granular polycrystal with homogeneous elasticity is in fact predicted accurately by the so-called
Sachs bound based on the ansatz of uniform stress. We also present a simple example where the onset of phase transformation
is given by the Sachs bound, and the extent of phase transformation is given by the constant strain Taylor bound. Finally
we discuss the stress–strain relations of the general problem using Milton–Serkov bounds. 相似文献
184.
Anja Schlömerkemper 《PAMM》2006,6(1):507-508
In earlier work [3], a Sachs and a Taylor bound on the transformation yield stress in shape memory polycrystals were derived in the context of a variational model. The aim of this article is to compare the Sachs with the Taylor bound for cubic-toorthorhombic phase transformations under biaxial loading, where the material parameters are chosen explicitly (CuAlNi). It turns out that the gap between the two bounds can be quite large depending on the underlying texture and the loading direction. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
185.
Christian Leischner Markus Burkard Anja Michel Susanne Berchtold Heike Niessner Luigi Marongiu Christian Busch Jan Frank Ulrich M. Lauer Sascha Venturelli 《Molecules (Basel, Switzerland)》2021,26(18)
Resveratrol, a natural plant phytoalexin, is produced in response to fungal infection or− UV irradiation. It exists as an isomeric pair with cis- and trans-conformation. Whereas multiple physiological effects of the trans-form, including a pronounced anti-tumoral activity, are nowadays elucidated, much less knowledge exists concerning the cis-isomer. In our work, we analyzed the antiproliferative and cytotoxic properties of cis-resveratrol in four different human tumor entities in direct comparison to trans-resveratrol. We used human cell lines as tumor models for hepatocellular carcinoma (HCC; HepG2, Hep3B), colon carcinoma (HCT-116, HCT-116/p53(−/−)), pancreatic carcinoma (Capan-2, MiaPaCa-2), and renal cell carcinoma (A498, SN12C). Increased cytotoxicity in all investigated tumor cells was observed for the trans-isomer. To verify possible effects of the tumor suppressor p53 on resveratrol-induced cell death, we used wild type and p53-deleted or -mutated cell lines for every tested tumor entity. Applying viability and cytotoxicity assays, we demonstrated a differential, dose-dependent sensitivity towards cis- or trans-resveratrol among the respective tumor types. 相似文献
186.
187.
Jrg Schrder Herbert Wenzel Hans‐Georg Stammler Anja Stammler Beate Neumann Harald Tschesche 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(5):593-596
The title compounds, (2S)‐N‐[5‐(4‐chlorophenyl)‐2,3‐dihydro‐6H‐1,3,4‐thiadiazin‐2‐ylidene]‐2‐[(phenylsulfonyl)amino]propanamide, C18H17ClN4O3S2, (I), (2R)‐N‐[5‐(4‐fluorophenyl)‐6H‐1,3,4‐thiadiazin‐2‐yl]‐2‐[(phenylsulfonyl)amino]propanamide, C18H17FN4O3S2, (II), and (2S)‐N‐[5‐(5‐chloro‐2‐thienyl)‐6H‐1,3,4‐thiadiazin‐2‐yl]‐2‐[(phenylsulfonyl)amino]propanamide, C16H15ClN4O3S3, (III), are potent inhibitors of matrix metalloproteinases. In all three compounds, the thiadiazine ring adopts a screw‐boat conformation. The molecules of compound (I) show a short intramolecular NAla—H?Nexo hydrogen bond [N?N 2.661 (3) Å] and are linked into a chain along the c axis by Nendo—H?Sendo and Nendo—H?OAla hydrogen bonds [N?S 3.236 (3) and N?O 3.375 (3) Å] between neighbouring molecules. In compound (II), the molecules are connected antiparallel into a chain along the a axis by Nexo—H?OAla and NAla—H?Nendo hydrogen bonds [N?O 2.907 (6) and N?N 2.911 (6) Å]. The molecules of compound (III) are dimerized antiparallel through Nexo—H?Nendo hydrogen bonds [N?N 2.956 (7) and 2.983 (7) Å]. The different hydrogen‐bonding patterns can be explained by an amido–imino tautomerism (prototropic shift) shown by different bond lengths within the 6H‐1,3,4‐thiadiazine moiety. 相似文献
188.
Mathilde Briday Franois Hall Lauriane Lecoq Sylvie Radix Juliette Martin Roland Montserret Marie Dujardin Marie-Laure Fogeron Michael Nassal Beat H. Meier Thierry Lomberget Anja Bckmann 《Chemical science》2022,13(30):8840
Hepatitis B virus (HBV) is a small enveloped retrotranscribing DNA virus and an important human pathogen. Its capsid-forming core protein (Cp) features a hydrophobic pocket proposed to be central notably in capsid envelopment. Indeed, mutations in and around this pocket can profoundly modulate, and even abolish, secretion of enveloped virions. We have recently shown that Triton X-100, a detergent used during Cp purification, binds to the hydrophobic pocket with micromolar affinity. We here performed pharmacomodulation of pocket binders through systematic modifications of the three distinct chemical moieties composing the Triton X-100 molecule. Using NMR and ITC, we found that the flat aromatic moiety is essential for binding, while the number of atoms of the aliphatic chain modulates binding affinity. The hydrophilic tail, in contrast, is highly tolerant to changes in both length and type. Our data provide essential information for designing a new class of HBV antivirals targeting capsid–envelope interactions.Small-molecule binding to the Hepatitis B virus core protein hydrophobic pocket, a possible strategy for targeting viral particle assembly. 相似文献
189.
Lucas Wickemeyer Niklas Aders Andreas Mix Beate Neumann Hans-Georg Stammler Jorge J. Cabrera-Trujillo Israel Fernndez Norbert W. Mitzel 《Chemical science》2022,13(27):8088
The reaction of tBu2P(O)H with Bis2AlH (Bis = CH(SiMe3)2) afforded the adduct tBu2P(H)–O–Al(H)Bis2 (3). It slowly releases H2 to form the first oxygen-bridged geminal Al/P frustrated Lewis pair tBu2P–O–AlBis2. It is capable of reversibly binding molecular hydrogen to afford 3, shown by NMR and H/D scrambling experiments, and forms a 1,2-adduct with CO2. Importantly, the H2 adduct 3 reduces CO2 in a stoichiometric reaction leading to the formic acid adduct tBu2P(H)–O–Al(CO2H)Bis2. The formation of the different species was explored by density functional theory calculations which provide support for the experimental results. All products were characterized by NMR spectroscopy as well as X-ray diffraction experiments and elemental analyses.Addition vs. reduction: the geminal FLP Bis2Al–O–PtBu2 can reversibly bind molecular hydrogen, it reacts with CO2 to give an adduct, and its hydrogen adduct reduces CO2 to an adduct of formic acid. 相似文献
190.
Robin F. Weitkamp Beate Neumann Dr. Hans-Georg Stammler Prof. Dr. Berthold Hoge 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(21):6460-6464
The reaction of the strong monophosphazene base with the weakly acidic phenol leads to the formation of a phenol–phenolate anion with a moderately strong hydrogen bond. Application of the more powerful tetraphosphazene base (Schwesinger base) renders the isolation of the corresponding salt with a free phenolate anion possible. This compound represents the first species featuring the free phenolate anion [H5C6-O]−. The deprotonation of phenol derivatives with tetraphosphazene bases represents a great way for the clean preparation of salts featuring free phenolate anions and in addition allows the selective syntheses of hydrogen bonded phenol-phenolate salts. This work presents a phosphazenium phenolate salt with a redox potential of −0.72 V and its capability for the selective activation of the chemically inert greenhouse gas SF6. The performed two-electron reduction of SF6 leads to phosphazenium pentafluorosulfanide ([SF5]−) and fluoride salts. 相似文献