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   4544篇
  免费   29篇
电工技术   30篇
综合类   1篇
化学工业   262篇
金属工艺   20篇
机械仪表   38篇
建筑科学   81篇
矿业工程   5篇
能源动力   37篇
轻工业   118篇
水利工程   25篇
石油天然气   8篇
无线电   287篇
一般工业技术   304篇
冶金工业   3099篇
原子能技术   25篇
自动化技术   233篇
  2020年   19篇
  2019年   18篇
  2018年   16篇
  2017年   12篇
  2016年   25篇
  2015年   19篇
  2014年   22篇
  2013年   81篇
  2012年   49篇
  2011年   50篇
  2010年   46篇
  2009年   48篇
  2008年   66篇
  2007年   48篇
  2006年   74篇
  2005年   62篇
  2004年   35篇
  2003年   50篇
  2002年   45篇
  2001年   55篇
  2000年   43篇
  1999年   121篇
  1998年   984篇
  1997年   560篇
  1996年   369篇
  1995年   221篇
  1994年   192篇
  1993年   211篇
  1992年   48篇
  1991年   47篇
  1990年   65篇
  1989年   55篇
  1988年   66篇
  1987年   56篇
  1986年   67篇
  1985年   50篇
  1984年   30篇
  1983年   37篇
  1982年   26篇
  1981年   28篇
  1980年   25篇
  1979年   24篇
  1978年   26篇
  1977年   64篇
  1976年   159篇
  1975年   20篇
  1974年   19篇
  1973年   22篇
  1972年   11篇
  1971年   15篇
排序方式: 共有4573条查询结果,搜索用时 15 毫秒
61.
This report describing the radiology of transsphenoidal hypophysectomy based on a review of 100 consecutive surgical procedures. Preoperative laminographic evaluation of the sphenoid sinus is an important aid in planning the most direct surgical approach to the pituitary. It is also useful in defining the many anatomic structures that may be injured inadvertently at the time of surgery. Intraoperative radiography or fluoroscopy is helpful in identifying the sella floor and as an aid in preventing loss of orientation within a capacious sinus. Various changes occur within the sphenoid sinus following surgery, some transient and others persistent. The surgical defect is usually difficult to identify on routine roentgenograms but is clearly visible on lateral laminography. A persistent soft tissue mass within the sinus is usually a manifestation of fascia and fat placed as a seal within the sinus.  相似文献   
62.
Optimal conditions for obtaining the proliverative response in mixed kidney cell-lymphocyte culture (MKLC) have been determined in rats. The addition of 2-mercaptoethanol to the culture medium was essential for successful stimulation of lymphocytes by allogeneic kidney cells. Proliferative responses by standard MLC and MKLC were compared in rats with the same or a different Ag-B locus. In most strain combinations, there was a significant correlation between MLC and MKLC reactions, However, the DA-ACI combination, compatible at the Ag-B locus, consistently showed negative MLC and positive MKLC reactions. This suggested the possibility that this technique allowed the expression of kidney specific antigens.  相似文献   
63.
A transnasal trans-sphenoidal surgical approach to the pituitary gland is described. The operative and post-operative experiences with the use of this technique on 21 patients with hormone-dependent malignant disease are reported. In 2 patients the procedure was abandoned because of intrasellar haemorrhage and in 1 an empty sella was found. Fifteen patients developed diabetes insipidus and 1 patient died in the postoperative period.  相似文献   
64.
65.
Identical distribution of C2- and Cx-cellulase activities of enzyme complexes produced by Trichoderma lignorum on a medium with lactose, a soluble "inductor", and on a medium with cellulose was found by means of disc elestrophoresis in polyacrylamide gel. The maximum rate of synthesis of cellulases on the medium with lactose was registered during the highest deceleration, and even complete cessation, of the fungal growth. During this phase, only one electrophoretically homogeneous cellulase component with Rf of 0.44 possessing all types of the cellulase activity is present in the cultural broth. In the course of growth of the fungus on cellulose after 48 hours, also only one electrophoretically homogeneous component with Rf of 0.44 was found in the cultural broth when the rate of the substrate degradation was highest. The appearance of minor protein components with the activity of cellulase at later stages of cultivation after cessation of the fungal growth is supposed to be caused by modification of the main cellulase component with Rf of 0.44 by the growth medium.  相似文献   
66.
Assessed the effectiveness of a battery of commonly used cognitive and psychometric tasks in predicting achievement in reading and arithmetic in Grades 1-3. Tasks were administered to 255 children (mean age, 5.4 yrs) prior to kindergarten. Teachers' ratings were obtained in kindergarten. Combinations of 4 tasks yielded optimal predictions of achievement. More effective prediction could be made from prekindergarten tasks than from teachers' ratings. After Grade 1, the most effective prediction was derived from scores on prior tests of achievement. Relations among various tests of achievement both within and across years and the relation of achievement scores to age, IQ, and parental education were determined. Predictive tasks and teachers' ratings were used to select children who later had difficulty in school. Caution is urged, however, in using prekindergarten tasks to identify children who need extra help. Because prediction is imperfect, such tasks ought not to be used to assign children to special groups. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
67.
It is a well-established fact that prolonged odor stimulation leads to marked sensory adaptation. This study demonstrates comparable electrophysiological phenomena occurring at the level of the olfactory receptor and at more central olfactory structures. Recordings of overall receptor response and of olfactory bulb unit responses were made during repeated odor stimulation. During the course of a single, continuous odor presentation response decrements were seen in the EOG (at the olfactory receptors) and were mirrored at the mitral cell layer of the bulb. When brief periods without stimulation were introduced between such odor presentations, receptor responsiveness rebounded to its original level, but mitral cell responses did not. On the basis of this dissociation it is suggested that the pattern of response decrement within the bulb represents a case of stimulus-specific habituation in a simple cortical subsystem and is well worth future investigation as a model of neural plasticity. Surgical disconnection of the olfactory bulb from one or more of its centrifugal inputs results in hyperactive, hyperresponsive mitral cells, which habituate more rapidly and show longer recovery times than do those in the intact bulb. In addition, the synchronization of such units to the inhalation cycle is markedly reduced as compared with normal preparations. These facts together suggest that the habituation of mitral cell activity does not depend on centrifugal inputs, although one or more of such inputs act indirectly in an inhibitory fashion to modulate and tune mitral cell response characteristics.  相似文献   
68.
A review of 227 cases of invasive carcinoma of the cervix was undertaken to determine the efficacy of procedures using in the staging of this disease. All patients had a pretreatment chest radiography and intravenous pyelogram. 96.5% had pretreatment cystoscopy, 98.6% had pretreatment proctoscopy, and 92% had a pretreatment barium enema. These patients were retrospectively staged on the findings of physical examination only. Each additional procedure was then evaluated by comparison with the initial staging. Cystoscopy and chest film findings each would have changed the clinical stage in fewer than 1% of cases, barium enema in 1.4%, and proctoscopy in 2.2%. No patient had a positive barium enema without a positive proctoscopy, while two patients had positive proctoscopies with negative barium enemas. The overall yield of positive findings by pretreatment intravenous pyelography was 7.3%. Lymphangiography, although inconsistently done, yielded positive findings in all stages. Chest radiographs, intravenous pyelography, proctoscopy, and lymphangiography are recommended as part of the pretreatment workup of patients with carcinoma of the cervix. Routine barium enema is no longer recommended, and cystoscopy is only recommended in patients with clinical stage IIB disease or greater.  相似文献   
69.
70.
Various existing methods of recording motor activity in animals are briefly reviewed. An electronic adaptation of an old one, the Jiggle cage, is described. The relative advantages and demerits in recording behaviour of mice under drug effects are compared with those of the traditional Jiggle cage, an electromagnetic activity counter and observational ratings.  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