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   2010篇
  免费   15篇
  国内免费   3篇
综合类   3篇
化学工业   17篇
金属工艺   3篇
机械仪表   3篇
建筑科学   5篇
矿业工程   1篇
能源动力   3篇
轻工业   6篇
水利工程   13篇
石油天然气   6篇
无线电   5篇
一般工业技术   20篇
冶金工业   1928篇
自动化技术   15篇
  2022年   1篇
  2021年   1篇
  2020年   2篇
  2018年   2篇
  2017年   1篇
  2016年   7篇
  2015年   6篇
  2014年   4篇
  2013年   5篇
  2012年   2篇
  2011年   3篇
  2010年   5篇
  2009年   4篇
  2008年   4篇
  2007年   3篇
  2006年   3篇
  2005年   5篇
  2004年   6篇
  2003年   9篇
  2002年   5篇
  2001年   2篇
  2000年   2篇
  1999年   57篇
  1998年   675篇
  1997年   299篇
  1996年   228篇
  1995年   115篇
  1994年   98篇
  1993年   120篇
  1992年   10篇
  1991年   23篇
  1990年   28篇
  1989年   32篇
  1988年   34篇
  1987年   27篇
  1986年   15篇
  1985年   14篇
  1984年   1篇
  1983年   3篇
  1982年   4篇
  1981年   13篇
  1980年   14篇
  1978年   1篇
  1977年   27篇
  1976年   104篇
  1973年   1篇
  1971年   1篇
  1956年   1篇
  1955年   1篇
排序方式: 共有2028条查询结果,搜索用时 46 毫秒
121.
OBJECTIVES: This report describes how the 1995 National Survey of Family Growth (NSFG) was designed, planned, and implemented. The NSFG is a national survey of women 15-44 years of age designed to provide national estimates of factors affecting pregnancy and birth rates and the health of women and infants. Planning for the 1995 NSFG began in 1990 at a formal conference with the survey's data users. Suggestions for substantial changes and improvements in the survey were made there and carried out by NSFG staff and the NSFG contractor--the Research Triangle Institute (RTI). METHODS: The survey was converted from paper and pencil interviewing to Computer-Assisted Personal Interviewing (CAPI) to improve the quality, consistency, and timeliness of the data. At the same time, event histories of the respondent's work, education, family background, cohabitation, and sexual partners were added to lend explanatory power to the survey. These changes made the interview and the CAPI program long--average interview length was 103 minutes--and complex, but the CAPI program worked very well. RESULTS: About 260 female interviewers were trained for 7 days in January 1995. These interviewers completed a total of 10,847 interviews with women 15-44 years of age, for a response rate of 79 percent. This report describes how the survey was planned and designed and how the data were collected, edited, and processed for public use. This report may be of interest to NSFG data users and to those planning other computer-assisted surveys.  相似文献   
122.
123.
124.
125.
RATIONALE AND OBJECTIVES: The authors sought to correlate the radiologic findings of hepatobiliary fascioliasis with pathologic features. METHODS: Serial ultrasound, computed tomography (CT), and magnetic resonance findings in seven rabbits with experimentally induced fascioliasis were obtained every other week. Direct cholangiogram was also obtained after the rabbits were killed. Radiology-pathology correlation was done in specimens. RESULTS: In the parenchymal phase (an acute phase of parenchymal invasion of a larva), CT showed subcapsular clustered areas of low attenuation. Magnetic resonance appearance was similar in shape but better than CT in characterizing the hemorrhagic nature of the lesion. Ultrasound findings were nonspecific in this phase. In the ductal phase (a stationary phase after residing in the bile duct), CT showed dilatation of central ducts with symmetric periportal hypoattenuation (periportal tracking). Magnetic resonance could not depict mild ductal dilatation. Ultrasound was most valuable in demonstrating the moving worm within the dilated duct. Pathologically, the hepatic parenchymal lesions consisted of a cluster of eosinophilic granulomas with hemorrhagic change (migratory tract of the flukes). Ductal changes were observed predominantly in the central bile ducts. Periportal lymphangiectasia was also noted. CONCLUSIONS: Computed tomography or magnetic resonance can demonstrate the characteristic evolutionary pattern of fascioliasis that reflects the unique life cycle of Fasciola hepatica. The role of ultrasound, although limited in the parenchymal phase, was most useful in the ductal phase in that it demonstrated the moving worms themselves.  相似文献   
126.
Syntaxin 1, synaptobrevins or vesicle-associated membrane proteins, and the synaptosome-associated protein of 25 kDa (SNAP-25) are key molecules involved in the docking and fusion of synaptic vesicles with the presynaptic membrane. We report here the molecular, cell biological, and biochemical characterization of a 32-kDa protein homologous to both SNAP-25 (20% amino acid sequence identity) and the recently identified SNAP-23 (19% amino acid sequence identity). Northern blot analysis shows that the mRNA for this protein is widely expressed. Polyclonal antibodies against this protein detect a 32-kDa protein present in both cytosol and membrane fractions. The membrane-bound form of this protein is revealed to be primarily localized to the Golgi apparatus by indirect immunofluorescence microscopy, a finding that is further established by electron microscopy immunogold labeling showing that this protein is present in tubular-vesicular structures of the Golgi apparatus. Biochemical characterizations establish that this protein behaves like a SNAP receptor and is thus named Golgi SNARE of 32 kDa (GS32). GS32 in the Golgi extract is preferentially retained by the immobilized GST-syntaxin 6 fusion protein. The coimmunoprecipitation of syntaxin 6 but not syntaxin 5 or GS28 from the Golgi extract by antibodies against GS32 further sustains the preferential interaction of GS32 with Golgi syntaxin 6.  相似文献   
127.
128.
129.
Middiaphyseal 2.5-cm segmental defects in the right femurs of 12 sheep were stabilized with stainless steel plates and implanted with (1) 2 mg recombinant human bone morphogenetic protein 2 and poly[D,L-(lactide-co-glycolide)] bioerodible polymer with autologous blood (n = 7), (2) 4 mg recombinant human bone morphogenetic protein 2 and poly[D,L-(lactide-co-glycolide)] and blood (n = 3), or (3) poly[D,L-(lactide-co-glycolide)] and blood only (n = 2). Bone healing was evaluated for 1 year using clinical, radiographic, gross pathologic, and histologic techniques. Union occurred in three sheep in Group 1, two in Group 2, and none in Group 3. In the animals that healed, new bone first was visible radiographically between Weeks 2 and 6 after implantation; new bone mineral content equaled that of the intact femur not surgically treated by Week 16; recanalization of the medullary cavity approached completion at Week 52; and at necropsy the surgical treated femurs were rigidly healed, the poly[D,L-(lactide-co-glycolide)] was resorbed completely, and woven and lamellar bone bridged the defect site. In two Group 1 sheep euthanized at Weeks 2 and 6, polymer particles were permeated by occasional multinucleated giant cells. Some plasma cells, lymphocytes, and neutrophils were present locally. The poly[D,L-(lactide-co-glycolide)] tended to fragment during surgical implantation. Despite these observations, the recombinant human bone morphogenetic protein 2/poly[D,L-(lactide-co-glycolide)] implant was able to heal large segmental bone defects in this demanding model.  相似文献   
130.
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