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1.
The calcium pump (sarco/endoplasmic reticulum Ca2+-ATPase, SERCA) plays a major role in calcium homeostasis in muscle cells by clearing cytosolic Ca2+ during muscle relaxation. Active Ca2+ transport by SERCA involves the structural transition from a low-Ca2+ affinity E2 state toward a high-Ca2+ affinity E1 state of the pump. This structural transition is accompanied by the countertransport of protons to stabilize the negative charge and maintain the structural integrity of the transport sites and partially compensate for the positive charges of the two Ca2+ ions passing through the membrane. X-ray crystallography studies have suggested that a hydrated pore located at the C-terminal domain of SERCA serves as a conduit for proton countertransport, but the existence and function of this pathway have not yet been fully characterized. We used atomistic simulations to demonstrate that in the protonated E2 state and the absence of initially bound water molecules, the C-terminal pore becomes hydrated in the nanosecond timescale. Hydration of the C-terminal pore is accompanied by the formation of water wires that connect the transport sites with the cytosol. Water wires are known as ubiquitous proton-transport devices in biological systems, thus supporting the notion that the C-terminal domain serves as a conduit for proton release. Additional simulations showed that the release of a single proton from the transport sites induces bending of transmembrane helix M5 and the interaction between residues Arg762 and Ser915. These structural changes create a physical barrier against full hydration of the pore and prevent the formation of hydrogen-bonded water wires once proton transport has occurred through this pore. Together, these findings support the notion that the C-terminal proton release pathway is a functional element of SERCA and also provide a mechanistic model for its operation in the catalytic cycle of the pump.  相似文献   
2.
Leucokinins (LKs) constitute a family of neuropeptides identified in numerous insects and many other invertebrates. LKs act on G-protein-coupled receptors that display only distant relations to other known receptors. In adult Drosophila, 26 neurons/neurosecretory cells of three main types express LK. The four brain interneurons are of two types, and these are implicated in several important functions in the fly’s behavior and physiology, including feeding, sleep–metabolism interactions, state-dependent memory formation, as well as modulation of gustatory sensitivity and nociception. The 22 neurosecretory cells (abdominal LK neurons, ABLKs) of the abdominal neuromeres co-express LK and a diuretic hormone (DH44), and together, these regulate water and ion homeostasis and associated stress as well as food intake. In Drosophila larvae, LK neurons modulate locomotion, escape responses and aspects of ecdysis behavior. A set of lateral neurosecretory cells, ALKs (anterior LK neurons), in the brain express LK in larvae, but inconsistently so in adults. These ALKs co-express three other neuropeptides and regulate water and ion homeostasis, feeding, and drinking, but the specific role of LK is not yet known. This review summarizes Drosophila data on embryonic lineages of LK neurons, functional roles of individual LK neuron types, interactions with other peptidergic systems, and orchestrating functions of LK.  相似文献   
3.
Microtomography (μCT) and nuclear magnetic resonance (NMR) have been used to characterize porous media for decades. Magnetic resonance imaging (MRI) enables direct visualization of pore architecture and many pulse sequences exist. In this work, we tested the MRI pulse sequence Zero Echo Time (ZTE) to study sandstone and carbonate for its ability to address short relaxation times. We aimed at resolving two fluid conduit scales, that is, pores and fractures. In this research, we study tighter porous systems than those previously reported using ZTE. Additionally, pore cluster analysis (PCA), combined with ZTE, can be used to analyze pore-fracture connectivity of relatively large core plugs. We show that ZTE can resolve two-scale pore systems simultaneously, that is, fractures and pores. By combining time-domain NMR pore-size analysis and PCA, we show that careful selection of resolution is necessary to understand transport in porous media.  相似文献   
4.
Using headspace solid-phase microextraction (HS–SPME), equilibrium distributions could be determined for hydrophobic solutes in closed systems containing vapor and aqueous solution, either in the absence or presence of two short-chain phospholipids, dihexanoyl-phosphatidylcholine (diC6PC) and diheptanoyl-phosphatidylcholine (diC7PC). Without phospholipid, HS–SPME with short extraction times was used to measure water–vapor partition coefficients for d-limonene at five temperatures within 15–40°C, with results in good agreement with existing literature. The temperature dependence of yielded the enthalpy of volatilization 34.5 kJ/mol for limonene. At 25°C, solubility values for d-limonene, 1-octanol, and n-decane were obtained using similar measurements above aqueous solutions of various solute concentrations. Short-time HS–SPME extraction of limonene in closed vials containing diC6PC or diC7PC micelles was also used to evaluate distributions of solute between vapor, aqueous dissolution, and micelles, for various surfactant concentrations at 15–40°C. Resulting vapor phase concentrations were analyzed using a mass balance and measured values, to obtain micelle–water partition coefficients and critical micelle concentrations. in diC6PC solutions (1–2 mM−1) weakly increased with temperature, but decreased significantly with increased temperature for diC7PC micelles (2–4 mM−1). Solubilization in short-chain PC micelles has previously received little attention, and our results show that the extent of partitioning into these diacyl (i.e., two-tailed) lipids is comparable to that for single-tailed anionic or nonionic surfactants.  相似文献   
5.
The effects of particle size and carbon dioxide concentration on chemical conversion in engineered spherical particles undergoing calcium oxide looping are investigated. Particles are thermochemically cycled in a furnace under different carbon dioxide concentrations. Changes in composition due to chemical reactions are measured using thermogravimetric analysis. Gas composition at the furnace exit is evaluated with mass spectroscopy. A numerical model of thermal transport phenomena developed previously is adapted to match the physical system investigated in the present study. The model is used to elucidate effects of reacting medium characteristics on particle temperature and reaction extent. Experimental and numerical results show that (1) an increase in particle size results in a decrease in carbonation extent, and (2) the carbonation step consists of fast and slow reaction regimes. The reaction rates in the fast and slow carbonation regimes increase with increasing carbon dioxide concentration. The effect of carbon dioxide concentration and the distinction between the fast and slow regimes become more pronounced with increasing particle size.  相似文献   
6.
Grass pea (Lathyrus sativus) is a leguminous plant of outstanding tolerance to abiotic stress. The aim of the presented study was to describe the mechanism of grass pea (Lathyrus sativus L.) photosynthetic apparatus acclimatisation strategies to salinity stress. The seedlings were cultivated in a hydroponic system in media containing various concentrations of NaCl (0, 50, and 100 mM), imitating none, moderate, and severe salinity, respectively, for three weeks. In order to characterise the function and structure of the photosynthetic apparatus, Chl a fluorescence, gas exchange measurements, proteome analysis, and Fourier-transform infrared spectroscopy (FT-IR) analysis were done inter alia. Significant differences in the response of the leaf and stem photosynthetic apparatus to severe salt stress were observed. Leaves became the place of harmful ion (Na+) accumulation, and the efficiency of their carboxylation decreased sharply. In turn, in stems, the reconstruction of the photosynthetic apparatus (antenna and photosystem complexes) activated alternative electron transport pathways, leading to effective ATP synthesis, which is required for the efficient translocation of Na+ to leaves. These changes enabled efficient stem carboxylation and made them the main source of assimilates. The observed changes indicate the high plasticity of grass pea photosynthetic apparatus, providing an effective mechanism of tolerance to salinity stress.  相似文献   
7.
Large interfacial resistance plays a dominant role in the performance of all-solid-state lithium-ion batteries. However, the mechanism of interfacial resistance has been under debate. Here, the Li+ transport at the interfacial region is investigated to reveal the origin of the high Li+ transfer impedance in a LiCoO2(LCO)/LiPON/Pt all-solid-state battery. Both an unexpected nanocrystalline layer and a structurally disordered transition layer are discovered to be inherent to the LCO/LiPON interface. Under electrochemical conditions, the nanocrystalline layer with insufficient electrochemical stability leads to the introduction of voids during electrochemical cycles, which is the origin of the high Li+ transfer impedance at solid electrolyte-electrode interfaces. In addition, at relatively low temperatures, the oxygen vacancies migration in the transition layer results in the formation of Co3O4 nanocrystalline layer with nanovoids, which contributes to the high Li+ transfer impedance. This work sheds light on the mechanism for the high interfacial resistance and promotes overcoming the interfacial issues in all-solid-state batteries.  相似文献   
8.
郭保玲  窦启龙  乔佳  常旭宁  闫松 《煤气与热力》2021,(2):10008-10010,10022,10045
介绍全球LNG海运现状,对LNG运输船关键技术进行分析。随着LNG需求及贸易的不断增长,全球LNG贸易商对LNG运输船需求将明显增长,LNG运输船容积向大型化发展。LNG运输船推进系统是制约其发展的关键技术之一,节省燃料、高效、可回收BOG的推进系统,是未来发展的方向。LNG运输船液货舱主要以薄膜型、独立球型液舱储罐为主,薄膜型液舱储罐性能更优,造价低,受到船东青睐。  相似文献   
9.
空间电荷是影响高压直流电缆绝缘电树枝特性的主要原因之一。基于双极性载流子输运模型,对±20 kV、±22.5 kV和±25 kV直流预压下3 600 s内二维针板电极模型空间电荷分布进行仿真分析,并对比分析空间电荷分布与直流接地电树枝引发特性。结果表明:空间电荷浓度及注入深度随预压幅值及时间的增加而增大;直流接地电树枝引发长度随预压时间及幅值的增加而增加。空间电荷注入深度与电树枝引发长度两者之间高度相似。接地电树枝引发特性存在差异的主要原因是针尖附近空间电荷的分布特性。  相似文献   
10.
In nature, the feathers of the goose Anser cygnoides domesticus stay superhydrophobic over a long term, thought as the main reason for keeping the surface clean. However, contaminants, especially those that are oleophilic or trapped within textures, cannot be removed off the superhydrophobic feathers spontaneously. Here, a different self-cleaning strategy based on superhydrophilic feathers is revealed that is imparted by self-coating of the amphiphilic saliva, which enables removing away low-surface-tension and/or small-size contaminants by forming directional water sheeting depending on their unique anisotropic microstructures. Particularly, the surface superhydrophilicity is switchable to superhydrophobicity upon exposure to air for maintaining a clean surface for a long time, which is further enhanced by coating with self-secreted preening oil. By alternate switching between a transient superhydrophilicity and a long-term stable superhydrophobicity, the goose feathers exhibit an integrated smart self-cleaning strategy, which is also shared by other aquatic birds. An attractive point is the re-entrant structure of the feathers, which facilitates not only liquid spreading on superhydrophilic feathers, but also long-term stability of the cleaned surface by shedding water droplets off the superhydrophobicity feathers. Thus, artificial self-cleaning microtextures are developed. The result renews the common knowledge on the self-cleaning of aquatic bird feathers, offering inspiration for developing bioinspired self-cleaning microtextures and coatings.  相似文献   
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