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91.
Given A. Brewer 《Experimental Mechanics》1972,12(3):159-168
The failure at sea of a number of merchantship propeller blodes initiated a research program supported by the Maritime Administration, the American Bureau of Shipping, the American President Lines and the States Steamship Company. Although extensive theoretical work has been carried out in the past (predicting propeller operating stresses), very little full-scale experimental stress measurements have been obtained. Brewer Engineering Laboratories, Inc. was retained by the sponsors to attach and protect fifty strain gages on the test propeller at the locations chosen by Littleton Research and Engineering Corporation. The propeller strain gages were protected from the severe environment by means of synthetic rubber and metallic overlays. The gage wiring was led down each blade and into a specially machined, hollow tailshaft through a waterproof bulkhead. The S.S. “Michigan”, with the test group aboard, sailed from Long Beach, Calif., in April 1970. The ship called at the ports of San Francisco, Yokohama, Naha, Manila, Bogo and Hong Kong during the test period. Throughout the trip across the Pacific, the gaging and instrumentation functioned without degradation or evidence of distress after onemillion propeller shaft turns. At the end of five weeks at sea and two-million turns, all but eight gages exhibited low ground resistance. The S.S. “Michigan” went into dry dock at the Bethlehem Steel Shipyard at Terminal Island, Calif., on June 15, 1970. The propeller was removed and all strain gages checked for continuity and ground resistance. Forty-two of the original 50 strain gages were found to be intact. No sign of deterioration due to cavitation or electrolysis attack existed on the metallic overlays or spot welding. Wire chafing within the fairwater adapter cap accounted for the low ground resistance values observed at the end of the voyage to Hong Kong. 相似文献
92.
This paper describes certain tests and techniques employed in measuring stresses within an experimental nuclear-reactor head of unusual design. The incorporation of certain desired design features necessitated that the head be extremely thick. Due to the thickness and its complex geometry, it was considered desirable to determine stress distribution within the head under conditions of steady-state pressure combined with rapid heating and cooling transients within the reactor, in order to determine safe limits for the operation of the head. A photoelastic study of a three-dimensional model of the reactor head was completed in 1956; this study permitted prediction of the stress distribution throughout the head as a function of internal pressure, but it was not possible to assimilate the head thermal stresses by photoelastic means. It is the purpose of this paper to describe the technique employed in measuring thermal stresses in the interior of the head, under simulated operating conditions of steady-state pressure and temperature transients. 相似文献
93.
To study combustion chemistry at low temperatures in a shock tube, it is of great importance to increase experimental test times, and this can be done by tailoring the interface between the driver and driven gases. Using unconventional driver-gas tailoring with the assistance of tailoring curves, shock-tube test times were increased from 1 to 15 ms for reflected-shock temperatures below 1,000 K. Provided in this paper is the introduction of tailoring curves, produced from a one-dimensional perfect gas model for a wide range of driver gases and the production and demonstration of successful driver mixtures containing helium combined with either propane or carbon dioxide. The He/CO2 and He/C3H8 driver mixtures provide a unique way to produce a tailored interface and, hence, longer test times, when facility modification is not an option. The tailoring curves can be used to guide future applications of this technique to other configurations. Nonreacting validation experiments using driver mixtures identified from the tailoring curves were performed over a range of reflected-shock temperatures from approximately 800 to 1,400 K, and some examples of ignition-time experiments that could not have otherwise been erformed are presented. 相似文献
94.
95.
Application of an Itô-based approximation method to random vibration of a pinching hysteretic system
In this paper, an extension of the Cumulant-Neglect closure scheme is utilized for the random vibration analysis of a single degree of freedom system with a general pinching hysteresis restoring force. The hysteresis element used in the system model can simulate commonly observed forms of stiffness, strength and pinching degradations. The second order statistics of the system response to a stationary Gaussian white noise input are derived using an Itô-based approximation technique. The validity of these response statistics are then verified by comparing them to Monte Carlo simulation results. The numerical studies performed for different combinations of degradation parameters and excitation levels show that the response estimates obtained by this solution method are in good agreement with Monte Carlo simulation. These studies also indicate the applicability of this technique for response analysis of complicated forms of non-linearities. 相似文献
96.
The use of a sliding plate rheometer (SPR) to determine the first normal stress difference of molten polymers and elastomers
at high shear rates is demonstrated. The simple shear flow in this instrument is not subject to the flow instabilities that
limit the use of rotational rheometers to shear rates often below 1 s−1. However, issues of secondary flow and wall slip must be addressed to obtain reliable data using an SPR. A highly entangled,
monodisperse polybutadiene and a commercial polystyrene were the polymers studied. The inclusion of the polystyrene made it
possible to compare data with those obtained by Lodge using a stressmeter, which is an instrument based on the measurement
of the hole pressure. The data from the two instruments are in good agreement and are also close to the predictions of an
empirical equation of Laun based on the storage and loss moduli. 相似文献
97.
Mark D. Noirot Elizabeth G. Bent Arlan D. Norman 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):177-180
Abstract Reaction of the 1,3,2,4-diazadiphosphetidine, trans-[C6H5N(H)P(S)NC6H5]2 with LiR (R = Me, n-Bu) followed by treatment of the resulting dianions with Me3SiCl and Me3GeBr produced trans-[C6H5N(R)P(S)NC6H5]2(R = Me3Si, 2; Me3Ge, 3). Substitution occurs without cis-trans isomerization or significant cleavage of the 1,3,2,4-diazadiphosphetidine ring. 2 and 3 have been characterized by spectral (1H and 31P NMR, IR, and MS) and elemental analytical data. Analogous reactions involving Me3SnCl yield mixtures containing [C6H5N(SnMe3)P(S)NC6H5]2 which could not be isolated or completely characterized. 相似文献
98.
Catherine E. Davies Thomas D. Heightman Stephen A. Hermitage Mark G. Moloney 《合成通讯》2013,43(4):687-696
Short, convenient syntheses of racemic and enantiopure methyl 6-oxopipecolate are described, starting from either pipecolic acid or (S)-lysine respectively. The sequence for the latter compound relies upon improved methodology for the oxidation of C-6 of lysine. 相似文献
99.
Fabian Benz Christoph Roderburg David Vargas Cardenas Mihael Vucur Jérémie Gautheron Alexander Koch Henning Zimmermann J?rn Janssen Lukas Nieuwenhuijsen Mark Luedde Norbert Frey Frank Tacke Christian Trautwein Tom Luedde 《Experimental & molecular medicine》2013,45(9):e42
MicroRNA (miRNA) levels in serum have recently emerged as potential novel biomarkers for various diseases. miRNAs are routinely measured by standard quantitative real-time PCR (qPCR); however, the high sensitivity of qPCR demands appropriate normalization to correct for nonbiological variation. Presently, RNU6B (U6) is used for data normalization of circulating miRNAs in many studies. However, it was suggested that serum levels of U6 themselves might differ between individuals. Therefore, no consensus has been reached on the best normalization strategy in ‘circulating miRNA''. We analyzed U6 levels as well as levels of spiked-in SV40-RNA in sera of 44 healthy volunteers, 203 intensive care unit patients and 64 patients with liver fibrosis. Levels of U6 demonstrated a high variability in sera of healthy donors, patients with critical illness and liver fibrosis. This high variability could also be confirmed in sera of mice after the cecal ligation and puncture procedure. Most importantly, levels of circulating U6 were significantly upregulated in sera of patients with critical illness and sepsis compared with controls and correlated with established markers of inflammation. In patients with liver fibrosis, U6 levels were significantly downregulated. In contrast, levels of spiked-in SV40 displayed a significantly higher stability both in human cohorts (healthy, critical illness, liver fibrosis) and in mice. Thus, we conclude that U6 levels in the serum are dysregulated in a disease-specific manner. Therefore, U6 should not be used for data normalization of circulating miRNAs in inflammatory diseases and previous studies using this approach should be interpreted with caution. Further studies are warranted to identify specific regulatory processes of U6 levels in sepsis and liver fibrosis. 相似文献