全文获取类型
收费全文 | 367449篇 |
免费 | 10605篇 |
国内免费 | 5375篇 |
专业分类
电工技术 | 10468篇 |
技术理论 | 2篇 |
综合类 | 6293篇 |
化学工业 | 54090篇 |
金属工艺 | 16012篇 |
机械仪表 | 13591篇 |
建筑科学 | 13093篇 |
矿业工程 | 3427篇 |
能源动力 | 9575篇 |
轻工业 | 29496篇 |
水利工程 | 4829篇 |
石油天然气 | 9648篇 |
武器工业 | 718篇 |
无线电 | 45173篇 |
一般工业技术 | 67739篇 |
冶金工业 | 55362篇 |
原子能技术 | 8501篇 |
自动化技术 | 35412篇 |
出版年
2022年 | 3907篇 |
2021年 | 5709篇 |
2020年 | 4124篇 |
2019年 | 4138篇 |
2018年 | 5907篇 |
2017年 | 6455篇 |
2016年 | 6331篇 |
2015年 | 5865篇 |
2014年 | 8759篇 |
2013年 | 17571篇 |
2012年 | 13042篇 |
2011年 | 16379篇 |
2010年 | 13339篇 |
2009年 | 14339篇 |
2008年 | 14607篇 |
2007年 | 14401篇 |
2006年 | 12849篇 |
2005年 | 11370篇 |
2004年 | 9986篇 |
2003年 | 9269篇 |
2002年 | 9031篇 |
2001年 | 8828篇 |
2000年 | 8354篇 |
1999年 | 8669篇 |
1998年 | 18066篇 |
1997年 | 13102篇 |
1996年 | 10280篇 |
1995年 | 7999篇 |
1994年 | 6913篇 |
1993年 | 6788篇 |
1992年 | 4979篇 |
1991年 | 4624篇 |
1990年 | 4436篇 |
1989年 | 4341篇 |
1988年 | 3992篇 |
1987年 | 3557篇 |
1986年 | 3537篇 |
1985年 | 3870篇 |
1984年 | 3553篇 |
1983年 | 3286篇 |
1982年 | 3086篇 |
1981年 | 3091篇 |
1980年 | 3075篇 |
1979年 | 2862篇 |
1978年 | 2900篇 |
1977年 | 3170篇 |
1976年 | 4146篇 |
1975年 | 2430篇 |
1974年 | 2396篇 |
1973年 | 2415篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
31.
32.
In this study, the effect and side-effect of epidural injection with lappaconitine compound for post-operative analgesia was observed. One hundred and twenty patients were randomly divided into 4 groups. Lappaconitine compound (LB) consisted of 12 mg of lappaconitine and 22.5 mg of bupivacaine, was given to group A (the group of observation), and lappaconitine 12 mg, bupivacaine 22.5 mg and morphine 2 mg to group B, C and D respectively for control. All were given by epidural injection with single blind method during post-operative pain of incision operation. Result showed that the initiating of analgesia was quicker in group A and C than that in group B and D, and the efficacy was group D > A > C > B. There was significant difference between group A and B in the above two parameters, P < 0.01 and P < 0.05. The analgisia maintenence time of single injection was D > A > B > C, that of group D was significantly longer than that of group A (P < 0.01). It indicated that the epidural injection with LB was more rapid and potent than that with lappaconitine alone in post-operative analgesia, and the former had no side-effect, it was safer than morphine. 相似文献
33.
P Rutgeerts 《Canadian Metallurgical Quarterly》1996,19(1):44-46
Absorbable and nonabsorbable buried sutures were studied in primary cleft lip repair. Group 1 (N = 56) consisted of patients repaired with buried nonabsorbable material (monofilament nylon). Group 2 (N = 47) consisted of patients repaired with absorbable materials (polyglyconate, polydioxanone). All patients were monitored for 12 months. There were stitch abscesses in Group 1 (14%). There were no abscesses in Group 2. This difference was significant (p = 0.007). Abscesses were located in the suture line with no identifiable distribution. There was no significant difference in the cosmetic appearance of the scars in Groups 1 and 2. These results support the view that absorbable sutures are preferable to nonabsorbable sutures for primary cleft lip repair. 相似文献
34.
35.
Auld B.A. Chimenti D.E. Shull P.J. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1996,43(2):319-325
The transverse resonance approach to guided wave analysis is applied to shear horizontal (SH) wave propagation in periodically layered composites. It is found for SH waves that at high values of the guided wavevector β, the wave energy is trapped in the slower of the two media and propagates accordingly at the slower wavespeed. At low values of β, however, the modes demonstrate a clustering behavior, indicative of the underlying Floquet wave structure. The number of modes in a cluster is observed to correlate with the number of unit cells in the layered plate. New physical insights into the behavior of these systems are obtained by analyzing the partial waves of the guided SH modes in terms of Floquet waves. We show that the fast and slow shear waves in the periodically layered composite play an analogous role to the longitudinal and shear partial waves comprising Lamb waves in a homogeneous plate 相似文献
36.
T P?usa P Górski H Frank-Piskorska M Kowalski J Kruszewski P Kuna M Kurek R Kurzawa W Silny E Zawisza 《Canadian Metallurgical Quarterly》1996,1(4):292-293
A review of isolates of Neisseria meningitidis and other laboratory evidence of meningococcal infection was carried out for the period 1990-1995. Thirty-three patients with evidence of meningococcal disease were identified over the six year period. Group B organisms were the most commonly identified, but an increase in Group C has occurred and is almost equal in number. Data from clinical, laboratory and public health sources should be centralized in a National Surveillance Centre. 相似文献
37.
Thanapalan Murugesan G. S. Venkat Rathnam S. Panduranga Rao P. Gangadhar Rao 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,63(3):290-294
In the present study of gas–liquid contactors, mean residence/contact time was calculated from knowledge of superficial velocity and the gas phase hold-up, for various gas rates and impeller geometry and speeds, and compared with values obtained from RTD measurements. A new correlation, involving Flow Number, Froude Number, system geometry and the physical properties, is proposed. This uses the authors data and those available in literature. 相似文献
38.
C Di Biasi M Accorinti G Trasimeni P Pivetti Pezzi A Melone G Gualdi 《Canadian Metallurgical Quarterly》1997,93(4):348-351
OBJECTIVE: To evaluate the relationships between patient and physician pretreatment expectations of pain relief and subsequent pain relief reported by chronic pain patients immediately after treatment. DESIGN: Prospective study of consecutive patients undergoing a procedure in a pain clinic for treatment of chronic pain. Patients rated their current pain level and their expectation of pain relief immediately prior to undergoing a procedure (e.g., intravenous drug infusion, nerve block) for the treatment of chronic pain. Simultaneously and independently, the treating physician completed a similar questionnaire. At completion of the procedure, patients rated their current pain level and degree of pain relief. SETTING: University of Washington Multidisciplinary Pain Center procedure suite. PATIENTS: Forty-six consecutive chronic pain patients. INTERVENTION: Intravenous drug infusions and nerve blocks. OUTCOME MEASURES: Current pain and pain relief ratings. RESULTS: Patients' pain relief expectation ratings were not correlated significantly with their postprocedure pain relief ratings or pre-post procedure changes in pain ratings. However, a statistically significant correlation was found between physician expectations of pain relief and patient pain relief ratings and patient pre-post procedure changes in pain. CONCLUSIONS: The results of this study suggest that physicians are better predictors than are patients of patients responses to these procedures and/or that physicians may somehow subtly communicate their expectations to patients during the procedure, and these expectations then influence patient response. Patient pretreatment expectations may not always play a significant role in nonspecific treatment effects. 相似文献
39.
BACKGROUND: Elevated serum sialic acids are associated with increased cardiovascular mortality, but sialic acid levels have not been studied in cardiac tissue. METHODS: Myocardial samples were obtained at the time of transplantation from 23 patients (age 54 +/- 12 years) with heart failure secondary to ischemic heart disease and 16 patients (age 51 +/- 7 years) with idiopathic dilated cardiomyopathy (DCM). A control group comprised postmortem samples obtained from 14 patients (age 70 +/- 5 years) who died of non-cardiovascular causes. Ventricular sialylation was quantitated using the sialic acid-specific lectins Maackia amurensis agglutinin (MAA) and Sambucus nigra agglutinin (SNA) using a chemiluminescence assay. Results are expressed as the percentage (+/-standard error of the mean) of the binding of lectin to a standardized control sample of human myocardium. RESULTS: Ventricular sialylation recognized by MAA was 55 +/- 7% in patients with heart failure secondary to ischemic heart disease compared with 26 +/- 7% for DCM (p = 0.006) and 32 +/- 8% for controls (p = 0.04), and that recognized by SNA was 69 +/- 7% in patients with heart failure secondary to ischemic heart disease compared with 42 +/- 6% for DCM (p = 0.006) and 38 +/- 7% for controls (p = 0.006). No significant difference in ventricular sialylation was observed between patients with DCM and controls. CONCLUSION: Myocardial levels of sialic acids are significantly increased in patients with heart failure secondary to ischemic heart disease compared with patients with idiopathic dilated cardiomyopathy and controls. Our findings are important in view of recent reports of an association between serum sialic acid concentration and cardiovascular mortality and require further investigation. 相似文献
40.
Lauren P.D. Nandhakumar N. 《IEEE transactions on pattern analysis and machine intelligence》1997,19(5):417-430
The ability to determine the viewing parameters of objects from their projections has enabled well established tomographic techniques to be employed in the 3D reconstruction of objects from images obtained via modalities where the orientation of the objects cannot be controlled. A method is described for the determination of the viewing parameters of randomly acquired projections of asymmetric objects. It extends upon the common lines algorithm by determining the relative orientation of projections from the location of lines of intersection among the Fourier transforms of the projections in 3D Fourier space. A new technique for finding the lines of intersection in the presence of translational displacement, and for subsequently finding the translational displacement, is presented. The complete algorithm is described and its efficacy is demonstrated using real data. A new technique for dealing with noise is also discussed 相似文献