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   1062篇
  免费   61篇
电工技术   15篇
化学工业   221篇
金属工艺   47篇
机械仪表   19篇
建筑科学   42篇
矿业工程   1篇
能源动力   41篇
轻工业   65篇
水利工程   3篇
无线电   101篇
一般工业技术   190篇
冶金工业   160篇
原子能技术   12篇
自动化技术   206篇
  2024年   3篇
  2023年   18篇
  2022年   32篇
  2021年   43篇
  2020年   26篇
  2019年   25篇
  2018年   30篇
  2017年   45篇
  2016年   45篇
  2015年   31篇
  2014年   39篇
  2013年   57篇
  2012年   84篇
  2011年   82篇
  2010年   57篇
  2009年   61篇
  2008年   70篇
  2007年   43篇
  2006年   33篇
  2005年   30篇
  2004年   21篇
  2003年   21篇
  2002年   10篇
  2001年   7篇
  2000年   11篇
  1999年   9篇
  1998年   38篇
  1997年   23篇
  1996年   15篇
  1995年   8篇
  1994年   9篇
  1993年   8篇
  1992年   4篇
  1991年   8篇
  1990年   7篇
  1989年   6篇
  1988年   3篇
  1987年   9篇
  1986年   7篇
  1985年   4篇
  1984年   5篇
  1982年   3篇
  1981年   4篇
  1980年   4篇
  1979年   3篇
  1977年   2篇
  1976年   7篇
  1973年   3篇
  1967年   2篇
  1964年   1篇
排序方式: 共有1123条查询结果,搜索用时 10 毫秒
121.
Two experiments were carried out to study the role of gender category in evaluations of face distinctiveness. In Experiment 1, participants had to evaluate the distinctiveness and the femininity-masculinity of real or artificial composite faces. The composite faces were created by blending either faces of the same gender (sexed composite faces, approximating the sexed prototypes) or faces of both genders (nonsexed composite faces, approximating the face prototype). The results show that the distinctiveness ratings decreased as the number of blended faces increased. Distinctiveness and gender ratings did not covary for real faces or sexed composite faces, but they did vary for nonsexed composite faces. In Experiment 2, participants were asked to state which of two composite faces, one sexed and one nonsexed, was more distinctive. Sexed composite faces were selected less often. The results are interpreted as indicating that distinctiveness is based on sexed prototypes. Implications for face recognition models are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
122.
The purpose of the study was to evaluate the association between smoking during pregnancy and preterm birth. The overall rate of preterm delivery was 4.3%. Smokers had a 40% higher risk of preterm birth compared to non-smokers. A dose response relationship was found between smoking and risk of preterm birth. Adjustment for women's height, pre-pregnant weight, age of the mother, marital status, education, occupational status, and alcohol intake did not change the results. Among women with an intake of less than 400 mg of caffeine per day no difference in the risk of preterm birth between smokers and non-smokers was found. However, among women with an intake of more than 400 mg of caffeine per day, the risk of preterm birth was increased almost threefold among smokers compared to non-smokers. Furthermore, among women with a high intake of caffeine a dose response relationship was found between smoking and risk of preterm delivery.  相似文献   
123.
STUDY OBJECTIVE: To determine the prognostic significance of supraclavicular lymph node (SCLN) involvement in small cell lung cancer. MATERIALS AND METHODS: Patients (1,370) with small cell lung cancer were included in four consecutive clinical trials and classified as having either limited or extensive forms of disease using the Veterans Administration staging system. RESULTS: SCLN was present in 17% of patients (n = 234). Median survival was 258 days for patients with SCLN (n = 234) and 297 days for patients without SCLN (n = 1136) (p = 0.002). SCLN involvement was correlated with the presence of distant metastases at baseline (169 vs 65, p = < 0.001). Median survival was 375 days for patients with limited forms without SCLN (n = 529), 332 days for those with limited forms with SCLN (n = 65) (p = 0.12), 244 days for those with extensive forms without SCLN (n = 604), and 228 days for those with extensive forms with SCLN (n = 169) (p = 0.94). The 2-year survival rates were 17%, 12%, 2%, and 4%, respectively. Cox models confirmed that SCLN did not provide any significant additional prognostic information. CONCLUSION: SCLN is highly correlated with extensive forms explaining its overall prognostic value. In limited disease, SCLN is only a minor poor prognostic factor, not justifying any amendment to the staging system currently used.  相似文献   
124.
Tuberculosis is a significant health problem in Azerbaijan. In prisons, this problem is compounded by overcrowding, poor general health, a high representation of risk groups, late case finding, and incomplete treatments. The present study investigated the extent of drug resistance at the Central Penitentiary Hospital in Baku--the country's only treatment center for prisoners with tuberculosis. This International Committee of the Red Cross program, established in 1995, uses the directly observed treatment, short course (DOTS) strategy. Sputum samples were collected from two groups of prisoners: 1) 28 patients who failed to respond, clinically or bacteriologically, after a minimum of 8 weeks to the treatment regimen recommended by the World Health Organization and 2) 38 patients consecutively enrolled over a 4-week period from whom sputum was taken before the start of treatment. Mycobacterium tuberculosis was isolated from all 66 sputum specimens. In the first group, 25 strains (98%) were multidrug resistant (to rifampicin and isoniazid). Such resistance occurred in all new cases and 14 (82%) of the 17 failure or relapse cases. In the second group, 9 strains (24%) were multidrug resistant and only 12 (32%) were fully susceptible. This resistance was found in 3 strains (15%) among the 20 new cases and in 6 strains (33%) among the 18 cases of treatment failure or relapse. These findings suggest that prisoners may have an important future role in the transmission of tuberculosis, especially multidrug resistant forms, in the former Soviet Union.  相似文献   
125.
The microstructure and the corrosion behaviour of high pressure die-cast and semi-solid cast AZ91D magnesium alloys have been investigated. Semi-solid processing leads to a structure with large rounded grains of a solid solution of magnesium (α phase) whereas die-cast alloys are more homogeneous. Electrochemical measurements, particularly with impedance spectroscopy, have shown that the semi-solid cast alloy possesses a corrosion rate at least 35% below that of the die-cast alloy. This can be explained with considering the differences between the composition of the primary α phase and the volume fraction of the β phase, in the two types of alloy.  相似文献   
126.
The relative motion of the electron-hole pairs which constitute Wannier-Mott excitons in semiconductor quantum wells, superlattices, and quantum wires can never be considered strictly 1-D, 2-D, or 3-D. We propose an exact generalization of the well-known calculations of Elliott in the 3-dimensional case, and of Shinada and Sugano for 2-dimensional media-we calculate the absorption spectrum by bound and unbound excitonic states, by using a metric space with a noninteger dimension α>1. Whatever the dimensionality, i.e., for any quantum-sized structure, the whole optical density spectrum is obtained from a single compact equation, in excellent agreement with experimental data and with the most accurate available theories. We present examples of calculated spectra for quantum wells under applied perpendicular electric fields, and for quantum wires  相似文献   
127.
128.
Sham-operated and parathyroidectomized (PTX) rats were divided into two pair-fed groups, one on a normal mineral intake (0.5% Ca, 0.3% P), the other on a regimen low in phosphorus (0.5% Ca, 0.03% P). P depletion led to a drop in plasma P and urine P, a rise in plasma Ca and a marked rise in urine Ca, a drop in serum magnesium and a rise in urine Mg. The changes were more pronounced in the PTX animals, but final values were the same in both groups. Parallel bone-seeking isotope (85Sr, 177Lu, 237Np) studies in nonablated animals revealed an increase in the urinary nuclide output and in the urine/tibia ratio in P-deficient animals. Normal and primary bone osteocytes decreased and enlarged osteocytes increased as a result of P deficiency; osteoclasts and osteoblasts also increased. Bone composition showed a drop in ash content and a rise in water, with a light decrease in both Ca and P, and a corresponding rise in hydroxyproline and nitrogen in the P-deficient animals. The results are interpreted to mean that P-deficiency in the young growing rat leads to an increase in bone resorption which occurs also in the absence of parathyroid hormone (PTH). The fact that final values were similar in the control and PTX P-deficient animals suggests that steady-state regulation can also occur without PTH. Because P-deficiency leads to rapid hypercalcemia and rapid marked hypercalciuria, there may exist a mechanism for phosphate regulation which would then supersede Ca homeostasis. The change in serum and urine Mg levels may reflect a decrease in tubular Ca and Mg reabsorption associated with P-deficiency.  相似文献   
129.
New Differential Thermo Analysis Apparatus for the Testing of Organic Substances The authors describe, a new heating and regulating apparatus for the differential thermo analysis of organic substances in a range of ?100° to +300°C. The apparatus has a contact thermometer whose range can be changed by a right-left changeable synchronmotor. The heating capacity is changed with an automatically controlled regulating transformer which receives the regulating impulses apart from a contact thermometer from a R-C-part as well. It is therefore possible to divide heating and cooling in separate time and thermal steps. Again the control gives the amount of correction for the regulation of heating so that the reproducible thermal and time cycles are run which permit the accurate analysis of, for example, the transformation points of the triglycerides. Along with the circuit diagram and a functional diagram, two examples of thermograms taken with this apparatus are given.  相似文献   
130.
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