首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   19489篇
  免费   648篇
  国内免费   83篇
耳鼻咽喉   985篇
儿科学   564篇
妇产科学   1177篇
基础医学   2467篇
口腔科学   145篇
临床医学   1156篇
内科学   4093篇
皮肤病学   232篇
神经病学   1970篇
特种医学   408篇
外科学   1551篇
综合类   114篇
一般理论   4篇
预防医学   1315篇
眼科学   614篇
药学   2634篇
中国医学   55篇
肿瘤学   736篇
  2023年   94篇
  2022年   211篇
  2021年   382篇
  2020年   187篇
  2019年   330篇
  2018年   646篇
  2017年   429篇
  2016年   476篇
  2015年   417篇
  2014年   706篇
  2013年   1038篇
  2012年   1250篇
  2011年   1514篇
  2010年   802篇
  2009年   376篇
  2008年   970篇
  2007年   1339篇
  2006年   1422篇
  2005年   1320篇
  2004年   1393篇
  2003年   1388篇
  2002年   1119篇
  2001年   487篇
  2000年   521篇
  1999年   324篇
  1998年   117篇
  1997年   40篇
  1996年   28篇
  1995年   28篇
  1992年   29篇
  1991年   34篇
  1990年   54篇
  1989年   27篇
  1988年   34篇
  1987年   30篇
  1986年   40篇
  1985年   34篇
  1984年   24篇
  1983年   30篇
  1982年   24篇
  1981年   37篇
  1980年   27篇
  1979年   40篇
  1978年   40篇
  1977年   25篇
  1976年   22篇
  1975年   29篇
  1974年   22篇
  1972年   31篇
  1971年   23篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Zusammenfassung Aus mitteleuropäischen Singvögeln werden die folgenden neuen Menacanthus-Arten beschrieben: M. festivus nov. spec. von Fringilla coelebs, M. pius nov. spec. von Turdus merula, M. polonicus nov. spec. von Turdus pilaris, M. vistulanus nov. spec. von Sylvia borin und M. wipszyckii nov. spec. von Chloris chloris. Die Tatsache, daß das insgesamt aus mehreren Funden und besonders für M. pius nov. spec. aus zahlreichen Exemplaren bestehende, dieser Arbeit zugrunde liegende Untersuchungsmaterial fast ausschließlich Weibchen enthält, wird als Ausgangspunkt für eine Diskussion des Speziesbegriffs bei uniparentalen Mallophagenarten herangezogen. Zur Klärung dieser auch evolutionstheoretisch bemerkenswerten Problematik wird ein Forschungsprogramm für Menacanthus-Arten entwickelt.Mit 10 Textabbildungen  相似文献   
22.
The results of brain MRI are presented in 22 patients with documented Nijmegen breakage syndrome (NBS), aged from 1 and 9/12 to 20 years. T1-, PD or FLAIR and T2-weighted SE/TSE images in three planes were obtained. Twenty-one patients showed microcephaly. Decreased size of frontal lobes and narrow frontal horns of the lateral ventricles was observed in all cases. In 6 patients agenesis of the posterior part of the corpus callosum was found as well as colpocephaly and temporal horn dilatation. In 2 patients callosal hypoplasia was accompanied by other anomalies: abnormal cerebrospinal fluid spaces. Sinusitis was present in all patients as a result of primary immunodeficiency. As in ataxia teleangiectasia and other breakage syndromes, NBS patients show inherited malignancy susceptibility and hypersensitivity to X and gamma radiation. Because of that computed tomography is contraindicated in these patients and MRI should be the method of choice in diagnostic imaging.  相似文献   
23.
Nodular fasciitis, proliferative fasciitis, and proliferative myositis are tumorous proliferative soft tissue changes which on histological examination are quite often erroneously diagnosed as malignant neoplasms. Reported are cytological and histological findings recorded from nodular fasciitis in a man aged 34 years. The cytomorphology of nodular fasciitis is sufficiently characteristic, so that the lesion can be differentiated with certainty from malignant processes, since the cells have no features of malignancy, and the admixture of granulocytes and histiocytes in smears suggests a proliferative inflammatory process.  相似文献   
24.
Racemic lactide was polymerized with various initiators containing Zn and Al, and the structures of the obtained polymers were determined by means of 13C NMR spectroscopy. The extent of transesterification reactions was calculated on the basis of the analysis of the methine carbon signal in the polymer 13C NMR spectra. Three groups of initiators can be distinguished in view of their influence on transesterification: ZnCl2 exhibits the strongest transesterification activity, ZnEt2 and ZnEt2/Al(OiPr)3 are among those of medium activity, and Al(acac)3 does not show transesterification activity at all.  相似文献   
25.
Pertussis toxin (PT), a typical A-B oligomer exotoxin of Bordetella pertussis, has been demonstrated to be an essential protective antigen for acellular pertussis vaccine against whooping cough. In order to investigate the associated functionality ascribed to its components, we have purified A and B oligomers for the activity study. The A oligomer (S1 subunit) of PT was expressed in E. coli B834 (DE3) harboring expression vector (pET-20b) with the insert of S1 coding region and purified by metal-chelating column. The B oligomer was isolated by a single-step purification procedure. Individually, recombinant S1 and B oligomer exhibited quite distinct biological activities in vivo. S1 subunit induced leukocytosis-promoting (LP) activity, but did not affect mouse body weight-gain. On the contrary, B oligomer reduced mouse body weight-gain but did not reveal LP activity. In vitro, the combination of S1 subunit and B oligomer could enhance the toxic activities as exhibited by native PT and showed an additive toxicity in CHO cell clustering test and hemagglutination assay.  相似文献   
26.
COPD is the most frequent chronic lung disease in Poland. The disease is however under-diagnosed, especially at the early stages. The aim of the study was to assess the efficacy of spirometric screening for COPD in middle aged smokers. Informations on causes and symptoms of COPD were disseminated in mass media in 14 large cities. Subject aged over 39 and with smoking history of > 10 packyears were invited for a free spirometry in local chest clinic. However, everyone attending had the spirometry performed. Spirometry was performed according to ATS recommendations. Airway obstruction (AO) was diagnosed when FEV1/FVC < 85% of N and categorised as mild (FEV1 > 70% of N), moderate (FEV1 50-69% of N) or severe (FEV1 < 50% of N). Spirometry was accompanied by an antismoking advice. RESULTS: 12.781 subjects were screened (mean age 52 +/- 12 years, 57% males). In 8.269 subjects who complied with inclusion criteria AO was diagnosed in 29.8% (mild in 10.9%, moderate in 12% and severe in 6.9%). In smokers < 40 years of age and a history of < 10 packyears AO was found in 8.8% (mild in 6.0%, moderate in 1.8% and severe in 1.0%). CONCLUSION: Mass spirometry is an effective and easy method for early detection of COPD.  相似文献   
27.
CD80 and CD86 seem to play an important role in the allergen-induced secretion of interleukin (IL)-5 and IL-13. Up to now, the expressions of CD80 (B7.1) and CD86 (B7.2) on monocytes and the kinetics of the expression of these molecules on lipopolysaccharide-stimulated monocytes in nonatopic asthma have not been defined. Using monoclonal antibodies, we have compared the expressions of CD80 (B7.1) and CD86 (B7.2) on the monocytes of healthy persons and nonatopic asthmatic patients. We have also assessed the effect of CD80 and CD86 inactivation on IL-4 and interferon (IFN)-gamma production in nonatopic asthmatics and healthy subjects. We found that a low expression of CD80 (1.64 +/- 0.65 vs. 3.53 +/- 1.43%) and a moderate expression of CD86 (41.25 +/- 13.4 vs. 49.46 +/- 11.49%) on the studied monocytes were characteristic for asthma. In nonatopic asthma patients inactivation of CD80 or CD86 blockade significantly reduced IFN-gamma production by T lymphocytes (p < 0.02; p < 0.03). In both the studied groups, anti-CD80 antibodies did not diminish T lymphocyte production of IL-4. However, anti-CD86 antibodies significantly (p < 0.04) reduced the IL-4 concentration in culture supernatants. Our results confirm that both the CD80 and CD86 molecules play an important role in the maintenance and amplification of the inflammatory process. It suggests that in the inflammatory process that occurs in nonatopic bronchial asthma, Th1 as well as Th2 lymphocytes are equally important.  相似文献   
28.
We studied pulmonary haemodynamics and nocturnal desaturation in 17 patients with an overlap syndrome (OS), all males, mean age 51.4 +/- 8.3 years, mean BMI 37 +/- 4.2 kg/m2. Diagnosis of COPD was based on pts history, clinical examination, lung function tests and chest radiography. Spirometry showed: FVC 2.7 +/- 0.7 L (59 +/- 16% N), FEV1 1.5 +/- 0.7 L (43 +/- 16% N), FEV1% FVC 54 +/- 13%, Raw 0.58 +/- 0.4 kP.s/L, RV 3.3 +/- 1.2 L (144 +/- 51% N), TLC 6.6 +/- 1.3 L (100 +/- 14% N) and RV% TLC (49.5 +/- 12.1%. Arterial blood gas values were: PaO2 56.9 +/- 9.5 mmHg, PaCO2 46.9 +/- 9.8 mmHg, pH 7.37 +/- 0.05. Mean apnoea/hypopnoea index (AHI) was 63.9 +/- 18.9. Pulmonary haemodynamics at rest (Swan Ganz thermodilution catheter) were: mean pulmonary artery pressure (PAP-SP) 24.2 +/- 7.4 mmHg, mean pulmonary wedge pressure (PW-SP) was 9.1 +/- 7.3 mmHg, cardiac output (CO-SP) was 5.6 +/- 2.3 L/min. and pulmonary vascular resistance (PVR) was 229 +/- 97 dyn.sec.cm-5. During exercise (40 Watts, 7 mins, in 8 pts) PAP rose from 19 +/- 6 mmHg to 41.2 +/- 15.1 mmHg, PW rose from 7.4 +/- 7.2 mmHg to 11 +/- 10.2 mmHg, CO rose from 5.8 +/- 2.7 L/min to 12.7 +/- 2.4 L/min. Overnight pulse oximetry showed: mean oxygen saturation (SaO2 mean) 80.2 +/- 8.5%, minimal saturation (SaO2 min) was 50.7 +/- 19.7%. Time spent in desaturation SaO2 < 90% (T 90) was 76.9 +/- 25.7%. We conclude that pts with OS have resting pulmonary hypertension and elevated PVR. During low grade exercise the rise in PAP was highly abnormal. Statistical analysis showed no correlations between nocturnal SaO2 and diurnal pulmonary haemodynamics data.  相似文献   
29.
Summary The effects of two types of acute exercise (1 h treadmill running at 20 m· min–1, or 6 × 10-s periods at 43 m · min–1, 0° inclination), as well as two training regimes (endurance and sprint) on the sensitivity of epitrochlearis muscle [fast twitch (FT) fibres] to insulin were measured in vitro in rats. The hormone concentration in the incubation medium producing the half maximal stimulation of lactate (la) production and glycogen synthesis was determined and used as an index of the muscle insulin sensitivity. A single period of moderate endurance as well as the sprint-type exercise increased the sensitivity of la production to insulin although the rate of la production enhanced markedly only after sprint exercise at 10 and 100 U· ml–1 of insulin. These effects persisted for up to 2 h after the termination of exercise. Both types of exercise significantly decreased the muscle glycogen content, causing a moderate enhancement in the insulin-stimulated rates of glycogen synthesis in vitro for up to 2 h after exercise. However, a significant increase in the sensitivity of this process to insulin was found only in the muscle removed 0.25 h after the sprint effort. Training of the sprint and endurance types increased insulin-stimulated rates of glycolysis 24 h after the last period of exercise. The sensitivity of this process to insulin was also increased at this instant. Both types of training increased the basal and maximal rates of glycogen snythesis, as well as the sensitivity of this process to insulin at the 24th following the last training session. It was concluded that in the epitrochlearis muscle, containing mainly FT fibres, both moderate and intensive exercise (acute and repeated) were effective in increasing sensitivity of glucose utilization to insulin. Thus, the response in this muscle type to increased physical activity differs from that reported previously in the soleus muscle, representing the slow-twitch, oxidative fibres in which sprint exercise did not produce any changes in the muscle insulin sensitivity.  相似文献   
30.
Between 1984 and 2000 in the Thoracic Surgery Centre pneumonectomies were performed in 947 patients. Postpneumonectomy empyema (PE) occurred in 67 (7%) patients. The aim of this paper were: analysis the reasons of postpneumonectomy empyema appearance, defined bacterial flora, clinical course and optimal management. The causes of PE were: pleural cavity haematoma (20 patients-29.8%), wound suppuration (18 patients-26.8%), bronchial fistula (31 patients-46.2%). These complications appeared singly or together in 49 (73.1%) patients. In 2 (3.0%) patients a long treatment in the Intensive Care Unit because of postoperative shock was the cause of infection. In 3 (4.5%) cases the cause of empyema was associated with infection during the operation. In 13(19.4%) cases the cause of empyema was not established. In 55 patients infections of pleural cavities were diagnosed in the first 8 weeks after operations. In 12 patients empyemas were established later. 12 (17.9%) patients died during the analyzed 1 year period after operation. In 18 (26.9%) patients infections were caused by only one bacterial strain and in 49 (73.1%) by two or three bacterial strains. The different methods of treatment (thoracentesis, drainage, operation) depending on general condition of patient were done.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号