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   2260篇
  免费   2篇
电工技术   7篇
综合类   1篇
化学工业   116篇
金属工艺   1篇
机械仪表   3篇
建筑科学   28篇
能源动力   11篇
轻工业   38篇
水利工程   2篇
石油天然气   18篇
无线电   37篇
一般工业技术   32篇
冶金工业   1917篇
原子能技术   1篇
自动化技术   50篇
  2023年   2篇
  2021年   8篇
  2020年   2篇
  2019年   5篇
  2017年   2篇
  2016年   2篇
  2014年   16篇
  2013年   17篇
  2012年   18篇
  2011年   14篇
  2010年   17篇
  2009年   18篇
  2008年   13篇
  2007年   22篇
  2006年   9篇
  2005年   14篇
  2004年   11篇
  2003年   26篇
  2002年   23篇
  2001年   10篇
  2000年   4篇
  1999年   64篇
  1998年   560篇
  1997年   318篇
  1996年   249篇
  1995年   128篇
  1994年   115篇
  1993年   118篇
  1992年   23篇
  1991年   32篇
  1990年   38篇
  1989年   32篇
  1988年   40篇
  1987年   26篇
  1986年   29篇
  1985年   27篇
  1984年   5篇
  1983年   7篇
  1982年   14篇
  1981年   20篇
  1980年   15篇
  1979年   3篇
  1978年   7篇
  1977年   45篇
  1976年   82篇
  1972年   2篇
  1966年   1篇
  1965年   1篇
  1962年   1篇
  1960年   1篇
排序方式: 共有2262条查询结果,搜索用时 0 毫秒
31.
OBJECTIVE: To identify any clinical and pathologic features of treatment modalities that are predictive of outcome in patients with epithelioid sarcoma, a rare slow-growing soft tissue tumor most commonly occurring in the distal extremities of young adults. DESIGN: We reviewed the institutional files for cases of epithelioid sarcoma for the period 1956 to 1991 and analyzed the effect of various factors on survival. MATERIAL AND METHODS: Fifty-five cases of epithelioid sarcoma were found, and the relevant clinical, pathologic, treatment, follow-up, and outcome features were assessed. RESULTS: All tumors were treated initially by operative resection. The recurrence rate progressively decreased with increasing aggressiveness of the initial operation; however, no difference was noted in metastatic rate. Overall, the recurrence rate was 38% and the metastatic rate was 47%. At the end of a mean follow-up of 102 months, 69% of patients had no evidence of disease, 27% had died of the disease, and 4% were alive with disease. Increasing tumor size, necrosis of more than 30%, and vascular invasion correlated significantly with a worse prognosis. CONCLUSION: Epithelioid sarcoma should be considered a malignant neoplasm with a significant potential for aggressive behavior, and close follow-up of affected patients should be maintained for many years. Initial treatment should be aggressive in an attempt to prevent recurrence.  相似文献   
32.
BACKGROUND: The efficacy of squamous cell carcinoma antigen (SCC-Ag) in laryngeal cancer to predict those patients who will relapse after primary treatment (surgery or radiotherapy) and its utility to detect relapses early and thereby increase salvage rates and cure were assessed. METHODS: Sixty healthy donors and 168 patients with laryngeal cancer were included in this prospective trial. Squamous cell carcinoma antigen was measured at diagnosis in all patients, 24 hours and 1 week after surgery in 113 patients and every 10 Gy of administered dose and 2 weeks after treatment in 49 patients primarily referred to radiotherapy. The marker was determined every 3-6 months during follow-up. All patients who relapsed had SCC-Ag studies before and after salvage treatment. RESULTS: The selected cut-off value was 1.5 ngr/ml (mean value in control group, 0.65 + 2 standard deviation [0.38]). Seventy-eight percent of patients with cancer had elevated SCC-Ag values at diagnosis. Squamous cell carcinoma antigen was statistically related to TNM categories (T, P < 0.04; N, P < 0.05; Stage, P < 0.01). Seventy-five percent of those patients with previously elevated pretreatment values normalized after treatment. Incomplete surgical resection (P < 0.0001) or persistence of the disease after radiotherapy (P < 0.01) were related to high posttreatment values. Squamous cell carcinoma antigen was elevated in 88% of the patients who relapsed. In 55% of the recurrences, SCC-Ag was elevated 3 months before pathologic confirmation of relapse. Salvage by surgery or radiotherapy was effective in 70% of the patients. Squamous cell carcinoma antigen posttreatment values were the most important factor in predicting disease free survival (DFS) (P < 0.0001) and overall survival (P < 0.03). CONCLUSIONS: Squamous cell carcinoma antigen is an excellent marker of residual disease after primary treatment that can lead to the addition of other therapeutic procedures (surgery and postoperative radiotherapy). The absence of posttreatment SCC-Ag is the best predictor of DFS, its presence detects recurrence in early stages, permitting salvage of an increased proportion of patients primarily referred for palliative treatment.  相似文献   
33.
The multicopy c subunit of the H+-transporting ATP synthase of Escherichia coli folds through the transmembrane F0 sector as a hairpin of two hydrophobic alpha-helices with the proton-translocating aspartyl-61 side chain centered in the second transmembrane helix. The number of subunits c in the F0 complex, which is thought to determine the H+-pumping/ATP stoichiometry, was previously not determined with exactness but thought to range from 9-12. The studies described here indicate that the exact number is 12. Based upon the precedent of the subunit c in vacuolar-type ATPases, which are composed of four transmembrane helices and seem to have evolved by gene duplication of an F0-type progenitor gene, we constructed genetically fused dimers and trimers of E. coli subunit c. Both the dimeric and trimeric forms proved to be functional. These results indicate that the total number of subunit c in F0 should be a multiple of 2 and 3. Based upon a previous study in which the oligomeric organization of c subunits in F0 was determined by cross-linking of Cys-substituted subunits (Jones, P. C. , Jiang, W., and Fillingame, R. H. (1998) J. Biol. Chem. 273, 17178-17185), we introduced Cys into the first and last transmembrane helices of subunit c monomers, dimers, and trimers and attempted to generate cross-linked products by oxidation with Cu(II)-(1,10-phenanthroline)2. Double Cys substitutions at two sets of positions gave rise to extensive cross-linked multimers. Multimers of the monomer that extended up to the position of c12 were correlated and calibrated with distinct cross-linked species of the appropriate doubly Cys-substituted dimers (i.e. c2, c4, . c12) and doubly Cys-substituted trimers (i.e. c3, c6, c9, c12). The results show that there are 12 copies of subunit c per F0 in E. coli, the exact number having both mechanistic and structural significance.  相似文献   
34.
Twelve specific pathogen-free cats were infected either by intra-articular inoculation or by contact exposure to one of two strains of feline calicivirus (FCV), either F65, a field strain originating from an outbreak of lameness in a group of cats, or a vaccine strain. Following either route of exposure, both strains induced signs typical of FCV infection including oral and nasal ulceration, conjunctivitis and ocular discharge. These signs were of equal severity for both virus strains, but overall, following either route of infection, F65 induced more severe disease than the vaccine strain, with marked pyrexia, lethargy and lameness. Vaccine virus only induced a relatively mild lameness following intra-articular inoculation. Gross pathological and histopathological lesions were seen in some of the joints, but again changes were more severe in the F65-exposed cats. Virus was isolated from both normal and affected joints from both groups of F65-exposed cats, and from a joint from each cat inoculated intra-articularly with vaccine virus. Mild transient lameness was also seen in one of two control cats inoculated intra-articularly, but no pathological changes were seen or virus isolated from joints. A cDNA probe used in RNA dot blot hybridisation experiments was found to be specific and more sensitive than virus isolation in detecting FCV in selected tissues. This may be useful in future studies on the pathogenesis of FCV disease and in studies on viral persistence in FCV carriers.  相似文献   
35.
Resistance-modifying agents (RMAs) such as Verapamil have been proved to be effective in reversing multi-drug resistance (MDR) in many in vitro assays. In this study we have investigated the efficacy of Dex-Verapamil, the R-isomer of Verapamil, as a chemosensitizer in a murine leukemia cell line (P388) and in its resistant counterpart (P388/Dx) expressing a typical MDR phenotype. We have examined in vivo the effect of the co-administration of Dex-Verapamil and Doxorubicin in mice transplanted with P388 or P388/Dx cells. Mice treated with the combination of Doxorubicin plus RMA had a significant increase in survival rate as compared to controls; however, the effect was modest. On the contrary, in vitro Dex-Verapamil can enhance Doxorubicin cytotoxicity in P388/Dx cells with a much greater effect depending on the treatment scheme used, by increasing the intracellular content of drug. Taken together our data indicate that Dex-Verapamil can indeed increase the sensitivity to Doxorubicin in resistant cells, but the limited efficacy shown in vivo demonstrates that this phenomenon is strongly dependent on the treatment scheme used and on the maintenance of constantly elevated serum levels.  相似文献   
36.
Adult male White Leghorn chickens were used in an experimental model system to study atherogenesis, and the effects of an atherogenic diet on plasma lipoprotein composition including carotenoids were determined. This model also included treatment with diazepam, a drug known to reduce formation of atherogenic plaques. After 6 wk consumption of a high-cholesterol, high-triglyceride diet, chickens had mean total plasma cholesterol, triglyceride, and carotenoid concentrations that were significantly increased over those from chicks that consumed the standard diet. Diazepam treatment had no significant effect on whole plasma concentrations of these lipids. Total body weight gain was unaffected by diet, but liver weight expressed as percentage of body weight was significantly increased in chickens that consumed the atherogenic diet. High density lipoprotein (HDL) and low density lipoprotein (LDL) fractions were isolated from plasma samples by ultracentrifugation. The atherogenic diet increased the carotenoid, cholesterol, and protein content of the LDL fractions but not the HDL fractions.  相似文献   
37.
OBJECTIVES--(1) to evaluate regional cerebral blood flow (rCBF) with single photon emission computed tomography and 99mTc-hexamethylpropyleneamine oxime in patients with the idiopathic adult hydrocephalus syndrome (IAHS); (2) to examine regional cerebral blood flow (rCBF), gait, and psychometric functions before and after CSF removal (CSF tap test); (3) to assess abnormalities in subcortical white matter by MRI. METHODS--Thirty one patients fulfilling the criteria for IAHS (according to history and clinical and neuroradiological examination) were studied. Quantified gait measurements, psychometric testing, and rCBF before and after removal of CSF were obtained. Pressure of CSF and CSF outflow conductance were investigated with a constant pressure infusion method. Brain MRI was used to quantify the severity of white matter lesions and periventricular hyperintensities. In IAHS a widespread rCBF hypoperfusion pattern was depicted, with a caudal frontal and temporal grey matter and subcortical white matter reduction of rCBF as the dominant feature. Removal of CSF was not accompanied by a concomitant increase in rCBF. Significant white matter lesions were detected only in a minority of patients by MRI. An altered CSF hydrodynamic state with a higher CSF pressure and lower conductance was confirmed. IAHS is characterised by an abnormal CSF hydrodynamic state, associated with a widespread rCBF reduction with preference for subcortical white matter and frontal-temporal cortical regions. Furthermore in most patients MRI did not show white matter changes suggestive of a coexistent subcortical arteriosclerotic encephalopathy. At least in the idiopathic group of patients with AHS, measurements of rCBF before and after temporary relief of the CSF hydrodynamic disturbance will not provide additional information that would be helpful in the preoperative evaluation but is suggestive of a preserved autoregulation of rCBF.  相似文献   
38.
Diaspirin crosslinked hemoglobin (DCHb) is a new blood substitute manufactured from human blood. To evaluate its microvascular filtration properties, we infused DCLHb into unanesthetized sheep (10%, 20 ml/kg) and measured the flow and composition of lung and soft tissue lymph. For comparison, we also infused human serum albumin (HSA; 10%, 20 ml/kg). DCLHb raised systemic and pulmonary arterial pressures from baseline values of 83 +/- 7 and 13 +/- 2 mm Hg, respectively, to peak values of 113 +/- 9 and 26 +/- 3 mm Hg (p < 0.05 versus baseline). These increases were significantly greater than those associated with HSA, which raised systemic and pulmonary arterial pressures from baseline values of 86 +/- 4 and 13 +/- 2 mm Hg, respectively, to peak values of 97 +/- 3 and 21 +/- 7 mm Hg (p <= 0.05 versus baseline and versus DCLHb). These differences reflect the known pressor properties of DCLHb. Accordingly, DCLHb raised lung and soft tissue lymph flows to peak values of 12.2 +/- 3.8 and 1.6 +/- 0.7 ml/30 min, respectively, while HSA raised lung and soft tissue lymph flows to peak values of 7.5 +/- 4.8 and 4.6 +/- 1.9 ml/30 min, respectively (p <= 0.05 versus DCLHb). The half-times of DCLHb equilibration from plasma into lung and soft tissue lymph of 1. 0 +/- 0.3 and 2.1 +/- 1.1 h, respectively, were significantly faster than HSA equilibration half-times of 3.1 +/- 0.2 and 3.8 +/- 0.9 h. Filtration differences between DCLHb and HSA appear to be due to the pressor properties DCLHb.  相似文献   
39.
This laboratory study examined mothers' and fathers' sensitivity during face-to-face interactions with their infants as well as infants' affective and regulatory responses during mother-infant versus father-infant still face (SF). The degree to which infant gender and temperament as well as parental sensitivity predicted SF responses was also examined. Participants included 94 healthy, primarily White, middle-class 4-month-olds and their parents. Results indicated that mothers and fathers were equally sensitive toward their infants. Infants' affect and regulatory behaviors were also significantly stable across mother- and father-infant SF situations, although several differences in mean levels of regulation emerged. Finally, the extent to which exogenous and endogenous variables predicted infant SF responses differed as a function of which affect or regulatory variable was being examined and with which parent the infant was experiencing SF.  相似文献   
40.
The degree and nature of patient involvement in consultations with health professionals influences problem and needs recognition and management, and public accountability. This paper suggests a framework for understanding the scope for patient involvement in such consultations. Patients are defined as co-producers of formal health services, whose potential for involvement in consultations depends on their personal rights, responsibilities and preferences. Patients' rights in consultations are poorly defined and, in the National Health Service (NHS), not legally enforceable. The responsibilities of patients are also undefined. I suggest that these are not to deny, of their own volition, the rights of others, which in consultations necessitate mutuality of involvement through information-exchange and shared decision-making. Preferences should be met insofar as they do not militate against responsibilities and rights.  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