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   3585篇
  免费   60篇
  国内免费   1篇
电工技术   14篇
综合类   4篇
化学工业   413篇
金属工艺   50篇
机械仪表   36篇
建筑科学   71篇
矿业工程   5篇
能源动力   49篇
轻工业   143篇
水利工程   19篇
石油天然气   9篇
无线电   203篇
一般工业技术   260篇
冶金工业   2176篇
原子能技术   10篇
自动化技术   184篇
  2022年   21篇
  2021年   18篇
  2020年   17篇
  2019年   16篇
  2018年   29篇
  2017年   26篇
  2016年   30篇
  2015年   24篇
  2014年   38篇
  2013年   82篇
  2012年   43篇
  2011年   69篇
  2010年   34篇
  2009年   52篇
  2008年   53篇
  2007年   69篇
  2006年   39篇
  2005年   40篇
  2004年   32篇
  2003年   29篇
  2002年   38篇
  2001年   37篇
  2000年   25篇
  1999年   102篇
  1998年   665篇
  1997年   399篇
  1996年   258篇
  1995年   163篇
  1994年   131篇
  1993年   150篇
  1992年   41篇
  1991年   34篇
  1990年   38篇
  1989年   50篇
  1988年   53篇
  1987年   72篇
  1986年   34篇
  1985年   33篇
  1984年   30篇
  1983年   29篇
  1982年   40篇
  1981年   34篇
  1980年   37篇
  1979年   20篇
  1978年   22篇
  1977年   59篇
  1976年   151篇
  1974年   14篇
  1973年   16篇
  1969年   15篇
排序方式: 共有3646条查询结果,搜索用时 15 毫秒
31.
32.
Individually housed DBA/2J mice were fed a liquid diet in which ethanol supplied 33% of the calories. The level of physical dependence that developed was estimated by scoring convulsions, elicited by handling the mice, after discontinuing the alcohol diet. The severity of the withdrawal reaction increased progressively with duration (5-12 days) of alcohol administration. A 2-day period on the diet produced no withdrawal reaction. Pretreatment of the mice with alcohol in their drinking water slightly increased the subsequent intake of the liquid diet. "Effective" alcohol intake was defined as uninterrupted alcohol consumption above 10 g/kg/day. Withdrawal scores correlated better with effective intake than with total intake under a variety of conditions. We interpret this to mean that brief interruptions in drinking (1 day) may allow the accrued physical dependence to disappear. On the basis of their effective alcohol intake, mice could be assigned to nondependent, moderately dependent or severely dependent groups for further study of the nature of physical dependence.  相似文献   
33.
The elemental composition of different types of keratohyalin granules from the epidermis of newborn and adult rats was studied by means of an EMMA-4 analytical electron microscope, equipped with an energy-dispersive X-ray spectrometer. An absolute quantitation of the sulphur concentration in keratohyalin granules was performed. The results demonstrate that epidermal keratohyalin granules are chemically heterogeneous. A type of keratohyalin granule present in the nuclei and cytoplasm of epidermal cells from both newborn and adult rats - termed single granules - is rich in sulphur, having a content of 2-5-3-6%. Other types of keratohyalin granules, which differ in newborn and adult rats, contain a sulphur-poor component; they often have a sulphur-rich component as well. The sulphur-poor keratohyalin contains 0-6-0-9% sulphur. It is suggested that the sulphur-rich keratohyalin granules are the source of the peripheral envelope protein of cornified cells.  相似文献   
34.
Myocardial imaging with technetium-99m stannous polyphosphate was performed on 46 patients. Eleven patients had no cardiac disease, 22 had acute myocardial infarction, and 13 had stable arteriosclerotic heart disease. Distinct patterns of myocardial activity were noted: (1) the patients with no obvious cardiac disease showed no cardiac activity; (2) stable arteriosclerotic heart disease showed faint, ill-defined cardiac activity, primarily in the anterior or inferior aspect of the left ventricle; (3) acute myocardial infarction showed intense, focal, well-defined activity, with a shape that characterized the location of the infarct.  相似文献   
35.
This study was undertaken to learn the significance of focal glomerular sclerosis in children who have nephrotic syndrome. Tissue obtained by percutaneous renal biopsy 10-15 years previously was re-examined. Initially, two of the 29 biopsy specimens contained focal segmental hyalinosis or sclerosis and five of the 29 had focal glomerular obsolescence. The paraffin blocks were serially sectioned and examined. Following this procedure, seven of the 29 biopsies had focal segmented hyalinosis and 16 of the 29 had focal glomerular obsolescence. The percentages of focal segmental hyalinosis and focal glomerular obsolescence were recorded. Only those patients whose focal segmental hyalinosis exceeded 2% progressed to renal failure. Age-matched autopsy material from patients dying without renal dysfunction was used as a control. Focal glomerular sclerosis was seen in 75.8% of the control specimens, although few glomeruli within each specimen were involved. Focal glomerular sclerosis may be found normally; it may be found in nephrotic children who do not develop renal failure. The quantification of sclerotic lesions may be of prognostic significance in childhood nephrosis.  相似文献   
36.
37.
The ratio of pulmonary to systemic vascular resistance (Rp/Rs) largely determines the amount of left-to-right shunting and pulmonary to systemic flow rat (Qp/Qs) in the presence of a large isolated ventricular septal defect. The possibility that pharmacologic reduction of systemic vascular resistance with alpha-adrenergic receptor blockade or beta-adrenergic receptor stimulation would increase the ratio Rp/Rs, and therefore reduce the ratio Qp/Qs, was studied in dogs in which ventricular septal defects had been surgically created. Administration of phentolamine and phenoxybenzamine caused a 42% reduction in Rs and no reduction in Rp. Qs was unchanged and Qp declined by 24% and the ratio Qp/Qs fell by 32%. Infusion of the beta-adrenergic receptor stimulant isoproterenol also reduced Qp/Qs. However, this was accomplished as a result of an increase in Qs and at the expense of an increase in heart rate. As a decline in the ratio Qp/Qs has been shown to be beneficial to patients with large left-to-right shunts, pharmacologic reduction of systemic vascular resistance may prove to be helpful in treating congestive heart failure in those patients with large left-to-right shunts at the ventricular level who are refractory to the usual decongestive measures.  相似文献   
38.
39.
The synthesis of immunoglobulins G, A, and M has been studied in Peyer's patches together with closely associated intestinal mucosa and in small intestine distant from Peyer's patches in specific-pathogen-free (SPF) Swiss mice and conventional and germ-free C3H mice. Thissue fragments were cultured in vitro in medium containing 14C-labelled amino acids, and newly synthesized proteins were detected by radioimmunoelectrophoresis. Small intestine from SPF and conventional animals synthesized almost exclusively IgA. No immunoglobulin synthesis was detectable in germ-free intestine. In contrast, the Peyer's patches and associated mucosa of all the groups of mice synthesized IgG, IgA, and IgM. This observation is discussed in relation to the possible role of the Peyer's patches as a source of precursors for immunoglobulin-producing cells in the intestine.  相似文献   
40.
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