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   2641篇
  免费   8篇
电工技术   4篇
化学工业   106篇
金属工艺   6篇
机械仪表   12篇
建筑科学   24篇
能源动力   5篇
轻工业   57篇
水利工程   8篇
石油天然气   1篇
无线电   58篇
一般工业技术   111篇
冶金工业   2201篇
原子能技术   1篇
自动化技术   55篇
  2023年   5篇
  2022年   4篇
  2021年   9篇
  2019年   9篇
  2018年   6篇
  2017年   7篇
  2016年   7篇
  2013年   45篇
  2012年   16篇
  2011年   32篇
  2010年   13篇
  2009年   15篇
  2008年   11篇
  2007年   17篇
  2006年   13篇
  2005年   18篇
  2004年   14篇
  2003年   14篇
  2002年   9篇
  2001年   11篇
  2000年   9篇
  1999年   78篇
  1998年   667篇
  1997年   392篇
  1996年   229篇
  1995年   123篇
  1994年   115篇
  1993年   145篇
  1992年   24篇
  1991年   30篇
  1990年   33篇
  1989年   47篇
  1988年   40篇
  1987年   52篇
  1986年   38篇
  1985年   25篇
  1983年   14篇
  1982年   17篇
  1981年   17篇
  1980年   22篇
  1978年   7篇
  1977年   57篇
  1976年   114篇
  1975年   9篇
  1974年   5篇
  1972年   4篇
  1970年   7篇
  1955年   6篇
  1938年   3篇
  1937年   5篇
排序方式: 共有2649条查询结果,搜索用时 828 毫秒
21.
Although reticulocyte counts can be reliably performed for up to 48 h after storage in EDTA, it is unclear whether this is applicable to the pediatric age group. In order to evaluate this, manual reticulocyte counts were performed on 20 specimens from pediatric patients stored at 4 degrees C for up to 24 h post collection. Samples were evaluated at 1-3, 6, 12, 18, and 24 h after storage in EDTA vacutainer tubes at 4 degrees C. The age of the subjects ranged from 1 day to 9 years with a median age of 3 years. Patients' reticulocyte counts ranged from 0 to 27% (5.89 +/- 7.21). No clinically significant changes were evident in the reticulocyte count over 24 h after specimen collection. The mean of the 20 specimens at 1-3 h was 5.50 and at 24 h was 5.40 (P > .05). The standard deviation of the mean values ranged from 7.03 to 7.26 (P > .05). The results indicate that reticulocyte counts may be performed on previously drawn blood held at 4 degrees C for up to 24 h post collection in a pediatric population without significant difference from baseline values.  相似文献   
22.
The enzyme steroid 5 alpha-reductase (EC 1.3.99.5) is a component of an intercellular signaling pathway that determines cell fate in the primordium of the mammalian reproductive tract. During male phenotypic sexual differentiation, the dihydrotestosterone product of this enzyme binds to the androgen receptor and initiates development of the external genitalia and prostate. Genes encoding two isozymes of steroid 5 alpha-reductase with different biochemical properties and tissue distributions have recently been isolated. In the current study, we utilize in situ hybridization analysis to determine cell-type-specific expression patterns of the 5 alpha-reductase isozyme mRNAs in two androgen target tissues (regenerating ventral prostate and epididymis) and a peripheral tissue (liver). In regenerating ventral prostate, the type 1 mRNA is expressed in basal epithelial cells whereas expression of the type 2 mRNA is largely confined to stromal cells. These results were confirmed by immunohistochemical analysis and are consistent with distinct roles played by the isozymes in the prostate. In the epididymis, both 5 alpha-reductase isozyme mRNAs are expressed in epithelial cells. Only the type 1 mRNA is present in the liver. This mRNA is distributed in a striking spatial gradient extending from hepatocytes surrounding the portal triad (high expression) to those surrounding the central vein (low to absent expression). These findings demonstrate cell-type-specific expression of the steroid 5 alpha-reductase isozymes and underscore their distinct and overlapping functions in androgen physiology.  相似文献   
23.
岩心PI值试验研究及应用   总被引:5,自引:0,他引:5  
主要论述了在多功能采油化学用剂评价仪上进行的岩心PI值试验的步骤,现象及结论。重点考察了岩心PI值与渗透率、流量及注入截面面积的关系;平行管岩心复合PI值和其中单管岩心PI值的关系。  相似文献   
24.
25.
26.
27.
28.
29.
30.
The longitudinal, expert, all data (LEAD) procedure has been employed as a criterion for the assessment of the procedural validity of diagnostic instruments. This study evaluated the procedure's concurrent, discriminant and predictive validity. Interview and questionnaire data obtained from 100 individuals in a substance abuse treatment program were used to assess current and lifetime substance use disorders and common comorbid disorders. An experienced, doctoral-level clinician formulated LEAD diagnoses for each patient, based on an initial interview, ongoing clinical contact and the results of the research assessment and all available clinical records. LEAD-derived substance use diagnoses showed good concurrent, discriminant and predictive validity. The validity of comorbid diagnoses obtained using the LEAD procedure was generally fair to good. Comparison with diagnoses based only on the clinician's unstructured initial interview showed that the availability of additional data enhanced diagnostic validity. Diagnoses derived by a research technician using the Structured Clinical Interview for DSM-III-R showed validity comparable to that of LEAD diagnoses. To enhance its diagnostic validity, applications of the LEAD standard should include a structured interview. Other variations in the application of the LEAD standard, including a longer evaluation period, may also enhance its performance as a diagnostic criterion measure.  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