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991.
Reactions of polypeptide ions with electrons in the gas phase   总被引:9,自引:0,他引:9  
Reactions of electrons in the energy range below 70 eV with polypeptide cations and anions are reviewed, as well as their applications for the structural analysis of polypeptides. At very low energies (相似文献   
992.
Preparation of flat carbon support films   总被引:1,自引:0,他引:1  
Wrinkling of carbon support films is known to limit the resolution of electron microscopy images of protein two-dimensional crystals. The origin of carbon wrinkling during preparation of the support films was investigated by reflected light microscopy. We observed that carbon films go through several states during their preparation. While dried carbon films have a tendency to be wrinkled, a flat state is observed transiently before complete drying. This state could be stabilized by the addition of sugars or tannic acid to the embedding medium. An alternative method for preparing flat carbon films was developed, in which a sandwich is formed by two symmetrical carbon films positioned on both sides of a grid. The formation of sandwiched carbon films was facilitated by the use of grids with thin bars. The carbon sandwich films were flat, stable, and easily and reproducibly prepared.  相似文献   
993.
Die Sicherstellung eines ausreichenden Zuverlässigkeitsniveaus im Rahmen der Erhaltung von Bauwerken und insbesondere Betonbrücken, welche durch Verkehrs‐ und Umwelteinflüsse einer kontinuierlichen Verschlechterung im Laufe ihrer Lebenszeit unterliegen, ist in der Regel eine komplexe und teure Aufgabenstellung. Besonders in Regionen mit Streusalzeinsatz in der Winterzeit beeinflusst die Chloridbelastung sowohl den Entwurf als auch die Erhaltung der Bauwerke durch ihren Einfluss auf die Dauerhaftigkeit wesentlich. In diesem Beitrag wird eine Bewertungsstrategie für die durch die Chloridbelastung hervorgerufene Zustandsverschlechterung von Betonstrukturen und deren Auswirkung auf das Sicherheitsniveau sowie die verbliebene Lebenszeit an einem Fallbeispiel vorgestellt. Hierbei werden die Entnahme von Proben, deren Untersuchung, die inverse Analyse des Eindringverhaltens und infolge die Prognose der Chloridkonzentration im Bauteil, die Vorhersage der Korrosionsentwicklung über die Zeit und schließlich die Bestimmung des gegenwärtigen und zukünftigen Zuverlässigkeitsniveaus unter Beachtung der normativ festgelegten Grenzzustände für Tragfähigkeit und Gebrauchstauglichkeit behandelt. Schlussendlich werden unterschiedliche Erhaltungsstrategien in Bezug auf die zu erwartenden Lebenszykluskosten verglichen. Approach for the Assessment of Concrete Structures Subjected to Chloride Induced Deterioration The maintenance of an adequate safety level of concrete bridges under their gradual degradation due to traffic and environmental actions during service life is an expensive, problematic and questionable task. Chloride ion ingress is an important aspect of durability design and maintenance, especially in regions where winter salt application for traffic safety is common, e. g. for highways. A feasible approach for the assessment of chloride induced deterioration and its consequences on the safety level, remaining service life and thus maintenance planning will be presented by a case study. Steps include the extraction of samples, laboratory test, inverse analysis and prognosis of chloride ingress, prediction of likely corrosion propagation over time and determination of the current and future safety level with regard to code based service limit states and ultimate limit states. Finally different maintenance strategies are compared with respect to the total life cycle costs.  相似文献   
994.
Mixed-dual formulations of the finite element method were successfully applied to the neutron diffusion equation, such as the Raviart–Thomas method in Cartesian geometry and the Raviart–Thomas–Schneider in hexagonal geometry. Both methods obtain system matrices which are suitable for solving the eigenvalue problem with the preconditioned power method. This method is very fast and optimized, but only for the calculation of the fundamental mode. However, the determination of non-fundamental modes is important for modal analysis, instabilities, and fluctuations of nuclear reactors. So, effective and fast methods are required for solving eigenvalue problems. The most effective methods are those based on Krylov subspaces projection combined with restart, such as Krylov–Schur. In this work, a Krylov–Schur method has been applied to the neutron diffusion equation, discretized with the Raviart–Thomas and Raviart–Thomas–Schneider methods.  相似文献   
995.
Silica gel modified by the addition of 2-mercapto-5-phenylamino-1,3,4-thiadiazole (MPATD) was developed for the preconcentration of Pb(II), Cd(II), Cu(II) and Hg(II) at trace levels. A "series" experimental procedure permitted the determination of the optimal working conditions (time and pH) and an "on-column" experimental method permitted the determination of the quantity of MPATD retained on silica gel, the uptake capacity, the most suitable eluent and the minimum volume of eluent for which the maximum quantity of metal cations is recovered. The maximal retention capacity on the impregnated silica gel columns was obtained at pH 7.5-8 and was 1500 micrograms g-1 for Pb(II) and about 1000 micrograms g-1 for Cd(II), Cu(II) and Hg(II). The effect of preconcentration is relevant; on passing 1 l of solution containing 1 microgram ml-1 of cation through a column containing 5 g of impregnated silicagel, after elution with 30-50 ml of the appropriate eluent the cation concentration increased about 15-20-fold. The determination of cations by flame AAS was statistically evaluated and showed recoveries higher than 96% for Pb(II), 98.5% for Cd(II) and 97.95% for Cu(II) after elution with 4 M HNO3 and about 99.15% for Hg(II) after elution with thiourea.  相似文献   
996.
The purpose of this work was research into influence of ultra-violet radiation on size of run of regional and screw dislocations in beams of dislocation sockets, formed at indentation surface of alkali-halide crystals. In experiments it was used crystals NaCl, with the quantitative maintenance of impurity 10-2 -10-3weight%, the wave length of UV-radiation λ=250 nanometers, the sizes of samples 10mm× 20mm× 2mm,temperature of samples was constant T=290 K.It is established that indentation and the simultaneous irradiation of samples a ultraviolet is increases size of run of head dispositions in dislocation sockets..It is marked, that influence UV-radiation nonequivalence for various times of an exposition. At small times (till 5 minutes) the size of run grows. The length of beams increases on ~ 50 %. At the further increase in time of influence of a ultraviolet the length of beams is reduced till the sizes corresponding stressing without an irradiation (Figs. 1, 2, 3). The effect is observed on dislocation beams of regional and screw orientations and most expressed at small loadings (in our experiments-10 grams) (Fig. 3).Observable effects are explained from positions dislocation-exciton interactions. At UV-radiation exciton cooperates with the charged step on a disposition, causing movement of a step along a disposition on one internuclear distance. Due to this interaction overcoming by a disposition of a grid of stoppers is facilitated.Big times of endurance cause a relaxation of pressure directly in a print that provides convertible movement of dispositions in area of a print and as consequence, reduction of length of beams of dislocation sockets.  相似文献   
997.
Lightning striking distance of complex structures   总被引:1,自引:0,他引:1  
Traditionally, the location of lightning strike points has been determined by using the rolling sphere method, but recently the collection volume method (CVM) has also been proposed for the placement of air terminals on complex structures. Both these methods are empirical in nature and a more advanced model based on physics of discharges is needed to improve the state of affairs. This model is used to evaluate the striking distance from corners and air terminals on actual buildings and the results are qualitatively compared with the predictions of the rolling sphere method and the CVM. The results show that the striking distance not only depends upon the prospective return stroke current and the geometry of the building, but also on the lateral position of the downward leader with respect to the strike point. A further analysis is performed to qualitatively compare the lightning attraction zones obtained with the CVM and the leader inception zones obtained for a building with and without air terminals. The obtained results suggest that the collection volume concept overestimates the protection areas of air terminals placed on complex structures, bringing serious doubts on the validity of this method.  相似文献   
998.
A model for the RIE process design of metal oxide surfaces based on density functional theory-based total energy calculations has been developed. Cluster and periodic systems were employed in order to develop the model and hence gain a deeper understanding of the process mechanisms on an atomic scale. In the present study, Fe3O4 was used for the cluster system, and NiO for the periodic system as metal oxide surfaces. Possible gas combinations and by-products were studied with the aim of producing a more efficient and effective RIE process for metal oxide thin films. This study can be considered as fundamental groundwork required for the understanding of the reactivity in the etching of metal oxide surfaces and a means of decreasing the processing period of RIE for metal oxide thin films by optimum selection of gas combinations with a knowledge of their probable by-products.  相似文献   
999.
The results of a series of experiments on superdeep penetration of copper-powder particles into a steel target are presented. The main parameters of the process and its efficiency are determined on the basis of statistical processing of the data on sequential breakdown of foil layers that are placed in the target perpendicular to the direction of motion of the penetrating particles. Translated from Inzhenerno-Fizicheskki Zhurnal, Vol. 73, No. 5, pp. 1056–1063, September–October, 2000.  相似文献   
1000.
We show how periodic motions can be represented by a small number of eigenshapes that capture the whole dynamic mechanism of the motion. Spectral decomposition of a silhouette of a moving object serves as a basis for behavior classification by principle component analysis. The boundary contour of the walking dog, for example, is first computed efficiently and accurately. After normalization, the implicit representation of a sequence of silhouette contours given by their corresponding binary images, is used for generating eigenshapes for the given motion. Singular value decomposition produces these eigenshapes that are then used to analyze the sequence. We show examples of object as well as behavior classification based on the eigendecomposition of the binary silhouette sequence.  相似文献   
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