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   8596篇
  免费   377篇
  国内免费   195篇
电工技术   238篇
综合类   248篇
化学工业   966篇
金属工艺   266篇
机械仪表   319篇
建筑科学   435篇
矿业工程   119篇
能源动力   177篇
轻工业   652篇
水利工程   223篇
石油天然气   123篇
武器工业   74篇
无线电   781篇
一般工业技术   1049篇
冶金工业   2458篇
原子能技术   132篇
自动化技术   908篇
  2023年   40篇
  2022年   116篇
  2021年   175篇
  2020年   125篇
  2019年   119篇
  2018年   119篇
  2017年   121篇
  2016年   125篇
  2015年   181篇
  2014年   262篇
  2013年   423篇
  2012年   341篇
  2011年   422篇
  2010年   336篇
  2009年   340篇
  2008年   376篇
  2007年   377篇
  2006年   295篇
  2005年   269篇
  2004年   209篇
  2003年   195篇
  2002年   231篇
  2001年   175篇
  2000年   149篇
  1999年   207篇
  1998年   643篇
  1997年   441篇
  1996年   307篇
  1995年   164篇
  1994年   150篇
  1993年   169篇
  1992年   67篇
  1991年   81篇
  1990年   55篇
  1989年   72篇
  1988年   88篇
  1987年   51篇
  1986年   61篇
  1985年   66篇
  1984年   79篇
  1983年   57篇
  1982年   54篇
  1981年   63篇
  1980年   61篇
  1979年   58篇
  1978年   54篇
  1977年   103篇
  1976年   180篇
  1974年   47篇
  1973年   41篇
排序方式: 共有9168条查询结果,搜索用时 15 毫秒
101.
MJ Hickey  Y Wilson  JV Hurley  WA Morrison 《Canadian Metallurgical Quarterly》1998,101(5):1296-304; discussion 1305-6
This study, using 62 rabbits, examines the rate and pattern of vascular outgrowth from a subcutaneously implanted vascular pedicle, how the newly formed vessels connect to preexisting skin vessels, and whether local application of basic fibroblast growth factor can accelerate the angiogenic process. When the femoral artery and vein of rabbits are implanted beneath the skin, angiogenesis from both the pedicle and small blood vessels within the adjacent skin begins within 3 days. Perfusion with India ink reveals connections between the pedicle and dermal vessels as early as 5 days after implantation of the pedicle. Provided the pedicle does not thrombose, skin flaps based on it may survive completely when elevated as early as 2 weeks after implantation. Flap survival depends on the development of a small number of vascular connections between vessels arising from the pedicle and preexisting dermal vessels. If elevation is delayed until 4 weeks after implantation a flap may survive even if its pedicle has thrombosed. Prolonged release of basic fibroblast growth factor adjacent to the pedicle significantly increases the survival of flaps elevated 1 week after implantation but does not alter the survival of flaps elevated at 2 and 4 weeks.  相似文献   
102.
Mutations in the human mismatch repair protein hMSH2 have been found to cosegregate with hereditary nonpolyposis colorectal cancer (HNPCC). Previous biochemical and physical studies have shown that hMSH2 forms specific mispair binding complexes with hMSH3 and hMSH6. We have further characterized these protein interactions by mapping the contact regions within the hMSH2-hMSH3 and the hMSH2-hMSH6 heterodimers. We demonstrate that there are at least two distinct interaction regions of hMSH2 with hMSH3 and hMSH2 with hMSH6. Interestingly, the interaction regions of hMSH2 with either hMSH3 or hMSH6 are identical and there is a coordinated linear orientation of these regions. We examined several missense alterations of hMSH2 found in HNPCC kindreds that are contained within the consensus interaction regions. None of these missense mutations displayed a defect in protein-protein interaction. These data support the notion that these HNPCC-associated mutations may affect some other function of the heterodimeric complexes than simply the static interaction of hMSH2 with hMSH3 or hMSH2 with hMSH6.  相似文献   
103.
Growth and voluntary feed intake (VFI) in grazing temperate farmed deer species are influenced by the feeding value of the forage and the stage of the deer's seasonal cycle. Liveweight gain (LWG) of growing red deer was greater when perennial ryegrass (0.80)/white clover (0.20) pasture was grazed at 10 cm than 5 cm surface height, but venison production by one year of age was still low. Chicory and red clover were of superior feeding value for deer than perennial ryegrass-based pastures, increasing LWG of young red and hybrid (0.25 elk; 0.75 red deer) deer during summer and autumn, due to higher VFI and to higher organic matter digestibility. Relative to perennial ryegrass, chicory disintegrated faster in the rumen, with very low rumination time and faster rumen outflow rates of liquid and particulate matter. Inputs of red clover and chicory substantially increased venison carcass weights at one year of age from grazing red and hybrid stags. In indoor pen feeding studies, red deer were shown to have a seasonal cycle of digestive function, with greater rumen mean retention time (MRT) and greater rates of rumen ammonia production in summer than in winter. It was deduced that the purpose of the digestive cycle was to maintain apparent digestibility constant as VFI increased during summer. Tropical sambar deer were also shown to have seasonal cycles in growth and VFI that were of reduced amplitude compared with red deer. Peak VFI and growth occurred in autumn and minimum VFI and growth occurred in spring. Feed conversion (kg DM eaten/kg LWG) was more efficient for sambar than for red deer, due to lower VFI and lower heat production, but there was no difference between species in digestive efficiency.  相似文献   
104.
Aim of the study was investigate the cross-sectional relationship between body composition and bone mineral density (BMD) in very old men and women. The study sample consisted of 504 women and 285 men, aged 72-93 yr, participating in examination 22 (1992-1993) of the Framingham Heart Study. Total body BMD, regional BMD, and soft-tissue body composition was measured by dual-energy X-ray absorptiometry. Both muscle mass and percentage body fat were positively associated with total body BMD in women. After adjustment for age, physical activity, smoking status, estrogen use, and thiazide use, BMD increased with increasing tertile of muscle mass (p = 0.007) and with increasing tertile of percentage body fat (p = 0.0001) in women. In men muscle mass, not percentage body fat, was positively associated with BMD. After adjustment for potential confounders, BMD remained associated with muscle mass only (p = 0.02). These results were similar for leg BMD and arm BMD. The study suggests that the influence of muscle and fat mass on bone mineral density is different between very old men and women.  相似文献   
105.
The MPC105 peripheral component interconnection bridge/memory controller provides a platform-specification-compliant bridge between Power PC microprocessors and the PCI bus. With it, designers can create systems using peripherals already designed for a variety of standard PC interfaces. This bridge chip also integrates a secondary cache controller and high-performance memory controller that supports DRAM or synchronous DRAM and ROM or flash ROM  相似文献   
106.
OBJECTIVE: The objective of this study was to assess somatic and inherited androgen receptor gene mutations in families with only one affected individual. METHODS: Molecular genetic analysis of the androgen receptor gene in DNA derived from blood leukocytes from 30 families with single-strand conformation analysis, direct sequencing, and restriction fragment analysis was performed. RESULTS: In 22 families the mothers and all investigated grandmothers were heterozygous carriers. However, within the sisters and aunts, both heterozygous carriers and noncarriers were present. In eight families a de novo mutation was characterized. In three of these patients indication for somatic mosaicism was found. CONCLUSIONS: De novo mutations occur at a high rate within the androgen receptor gene (8 of 30 = 26.7%); a high proportion (3 of 8) arise after the zygote stage. Thus only direct analysis of the underlying mutation of the androgen receptor gene in the proband and his or her family can provide the basis for genetic counseling.  相似文献   
107.
The routine wearing of gloves during the dental treatment of patients forms an integral part of the recommended guidelines of many authorities worldwide. Compliance has been variable but there is evidence to show that this is increasing, as are other cross-infection control measures. A survey of glove use by general dental practitioners in England and Wales was carried out in 1989. This paper reports a follow up study in 1991/2 which aimed to identify any differences that had occurred in the interim. The results indicated that there was increasing compliance with recommended cross-infection control measures, although only one fifth of respondents were found to change gloves between patients. Of those practitioners who did not change gloves between patients, half considered that blood contact was not a reason for changing gloves. Comparisons are made with compliance rates in other countries and recommendations made for further education within the dental profession on the subject of cross-infection control.  相似文献   
108.
109.
110.
Scanning with Tc-99m labeled RBC was performed in two patients with recurrent postoperative gastrointestinal bleeding after partial colonic resection. Imaging correctly identified the source of bleeding at the anastomotic site in the large bowel, effectively contributing in the patient's treatment planning. Radionuclide scintigraphy provides a simple, noninvasive modality to diagnose and manage difficult clinical situations such as postoperative bleeding.  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