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   588601篇
  免费   7579篇
  国内免费   1856篇
电工技术   10612篇
综合类   478篇
化学工业   89614篇
金属工艺   23362篇
机械仪表   17886篇
建筑科学   14878篇
矿业工程   2975篇
能源动力   14901篇
轻工业   53250篇
水利工程   5950篇
石油天然气   9453篇
武器工业   35篇
无线电   72083篇
一般工业技术   115271篇
冶金工业   105069篇
原子能技术   11653篇
自动化技术   50566篇
  2021年   4503篇
  2019年   4210篇
  2018年   7162篇
  2017年   7280篇
  2016年   7792篇
  2015年   5391篇
  2014年   9006篇
  2013年   26572篇
  2012年   14938篇
  2011年   20592篇
  2010年   16160篇
  2009年   18332篇
  2008年   19298篇
  2007年   19583篇
  2006年   17275篇
  2005年   16069篇
  2004年   15278篇
  2003年   14915篇
  2002年   14415篇
  2001年   14651篇
  2000年   13626篇
  1999年   14141篇
  1998年   32351篇
  1997年   23476篇
  1996年   18415篇
  1995年   14362篇
  1994年   12724篇
  1993年   12590篇
  1992年   9631篇
  1991年   9270篇
  1990年   8859篇
  1989年   8578篇
  1988年   8340篇
  1987年   7110篇
  1986年   7113篇
  1985年   8472篇
  1984年   7960篇
  1983年   7082篇
  1982年   6546篇
  1981年   6462篇
  1980年   6320篇
  1979年   6217篇
  1978年   5940篇
  1977年   6833篇
  1976年   8728篇
  1975年   5139篇
  1974年   4910篇
  1973年   4899篇
  1972年   4128篇
  1971年   3651篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Close to three-fourths of patients with chronic obstructive pulmonary disease (COPD) suffer from weight loss. Identifying a single cause for this is difficult, as several factors-including chronic mouth breathing, dyspnea, aerophagia, certain medications, and depression-often act in concert. Malnutrition can exacerbate symptoms of COPD by decreasing ventilatory muscle strength, exercise tolerance, and immunocompetence, and by increasing the risk of depression and anxiety. Goals of nutrition intervention are to prevent or reverse malnutrition without worsening the disease process and to improve respiratory function, thereby reducing morbidity and delaying mortality. Recommendations for intake of fats, carbohydrates, protein, and water must be individualized.  相似文献   
992.
993.
The constant modulus (CM) array is a blind adaptive beamformer capable of recovering a narrowband signal among several cochannel sources without using a pilot or training signal. It is a conventional weight-and-sum adaptive beamformer whose weights are updated by the constant modulus algorithm. An adaptive signal canceller follows the beamformer to remove the captured signal from the array input and to provide an estimate of its direction vector. Based on a Wiener model, we investigate the steady-state properties of the CM array and the signal canceller. For mutually uncorrelated sources and noise, it is shown that the signal canceller exactly removes the source captured by the array. Thus, identical stages of the CM array and signal canceller may be used in a multistage system to recover several cochannel sources. Computer simulations are presented to verify the analytical results and to illustrate the transient behavior of the system  相似文献   
994.
Medical conditions often have an important causal role in urinary incontinence in the elderly. Aside from causing functional impairments, such diseases directly may involve the genitourinary system--particularly its neurologic control--resulting in specific lower urinary tract pathophysiology. Knowledge of the specific effects that medical conditions may have on the genitourinary system and continence can assist the urologic specialist in determining the often complex cause(s) of UI in older persons.  相似文献   
995.
The definition of the curl operator in terms of an integral is shown to lead to a method for numerical solutions that facilitates the use of mixtures of cells having different shapes and different dielectric properties. The derivation is followed by examples for, waveguides, mixtures of different cells, and a method for increasing the accuracy when an equation is known for the field on the outer boundary. Thus, these results suggest that the formal definition of the curl operator has more than pedagogical value. This definition is taught in an undergraduate class at Florida International University  相似文献   
996.
Undoped and phosphorus (P)-doped diamond-clad Si field emitter arrays have been successfully fabricated using microwave plasma chemical vapor deposition (MPCVD) technology. The electron emission from the blunt diamond-clad microtips are much higher than those for the pure Si tips with sharp curvature due to a lower work function. Furthermore, the characteristics of emission current against applied voltage for the P-doped diamond-clad tips show superior emission at lower field to the undoped ones. After the examination of Auger electron spectroscopy (AES) and electrical characteristics of as-grown diamond, such a significant enhancement of the electron emission from the P-doped diamond-clad tips is attributed to a higher electron conductivity and defect densities  相似文献   
997.
The width of the transition layer between the crystalline and amorphous zones in nylon 1010 was determined by SAXS with point collimation and long-slit collimation, respectively. The width of the transition layer, E, was found to be 1.7 nm. The results show that the width of the transition layer is independent of crystallinity.  相似文献   
998.
We consider extinction of various dispersed systems. Isolated boron particles and boron particles in gases are studied. Stability analysis of steady-state thermal regimes of reacting heterogeneous systems for the case of two parallel reactions on the reaction surface using the Frank-Kamenetskii method gives extinction conditions in oxygen-containing media. Curves of the extinction particle size versus the ambient temperature, oxidizer concentration, and, for particles in gases, also versus the oxidizer-to-fuel ratio are plotted. Approximate analytical calculations showed that the extinction process can be most actively controlled by varying the combustion temperature: a decrease in the latter increases the extinction particle size and decreases the completeness of fuel combustion. It is shown that at low ambient temperatures the extinction particle size for suspensions is larger than that for isolated particles. This effect is caused by a decrease in the oxidizer concentration during combustion of suspensions. At high temperatures, the role of this factor weakens.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 6, pp. 12–19, November–December, 1996.  相似文献   
999.
1000.
Platelets (PLT) play an important role in hemostasis, modulation of immunological and inflammatory processes. There is also evidence that PLT takes part in the development of atherosclerosis and glomerulosclerosis. The aim of presented study was to determine morphological and functional changes of platelets and their relation to the lipid, protein and coagulation factors disturbances in patients with chronic glomerulonephritis (CGN). The studies were carried out in 60 patients with CGN diagnosed by renal biopsy: 30 patients without nephrotic syndrome (NS)-CGN and 30 patients with NS-CGN+NS. Protein and lipid disturbances, coagulation factors were estimated using routine laboratory methods. Platelet count (PLT), mean platelet volume (MPV) and modal platelet volume (PLT-Mode) were measured using Technicon H1 hematological autoanalyser. Platelet function was assessed by aggregometry using turbidimetric method (inductors: ADP 1-3 microM, collagen 50g/ml, epinephrine 0.25-5 microM). Spontaneous platelet aggregation (SPA) was measured in platelet rich plasma (PRP) without inductors for 15 min, in 1-2 hours after venesection. SPA was observed in 9 of 30 patients with CGN and in 19 of 30 patients with CGN+NS. MPV and PLT Mode were significantly higher in patient showing SPA compared with those without. Significant correlations between SPA and the concentration of plasma albumin (r = -0,70; p < 0.02) TG and CH-LDL (r = 0,61; p < 0.05) were found in CGN+NS patients. APTT was significantly shorter in patients showing SPA compared with those without and negative significant correlation between SPA and APTT was found. Platelet aggregation to inductors in CGN and CGN+NS patients was diminished compared with control group. Lack of second phase aggregation in response to aggregation inducers was observed in patients with SPA. Conclusions. 1. Platelet hyperaggregation play an important role in hypercoagulation state in CGN patients. 2. SPA in vitro was observed in majority of CGN+NS patients and in some without NS. 3. Pathomechanism of SPA is probably multifactorial (hypoalbuminemia, dyslipidemia, changes in concentration of coagulation parameters).  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