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   5100篇
  免费   17篇
电工技术   19篇
综合类   3篇
化学工业   173篇
金属工艺   7篇
机械仪表   14篇
建筑科学   41篇
矿业工程   2篇
能源动力   28篇
轻工业   72篇
水利工程   1篇
石油天然气   3篇
无线电   123篇
一般工业技术   89篇
冶金工业   4440篇
原子能技术   26篇
自动化技术   76篇
  2021年   16篇
  2020年   7篇
  2019年   4篇
  2018年   11篇
  2017年   14篇
  2016年   11篇
  2015年   6篇
  2014年   17篇
  2013年   30篇
  2012年   17篇
  2011年   30篇
  2010年   18篇
  2009年   29篇
  2008年   29篇
  2007年   32篇
  2006年   31篇
  2005年   24篇
  2004年   31篇
  2003年   25篇
  2002年   33篇
  2001年   21篇
  2000年   22篇
  1999年   156篇
  1998年   1372篇
  1997年   781篇
  1996年   500篇
  1995年   302篇
  1994年   216篇
  1993年   279篇
  1992年   57篇
  1991年   62篇
  1990年   58篇
  1989年   86篇
  1988年   67篇
  1987年   73篇
  1986年   54篇
  1985年   64篇
  1984年   8篇
  1983年   17篇
  1982年   22篇
  1981年   38篇
  1980年   33篇
  1979年   8篇
  1978年   12篇
  1977年   119篇
  1976年   228篇
  1975年   12篇
  1974年   4篇
  1972年   4篇
  1970年   6篇
排序方式: 共有5117条查询结果,搜索用时 10 毫秒
991.
We examined the pregnancy outcome of 112 women classified as minor degrees of glucose intolerance (MDGI) in pregnancy in a screening program based on Carpenter and Coustan's criteria. The MDGI group comprised 49 women with abnormal oral glucose challenge test (OGCT) followed by normal OGTT (group A), and 63 with "borderline" OGTT (1 abnormal value, group B). No treatment was offered to 88 MDGI women, while 26 received dietary advice and metabolic monitoring. A control group was constituted from 112 age- and BMI-matched negative screenees. Similar rates of cesarean sections and macrosomia, but higher rate of large for gestational age (LGA) babies (25.9% vs 14.3%) were found in MDGI, without difference between groups A and B. When comparing treated and untreated MDGI, lower LGA incidence (11.5% vs 30.2%) and no macrosomia were found in the former. In conclusion, untreated MDGI may present excessive fetal growth, which can be normalized by dietary treatment and metabolic monitoring.  相似文献   
992.
The toxic effects of the Fusarium graminearum trichothecene toxin deoxynivalenol were determined on ribosomes and leaf tissues of the fusarium head blight-resistant spring wheat cultivar Frontana and the susceptible spring wheat cultivar Casavant. The use of a poly-U-directed 14C-phenylalanine and deoxynivalenol ribosome-binding assays provided evidence of resistance to the protein-synthesis inhibition effects of deoxynivalenol in the head blight-resistant cultivar Frontana. This is probably due to the existence of a mutation in the peptidyl transferase. This cultivar also exhibited resistance to the membrane-damaging properties of this toxin compared to the other cultivar. This report summarizes the evidence for various kinds of "trichothecene tolerance" mechanisms in fusarium head blight-resistant wheat genotypes.  相似文献   
993.
Alignments of homologous genes typically reveal a great diversity of intron locations, far more than could fit comfortably in a single gene. Thus, a minority of these intron positions could be inherited from a single ancestral gene, but the larger share must be attributed to subsequent events of intron gain or intron "sliding" (movement from one position to another within a gene). Intron sliding has been argued from cases of discordant introns and from putative spatial clustering of intron positions. A list of 32 cases of discordant introns is presented here. Most of these cases are found to be artefactual. The spatial and phylogenetic distributions of intron positions from five published compilations of gene data, comprising 205 intron positions, have been examined systematically for evidence of intron sliding. The results suggest that sliding, if it occurs at all, has contributed little to the diversity of intron positions.  相似文献   
994.
In this report, we describe the effect of staged bilateral posteroventral pallidotomy in three patients with advanced Parkinson's disease who were all of the young-onset type. Two patients had developed response fluctuations after the use of levodopa, with severe hypokinesia, painful dystonia, and rigidity in the "off" phase and violent dyskinesias in the "on" phase. One patient, in a continuous hypokinetic rigid state, was totally unresponsive to dopaminergic medication. All were at Hoehn and Yahr stage 5 in the "off" phase before surgery. After surgery, the hypokinetic state was reversed and dyskinesias were abolished in all patients. Hoehn and Yahr stages were 3 in the "off" phase postoperatively. Overall functional improvement was marked and lasting after follow-up for 7, 12, and 13 months, respectively. Complications were visual field deficit and transient central facial paresis, both in the same patient. Bilateral posteroventral pallidotomy can ameliorate response fluctuations, hypokinesia, rigidity, and painful dystonia in advanced Parkinson's disease.  相似文献   
995.
BACKGROUND: The role of nonanatomic wedge resection in the management of stage I (T1 N0 M0) non-small-cell lung cancer continues to be debated against the present gold standard of care--anatomic lobectomy. METHODS: We analyzed the results of 219 consecutive patients with pathologic stage I (T1 N0 M0) non-small-cell lung cancer who underwent open wedge resection (n = 42), video-assisted wedge resection (n = 60), and lobectomy (n = 117) to assess morbidity, recurrence, and survival differences between these approaches. RESULTS: There were no differences among the three groups with regard to histologic tumor type. Analysis demonstrated the wedge resection groups to be significantly older and to have reduced pulmonary function despite a higher incidence of treatment for chronic obstructive pulmonary disease when compared with patients having lobectomy. The mean hospital stay was significantly less in the wedge resection groups. There were no operative deaths among patients having wedge resection; however, a 3% operative mortality occurred among patients having lobectomy (p = 0.20). Kaplan-Meier survival curves were nearly identical at 1 year (open wedge resection, 94%; video-assisted wedge resection, 95%; lobectomy, 91%). At 5 years survival was 58% for patients having open wedge resection, 65% for those having video-assisted wedge resection, and 70% for those having lobectomy. Log rank testing demonstrated significant differences between the survival curves during the 5-year period of study (p = 0.02). This difference was a result of a significantly greater non-cancer-related death rate by 5 years among patients having wedge resection (38% vs 18% for those having lobectomy; p = 0.014). CONCLUSION: Wedge resection, done by open thoracotomy or video-assisted techniques, appears to be a viable "compromise" surgical treatment of stage I (T1 N0 M0) non-small-cell lung cancer for patients with cardiopulmonary physiologic impairment. Because of the increased risk for local recurrence, anatomic lobectomy remains the surgical treatment of choice for patients with stage I non-small-cell lung cancer who have adequate physiologic reserve.  相似文献   
996.
This paper reports a study on the mechanical and tribological properties of ab- and a (b) c?planes of YBa2Cu3O7?δ single crystals. The single crystals were grown using a CuO-BaO self-flux method. The oxygenation effect on the mechanical and tribological properties of ab- and a (b) c?planes is reported. For the ab- plane, the hardness and elastic modulus were around 6 and 50 GPa, respectively. In this case, significant differences were not observed among the hardness and elastic modulus at different oxygenation states. However, the hardness and elastic modulus for as-grown and oxygenated YBa2Cu3O7?δ single crystals were different from that of the a (b) c?plane, and were observed to be slightly higher for the as-grown than for the oxygenated samples. For as-grown and oxygenated samples, we observed hardness values around 4.7 and 2.0 GPa, respectively. Regarding the elastic modulus, the values were 75 and 40 GPa, respectively. The indentation fracture toughness values on the ab- plane for the as-grown and oxygenated YBa2Cu3O7?δ single crystal were 3.7 ± 1.2 and 2.9 ± 1.2 MPa m1/2, respectively. For the ab- plane, the scratch resistance of the as-grown sample was higher than that of the oxygenated sample and the scratches under load were deeper for the oxygenated sample. As regards the a (b) c?plane, the scar features were seemingly constant through all the scratch lengths and the scratches under load were deeper and larger for the oxygenated than that for the as-grown sample.  相似文献   
997.
Current thinking attributes the balance between T helper 1 (Th1) and Th2 cytokine response patterns in immune responses to the nature of the antigen, the genetic composition of the host, and the cytokines involved in the early interaction between T cells and antigen-presenting cells. Here we introduce glutathione, a tripeptide that regulates intracellular redox and other aspects of cell physiology, as a key regulatory element in this process. By using three different methods to deplete glutathione from T cell receptor transgenic and conventional mice and studying in vivo and/or in vitro responses to three distinct antigens, we show that glutathione levels in antigen-presenting cells determine whether Th1 or Th2 response patterns predominate. These findings present new insights into immune response alterations in HIV and other diseases. Further, they potentially offer an explanation for the well known differences in immune responses in "Th1" and "Th2" mouse strains.  相似文献   
998.
Haas  Julia 《Minds and Machines》2020,30(2):219-246
Minds and Machines - I describe a suite of reinforcement learning environments in which artificial agents learn to value and respond to moral content and contexts. I illustrate the core principles...  相似文献   
999.
The butyl amide of ricinoleic acid (N-n-butyl-12-hydroxy-(9Z)-octadecenamide) was prepared from a neat mixture of castor oil andn-butylamine (fatty ester/amine molar ratio, 1:1.3). No catalyst was required. The identity and purity of the amide was assessed by thin-layer chromatography and confirmed by elemental analysis and by infrared and C13 nuclear magnetic resonance spectroscopy. High product yields were achieved at 45 and 65°C in 48 and 20 h, respectively. The reaction was inhibited by the addition of trimethylpentane and dioxane, but not by water. An attempt was made to prepare the amide from methyl ricinoleate, rather than castor oil; even after 10 d only partial conversion was achieved. Attempts to prepare the amide from methyl-n-butylamine, rather thann-butylamine, were also unsuccessful. The ease with which secondary fatty amides can be produced from an oil that consists primarily of the glycerol esters of hydroxylated fatty acids indicates that the described procedure has industrial utility.  相似文献   
1000.
Rapid 3D positioning and modeling in construction can be used to more effectively plan, visualize, and communicate operations before execution. It can also help to optimize equipment operations, significantly improve safety, and enhance a remote operator's spatial perception of the workspace. A new framework for rapid local area sensing and 3D modeling for better planning and control of construction equipment operation is described and demonstrated. By combining human-assisted graphical workspace modeling with pre-stored Computer-Aided Design (CAD) models and simple sensors (such as single-axis laser rangefinders and remote video cameras), modeling time can be significantly reduced while potentially increasing modeling accuracy.  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