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   3082篇
  免费   2篇
综合类   2篇
化学工业   21篇
金属工艺   9篇
机械仪表   8篇
建筑科学   4篇
能源动力   9篇
轻工业   11篇
水利工程   2篇
石油天然气   3篇
无线电   5篇
一般工业技术   16篇
冶金工业   2990篇
原子能技术   1篇
自动化技术   3篇
  2022年   5篇
  2021年   2篇
  2020年   4篇
  2019年   1篇
  2017年   5篇
  2016年   2篇
  2015年   2篇
  2014年   5篇
  2013年   12篇
  2012年   5篇
  2011年   4篇
  2010年   4篇
  2009年   3篇
  2007年   4篇
  2006年   1篇
  2005年   4篇
  2004年   1篇
  2003年   2篇
  2002年   8篇
  2001年   3篇
  2000年   3篇
  1999年   88篇
  1998年   831篇
  1997年   456篇
  1996年   296篇
  1995年   188篇
  1994年   126篇
  1993年   201篇
  1992年   35篇
  1991年   39篇
  1990年   38篇
  1989年   54篇
  1988年   45篇
  1987年   47篇
  1986年   46篇
  1985年   49篇
  1984年   2篇
  1983年   3篇
  1982年   14篇
  1981年   34篇
  1980年   32篇
  1979年   2篇
  1978年   7篇
  1977年   106篇
  1976年   246篇
  1975年   14篇
  1963年   1篇
  1955年   4篇
排序方式: 共有3084条查询结果,搜索用时 0 毫秒
21.
The presence of various types of birthmarks was determined in 1,058 newborn infants under 72 hours of age. Of these, 79.5% were white, 6.2% were black, 11.2% were ladinos, and 2.6% were Asiatic. Mongol spots were present in 9.6% of the white babies, 95.5% of the black babies, 81% of the Asiatic babies, and 70.1% of ladino infants. Pigmented lesions were present in 42 (4%) of the infants. Biopsies obtained in 34 (3.2%) revealed that only one-third (11) of these were melanocytic nevi. Salmon patches were present in 40.3% of the infants, recognizable early strawberry marks in 2.6%, and port-wine strains in 0.3%. In addition to birthmarks, it was determined that 30.3% of the 508 babies examined at one of the two hospitals had toxic erythema of the newborn.  相似文献   
22.
1. Blood pressure, blood volume and renal blood flow were determined in 101 men; forty-three were normal subjects and fifty-eight were untreated permanent essential hypertensive patients with normal renal function and equilibrated sodium balance. 2. A significant negative pressure-volume relationship was observed overall. The relationship could be expressed as a hyperbola whose slope expressed the reduction in blood volume per unit rise in pressure: the higher the blood pressure, the lower the slope. Thus essential hypertensive subjects have a smaller decrement in blood volume per unit rise in pressure than normal subjects. 3. The relation between change in blood volume and change in pressure was confirmed in each individual by defining for each a ration deltaV/deltaP, statistically identical with the hyperbolic slope dV/dP. The deltaV/deltaP ratio was found to be well correlated with the renal blood flow and the creatinine clearance. No correlation existed between the total blood volume and these two renal parameters. 4. It is concluded that the present study demonstrates a blood volume regulation disturbance in essential hypertension and provides evidence from human studies that a renal defect accompanies high blood pressure.  相似文献   
23.
24.
Percutaneous transfemoral arterial balloon occlusion or gelatin sponge embolization of the splenic artery or both were carried out in three high-risk patients with hepatic cirrhosis to reduce splenic hyperfunction and improve severe thrombocytopenia. Although this maneuver raised peripheral platelet counts in each patient, in one patient left upper quadrant pain with splinting of the lower chest cage led to hypostatic lower lobe pneumonia, while in another septic splentitis with gas-forming organisms necessitated splecectomy. Transfemoral occlusion of the splenic artery, although an effective, noninvasive approach to control splenic hyperfunction, has at the same time potential dangers that should be viewed with extreme caution in therapeutic application.  相似文献   
25.
26.
We studied a 14-year-old girl who suffered fractures of her mandible and tegmen following a fall from a balance beam. Thirteen days after hospitalization, she developed severe, protracted, recurrent episodes of hyperventilation; subsequently, she suffered posthyperventilation apnea, which at times was prolonged and association with severe hypoxemia with an arterial oxygen pressure as low as 25 mm Hg. The patient was treated with added dead space and chlorpromazine hydrochloride (Thorazine). Postulated mechanisms for her disorder are discussed. The importance of close clinical and laboratory observation in similar cases is stressed.  相似文献   
27.
28.
29.
Ceramic chip capacitors used in hybrid microelectronics for cardiac pacemakers are usually highly reliable. However, under certain conditions of capacitor construction, capacitor materials, mounting techniques, and environmental conditions, high failure rates may occur. A specific example is presented in which a ceramic capacitor used in an implanted pacemaker delaminated and failed approximately 30 days after being implanted. The failed capacitor caused a pulse rate rise, but due to circuit design techniques, the rate increase was limited to an acceptable value. The capacitor that failed was from an isolated lot of capacitors that was manufactured using pure palladium plates. The circuit containing this capacitor was hermetically sealed within a titanium case by welding. During the welding, a small amount of hydrogen was released from the titanium which, over a period of 2 to 4 weeks, was absorbed by the palladium plates in the capacitor. By absorbing the hydrogen, the palladium plates exhibit a volumetric expansion of sufficient magnitude to crack and delaminate the capacitor to the point of failure. Subsequently, the recurrence of this failure mode has been avoided by using capacitors containing special palladium alloys that cannot absorb hydrogen. This phenomenon is of interest to pacemaker designers since mercury batteries used in conventional pacemakers generate large amounts of hydrogen and potentially may be responsible for complications when used in conjunction with capacitors containing palladium.  相似文献   
30.
As a step toward defining in molecular terms the sperm-triggered block to polyspermy reaction established by the egg at fertilization, vitelline (VE) and fertilization (FE) envelopes were isolated from eggs of the Sounth African clawed toad Xenopus laevis and some of their physicochemical properties determined. Envelopes were isolated after lysis of the fertilized or unfertilized eggs by sieving techniques; isolated envelopes retained their in situ morphology as determined by electron microscopy. The isolated envelopes had different solubility properties and, in general, VE was more readily dissolved by aqueous solvents than FE, although both could be completely dissolved by detergents or chaotropic agents. Changes in envelope solubility correlated with the progression of the cortical reaction implicating a role for cortical granule material in modifying the solubility properties of the envelope. The VE and FE were composed of protein and carbohydrate with no lipid components detected. As determined by immunodiffusion experiments, the FE contained the same antigens as the VE plus components derived from the cortical granules and the innermost jelly layer, J. The macromolecular composition of the envelopes was determined by sodium dodecyl sulfate gel electrophoresis. The VE contained at least 11 glycoproteins with molecular weights ranging from 125 000 to less than 16 000 with two components (40 000 and 33 000) accounting for almost two-thirds of the total stainable material. The FE contained ten glycoproteins that had the same molecular weights as those in the VE. One glycoprotein component underwent a reduction in molecular weight from 77 000 to 67 500 when the VE was converted to the FE. This molecular weight change was interpreted as the probable result of limited proteolysis. In addition, the FE gel electrophoresis patterns contained macromolecular components derived from the cortical granules and jelly layer, J, consistent with the immunodiffusion experiments. These components were absent when the FE was prepared in the absence of Ca2+, suggesting a role for Ca2+ in binding the VE, cortical granules, and J components together. We concluded that the conversion of the glycoproteinaceous VE to FE at fertilization is caused by interaction of the VE with components from the cortical granules and jelly layer J. These interactions are of both a chemical and physical nature.  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