全文获取类型
收费全文 | 683604篇 |
免费 | 8769篇 |
国内免费 | 1462篇 |
专业分类
电工技术 | 12562篇 |
综合类 | 572篇 |
化学工业 | 107235篇 |
金属工艺 | 28511篇 |
机械仪表 | 21805篇 |
建筑科学 | 15232篇 |
矿业工程 | 5344篇 |
能源动力 | 17495篇 |
轻工业 | 53907篇 |
水利工程 | 8554篇 |
石油天然气 | 17927篇 |
武器工业 | 52篇 |
无线电 | 73041篇 |
一般工业技术 | 141037篇 |
冶金工业 | 117878篇 |
原子能技术 | 17342篇 |
自动化技术 | 55341篇 |
出版年
2021年 | 6512篇 |
2019年 | 6200篇 |
2018年 | 10711篇 |
2017年 | 10902篇 |
2016年 | 11485篇 |
2015年 | 7160篇 |
2014年 | 12093篇 |
2013年 | 31163篇 |
2012年 | 18671篇 |
2011年 | 25033篇 |
2010年 | 19965篇 |
2009年 | 22424篇 |
2008年 | 22740篇 |
2007年 | 22376篇 |
2006年 | 19436篇 |
2005年 | 17673篇 |
2004年 | 16761篇 |
2003年 | 16370篇 |
2002年 | 15766篇 |
2001年 | 15455篇 |
2000年 | 14807篇 |
1999年 | 14613篇 |
1998年 | 34804篇 |
1997年 | 24981篇 |
1996年 | 19429篇 |
1995年 | 14817篇 |
1994年 | 13322篇 |
1993年 | 13155篇 |
1992年 | 10143篇 |
1991年 | 9850篇 |
1990年 | 9633篇 |
1989年 | 9363篇 |
1988年 | 9109篇 |
1987年 | 8146篇 |
1986年 | 7997篇 |
1985年 | 9067篇 |
1984年 | 8217篇 |
1983年 | 7903篇 |
1982年 | 7119篇 |
1981年 | 7165篇 |
1980年 | 6959篇 |
1979年 | 7081篇 |
1978年 | 6958篇 |
1977年 | 7646篇 |
1976年 | 9421篇 |
1975年 | 6251篇 |
1974年 | 5987篇 |
1973年 | 6121篇 |
1972年 | 5308篇 |
1971年 | 4950篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
M Kanazawa M Yano C Namchai S Yamamoto A Ohtake M Takayanagi M Mori H Niimi 《Canadian Metallurgical Quarterly》1997,239(2):580-584
cDNAs for green fluorescent protein (GFP) and for a GFP fusion protein containing the presequence of human ornithine transcarbamylase (pOTC-GFP) were transfected into cultured human fibroblasts. GFP cDNA gave diffuse fluorescence throughout the cytoplasm and the nucleus, whereas pOTC-GFP cDNA gave mitochondria-associated fluorescence. Fluorescent mitochondrial structures could be classified into five patterns: thread-like mitochondria, fine thread-like ones, rod-like ones, granular ones, and granular ones with weak cytosolic fluorescence. pOTC-GFP mutants resulted in a loss of mitochondrial fluorescence and an appearance of weak fluorescence throughout the cytoplasm. pOTC-GFP cDNA was transfected into fibroblasts from patients with various mitochondrial diseases. Higher ratios of fibroblasts with granular mitochondria and those with fine thread-like ones were observed in a patient with Reye's syndrome and a patient with Kearns-Sayre syndrome. Weak cytosolic fluorescence was sometimes observed in fibroblasts from these patients. This method will be useful to analyze mitochondrial structural alterations and disorders of mitochondrial protein import. 相似文献
942.
943.
Sixty-two women (mean age 68.7 +/- 0.9 yr) with postmenopausal spinal osteoporosis were treated with cyclical etidronate therapy (400 mg for 2 weeks alternating with 12 weeks of 1 gm elemental calcium and 400 IU Vitamin D3) for a minimum of 2 yr. Bone mineral density (BMD) of the lumbar spine (g/cm2) increased significantly (p < 0.0001) after yr 1 (4.1 +/- 0.5 per cent) and yr 2 compared with yr 1 (2.2 +/- 0.5 per cent). The response rate was 89 per cent after yr 1 and 84 per cent after yr 2. BMD of the hip (30 patients) increased by 1.5 +/- 0.9 per cent after yr 1 and 5.5 +/- 1.1 per cent (p < 0.0001) after yr 2 when compared with baseline. The response rate was 63 per cent after yr 1 and 80 per cent after yr 2. Smaller numbers of patients continued with treatment up to 4 yr with no adverse long-term effects. 相似文献
944.
P Klein R Béliard A Glacet S Moitel T Ducrot D Bourel 《Canadian Metallurgical Quarterly》1997,8(1):17-25
The aim of this study was to investigate how intrauterine growth retardation affects body proportions in VLBW infants. The cohort consisted of 135 surviving and 80 deceased preterm infants weighing less than 1250 grams at birth. Gestational age varied between 24 and 36 weeks (mean age 29.7 and 27.5 weeks, respectively). Birth weight was more than 2 SD below the mean birth standard values in 32% of the surviving, and in 27% of the deceased infants. Reduction of weight, length and head circumference at birth was analysed using Z scores based on Swedish birth standards. Z scores of weight, length and head circumference were highly correlated in the surviving and the deceased infants (r = 0.78 to 0.94 and 0.65 to 0.97, respectively). Length was significantly more affected by growth retardation than weight. Weight and head circumference were proportionately reduced. Intrauterine growth retardation influences body proportions in VLBW infants differently than in larger preterm and term infants. 相似文献
945.
946.
Cresswell M.W. Allen R.A. Guthrie W.F. Sniegowski J.J. Ghoshtagore R.N. Linholm L.W. 《Semiconductor Manufacturing, IEEE Transactions on》1998,11(2):182-193
The physical widths of reference features incorporated into electrical linewidth test structures patterned in films of monocrystalline silicon have been determined from Kelvin voltage measurements. The films in which the test structures are patterned are electrically insulated from the bulk-silicon substrate by a layer of silicon dioxide provided by SIMOX (Separation by the IMplantation of OXygen) processing. The motivation is to facilitate the development of linewidth reference materials for critical-dimension (CD) metrology-instrument calibration. The selection of the (110) orientation of the starting silicon and the orientation of the structures' features relative to the crystal lattice enable a lattice-plane-selective etch to generate reference-feature properties of rectangular cross section and atomically planar sidewalls. These properties are highly desirable for CD applications in which feature widths are certified with nanometer-level uncertainty for use by a diverse range of CD instruments. End applications include the development and calibration of new generations of CD instruments directed at controlling processes for manufacturing devices having sub-quarter-micrometer features 相似文献
947.
The value of flexible videoendoscopy as a biofeedback tool in conservative swallowing rehabilitation of patients suffering from aspiration after head and neck surgery was examined. For this purpose, the outcomes of conventional swallowing therapy and of swallowing therapy with support of videoendoscopic biofeedback were compared. In the first 40 days of swallowing therapy, videoendoscopic biofeedback significantly increased the chance of therapeutic success, shortening the period of functional rehabilitation in comparison to conventional swallowing therapy. Limitations of this visual biofeedback procedure are poor cognitive skills of the patient, rejection of the procedure by the patient and local factors that make the positioning of the endoscope difficult. 相似文献
948.
A new commercially available diode model is described. This unified model is capable of simulating the widest range of diode technologies of any presently available. The emphasis of this paper is on describing the model's extensive features and flexibility in the different domains of operation and is of particular interest in power applications 相似文献
949.
Y. N. Lenets 《Fatigue & Fracture of Engineering Materials & Structures》1997,20(2):249-256
Abstract— The behaviour of fatigue cracks in an Al-alloy under cyclic compression, either with or without overloads, was studied. For constant-amplitude compressive cycling, a non-catastrophic (saturation) character of the fatigue crack behaviour was confirmed, with the final depth of a crack depending on the applied load level. Single (tensile or compressive) intermittent overloads were shown to re-activate a previously arrested crack while reversed (tensile—compressive or compressive—tensile) ones were also shown to maintain continual fatigue crack extension under otherwise fully compressive cycling. 相似文献
950.
AM Mansour K Kassak M Chaya T Hourani A Sibai MN Alameddine 《Canadian Metallurgical Quarterly》1997,81(10):905-906
Here we report a case that presented with sudden onset of neurological symptoms and was treated with ganciclovir. Polymerase chain reaction analysis for human herpes virus-6 (HHV-6) from his cerebrospinal fluid was later found to be positive. He subsequently recovered with minimal residual neurological symptoms. Encephalitis secondary to this virus may be more common than previously thought in patients undergoing bone marrow transplantation. This condition should be considered in the differential diagnosis of sudden onset neurological symptoms after bone marrow transplantation. 相似文献