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951.
The increasing interest in studying enzyme kinetics under in vivo conditions requires practical methods to estimate control parameters from experimental data. In contrast to currently established approaches of dynamic modelling, this paper addresses the steady-state analysis of metabolic pathways. Within the framework of metabolic control analysis (MCA), elasticity coefficients are used to describe the control properties of a local enzyme reaction. The double modulation method is one of the first experimental approaches to estimate elasticity coefficients from measurements of steady-state flux rates and metabolite concentrations. We propose a generalized form of the double modulation method and compare it to the recently developed linear-logarithmic approach. 相似文献
952.
A spin probe method was used to study microviscosity of aqueous medium in embryos and endosperm of maize (Zea mays L.) seeds after their irradiation with a Lvov-1 Elektronika laser device. Based on parameters of electron spin resonance (ESR) spectra of nitroxyl radicals (probes) absorbed by imbibing seeds during water uptake, correlation times τC were determined for the rotational diffusion of probes in embryos and endosperm of seeds. The τC values were found smaller in embryos of irradiated seeds than in untreated seeds; the dependence of τC on the duration of seed imbibition was determined. It is concluded that laser irradiation of seeds decreases the microviscosity of aqueous medium in embryo cells and elevates the mobility of the probes. Effect of laser irradiation on τC in seed endosperm was less pronounced but also led to the increase in probe mobility. 相似文献
953.
Life cycle assessment of a multi-material car component 总被引:1,自引:1,他引:0
Catarina Ribeiro José V. Ferreira Paulo Partidário 《The International Journal of Life Cycle Assessment》2007,12(5):336-345
Background, Aims and Scope In recent years, the automotive industry has been experiencing an increasing concern with environmental requirements. A particular
focus is being given to light-weighting of cars, to reducing fuel consumption and to the use of different recycling materials.
Consequently, decisions on product design and development must involve economic and technological as well as environmental
considerations. In adequate conditions, the LCA methodology enables one to assist an effective integration of the environmental
considerations in the decision-making process [1]. In this paper, a multi-material car component which is part of the current
automotive brake system, has been modified by its original manufacturer. Such a modification included the use of a new multi-material
injection moulding process and the consumption of recyclable materials. The new and the current component were comparatively
assessed throughout their life cycles in order to evaluate their respective environmental impacts and, thus, to verify if
the new component offers a lower environmental load. The results described in this paper are part of the outcome of a broader
research project involving industrial companies, university, technological centres and research institutes based in Portugal,
Spain and Germany.
Main Features The car component under focus has four subcomponents whose base materials consist of steel and plastic. The LCA methodology
is used to evaluate two scenarios describing the new car component, on the one hand, and the reference scenario, which consists
of the existing car component, on the other. The former results from the selection of new subcomponents materials, aiming
to use a new production process together with a recycling strategy.
Results and Discussion The inventory analysis shows a lower energy consumption in the alternative scenario (4.2 MJ) compared to the reference scenario
(6.1 MJ). Most of that energy is still non-renewable, relating in particular to crude consumption in the car use phase and
in the production phase (transports and plastics production). The life cycle inventory analysis indicates also that the alternative
scenario has lower air emissions of CO2, CO, NOx, SOx, NM VOC and PM10, as well as lower solid wastes and water emissions of oils and BOD5. Otherwise, the water emissions of undissolved
substances and COD are higher for the alternative scenario. Most of the energy consumed and the air pollutants inventoried
occur as a consequence of the use phase. Otherwise, for most of the life cycle water emissions inventoried and solid wastes,
the production phase is the major contributor. The impact assessment, performed with the CML method, allows one to conclude
that the alternative scenario exhibits lower results in all the impact categories. Both scenarios have similar environmental
profiles, being: (i) the use phase, the major contributor for the abiotic depletion, global warming, photochemical oxidation,
acidification and eutrophication; and (ii) the production phase, the main contributor for ozone depletion, human toxicity,
fresh water aquatic ecotoxicity, marine aquatic ecotoxicity and terrestrial ecotoxicity. The sensitivity analysis, with respect
to the fuel consumption reduction value, the impact assessment method and the final disposal scenario, performed in this study
allows one to confirm, as a main conclusion, that the alternative scenario is environmentally preferable to the reference
scenario.
Conclusion The results obtained through the application of the LCA methodology enable one to conclude that the alternative component
has a lower environmental load than the reference component.
Recommendations and Perspectives Considering that the time required for the inventory data collection is a critical issue in LCA practise, the insights provided
by this particular case study are likely to be useful to product developers in the car component manufacturing industry, particularly
to brake system manufacturers supporting the environmental design within the sector. 相似文献
954.
Non-linear and anisotropic heart valve leaflet tissue mechanics manifest principally from the stratification, orientation, and inhomogeneity of their collagenous microstructures. Disturbance of the native collagen fiber network has clear consequences for valve and leaflet tissue mechanics and presumably, by virtue of their intimate embedment, on the valvular interstitial cell stress–strain state and concomitant phenotype. In the current study, a set of virtual biaxial stretch experiments were conducted on porcine pulmonary valve leaflet tissue photomicrographs via an image-based finite element approach. Stress distribution evolution during diastolic valve closure was predicted at both the tissue and cellular levels. Orthotropic material properties consistent with distinct stages of diastolic loading were applied. Virtual experiments predicted tissue- and cellular-level stress fields, providing insight into how matrix-to-cell stress transfer may be influenced by the inhomogeneous collagen fiber architecture, tissue anisotropic material properties, and the cellular distribution within the leaflet tissue. To the best of the authors’ knowledge, this is the first study reporting on the evolution of stress fields at both the tissue and cellular levels in valvular tissue and thus contributes toward refining our collective understanding of valvular tissue micromechanics while providing a computational tool enabling the further study of valvular cell–matrix interactions. 相似文献
955.
956.
Satoru G. Itoh 《Molecular simulation》2015,41(10-12):1021-1026
In order to predict the native structures of proteins and peptides and to investigate the functions of these biomolecules, it is essential to realise efficient sampling in the conformational space. We had recently proposed a new generalised-ensemble algorithm, which is referred to as the replica-permutation method (RPM), to sample the conformational space efficiently. We introduce this RPM and demonstrate its usefulness by applying to three systems: particles in a double-well potential energy, Met-enkephalin in a vacuum, and a C-peptide analogue of ribonuclease A in explicit water. Replica-exchange simulations were performed to compare their results with the results of the replica-permutation simulations. It is shown that the RPM sampled not only the temperature space but also the conformational space more efficiently than the replica-exchange method. The folding pathway of C-peptide is also presented. 相似文献
957.
Ambrish Kumar Srivastava 《Molecular simulation》2015,41(15):1278-1282
Superatoms can be considered as potential building blocks not only of non-traditional species but also of many traditional species. This idea is demonstrated by considering Li2F2, traditionally a dimer of LiF which can be formed either by LiF2–Li interaction or by Li2F–F interaction using MP2/aug-cc-pVDZ method. The existence of superatomic motifs is discussed in the resulting linear as well as square conformers of Li2F2 which are compared on the basis of the highest occupied molecular orbitals and vibrational properties. Finally, we have established that formation of Li2F2 by these interactions is exothermic at CCSD(T)//MP2/aug-cc-pVDZ level. This study is expected to provide further insights into superatomic interactions and formations of traditional salts. 相似文献
958.
屋面绿化卷材根系层土壤温度变化特征 总被引:1,自引:0,他引:1
根据3种厚度屋面绿化卷材根系层土壤温度、自然条件下的土壤温度和附近气象站大气温度观测资料,采用对比分析、线性回归等方法,对不同屋面绿化卷材根系层土壤温度的变化特征进行了研究。结果表明:屋面绿化卷材根系层土壤温度年变化规律与大气温度年变化规律基本一致;卷材具有一定的隔热保温作用,且随着薄膜厚度的增加,绿化卷材保温隔热效果越明显;不同型号卷材根系层土壤温度的日变幅随薄膜厚度的增加而减小;根系层土温日变幅与厚度关系可拟合成指数函数;不同厚度屋面卷材根系层土壤温度同大气温度之间均存在极显著的线性关系。 相似文献
959.
Daisuke Koga Satoshi Kusumi Hiroki Bochimoto Tsuyoshi Watanabe Tatsuo Ushiki 《The journal of histochemistry and cytochemistry》2015,63(12):968-979
Although the osmium maceration method has been used to observe three-dimensional (3D) structures of membranous cell organelles with scanning electron microscopy (SEM), the use of osmium tetroxide for membrane fixation and the removal of cytosolic soluble proteins largely impairs the antigenicity of molecules in the specimens. In the present study, we developed a novel method to combine cryosectioning with the maceration method for correlative immunocytochemical analysis. We first immunocytochemically stained a semi-thin cryosection cut from a pituitary tissue block with a cryo-ultramicrotome, according to the Tokuyasu method, before preparing an osmium-macerated specimen from the remaining tissue block. Correlative microscopy was performed by observing the same area between the immunostained section and the adjacent face of the tissue block. Using this correlative method, we could accurately identify the gonadotropes of pituitary glands in various experimental conditions with SEM. At 4 weeks after castration, dilated cisternae of rough endoplasmic reticulum (RER) were distributed throughout the cytoplasm. On the other hand, an extremely dilated cisterna of the RER occupied the large region of the cytoplasm at 12 weeks after castration. This novel method has the potential to analyze the relationship between the distribution of functional molecules and the 3D ultrastructure in different composite tissues. 相似文献
960.