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   1473篇
  免费   1篇
  国内免费   1篇
电工技术   12篇
化学工业   19篇
金属工艺   10篇
机械仪表   7篇
建筑科学   9篇
能源动力   4篇
轻工业   9篇
石油天然气   2篇
无线电   9篇
一般工业技术   36篇
冶金工业   1344篇
原子能技术   5篇
自动化技术   9篇
  2022年   3篇
  2019年   3篇
  2018年   2篇
  2016年   2篇
  2015年   3篇
  2013年   6篇
  2012年   7篇
  2011年   4篇
  2010年   2篇
  2009年   4篇
  2008年   5篇
  2007年   3篇
  2006年   2篇
  2005年   6篇
  2004年   3篇
  2003年   6篇
  2002年   3篇
  2001年   4篇
  1999年   33篇
  1998年   452篇
  1997年   276篇
  1996年   143篇
  1995年   89篇
  1994年   62篇
  1993年   79篇
  1992年   13篇
  1991年   26篇
  1990年   29篇
  1989年   22篇
  1988年   26篇
  1987年   14篇
  1986年   14篇
  1985年   9篇
  1983年   3篇
  1982年   5篇
  1981年   6篇
  1980年   13篇
  1979年   3篇
  1978年   4篇
  1977年   20篇
  1976年   41篇
  1975年   3篇
  1974年   4篇
  1973年   3篇
  1969年   1篇
  1966年   1篇
  1965年   1篇
  1944年   2篇
  1942年   1篇
  1937年   1篇
排序方式: 共有1475条查询结果,搜索用时 0 毫秒
1.
The importance of abnormalities of function and epididymis structure in the etiology of male infertility is still not well understood. We studied 52 individuals distributed in five age groups: fetuses, children, adolescents, adults and the elderly. The region of the body of epididymis was obtained by autopsy and immediately fixed by immersion in a solution of 10% buffered formaldehyde, embedded in paraffin and histologically prepared. The samples were observed under an optic microscope. Test-points were counted in 12 random microscopic fields with the M42 test-system. The following stereological parameters were determined: ductal area, volumetric densities (Vv) of the duct, smooth muscle, connective tissue, epithelial duct and blood vessels. The main results distinguished by those whose averages were statistically significant (p < 0.05), showed that the ductal area is 9.7 times greater in the adolescent/adult/elderly group than the children's group. The Vv of the lumen of the epididymis duct occupies 11.7% of the epididymis body in the fetal period, 5.3% in the child and in individuals after puberty this figures reaches more than 15%. The Vv of smooth muscle occupies 28.3% of the body of the epididymis in the fetus and 35.9% in children, but after puberty this figures stays around 22%. The Vv of the connective tissue occupies 26% in prenatal life, 37% in children, and after puberty these figures range from 21 to 27.5%. Comparing the results of the adult group with that of the elderly group there is an increase in the volumetric density of the connective tissue by 18.1%. In conclusion, the epididymal duct area and the Vv of the ductal lumen, smooth muscle and connective tissue were significant comparing the different groups. However, the quantitative relative differences of the duct's epithelium and the blood vessels were not significant comparing these groups. The study of quantitative aspects of the normal human epididymis can increase our knowledge about male fertility.  相似文献   
2.
3.
Many proteins require enzymatic assistance in order to achieve a functional conformation. One rate-limiting step in protein folding is the cis-trans isomerization of prolyl residues, a reaction catalyzed by prolyl isomerases. SurA, a periplasmic protein of Escherichia coli, has sequence similarity with the prolyl isomerase parvulin. We tested whether SurA was involved in folding periplasmic and outer membrane proteins by using trypsin sensitivity as an assay for protein conformation. We determined that the efficient folding of three outer membrane proteins (OmpA, OmpF, and LamB) requires SurA in vivo, while the folding of four periplasmic proteins was independent of SurA. We conclude that SurA assists in the folding of certain secreted proteins.  相似文献   
4.
Übersicht Die spannungsabhängigen Anlaufströme und Drehmomente eines 2800 kW Asynchron-Käfigläufermotors werden mit der Methode der finiten Differenzen und einem neuen Block-SOR-Iterationsverfahren berechnet. Es wird ber die Ergebnisse für Rechteck-, Trapez- und andere Rotorstabformen berichtet. Die numerisch berechneten Daten werden mit den nach konventionellen Regeln ermittelten Zahlen verglichen. Der Sättigungseffekt ist unerwartet groß, als Folge des großen Nennstrombelages. Die ungesättigten werte stimmen sehr gut überein.
On the calculation of the starting data of A.C. squirrel-cage motors with different bar shapes by the method of finite differences
Contents The voltage dependent starting currents and torques of a 2,800 kW 3-phase a.c. squirrel cage motor are calculated by the method of finite differences using a new block-SOR iteration technique. The paper describes the results for different rotor bars with rectangular, trapezoidal and other shapes. The calculated data are compared with conventionally determined figures. The saturation effect is rather large due to the high values of the rated current loading per air gap periphery. The unsaturated values agree very good.
  相似文献   
5.
Vascular input impedance and associated hydraulic power was measured in rabbit isolated lungs. The study was focused on changes in impedance and in pulsatile hydraulic power during relaxation and contraction of vascular smooth muscle. Pulsatile power was found to be at a minimum when smooth muscle tone was such that the pulmonary arterial pressure was in the physiological range, and increased both when the vessels were relaxed and further constricted. Input impedance was found to be determined mainly by the large, proximal ('extra-alveolar') arteries.  相似文献   
6.
7.
Hams from Landrace, Duroc and Hampshire pigs slaughtered at ages 6, 7.5 and 9 months were processed to generate Norwegian Parma‐style hams. Lipid contents and the compositions of fatty acid classes (ΣSFA, ΣMUFA, ΣPUFA) within neutral lipids, phospholipids and free fatty acids were determined. Small differences in lipid degradation and composition of the classes were revealed. However, significant sensory differences related to lipids were observed. Breed was more important than age. Dry‐cured Hampshire hams gave a more intense mature odour that may be associated with higher overall lipid degradation. Unexpectedly, these hams also demonstrated high juiciness and tenderness, which could be related to the melting characteristics of the fat. Dry‐cured Duroc hams showed a higher susceptibility towards rancidity, presumably associated with preferential oxidation of n‐6 fatty acids relative to C18:1 n‐9. Dry‐cured Landrace hams showed the lowest juiciness and tenderness, likely due to their lower fat content (marbling).  相似文献   
8.
This paper describes the application of 3-D synthetic aperture focusing (SAF) to a single-element trans-rectal ultrasound transducer. The transducer samples a 3-D volume by simultaneous rotation and translation, giving a helical motion. Two different 3-D SAF methods are investigated, a direct and a two-step approach. Both methods perform almost identically for simulated scatterers and give a significant improvement in azimuth resolution and a constant resolution in elevation. Side lobes below -60 dB are achievable for both methods. Validation of the method is achieved by scanning a simple wire phantom and a complex phantom containing wires in azimuth and elevation. The simple wire phantom shows the same results as that found through simulation. The complex phantom shows simultaneous focusing in azimuth and elevation for the wire scatterers. Consideration of the processing requirements for both 3-D SAF methods shows that the two-step approach can give equivalent performance using an order of magnitude fewer calculations. This reduction requires a temporary storage of 9.1 GB of data for the investigated setup.  相似文献   
9.
    
Recent studies support the concept that pulmonary granulomatous inflammation directed by interferon (IFN)-gamma, interleukin (IL)-12, and nitric oxide usually resolves in the absence of fibrosis. To determine whether nitric oxide participates in modulating the fibrotic response during the development of pulmonary granulomas in response to purified protein derivative (PPD), mice presensitized to PPD received daily intraperitoneal injections of N(G)-nitro-D-arginine-methyl ester (D-NAME), N(G)-nitro-L-arginine-methyl ester (L-NAME), or aminoguanidine after delivery of PPD-coated beads to the lungs. Eight days later, morphometric analysis of lung granulomas revealed that L-NAME-treated mice when challenged with PPD in vitro for 36 hours had the largest pulmonary granulomas and the greatest collagen deposition among the treated groups. In addition, equivalent numbers of dispersed lung cells from L-NAME- and aminoguanidine-treated mice produced significantly higher levels of IL-4, monocyte chemoattractant protein (MCP)-1, and macrophage inflammatory protein (MIP)-1alpha and significantly lower levels of eotaxin compared with D-NAME-treated mice. Cultures of dispersed lung cells from L-NAME-treated mice also produced significantly more IL-10 and less IL-12 compared with similar numbers of dispersed lung cells from D-NAME-treated mice. Cultures of isolated lung fibroblasts from L-NAME-treated mice expressed higher levels of C-C chemokine receptor 2 (CCR2) and CCR3 mRNA and contained less MCP-1 and eotaxin protein than a similar number of fibroblasts from D-NAME-treated mice. Thus, nitric oxide appears to regulate the deposition of extracellular matrix in lung granulomas through the modulation of the cytokine and chemokine profile of these lesions. Alterations in the cytokine, chemokine, and procollagen profile of this lesion may be a direct effect of nitric oxide on the pulmonary fibroblast and provide an important signal for regulating fibroblast activity during the evolution of chronic lung disease.  相似文献   
10.
    
Provision of automated support for planning protocol-directed therapy requires a computer program to take as input clinical data stored in an electronic patient-record system and to generate as output recommendations for therapeutic interventions and laboratory testing that are defined by applicable protocols. This paper presents a synthesis of research carried out at Stanford University to model the therapy-planning task and to demonstrate a component-based architecture for building protocol-based decision-support systems. We have constructed general-purpose software components that (1) interpret abstract protocol specifications to construct appropriate patient-specific treatment plans; (2) infer from time-stamped patient data higher-level, interval-based, abstract concepts; (3) perform time-oriented queries on a time-oriented patient database; and (4) allow acquisition and maintenance of protocol knowledge in a manner that facilitates efficient processing both by humans and by computers. We have implemented these components in a computer system known as EON. Each of the components has been developed, evaluated, and reported independently. We have evaluated the integration of the components as a composite architecture by implementing T-HELPER, a computer-based patient-record system that uses EON to offer advice regarding the management of patients who are following clinical trial protocols for AIDS or HIV infection. A test of the reuse of the software components in a different clinical domain demonstrated rapid development of a prototype application to support protocol-based care of patients who have breast cancer.  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