全文获取类型
收费全文 | 5480篇 |
免费 | 134篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 42篇 |
综合类 | 4篇 |
化学工业 | 560篇 |
金属工艺 | 53篇 |
机械仪表 | 85篇 |
建筑科学 | 82篇 |
矿业工程 | 3篇 |
能源动力 | 118篇 |
轻工业 | 189篇 |
水利工程 | 34篇 |
石油天然气 | 44篇 |
无线电 | 292篇 |
一般工业技术 | 492篇 |
冶金工业 | 3260篇 |
原子能技术 | 17篇 |
自动化技术 | 350篇 |
出版年
2023年 | 43篇 |
2022年 | 83篇 |
2021年 | 133篇 |
2020年 | 98篇 |
2019年 | 103篇 |
2018年 | 136篇 |
2017年 | 109篇 |
2016年 | 131篇 |
2015年 | 85篇 |
2014年 | 135篇 |
2013年 | 220篇 |
2012年 | 125篇 |
2011年 | 157篇 |
2010年 | 105篇 |
2009年 | 86篇 |
2008年 | 68篇 |
2007年 | 55篇 |
2006年 | 66篇 |
2005年 | 37篇 |
2004年 | 48篇 |
2003年 | 31篇 |
2002年 | 19篇 |
2001年 | 26篇 |
2000年 | 24篇 |
1999年 | 88篇 |
1998年 | 941篇 |
1997年 | 547篇 |
1996年 | 410篇 |
1995年 | 250篇 |
1994年 | 177篇 |
1993年 | 197篇 |
1992年 | 39篇 |
1991年 | 47篇 |
1990年 | 37篇 |
1989年 | 40篇 |
1988年 | 38篇 |
1987年 | 37篇 |
1986年 | 29篇 |
1985年 | 35篇 |
1984年 | 13篇 |
1983年 | 18篇 |
1982年 | 28篇 |
1981年 | 30篇 |
1980年 | 37篇 |
1979年 | 12篇 |
1978年 | 18篇 |
1977年 | 135篇 |
1976年 | 265篇 |
1975年 | 15篇 |
1974年 | 5篇 |
排序方式: 共有5625条查询结果,搜索用时 31 毫秒
81.
Undecalcified embedment of large bone specimens is often challenging. A method is presented here that is suitable for methacrylate embedment of sections of canine vertebrae while retaining the ability to localize tartrate-resistant acid phosphatase and alkaline phosphatase activity. Specimens also retained tetracycline labelling, and sectioned preparations were readily stained with routine bone procedures. A modification of the Bodian silver stain, used for examining the nerves and spinal cord in these specimens, provided a useful stain for canaliculi and cement lines in trabecular and cortical bone. This stain is advantageous when both bone and nerve tissue are of interest, as in spinal fusion studies. 相似文献
82.
This paper presents a new massively parallel MIMD architecture, halfway between the Connection Machine and hypercubes based on 32-bit processors. It is built from specific 8-bit processors arranged in a 2-D grid and communicating by message transfers. We discuss the communication problems, the instruction set of the basic processing unit, the programmation of the whole array and the use of a high level data-flow language. 相似文献
83.
AA De Smet 《Canadian Metallurgical Quarterly》1993,22(7):479-484
Magnetic resonance (MR) images of skeletal muscle tears can clearly delineate the severity of muscle injury. Although MR imaging is seldom necessary in patients with acute muscle trauma, it can be helpful in deciding on clinical management. The two major MR findings in acute muscle tears are deformity of the muscle and the presence of abnormal signal reflecting hemorrhage and edema. In acute tears, methemoglobin within the extravascular blood causes high-signal areas on both T1- and T2-weighted images. With partial tears, the blood may dissect in a distinctive linear pattern along the muscle bundles and fibers. As healing begins, the muscle signal diminishes, first on the T1-weighted images and then on the T2-weighted images. When there is residual abnormal signal on images obtained more than several months after the injury, it is presumed to represent hemorrhage from recurrent tears. In patients with a questionable history of a remote injury, the clinical presentation may be that of persistent pain or a soft tissue mass. In these cases MR imaging may identify the cause of the pain and can exclude a neoplasm by proving that the mass is a hypertrophied or retracted muscle. Thus, MR imaging has a limited, but occasionally important role in selected patients with skeletal muscle tears. 相似文献
84.
The spermatogenesis of Pseudis limellum, from the Southern Pantanal, Brazil, was studied from July 1995 to May 1996, through histological sections of the testis. The cells could be differentiated as: primary spermatogonia, large cells, generally with bilobed nucleus; secondary spermatogonia, smaller cells, with darker cytoplasm, chromatin of radial form; primary and secondary spermatocytes, differentiated according to the different stages of the nucleus during the successive cells divisions. Furthermore, we observed cells in process of morphologic differentiation: rounded spermatids much smaller, with nucleus containing chromatin in compacting process and cytoplasm reduction; elongated spermatids, generally parallel organized in well defined bundles, with the anterior region directed toward the periphery of the seminiferous tubule and the tail directed toward the lumen. Spermatozoa are free in the lumen of the seminiferous tubule. All the cells are organized as cysts, which are supported by a large amount of Sertoli cells. The spermatogenesis in P. limellum is very similar to that of other anurans, but peculiarities were observed regarding the organization of the germ cells, the great amount of free Sertoli cells in the lumen of testis collected in May, and the long cytoplasmatic extensions of the cells bearing pigments and involving the seminiferous tubule. The diameter of the seminiferous tubule (SD) exhibited an annual mean of 251.79 +/- 37.57 microm. Spermatozoa number by seminiferous tubule (SN) exhibited an annual mean of 306.66 +/- 39.83, also with higher and lower values at each month. Variations in SD and SN were not significantly correlated with climatic variables. In this species, reproduction occurs throughout the year in ponds and flooded areas, despite the seasonal climate of the Pantanal. Although males varied in their annual reproductive activity, they were considered potentially reproductive in all months throughout the year. 相似文献
85.
86.
87.
The article explores the relationship between the cost and the quality of hospital care by elaborating a conceptual model of hospital performance. The model relates the financial health status of an organization (financial integrity) to the quality of care provided by that organization (clinical integrity) within an environment that is characterized by various forms of risk. The model suggests that both concepts determine the corporate destiny (success, bankruptcy, or merger) of the organization. If this model proves valid empirically, the results could be used as an early warning system to identify hospitals that might experience financial or clinical distress. 相似文献
88.
AA Schreiber K Frei W Lichtensteiger M Schlumpf 《Canadian Metallurgical Quarterly》1993,38(3-4):265-272
Prenatal exposure to diazepam and other benzodiazepines (BDZ) has been found to result in a marked reduction of T-lymphocyte proliferation during postnatal development of rats. In search for pathogenic changes underlying this effect, we investigated the mitogen lipopolysaccharide (LPS) and concanavalin A (ConA) stimulated release of tumour necrosis factor (TNF)-alpha by mixed splenocytes of male offspring from Long Evans rats treated with 1.25 mg/kg per day diazepam from gestational day 14 to 20. In response to LPS, TNF-alpha release was found to be significantly lower in mixed splenocytes of two- and four-week-old treated than in control offspring. However, at eight weeks of age, prenatally diazepam-treated animals showed a significantly higher LPS-induced TNF-alpha release than control rats. Since monocytes/macrophages represent a major source of TNF-alpha, additional experiments were performed on purified spleen macrophages and lymphocytes stimulated with LPS. TNF-alpha release was only detectable in supernatants of adherent spleen macrophages and not in supernatants of lymphocytes. Thus, our data indicate that a disturbance in TNF-alpha release from macrophages is involved in the deficient immune response of prenatally diazepam-exposed rats. 相似文献
89.
90.