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991.
Bennett JS Feigley CE Khan J Hosni MH 《Applied occupational and environmental hygiene》2000,15(1):131-144
For many years exposure to airborne contaminants has been estimated by air or biological monitoring. In occupational settings, mathematical models increasingly are employed as adjuncts to monitoring, for instance, during process design or in retrospective epidemiological studies. Models can make predictions in a wide variety of scenarios, can be used for rapid screening, and may reduce the need for monitoring in exposure assessment. However, models make simplifying assumptions regarding air flow and contaminant transport. The errors resulting from these assumptions have not been systematically evaluated. Here we compare exposure estimates from the single-zone completely mixed (CM-1), two-zone completely mixed (CM-2), and uniform diffusivity (UD) models with workroom concentration fields predicted by computational fluid dynamics (CFD). The room air flow, concentration fields, and the breathing zone concentration of a stationary worker were computed using Fluent V4.3 for factorial combinations of three source locations, three dilution air flow rates and two emission rate profiles, constant and time-varying. These numerical experiments were used to generate plausible concentration fields, not to simulate exactly the processes in a real workroom. Thus, "error" is defined here as difference between model and CFD predictions. For both constant and time-varying emission sources, exposure estimates depended on receptor and source location. For the constant source case, ventilation rate was shown to be inconsequential to CM-1 model error. CM-1, CM-2, and UD models differed in their agreement with CFD. UD was closest to CFD for estimating concentration in the simulated breathing zone (BZ) near the source, although large errors resulted when the model was applied to the plane of possible breathing zones. CM-1 performed better for this plane but underestimated the near-source BZ exposure. For the near-source BZ location, CM-2 replicated CFD predictions more closely than CM-1 did, but less closely than UD did. Error in CM-1 model estimation of short-term average exposure to a time-varying source was highly dependent on ventilation rate. Error decreased as ventilation rate increased. 相似文献
992.
993.
The presence of tissue amyloid P component was determined by using a direct immunofluorescence technique on frozen sections of normal human placentae and umbilical cords from gestations of various durations. Amyloid P component was first detected at the 16th week of gestation and appeared to increase progressively in amount so as to be present in abundance in the term placenta. Placental amyloid P component was present in the perifetal capillary zone where basement membrane-like material and reticulin fibres are also found. Amyloid P component may be related to the maturation of the placenta. 相似文献
994.
995.
Cystic lung disease in Down's syndrome: a report of two cases 总被引:1,自引:0,他引:1
Previously unreported lung disease found at autopsy in 2 young infants with Down's syndrome and congenital heart disease (complete atrioventricular canal malformation with left-to-right shunt) is described. The perinatal and neonatal period was unremarkable, and there was no history of mechanical ventilation or administration of high concentration of oxygen for extended periods. In 1 of the cases respiratory symptoms and hyperinflation with focal cystic changes in the lung fields on chest X-ray were noted at 5-7 months of age. Pathologically there was cystic dilatation of alveoli with focal cuboidal metaplasia of alveolar epithelium and mild to moderate focal alveolar septal fibrosis. Wilson-Mikity syndrome, congenital pulmonary lymphagiectasia, bronchopulmonary dysplasia, and idiopathic interstitial fibrosis of lungs were ruled out on clinical and/or pathologic grounds. Factors such as compression of bronchi by enlarged pulmonary arteries or cardiac chambers, peribronchiolar accumulation of fluid, pulmonary hypoplasia occurring in Down's syndrome, and episodes of pulmonary arterial hypoperfusion associated with severe congenital heart disease may be related to the pathogenesis of the lesion. 相似文献
996.
A 68-year-old woman presented with generalized weakness and a rash on her lower extremities. The weakness began one week earlier, shortly after treatment for leg cramps and two days before the rash appeared. She had also had blood-streaked sputum a few days before admission. There was no history of bleeding diathesis, nose bleeding, hematuria, vasculitis, muscle or joint aches, cinchonism, or exposure to tuberculosis. She denied fever, chills, night sweats, leg pain or swelling, chest pain, or abdominal pain. 相似文献
997.
This report presents results from a 6-month study over the period 16 November 1986 to 15 May 1987 which was designed to investigate the prevalence of cryptosporidiosis in Dammam and Alkhobar, Saudi Arabia. A total of 209 stool specimens from children and 112 from adults with diarrhoea were examined. Only two (1%) of the children, both aged 2 years, were positive for Cryptosporidium spp. Giardia lamblia was found in 13 (4%) cases and was found to be the most common protozoan parasite, whereas Salmonella spp. was seen in 19 (6%) cases. Stool specimens were examined for rotavirus from children under 2 years of age; 31 (41%) of the specimens were positive. 相似文献
998.
Tetanic convulsions are not uncommon among severely dehydrated children in the developing countries. This raises the question whether these children have disturbances in the homeostasis of divalent ions. Serum values are reported of calcium, magnesium, phosphorus, sodium and potassium, as well as blood pH in children below 3 years of age with acute watery diarrhoea and with an estimated weight loss of about 10%. The study was performed on dehydrated children with (DC) or without (D) convulsions. Values were obtained on admission and following rehydration therapy (RT). On admission serum calcium was low in both D and DC children. Serum phosphorus was likewise elevated in both D and DC children. Serum magnesium was slightly elevated in the DC but not in the D group. No patient had hypernatremia. During RT, serum calcium increased significantly and serum phosphorus decreased significantly in D and DC children. Serum calcium showed a significant inverse correlation with serum phosphorus and a significant direct correlation with blood pH. Treatment of DC children with i.v. calcium and i.m. magnesium had no immediate effect on the convulsions. Our conclusion is that severely dehydrated children will develop hypocalcemia. The cause may be a redistribution of calcium into the cells, parallelled by a redistribution of phosphorus from the intra- to the extracellular space. 相似文献
999.
A new surgical technique to close bladder defects using well vascularized myouterine flap is described. The flap serves as a temporary scaffold while the bladder is being bridged by natural bladder regeneration. The advantage of this flap is that it is not a free flap, being well vascularized through its pedicle, enhancing optimal bladder regeneration. This technique may be a useful surgical alternative for repair of large bladder defects. 相似文献
1000.
M. U. Khan M.B.B.S. D.P.H. M. M. Shahidullah M.Sc. T. Begum B.A. 《Indian journal of pediatrics》1983,50(5):493-495
Breast feeding was found to give protection against many gastrointestinal infections in infants. A study has been conducted to examine whether breastfeeding protects children from contracting ascaris lumbricoides and hookworm infections. History of breast feeding and supplementation in urban children from low economic strata were obtained and stools were examined for ova of ascaris and hookworm. There was no significant difference in the presence of hookworm ova between the only breastfed group and the breastfed with supplemented group by two years of age. By the age of six and 24 months the presence of ascaris ova was significantly higher in the breastfed with supplemented group than the breastfed only group. It appears that exclusive breast feeding may have some role in preventing acquisition of ascaris infection in urban slums with poor sanitation facilities. 相似文献