全文获取类型
收费全文 | 14120篇 |
免费 | 1177篇 |
国内免费 | 81篇 |
专业分类
耳鼻咽喉 | 117篇 |
儿科学 | 551篇 |
妇产科学 | 338篇 |
基础医学 | 1782篇 |
口腔科学 | 225篇 |
临床医学 | 1573篇 |
内科学 | 2785篇 |
皮肤病学 | 445篇 |
神经病学 | 1353篇 |
特种医学 | 478篇 |
外科学 | 1841篇 |
综合类 | 355篇 |
一般理论 | 7篇 |
预防医学 | 1205篇 |
眼科学 | 256篇 |
药学 | 818篇 |
中国医学 | 4篇 |
肿瘤学 | 1245篇 |
出版年
2021年 | 162篇 |
2020年 | 106篇 |
2019年 | 181篇 |
2018年 | 214篇 |
2017年 | 160篇 |
2016年 | 178篇 |
2015年 | 194篇 |
2014年 | 269篇 |
2013年 | 413篇 |
2012年 | 565篇 |
2011年 | 631篇 |
2010年 | 328篇 |
2009年 | 347篇 |
2008年 | 583篇 |
2007年 | 614篇 |
2006年 | 590篇 |
2005年 | 608篇 |
2004年 | 542篇 |
2003年 | 504篇 |
2002年 | 505篇 |
2001年 | 483篇 |
2000年 | 509篇 |
1999年 | 430篇 |
1998年 | 181篇 |
1997年 | 168篇 |
1996年 | 117篇 |
1995年 | 130篇 |
1994年 | 124篇 |
1992年 | 363篇 |
1991年 | 352篇 |
1990年 | 366篇 |
1989年 | 349篇 |
1988年 | 267篇 |
1987年 | 299篇 |
1986年 | 307篇 |
1985年 | 307篇 |
1984年 | 203篇 |
1983年 | 229篇 |
1982年 | 124篇 |
1979年 | 202篇 |
1978年 | 140篇 |
1977年 | 124篇 |
1976年 | 139篇 |
1975年 | 134篇 |
1974年 | 144篇 |
1973年 | 136篇 |
1972年 | 107篇 |
1971年 | 101篇 |
1970年 | 119篇 |
1969年 | 104篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Kay Fisher Neville A McBrien Kenneth J Ciuffreda 《Clinical & experimental optometry》1997,80(4):139-144
The influence of continuous variation in dioptric demand on the accommodative hysteresis induced at near distances was examined in 14 visually-normal young adults. Tonic accommodation was measured before and after 10 minutes of sustained focus using a constant stimulus at 5 D, 6.5 D, and 8 D, as well as a stimulus which slowly and alternately increased and decreased over the continuous range from 5 D to 8 D. For approximately half the subjects, dioptric demand had to be very high (8 D) under static conditions to produce moderate but significant hysteresis, yet little or no attenuation of the effect occurred under the dynamic condition. For other subjects who consistently showed very large tonic changes (1.4 D or more) under static conditions, the hysteresis effect generated under dynamic conditions was greatly reduced (approximately 50 per cent) in magnitude. These findings suggest that the degree to which continuous variation in dioptric demand will disrupt the adaptive process may depend on individual differences in the rate and/or maximum level of tonic accommodative change. Such a relationship could have bearing on the particular strategy recommended for individuals who tend to experience blur at distance following nearwork. 相似文献
42.
S W Fisher 《Ecotoxicology and environmental safety》1992,23(1):11-21
Chlordimeform (CDF) was tested for its ability to act jointly with an organophosphorus insecticide (parathion) and a series of carbamate insecticides. Three arthropod species were used as test subjects: the two-spotted spider mite, Tetranychus urticae; the German cockroach, Blatella germanica; and the flour beetle, Tenebrio castaneum. However, CDF antagonized the toxicity of parathion toward B. germanica while it acted in a greater than additive fashion toward T. castaneum. No combination of CDF and insecticide tested acted jointly toward T. urticae. Species-specific differences in sensitivity, absorption, metabolism, and mode of delivery account for the varying results. Metabolic studies of pairs of compounds using two radiolabeled carbamates showed that CDF altered the metabolic detoxification of both carbaryl and aldicarb. The results suggest that CDF may inhibit MFOs as its mode of action. 相似文献
43.
A comparative analysis of radiological and surgical placement of central venous catheters 总被引:3,自引:1,他引:2
Kieran D. McBride Ross Fisher Neil Warnock David A. Winfield Malcolm W. Reed Peter A. Gaines 《Cardiovascular and interventional radiology》1997,20(1):17-22
Purpose To compare the differences in practice and outcome of all radiologically and surgically placed central venous catheters retrospectively
over a 2-year period simultaneously, at a single institution.
Methods A total of 253 Hickman catheters were inserted in 209 patients; 120 were placed radiologically in 102 patients and 133 were
placed surgically in 107 patients. The indication was chemotherapy in 76% of radiological and in 47% of surgical cases; the
remainder were for total parenteral nutrition and venous access.
Results There were 6 (4.5%) primary surgical failures and a further 17 (13%) surgical cases requiring multiple placement attempts.
Pneumothorax occurred once (0.8%) surgically and four times (3.3%) radiologically. There were no radiological primary misplacements
but there were five (3.7%) surgical ones. Catheter or central vein thrombosis occurred in four (3.3%) radiological and five
(3.7%) surgical cases. The rate of infection per 1000 catheter-days was 1.9 in radiologically placed catheters and 4.0 in
surgically placed ones (p<0.001). Average catheter life-span was similar for the two placement methods (100±23 days).
Conclusion Radiological placement is consistently more reliable than surgical placement. There are fewer placement complications and
fewer catheter infections overall. 相似文献
44.
We have tested the hypothesis that intradermal testing is a more effective
method for determining the drug responsible for anaesthetic anaphylactic
reactions than prick testing in 212 consecutive patients, aged more than 10
yr, referred to an anaesthetic allergy clinic over a 4-yr period. The study
was a prospective, non-randomized design. Intradermal testing was conducted
using a previously described method and diluted drugs, and prick testing
using undiluted drugs (with the exception of opioid analgesics which were
diluted 1:10). The tests were performed on individual patients' forearms on
the same occasion. Patients were followed-up to determine the results of
subsequent anaesthesia and the difference between tests was analysed using
kappa and tau statistics. There was 93% agreement overall between the
paired tests. Which test detected the drug responsible was dependent on
diagnostic criteria for positivity. The differences between the tests were
not statistically significant. Using both tests improved predictability by
67% (tau = 0.67, P < 0.001). We conclude that in the absence of data to
support one test being superior, other factors influence the choice of
test. Prick testing was cheaper, and the reduction in pain and trauma with
prick testing makes it more suitable for children. However, there are no
data available on the safety of subsequent anaesthesia based on the results
of prick testing alone, and reliability with time has not been assessed.
Intradermal testing may be easier for the infrequent user. Skin testing is
valuable in the investigation of anaesthetic anaphylaxis whichever test is
chosen. When there is doubt both tests should be performed.
相似文献
45.
V P Addonizio C A Fisher J F Strauss V A Ewan F R Rickles E F Rosato A H Harken W Y Inouye 《Surgery》1987,101(6):753-762
Disseminated intravascular coagulation invariably accompanies placement of peritoneovenous (LeVeen) shunts, which suggests that ascitic fluid contains procoagulant material capable of activating blood coagulation. In this study, we identified thrombogenic activity in human ascites and the hemostatic pathway by which it acts. Peritoneal fluid was removed percutaneously from patients with ascites due to various causes. Four fractions were prepared by centrifugation: cells, a low-speed, cell-free fluid, a high-speed supernatant, and the precipitate from the high-speed centrifugation. Cellular fractions from all ascitic fluids shortened a one-stage clotting time of normal pooled plasma by 68% in comparison with saline solution and endotoxin controls. Similarly, the cell-free fluids also shortened the clotting time of normal pooled plasma by 41%. The cellular and cell-free fractions shortened the clotting time of factor VIII-deficient plasma but failed to demonstrate procoagulant activity in factor VII-deficient plasma. These fractions had no effect on platelet aggregation or the platelet release reaction. The high-speed precipitate was dissociated by ethylenediaminetetra-acetate (EDTA) into fluid phase and precipitate, both of which demonstrated procoagulant activity. Furthermore, high-speed precipitate contained protein, phospholipid, and sterol in proportions similar to those of plasma membranes and contained membrane-bound vesicles as identified by means of electron microscopy. This material could be rendered inactive by heating to 100 degrees C for 2 minutes or by incubation with phospholipase C for 15 minutes. Finally, the ability of the high-speed precipitate to shorten the clotting time was prevented by preincubation with a monoclonal antibody, which is known to inhibit the procoagulant activity of human tissue factor. We suggest that several entities contribute to the procoagulant properties of human ascites, with procoagulant material deriving at least in part from peritoneal cells. The sedimentable procoagulant factor appears to be associated with cellular membranes or membrane fragments and is thromboplastin-like in its chemical composition, immunoreactivity, and substrate specificity. 相似文献
46.
47.
S G Lalka J M Malone D F Fisher V M Bernhard D Sullivan D Stoeckelmann R F Bergstrom 《Journal of vascular surgery》1989,10(5):501-9; discussion 509-10
This prospective study examined microbiologic features of arterial tissue and pharmacokinetics and bioactivity of cefamandole and cefazolin in patients undergoing elective primary prosthetic aortoiliofemoral/infrainguinal reconstruction. Double-blind, randomized, perioperative prophylaxis (1 gm intravenously every 6 hours for nine doses) with cefamandole or cefazolin was administered to 47 patients. Specimens of blood serum, subcutaneous fat, thrombus, atheroma, and arterial wall were obtained for culture and minimal inhibitory concentration and drug level analysis by high-pressure liquid chromatography. The serum half-life (hr +/- SEM) was 1.43 +/- 0.36 for cefamandole and 2.22 +/- 0.40 for cefazolin. Over the first 2 hours of surgery and for all time intervals combined, the serum concentration of cefazolin was significantly higher (p less than 0.025) than cefamandole. Irrespective of sampling time, the tissue concentration of cefazolin was significantly greater (p less than 0.005) than cefamandole. Positive arterial tissue cultures were obtained in 12 of 29 patients (41.4%) from 23 of 116 (19.8%) arterial tissue specimens. Coagulase-negative Staphylococcus was the predominant isolate, 64 of 93 (68.8%). Twenty-five of the 51 coagulase-negative staphylocci tested (49%) were slime-producers. During surgery, the arterial tissue concentration of cefamandole fell below the geometric mean minimal inhibitory concentration against all organisms combined, and against S. aureus (with the highest minimal inhibitory concentration of the prevalent isolates), significantly more often than the concentration of cefazolin. The data show that a significant number of primary elective aortoiliofemoral/infrainguinal reconstructions are associated with positive arterial tissue cultures, which represent a potential source of graft infection.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
48.
49.
Vein patch versus primary closure for carotid endarterectomy. A randomized prospective study in a selected group of patients 总被引:2,自引:0,他引:2
G P Clagett C B Patterson D F Fisher R E Fry J F Eidt T H Humble W J Fry 《Journal of vascular surgery》1989,9(2):213-223
During a 4-year period, 136 patients undergoing 152 carotid endarterectomies consented to be randomized to primary or saphenous vein patch closure of the arteriotomy. At operation, before randomization, careful assessment of arterial dimensions and anatomy was made. Patients who had an internal carotid artery (ICA) diameter less than 5 mm, arteriotomy extending more than 3 cm beyond the origin of the ICA, or tortuous or kinked ICAs were not randomized; they received obligatory vein patch closure (necessary in 20% cases). All patients were followed up every 3 months for 1 year and every 6 months thereafter with duplex scanning, ocular pneumoplethysmography, and neurologic assessment. The incidence of atherosclerotic risk factors was equal in the groups and all except one of the patients were male. Perioperative morbidity was not significantly different among those having primary closure (n = 60), saphenous vein patch closure (n = 62), and obligatory vein patch closure (n = 30). Operative time among patients having primary closure (122 +/- 4 minutes) was significantly less (p less than 0.001) than among those having saphenous vein patch closure (150 +/- 3 minutes). Three perioperative strokes were evenly distributed among the groups (2% for all procedures); no deaths and no acute postoperative occlusions occurred. Recurrent disease occurred in 12.9% of patients having saphenous vein patch closure compared with its occurrence in 1.7% of those having primary closure (p less than 0.05). However, most recurrences were moderate stenoses (25% to 50% diameter reduction), all were smooth-surfaced, and none required a second operation. All except one of the recurrences among those patients with saphenous vein patch closure were in the bulb and the origin of the ICA; two had evidence of regression. This finding suggested that thrombus layering in the dilated part of the saphenous vein patch reconstruction was the cause. This study demonstrates that in men with carotid arteries of predetermined minimal dimensions undergoing carotid endarterectomy routine saphenous vein patch closure does not produce superior results, is associated with a higher incidence of early recurrence, and increases operative time. In selected patients with anatomic risk factors for recurrent disease or acute postoperative occlusion, saphenous vein patch closure is appropriate. 相似文献
50.
Visual hallucinations on eye closure associated with atropine toxicity. A neurological analysis and comparison with other visual hallucinations 总被引:1,自引:0,他引:1
C M Fisher 《The Canadian journal of neurological sciences. Le journal canadien des sciences neurologiques》1991,18(1):18-27
Visual hallucinations of remarkable intensity began shortly after intravenous atropine and persisted for 11 days. They were present only when the eyes were closed and were associated with heightened dreaming and disturbed sleep. The patient remained lucid and described his experiences to his attendants. Our patient's hallucinations bore some resemblance to hypnagogic hallucinations and this became the basis for the hypothesis that the hallucinations originated in the sleep-dream system of the brain stem. It is speculated that a similar site--a metabolic locus minoris resistentiae may play a part in other types of visual hallucinations and in delirium. 相似文献