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   1345篇
  免费   16篇
  国内免费   1篇
化学工业   82篇
金属工艺   9篇
机械仪表   20篇
建筑科学   9篇
矿业工程   1篇
能源动力   4篇
轻工业   31篇
水利工程   4篇
石油天然气   1篇
无线电   53篇
一般工业技术   61篇
冶金工业   1029篇
原子能技术   10篇
自动化技术   48篇
  2023年   5篇
  2021年   4篇
  2019年   5篇
  2018年   8篇
  2017年   3篇
  2016年   6篇
  2015年   8篇
  2014年   6篇
  2013年   17篇
  2012年   13篇
  2011年   12篇
  2010年   11篇
  2009年   11篇
  2008年   15篇
  2007年   12篇
  2006年   10篇
  2005年   10篇
  2004年   12篇
  2003年   16篇
  2002年   4篇
  2001年   17篇
  2000年   12篇
  1999年   38篇
  1998年   314篇
  1997年   163篇
  1996年   109篇
  1995年   55篇
  1994年   46篇
  1993年   63篇
  1992年   15篇
  1991年   25篇
  1990年   16篇
  1989年   19篇
  1988年   19篇
  1987年   23篇
  1986年   15篇
  1985年   21篇
  1984年   10篇
  1983年   11篇
  1982年   7篇
  1981年   15篇
  1980年   11篇
  1978年   9篇
  1977年   36篇
  1976年   55篇
  1975年   9篇
  1974年   4篇
  1968年   3篇
  1965年   3篇
  1963年   3篇
排序方式: 共有1362条查询结果,搜索用时 15 毫秒
1.
OBJECTIVE: To examine the relationship between pregnancy incidence and the level of serum E2 during danazol therapy. DESIGN: Danazol was given by 200 mg four times daily for 3 months. Serum E2 level was checked after completing the therapy, but before stopping medication. Patients then were advised to conceive at the appropriate time over a 6-month period. SETTING: Reproductive and Endocrine Laboratory of the Department of Obstetrics and Gynecology, Keelung Chang Gung Memorial Hospital, Keelung, Taiwan. PATIENTS: Infertile women with invasive endometriosis receiving conservative surgery and danazol treatment. INTERVENTIONS: Serum E2 is checked before medication and at the end of danazol therapy, but before stopping medication. MAIN OUTCOME MEASURES: Whether pregnancy is related to the change of serum E2 caused by danazol therapy. RESULTS: There were 24 pregnancies in 38 patients with invasive endometriosis after treatment. Pregnant patients had significantly lower serum E2 levels as compared with the nonpregnant patients. CONCLUSIONS: After conservative surgery for invasive endometriosis associated with infertility, the therapeutic period of danazol treatment could be shortened to 3 months. Because there is significant correlation of fecundability and serum E2 after danazol medication, serum E2 could be a guideline for predicting pregnancy or for prolonging or changing of treatment after danazol therapy.  相似文献   
2.
3.
4.
Skeletal development of transgenic mice with a type II collagen mutation was analyzed and compared with wild-type littermates. The single base substitution in Col2a1 resulted in a glycine to serine mutation within the helical domain and corresponded to one previously identified in a patient with the lethal human chondrodysplasia, hypochondrogenesis (Horton et al. [1992] Proc. Natl. Acad. Sci. U.S.A. 89:4583-4587). Skeletal staining of embryos from 14.5 through 18.5 days of gestation demonstrated a dwarf phenotype in the transgenic embryos, most notably short limb bones and vertebral column that was first detected at 15.5 days post-coitus. In addition to the reduced length, the extent of ossification was less in the transgenic mice. The architecture of the long bone growth plate was abnormal in the transgenic tissue, in particular there was no discernible proliferative zone. There were few stacks of characteristically flattened cells and the overall length of the growth plate in the mutant embryos was reduced. At the ultrastructural level, there were fewer collagen fibrils present in the transgenic mouse cartilage compared to that of wild-type littermates. Ultrastructural localization of collagen types II, IX and XI revealed a similar pattern between the transgenic and wild-type pups, suggesting that the collagen fibrils present in the matrix of littermates with both phenotypes had a similar composition. Skeletal analysis and cartilage histochemistry indicated that effect of the type II collagen mutation was to reduce the density of the collagen fibrils within the cartilage matrix which was associated with delayed bone formation and resulted in a short-limbed phenotype.  相似文献   
5.
The perception and discrimination of rapidly changing texture stimuli by pigeons was examined in a target localization task. Five experienced pigeons were rewarded for finding and pecking at a randomly placed odd target block of small repeated elements embedded in a larger rectangular array of contrasting distractor elements. On dynamic color test trials, the color of the target, distractor, or both of these regions changed at rates of 100, 250, 500, or 1000 ms per frame. The number of colors appearing within such trials also varied. Pigeons performed well above chance in all test conditions, with target-associated changes producing the best discrimination. The results suggest: (a) global relational information can exclusively guide target localization behavior, (b) pigeons can perceptually group and segregate colored textured differences quite rapidly (< or = 100 ms), and (c) pigeons may possess automatic search control processes that can be captured by stimulus-driven changes in the display.  相似文献   
6.
OBJECTIVE: The racial impact on graft outcome is not well defined in diabetic recipients. The purpose of this study is to analyze our experience with kidney-alone (A) and kidney-pancreas (KP) transplantation in type 1 diabetic recipients and evaluate the impact of racial disparity on outcome. RESEARCH DESIGN AND METHODS: The records of 217 kidney transplants (118 KA, 99 KP) performed on type 1 diabetic patients between 1985 and 1995 at the Medical University of South Carolina and the University of Texas Medical Branch were reviewed. RESULTS: A total of 53 (31%) white patients and 15 (33%) black patients experienced at least one episode of biopsy-proven acute rejection of the renal graft (NS). Patient survival at 1, 2, and 5 years was similar in white (92, 87, 69%) and black (91, 91, 69%) patients (NS). Kidney graft survival at 1, 2, and 5 years in the KA group was 72, 62, and 42% in blacks, compared with 79, 76, and 53% in whites (NS). Kidney graft survival at 1, 2, and 5 years in the KP group was 92, 92, and 74% in blacks, compared with 83, 77, and 58% in whites (NS). Pancreas graft survival at 1, 2, and 5 years was 81, 81, and 81% in blacks, compared with 81, 75, and 62% in whites (NS). Cox regression analysis revealed that donor age > or = 40 years increased the risk of renal graft failure 6.2-fold (P = 0.0001), whereas the addition of a pancreas transplant to a kidney and a living-related transplant decreased the risk of failure of the kidney graft 0.2 (P = 0.005) and 0.1 times (P = 0.005). CONCLUSIONS: Our results suggest that when compared with whites, there may be a trend toward an improved kidney and pancreas graft outcome in blacks undergoing KP transplants. These findings suggest that diabetes may override the risk factors that account for the pronounced disparity in outcome observed between nondiabetic white and black recipients.  相似文献   
7.
Seven cardiac electrophysiology stimulators from four manufacturers (Biotronik, Bloom, Digitimer and Medtronic) in common current use are reviewed. The stimulators differ in the features provided and the design adopted to achieve these features. The number of output channels ranges from one to four, the number of extra-stimuli available ranges from two to six, and these can be delivered as a variety of sequences. Some of the stimulators (Digitimer and Bloom) are modular while others (Biotronik and Medtronic 532 series) are of an integrated design comprising a single physical unit. The design of the Medtronic EP-2 has both integrated and modular characteristics. The features of the stimulators associated with input, output, control and the user interface are specifically reviewed. The features are also compared against the published recommendations of the American Heart Association. In addition, a summary of stimulator user comments from a number of electrophysiology centres is presented. All of the stimulators fulfil, or are close to fulfilling, basic electrophysiological requirements, but some provide more complex facilities such as would be required by specialist centres.  相似文献   
8.
BACKGROUND: This retrospective study assesses the outcomes and patterns of failure in patients with squamous cell carcinoma metastatic to cervical lymph nodes from an unknown primary site treated with combined surgery and postoperative radiotherapy. METHODS: One hundred thirty-six patients with squamous cell carcinoma metastatic to cervical lymph nodes from an unknown primary source were treated postoperatively with radiotherapy at the University of Texas M. D. Anderson Cancer Center between the years 1968 and 1992. Stage distribution was: N1, 31 patients; N2a, 49; N2b, 25; N2c, 3; N3, 18; and Nx, 10. Thirty-nine patients had excisional biopsies only, 64 patients underwent modified neck dissections, and 33 had radical neck dissections. Extracapsular extension was present in 87 cases. Fifty-nine patients had multiple nodes involved. The median duration of follow-up for surviving patients was 8.7 years. RESULTS: Twelve patients, all with extracapsular nodal disease, developed regional relapse. The 5-year actuarial rates of regional relapse in patients with and without extracapsular nodal disease were 16% and 0%, respectively (p = .004). Nine patients (22%) with extracapsular disease and multiple nodes relapsed compared with three patients (7%) with extracapsular disease and a solitary node (p = .02). None of the patients treated with excisional biopsy and radiotherapy relapsed regionally. No statistically significant relationship between dose, treatment duration, time interval between surgery, and the start of radiotherapy and relapse was detected. The 2-, 5-, and 10-year actuarial disease-specific survival rates were 82%, 74%, and 68%, respectively. Fourteen patients developed cancers in head and neck mucosal sites; six of these cancers were located in unirradiated tissues. CONCLUSIONS: Relapse occurred infrequently in patients treated with excisional biopsies and postoperative radiotherapy. Extracapsular extension and multiple nodes were associated with worse regional control and disease-specific survival. These results appear consistent with those expected for patients with advanced neck disease and a known primary site, and the absence of a primary site should not exclude patients from studies aiming to improve outcomes in patients with extensive neck disease from a head and neck squamous cell cancer. We continue to recommend radiation to the necks and pharyngeal axis for patients suspected of having residual microscopic disease following surgery for squamous cell carcinoma metastatic to the neck from an unknown primary site.  相似文献   
9.
The effects of physical training on elderly, fragile patients with rheumatoid arthritis (RA) who are on low-dose steroids were investigated. The controlled study included 24 patients who had been treated with low-dose steroids for 2 years. Each patient was assigned either to a treatment group receiving training or to an untrained control group. The training took place over a 3-month period and was based on a protocol using progressive interval training consisting of bicycle exercises, heel lifts, and step-climbing. The exercises were performed twice weekly for 45 minutes. Comparison of the two groups showed that disease activity did not increase in the trained group and that fewer, but not significantly fewer, swollen joints were observed in this group (p = 0.06). No significant changes were noticed in erythrocyte sedimentation rate, tender joints, or morning stiffness. The work capacity of the trained patients were doubled and the numbers of repetitions increased 76%. Individually adapted exercise programs can therefore be recommended for elderly rheumatoid arthritis patients on steroid treatment.  相似文献   
10.
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