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   18952篇
  免费   1805篇
  国内免费   1234篇
电工技术   1588篇
综合类   1742篇
化学工业   2030篇
金属工艺   838篇
机械仪表   1161篇
建筑科学   1048篇
矿业工程   505篇
能源动力   446篇
轻工业   1728篇
水利工程   394篇
石油天然气   380篇
武器工业   247篇
无线电   1897篇
一般工业技术   1510篇
冶金工业   3477篇
原子能技术   306篇
自动化技术   2694篇
  2024年   85篇
  2023年   258篇
  2022年   545篇
  2021年   720篇
  2020年   518篇
  2019年   389篇
  2018年   393篇
  2017年   465篇
  2016年   393篇
  2015年   674篇
  2014年   792篇
  2013年   1062篇
  2012年   1268篇
  2011年   1290篇
  2010年   1293篇
  2009年   1214篇
  2008年   1244篇
  2007年   1219篇
  2006年   1034篇
  2005年   906篇
  2004年   631篇
  2003年   460篇
  2002年   442篇
  2001年   398篇
  2000年   339篇
  1999年   213篇
  1998年   804篇
  1997年   468篇
  1996年   339篇
  1995年   240篇
  1994年   212篇
  1993年   218篇
  1992年   84篇
  1991年   73篇
  1990年   97篇
  1989年   88篇
  1988年   88篇
  1987年   62篇
  1986年   71篇
  1985年   75篇
  1984年   44篇
  1983年   52篇
  1982年   51篇
  1981年   54篇
  1980年   51篇
  1979年   28篇
  1978年   42篇
  1977年   92篇
  1976年   193篇
  1974年   30篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Tripe palms is a cutaneous paraneoplastic syndrome. We report a case of tripe palms in a 71-year-old man with non-small cell lung cancer. Approximately 90% of patients with tripe palms have an associated cancer, most commonly involving the lung or the stomach. Any patient with tripe palms must have a complete cancer workup, especially for lung and stomach cancer.  相似文献   
92.
S. L. Grossman  S. Davidi  Haim Cohen   《Fuel》1995,74(12):1772-1775
Bituminous coal piles stored in the open air can undergo autocatalytic heating accompanied by the emission of small but appreciable amounts of molecular hydrogen. When the coal is contained in a confined space and the temperature reaches 40°C, accumulation of hydrogen is expected. This process has been observed for a wide variety of bituminous coals. The amount of hydrogen gas expected to accumulate in the air pocket above the coal cargo in ship holds (assuming that the coal's temperature approaches 40°C during the voyage) has been calculated. The results clearly indicate that in most cases the hydrogen concentration will be appreciably above the lower explosion limit in air. Hence when bituminous coals are stored in a confined space (e.g. a ship hold), the explosive risk of hydrogen should be taken into account.  相似文献   
93.
The relative populations and transverse relaxation times of the solid-like hydrogen pool (PB and T2B) and the magnetization transfer (MT) rates between the solid-like and liquid-like hydrogen pools (kappa) have been determined for three different agar gel concentrations (2%, 4%, and 8% by weight) as well as excised fibroglandular breast tissue specimens. PB was determined to be .003(.001), .01(.002), .02(.01), and .06(.01); T2B was determined to be 13.0(.2), 14.0(.1), 14.5(.1) and 15.2(1.3) microseconds; and kappa was determined to be 0.78(.01), 1.15(.02), 2.00(.02), and 3.55(1.5) sec-1 for the 2%, 4%, and 8% agar gels and the fibroglandular tissue, respectively. The image signal intensities of a pulsed MTC-prepared gradient-echo imaging technique are predicted using these MT parameters and are shown to agree well with experimental data obtained from a clinical MR imaging system. This technique is shown to suppress signal intensity of fibroglandular breast tissue by 40%-50% without exceeding SAR limits (< or = 8 W/kg) and is helpful for visualizing lesions and silicone implants.  相似文献   
94.
There are many in vivo animal models for studying airway mucus secretion and hypersecretion, each with advantages and disadvantages. Use of a particular test system will depend upon the aspect of secretion to be modelled. Airway hypersecretory diseases exhibit chronic mucus hypersecretion, of which the clinical impact is predominantly in the distal airways. The majority of documented test preparations study acute secretion, invariably using tracheal preparations, but have been invaluable in elucidating the normal physiology of airway mucus secretion. Chronic models of the hypersecretory state in the distal airways have been developed, but are predominantly histologic in nature (for example quantification of increased goblet cell number). There are few investigations of mucus hypersecretion. Examination of the 'antisecretory' potential of pharmaceutical compounds has been investigated predominantly in chronic histologic models with the drug being given 'prophylactically' rather than 'therapeutically'. Refinement of chronic hypersecretory models should lead to elucidation of the connection between airway irritation, inflammation, MUC gene expression, mucous cell hyperplasia/metaplasia, airway hypersecretion and bronchial hypersecretory disease.  相似文献   
95.
Two hundred and fifteen children aged 4 months 6 years with acute otitis media (AOM) were randomized to be treated either by a single i.m. injection of ceftriaxone, 50 mg/kg, with a second dose in the event of unsatisfactory response after 48 h or a history of recurrent AOM (109 patients) or amoxicillin clavulanate 12.5 mg tid (106 patients). The failure rate was similar in children treated by ceftriaxone and amoxicillin clavulanate, 4.6% and 4.7%, respectively (standard error for intergroup difference -2.87%, 95% confidence interval -5.62% to 5.87%). No significant differences between the groups were found in the dynamics of the resolution of the acute symptomatology, otoscopy findings, relapse rate at 30 days or tympanographic evidence of middle ear effusion at the scheduled visits on days 30, 60 and 90. Recurrence of AOM between days 31 and 90 was observed significantly in more children treated with amoxicillin clavulanate than with ceftriaxone--25 out of 84 (29.4%) versus 11 out of 81 (13.6%) (P = 0.012). Conclusion: Ceftriaxone injection(s) is as efficient at least as 10-day oral amoxicillin clavulanate for treatment of acute otitis media in children. Although not recommended as routine, ceftriaxone can be considered in the management of acute otitis media under special circumstances, particularly in cases when the ability to tolerate or absorb oral drugs is compromised, in children refusing or unable to take oral therapy or when the compliance is questionable.  相似文献   
96.
Load sharing of the phases in 1080 steel during low-cycle fatigue   总被引:2,自引:0,他引:2  
By means of X-ray diffraction, the stress response of the individual phases in a 1080 steel were measured. Specimens with pearlitic, spheroidal, and tempered martensitic microstructures were subjected to low-cycle fatigue and the stress-strain hysteresis loops were separated into components for the carbide and matrix phases. Calculations of the microstresses formed by differential plastic deformation of the matrix and inclusions accurately model the spheroidite. Measured microstresses in the pearlite are smaller than the predicted values, probably due to yielding of the cementite and limitations on modeling the morphology. Work-hardening rates associated with the microstresses also qualitatively agree with the measurements. The tempered martensite cyclically softens with fatigue loading. The increased plastic strain range in the tempered martensite with cyclic softening is accompanied by an increase in the microstresses. These microstresses are significantly larger than predicted. Formerly Research Assistant, Department of Materials Science and Engineering, McCormick School of Engineering, Northwestern University  相似文献   
97.
This 533-MHz BiCMOS very large scale integration (VLSI) implementation of the PowerPC architecture contains three pipelines and a large on-chip secondary cache to achieve a peak performance of 1600 MIPS. The 15 mm×10 mm die contains 2.7 M transistors (2M CMOS and 0.7 M bipolar) and dissipates less than 85 W. The die is fabricated in a six-level metal, 0.5-μm BiCMOS process and requires 3.6 and 2.1 V power supplies  相似文献   
98.
This study focused on the self-representations of suicidal adolescent. Twenty-six Israeli suicidal inpatients, 24 nonsuicidal inpatients, and 24 control participants completed scales on suicidal tendencies, the hedonic value of self-representations, the complexity (differentiation, integration) of these self-representations, and the discrepancies among self domains (actual, ideal, ought). Suicidal adolescents showed more negative self-representations, a less differentiated and less integrated organization of self-attributes, and more discrepancies between the 3 assessed domains of the self than did control participants. In addition, compared with psychiatric nonsuicidal participants, suicidal adolescents showed a less complex organization of self-attributes and a higher discrepancy between ideal self and ought self. Results were discussed in terms of the vulnerable self of suicidal adolescents, characterized by uneven processing of positive and negative information, confusion, and simplicity.  相似文献   
99.
We have made reasonably comprehensive measurements of action potential activity in the Aplysia californica abdominal ganglion to determine the amount of feedback the central nervous system (CNS) receives from a movement which it initiates. Voltage-sensitive dye measurements of action potential activity of cells in the ganglion were made during the gill-withdrawal reflex elicited by siphon stimulation. We compared recordings in two situations which differed dramatically in the amount the gill moved. In the control sea water, the gill withdrawal was normal; in low-Ca2+, high-Mg2+ sea water, the gill movement was blocked. Both the timing and the number of spikes of the individual neurons were similar in the two situations. Histograms of the summed spike activity versus time and histograms of the number of active neurons versus time in the two conditions were also similar. Finally, two numerical measures of trial-to-trial differences, a paired t-test and a measure we named fractional similarity, did not indicate larger differences between two trials in the different sea waters than two trials in the same sea water. Feedback from sensory neurons activated by the gill movement itself does not make a large contribution to the spike activity in the abdominal ganglion. Apparently the Aplysia CNS issues the command for the withdrawal and does not make adjustments for the magnitude of the actual withdrawal. It may not even receive the information necessary for such adjustments to be made. A second motivation for these experiments was to test whether removing the feedback might simplify the neuronal activity that occurs during the gill-withdrawal reflex. This did not occur.  相似文献   
100.
Internal stability and discriminant validity of the Neuropsychology Behavior and Affect Profile (L. Nelson et al, 1989) were examined in samples of 70 stroke patients and 88 elderly controls. The test is designed to yield indices of premorbid (before-item subset) and present (now-item subset) levels of emotional functioning in each of 5 scales. With coefficient alphas ranging from .76 to .87, results indicated moderate to high internal stability. The test was also able to reliably distinguish between the criterion stroke sample (n?=?42) and a matched group of elderly controls in terms of present levels of emotional functioning (2 wks poststroke). When discriminant validity was examined in terms of premorbid emotional status (before-item subset), group differences were unexpectedly obtained. Clinical and research implications of these results are discussed, noting the possibility of early, noncognitive correlates preceding stroke. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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