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   7012篇
  免费   272篇
  国内免费   8篇
电工技术   79篇
化学工业   1093篇
金属工艺   109篇
机械仪表   132篇
建筑科学   212篇
矿业工程   11篇
能源动力   179篇
轻工业   543篇
水利工程   50篇
石油天然气   10篇
无线电   647篇
一般工业技术   1205篇
冶金工业   1966篇
原子能技术   64篇
自动化技术   992篇
  2023年   43篇
  2022年   75篇
  2021年   111篇
  2020年   83篇
  2019年   125篇
  2018年   141篇
  2017年   125篇
  2016年   124篇
  2015年   111篇
  2014年   179篇
  2013年   343篇
  2012年   229篇
  2011年   329篇
  2010年   245篇
  2009年   237篇
  2008年   279篇
  2007年   271篇
  2006年   205篇
  2005年   176篇
  2004年   155篇
  2003年   157篇
  2002年   146篇
  2001年   116篇
  2000年   119篇
  1999年   141篇
  1998年   484篇
  1997年   292篇
  1996年   214篇
  1995年   160篇
  1994年   152篇
  1993年   149篇
  1992年   82篇
  1991年   72篇
  1990年   77篇
  1989年   87篇
  1988年   78篇
  1987年   70篇
  1986年   50篇
  1985年   58篇
  1984年   86篇
  1983年   70篇
  1982年   60篇
  1981年   59篇
  1980年   62篇
  1979年   72篇
  1978年   55篇
  1977年   75篇
  1976年   125篇
  1975年   49篇
  1974年   43篇
排序方式: 共有7292条查询结果,搜索用时 0 毫秒
51.
Twenty mothers of preterm babies who had survived to 1 year old, were matched for age and parity of the mother and time of birth of the baby, with 20 mothers delivering fullterm. Bone mineral, body composition and anthropometric measurements were obtained for each mother and analysed using paired t-tests. The only significant difference (P < 0.01) between the groups was a lower fat-free mass in the preterm mothers calculated from skinfold thickness measurements.  相似文献   
52.
Rheological property and stress development of tape-cast ceramic layers derived from nonaqueous alumina (A12O3)-poly(vinyl butyral) (PVB) suspensions were observed during drying. Casting suspensions exhibited strong shear-thinning behavior, with a low shear Newtonian plateau apparent viscosity >102 Pa.s. The apparent suspension viscosity displayed a power-law dependence on the A12O3 volume fraction during the initial stage of drying (<30% solvent loss). Stress development, measured by a cantilever deflection method, and parallel weight loss measurements were performed during the drying of tape-cast layers and pure binder coatings. Maximum drying stresses (σmax) of 1.37-0.77 MPa were observed for plasticized tapes cast at gap heights of 150-400 μm. In contrast, nonplasticized tapes of similar thickness displayed a more gradual stress increase, with σmax values approximately an order of magnitude higher than their plasticized counterparts. The stress histories of the corresponding binder coatings were quite similar to the tape-cast layers, albeit slightly lower σ max values were observed. Stresses decayed beyond σmax with a logarithmic time dependence to an almost constant value of 0.2-0.4 MPa for the plasticized tapes. Based on these observations, process methodologies have been offered to minimize stress development and retention in tape-cast ceramic layers  相似文献   
53.
54.
Simultaneous near-field scanning optical and atomic force imaging of bacteria is presented. The bacteria imaged in these studies were unstained. The near-field optical images had excellent signal-to-noise and showed excellent contrast even in these unstained specimens. The images obtained were interpreted in terms of the images that have been obtained by transmission electron microscopy and X-ray imaging. The results show that bacterial near-field optical imaging is going to be a very important tool in the arsenal of the bacteriologist both in terms of understanding the fundamental processes in the life cycle of bacteria with and without cytochemical staining and in terms of clinical diagnostic applications.  相似文献   
55.
There exists a movement within the field of psychology to incorporate religious material into the overall conceptualization and treatment of the client. This article questions the appropriateness of such incorporation and emphasizes instead the distinction the therapist needs to make between religious and psychological material in the psychotherapeutic setting. The therapist must also be aware of how religious material can intensify the transference, resistance, and countertransference, thereby complicating the therapeutic process. Client issues that relate to the religious identity of the therapist or invoke a sense of exclusive similarity in the therapeutic dyad can further complicate the therapy. Such complications suggest that the avoidance of both overt and covert messages that communicate the therapist's personal values and beliefs may be beneficial for therapy. Case examples with 4 clients (aged 18–56 yrs) are presented. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
56.
We describe two cases of congenital chylothorax in siblings with important differences from previously described familial cases. Our findings support the likelihood of an autosomal recessive inheritance in some cases of this condition, rather than X-linked recessive inheritance, which has also been suggested. Autopsy findings from one of these cases and others previously described suggest that the pathophysiological mechanisms involved may be variable.  相似文献   
57.
58.
During studies to develop serum tests of small intestinal permeability, we detected an unidentified disaccharide in HPLC traces of sera from untreated celiacs. This present study aimed to identify the disaccharide and determine whether the presence of the disaccharide in the serum after an oral challenge had potential as a simple screening test for celiac disease. The disaccharide was identified as sucrose by incubation studies of sera with disaccharidases. Twenty untreated celiacs, 15 treated celiacs, and 20 normal or dyspeptic controls were studied for the presence of sucrose in their serum after an oral load (8 g). The results in celiacs were compared with the presence of serum IgA endomysial antibodies. The 10 normal controls were also given a larger sucrose challenge (50 g). Ten of the untreated celiacs and 10 controls had their brush border disaccharidase activities measured. Sucrose eluted in the same position as the unidentified disaccharide in the HPLC trace and the latter could be removed by incubation with sucrase. All untreated celiacs but none of the treated celiacs had sucrose in their serum after the 8-g oral challenge. None of the controls had sucrose in their serum after the 8-g or 50-g challenges. Three untreated celiacs were IgA endomysial antibody negative as were all the treated cases. Brush border sucrase activity was low in untreated celiac disease. The presence of sucrose in the serum after an oral load shows promise as a noninvasive test for celiac disease.  相似文献   
59.
The Women's Health Trial:Feasibility Study in Minority Populations (WHT:FSMP) examined the feasibility of recruiting postmenopausal women from a broad range of racial and socioeconomic backgrounds into a primary prevention trial requiring marked reductions in dietary fat. Postmenopausal women aged 50-79 yr who had no history of cardiovascular disease or cancer and who consumed 36% or more total energy from fat qualified to participate. We randomized the women into dietary intervention (60%) or control (40%) groups; we aimed to randomize 750 women in 18 months in each of the three clinical centers. All centers achieved goals for randomization based on ethnicity, and two centers exceeded overall recruitment goals. The greatest source of randomized participants was mass mailing, followed by items in the media, referrals, and community outreach. Recruitment yields were generally similar for the ethnic groups but lower for less-educated participants. The experience of WHT:FSMP indicates that postmenopausal women from the African-American, Hispanic, and non-Hispanic white communities can be recruited into dietary intervention studies for the prevention of disease.  相似文献   
60.
Beneficial use impairments (BUIs) under the Great Lakes Water Quality Agreement identify environmental issues requiring remedial action within the Great Lakes Areas of Concern (AOCs). We conducted this study to support the assessment of the wildlife component of BUI 3: degradation of fish and wildlife populations. We compared bird and amphibian (frogs and toads) data from the Toronto and Region Conservation Authority’s Terrestrial Long-term Monitoring Program in the Toronto and Region AOC to an adjacent, but otherwise similar, reference watershed, Duffins Creek. Twelve of 13 targets were met within the AOC for forest bird, wetland bird, meadow bird and amphibian populations based on averages of mean annual values at sites within the AOC that were within two standard deviations of averages at sites in the Duffins Creek reference watershed between 2008 and 2017. Even though wildlife populations within the AOC were within the normal range of variability expected from a reference watershed, they were often at lower levels than within the Duffins Creek reference watershed. In addition, forest bird and amphibian populations were negatively affected by urbanization within the AOC and meadow bird indices declined. We conclude that while wildlife populations within the AOC currently meet targets for BUI 3, they continue to be negatively impacted by numerous stressors that are primarily related to past and ongoing urbanization. Thus, continued restoration of wildlife habitat and protection of existing habitat within the AOC is highly recommended.  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