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排序方式: 共有8313条查询结果,搜索用时 15 毫秒
981.
S.-M. Lai J.-L. Liu C.-Y. Huang Wei-Jen Lai Jiun-Wei Zeng K.-C. Cheng 《Journal of Macromolecular Science: Physics》2013,52(10):1355-1371
A near infrared reflective (NIR, nickel antimony titanium yellow rutile) pigment filler was incorporated into a polyethylene terephthalate (PET) matrix via a melt blending approach to increase the infrared reflection of PET and limit the thermal heat accumulation in light of environmental and energy conservation concerns. Two different types of surface modifiers, polyethylene glycol (PEG) and cetyltrimethylammonium bromide (CTAB), were used to modify the NIR surface, as NIR–PEG and NIR–CTAB fillers, to investigate the surface modification effect. Fourier transform infrared spectroscopy (FTIR), a Zetasizer, and electron spectroscopy for chemical analysis (ESCA) results suggested a successful adsorption of the organic modifiers onto the NIR surface. Thermogravimetric analysis indicated a higher adsorption degree for the CTAB modifier than the PEG modifier due to the electronic interaction between CTAB and NIR. The thermal crystallization temperature (Tc) for neat NIR-filled samples decreased with increasing NIR content within the PET matrix at first, up to 9°C, but then tended to increase again up to a measurable difference of 6°C with respect to pure PEG, indicating the promotion of the crystallization kinetics of the neat NIR within the PET matrix. On the other hand, a decrease in Tc for all NIR-CTAB or NIR-PEG loadings was found, with the depression close to 10°C for all NIR-CTAB samples regardless of the loading. CTAB modified NIR gave the highest improvement in tensile strength and strain at break in comparison with NIR and NIR-PEG filled samples. The near infrared reflection values of modified PET were higher than those of neat PET. The reflection values appeared to be the highest for some concentrations of the NIR-CTAB filled samples, but were of similar orders of magnitude with those for NIR or NIR-PEG filled samples. 相似文献
982.
Ludwig Kuznia Bo Zeng Grisselle Centeno Zhixin Miao 《Annals of Operations Research》2013,210(1):411-432
This paper presents a stochastic mixed integer programming model for a comprehensive hybrid power system design problem, including renewable energy generation, storage device, transmission network, and thermal generators, for remote areas. Given the complexity of the model, we developed a Benders’ decomposition algorithm with two additional types of cutting planes: Pareto-optimal cuts generated using a modified Magnanti-Wong method and cuts generated from a maximum feasible subsystem. Computational results show significant improvement in our ability to solve this type of problem in comparison to a state-of-the-art professional solver. This model and the solution algorithm provide an analytical decision support tool for the hybrid power system design problem. 相似文献
983.
We study a general filtering problem with marked point process observations. The motivation comes from modeling financial ultra-high frequency data. First, we rigorously derive the unnormalized filtering equation with marked point process observations under mild assumptions, especially relaxing the bounded condition of stochastic intensity. Then, we derive the Poisson chaos expansion for the unnormalized filter. Based on the chaos expansion, we establish the uniqueness of solutions of the unnormalized filtering equation. Moreover, we derive the Poisson chaos expansion for the unnormalized filter density under additional conditions. To explore the computational advantage, we further construct a new consistent recursive numerical scheme based on the truncation of the chaos density expansion for a simple case. The new algorithm divides the computations into those containing solely system coefficients and those including the observations, and assign the former off-line. 相似文献
984.
Zeng Guangxing 《代数通讯》2013,41(10):3052-3063
The purpose of this article is to introduce the notion of real valuations on modules over commutative rings. These real valuations are characterized by their associated valuation triples, and a necessary and sufficient condition for a module to possess a real valuation is established. Moreover, the close interplay between valuations and orderings on a module is investigated by introducing the compatibility of valuations with orderings. Via the compatibility of valuations with orderings, the reality of valuations on a module also is characterized. 相似文献
985.
Synthesis and Characterization of Bis(methyl-2-pyridylmethylidenedrazinecarbodithioate)manganese(II)
Mao-Sheng Liu Qiong-Yan Yu Zheng-Yuan Zhou Qing-Guang Zhan He-Ping Zeng Yue-Peng Cai 《Journal of chemical crystallography》2008,38(11):845-849
Abstract Brown crystals of title compound, bis(methyl-2-pyridylmethylidene-drazinecarbodithioate)manganese(II), was formed by reaction
of methyl-2-pyridylmethylidenehydrazinecarbodithioate(HNNS) with manganese perchlorate at 323 K temperature and recrystallized
from ethanol at room temperature, crystallizing in the monoclinic system, space group P2(1)/n, with a = 11.631(2), b = 14.010(3), c = 13.128(3) ?, β = 105.791(11)°; V = 2058.6(7) ?3, D
c
= 1.533 g/cm3, Z = 4, C16H16N6MnS4, M
r
= 475.53, μ(M0 K
α
) = 1.060 mm−1, F (000) = 972. The structure was refined to R = 0.0441, wR = 0.1196 for 3,682 (I > 2σ(I)) reflections and S = 1.110. In title complex the coordination geometry about manganese is distorted octahedral and the two
ligands in the mer configuration (S and tertiary N atom cis to each other and the iminic N atoms trans). Furthermore, the neutral molecule units MnII(NNS)2 are connected by hydrogen bonds C–H···N and C–H···S and form a three dimensional ordered network structure.
Graphical Abstract The title compound, Mn(NNS)2, exists as discrete molecules in which the central MnII
atom is coordinated by two S atoms and four N atoms from two ligands NNS- molecules
in a mer-octahedral configuration.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
986.
The major challenge of nuclear magnetic resonance (NMR) microscopy at a spatial resolution of a few micrometers is to obtain a sufficiently high signal-to-noise-ratio (SNR) within a reasonable measurement time. As a particular difficulty, molecular self-diffusion poses a serious limitation to true spatial resolution and SNR if conventional Fourier encoding techniques are used. Opposed to that, the alternative DESIRE (Diffusion Enhancement of SIgnal and REsolution) approach to NMR microscopy utilises diffusion to increase the SNR. Being a real-space imaging method, spatial localisation is accomplished by saturation pulses while diffusion continuously replaces the saturated by unsaturated spins. For this technique a signal enhancement of up to three orders of magnitude has been predicted and initial experimental data have provided a proof of principle. In the present work, a detailed investigation of one-dimensional (1D) DESIRE is presented including simulations of a real implementation of the method, a quantitative experimental analysis, and basic 1D imaging. The simulations reveal the importance and provide the means of ensuring the true spatial resolution for this particular way of localisation, enable the selection of useful experimental parameters, and predict the specific image contrast to be expected around barriers restricting diffusion. Experimental data are presented with resolutions down to 3 microm and DESIRE enhancement up to 25 that are in good agreement with the simulation results. In particular, 1D DESIRE imaging in a phantom confirms the expected signal drop close to barriers due to spatially restricted diffusion. 相似文献
987.
Light‐harvesting complexes (LHC) in photosynthetic organisms perform the major function of light absorption and energy transportation. Optical spectrum of LHC provides a detailed understanding of the molecular mechanisms involved in the excitation energy transfer (EET) processes, which has been widely studied. Here, we study how the geometric property of LHC in Rhodospirillum (Rs.) molischianum would affect its spectral characteristics and energy transfer process. By adopting the effective Hamiltonian and the dipole–dipole approximation, we calculate the exciton level structures for the LH2 ring and LH1 ring and the energy transfer time between different LHCs under various structural parameters and different rotational symmetries. Our numerical results show that the LHC's absorption peaks and the energy transfer time between different LHCs can be modified by changing the geometric configurations. Our study may be beneficial to the applications in designing highly efficient photovoltaic cell and other artificial photosynthetic systems. 相似文献
988.
Lin Zeng Xiao-Qiang Guo Zai-Jun Yang Ya Gan Lian-Mei Chen Tai-Ran Kang 《Tetrahedron letters》2019,60(33):150943
A cascade cyclization/nucleophilic aromatic substitution (SNAr) reaction of α,β-unsaturated N-tosylhydrazones with N-heteroaryl chlorides was developed for the synthesis of N-heteroaryl pyrazole derivatives. This one-pot reaction provided bi(heteroaryl) derivatives in good to excellent yields and with excellent regioselectivity. The procedure is operationally simple and applicable to large-scale synthesis. 相似文献
989.
Haichun Zeng Guoping Yin Qian Wei Dehai Li Yi Wang Youcai Hu Changhua Hu Yi Zou 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(20):6641-6645
Fenestranes, a specific class of natural products, contain four fused rings that share a central quaternary carbon atom. The fungal natural product penifulvin A ( 1 ) is a potent insecticidal sesquiterpene that features the [5.5.5.6]dioxafenestrane ring. Although the chemical synthesis of 1 has been achieved recently, the enzymes catalysing the cyclization and oxidation of FPP to 1 remain unknown. In this work, we identified a concise pathway that uses only three enzymes to produce 1 . A new sesquiterpene cyclase (PeniA) generates the angular triquinane scaffold silphinene ( 6 ). A cytochrome P450 (PeniB) and a flavin‐dependent monooxygenase (PeniC) catalyse a series of oxidation reactions to transform 6 into 1 , including oxidation of the C15 methyl group to a carboxylate moiety, oxidative coupling of the C15 carboxylate and the C1‐C2 olefin to form a γ‐lactone, and Baeyer–Villiger oxidation to form a δ‐lactone. Our results demonstrate the highly concise and efficient ways in which fungal biosynthetic pathways can generate complex sesquiterpene scaffolds. 相似文献
990.
Jin‐Yue Zeng Xiao‐Shuang Wang Yong‐Dan Qi Yun Yu Xuan Zeng Xian‐Zheng Zhang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(17):5748-5752
Polycyclic aromatic derivatives can trap 1O2 to form endoperoxides (EPOs) for O2 storage and as sources of reactive oxygen species. However, these materials suffer from structural amorphism, which limit both practical applications and fundamental studies on their structural optimization for O2 capture and release. Metal–organic frameworks (MOFs) offer advantages in O2 binding, such as clear structure–performance relationships and precise controllability. Herein, we report the reversible binding of O2 is realized via the chemical transformation between anthracene‐based and the corresponding EPO‐based MOF. It is shown that anthracene‐based MOF, the framework featuring linkers with polycyclic aromatic structure, can rapidly trap 1O2 to form EPOs and can be restored upon UV irradiation or heating to release O2. Furthermore, we confirm that photosensitizer‐incorporated anthracene‐based MOF are promising candidates for reversible O2 carriers controlled by switching Vis/UV irradiation. 相似文献