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1.
We use pulmonary function measurements on pre-adolescent children and indoor air pollution measurements in the homes of these children to illustrate estimation techniques for linear regression models containing independent variables measured with error. In our data set, replicate measures of indoor air pollutant concentrations provide one method of estimating measurement error variances. Surrogate information in the form of cigarettes smoked is also available for the pollutant of interest. Several estimation procedures are presented, and we combine two estimators, one based on surrogate information and one based on replication information, using generalized least squares. 相似文献
2.
K.W.E. DENSON 《International journal of laboratory hematology》1988,10(3):315-328
A more sensitive or higher concentration of rabbit brain thromboplastin does not result in greater accuracy and precision of results in oral anticoagulant therapy and is unable to mimic the PIVKA sensitivity of human brain. In terms of International Normalized Ratios the British Comparative Thromboplastin and Manchester Comparative Reagent (both now discontinued) and the Manchester Reagent had the poorest sensitivity to factor VII of all the reagents studied. It is not possible accurately to calibrate rabbit brain against human brain thromboplastin in the upper therapeutic range and beyond. 相似文献
3.
对于眼底图像 ,由于不在正视点取像造成的几何畸变和由于荧光素从血管壁渗漏等造成的灰度畸变 ,几乎是不可避免的。为临床诊断提供丰富信息的需要出发 ,进行多幅眼底图像的拼接是必要的。本文为此提出了几个新的处理方法 ,如基于大窗口的滤波灰度校正方法、基于透视投影原理的几何校正方法与基于小波子空间上的拼接算法 ,均具有效果好和耗时少的优点。 相似文献
4.
D. Willoughby Roger C. Thomas Christof J. Schwiening 《Pflügers Archiv : European journal of physiology》1998,436(4):615-622
We have evaluated the pyrene-based ratiometric fluorescent dye, 8-hydroxypyrene-1,3,6-trisulphonic acid (HPTS), by using
it in conjunction with glass pH-sensitive microelectrodes to measure intracellular pH (pHi) in voltage-clamped snail neurones. Intracellular acidification with propionic acid, and alkalinization following the activation
of H+ channels allowed the calibration of the dye to be compared with that of the pH microelectrode over the pH range 6.50–7.50.
HPTS calibrated in vitro and glass pH-sensitive microelectrodes produced similar absolute resting pHi values, 7.16±0.05 (n=10) and 7.17±0.06 (n=9) respectively in nominally CO2/HCO3
–-free saline. At both extremes of the pH range there were small discrepancies. At acidic pHi, 6.87±0.09 (n=5), the intracellular HPTS measurement differed by –0.08±0.03 pH units from the pH-sensitive microelectrode measurement.
At alkaline pHi,7.32±0.10 (n=5), HPTS measurements produced pH values that differed by +0.07±0.04 pH units from those of the pH-sensitive microelectrode.
Some of the discrepancy could be accounted for by the slow response of the recessed-tip pH-sensitive microelectrode (time
constant 77±15 s, n=3). Further experiments showed that HPTS, used at an intracellular concentration of 200 μM to 2 mM, did not block activity-dependent
pHi changes. The intracellular HPTS concentration was calculated by measurement of intracellular chloride during a series of
HPTS-KCl injections. Comparison of HPTS with 2′,7′-bis(2-carboxyethyl)-5,6-carboxyfluorescein (BCECF), at the same concentration,
showed that HPTS produces a larger change in ratio over the pH range 6.00–8.00.
Received: 19 February 1998 / Received after revision and accepted: 22 April 1998 相似文献
5.
A simple, inexpensive device described here will produce a spike whose amplitude, shape, and output impedance are similar to those of the human QRS complex. Several reliable spike rates can be selected. 相似文献
6.
The intensity of acoustic stimulation is frequently a variable of interest in psychophysiological studies but calibration procedures, particularly when earphones are employed, are not always adequate. The present study demonstrates that intensity is underestimated, more seriously at low frequencies, when calibration does not employ an appropriate coupler. Several standardized calibration methods are discussed in terms of their suitability For routine laboratory use. 相似文献
7.
V. Nougier C. Bard M. Fleury N. Teasdale J. Cole R. Forget J. Paillard Y. Lamarre 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1996,109(3):473-482
Two deafferented patients and several control subjects participated in a series of experiments to investigate how accurate single-joint movements are programed, spatially calibrated, and updated in the absence of proprioceptive information. The deafferented patients suffered from a permanent and severe loss of large sensory myelinated fibers below the neck. Subjects performed, with and without vision, sequences of forearm supinations and pronations with two temporal delays between each movement (0 s and 8 s). Overall, the lack of proprioception did not yield any significant decrease in movement accuracy when vision was available. Without vision, the absence of proprioceptive afferents yielded (1) significantly larger spatial errors, (2) amplitude errors similar to those of control subjects, and (3) a significant drift when an 8-s delay was introduced between two successive movements. Subjects also performed, without vision, a 20 supination followed by a 20 pronation that brought back the wrist to the starting position. On some trials, the supination was blocked unexpectedly by way of a magnetic brake. When the supination was blocked, subjects were already on the second target and no pronation was required when the brake was released. The defferented patients, unaware of the procedure, always produced a 20 pronation. These data confirm that deafferented patients were not coding a final position. It rather suggests that they coded an amplitude and translated the spatial distance between the two targets in a corresponding force pulse. Overall, the results highlight the powerful and key role of proprioceptive afferents for calibrating the spatial motor frame of reference. 相似文献
8.
A large linear flow range and a small instrumental dead space volume are incompatible properties for a pneumotachometer (PTM). The linearity of a Fleisch number 2 PTM is studied for flows up to 6 litre s-1 (nominal range 0-2 litre s-1) with various up- and downstream geometries. It is hypothesised that using an array of calibration factors (conductance; flow/pressure), instead of a single calibration factor over the entire flow range, could improve accuracy and also extend the applicable flow range. The conductance against pressure characteristics are calculated with a previously described weighted averaging technique based on multiple strokes from a precision syringe. A single conductance value gives stroke volume errors in the range of -5 to 3% (0-2 litre s-1) and -6 to 11% (0-6 litre s-1) for validation using the same geometry as for calibration. The pressure dependent conductance improves accuracy to within -3% and 1% independent of flow range. However, for validation using a different geometry than for calibration, errors range from -5% to +8%. The degree of non-linearity varies between the geometries (range 3-15%) and is highest when using a one-directional valve upstream of the PTM and a Y-shaped connector. In conclusion, a pressure-dependent conductance improves accuracy and can also be used to extend the applicable flow range up to at least three times the nominal flow range. 相似文献
9.
10.