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   1676篇
  免费   7篇
  国内免费   1篇
综合类   1篇
化学工业   37篇
金属工艺   5篇
机械仪表   6篇
建筑科学   12篇
矿业工程   1篇
能源动力   3篇
轻工业   17篇
石油天然气   2篇
无线电   16篇
一般工业技术   33篇
冶金工业   1529篇
自动化技术   22篇
  2023年   4篇
  2022年   3篇
  2021年   8篇
  2020年   2篇
  2019年   5篇
  2018年   14篇
  2017年   7篇
  2016年   4篇
  2015年   3篇
  2013年   16篇
  2012年   5篇
  2011年   7篇
  2010年   6篇
  2009年   7篇
  2008年   2篇
  2007年   5篇
  2006年   9篇
  2005年   6篇
  2004年   4篇
  2003年   7篇
  2002年   2篇
  2001年   4篇
  1999年   45篇
  1998年   481篇
  1997年   266篇
  1996年   183篇
  1995年   85篇
  1994年   76篇
  1993年   91篇
  1992年   11篇
  1991年   10篇
  1990年   20篇
  1989年   13篇
  1988年   15篇
  1987年   11篇
  1986年   15篇
  1985年   17篇
  1982年   6篇
  1981年   11篇
  1980年   21篇
  1978年   7篇
  1977年   50篇
  1976年   99篇
  1975年   5篇
  1970年   1篇
  1969年   1篇
  1968年   1篇
  1964年   2篇
  1955年   2篇
  1954年   1篇
排序方式: 共有1684条查询结果,搜索用时 31 毫秒
51.
OBJECTIVES: To determine whether oxytocin exists in the cerebrospinal fluid (CSF) of dogs and whether the amount of oxytocin in the CSF of dogs with neck or back pain caused by spinal cord compression is significantly different than that in the CSF of clinically normal dogs. STUDY DESIGN: Prospective controlled study. ANIMAL POPULATION: A total of 15 purpose-bred beagles and 17 client-owned dogs. METHODS: CSF was collected by needle puncture of the cerebellar medullary cistern after induction of general anesthesia. Oxytocin levels within the samples were determined through radioimmunoassay. RESULTS: Dogs with spinal cord compression had significantly more oxytocin in their CSF than the clinically normal dogs (13.76 +/- 2.0 pg/mL and 3.61 +/- 0.63 pg/mL, respectively; P < .0001). Dogs with chronic signs (>7 days) had significantly more oxytocin in their CSF than dogs with acute signs (<7 days) (21.60 +/- 0.86 pg/mL and 6.80 +/- 0.81 pg/mL, respectively; P < .0001). Both acutely and chronically affected dogs had significantly more oxytocin in their CSF than the controls (P < .005 and P < .0001 respectively). CONCLUSIONS: Dogs with neck and back pain caused by spinal cord compression have significantly more oxytocin in their CSF than clinically normal dogs. Dogs with chronic clinical signs have significantly more oxytocin in their CSF than dogs with acute clinical signs. CLINICAL RELEVANCE: In humans, intrathecal injection of oxytocin is effective in treating low back pain for up to 5 hours. Intrathecal oxytocin may be a logical choice for perioperative analgesia in dogs undergoing myelography because the intrathecal space is accessed for injection of contrast agent.  相似文献   
52.
We report two patients where the finding of isolated fetal hydrocephalus led to the detection of severe fetal thrombocytopenia, using fetal blood sampling. Serological investigation led to the diagnosis of fetomaternal alloimmune thrombocytopenia (FMAIT) due to anti-HPA-1a. Both women had had previous unsuccessful pregnancies probably due to FMAIT; one had had four miscarriages at 17-18 weeks' gestation. The other had had one previous pregnancy complicated by severe fetal anaemia, and eventually hydrocephalus developed and the fetus died without the diagnosis of FMAIT being considered. Subsequent pregnancies in the two women were also affected by FMAIT, but prenatal treatment, predominantly with serial fetal platelet transfusions, resulted in a successful outcome in both cases. These observations suggest that FMAIT should be suspected if there is isolated fetal hydrocephalus, unexplained fetal anaemia, or recurrent miscarriages. The accurate diagnosis of FMAIT is important because recent advances in prenatal management can improve the outcome of subsequently affected pregnancies.  相似文献   
53.
The application of nonradioactive RNA probes for Northern blotting offers the advantage of a rapid turn-around time for results without the loss of sensitivity for target mRNA detection. However, a problem that has impeded the widespread use of nonradioactive RNA probes for use in Northern blotting is the difficulty in stripping these probes from nylon membranes after hybridization. In this report we describe two protocols for stripping digoxigenin (Dig)-labeled RNA probes from nylon membranes. One protocol utilizes a phosphate-buffered formamide stripping solution to remove nonchemically modified (regular) RNA probes while the other method utilizes strippable probes that were produced with a chemically modified nucleotide (CTP) and removed by a specific stripping solution. This latter method was developed by Ambion Inc. and is called Strip-EZ. We also describe a protocol for the detection of two separate rat mRNAs using both biotin and digoxigenin-labeled RNA probes that does not require stripping the membrane after hybridization. Finally, we describe the use of another new labeling technology, called Chem-Link, that quickly and conveniently labels RNA for use in Northern blotting.  相似文献   
54.
This study examines the diagnostic utility of the polymerase chain reaction (PCR) in 156 patients (five human immunodeficiency virus (HIV) seropositive) suspected of extrapulmonary tuberculosis. The results of PCR in 226 samples from 11 different sites were compared with the results of microscopy and culture. Positive culture results were predicted in 86% of samples by PCR but in only 31% by microscopy. Specificity of PCR was 92%. In cases with culture-proven tuberculosis, PCR identified all 11 microscopy positive cases and 19 of 24 (79%) of the microscopy-negative cases. In four patients, PCR excluded the diagnosis of tuberculosis in microscopy-positive samples, which were later shown to contain mycobacteria other than Mycobacterium tuberculosis or laboratory contaminants. In 20 patients (microscopy, PCR and culture negative) a trial of antituberculous drugs was given, but patients showed no improvement and treatment was stopped. In 17 patients, all culture negative (in nine PCR was positive, three of whom also had positive microscopy) the diagnosis was probable tuberculosis based on clinical findings and response to treatment. This polymerase chain reaction has a much higher sensitivity than microscopy and can facilitate therapeutic decisions for those with suspected extrapulmonary tuberculosis.  相似文献   
55.
Batch experiments were carried out to asses the effect of Cu(II) and Zn(II) on the biosorption of lead(II) ions by non-living Chlorella vulgaris. The uptake of Pb(II) was examined for single, binary and ternary solutions at different initial concentrations and different pH values. The experimental results showed that the uptake increased with increasing pH from 3.0 to an optimum value of 5.0. The biosorption of Pb(II) was found to be adversely affected by the presence of Cu(II) ions, while Zn(II) ions seemed to have negligible effect on the process. The equilibrium data were fitted to four isotherm models: Langmuir, Freundlich, Sips and Dubinin–Radushkevich; the Sips isotherm gave the best fit for the data. Modeling of the controlling mechanisms indicated that both intrinsic kinetics and mass transfer played major roles in controlling the process. A new dimensionless parameter, Ψ, was defined to asses the relative contributions of the two mechanisms to the biosorption of lead(II). Mass transfer seemed to be the dominant mechanism at low initial lead(II) concentrations, while intrinsic kinetics dominates at high concentrations.  相似文献   
56.
Grafted copolymer of poly(tetrafluoroethylene ethylene) (ET) with acrylic acid (AAc) was prepared by direct radiation method. The obtained films were modified by treating with small amounts of Co2+ and K+ ions (1.0 wt %). The effects of such treatment on the thermal stability and electrical conductivity of these films were studied. Cobalt treatment did not much affect the thermal degradation of the films. The results obtained revealed that k+ treatment enhanced the thermal degradation of ET‐g‐PAAc, which started 273 K lower than that observed in the case of the untreated and Co2+‐treated films. Potassium and cobalt treatment of the investigated films increased their electrical conductivity (σ) and decreased the activation energy ΔEσ. The increase in σ values was, however, more pronounced in the case of K+‐treated film. These results were discussed in terms of the effective increase in the hydrophilicity of the films, especially those treated with potassium. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 867–871, 2005  相似文献   
57.
Multimedia Tools and Applications - Automated segmentation has an essential role in detecting several diseases, such as skin lesions. In segmentation, the active contour (AC) is an efficient method...  相似文献   
58.
针对当前大型互联网站提升用户体验的需求,本研究创造性地提出基于本体的用户行为分析引擎的思想,它通过上下文感知技术,实时获取用户访问页面时的上下文信息(以下也称为动态行为),基于本体对用户行为建模,建立基于规则的上下文推理算法,对监测到的动态用户行为进行实时推理,及时反馈结果信息给用户。实验表明:本研究理论上独辟蹊径,设计实现上结合了云存储技术,能够一定程度改善用户体验效果。  相似文献   
59.
The inhibiting effect of benzotriazole (BTA) on the corrosion of -Al-bronze (Cu-7% Al) in 3.4% NaCl was studied. BTA showed good inhibition effects from short up to extended periods of time (about six weeks). The morphologies of the alloy surface were monitored after various periods of corrosion in the absence and presence of BTA, using SEM. The corrosion products were identified by X-ray diffraction. Corrosive attack occurs very early in the absence of BTA, leading to general and pitting corrosion. BTA was found to have a stronger inhibiting effect on the anodic dissolution of copper than on the cathodic reduction of oxygen. The current-potential relation is divided into two regions: region I within which BTA has a strong effect on the charge transfer kinetics, and a limiting current region where BTA has no significant inhibiting effect. It is also shown that the interaction of BTA with a Cu20-covered alloy surface is faster than on reduced alloy surfaces, although the protection efficiency on the latter is slightly better than on the former.  相似文献   
60.
Drug abusers, particularly those who inject drugs s.c. ("skin popping"), may develop amyloidosis. Chronic infections are thought to play a pathogenetic role in this setting. A patient is presented who had a history of "skin popping" cocaine and heroin and developed nephrotic syndrome, with an elevated serum creatinine and a creatinine clearance of 61 mL/min. Renal biopsy demonstrated amyloidosis. Treatment with colchicine was initiated, and proteinuria decreased to near normal levels after 12 months. Concomitant with the decrease in proteinuria, creatinine clearance improved, although a repeat renal biopsy failed to show any significant improvement in amyloid burden. These observations suggest that colchicine may be a useful treatment in reversing the proteinuria of renal amyloidosis associated with drug abuse. Furthermore, clinical improvement may occur before any demonstrable regression in the amyloidosis.  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