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   19816篇
  免费   1938篇
  国内免费   1163篇
电工技术   1202篇
技术理论   1篇
综合类   1330篇
化学工业   2917篇
金属工艺   1228篇
机械仪表   1130篇
建筑科学   1347篇
矿业工程   441篇
能源动力   562篇
轻工业   1948篇
水利工程   472篇
石油天然气   644篇
武器工业   173篇
无线电   2085篇
一般工业技术   2441篇
冶金工业   1885篇
原子能技术   246篇
自动化技术   2865篇
  2024年   106篇
  2023年   329篇
  2022年   786篇
  2021年   1096篇
  2020年   766篇
  2019年   560篇
  2018年   639篇
  2017年   734篇
  2016年   624篇
  2015年   841篇
  2014年   1082篇
  2013年   1217篇
  2012年   1412篇
  2011年   1512篇
  2010年   1305篇
  2009年   1250篇
  2008年   1224篇
  2007年   1105篇
  2006年   980篇
  2005年   783篇
  2004年   559篇
  2003年   446篇
  2002年   437篇
  2001年   384篇
  2000年   325篇
  1999年   274篇
  1998年   500篇
  1997年   381篇
  1996年   259篇
  1995年   169篇
  1994年   136篇
  1993年   131篇
  1992年   57篇
  1991年   40篇
  1990年   54篇
  1989年   40篇
  1988年   28篇
  1987年   35篇
  1986年   25篇
  1985年   27篇
  1984年   24篇
  1983年   19篇
  1982年   18篇
  1981年   40篇
  1980年   21篇
  1979年   18篇
  1978年   13篇
  1977年   28篇
  1976年   32篇
  1975年   11篇
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
111.
112.
Clinical and pathological changes of the mammary gland have been studied in 64 women affected by symptomatic Benign Breast Disease (BBD) coexisting with endometriosis or uterine leiomyomata. These patients were rendered hypoestrogenic by subcutaneous administration of the LH-RH analogue Goserelin depot [D-ser (tBu)6 Aza-Gly10-GnRH (ICI118630)] performed every 28 days, for six months. They were evaluated clinically and ultrasonographically before and after treatment to find possible changes of BBD as well as of endometriosis or uterine leiomyomata. Mammary biopsies were performed before and after treatment in all the patients to study the changes of EGF-R expression. Results showed that clinical improvement is accompanied with a reduction of EGF-R expression.  相似文献   
113.
关系数据库在专家系统中的应用   总被引:6,自引:0,他引:6  
在传统的专家系统中,对推理机工作过程的控制是程序实现的。本文介绍了一个用数据库技术引导推理过程的专家系统-精神分裂症诊断专家系统(ESSD)的推理控制策略。在这个专家系统中,作者将有关推理过程的控制信息用关系数据库技术进行存储和管理,达到了将控制策略数据化的目的。将数据库技术引入到专家系统的推进控制机制中可以使控制策略比较容易调整,且而可以大大压缩程序篇幅,显著提高系统运行效率,为专家系统的结构设  相似文献   
114.
Fifty human temporal bones from necropsies were used to study the frequency of canal dehiscences in detail along the course of the facial nerve. Specifically, the study focused on bony dehiscences in the fallopian canal and vascular communications between the facial nerve and the surrounding bone. High frequency of dehiscences at the oval window (60%) and in the pyramidal segment (54%) were found. These dehiscence rates are in agreement with published reports. A 20% rate of dehiscences at the most anterior segment of the tympanic segment was noted and a non-reported high rate (20%) of multiple dehiscences along the course of the fallopian canal in the same temporal bone in specimens of newborns and young children. The significance of these findings in terms of clinical implications is discussed.  相似文献   
115.
The complete mechanism by which pathogenic mtDNA mutations cause cellular pathophysiology and in some cases cell death is unclear. Oxidant stress is especially toxic to excitable nerve and muscle cells, cells that are often affected in mitochondrial disease. The sensitivity of cells bearing the LHON, MELAS, and MERRF mutations to oxidant stress was determined. All were significantly more sensitive to H2O2 exposure than their nonmutant cybrid controls, the order of sensitivity was MELAS > LHON > MERRF > controls. Depletion of Ca2+ from the medium protected all cell lines from oxidant stress, consistent with the hypothesis that death induced by oxidant stress is Ca(2+)-dependent. A potential downstream target of Ca2+ is the mitochondrial permeability transition, MPT, which is inhibited by cyclosporin A. Treatment of MELAS, LHON, and MERRF cells with cyclosporin A caused significant rescue from oxidant exposure, and in each case significantly greater rescue of mutant than control cells. The pronounced oxidant-sensitivity of mutant cells, and their protection by Ca2+ depletion and CsA, has potential implications for both the pathophysiological mechanism and therapy of these mitochondrial genetic diseases.  相似文献   
116.
Mevalonic acid (mevalonate or MVA), is an obligate precursor in the biosynthetic pathway of cholesterol. It is partially metabolized by the kidneys and its plasma concentrations are an index of endogenous cholesterol synthesis. The aim of the present study was to evaluate plasma MVA concentrations in uremic patients with different degrees of chronic renal failure (CRF; group A), and the effects of a single hemodialysis treatment on plasma MVA in a group of patients with end-stage renal disease (ESRD; group B). CRF patients exhibited a higher mean basal mevalonate concentration (13.3 +/- 6.5 ng/ml) than control subjects (4.68 +/- 1.32 ng/ml; P < 0.001). A statistically significant direct correlation was evident in CRF patients between mevalonate and creatinine plasma levels (r = 0.86; P < 0.001). A single hemodialysis treatment was associated with a significant reduction of plasma mevalonate concentrations four hours after the hemodialysis session (-57%; P < 0.001) and an increase up to the basal values 24 hours after the end of the treatment. In conclusion, our results demonstrated: (i) higher plasma MVA concentrations in patients with decreased renal function; (ii) a direct relationship between plasma MVA levels and the degree of kidney failure as expressed by creatinine plasma concentrations; and (iii) a clear cut reduction of elevated plasma MVA levels after a single hemodialysis treatment.  相似文献   
117.
]n recent years, hemodialysis treatment for chronic renal failure has been increasing. Although the technical evolutions have improved the therapy, the problem of microbial, toxic and chemical contamination of the dialysis fluid is now re-emerging. Most of all, because of increasing use of high-flux dialysis and its potential for transmembrane transport of bacteria into patients, one should be aware that dialysis fluid pathways may be colonised with bacteria. On the bacterial point of view, the French legislation proposed 100 CFU/mL as a maximum for total count of aerobic bacteria in the bi-osmosed water used for dilution of the dialysis concentrate. This study took place during 8 weeks in the children-hospital dialysis unit in Nancy (France). Our laboratory have succeeded in validating an aseptic bacteriological sampling procedure within fluid pathways of haemodialysis monitors Cobe CS3 and AK 100. It has also be shown that 6 to 12 hours of dialysis monitoring doesn't affect the quantitative and qualitative bacterial contamination of the biosmosed water (mean: 5 CFU/100 mL) drained through the 5 years' old internal pipes of the 2 monitors. So it has whatever the 4 different disinfection procedures applied and on the monitors (Formol or Formol + Citric acid + Chlorine or Heat or Heat + dehydrated Citric acid).  相似文献   
118.
The recrystallization behaviour of cold drawn MP159 alloy was investigated by optical and TEM examinations. It is found that the platelet ε phase in the MP alloy inhibits the recrystallization,and this effect makes the MP159 alloy with high recrystallization temperature of about 920℃.This inhibition mainly comes from the increasing of the interfacial energy, which results from the change of the coherent interfaces of (0001)hcp//(111)fcc into the incoherent interfaces when the recrystallizing grain fronts bypass the platelet ε martensite. The increasing of the interfacial energy also causes the dissolution of a few segments on the ε martensite platelets, which decreases the strength of the MP alloy  相似文献   
119.
Salicylate-kodein is a widely used analgesic agent, particularly in outpatient practice. Salicylates have been incriminated in hepatic injury while kodein may induce biliary spasm. We report here a case of granulomatous hepatitis attributed to prolonged intake of this combination, which has never been reported previously to our knowledge.  相似文献   
120.
The authors present an overview of an `inspection and control' package to perform automatic quality control of industrial components, specifically electronic circuit boards. This application has grown out of a set of tools designed initially to aid the development of point distribution models (PDMs) and grey-level models (GLMs) pioneered at the Wolfson Image Analysis Unit in Manchester. These models are both generic and specific. Generic, because they can be applied to most image classification problems; specific, because they aim at the full interpretation of the variability of the objects to be modelled. The underlying vision processing techniques are based on statistical pattern matching. Two synergetic approaches have been followed. The system is trained to recognise the components from either their shape or their grey level appearance or both  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